Internet Draft Cengiz Alaettinoglu
Expires May 17, 1999 USC/Information Sciences Institute
draft-ietf-rps-rpsl-v2-00.txt Curtis Villamizar
ANS
Elise Gerich
At Home Network
David Kessens
Qwest
David Meyer
University of Oregon
Tony Bates
Cisco Systems
Daniel Karrenberg
RIPE
Marten Terpstra
Bay Networks
November 17, 1998
Routing Policy Specification Language (RPSL)
Status of this Memo
RPSL allows a network operator to be able to specify routing policies at
various levels in the Internet hierarchy; for example at the Autonomous
System (AS) level. At the same time, policies can be specified with
sufficient detail in RPSL so that low level router configurations can be
generated from them. RPSL is extensible; new routing protocols and new
protocol features can be introduced at any time.
This document is an Internet Draft, and can be found as draft-ietf-rps-rpsl-
v2-00.txt in any standard internet drafts repository. Internet Drafts are
working documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute working
documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six months.
Internet Drafts may be updated, replaced, or obsoleted by other documents
at any time. It is not appropriate to use Internet Drafts as reference
material, or to cite them other than as a ``working draft'' or ``work in
progress.''
Please check the I-D abstract listing contained in each Internet Draft
directory to learn the current status of this or any other Internet Draft.
Internet Draft RPSL November 17, 1998
Contents
1 Introduction 3
2 RPSL Names, Reserved Words, and Representation 4
3 Contact Information 7
3.1 mntner Class . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2 person Class . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3 role Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4 route Class 10
5 Set Classes 12
5.1 route-set Class . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2 as-set Class . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.3 Predefined Set Objects . . . . . . . . . . . . . . . . . . . . . . 16
5.4 Hierarchical Set Names . . . . . . . . . . . . . . . . . . . . . . 16
6 aut-num Class 17
6.1 import Attribute: Import Policy Specification . . . . . . . . . . 17
6.1.1Peering Specification . . . . . . . . . . . . . . . . . . . . . 18
6.1.2Action Specification . . . . . . . . . . . . . . . . . . . . . . 20
6.1.3Filter Specification . . . . . . . . . . . . . . . . . . . . . . 21
6.1.4Example Policy Expressions . . . . . . . . . . . . . . . . . . . 25
6.2 export Attribute: Export Policy Specification . . . . . . . . . . 26
6.3 Other Routing Protocols, Multi-Protocol Routing Protocols, and
Injecting Routes Between Protocols . . . . . . . . . . . . . . . . . 26
6.4 Ambiguity Resolution . . . . . . . . . . . . . . . . . . . . . . . 28
6.5 default Attribute: Default Policy Specification . . . . . . . . . 30
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6.6 Structured Policy Specification . . . . . . . . . . . . . . . . . . 31
7 dictionary Class 35
7.1 Initial RPSL Dictionary and Example Policy Actions and Filters . . 38
8 Advanced route Class 42
8.1 Specifying Aggregate Routes . . . . . . . . . . . . . . . . . . . . 42
8.1.1Interaction with policies in aut-num class . . . . . . . . . . . 47
8.1.2Ambiguity resolution with overlapping aggregates . . . . . . . . 48
8.2 Specifying Static Routes . . . . . . . . . . . . . . . . . . . . . 49
9 inet-rtr Class 50
10Extending RPSL 51
10.1Extensions by changing the dictionary class . . . . . . . . . . . . 51
10.2Extensions by adding new attributes to existing classes . . . . . . 52
10.3Extensions by adding new classes . . . . . . . . . . . . . . . . . 52
10.4Extensions by changing the syntax of existing RPSL attributes . . . 52
11Security Consideration 53
12Acknowledgements 53
A Routing Registry Sites 55
B Authors' Addresses 55
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1 Introduction
This Internet Draft is the reference document for the Routing Policy
Specification Language (RPSL). RPSL allows a network operator to be able to
specify routing policies at various levels in the Internet hierarchy; for
example at the Autonomous System (AS) level. At the same time, policies
can be specified with sufficient detail in RPSL so that low level router
configurations can be generated from them. RPSL is extensible; new routing
protocols and new protocol features can be introduced at any time.
RPSL is a replacement for the current Internet policy specification language
known as RIPE-181 [5] or RFC-1786 [6]. RIPE-81 [7] was the first language
deployed in the Internet for specifying routing policies. It was later
replaced by RIPE-181 [5]. Through operational use of RIPE-181 it has
become apparent that certain policies cannot be specified and a need for an
enhanced and more generalized language is needed. RPSL addresses RIPE-181's
limitations.
RPSL was designed so that a view of the global routing policy can be
contained in a single cooperatively maintained distributed database to
improve the integrity of Internet's routing. RPSL is not designed to
be a router configuration language. RPSL is designed so that router
configurations can be generated from the description of the policy for
one autonomous system (aut-num class) combined with the description of
a router (inet-rtr class), mainly providing router ID, autonomous system
number of the router, interfaces and peers of the router, and combined with
a global database mappings from AS sets to ASes (as-set class), and from
origin ASes and route sets to route prefixes (route and route-set classes).
The accurate population of the RPSL database can help contribute toward
such goals as router configurations that protect against accidental (or
malicious) distribution of inaccurate routing information, verification of
Internet's routing, and aggregation boundaries beyond a single AS.
RPSL is object oriented; that is, objects contain pieces of policy and
administrative information. These objects are registered in the Internet
Routing Registry (IRR) by the authorized organizations. The registration
process is beyond the scope of this document. Please refer to [1, 16, 3]
for more details on the IRR.
In the following sections, we present the classes that are used to define
various policy and administrative objects. The "mntner" class defines
entities authorized to add, delete and modify a set of objects. The
"person" and "role" classes describes technical and administrative contact
personnel. Autonomous systems (ASes) are specified using the "aut-num"
class. Routes are specified using the "route" class. Sets of ASes
and routes can be defined using the "as-set" and "route-set" classes.
The "dictionary" class provides the extensibility to the language. The
"inet-rtr" class is used to specify routers. Many of these classes were
originally defined in earlier documents [5, 12, 15, 11, 4] and have all been
enhanced.
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This document is self-contained. However, the reader is encouraged to read
RIPE-181 [6] and the associated documents [12, 15, 11, 4] as they provide
significant background as to the motivation and underlying principles behind
RIPE-181 and consequently, RPSL. For a tutorial on RPSL, the reader should
read the RPSL applications document [3].
2 RPSL Names, Reserved Words, and Representation
Each class has a set of attributes which store a piece of information about
the objects of the class. Attributes can be mandatory or optional: A
mandatory attribute has to be defined for all objects of the class; optional
attributes can be skipped. Attributes can also be single or multiple
valued. Each object is uniquely identified by a set of attributes, referred
to as the class ``key''.
The value of an attribute has a type. The following types are most widely
used. Note that RPSL is case insensitive and only the characters from the
ASCII character set can be used.
<object-name>Many objects in RPSL have a name. An <object-name> is made
up of letters, digits, the character underscore ``_'', and the character
hyphen ``-''; the first character of a name must be a letter, and the
last character of a name must be a letter or a digit. The following
words are reserved by RPSL, and they can not be used as names:
any as-any rs-any peeras
and or not
atomic from to at action accept announce except refine
networks into inbound outbound
Names starting with certain prefixes are reserved for certain object
types. Names starting with ``as-'' are reserved for as set names.
Names starting with ``rs-'' are reserved for route set names.
<as-number>An AS number x is represented as the string ``ASx''. That is,
the AS 226 is represented as AS226.
<ipv4-address>An IPv4 address is represented as a sequence of four integers
in the range from 0 to 255 separated by the character dot ``.''. For
example, 128.9.128.5 represents a valid IPv4 address. In the rest of
this document, we may refer to IPv4 addresses as IP addresses.
<address-prefix>An address prefix is represented as an IPv4 address
followed by the character slash ``/'' followed by an integer in the
range from 0 to 32. The following are valid address prefixes:
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128.9.128.5/32, 128.9.0.0/16, 0.0.0.0/0; and the following address
prefixes are invalid: 0/0, 128.9/16 since 0 or 128.9 are not strings
containing four integers.
<address-prefix-range>An address prefix range is an address prefix followed
by an optional range operator. The range operators are:
^- is the exclusive more specifics operator; it stands for the
more specifics of the address prefix excluding the address prefix
itself. For example, 128.9.0.0/16^- contains all the more
specifics of 128.9.0.0/16 excluding 128.9.0.0/16.
^+ is the inclusive more specifics operator; it stands for the
more specifics of the address prefix including the address prefix
itself. For example, 5.0.0.0/8^+ contains all the more specifics
of 5.0.0.0/8 including 5.0.0.0/8.
^n where n is an integer, stands for all the length n specifics of the
address prefix. For example, 30.0.0.0/8^16 contains all the more
specifics of 30.0.0.0/8 which are of length 16 such as 30.9.0.0/16.
^n-m where n and m are integers, stands for all the length n to length
m specifics of the address prefix. For example, 30.0.0.0/8^24-32
contains all the more specifics of 30.0.0.0/8 which are of length
24 to 32 such as 30.9.9.96/28.
Range operators can also be applied to address prefix sets. In this
case, they distribute over the members of the set. For example, for
a route-set (defined later) rs-foo, rs-foo^+ contains all the inclusive
more specifics of all the prefixes in rs-foo.
It is an error to follow a range operator with another one (e.g.
30.0.0.0/8^24-28^+ is an error). However, a range operator can be
applied to an address prefix set that has address prefix ranges in it
(e.g. {30.0.0.0/8^24-28}^27-30 is not an error). In this case, the
outer operator ^n-m distributes over the inner operator ^k-l and becomes
the operator ^max(n,k)-m if m is greater than or equal to max(n,k), or
otherwise, the prefix is deleted from the set. Note that the operator
^n is equivalent to ^n-n; prefix/l^+ is equivalent to prefix/l^l-32;
prefix/l^- is equivalent to prefix/l^(l+1)-32; {prefix/l^n-m}^+ is
equivalent to {prefix/l^n-32}; and {prefix/l^n-m}^- is equivalent to
{prefix/l^(n+1)-32}. For example,
{128.9.0.0/16^+}^- == {128.9.0.0/16^-}
{128.9.0.0/16^-}^+ == {128.9.0.0/16^-}
{128.9.0.0/16^17}^24 == {128.9.0.0/16^24}
{128.9.0.0/16^20-24}^26-28 == {128.9.0.0/16^26-28}
{128.9.0.0/16^20-24}^22-28 == {128.9.0.0/16^22-28}
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{128.9.0.0/16^20-24}^18-28 == {128.9.0.0/16^20-28}
{128.9.0.0/16^20-24}^18-22 == {128.9.0.0/16^20-22}
{128.9.0.0/16^20-24}^18-19 == {}
<date>A date is represented as an eight digit integer of the form YYYYMMDD
where YYYY represents the year, MM represents the month of the year (01
through 12), and DD represents the day of the month (01 through 31).
All dates are in UTC unless otherwise specified. For example, June 24,
1996 is represented as 19960624.
<email-address>is as described in RFC-822[9].
<dns-name>is as described in RFC-1034[17].
<nic-handle>is a uniquely assigned identifier[14] used by routing, address
allocation, and other registries to unambiguously refer to contact
information. person and role classes map NIC handles to actual person
names, and contact information.
<free-form>is a sequence of ASCII characters.
<X-name>is a name of an object of type X. That is <mntner-name> is a name
of a mntner object.
<registry-name>is a name of an IRR registry. The routing registries are
listed in Appendix A.
