• The route points to a next-hop interface that is internal to the VRF and created
automatically when the VR comes up. This interface is hidden and cannot be displayed
with the show ip interface command. You must use the show ip route or show ip
static commands to display the interface.
• If the interface in the parent VR goes down or is deleted, the static route added in the
VRF will continue to exist.
• Example
host1(config-vrf)#ip route parent-router vr1stat
• Use the no version to remove the static route.
• See ip route.
Achieving Fast Reconvergence in VPN Networks
By default, BGP does not confirm the reachability of the BGP indirect next hop of VPNv4
routes received over an MP-IBGP session until those routes have been imported into a
VRF.
To BGP, the next hops of VPNv4 routes that are still in the global VPNv4 table (viewable
with the show ip bgp vpnv4 all command) are always reachable. As a result, VPNv4
route reflectors that have multiple paths to the same prefix select the best route to reflect
without taking into account the reachability of the BGP indirect next hop. Instead,
best-path selection is based on weight, local preference, AS-path length, and other
attributes.
After the route has been imported into a VRF, the reachability of the BGP indirect next
hop is based on the presence of an MPLS tunnel (LDP or RSVP-TE) to the next-hop
address and not on the presence of an IP route to the next-hop address.
Disregarding the reachability of the BGP indirect next hop when the router selects the
best route to reflect can cause very slow reconvergence (up to 90 seconds) after a
topology change in BGP/MPLS VPN networks that match all of the following conditions:
•
Have a full mesh of LDP MPLS tunnels
•
Have multihomed CE routers
•
Use the same RD for multiple VRFs
•
Rely on VPNv4 route reflectors as arbiters for selecting the best VPNv4 route from a
set of clients
If a PE router fails in such a network, the route reflector must quickly reflect the VPNv4
route from the next-best PE router without having to wait for the BGP session to the
failed PE router to time out. Depending on the network topology, you can achieve fast
reconvergence by assigning unique RDs to each VRF or by enabling next-hop reachability
checking.
455Copyright © 2010, Juniper Networks, Inc.
Chapter 6: Configuring BGP-MPLS Applications
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