Hi Eric, On 11/9/15, 10:22 AM, "spring on behalf of Eric C Rosen" <spring-boun...@ietf.org on behalf of ero...@juniper.net> wrote:
>Hi Stefano, > >>> If a BGP route is received that contains a Prefix-SID attribute >>>with an >>> Originator SRGB TLV, but the prefix field of the NLRI does not >>>contain a >>> host address, the attribute SHOULD be regarded as malformed. If a >>> Prefix-SID attribute contains more than one SRGB TLV, it SHOULD be >>> regarded as malformed. See section 7 for the treatment of a >>>malformed >>> Prefix-SID attribute. >>> >>> When a route carrying the Prefix-SID attribute is propagated, the >>> Originator SRGB TLV (if present) MUST NOT be changed. > >> why would you need such limitation ? A prefix may have a shorter mask >> than 32 (or 128) and still be ok for the Originator SRGB to be there. > >The SRGB is a property of a node, not a property of a prefix. To make >use of the "Originator SRGB", you have to know the node whose property >it is. And you have to be able to tunnel packets to that node. In the >text I wrote above, the prefix field in the NLRI identifies the node to >which the "Originator SRGB" belongs, and the prefix-SID field >essentially gives you a node-SID that you can use to tunnel to the node >in question. I agree the predominant use case will be advertisement of a loopback. However, independent of whether or not the Originator-SRGB TLV is included, I see no reason why a BGP Speaker could not associate a label-index with a locally attached subnet. Thanks, Acee > >> The Originator-SRGB may only be inserted by the originator of the >> prefix, maybe we should emphasize that, but the masklength is mostly >> irrelevant here. > >I don't see that the Originator-SRGB TLV is useful without an explicit >identification of the node whose SRGB it describes. Certainly if you >are trying to set up an explicitly routed path (perhaps as a loose >source route) what you need are the node-SIDs are of the hops you want >to specify, and the SRGB of each hop. > >When you talk about "the originator of the prefix", I think what you >really mean is "the last node of the BGP prefix segment". But I don't >think that that term necessarily denotes a unique node, as there might >be multiple ECMP paths to the prefix, and the prefix-SID does not >distinguish among them. E.g., the prefix itself might be multi-homed, >or there might be multiple exit points from the SR domain, all of which >are equidistant from the prefix. In cases like that, you have no way of >knowing whether a label computed from the Originator-SRGB is actually >going to be correctly interpreted, because you don't really know the >path a packet will take when it is labeled with the prefix-SID. > >Eric > > > > >_______________________________________________ >spring mailing list >spring@ietf.org >https://www.ietf.org/mailman/listinfo/spring _______________________________________________ spring mailing list spring@ietf.org https://www.ietf.org/mailman/listinfo/spring