A value of an attribute may also be a list of one of these types. A list is
represented by separating the list members by commas ``,''. For example,
``AS1, AS2, AS3, AS4'' is a list of AS numbers. Note that being list valued
and being multiple valued are orthogonal. A multiple valued attribute has
more than one value, each of which may or may not be a list. On the other
hand a single valued attribute may have a list value.
An RPSL object is textually represented as a list of attribute-value pairs.
Each attribute-value pair is written on a separate line. The attribute name
starts at column 0, followed by character ``:'' and followed by the value
of the attribute. The object's representation ends when a blank line is
encountered. An attribute's value can be split over multiple lines, by
having a space, a tab or a plus ('+') character as the first character of
the continuation lines. The character ``+'' for line continuation allows
attribute values to contain blank lines. More spaces may optionally be used
after the continuation character to increase readability. The order of
attribute-value pairs is significant.
An object's description may contain comments. A comment can be anywhere in
an object's definition, it starts at the first ``#'' character on a line and
ends at the first end-of-line character. White space characters can be used
to improve readability.
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An integer can be specified using (1) the C programming language notation
(e.g. 1, 12345); (2) sequence of four 1-octet integers (in the range from 0
to 255) separated by the character dot ``.'' (e.g. 1.1.1.1, 255.255.0.0),
in this case a 4-octet integer is formed by concatenating these 1-octet
integers in the most significant to least significant order; (3) sequence
of two 2-octet integers (in the range from 0 to 65535) separated by the
character colon ``:'' (e.g. 3561:70, 3582:10), in this case a 4-octet
integer is formed by concatenating these 2-octet integers in the most
significant to least significant order.
3 Contact Information
The mntner, person and role classes, admin-c, tech-c, mnt-by, changed, and
source attributes of all classes describe contact information. The mntner
class also specifies authenticaiton information required to create, delete
and update other objects. These classes do not specify routing policies
and each registry may have different or additional requirements on them.
Here we present the common denominator for completeness which is the RIPE
database implementation [16]. Please consult your routing registry for
the latest specification of these classes and attributes. The ``Routing
Policy System Security'' document [20] describes the authenticaiton and
authorization model in more detail.
3.1 mntner Class
The mntner class specifies authenticaiton information required to create,
delete and update RPSL objects. A provider, before he/she can create RPSL
objects, first needs to create a mntner object. The attributes of the
mntner class are shown in Figure 1. The mntner class was first described
in [12].
The mntner attribute is mandatory and is the class key. Its value is an
RPSL name. The auth attribute specifies the scheme that will be used to
identify and authenticate update requests from this maintainer. It has the
following syntax:
auth: <scheme-id> <auth-info>
E.g.
auth: NONE
auth: CRYPT-PW dhjsdfhruewf
auth: MAIL-FROM .*@ripe\.net
The <scheme-id>'s currently defined are: NONE, MAIL-FROM, PGP-KEY and
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Attribute Value Type
mntner <object-name> mandatory, single-valued, class key
descr <free-form> mandatory, single-valued
auth see description in text mandatory, multi-valued
upd-to <email-address> mandatory, multi-valued
mnt-nfy <email-address> optional, multi-valued
tech-c <nic-handle> mandatory, multi-valued
admin-c <nic-handle> optional, multi-valued
remarks <free-form> optional, multi-valued
notify <email-address> optional, multi-valued
mnt-by list of <mntner-name> mandatory, multi-valued
changed <email-address> <date> mandatory, multi-valued
source <registry-name> mandatory, single-valued
Figure 1: mntner Class Attributes
CRYPT-PW. The <auth-info> is additional information required by a particular
scheme: in the case of MAIL-FROM, it is a regular expression matching
valid email addresses; in the case of CRYPT-PW, it is a password in UNIX
crypt format; and in the case of PGP-KEY, it is a pointer to key-certif
object [22] containing the PGP public key of the user. If multiple auth
attributes are specified, an update request satisfying any one of them is
authenticated to be from the maintainer.
The upd-to attribute is an email address. On an unauthorized update
attempt of an object maintained by this maintainer, an email message will
be sent to this address. The mnt-nfy attribute is an email address. A
notification message will be forwarded to this email address whenever an
object maintained by this maintainer is added, changed or deleted.
The descr attribute is a short, free-form textual description of the object.
The tech-c attribute is a technical contact NIC handle. This is someone to
be contacted for technical problems such as misconfiguration. The admin-c
attribute is an administrative contact NIC handle. The remarks attribute is
a free text explanation or clarification. The notify attribute is an email
address to which notifications of changes to this object should be sent.
The mnt-by attribute is a list of mntner object names. The authorization
for changes to this object is governed by any of the maintainer objects
referenced. The changed attribute documents who last changed this object,
and when this change was made. Its syntax has the following form:
changed: <email-address> <YYYYMMDD>
E.g.
changed: johndoe@terabit-labs.nn 19900401
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The <email-address> identifies the person who made the last change.
<YYYYMMDD> is the date of the change. The source attribute specifies the
registry where the object is registered. Figure 2 shows an example mntner
object. In the example, UNIX crypt format password authentication is used.
mntner: RIPE-NCC-MNT
descr: RIPE-NCC Maintainer
admin-c: DK58
tech-c: OPS4-RIPE
upd-to: ops@ripe.net
mnt-nfy: ops-fyi@ripe.net
auth: CRYPT-PW lz1A7/JnfkTtI
mnt-by: RIPE-NCC-MNT
changed: ripe-dbm@ripe.net 19970820
source: RIPE
Figure 2: An example mntner object.
The descr, tech-c, admin-c, remarks, notify, mnt-by, changed and source
attributes are attributes of all RPSL classes. Their syntax, semantics, and
mandatory, optional, multi-valued, or single-valued status are the same for
for all RPSL classes. Only exception to this is the admin-c attribute which
is mandatory for the aut-num class. We do not further discuss them in other
sections.
3.2 person Class
A person class is used to describe information about people. Even though it
does not describe routing policy, we still describe it here briefly since
many policy objects make reference to person objects. The person class was
first described in [15].
Attribute Value Type
person <free-form> mandatory, single-valued
nic-hdl <nic-handle> mandatory, single-valued, class key
address <free-form> mandatory, multi-valued
phone see description in text mandatory, multi-valued
fax-no same as phone optional, multi-valued
e-mail <email-address> mandatory, multi-valued
Figure 3: person Class Attributes
The attributes of the person class are shown in Figure 3. The person
attribute is the full name of the person. The phone and the fax-no
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attributes have the following syntax:
phone: +<country-code> <city> <subscriber> [ext. <extension>]
E.g.:
phone: +31 20 12334676
phone: +44 123 987654 ext. 4711
Figure 4 shows an example person object.
person: Daniel Karrenberg
address: RIPE Network Coordination Centre (NCC)
address: Singel 258
address: NL-1016 AB Amsterdam
address: Netherlands
phone: +31 20 535 4444
fax-no: +31 20 535 4445
e-mail: Daniel.Karrenberg@ripe.net
nic-hdl: DK58
changed: Daniel.Karrenberg@ripe.net 19970616
source: RIPE
Figure 4: An example person object.
3.3 role Class
The role class is similar to the person object. However, instead of
describing a human being, it describes a role performed by one or more
human beings. Examples include help desks, network monitoring centers,
system administrators, etc. Role object is particularly useful since often
a person performing a role may change, however the role itself remains.
The attributes of the role class are shown in Figure 5. The nic-hdl
attributes of the person and role classes share the same name space. The
trouble attribute of role object may contain additional contact information
to be used when a problem arises in any object that references this role
object. Figure 6 shows an example role object.
4 route Class
Each interAS route (also referred to as an interdomain route) originated by
an AS is specified using a route object. The attributes of the route class
are shown in Figure 7. The route attribute is the address prefix of the
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Attribute Value Type
role <free-form> mandatory, single-valued
nic-hdl <nic-handle> mandatory, single-valued, class key
trouble <free-form> optional, multi-valued
address <free-form> mandatory, multi-valued
phone see description in text mandatory, multi-valued
fax-no same as phone optional, multi-valued
e-mail <email-address> mandatory, multi-valued
Figure 5: role Class Attributes
role: RIPE NCC Operations
trouble:
address: Singel 258
address: 1016 AB Amsterdam
address: The Netherlands
phone: +31 20 535 4444
fax-no: +31 20 545 4445
e-mail: ops@ripe.net
admin-c: CO19-RIPE
tech-c: RW488-RIPE
tech-c: JLSD1-RIPE
nic-hdl: OPS4-RIPE
notify: ops@ripe.net
changed: roderik@ripe.net 19970926
source: RIPE
Figure 6: An example role object.
route and the origin attribute is the AS number of the AS that originates
the route into the interAS routing system. The route and origin attribute
pair is the class key.
Figure 8 shows examples of four route objects (we do not include contact
attributes such as admin-c, tech-c for brevity). Note that the last two
route objects have the same address prefix, namely 128.8.0.0/16. However,
they are different route objects since they are originated by different ASes
(i.e. they have different keys).
The withdrawn attribute, if present, signifies that the originator AS no
longer originates this address prefix in the Internet. Its value is a date
indicating the date of withdrawal. In Figure 8, the last route object is
withdrawn (i.e. no longer originated by AS2) on June 24, 1996.
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Attribute Value Type
route <address-prefix> mandatory, single-valued, class key
origin <as-number> mandatory, single-valued, class key
withdrawn <date> optional, single-valued
member-of list of <route-set-names> optional, multi-valued
see Section 5
inject see Section 8 optional, multi-valued
components see Section 8 optional, single-valued
aggr-bndry see Section 8 optional, single-valued
aggr-mtd see Section 8 optional, single-valued
export-comps see Section 8 optional, multi-valued
holes see Section 8 optional, multi-valued
Figure 7: route Class Attributes
route: 128.9.0.0/16
origin: AS226
route: 128.99.0.0/16
origin: AS226
route: 128.8.0.0/16
origin: AS1
route: 128.8.0.0/16
origin: AS2
withdrawn: 19960624
Figure 8: Route Objects
5 Set Classes
To specify policies, it is often useful to define sets of objects. For
this purpose we define two classes: route-set and as-set. These classes
define a named set. The members of these sets can be specified by either
explicitly listing them in the set object's definition, or implicitly by
having route and aut-num objects refer to their names, or a combination of
both methods.
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5.1 route-set Class
The attributes of the route-set class are shown in Figure 9. The route-set
attribute defines the name of the set. It is an RPSL name that starts
with ``rs-''. The members attribute lists the members of the set. The
members attribute is a list of address prefixes or other route-set names.
Note that, the route-set class is a set of route prefixes, not of RPSL route
objects.
Attribute Value Type
route-set <object-name> mandatory, single-valued,
class key
members list of <address-prefix-range> or optional, multi-valued
<route-set-name> or
<route-set-name><range-operator>
mbrs-by-ref list of <mntner-names> optional, multi-valued
Figure 9: route-set Class Attributes
Figure 10 presents some example route-set objects. The set rs-foo contains
two address prefixes, namely 128.9.0.0/16 and 128.9.0.0/24. The set rs-bar
contains the members of the set rs-foo and the address prefix 128.7.0.0/16.
The set rs-empty contains no members.
route-set: rs-foo
members: 128.9.0.0/16, 128.9.0.0/24
route-set: rs-bar
members: 128.7.0.0/16, rs-foo
route-set: rs-empty
Figure 10: route-set Objects
An address prefix or a route-set name in a members attribute can be
optionally followed by a range operator. For example, the following set
route-set: rs-bar
members: 5.0.0.0/8^+, 30.0.0.0/8^24-32, rs-foo^+
contains all the more specifics of 5.0.0.0/8 including 5.0.0.0/8, all
the more specifics of 30.0.0.0/8 which are of length 24 to 32 such as
30.9.9.96/28, and all the more specifics of address prefixes in route set
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rs-foo.
