OSPF WG S. Venkata
Internet-Draft Google Inc.
Intended status: Standards Track S. Harwani
Expires: January 13, 2010 C. Pignataro
Cisco Systems
D. McPherson
Arbor Networks, Inc.
July 12, 2009
Dynamic Hostname Exchange Mechanism for OSPF
draft-ietf-ospf-dynamic-hostname-05
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Copyright Notice
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Abstract
This document defines a new OSPF Router Information (RI) TLV that
allows OSPF routers to flood their hostname-to-Router ID mapping
information across an OSPF network to provide a simple and dynamic
mechanism for routers running OSPF to learn about symbolic hostnames
just like for routers running IS-IS. This mechanism is applicable to
both OSPFv2 and OSPFv3.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Specification of Requirements . . . . . . . . . . . . . . 4
2. Possible solutions . . . . . . . . . . . . . . . . . . . . . . 4
3. Implementation . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Dynamic Hostname TLV . . . . . . . . . . . . . . . . . . . 6
3.1.1. Flooding Scope . . . . . . . . . . . . . . . . . . . . 7
3.1.2. Multiple OSPF Instances . . . . . . . . . . . . . . . 7
4. IPv6 Considerations . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
OSPF uses a 32-bit Router ID to uniquely represent and identify a
node in the network. For management and operational reasons, network
operators need to check the status of OSPF adjacencies, entries in
the routing table and the content of the OSPF link state database.
When looking at diagnostic information, numerical representations of
Router IDs (e.g., dotted-decimal or hexadecimal representations) are
less clear to humans than symbolic names.
One way to overcome this problem is to define a hostname-to-Router ID
mapping table on a router. This mapping can be used bidirectionally
(e.g., to find symbolic names for Router IDs, and to find Router IDs
for symbolic names) or unidirectionally (e.g., to find symbolic
hostnames for Router IDs). Thus every router has to maintain a table
with mappings between router names and Router IDs.
These tables need to contain all names and Router IDs of all routers
in the network. If these mapping tables are built by static
definitions, it can become a manual and tedious process in
operational networks currently; modifying these static mapping
entries when additions, deletions or changes occur becomes a non-
scalable process very prone to error.
This document analyzes possible solutions to this problem (see
Section 2) and provides a way to populate tables by defining a new
OSPF Router Information TLV for OSPF, the Dynamic Hostname TLV (see
Section 3). This mechanism is applicable to both OSPFv2 and OSPFv3.
1.1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Possible solutions
There are various approaches to providing a name-to-Router ID mapping
service.
One way to build this table of mappings is by static definitions.
The problem with static definitions is that the network administrator
needs to keep updating the mapping entries manually as the network
changes; this approach does not scale as the network grows, since
there needs to be an entry in the mapping table for each and every
router in the network, on every router in the network. Thus, this
approach greatly suffers from maintainability and scalability
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considerations.
Another approach is having a centralized location where the name-to-
Router ID mapping can be kept. The DNS could be used for this. A
disadvantage with this centralized solution is that it is a single
point of failure; and although enhanced availability of the central
mapping service can be designed, it may not be able to resolve the
hostname in the event of reachability or network problems, which can
be particularly problematic in times of problem resolution. Also,
the response time can be an issue with the centralized solution,
which can be equally problematic. If the DNS is used as the
centralized mapping table, a network operator may desire a different
name mapping than the existing mapping in the DNS, or new routers may
not yet be in the DNS.
Additionally for OSPFv3, in native IPv6 deployments, the 32-bit
Router ID value will not map to IPv4-addressed entities in the
network, nor will it be DNS resolvable (see Section 4).
The third solution that we have defined in this document is to make
use of the protocol itself to carry the name-to-Router ID mapping in
a TLV. Routers that understand this TLV can use it to create the
symbolic name-to-Router ID mapping and Routers that don't understand
can simply ignore it. This specification provides these semantics
and mapping mechanisms for OSPFv2 and OSPFv3, leveraging the OSPF
Router Information (RI) Link State Advertisement (LSA) ([RFC4970]).
3. Implementation
This extension makes use of the Router Information (RI) Opaque LSA
defined in [RFC4970] for both OSPFv2 and OSPFv3, by defining a new
OSPF Router Information (RI) TLV: The Dynamic Hostname TLV.
