Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.100.0 - Page 200

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 are maintained between confederations. To configure BGP confederations, use the following commands. • Specifies the confederation ID. CONFIG-ROUTER-BGP mode bgp confederation identifier as-number • as-number: from 0 to 65535 (2 Byte) or from 1 to 4294967295 (4 Byte). • Specifies which confederation sub-AS are peers. CONFIG-ROUTER-BGP mode bgp confederation peers as-number [... as-number] • as-number: from 0 to 65535 (2 Byte) or from 1 to 4294967295 (4 Byte). All Confederation routers must be either 4 Byte or 2 Byte. You cannot have a mix of router ASN support. To view the configuration, use the show config command in CONFIGURATION ROUTER BGP mode. Enabling Route Flap Dampening When EBGP routes become unavailable, they "flap" and the router issues both WITHDRAWN and UPDATE notices. A flap is when a route: • is withdrawn • is readvertised after being withdrawn • has an attribute change The constant router reaction to the WITHDRAWN and UPDATE notices causes instability in the BGP process. To minimize this instability, you may 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. In Dell Networking OS, that penalty value is 1024. As time passes and the route does not flap, the penalty value decrements or is decayed. However, if the route flaps again, it is assigned another penalty. The penalty value is cumulative and penalty is added under following cases: • Withdraw • Readvertise • Attribute change When dampening is applied to a route, its path is described by one of the following terms: • history entry - an entry that stores information on a downed route • dampened path - a path that is no longer advertised • penalized path - a path that is assigned a penalty To configure route flap dampening parameters, set dampening parameters using a route map, clear information on route dampening and return suppressed routes to active state, view statistics on route flapping, or change the path selection from the default mode (deterministic) to non-deterministic, use the following commands. • Enable route dampening. CONFIG-ROUTER-BGP mode bgp dampening [half-life | reuse | suppress max-suppress-time] [route-map map-name] Enter the following optional parameters to configure route dampening parameters: 200 Border Gateway Protocol IPv4 (BGPv4)