The mbrs-by-ref attribute is a list of maintainer names or the keyword ANY.
If this attribute is used, the route set also includes address prefixes
whose route objects are registered by one of these maintainers and whose
member-of attribute refers to the name of this route set. If the value of a
mbrs-by-ref attribute is ANY, any route object referring to the route set
name is a member. If the mbrs-by-ref attribute is missing, only the address
prefixes listed in the members attribute are members of the set.
route-set: rs-foo
mbrs-by-ref: MNTR-ME, MNTR-YOU
route-set: rs-bar
members: 128.7.0.0/16
mbrs-by-ref: MNTR-YOU
route: 128.9.0.0/16
origin: AS1
member-of: rs-foo
mnt-by: MNTR-ME
route: 128.8.0.0/16
origin: AS2
member-of: rs-foo, rs-bar
mnt-by: MNTR-YOU
Figure 11: route-set objects.
Figure 11 presents example route-set objects that use the mbrs-by-ref
attribute. The set rs-foo contains two address prefixes, namely
128.8.0.0/16 and 128.9.0.0/16 since the route objects for 128.8.0.0/16 and
128.9.0.0/16 refer to the set name rs-foo in their member-of attribute. The
set rs-bar contains the address prefixes 128.7.0.0/16 and 128.8.0.0/16. The
route 128.7.0.0/16 is explicitly listed in the members attribute of rs-bar,
and the route object for 128.8.0.0/16 refer to the set name rs-bar in its
member-of attribute.
Note that, if an address prefix is listed in a members attribute of a route
set, it is a member of that route set. The route object corresponding to
this address prefix does not need to contain a member-of attribute referring
to this set name. The member-of attribute of the route class is an
additional mechanism for specifying the members indirectly.
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5.2 as-set Class
The attributes of the as-set class are shown in Figure 12. The as-set
attribute defines the name of the set. It is an RPSL name that starts with
``as-''. The members attribute lists the members of the set. The members
attribute is a list of AS numbers, or other as-set names.
Attribute Value Type
as-set <object-name> mandatory, single-valued,
class key
members list of <as-numbers> or optional, multi-valued
<as-set-names>
mbrs-by-ref list of <mntner-names> optional, multi-valued
Figure 12: as-set Class Attributes
Figure 13 presents two as-set objects. The set as-foo contains two ASes,
namely AS1 and AS2. The set as-bar contains the members of the set as-foo
and AS3, that is it contains AS1, AS2, AS3.
as-set: as-foo as-set: as-bar
members: AS1, AS2 members: AS3, as-foo
Figure 13: as-set objects.
The mbrs-by-ref attribute is a list of maintainer names or the keyword ANY.
If this attribute is used, the AS set also includes ASes whose aut-num
objects are registered by one of these maintainers and whose member-of
attribute refers to the name of this AS set. If the value of a mbrs-by-ref
attribute is ANY, any AS object referring to the AS set is a member of the
set. If the mbrs-by-ref attribute is missing, only the ASes listed in the
members attribute are members of the set.
as-set: as-foo
members: AS1, AS2
mbrs-by-ref: MNTR-ME
aut-num: AS3 aut-num: AS4
member-of: as-foo member-of: as-foo
mnt-by: MNTR-ME mnt-by: MNTR-OTHER
Figure 14: as-set objects.
Figure 14 presents an example as-set object that uses the mbrs-by-ref
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attribute. The set as-foo contains AS1, AS2 and AS3. AS4 is not a member
of the set as-foo even though the aut-num object references as-foo. This is
because MNTR-OTHER is not listed in the as-foo's mbrs-by-ref attribute.
5.3 Predefined Set Objects
In a context that expects a route set (e.g. members attribute of the
route-set class), an AS number ASx defines the set of routes that are
originated by ASx; and an as-set AS-X defines the set of routes that are
originated by the ASes in AS-X. A route p is said to be originated by ASx if
there is a route object for p with ASx as the value of the origin attribute.
For example, in Figure 15, the route set rs-special contains 128.9.0.0/16,
routes of AS1 and AS2, and routes of the ASes in AS set AS-FOO.
route-set: rs-special
members: 128.9.0.0/16, AS1, AS2, AS-FOO
Figure 15: Use of AS numbers and AS sets in route sets.
The set rs-any contains all routes registered in IRR. The set as-any
contains all ASes registered in IRR.
5.4 Hierarchical Set Names
Set names can be hierarchical. A hierarchical set name is a sequence of set
names and AS numbers separated by colons ``:''. For example, the following
names are valid: AS1:AS-CUSTOMERS, AS1:RS-EXCEPTIONS, AS1:RS-EXPORT:AS2,
RS-EXCEPTIONS:RS-BOGUS. All components of an hierarchical set name which are
not AS numbers should start with ``as-'' or ``rs-'' for as sets and route
sets respectively. And at least one component must be a set name.
A set object with name X1:...:Xn-1:Xn can only be created by the maintainer
of the object with name X1:...:Xn-1. That is, only the maintainer of AS1
can create a set with name AS1:AS-FOO; and only the maintainer of AS1:AS-FOO
can create a set with name AS1:AS-FOO:AS-BAR. Please see RPS Security
Document [20] for details.
The purpose of an hierarchical set name is to partition the set name space
so that the controllers of the set name X1 controls the whole set name
space under X1, i.e. X1:...:Xn-1. This is important since anyone can
create a set named AS-MCI-CUSTOMERS but only the people created AS3561
can create AS3561:AS-CUSTOMERS. In the former, it is not clear if the
set AS-MCI-CUSTOMERS has any relationship with MCI. In the latter, we
can guarantee that AS3561:AS-CUSTOMERS and AS3561 are created by the same
entity.
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6 aut-num Class
Routing policies are specified using the aut-num class. The attributes
of the aut-num class are shown in Figure 16. The value of the aut-num
attribute is the AS number of the AS described by this object. The as-name
attribute is a symbolic name (in RPSL name syntax) of the AS. The import,
export and default routing policies of the AS are specified using import,
export and default attributes respectively.
Attribute Value Type
aut-num <as-number> mandatory, single-valued, class key
as-name <object-name> mandatory, single-valued
member-of list of <as-set-names> optional, multi-valued
import see Section 6.1 optional, multi valued
export see Section 6.2 optional, multi valued
default see Section 6.5 optional, multi valued
Figure 16: aut-num Class Attributes
6.1 import Attribute: Import Policy Specification
---------------------- ----------------------
| 7.7.7.1 |-------| |-------| 7.7.7.2 |
| | ======== | |
| AS1 | EX1 |-------| 7.7.7.3 AS2 |
| | | |
| 9.9.9.1 |------ ------| 9.9.9.2 |
---------------------- | | ----------------------
===========
| EX2
---------------------- |
| 9.9.9.3 |---------
| |
| AS3 |
----------------------
Figure 17: Example topology consisting of three ASes, AS1, AS2, and AS3;
two exchange points, EX1 and EX2; and six routers.
Figure 17 shows a typical interconnection of ASes that we will be using
in our examples throughout this section. In this example topology, there
are three ASes, AS1, AS2, and AS3; two exchange points, EX1 and EX2;
and six routers. Routers connected to the same exchange point peer with
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each other and exchange routing information. Each router would export a
subset of the routes it has to its peer routers. Peer routers would
import a subset of these routes. A router while importing routes would
set some route attributes. For example, AS1 can assign higher preference
values to the routes it imports from AS2 so that it prefers AS2 over AS3.
While exporting routes, a router may also set some route attributes in
order to affect route selection of other ASes. For example, AS2 may set
the MULTI-EXIT-DISCRIMINATOR BGP attribute so that AS1 prefers the routes
through router 9.9.9.2. Most interAS policies are specified by specifying
what route subsets can be imported or exported, and how the various BGP
route attributes are set and used.
In RPSL, an import policy is divided into import policy expressions. Each
import policy expression is specified using an import attribute. The import
attribute has the following syntax (we will extend this syntax later in
Sections 6.3 and 6.6):
import: from <peering-1> [action <action-1>]
. . .
from <peering-N> [action <action-N>]
accept <filter>
The action specification is optional. The semantics of an import attribute
is as follows: the set of routes that are matched by <filter> are imported
from all the peers in <peerings>; while importing routes at <peering-M>,
<action-M> is executed.
E.g.
aut-num: AS1
import: from AS2 action pref = 1; accept { 128.9.0.0/16 }
This example states that the route 128.9.0.0/16 is accepted from AS2 with
preference 1. In the next few subsections, we will describe how peerings,
actions and filters are specified.
6.1.1 Peering Specification
Our example above used an AS number to specify peerings. The peerings
can be specified at different granularities. The syntax of a peering
specification has two forms. The first one is as follows:
<peer-as> [<peer-router>] [at <local-router>]
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where <local-router> and <peer-router> are IP addresses of routers,
<peer-as> is an AS number. <peer-as> must be the AS number of
<peer-router>. Both <local-router> and <peer-router> are optional. If
neither router is specified, this peering specification identifies all the
peerings between the local AS and the <peer-as>. If both <local-router>
and <peer-router> are specified, only that particular peering between these
two routers are identified. If only the <local-router> is specified,
all peerings between the <local-router> and any router in <peer-as> are
identified. If only the <peer-router> is specified, all peerings from the
routers in the local AS to the <peer-router> are identified.
We next give examples. Consider the topology of Figure 17 where 7.7.7.1,
7.7.7.2 and 7.7.7.3 peer with each other; 9.9.9.1, 9.9.9.2 and 9.9.9.3 peer
with each other. In the following example 7.7.7.1 imports 128.9.0.0/16 from
7.7.7.2.
(1) aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1 accept { 128.9.0.0/16 }
In the following example 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2 and
7.7.7.3.
(2) aut-num: AS1
import: from AS2 at 7.7.7.1 accept { 128.9.0.0/16 }
In the following example 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2 and
7.7.7.3, and 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2.
(3) aut-num: AS1
import: from AS2 accept { 128.9.0.0/16 }
The second form of <peering> specification has the following syntax:
<as-expression> [at <router-expression>]
where <as-expression> is an expression over AS numbers and sets using
operators AND, OR, and NOT, and <router-expression> is an expression over
router IP addresses and DNS names using operators AND, OR, and NOT. The
DNS name can only be used if there is an inet-rtr object for that name
that binds the name to IP addresses. This form identifies all the
peerings between any local router in <router-expression> to any of their
peer routers in the ASes in <as-expression>. If <router-expression> is not
specified, it defaults to all routers of the local AS that peer with ASes in
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<as-expression>.
In the following example 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2 and
9.9.9.3.
(4) as-set: AS-FOO
members: AS2, AS3
aut-num: AS1
import: from AS-FOO at 9.9.9.1 accept { 128.9.0.0/16 }
In the following example 9.9.9.1 imports 128.9.0.0/16 from 9.9.9.2 and
9.9.9.3, and 7.7.7.1 imports 128.9.0.0/16 from 7.7.7.2 and 7.7.7.3.
(5) aut-num: AS1
import: from AS-FOO accept { 128.9.0.0/16 }
In the following example AS1 imports 128.9.0.0/16 from AS3 at router 9.9.9.1
(6) aut-num: AS1
import: from AS-FOO and not AS2
at not 7.7.7.1
accept { 128.9.0.0/16 }
This is because "AS-FOO and not AS2" equals AS3 and "not 7.7.7.1" equals
9.9.9.1.
6.1.2 Action Specification
Policy actions in RPSL either set or modify route attributes, such as
assigning a preference to a route, adding a BGP community to the BGP
community path attribute, or setting the MULTI-EXIT-DISCRIMINATOR attribute.
Policy actions can also instruct routers to perform special operations, such
as route flap damping.
