North American Network Operators Group|
Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical
Question on BGP Link-Local peering...
Greetings, In trying to follow the guidance in draft-kato-bgp-ipv6-link-local-00.txt while setting up a network using BGP link-local peering, I came up with a few questions I could not answer on my own. First, some network details: - eBGP sessions will be established across p2p links via link local address + each interface on the p2p link will ONLY be addressed with link-local addresses + each router on the ends of the link will have a single global unicast address tied to a loopback interface. Part of the draft (http://www.join.uni-muenster.de/Dokumente/drafts/draft-kato-bgp-ipv6-link-local-00.txt) states: """ A) BGP-4 speakers should ignore the IPv6 global address specified in the next hop field in a MP_REACH_NLRI attribute learned over a link-local E-BGP session, provided if it does not match with one of the IPv6 global prefixes assigned to the link. (It is possible to assign an IPv6 global prefix to an IX and have a link-local E-BGP session.) """ and """ C) BGP-4 implementations should be able to configure, at least per session basis, which IPv6 global address is to be filled in the next hop field of MP_REACH_NLRI attributes. In the case of link-local E- BGP sessions, arbitrary IPv6 address can be specified while in a typical case an IPv6 global address attached to the node (other interface or loopback) will be specified. """" In the network described above, peering will be configured using the link-local addresses, and the next-hop will be advertised with both the link-local address as well as the loopback global-unicast address (via a route-map). Here are the questions that arose out of this configuration: 1) What does "BGP-4 speakers should ignore the IPv6 global address specified in the next hop field in a MP_REACH_NLRI attribute learned over a link-local E-BGP session" mean from A referenced above. Would not the global address still need to be used for route propagation, rather than "ignored"? 2) Stemming from above, if a loopback global address is used as mentioned in C above ("in a typical case an IPv6 global address attached to the node (other interface or loopback) will be specified"), how will nodes in the attached network receiving the advertisement know how to reach this not-attached next-hop? I seem to be missing some magic that would allow this global address to be reachable and re-advertisable to iBGP peers as the upstream next-hop (since link-local will be useful only to the direct peer). - Is the global address ignores as referenced above and such peers must be configured to next-hop-self to their iBGP neighbors? - Does each neighbor then need a static route installed to the global loopback via the link-local address? - Is there some other behind-the-scenes magic that I'm missing that informs peer routers how to reach the global loopback address? Thanks! ~Aaron