Network Working Group J. Snijders
Internet-Draft Atrato IP Networks
Intended status: Informational August 9, 2013
Expires: February 10, 2014
The "import-via" and "export-via" attributes in RPSL Policy
Specifications
draft-snijders-rpsl-via-02
Abstract
This document defines two attributes in the aut-num Class which can
be used in RPSL policy specifications to publish desired routing
policy regarding non-adjacent networks.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Import and Export Via Syntax and Semantics . . . . . . . . . . 4
5. Example Usage . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Ambiguity Resolution . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Grammar Rules . . . . . . . . . . . . . . . . . . . . 7
Appendix B. Document Change Log . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
The Routing Policy Specification Language [RFC4012] allows operators
to specify routing policies regarding directly adjacent networks
through various import and export attributes. These attributes only
apply to directly adjacent networks.
This document proposes to extend RPSL according to the following
goals and requirements:
o Provide a way to describe what an adjacent network could use as
routing policy towards its adjacent networks.
o The extension should be backward compatible with minimal impact on
existing tools and processes, following Section 10.2 of [RFC2622].
The addition of the "import-via" and "export-via" attributes in the
aut-num Class will especially help participants of Multi-Lateral
Peering services to inform the intermediate autonomous system what
routing policy should be applied towards other participants.
2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
3. Background
The via keyword specifically benefits operators whom were assigned a
32 bit AS Number and transit providers when participating in Multi-
Lateral Peering Agreements facilitated by a Route Server.
Often Route Server operators overload BGP Communities [RFC1997]) to
facilitate signalling of desired routing policy between the
participants and the Route Server. Because BGP Communities have a
length of 32 bit, it is not possible to signal a 32 bit AS Number
coupled with an action. In practise this means Route Server
participants whom use a 32 bit AS Number cannot specifically be
included or excluded during path distribution calculations on the
Route Server unless a mapping system is applied.
Transit providers often have a routing policy which states that the
transit provider does not want to exchange paths with its downstream
customers through Route Servers via public Internet Exchanges. The
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import-via and export-via attributes allow transit providers to
participate in Multi-Lateral Peering services while instructing Route
Server operators through a simple routing policy specification that
paths should not be distributed to downstream customers and reducing
the likelihood of Path Hiding on the Route Server.
4. Import and Export Via Syntax and Semantics
The two attributes can be used within the aut-num class.
import-via:
export-via:
The syntax for these attributes is as follows:
Attribute Value Type
import-via [protocol <protocol-1>] [into <protocol-2>] optional,
[afi <afi-list>] multi-valued
<mp-peering-1>
from <mp-peering-2> [action <action-1>; ... <action-N>;]
. . .
<mp-peering-3>
from <mp-peering-M> [action <action-1>; ... <action-N>;]
accept <mp-filter> [;]
export-via [protocol <protocol-1>] [into <protocol-2>] optional,
[afi <afi-list>] multi-valued
<mp-peering-1>
to <mp-peering-2> [action <action-1>; ... <action-N>;]
. . .
<mp-peering-3>
to <mp-peering-M> [action <action-1>; ... <action-N>;]
announce <mp-filter> [;]
Figure 1
The import-via and export-via attributes are optional, and should be
ignored by implementations which do not support interpretation of
those attributes. The syntax closely mimicks the mp-import and mp-
export attributes described in Section 2.5 of [RFC4012], with the
exception that before the "from" and "to" keywords an <mp-peering> is
defined to indicate the common AS between two non-adjacent networks.
In the above example <peering-1> and <peering-3> are directly
adjacent networks, for instance a Multi-Lateral Peering service.
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<peering-2> is a non-adjacent network.
5. Example Usage
Putting it all together:
aut-num: AS5580
import-via: AS6777
from AS15562
action pref = 2;
accept AS-SNIJDERS
export-via: AS6777
to AS15562 action community.={5580:40};
announce AS-ATRATO
import-via: AS5580:AS-ROUTESERVERS
from AS5580:AS-CUSTOMERS
accept NOT ANY
export-via: AS5580:AS-ROUTESERVERS
to AS5580:AS-CUSTOMERS announce NOT ANY
import-via: AS6777
from AS4247483647
accept AS4247483647
export-via: AS6777
to AS4247483647 action community.={5580:40};
announce AS-ATRATO
Figure 2
In the above examples AS5580 and AS15562 are Route Server
participants. AS4247483647 is a participant whom has been assigned a
32 bit AS Number. AS6777 functions as a Route Server
[I-D.ietf-idr-ix-bgp-route-server] and AS-SET AS5580:AS-ROUTESERVERS
contains a list of Route Server AS Numbers. AS-SET AS5580:AS-
CUSTOMERS contains a list of downstream transit customers from
AS5580.
The intention of the above policy would be to enable the exchange of
NLRI's through AS6777 with two parties: AS15562 and AS4247483647, yet
prevent the Route Server from distributing NLRI's announced by AS5580
towards customers of said network. Publishing the policy that AS5580
will not accept customer routes through the Route Server can help
counteract the "path hiding" phenomenon as described in Section 2.3.1
of [I-D.ietf-idr-ix-bgp-route-server], as the Route Server now is
informed which NLRI's should not be considered in the best path
selection process.
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6. Ambiguity Resolution
The same peering can be covered by more than one "via" policy
attribute or by a combination of multi-protocol policy attributes, or
multi-protocol policy attributes (when specifying IPv4 unicast
policy) and the previously defined IPv4 unicast policy attributes.