The routing policy attributes whose values can be modified in policy actions
are specified in the RPSL dictionary. Please refer to Section 7 for a list
of these attributes. Each action in RPSL is terminated by the semicolon
character (';'). It is possible to form composite policy actions by listing
them one after the other. In a composite policy action, the actions are
executed left to right. For example,
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aut-num: AS1
import: from AS2
action pref = 10; med = 0; community.append(10250, 3561:10);
accept { 128.9.0.0/16 }
sets pref to 10, med to 0, and then appends 10250 and 3561:10 to the
BGP community path attribute. The pref attribute is the inverse of the
local-pref attribute (i.e. local-pref == 65535 - pref). A route with a
local-pref attribute is always preferred over a route without one.
6.1.3 Filter Specification
A policy filter is a logical expression which when applied to a set of
routes returns a subset of these routes. We say that the policy filter
matches the subset returned. The policy filter can match routes using any
path attribute, such as the destination address prefix (or NLRI), AS-path,
or community attributes.
The policy filters can be composite by using the operators AND, OR, and NOT.
The following policy filters can be used to select a subset of routes:
ANY The filter-keyword ANY matches all routes.
Address-Prefix Set This is an explicit list of address prefixes enclosed
in braces '{' and '}'. The policy filter matches the set of routes whose
destination address-prefix is in the set. For example:
{ 0.0.0.0/0 }
{ 128.9.0.0/16, 128.8.0.0/16, 128.7.128.0/17, 5.0.0.0/8 }
{ }
An address prefix can be optionally followed by a range operator (i.e. '^-',
'^+', '^n', or '^n-m'). For example, the set
{ 5.0.0.0/8^+, 128.9.0.0/16^-, 30.0.0.0/8^16, 30.0.0.0/8^24-32 }
contains all the more specifics of 5.0.0.0/8 including 5.0.0.0/8, all
the more specifics of 128.9.0.0/16 excluding 128.9.0.0/16, all the more
specifics of 30.0.0.0/8 which are of length 16 such as 30.9.0.0/16, and
all the more specifics of 30.0.0.0/8 which are of length 24 to 32 such as
30.9.9.96/28.
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Route Set Name A route set name matches the set of routes that are members
of the set. A route set name may be a name of a route-set object, an
AS number, or a name of an as-set object (AS numbers and as-set names
implicitly define route sets; please see Section 5.3). For example:
aut-num: AS1
import: from AS2 action pref = 1; accept AS2
import: from AS2 action pref = 1; accept AS-FOO
import: from AS2 action pref = 1; accept RS-FOO
The keyword PeerAS can be used instead of the AS number of the peer AS.
PeerAS is particularly useful when the peering is specified using an AS
expression. For example:
as-set: AS-FOO
members: AS2, AS3
aut-num: AS1
import: from AS-FOO action pref = 1; accept PeerAS
is same as:
aut-num: AS1
import: from AS2 action pref = 1; accept AS2
import: from AS3 action pref = 1; accept AS3
A route set name can also be followed by one of the operators '^-', '^+',
'^n' or '^n-m'. These operators are distributive over the route sets. For
example, { 5.0.0.0/8, 6.0.0.0/8 }^+ equals { 5.0.0.0/8^+, 6.0.0.0/8^+ }, and
AS1^- equals all the exclusive more specifics of routes originated by AS1.
AS Path Regular Expressions An AS-path regular expression can be used as
a policy filter by enclosing the expression in `<' and `>'. An AS-path
policy filter matches the set of routes which traverses a sequence of ASes
matched by the AS-path regular expression. A router can check this using
the AS_PATH attribute in the Border Gateway Protocol [19], or the RD_PATH
attribute in the Inter-Domain Routing Protocol[18].
AS-path Regular Expressions are POSIX compliant regular expressions over the
alphabet of AS numbers. The regular expression constructs are as follows:
ASN where ASN is an AS number. ASN matches the AS-path that is
of length 1 and contains the corresponding AS number (e.g.
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AS-path regular expression AS1 matches the AS-path ``1'').
The keyword PeerAS can be used instead of the AS number of the
peer AS.
AS-set where AS-set is an AS set name. AS-set matches the AS-paths that
is matched by one of the ASes in the AS-set.
. matches the AS-paths matched by any AS number.
[...] is an AS number set. It matches the AS-paths matched by the AS
numbers listed between the brackets. The AS numbers in the
set are separated by white space characters. If a `-' is used
between two AS numbers in this set, all AS numbers between the
two AS numbers are included in the set. If an as-set name is
listed, all AS numbers in the as-set are included.
[^...] is a complemented AS number set. It matches any AS-path which is
not matched by the AS numbers in the set.
^ Matches the empty string at the beginning of an AS-path.
$ Matches the empty string at the end of an AS-path.
We next list the regular expression operators in the decreasing order of
evaluation. These operators are left associative, i.e. performed left to
right.
Unary postfix operators * + ? {m} {m,n} {m,}
For a regular expression A, A* matches zero or more
occurrences of A; A+ matches one or more occurrences of A; A?
matches zero or one occurrence of A; A{m} matches m occurrence
of A; A{m,n} matches m to n occurrence of A; A{m,} matches m
or more occurrence of A. For example, [AS1 AS2]{2} matches AS1
AS1, AS1 AS2, AS2 AS1, and AS2 AS2.
Unary postfix operators ~* ~+ ~{m} ~{m,n} ~{m,}
These operators have similar functionality as the correspond-
ing operators listed above, but all occurrences of the regular
expression has to match the same pattern. For example, [AS1
AS2]~{2} matches AS1 AS1 and AS2 AS2, but it does not match AS1
AS2 and AS2 AS1.
Binary catenation operator
This is an implicit operator and exists between two regular
expressions A and B when no other explicit operator is
specified. The resulting expression A B matches an AS-path if
A matches some prefix of the AS-path and B matches the rest of
the AS-path.
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Binary alternative (or) operator |
For a regular expressions A and B, A | B matches any AS-path
that is matched by A or B.
Parenthesis can be used to override the default order of evaluation. White
spaces can be used to increase readability.
The following are examples of AS-path filters:
<AS3>
<^AS1>
<AS2$>
<^AS1 AS2 AS3$>
<^AS1 .* AS2$>.
The first example matches any route whose AS-path contains AS3, the second
matches routes whose AS-path starts with AS1, the third matches routes whose
AS-path ends with AS2, the fourth matches routes whose AS-path is exactly
``1 2 3'', and the fifth matches routes whose AS-path starts with AS1 and
ends in AS2 with any number of AS numbers in between.
Composite Policy Filters The following operators (in decreasing order of
evaluation) can be used to form composite policy filters:
NOT Given a policy filter x, NOT x matches the set of routes that are not
matched by x. That is it is the negation of policy filter x.
AND Given two policy filters x and y, x AND y matches the intersection of
the routes that are matched by x and that are matched by y.
OR Given two policy filters x and y, x OR y matches the union of the routes
that are matched by x and that are matched by y.
Note that an OR operator can be implicit, that is `x y' is equivalent to `x
OR y'.
E.g.
NOT {128.9.0.0/16, 128.8.0.0/16}
AS226 AS227 OR AS228
AS226 AND NOT {128.9.0.0/16}
AS226 AND {0.0.0.0/0^0-18}
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The first example matches any route except 128.9.0.0/16 and 128.8.0.0/16.
The second example matches the routes of AS226, AS227 and AS228. The third
example matches the routes of AS226 except 128.9.0.0/16. The fourth example
matches the routes of AS226 whose length are not longer than 18.
Routing Policy Attributes Policy filters can also use the values of other
attributes for comparison. The attributes whose values can be used in
policy filters are specified in the RPSL dictionary. Please refer to
Section 7 for details. An example using the the BGP community attribute is
shown below:
aut-num: AS1
export: to AS2 announce AS1 AND NOT community.contains(NO_EXPORT)
Filters using the routing policy attributes defined in the dictionary are
evaluated before evaluating the operators AND, OR and NOT.
6.1.4 Example Policy Expressions
aut-num: AS1
import: from AS2 action pref = 1;
from AS3 action pref = 2;
accept AS4
The above example states that AS4's routes are accepted from AS2 with
preference 1, and from AS3 with preference 2 (routes with lower integer
preference values are preferred over routes with higher integer preference
values).
aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 1;
from AS2 action pref = 2;
accept AS4
The above example states that AS4's routes are accepted from AS2 on peering
7.7.7.1-7.7.7.2 with preference 1, and on any other peering with AS2 with
preference 2.
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6.2 export Attribute: Export Policy Specification
Similarly, an export policy expression is specified using an export
attribute. The export attribute has the following syntax:
export: to <peering-1> [action <action-1>]
. . .
to <peering-N> [action <action-N>]
announce <filter>
The action specification is optional. The semantics of an export attribute
is as follows: the set of routes that are matched by <filter> are
exported to all the peers specified in <peerings>; while exporting routes at
<peering-M>, <action-M> is executed.
E.g.
aut-num: AS1
export: to AS2 action med = 5; community .= { 70 };
announce AS4
In this example, AS4's routes are announced to AS2 with the med attribute's
value set to 5 and community 70 added to the community list.
Example:
aut-num: AS1
export: to AS-FOO announce ANY
In this example, AS1 announces all of its routes to the ASes in the set
AS-FOO.
6.3 Other Routing Protocols, Multi-Protocol Routing Protocols, and Injecting
Routes Between Protocols
The more complete syntax of the import and export attributes are as follows:
import: [protocol <protocol-1>] [into <protocol-2>]
from <peering-1> [action <action-1>]
. . .
from <peering-N> [action <action-N>]
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accept <filter>
export: [protocol <protocol-1>] [into <protocol-2>]
to <peering-1> [action <action-1>]
. . .
to <peering-N> [action <action-N>]
announce <filter>
Where the optional protocol specifications can be used for specifying
policies for other routing protocols, or for injecting routes of one
protocol into another protocol, or for multi-protocol routing policies. The
valid protocol names are defined in the dictionary. The <protocol-1>
is the name of the protocol whose routes are being exchanged. The
<protocol-2> is the name of the protocol which is receiving these routes.
Both <protocol-1> and <protocol-2> default to the Internet Exterior Gateway
Protocol, currently BGP.
In the following example, all interAS routes are injected into RIP.
aut-num: AS1
import: from AS2 accept AS2
export: protocol BGP4 into RIP
to AS1 announce ANY
In the following example, AS1 accepts AS2's routes including any more
specifics of AS2's routes, but does not inject these extra more specific
routes into OSPF.
aut-num: AS1
import: from AS2 accept AS2^+
export: protocol BGP4 into OSPF
to AS1 announce AS2
In the following example, AS1 injects its static routes (routes which are
members of the set AS1:RS-STATIC-ROUTES) to the interAS routing protocol and
appends AS1 twice to their AS paths.
aut-num: AS1
import: protocol STATIC into BGP4
from AS1 action aspath.prepend(AS1, AS1);
accept AS1:RS-STATIC-ROUTES
In the following example, AS1 imports different set of unicast routes for
multicast reverse path forwarding from AS2:
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aut-num: AS1
import: from AS2 accept AS2
import: protocol IDMR
from AS2 accept AS2:RS-RPF-ROUTES
6.4 Ambiguity Resolution
It is possible that the same peering can be covered by more that one peering
specification in a policy expression. For example:
aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 2;
from AS2 7.7.7.2 at 7.7.7.1 action pref = 1;
accept AS4
This is not an error, though definitely not desirable. To break the
ambiguity, the action corresponding to the first peering specification is
used. That is the routes are accepted with preference 2. We call this rule
as the specification-order rule.
