Enabling Route Flap Dampening - Dell S4820T Configuration Manual

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When EBGP routes become unavailable, they "flap" and the router issues both WITHDRAWN and UPDATE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• is withdrawn
• is readvertised after being withdrawn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The constant router reaction to the WITHDRAWN and UPDATE notices causes instability in the BGP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
Border Gateway Protocol IPv4 (BGPv4)
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