Bgp Local Label Retention; Retain Allocated Local Label For Primary Path - Cisco NCS 5500 Series Configuration Manual

Implementing BGP
Example:
RP/0/RP0/CPU0:router(config-bgp)# address-family vpnv4 unicast
Specifies the address family or VRF address family and enters the address family or VRF address family configuration
submode.
Step 4
advertise best-external
Example:
RP/0/RP0/CPU0:router(config-bgp-af)# advertise best-external
Advertise the best–external path to the iBGP and route-reflector peers.
Step 5 commit

BGP Local Label Retention

When a primary PE-CE link fails, BGP withdraws the route corresponding to the primary path along with its
local label and programs the backup path in the Routing Information Base (RIB) and the Forwarding Information
Base (FIB), by default.
However, until all the internal peers of the primary PE reconverge to use the backup path as the new bestpath,
the traffic continues to be forwarded to the primary PE with the local label that was allocated for the primary
path. Hence the previously allocated local label for the primary path must be retained on the primary PE for
some configurable time after the reconvergence. BGP Local Label Retention feature enables the retention of
the local label for a specified period. If no time is specified, the local lable is retained for a default value of
five minutes.

Retain Allocated Local Label for Primary Path

Perform the following tasks to retain the previously allocated local label for the primary path on the primary
PE for some configurable time after reconvergence:
SUMMARY STEPS
1. configure
2. router bgp as-number
3. address-family { vpnv4 unicast | vpnv6 unicast }
4. retain local-label minutes
5. commit
DETAILED STEPS
Step 1 configure
Step 2 router bgp as-number
BGP Configuration Guide for Cisco NCS 5500 Series Routers, IOS XR Release 6.2.x
BGP Local Label Retention
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