notes: BGP next-hop tracking & Fast Peering Sessions

- This is enabled by default when a supporting Cisco IOS software image is installed.
- BGP prefixes are automatically tracked as peering sessions are established.
- Next-hop changes are rapidly reported to the BGP routing process as they are updated in the Routing Information Base (RIB).
- This optimization improves overall BGP convergence by reducing the response time to next-hop changes for routes installed in the
RIB. When a best-path calculation is run inbetween BGP scanner cycles, only next-hop changes are tracked and processed.

commands:

- Disables next-hop tracking (enabled by default)

router bgp {asn}

no bgp nexthop trigger enable

Fast Peering Sessions

- Enable BGP to monitor the peering session of a specified neighbor for adjacency changes and to deactivate the peering session.
- BGP fast peering session deactivation is event driven and is configured on a per-neighbor basis.
- Adjacency changes are detected, and terminated peering sessions are deactivated in between the BGP scanning intervals.
- A route-map can be used to deactivate the peering session based a specific prefix.
- Only the "match ip address" and "match source-protocol" commands are supported in fast peering route-maps.


configuration sets:

- Match any route with a prefix of /28 or more specific

ip prefix-list FILTER28 seq 5 permit 0.0.0.0/0 ge 28 

!

 - Reference the filter

route-map CHECK-NBR permit 10

match ip address prefix-list FILTER28

!

- Reset the session if a /28 or more specfic prefix dissappears

router bgp 45000

neighbor 192.168.1.2 remote-as 40000

neighbor 192.168.1.2 fall-over route-map CHECK-NBR


command:

- Enables BGP fast peering session fall-over

router bgp {asn}

neighbor {IP} fall-over [bfd | route-map]