Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

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•
VPLS—If you specify the VPLS address family, you can configure the router to exchange
layer 2 NLRI for a specified VPLS instance. For a description of VPLS, see “Configuring
VPLS” on page 589.
•
VPWS—If you specify the VPWS address family, you can configure the PE router to
exchange layer 2 NLRI for a specified VPWS instance. For a description of VPWS, see
“Configuring VPWS” on page 651.
For information about specifying an address family, see “Multicast Services over VPNs”
on page 421.
Equal-Cost Multipath Support
Equal-cost multipath (ECMP) is a traffic load-balancing feature that enables traffic to
the same destination to be distributed over multiple paths that have the same cost. BGP
ECMP support for BGP/MPLS VPNs enables MPLS VPN routes to be included in the list
of available equal-cost paths. You can specify that up to 16 equal-cost paths be
considered.
The set of ECMP legs in a network can contain MPLS indirect next hops, either as a leg
itself or pointed to by a leg. If the path to any of the MPLS indirect next hops fails, then
the routing protocol begins recalculating the set of viable routes as soon as it is notified
of the failure. When the recalculation has finished, the protocol then updates the routing
table with the new routes.
From the time the path fails until the routing table is updated, the traffic flowing over the
ECMP leg that has the failed MPLS indirect next hop is lost.
To reduce the amount of lost traffic, the failed path is quickly pruned from the ECMP set
as soon as the protocol is notified of the connectivity failure. Traffic for the destination
is then forwarded over the remaining equal-cost paths to the destination. When the
recalculated set of routes is installed in the routing table, traffic for the destination is
forwarded by means of the new route.
ECMP sets can have an MPLS indirect next hop as one of the legs in the following
scenarios:
•
In a BGP-MPLS VPN where a given VPN prefix is learned from multiple PE routers.
•
When multiple RSVP-TE tunnels are created over different paths to the same
destination.
• In a network that connects IPv6 islands across an IPv4 core, where a given IPv6 prefix
is learned from multiple egress PEs running IPv6.
Consider the simple ECMP scenario for a BGP/MPLS VPN shown in Figure 68 on page 386.
385 Copyright © 2010, Juniper Networks, Inc.
Chapter 6: Configuring BGP-MPLS Applications