Bgp Processing Of Received Routes; Labeled Unicast Routes; Unlabeled Unicast Routes; Resolving Ipv6 Indirect Next Hops - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BGP AND MPLS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

BGP Processing of Received Routes

Copyright © 2010, Juniper Networks, Inc.
When a BGP router does not report itself as the next hop, whether because of an explicit
neighbor next-hop-unchanged configuration or implicitly as a result of a participating
in an IBGP session, BGP does not allocate a new in label. Instead, if the route is advertised
as a labeled route, BGP uses the existing out label. This feature is used mainly on route
reflectors.
The determination to allocate an in label is made only after the outbound route map has
been processed. Therefore, the in label allocation and the creation of the
label-to-next-hop mapping are performed after the need is apparent, conserving the
number of in labels allocated.
BGP processes received routes differently depending on whether the route is labeled or
unlabeled, unicast or VPN.

Labeled Unicast Routes

When BGP receives a labeled route from a directly connected peer, BGP uses the MPLS
major interface that is next to the peer IP interface to resolve the route's BGP next hop.
If the MPLS major interface exists and is up, then the next hop is reachable.
When the received labeled route is not from a directly connected peer, BGP attempts to
resolve the BGP indirect next hop of the route in the IP tunnel routing table. When the
BGP indirect next hop is reachable, BGP adds the route to both the IP routing table and
to the IP tunnel routing table. The route is added as a U-T (unicast-tunnel-usable) route.

Unlabeled Unicast Routes

When BGP receives an unlabeled route from a directly connected peer, the route's next
hop is resolved to the directly connected interface.
When the received unlabeled route is not from a directly connected peer, BGP resolves
the BGP indirect next hop of the route in the IP routing table. If the BGP indirect next hop
is reachable, BGP adds the route to the IP routing table as a U (unicast) route.

Resolving IPv6 Indirect Next Hops

When the address of the indirect next hop is an IPv4-mapped IPv6 address, BGP resolves
the indirect next hop in the IPv4 routing table and IPv4 tunnel routing table. When the
indirect next hop is a native IPv6 address, the indirect next hop is resolved in the IPv6
routing table and IPv6 tunnel routing table.

Labeled VPN Routes

In the core VRF, when BGP receives a BGP-labeled VPN route from a multihop VPN peer,
it attempts to resolve the BGP indirect next hop in the IP tunnel routing table. If the labeled
VPN route is received from a nonmultihop peer, then the BGP indirect next hop is always
resolved, because a connected route to that peer exists in the IP tunnel routing table.
Table 91 on page 464 summarizes indirect next hop resolution.
Chapter 6: Configuring BGP-MPLS Applications
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