Consider the example:
aut-num: AS1
import: from AS2 action pref = 2;
from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; dpa = 5;
accept AS4
where both peering specifications cover the peering 7.7.7.1-7.7.7.2, though
the second one covers it more specifically. The specification order rule
still applies, and only the action ``pref = 2'' is executed. In fact, the
second peering-action pair has no use since the first peering-action pair
always covers it. If the intended policy was to accept these routes with
preference 1 on this particular peering and with preference 2 in all other
peerings, the user should have specified:
aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1 action pref = 1; dpa = 5;
from AS2 action pref = 2;
accept AS4
It is also possible that more than one policy expression can cover the same
set of routes for the same peering. For example:
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aut-num: AS1
import: from AS2 action pref = 2; accept AS4
import: from AS2 action pref = 1; accept AS4
In this case, the specification-order rule is still used. That is, AS4's
routes are accepted from AS2 with preference 2. If the filters were
overlapping but not exactly the same:
aut-num: AS1
import: from AS2 action pref = 2; accept AS4
import: from AS2 action pref = 1; accept AS4 OR AS5
the AS4's routes are accepted from AS2 with preference 2 and however AS5's
routes are also accepted, but with preference 1.
We next give the general specification order rule for the benefit of the
RPSL implementors. Consider two policy expressions:
aut-num: AS1
import: from peerings-1 action action-1 accept filter-1
import: from peerings-2 action action-2 accept filter-2
The above policy expressions are equivalent to the following three
expressions where there is no ambiguity:
aut-num: AS1
import: from peerings-1 action action-1 accept filter-1
import: from peerings-3 action action-2 accept filter-2 AND NOT filter-1
import: from peerings-4 action action-2 accept filter-2
where peerings-3 are those that are covered by both peerings-1 and
peerings-2, and peerings-4 are those that are covered by peerings-2 but not
by peerings-1 (``filter-2 AND NOT filter-1'' matches the routes that are
matched by filter-2 but not by filter-1).
Example:
aut-num: AS1
import: from AS2 7.7.7.2 at 7.7.7.1
action pref = 2;
accept {128.9.0.0/16}
import: from AS2
action pref = 1;
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accept {128.9.0.0/16, 75.0.0.0/8}
Lets consider two peerings with AS2, 7.7.7.1-7.7.7.2 and 9.9.9.1-9.9.9.2.
Both policy expressions cover 7.7.7.1-7.7.7.2. On this peering, the route
128.9.0.0/16 is accepted with preference 2, and the route 75.0.0.0/8 is
accepted with preference 1. The peering 9.9.9.1-9.9.9.2 is only covered by
the second policy expressions. Hence, both the route 128.9.0.0/16 and the
route 75.0.0.0/8 are accepted with preference 1 on peering 9.9.9.1-9.9.9.2.
Note that the same ambiguity resolution rules also apply to export and
default policy expressions.
6.5 default Attribute: Default Policy Specification
Default routing policies are specified using the default attribute. The
default attribute has the following syntax:
default: to <peering> [action <action>] [networks <filter>]
The <action> and <filter> specifications are optional. The semantics
are as follows: The <peering> specification indicates the AS (and the
router if present) is being defaulted to; the <action> specification,
if present, indicates various attributes of defaulting, for example a
relative preference if multiple defaults are specified; and the <filter>
specifications, if present, is a policy filter. A router chooses a default
router from the routes in its routing table that matches this <filter>.
In the following example, AS1 defaults to AS2 for routing.
aut-num: AS1
default: to AS2
In the following example, router 7.7.7.1 in AS1 defaults to router 7.7.7.2
in AS2.
aut-num: AS1
default: to AS2 7.7.7.2 at 7.7.7.1
In the following example, AS1 defaults to AS2 and AS3, but prefers AS2 over
AS3.
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aut-num: AS1
default: to AS2 action pref = 1;
default: to AS3 action pref = 2;
In the following example, AS1 defaults to AS2 and uses 128.9.0.0/16 as the
default network.
aut-num: AS1
default: to AS2 networks { 128.9.0.0/16 }
6.6 Structured Policy Specification
The import and export policies can be structured. We only reccomend
structured policies to advanced RPSL users. Please feel free to skip this
section.
The syntax for a structured policy specification is the following:
<import-factor> ::= from <peering-1> [action <action-1>]
. . .
from <peering-N> [action <action-N>]
accept <filter>;
<import-term> ::= <import-factor> |
LEFT-BRACE
<import-factor>
. . .
<import-factor>
RIGHT-BRACE
<import-expression> ::= <import-term> |
<import-term> EXCEPT <import-expression> |
<import-term> REFINE <import-expression>
import: [protocol <protocol1>] [into <protocol2>]
<import-expression>
Please note the semicolon at the end of an <import-factor>. If the policy
specification is not structured (as in all the examples in other sections),
this semicolon is optional. The syntax and semantics for an <import-factor>
is already defined in Section 6.1.
An <import-term> is either a sequence of <import-factor>'s enclosed within
matching braces (i.e. `{' and `}') or just a single <import-factor>. The
semantics of an <import-term> is the union of <import-factor>'s using the
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specification order rule. An <import-expression> is either a single
<import-term> or an <import-term> followed by one of the keywords "except"
and "refine", followed by another <import-expression>. Note that our
definition allows nested expressions. Hence there can be exceptions to
exceptions, refinements to refinements, or even refinements to exceptions,
and so on.
The semantics for the except operator is as follows: The result of
an except operation is another <import-term>. The resulting policy set
contains the policies of the right hand side but their filters are modified
to only include the routes also matched by the left hand side. The policies
of the left hand side are included afterwards and their filters are modified
to exclude the routes matched by the right hand side. Please note that
the filters are modified during this process but the actions are copied
verbatim. When there are multiple levels of nesting, the operations (both
except and refine) are performed right to left.
Consider the following example:
import: from AS1 action pref = 1; accept as-foo;
except {
from AS2 action pref = 2; accept AS226;
except {
from AS3 action pref = 3; accept {128.9.0.0/16};
}
}
where the route 128.9.0.0/16 is originated by AS226, and AS226 is a member
of the as set as-foo. In this example, the route 128.9.0.0/16 is accepted
from AS3, any other route (not 128.9.0.0/16) originated by AS226 is accepted
from AS2, and any other ASes' routes in as-foo is accepted from AS1.
We can come to the same conclusion using the algebra defined above.
Consider the inner exception specification:
from AS2 action pref = 2; accept AS226;
except {
from AS3 action pref = 3; accept {128.9.0.0/16};
}
is equivalent to
{
from AS3 action pref = 3; accept AS226 AND {128.9.0.0/16};
from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16};
}
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Hence, the original expression is equivalent to:
import: from AS1 action pref = 1; accept as-foo;
except {
from AS3 action pref = 3; accept AS226 AND {128.9.0.0/16};
from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16};
}
which is equivalent to
import: {
from AS3 action pref = 3;
accept as-foo AND AS226 AND {128.9.0.0/16};
from AS2 action pref = 2;
accept as-foo AND AS226 AND NOT {128.9.0.0/16};
from AS1 action pref = 1;
accept as-foo AND NOT
(AS226 AND NOT {128.9.0.0/16} OR AS226 AND {128.9.0.0/16});
}
Since AS226 is in as-foo and 128.9.0.0/16 is in AS226, it simplifies to:
import: {
from AS3 action pref = 3; accept {128.9.0.0/16};
from AS2 action pref = 2; accept AS226 AND NOT {128.9.0.0/16};
from AS1 action pref = 1; accept as-foo AND NOT AS226;
}
In the case of the refine operator, the resulting set is constructed by
taking the cartasian product of the two sides as follows: for each policy l
in the left hand side and for each policy r in the right hand side, the
peerings of the resulting policy are the peerings common to both r and l;
the filter of the resulting policy is the intersection of l's filter and r's
filter; and action of the resulting policy is l's action followed by r's
action. If there are no common peerings, or if the intersection of filters
is empty, a resulting policy is not generated.
Consider the following example:
import: { from AS-ANY action pref = 1; accept community.contains({3560,10});
from AS-ANY action pref = 2; ac-
cept community.contains({3560,20});
} refine {
from AS1 accept AS1;
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from AS2 accept AS2;
from AS3 accept AS3;
}
Here, any route with community {3560,10} is assigned a preference of 1 and
any route with community {3560,20} is assigned a preference of 2 regardless
of whom they are imported from. However, only AS1's routes are imported
from AS1, and only AS2's routes are imported from AS2, and only AS3's routes
are imported form AS3, and no routes are imported from any other AS. We can
reach the same conclusion using the above algebra. That is, our example is
equivalent to:
import: {
from AS1 action pref = 1; accept community.contains({3560,10}) AND AS1;
from AS1 action pref = 2; accept community.contains({3560,20}) AND AS1;
from AS2 action pref = 1; accept community.contains({3560,10}) AND AS2;
from AS2 action pref = 2; accept community.contains({3560,20}) AND AS2;
from AS3 action pref = 1; accept community.contains({3560,10}) AND AS3;
from AS3 action pref = 2; accept community.contains({3560,20}) AND AS3;
}
Note that the common peerings between ``from AS1'' and ``from AS-ANY'' are
those peerings in ``from AS1''. Even though we do not formally define
``common peerings'', it is straight forward to deduce the definition from
the definitions of peerings (please see Section 6.1.1).
Consider the following example:
import: {
from AS-ANY action med = 0; accept {0.0.0.0/0^0-18};
} refine {
from AS1 at 7.7.7.1 action pref = 1; accept AS1;
from AS1 action pref = 2; accept AS1;
}
where only routes of length 0 to 18 are accepted and med's value is set to 0
to disable med's effect for all peerings; In addition, from AS1 only AS1's
routes are imported, and AS1's routes imported at 7.7.7.1 are preferred over
other peerings. This is equivalent to:
import: {
from AS1 at 7.7.7.1 action med=0; pref=1; accept {0.0.0.0/0^0-
18} AND AS1;
from AS1 action med=0; pref=2; accept {0.0.0.0/0^0-
18} AND AS1;
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}
The above syntax and semantics also apply equally to structured export
policies with ``from'' replaced with ``to'' and ``accept'' is replaced with
``announce''.
7 dictionary Class
The dictionary class provides extensibility to RPSL. Dictionary objects
define routing policy attributes, types, and routing protocols. Routing
policy attributes, henceforth called rp-attributes, may correspond to actual
protocol attributes, such as the BGP path attributes (e.g. community, dpa,
and AS-path), or they may correspond to router features (e.g. BGP route flap
damping). As new protocols, new protocol attributes, or new router features
are introduced, the dictionary object is updated to include appropriate
rp-attribute and protocol definitions.
An rp-attribute is an abstract class; that is a data representation is not
available. Instead, they are accessed through access methods. For example,
the rp-attribute for the BGP AS-path attribute is called aspath; and it has
an access method called prepend which stuffs extra AS numbers to the AS-path
attributes. Access methods can take arguments. Arguments are strongly
typed. For example, the method prepend above takes AS numbers as arguments.
Once an rp-attribute is defined in the dictionary, it can be used to
describe policy filters and actions. Policy analysis tools are required
to fetch the dictionary object and recognize newly defined rp-attributes,
types, and protocols. The analysis tools may approximate policy analyses
on rp-attributes that they do not understand: a filter method may always
match, and an action method may always perform no-operation. Analysis tools
may even download code to perform appropriate operations using mechanisms
outside the scope of RPSL.
We next describe the syntax and semantics of the dictionary class. This
description is not essential for understanding dictionary objects (but it is
essential for creating one). Please feel free to skip to the RPSL Initial
Dictionary subsection (Section 7.1).
The attributes of the dictionary class are shown in Figure 18. The
dictionary attribute is the name of the dictionary object, obeying the RPSL
naming rules. There can be many dictionary objects, however there is always
one well-known dictionary object ``RPSL''. All tools use this dictionary by
default.