The Dynamic Hostname TLV (see Section 3.1) is OPTIONAL. Upon receipt
of the TLV a router may decide to ignore this TLV, or to install the
symbolic name and Router ID in its hostname mapping table.
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3.1. Dynamic Hostname TLV
The format of Dynamic Hostname TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Hostname ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type Dynamic Hostname TLV Type (TBD, see Section 6)
Length Total length of the hostname (value field) in octets, not
including the optional padding.
Value Hostname, a string of 1 to 255 octets, padded with zeroes to
4-octet alignment, encoded in the US-ASCII charset.
Routers that do not recognize the Dynamic Hostname TLV Type, ignore
the TLV (see [RFC4970]).
The value field identifies the symbolic hostname of the router
originating the LSA. This symbolic name can be the Fully Qualified
Domain Name (FQDN) for the Router ID, it can be a subset of the FQDN,
or it can be any string operators want to use for the router. The
use of FQDN or a subset of it is strongly recommended since it can be
beneficial to correlate the OSPF dynamic hostname and the DNS
hostname. The format of the DNS hostname is described in [RFC1035]
and [RFC2181]. If there is no DNS hostname for the Router ID, the
Router ID does not map to an IPv4-addressed entity (e.g., see
Section 4), or an alternate OSPF dynamic hostname naming convention
is desired, any string with significance in the OSPF routing domain
can be used. The string is not null-terminated. The Router ID of
this router is derived from the LSA header, in the Advertising Router
field of the Router Information (RI) Opaque LSA.
The Value field is encoded in 7-bit ASCII. If a user-interface for
configuring or displaying this field permits Unicode characters, that
user-interface is responsible for applying the ToASCII and/or
ToUnicode algorithm as described in [RFC3490] to achieve the correct
format for transmission or display.
The Dynamic Hostname TLV is applicable to both OSPFv2 and OSPFv3.
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3.1.1. Flooding Scope
The Dynamic Hostname TLV MAY be advertised within an area-local or
autonomous system (AS) scope Router Information (RI) LSA. But the
Dynamic Hostname TLV SHOULD NOT be advertised into an area in more
than one RI LSA irrespective of the scope of the LSA.
In other words, if a router originates a Dynamic Hostname TLV with an
IGP domain (AS) flooding scope, it SHOULD NOT send area-scoped
Dynamic Hostname TLV except into any attached Not-So-Stubby Area
(NSSA) area(s). Similarly, if a router originates area-scoped
Dynamic Hostname TLV (other than NSSA area scoped), it SHOULD NOT
send AS-scoped Dynamic Hostname TLV. When the Dynamic Hostname TLV
is advertised in more than one LSA (e.g., multiple area-scoped LSAs,
or AS-scoped LSAs plus NSSA area-scope LSA(s)), the hostname SHOULD
be the same.
If a router is advertising any AS scope LSA (other than Dynamic TLV
RI LSA) such router SHOULD advertise Dynamic TLV RI LSA in AS scope.
Otherwise, it SHOULD advertise Dynamic TLV RI LSA in area scope. For
example, an AS boundary router (ASBR) SHOULD send an AS scope Dynamic
Hostname TLV, whereas area boundary router (ABRs) and internal
routers SHOULD send an area scope Dynamic Hostname TLV.
The flooding scope is controlled by the Opaque LSA type in OSPFv2 and
by the S1 and S2 bits in OSPFv3. For area scope, the Dynamic
Hostname TLV MUST be carried within an OSPFv2 Type 10 RI LSA or an
OSPFv3 RI LSA with the S1 bit set and S2 bit clear. If the flooding
scope is the entire routing domain (AS scope), the Dynamic Hostname
TLV MUST be carried within an OSPFv2 Type 11 RI LSA or OSPFv3 RI LSA
with the S1 bit clear and the S2 bit set.
3.1.2. Multiple OSPF Instances
When an OSPF Router Information (RI) LSA, including the Dynamic
Hostname TLV, is advertised in multiple OSPF instances, the hostname
SHOULD either be preserved, or include a common base element. It may
be useful for debugging or other purposes to assign separate
instances different hostnames with a consistent set of suffixes or
prefixes that can be associated with a specific instance. In
particular, when an instance is used for a discrete address family or
non-routing information.
