]> Atrato IP Networks

Tupolevlaan 103a Schiphol-Rijk 1119 PA NL job.snijders@atrato.com

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.

The Routing Policy Specification Language 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: Provide a way to describe what an adjacent network could use as routing policy towards its adjacent networks. The extension should be backward compatible with minimal impact on existing tools and processes, following Section 10.2 of . The addition of the 'via-import' and 'via-export' 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.

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 .

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 ) 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 uphold a routing policy which intents that the transit provider does not want to exchange paths with its downstream customers through Route Servers. The via keyword allows 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 likelyhood of Path Hiding on the Route Server.

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>;] . . . &klt;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> [;]

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 , with the exception that before the "from" and "to" keywords an &klt;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. <peering-2> is a non-adjacent network.

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

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 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 , as the Route Server now is informed which NLRI's should not be considered in the best path selection process.

There are no security considerations for this specification.

This document has no IANA actions.

The authors would like to thank Remko van Mook for confirming that 'via' is a better keyword than 'through' or 'thru', Nick Hilliard for his unparalleled support and Jeffrey Haas for providing historic perspective.

HERE BE DRAGONS

(RFC Editor - this Appendix can be removed upon publication as RFC) Initial document. Changes to draft-snijders-rpsl-via-01.txt Moved from adding a new RPSL keyword to a new RPSL attribute to improve backwards compatibility.