The rp-attribute attribute has the following syntax:
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Attribute Value Type
dictionary <object-name> mandatory, single-valued, class key
rp-attribute see description in text optional, multi valued
typedef see description in text optional, multi valued
protocol see description in text optional, multi valued
Figure 18: dictionary Class Attributes
rp-attribute: <name>
<method-1>(<type-1-1>, ..., <type-1-N1> [, "..."])
...
<method-M>(<type-M-1>, ..., <type-M-NM> [, "..."])
where <name> is the name of the rp-attribute; and <method-i> is the name of
an access method for the rp-attribute, taking Ni arguments where the j-th
argument is of type <type-i-j>. A method name is either an RPSL name or
one of the operators defined in Figure 19. The operator methods with the
exception of operator() and operator[] can take only one argument.
operator= operator==
operator<<= operator<
operator>>= operator>
operator+= operator>=
operator-= operator<=
operator*= operator!=
operator/= operator()
operator.= operator[]
Figure 19: Operators
An rp-attribute can have many methods defined for it. Some of the methods
may even have the same name, in which case their arguments are of different
types. If the argument list is followed by ``...'', the method takes a
variable number of arguments. In this case, the actual arguments after the
Nth argument are of type <type-N>.
Arguments are strongly typed. A <type> in RPSL is either a predefined type,
a union type, a list type, or a dictionary defined type. The predefined
types are listed in Figure 20.
The integer and the real predefined types can be followed by a lower and
an upper bound to specify the set of valid values of the argument. The
range specification is optional. We use the ANSI C language conventions for
representing integer, real and string values. The enum type is followed
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integer[lower, upper] as_number
real[lower, upper] ipv4_address
enum[name, name, ...] address_prefix
string address_prefix_range
boolean dns_name
rpsl_word filter
free_text as_set_name
email route_set_name
Figure 20: Predefined Types
by a list of RPSL names which are the valid values of the type. The
boolean type can take the values true or false. as_number, ipv4_address,
address_prefix and dns_name types are as in Section 2. filter type is a
policy filter as in Section 6.
The syntax of a union type is as follows:
union <type-1>, ... , <type-N>
where <type-i> is an RPSL type. The union type is either of the types
<type-1> through <type-N> (analogous to unions in C[13]).
The syntax of a list type is as follows:
list [<min_elems>:<max_elems>] of <type>
In this case, the list elements are of <type> and the list contains at least
<min_elems> and at most <max_elems> elements. The size specification is
optional. If it is not specified, there is no restriction in the number
of list elements. A value of a list type is represented as a sequence of
elements separated by the character ``,'' and enclosed by the characters
``{'' and ``}''.
The typedef attribute in the dictionary defines named types as follows:
typedef: <name> <type>
where <name> is a name for type <type>. typedef attribute is paticularly
useful when the type defined is not a predefined type (e.g. list of unions,
list of lists, etc.).
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A protocol attribute of the dictionary class defines a protocol and a set of
peering parameters for that protocol (which are used in inet-rtr class in
Section 9). Its syntax is as follows:
protocol: <name>
MANDATORY | OPTIONAL <parameter-1>(<type-1-1>, ..., <type-1-
N1> [, "..."])
...
MANDATORY | OPTIONAL <parameter-M>(<type-M-1>, ..., <type-M-
NM> [, "..."])
where <name> is the name of the protocol; MANDATORY and OPTIONAL are
keywords; and <parameter-i> is a peering parameter for this protocol, taking
Ni many arguments. The syntax and semantics of the arguments are as in the
rp-attribute. If the keyword MANDATORY is used, the parameter is mandatory
and needs to be specified for each peering of this protocol. If the keyword
OPTIONAL is used, the parameter can be skipped.
7.1 Initial RPSL Dictionary and Example Policy Actions and Filters
dictionary: RPSL
rp-attribute: # preference, smaller values represent higher preferences
pref
operator=(integer[0, 65535])
rp-attribute: # BGP multi_exit_discriminator attribute
med
# to set med to 10: med = 10;
# to set med to the IGP metric: med = igp_cost;
operator=(union integer[0, 65535], enum[igp_cost])
rp-attribute: # BGP destination preference attribute (dpa)
dpa
operator=(integer[0, 65535])
rp-attribute: # BGP aspath attribute
aspath
# prepends AS numbers from last to first order
prepend(as_number, ...)
typedef: # a community value in RPSL is either
# - a 4 byte integer (ok to use 3561:70 notation)
# - internet, no_export, no_advertise (see RFC-1997)
community_elm union
integer[1, 4294967200],
enum[internet, no_export, no_advertise],
typedef: # list of community values { 40, no_export, 3561:70 }
community_list list of community_elm
rp-attribute: # BGP community attribute
community
# set to a list of communities
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operator=(community_list)
# append community values
operator.=(community_list)
append(community_elm, ...)
# delete community values
delete(community_elm, ...)
# a filter: true if one of community values is contained
contains(community_elm, ...)
# shortcut to contains: community(no_export, 3561:70)
operator()(community_elm, ...)
# order independent equality comparison
operator==(community_list)
rp-attribute: # next hop router in a static route
next-hop
# to set to 7.7.7.7: next-hop = 7.7.7.7;
# to set to router's own address: next-hop = self;
operator=(union ipv4_address, enum[self])
rp-attribute: # cost of a static route
cost
operator=(integer[0, 65535])
protocol: BGP4
# as number of the peer router
MANDATORY asno(as_number)
# enable flap damping
OPTIONAL flap_damp()
OPTIONAL flap_damp(integer[0,65535],# penalty per flap
integer[0,65535],# penalty value for supression
integer[0,65535],# penalty value for reuse
integer[0,65535],# halflife in secs when up
integer[0,65535],# halflife in secs when down
integer[0,65535])# maximum penalty
protocol: OSPF
protocol: RIP
protocol: IGRP
protocol: IS-IS
protocol: STATIC
protocol: RIPng
protocol: DVMRP
protocol: PIM-DM
protocol: PIM-SM
protocol: CBT
protocol: MOSPF
Figure 21: RPSL Dictionary
Figure 21 shows the initial RPSL dictionary. It has seven rp-attributes:
pref to assign local preference to the routes accepted; med to assign a
value to the MULTI_EXIT_DISCRIMINATOR BGP attribute; dpa to assign a value
to the DPA BGP attribute; aspath to prepend a value to the AS_PATH BGP
attribute; community to assign a value to or to check the value of the
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community BGP attribute; next-hop to assign next hop routers to static
routes; and cost to assign a cost to static routes. The dictionary defines
two types: community_elm and community_list. community_elm type is either
a 4-byte unsigned integer, or one of the keywords internet, no_export or
no_advertise (defined in [8]). An integer can be specified using two 2-byte
integers seperated by ``:'' to partition the community number space so that
a provider can use its AS number as the first two bytes, and assigns a
semantics of its choice to the last two bytes.
The initial dictionary (Figure 21) defines only options for the Border
Gateway Protocol: asno and flap_damp. The mandatory asno option is the AS
number of the peer router. The optional flap_damp option instructs the
router to damp route flaps[21] when importing routes from the peer router.
It can be specified with or without parameters. If parameters are missing,
they default to:
flap_damp(1000, 2000, 750, 900, 900, 20000)
That is, a penalty of 1000 is assigned at each route flap, the route is
suppressed when penalty reaches 2000. The penalty is reduced in half after
15 minutes (900 seconds) of stability regardless of whether the route is up
or down. A supressed route is reused when the penalty falls below 750. The
maximum penalty a route can be assigned is 20,000 (i.e. the maximum suppress
time after a route becomes stable is about 75 minutes). These parameters
are consistent with the default flap damping parameters in several routers.
Policy Actions and Filters Using RP-Attributes
The syntax of a policy action or a filter using an rp-attribute x is as
follows:
x.method(arguments)
x ``op'' argument
where method is a method and ``op'' is an operator method of the
rp-attribute x. If an operator method is used in specifying a composite
policy filter, it evaluates earlier than the composite policy filter
operators (i.e. AND, OR, NOT, and implicit or operator).
The pref rp-attribute can be assigned a positive integer as follows:
pref = 10;
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The med rp-attribute can be assigned either a positive integer or the word
``igp_cost'' as follows:
med = 0;
med = igp_cost;
The dpa rp-attribute can be assigned a positive integer as follows:
dpa = 100;
The BGP community attribute is list-valued, that is it is a list of
4-byte integers each representing a ``community''. The following examples
demonstrate how to add communities to this rp-attribute:
community .= { 100 };
community .= { NO_EXPORT };
community .= { 3561:10 };
In the last case, a 4-byte integer is constructed where the more significant
two bytes equal 3561 and the less significant two bytes equal 10. The
following examples demonstrate how to delete communities from the community
rp-attribute:
community.delete(100, NO_EXPORT, 3561:10);
Filters that use the community rp-attribute can be defined as demonstrated
by the following examples:
community.contains(100, NO_EXPORT, 3561:10);
community(100, NO_EXPORT, 3561:10); # shortcut
The community rp-attribute can be set to a list of communities as follows:
community = {100, NO_EXPORT, 3561:10, 200};
community = {};
In this first case, the community rp-attribute contains the communities 100,
NO_EXPORT, 3561:10, and 200. In the latter case, the community rp-attribute
is cleared. The community rp-attribute can be compared against a list of
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communities as follows:
community == {100, NO_EXPORT, 3561:10, 200}; # exact match
To influence the route selection, the BGP as_path rp-attribute can be made
longer by prepending AS numbers to it as follows:
aspath.prepend(AS1);
aspath.prepend(AS1, AS1, AS1);
The following examples are invalid:
med = -50; # -50 is not in the range
med = igp; # igp is not one of the enum values
med.assign(10); # method assign is not defined
community.append(AS3561:20); # the first argument should be 3561
Figure 22 shows a more advanced example using the rp-attribute community.
In this example, AS3561 bases its route selection preference on the
community attribute. Other ASes may indirectly affect AS3561's route
selection by including the appropriate communities in their route
announcements.
8 Advanced route Class
8.1 Specifying Aggregate Routes
The components, aggr-bndry, aggr-mtd, export-comps, inject, and holes
attributes are used for specifying aggregate routes [10]. A route object
specifies an aggregate route if any of these attributes, with the exception
of inject, is specified. The origin attribute for an aggregate route is
the AS performing the aggregation, i.e. the aggregator AS. In this section,
we used the term "aggregate" to refer to the route generated, the term
"component" to refer to the routes used to generate the path attributes of
the aggregate, and the term "more specifics" to refer to any route which is
a more specific of the aggregate regardless of whether it was used to form
the path attributes.
The components attribute defines what component routes are used to form the
aggregate. Its syntax is as follows:
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aut-num: AS1
export: to AS2 action community.={3561:90};
to AS3 action community.={3561:80};
announce AS1
as-set: AS3561:AS-PEERS
members: AS2, AS3
aut-num: AS3561
import: from AS3561:AS-PEERS
action pref = 10;
accept community.contains(3561:90)
import: from AS3561:AS-PEERS
action pref = 20;
accept community.contains(3561:80)
import: from AS3561:AS-PEERS
action pref = 20;
accept community.contains(3561:70)
import: from AS3561:AS-PEERS
action pref = 0;
accept ANY
Figure 22: Policy example using the community rp-attribute.
components: [ATOMIC] [[protocol <protocol>] <filter>
[protocol <protocol> <filter> ...]]
where <protocol> is a routing protocol name such as BGP, OSPF or RIP (valid
names are defined in the dictionary) and <filter> is a policy expression.
