API Guide
Confederations
Another way to organize routers within an AS and reduce the mesh for IBGP peers is to configure BGP confederations. As with
route reflectors, Dell EMC recommends BGP confederations only for IBGP peering involving many IBGP peering sessions per
router.
When you configure BGP confederations, you break the AS into smaller sub-ASs. To devices outside your network, the
confederations appear as one AS. Within the confederation sub-AS, the IBGP neighbors are fully meshed and the MED,
NEXT_HOP, and LOCAL_PREF attributes maintain between confederations.
1. Enter the confederation ID AS number in ROUTER-BGP mode (1 to 65535 for 2–byte, 1 to 4294967295 for 4–byte).
confederation identifier as-number
2. Enter which confederation sub-AS are peers in ROUTER-BGP mode, from 1 to 65535 for 2–byte, 1 to 4294967295 for 4–
byte. All Confederation routers must be either 4 bytes or 2 bytes. You cannot have a mix of router ASN support.
confederation peers as-number [... as-number]
Configure BGP confederations
OS10(config)# router bgp 65501
OS10(conf-router-bgp-65501)# confederation identifier 100
OS10(conf-router-bgp-65501)# confederation peers 65502 65503 65504
OS10(conf-router-bgp-65501)# neighbor 1.1.1.2
OS10(conf-router-neighbor)# remote-as 65502
OS10(conf-router-neighbor)# no shutdown
OS10(conf-router-neighbor)# exit
OS10(conf-router-bgp-65501)# neighbor 2.1.1.2
OS10(conf-router-neighbor)# remote-as 65503
OS10(conf-router-neighbor)# no shutdown
OS10(conf-router-neighbor)# exit
OS10(conf-router-bgp-65501)# neighbor 3.1.1.2
OS10(conf-router-neighbor)# remote-as 65504
OS10(conf-router-neighbor)# no shutdown
OS10(conf-router-neighbor)# exit
OS10(conf-router-bgp-65501)# end
OS10# show running-configuration bgp
!
router bgp 65501
confederation identifier 100
confederation peers 65502 65503 65504
!
neighbor 1.1.1.2
remote-as 65502
no shutdown
!
neighbor 2.1.1.2
remote-as 65503
no shutdown
!
neighbor 3.1.1.2
remote-as 65504
no shutdown
Route dampening
When EBGP routes become unavailable, they “flap” and the router issues both WITHDRAWN and UPDATE notices. A flap occurs
when a route is withdrawn, readvertised after being withdrawn, or has an attribute change.
The constant router reaction to the WITHDRAWN and UPDATE notices causes instability in the BGP process. To minimize this
instability, configure penalties (a numeric value) for routes that flap. When that penalty value reaches a configured limit, the
route is not advertised, even if the route is up, the penalty value is 1024.
As time passes and the route does not flap, the penalty value decrements or decays. If the route flaps again, it is assigned
another penalty. The penalty value is cumulative and adds underwithdraw, readvertise, or attribute change.
When dampening applies to a route, its path is described by:
600
Layer 3