4. IPv6 Considerations
Both OSPFv2 and OSPFv3 employ Router IDs with a common size of 32-
bits. In IPv4 the Router ID values were typically derived
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automatically from an IPv4 address configured on a loopback or
physical interface defined on the local system, or explicitly defined
within the OSPF process configuration. With broader deployment of
IPv6, it's quite likely that OSPF networks will exist that have no
native IPv4 addressed interfaces. As a result, a 32-bit OSPF Router
ID will either need to be explicitly specified, or derived in some
automatic manner that avoids collisions with other OSPF routers
within the local routing domain.
Because this 32-bit value will not map to IPv4-addressed entities in
the network, nor will it be DNS resolvable, it is considered
extremely desirable from an operational perspective that some
mechanism exist to map OSPF Router IDs to more easily interpreted
values, ideally, human-readable strings. This specification enables
a mapping functionality which eases operational burdens that may
otherwise be introduced with native deployment of IPv6.
5. Security Considerations
Since the hostname-to-Router ID mapping relies on information
provided by the routers themselves, a misconfigured or compromised
router can inject false mapping information, including a duplicate
hostname for different Router IDs. Thus, this information needs to
be treated with suspicion when, for example, doing diagnostics about
a suspected security incident.
There is potential confusion from name collisions if two routers use
and advertise the same Dynamic Hostname. Name conflicts are not
crucial and therefore there is no generic conflict detection or
resolution mechanism in the protocol. However, a router that detects
that a received hostname is the same as the local one can issue a
notification or a management alert.
The use of the FQDN as OSPF dynamic hostname potentially exposes
geographic or other commercial information that can be deduced from
the hostname when sent in the clear. OSPFv3 supports confidentiality
via transport mode IPsec (see [RFC4552]). OSPFv2 could be operated
over IPsec tunnels if confidentiality is required.
This document raises no other new security issues for OSPF. Security
considerations for the base OSPF protocol are covered in [RFC2328]
and [RFC5340]. The use of authentication for the OSPF routing
protocols is encouraged.
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6. IANA Considerations
IANA maintains the "OSPF Router Information (RI) TLVs" registry
reachable at [IANA-RI]. An additional OSPF Router Information TLV
Type is defined in Section 3. It is required to be assigned by IANA
from the Standards Action allocation range [RFC4970].
Registry Name: OSPF Router Information (RI) TLVs
Type Value Capabilities Reference
----------- -------------------------------------- ---------
TBD OSPF Dynamic Hostname This document
7. Acknowledgments
The authors of this document do not make any claims on the
originality of the ideas described. This document adapts format and
text from similar work done in IS-IS [RFC5301] (obsoletes [RFC2763]);
we would like to thank Naiming Shen and and Henk Smit, authors of
[RFC2763].
The authors would also like to thank Acee Lindem, Abhay Roy, Anton
Smirnov, and Dave Ward for their valuable comments and suggestions.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 4970, July 2007.
8.2. Informative References
[IANA-RI] Internet Assigned Numbers Authority, "Open Shortest Path
First v2 (OSPFv2) Parameters", April 2009,
<http://www.iana.org/assignments/ospfv2-parameters>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS
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Specification", RFC 2181, July 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2763] Shen, N. and H. Smit, "Dynamic Hostname Exchange Mechanism
for IS-IS", RFC 2763, February 2000.
[RFC3490] Faltstrom, P., Hoffman, P., and A. Costello,
"Internationalizing Domain Names in Applications (IDNA)",
RFC 3490, March 2003.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, June 2006.
[RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange
Mechanism for IS-IS", RFC 5301, October 2008.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
Authors' Addresses
Subbaiah Venkata
Google Inc.
Email: svenkata@google.com
URI: http://www.google.com
Sanjay Harwani
Cisco Systems
Email: sharwani@cisco.com
URI: http://www.cisco.com
Carlos Pignataro
Cisco Systems
Email: cpignata@cisco.com
URI: http://www.cisco.com
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Danny McPherson
Arbor Networks, Inc.
Email: danny@arbor.net
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