The routes that match one of these filters and are learned from the
corresponding protocol are used to form the aggregate. If <protocol> is
omitted, it defaults to any protocol. <filter> implicitly contains an "AND"
term with the more specifics of the aggregate so that only the component
routes are selected. If the keyword ATOMIC is used, the aggregation is
done atomically [10]. If a <filter> is not specified it defaults to more
specifics. If the components attribute is missing, all more specifics
without the ATOMIC keyword is used.
Figure 23 shows two route objects. In the first example, more specifics of
128.8.0.0/15 with AS paths starting with AS2 are aggregated. In the second
example, some routes learned from BGP and some routes learned form OSPF are
aggregated.
The aggr-bndry attribute is an expression over AS numbers and sets using
operators AND, OR, and NOT. The result defines the set of ASes which
form the aggregation boundary. If the aggr-bndry attribute is missing,
the origin AS is the sole aggregation boundary. Outside the aggregation
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route: 128.8.0.0/15
origin: AS1
components: <^AS2>
route: 128.8.0.0/15
origin: AS1
components: protocol BGP {128.8.0.0/16^+}
protocol OSPF {128.9.0.0/16^+}
Figure 23: Two aggregate route objects.
boundary, only the aggregate is exported and more specifics are suppressed.
However, within the boundary, the more specifics are also exchanged.
The aggr-mtd attribute specifies how the aggregate is generated. Its syntax
is as follow:
aggr-mtd: inbound
| outbound [<as-expression>]
where <as-expression> is an expression over AS numbers and sets using
operators AND, OR, and NOT. If <as-expression> is missing, it defaults to
AS-ANY. If outbound aggregation is specified, the more specifics of the
aggregate will be present within the AS and the aggregate will be formed
at all inter-AS boundaries with ASes in <as-expression> before export,
except for ASes that are within the aggregating boundary (i.e. aggr-bndry
is enforced regardless of <as-expression>). If inbound aggregation is
specified, the aggregate is formed at all inter-AS boundaries prior to
importing routes into the aggregator AS. Note that <as-expression> can not
be specified with inbound aggregation. If aggr-mtd attribute is missing, it
defaults to "outbound AS-ANY".
route: 128.8.0.0/15 route: 128.8.0.0/15
origin: AS1 origin: AS2
components: {128.8.0.0/15^-} components: {128.8.0.0/15^-}
aggr-bndry: AS1 OR AS2 aggr-bndry: AS1 OR AS2
aggr-mtd: outbound AS-ANY aggr-mtd: outbound AS-ANY
Figure 24: Outbound multi-AS aggregation example.
Figure 24 shows an example of an outbound aggregation. In this example, AS1
and AS2 are coordinating aggregation and announcing only the less specific
128.8.0.0/15 to outside world, but exchanging more specifics between each
other. This form of aggregation is useful when some of the components are
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within AS1 and some are within AS2.
When a set of routes are aggregated, the intent is to export only the
aggregate route and suppress exporting of the more specifics outside the
aggregation boundary. However, to satisfy certain policy and topology
constraints (e.g. a multi-homed component), it is often required to export
some of the components. The export-comps attribute serves this purpose. It
equals an RPSL export policy expression as follows (see Section6.2):
export-comps: to <peering-1> [action <action-1>]
. . .
to <peering-N> [action <action-N>]
announce <filter>
where <filter> matches the more specifics that need to be exported to the
peerings specified. While exporting to <peering-i>, the <action-i> is
executed to set the path attributes. If this attribute is missing, more
specifics are not exported outside the aggregation boundary. Note that, the
<filter> contains an implicit "AND" term with the more specifics of the
aggregate.
route: 128.8.0.0/15
origin: AS1
components: {128.8.0.0/15^-}
aggr-mtd: outbound AS-ANY
export-comps: to as-any announce { 128.8.8.0/24 }
Figure 25: Outbound aggregation with export exception.
Figure 25 shows an example of an outbound aggregation. In this example,
the more specific 128.8.8.0/24 is exported outside AS1 in addition to the
aggregate. This is useful, when 128.8.8.0/24 is multi-homed site to AS1
with some other AS.
The inject attribute specifies which routers perform the aggregation and
when they perform it. Its syntax is as follow:
inject: [at <router-expression>] ...
[action <action>]
[upon <condition>]
where <action> is an action specification (see Section 6.1.2), <condition>
is a boolean expression described below, and<router-expression> is an
expression over router IP addresses and DNS names using operators AND, OR,
and NOT. The DNS name can only be used if there is an inet-rtr object for
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that name that binds the name to IP addresses.
All routers in <router-expression> and in the aggregator AS perform the
aggregation. If a <router-expression> is not specified, all routers inside
the aggregator AS perform the aggregation. The <action> specification may
set path attributes of the aggregate, such as assign a preferences to the
aggregate.
The upon clause is a boolean condition. The aggregate is generated if and
only if this condition is true. <condition> is a boolean expression using
the logical operators AND and OR (i.e. operator NOT is not allowed) over:
HAVE-COMPONENTS { list of prefixes }
EXCLUDE { list of prefixes }
STATIC
The list of prefixes in HAVE-COMPONENTS can only be more specifics of the
aggregate. It evaluates to true when all the prefixes listed are present
in the routing table of the aggregating router. The list can also include
prefix ranges (i.e. using operators ^-, ^+, ^n, and ^n-m). In this case, at
least one prefix from each prefix range needs to be present in the routing
table for the condition to be true. The list of prefixes in EXCLUDE can
be arbitrary. It evaluates to true when none of the prefixes listed is
present in the routing table. The list can also include prefix ranges,
and no prefix in that range should be present in the routing table. The
keyword static always evaluates to true. If no upon clause is specified the
aggregate is generated if an only if there is a component in the routing
table (i.e. a more specific that matches the filter in the components
attribute).
route: 128.8.0.0/15
origin: AS1
components: {128.8.0.0/15^-}
aggr-mtd: outbound AS-ANY
inject: at 1.1.1.1 action dpa = 100;
inject: at 1.1.1.2 action dpa = 110;
route: 128.8.0.0/15
origin: AS1
components: {128.8.0.0/15^-}
aggr-mtd: outbound AS-ANY
inject: upon HAVE-COMPONENTS {128.8.0.0/16, 128.9.0.0/16}
holes: 128.8.8.0/24
Figure 26: Examples of inject.
Figure 26 shows two examples. In the first case, the aggregate is injected
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at two routers each one setting the dpa path attribute differently. In
the second case, the aggregate is generated only if both 128.8.0.0/16 and
128.9.0.0/16 are present in the routing table, as opposed to the first case
where the presence of just one of them is sufficient for injection.
The holes attribute lists the component address prefixes which are not
reachable through the aggregate route (perhaps that part of the address
space is unallocated). The holes attribute is useful for diagnosis
purposes. In Figure 26, the second example has a hole, namely 128.8.8.0/24.
This may be due to a customer changing providers and taking this part of the
address space with it.
8.1.1 Interaction with policies in aut-num class
An aggregate formed is announced to other ASes only if the export policies
of the AS allows exporting the aggregate. When the aggregate is formed,
the more specifics are suppressed from being exported except to the ASes in
aggr-bndry and except the components in export-comps. For such exceptions
to happen, the export policies of the AS should explicitly allow exporting
of these exceptions.
If an aggregate is not formed (due to the upon clause), then the more
specifics of the aggregate can be exported to other ASes, but only if the
export policies of the AS allows it. In other words, before a route
(aggregate or more specific) is exported it is filtered twice, once based on
the route objects, and once based on the export policies of the AS.
In Figure 27 shows an interaction example. By examining the route objects,
the more specifics 128.8.0.0/16 and 128.9.0.0/16 should be exchanged between
AS1, AS2 and AS3 (i.e. the aggregation boundary). Outbound aggregation
is done to AS4 and AS5 and not to AS3, since AS3 is in the aggregation
boundary. The aut-num object allows exporting both components to AS2,
but only the component 128.8.0.0/16 to AS3. The aggregate can only be
formed if both components are available. In this case, only the aggregate
is announced to AS4 and AS5. However, if one of the components is not
available the aggregate will not be formed, and any available component or
more specific will be exported to AS4 and AS5. Regardless of aggregation is
performed or not, only the more specifics will be exported to AS6 (it is not
listed in the aggr-mtd attribute).
When doing an inbound aggregation, configuration generators may eliminating
the aggregation statements on routers where import policy of the AS
prohibits importing of any more specifics.
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route: 128.8.0.0/16
origin: AS1
route: 128.9.0.0/16
origin: AS1
route: 128.8.0.0/15
origin: AS1
aggr-bndry: AS1 or AS2 or AS3
aggr-mtd: outbound AS3 or AS4 or AS5
components: {128.8.0.0/16, 128.9.0.0/16}
inject: upon HAVE-COMPONENTS {128.9.0.0/16, 128.8.0.0/16}
aut-num: AS1
export: to AS2 announce AS1
export: to AS3 announce AS1 and not {128.9.0.0/16}
export: to AS4 announce AS1
export: to AS5 announce AS1
export: to AS6 announce AS1
Figure 27: Interaction with policies in aut-num class.
8.1.2 Ambiguity resolution with overlapping aggregates
When several aggregate routes are specified and they overlap, i.e. one is
less specific of the other, they must be evaluated more specific to less
specific order. When an outbound aggregation is performed for a peer,
the aggregate and the components listed in the export-comps attribute for
that peer are available for generating the next less specific aggregate.
The components that are not specified in the export-comps attribute are
not available. A route is exportable to an AS if it is the least
specific aggregate exportable to that AS or it is listed in the export-comps
attribute of an exportable route. Note that this is a recursive definition.
In Figure 28, AS1 together with AS2 aggregates 128.8.0.0/16 and 128.9.0.0/16
into 128.8.0.0/15. Together with AS3, AS1 aggregates 128.10.0.0/16 and
128.11.0.0/16 into 128.10.0.0/15. But altogether they aggregate these four
routes into 128.8.0.0/14. Assuming all four components are available, a
router in AS1 for an outside AS, say AS4, will first generate 128.8.0.0/15
and 128.10.0.0/15. This will make 128.8.0.0/15, 128.10.0.0/15 and its
exception 128.11.0.0/16 available for generating 128.8.0.0/14. The router
will then generate 128.8.0.0/14 from these three routes. Hence for AS4,
128.8.0.0/14 and its exception 128.10.0.0/15 and its exception 128.11.0.0/16
will be exportable.
For AS2, a router in AS1 will only generate 128.10.0.0/15. Hence,
128.10.0.0/15 and its exception 128.11.0.0/16 will be exportable. Note
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route: 128.8.0.0/15
origin: AS1
aggr-bndry: AS1 or AS2
aggr-mtd: outbound
inject: upon HAVE-COMPONENTS {128.8.0.0/16, 128.9.0.0/16}
route: 128.10.0.0/15
origin: AS1
aggr-bndry: AS1 or AS3
aggr-mtd: outbound
inject: upon HAVE-COMPONENTS {128.10.0.0/16, 128.11.0.0/16}
export-comps: to as-any announce {128.11.0.0/16}
route: 128.8.0.0/14
origin: AS1
aggr-bndry: AS1 or AS2 or AS3
aggr-mtd: outbound
inject: upon HAVE-COMPONENTS {128.8.0.0/15, 128.10.0.0/15}
export-comps: to as-any announce {128.10.0.0/15}
Figure 28: Overlapping aggregations.
that 128.8.0.0/16 and 128.9.0.0/16 are also exportable since they did not
participate in an aggregate exportable to AS2.
Similarly, for AS3, a router in AS1 will only generate 128.8.0.0/15. In
this case 128.8.0.0/15, 128.10.0.0/16, 128.11.0.0/16 are exportable.
8.2 Specifying Static Routes
The inject attribute can be used to specify static routes by using "upon
static" as the condition:
inject: [at <router>] ...
