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This document defines the 'via' keyword 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 of . The addition of a 'via' keyword in import and export related attributes 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 via keyword can be used with the following policy attributes: import: export: mp-import: mp-export:

The syntax for these attributes is as follows: Attribute Value Type import [protocol <protocol-1>] [into <protocol-2>] optional, [via <peering-1>] optional, from <peering-2> [action <action-1>] . . . [via <peering-3>] optional, from <peering-N> [action <action-N>] accept <filter> export [protocol <protocol-1>] [into <protocol-2>] optional, [via <peering-1>] optional, to <peering-2> [action <action-1>] . . . [via <peering-3>] optional, to <peering-N> [action <action-N>] announce <filter> mp-import [protocol <protocol-1>] [into <protocol-2>] optional, [afi <afi-list>] multi-valued [via <peering-1>] optional, from <mp-peering-2> [action <action-1>; ... <action-N>;] . . . [via <peering-3>] optional, from <mp-peering-M> [action <action-1>; ... <action-N>;] accept <mp-filter> [;] mp-export [protocol <protocol-1>] [into <protocol-2>] optional, [afi <afi-list>] multi-valued [via peering-1>] optional, to <mp-peering-2> [action <action-1>; ... <action-N>;] . . . [via peering-3>] optional, to <mp-peering-M> [action <action-1>; ... <action-N>;] announce <mp-filter> [;]

The via keyword is optional, and should be ignored by implementations which do not support interpretation of the via keyword. 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 import: via AS6777 from AS5580:AS-CUSTOMERS accept NOT ANY import: via AS6777 from AS15562 from AS1 from AS2 via AS3 from AS4 accept PeerAS mp-import: afi ipv6.unicast via AS6777 from AS15562 accept AS-SNIJDERS mp-import: via AS6777 from AS65551 accept AS-SET-FROM-32BIT-ASN export: via AS6777 to AS15562 action community.={5580:40}; announce AS-ATRATO export: via AS5580:AS-ROUTESERVERS to AS5580:AS-CUSTOMERS announce NOT ANY mp-export: afi ipv6.unicast via AS6777 to AS15562 announce AS-ATRATO mp-export: via AS6777 to AS65551 announce AS-ATRATO

In the above examples AS5580 and AS15562 are Route Server participants. AS65551 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.

There are no security considerations for this specification.

The new set of mechanisms for route servers does not require any new allocations from IANA.

The authors would like to thank Remko van Mook for confirming that 'via' is a better keyword than 'through' or 'thru'.

HERE BE DRAGONS

(RFC Editor - this Appendix can be removed upon publication as RFC) Route Server operators whom believe this is a viable solution: ECIX EQUINIX Software projects which will receive patches to support the via keyword: RADB RIPE WHOIS Software that might need a patch: irrtoolset rpsltools

(RFC Editor - this Appendix can be removed upon publication as RFC) Initial document. Changes to draft-snijders-rpsl-via-01.txt derp derp