In these cases, implementations should follow the specification-order
rule as defined in Section 6.4 of RFC 2622 [1]. Operators should
take note that in order to break ambiguity, the action corresponding
to the first peering specification is used.
Consider the following example regarding ambiguity resolution.
aut-num: AS5580
export: to AS6777 195.69.144.255 to announce AS5580
export-via: AS6777 195.69.144.255 to AS-AMS-IX-RS announce AS-ATRATO
Figure 3
As both policy specifications cover the same peering with AS6777,
specification-order rule is used and Route Server AS6777
195.69.144.255 should only accept AS5580, instead of AS-ATRATO, even
though the export-via specification is more specific. If the
intended policy was to announce all routes which can be resolved
through AS-ATRATO on this particular peering, the operator should
have specified:
aut-num: AS5580
export-via: AS6777 195.69.144.255 to AS-AMS-IX-RS announce AS-ATRATO
export: to AS6777 195.69.144.255 to announce AS5580
Figure 4
7. Security Considerations
There are no security considerations for this specification.
8. IANA Considerations
This document has no IANA actions.
9. Acknowledgments
The authors would like to thank Remko van Mook for confirming that
"via" is a better keyword than 'through' or 'thru', Nick Hilliard for
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his unparalleled support, Jeffrey Haas for providing historic
perspective and David Croft for nitpicking.
10. References
10.1. Normative References
[RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP
Communities Attribute", RFC 1997, August 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2622] Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D.,
Meyer, D., Bates, T., Karrenberg, D., and M. Terpstra,
"Routing Policy Specification Language (RPSL)", RFC 2622,
June 1999.
[RFC4012] Blunk, L., Damas, J., Parent, F., and A. Robachevsky,
"Routing Policy Specification Language next generation
(RPSLng)", RFC 4012, March 2005.
10.2. Informative References
[I-D.ietf-idr-ix-bgp-route-server]
Jasinska, E., Hilliard, N., Raszuk, R., and N. Bakker,
"Internet Exchange Route Server",
draft-ietf-idr-ix-bgp-route-server-02 (work in progress),
February 2013.
Appendix A. Grammar Rules
Note that only relevant grammer rules have been listed. An example
implementation based on IRRd 2.3.10 is available at
<https://github.com/job/irrd>, and an updated version of the RIPE
Database whois code is available at: <https://github.com/job/whois>.
%type <string> line_autnum
%type <string> attr_autnum
%type <string> attr_import_via
%type <string> attr_export_via
%token T_IV_KEY //*** import-via: ***
%token T_EV_KEY //*** export-via: ***
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%token T_AFI T_PROTOCOL T_WORD T_INTO T_EXCEPT T_REFINE
%token T_ACCEPT T_ANNOUNCE T_TO T_FROM T_PRNGNAME
line_autnum: attr_autnum
| attr_import_via
| attr_export_via
attr_import_via: T_IV_KEY attr_import_syntax
attr_import_syntax: opt_protocol_from opt_protocol_into import_simple
| opt_protocol_from opt_protocol_into afi_import_exp
attr_export_via: T_EV_KEY attr_export_syntax
attr_export_syntax: opt_protocol_from opt_protocol_into export_simple
| opt_protocol_from opt_protocol_into afi_export_exp
opt_afi_specification:
| T_AFI afi_list
afi_list: afi_token
| afi_list ',' afi_token
afi_token: afi_name
opt_protocol_from:
| T_PROTOCOL T_WORD
opt_protocol_into:
| T_INTO T_WORD
import_simple: opt_afi_specification import_factor
export_simple: opt_afi_specification export_factor
afi_import_exp: opt_afi_specification import_exp
afi_export_exp: opt_afi_specification export_exp
import_exp: import_term
| import_term T_EXCEPT afi_import_exp
| import_term T_REFINE afi_import_exp
import_factor_list: import_factor ';'
| import_factor_list import_factor ';'
import_term: import_factor ';'
| '{' import_factor_list '}'
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export_exp: export_term
| export_term T_EXCEPT afi_export_exp
| export_term T_REFINE afi_export_exp
export_factor_list: export_factor ';'
| export_factor_list export_factor ';'
export_term: export_factor ';'
| '{' export_factor_list '}'
import_factor: import_peering_action_list T_ACCEPT filter
export_factor: export_peering_action_list T_ANNOUNCE filter
peering: as_expression opt_router_expression \
opt_router_expression_with_at
| T_PRNGNAME
// Below are two grammer rules that actually differ
// from mp-import: + mp-export:
import_peering_action_list: peering T_FROM peering opt_action
| import_peering_action_list peering T_FROM peering opt_action
export_peering_action_list: peering T_TO peering opt_action
| export_peering_action_list peering T_TO peering opt_action
Figure 5
Appendix B. Document Change Log
(RFC Editor - this Appendix can be removed upon publication as RFC)
1. Initial document.
2. Changes to draft-snijders-rpsl-via-01.txt
A. Moved from adding a new RPSL keyword to a new RPSL attribute
to improve backwards compatibility.
3. Changes to draft-snijders-rpsl-via-02.txt
A. Added grammer appendix.
B. Added section about Ambiguity Resolution.
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Author's Address
Job Snijders
Atrato IP Networks
Tupolevlaan 103a
Schiphol-Rijk 1119 PA
NL
Email: job.snijders@atrato.com
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