[action <action>]
upon static
In this case, the <router> executes the <action> and injects the route to
the interAS routing system statically. <action> may set certain route
attributes such as a next-hop router or a cost.
In the following example, the router 7.7.7.1 injects the route 128.7.0.0/16.
The next-hop routers (in this example, there are two next-hop routers) for
this route are 7.7.7.2 and 7.7.7.3 and the route has a cost of 10 over
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7.7.7.2 and 20 over 7.7.7.3.
route: 128.7.0.0/16
origin: AS1
inject: at 7.7.7.1 action next-hop = 7.7.7.2; cost = 10; upon static
inject: at 7.7.7.1 action next-hop = 7.7.7.3; cost = 20; upon static
9 inet-rtr Class
Routers are specified using the inet-rtr class. The attributes of the
inet-rtr class are shown in Figure 29. The inet-rtr attribute is a valid
DNS name of the router described. Each alias attribute, if present, is a
canonical DNS name for the router. The local-as attribute specifies the AS
number of the AS which owns/operates this router.
Attribute Value Type
inet-rtr <dns-name> mandatory, single-valued, class key
alias <dns-name> optional, multi-valued
local-as <as-number> mandatory, single-valued
ifaddr see description in text mandatory, multi-valued
peer see description in text optional, multi-valued
Figure 29: inet-rtr Class Attributes
The value of an ifaddr attribute has the following syntax:
<ipv4-address> masklen <integer> [action <action>]
The IP address and the mask length are mandatory for each interface.
Optionally an action can be specified to set other parameters of this
interface.
Figure 30 presents an example inet-rtr object. The name of the router is
``amsterdam.ripe.net''. ``amsterdam1.ripe.net'' is a canonical name for the
router. The router is connected to 4 networks. Its IP addresses and mask
lengths in those networks are specified in the ifaddr attributes.
Each peer attribute, if present, specifies a protocol peering with another
router. The value of a peer attribute has the following syntax:
<protocol> <ipv4-address> <options>
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inet-rtr: Amsterdam.ripe.net
alias: amsterdam1.ripe.net
local-as: AS3333
ifaddr: 192.87.45.190 masklen 24
ifaddr: 192.87.4.28 masklen 24
ifaddr: 193.0.0.222 masklen 27
ifaddr: 193.0.0.158 masklen 27
peer: BGP4 192.87.45.195 asno(AS3334), flap_damp()
Figure 30: inet-rtr Objects
where <protocol> is a protocol name, <ipv4-address> is the IP address of the
peer router, and <options> is a comma separated list of peering options
for <protocol>. Possible protocol names and attributes are defined in the
dictionary (please see Section 7). In the above example, the router has
a BGP peering with the router 192.87.45.195 in AS3334 and turns the flap
damping on when importing routes from this router.
10 Extending RPSL
Our experience with earlier routing policy languages and data formats
(PRDB [2], RIPE-81 [7], and RIPE-181 [6]) taught us that RPSL had to be
extensible. As a result, extensibility was a primary design goal for RPSL.
New routing protocols or new features to existing routing protocols can be
easily handled using RPSL's dictionary class. New classes or new attributes
to the existing classes can also be added.
This section provides guidelines for extending RPSL. These guidelines are
designed with an eye toward maintaining backward compatibility with existing
tools and databases. We next list the available options for extending RPSL
from the most preferred to the least preferred order.
10.1 Extensions by changing the dictionary class
The dictionary class is the primary mechanism provided to extend RPSL.
Dictionary objects define routing policy attributes, types, and routing
protocols.
We recommend updating the RPSL dictionary to include appropriate rp-
attribute and protocol definitions as new path attributes or router features
are introduced. For example, in an earlier version of the RPSL document,
it was only possible to specify that a router performs route flap damping
on a peer, but it was not possible to specify the parameters of route flap
damping. Later the parameters were added by changing the dictionary.
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When changing the dictionary, full compatibility should be maintained. For
example, in our flap damping case, we made the parameter specification
optional in case this level of detail was not desired by some ISPs. This
also achieved compatibility. Any object registered without the parameters
will continue to be valid. Any tool based on RPSL is expected to do
a default action on routing policy attributes that they do not understand
(e.g. issue a warning and otherwise ignore). Hence, old tools upon
encountering a flap damping specification with parameters will ignore the
parameters.
10.2 Extensions by adding new attributes to existing classes
New attributes can be added to any class. To ensure full compatibility,
new attributes should not contradict the semantics of the objects they are
attached to. Any tool that uses the IRR should be designed so that it
ignores attributes that it doesn't understand. Most existing tools adhere
to this design principle.
We recommend adding new attributes to existing classes when a new aspect of
a class is discovered. For example, RPSL route class extends its RIPE-181
predecessor by including several new attributes that enable aggregate and
static route specification.
10.3 Extensions by adding new classes
New classes can be added to RPSL to store new types of policy data.
Providing full compatibility is straight forward as long as existing classes
are still understood. Since a tool should only query the IRR for the
classes that it understand, full compatibility should not be a problem in
this case.
Before adding a new class, one should question if the information contained
in the objects of the new class could have better belonged to some other
class. For example, if the geographic location of a router needs to
be stored in IRR, it may be tempting to add a new class called, say
router-location class. However, the information better belongs to the
inet-rtr class, perhaps in a new attribute called location.
10.4 Extensions by changing the syntax of existing RPSL attributes
If all of the methods described above fail to provide the desired extension,
it may be necessary to change the syntax of RPSL. Any change in RPSL syntax
must provide backwards compatibility, and should be considered only as a
last resort since full compatibility may not be achievable. However, we
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require that the old syntax to be still valid.
11 Security Consideration
This document describes RPSL, a language for expressing routing policies.
The language defines a maintainer (mntner class) object which is the entity
which controls or "maintains" the objects stored in a database expressed by
RPSL. Requests from maintainers can be authenticated with various techniques
as defined by the "auth" attribute of the maintainer object.
The exact protocols used by IRR's to communicate RPSL objects is beyond the
scope of this document, but it is envisioned that several techniques may be
used, ranging from interactive query/update protocols to store and forward
protocols similar to or based on electronic mail (or even voice telephone
calls). Regardless of which protocols are used in a given situation, it is
expected that appropriate security techniques such as IPSEC, TLS or PGP/MIME
will be utilized.
12 Acknowledgements
We would like to thank Jessica Yu, Randy Bush, Alan Barrett, David
Kessens, Bill Manning, Sue Hares, Ramesh Govindan, Kannan Varadhan, Satish
Kumar, Craig Labovitz, Rusty Eddy, David J. LeRoy, David Whipple, Jon
Postel, Deborah Estrin, Elliot Schwartz, Joachim Schmitz, Mark Prior, Tony
Przygienda, David Woodgate, Rob Coltun, Sanjay Wadhwa, Ardas Cilingiroglu,
and the participants of the IETF RPS Working Group for various comments and
suggestions.
References
[1] Internet
routing registry. procedures. http://www.ra.net/RADB.tools.docs/,
http://www.ripe.net/db/doc.html.
[2] Nsfnet policy routing database (prdb). Maintained by MERIT
Network Inc., Ann Arbor, Michigan. Contents available from
nic.merit.edu.:/nsfnet/announced.networks/nets.tag.now by anonymous
ftp.
[3] C. Alaettinouglu, D. Meyer, and J. Schmitz. Application of routing
policy specification language (rpsl) on the internet. Internet Draft
draft-ietf-rps-appl-rpsl-01, July 1997. Work in progress.
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[4] T. Bates. Specifying an `internet router' in the routing registry.
Technical Report RIPE-122, RIPE, RIPE NCC, Amsterdam, Netherlands,
October 1994.
[5] T. Bates, E. Gerich, L. Joncheray, J-M. Jouanigot, D. Karrenberg,
M. Terpstra, and J. Yu. Representation of ip routing policies
in a routing registry. Technical Report ripe-181, RIPE, RIPE NCC,
Amsterdam, Netherlands, October 1994.
[6] T. Bates, E. Gerich, L. Joncheray, J-M. Jouanigot, D. Karrenberg,
M. Terpstra, and J. Yu. Representation of ip routing policies in
a routing registry. Technical Report RFC-1786, Network Information
Center, March 1995.
[7] T. Bates, J-M. Jouanigot, D. Karrenberg, P. Lothberg, and M. Terpstra.
Representation of ip routing policies in the ripe database. Technical
Report ripe-81, RIPE, RIPE NCC, Amsterdam, Netherlands, February 1993.
[8] R. Chandra, P. Traina, and T. Li. Bgp communities attribute. Request
for Comment RFC-1997, Network Information Center, August 1996.
[9] D. Crocker. Standard for the format of arpa internet text messages.
Request for Comment RFC-822, Network Information Center, August 1982.
[10] V. Fuller, T. Li, J. Yu, and K. Varadhan. Classless Inter-Domain
Routing (CIDR): an Address Assignment and Aggregation Strategy, 1993.
[11] D. Karrenberg and T. Bates. Description of inter-as networks in the
ripe routing registry. Technical Report RIPE-104, RIPE, RIPE NCC,
Amsterdam, Netherlands, December 1993.
[12] D. Karrenberg and M. Terpstra. Authorisation and notification of
changes in the ripe database. Technical Report ripe-120, RIPE, RIPE
NCC, Amsterdam, Netherlands, October 1994.
[13] B. W. Kernighan and D. M. Ritchie. The C Programming Language.
Prentice-Hall, 1978.
[14] D. Kessens, W. Woeber, and D. Conrad. Ride referencing. Internet Draft
draft-kessens-ride-referencing-00.txt, Network Information Center,
August 1997.
[15] A. Lord and M. Terpstra. Ripe database template for networks
and persons. Technical Report ripe-119, RIPE, RIPE NCC, Amsterdam,
Netherlands, October 1994.
[16] A. M. R. Magee. Ripe ncc database documentation. Technical Report
RIPE-157, RIPE, RIPE NCC, Amsterdam, Netherlands, May 1997.
[17] P. V. Mockapetris. Domain names - concepts and facilities. Request for
Comment RFC-1034, Network Information Center, November 1987.
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[18] Y. Rekhter. Inter-domain routing protocol (idrp). Journal of
Internetworking Research and Experience, 4:61--80, 1993.
[19] Y. Rekhter and T. Li. A border gateway protocol 4 (bgp-4). Request for
Comment RFC-1771, Network Information Center, March 1995.
[20] C. Villamizar, C. Alaettinouglu, D. Meyer, S. Murphy, and C. Orange.
Routing policy system security. Internet Draft draft-ietf-rps-auth-01,
Network Information Center, May 1998.
[21] C. Villamizar, R. Chandra, and R. Govindan. Bgp route flap damping.
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Center, October 1997.
[22] J. Zsako. Pgp authentication for ripe database updates. Internet Draft
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July 1998.
A Routing Registry Sites
The set of routing registries as of November 1996 are RIPE, RADB, CANet, MCI
and ANS. You may contact one of these registries to find out the current
list of registries.
B Authors' Addresses
Cengiz Alaettinoglu
USC Information Sciences Institute
4676 Admiralty Way, Suite 1001
Marina del Rey, CA 90292
email: cengiz@isi.edu
Tony Bates
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
email: tbates@cisco.com
Elise Gerich
At Home Network
385 Ravendale Drive
Mountain View, CA 94043
email: epg@home.net
Daniel Karrenberg
RIPE Network Coordination Centre (NCC)
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Kruislaan 409
NL-1098 SJ Amsterdam
Netherlands
email: dfk@ripe.net
David Meyer
University of Oregon
Eugene, OR 97403
email: meyer@antc.uoregon.edu
Marten Terpstra
c/o Bay Networks, Inc.
2 Federal St
Billerica MA 01821
email: marten@BayNetworks.com
Curtis Villamizar
ANS
email: curtis@ans.net
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