Concept Guide

automatically enables route reection to all clients. To disable route reection between all clients in this reector, use the no bgp
client-to-client reflection command in CONFIGURATION ROUTER BGP mode. All clients must be fully meshed before you
disable route reection.
To view a route reector conguration, use the show config command in CONFIGURATION ROUTER BGP mode or the show
running-config bgp in EXEC Privilege mode.
Conguring BGP Confederations
Another way to organize routers within an AS and reduce the mesh for IBGP peers is to congure BGP confederations.
As with route reectors, BGP confederations are recommended only for IBGP peering involving many IBGP peering sessions per router.
Basically, when you congure BGP confederations, you break the AS into smaller sub-AS, and to those 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 are maintained between confederations.
To congure BGP confederations, use the following commands.
• Species 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).
• Species 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 conguration, use the show config command in CONFIGURATION ROUTER BGP mode.
Enabling Route Flap Dampening
When EBGP routes become unavailable, they “ap” and the router issues both WITHDRAWN and UPDATE notices.
A ap 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• is withdrawn
• is readvertised after being withdrawn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The constant router reaction to the WITHDRAWN and UPDATE notices causes instability in the BGP process.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 congure penalties (a numeric value) for routes that ap. When that penalty value reaches a congured limit, the route is not
advertised, even if the route is up. In Dell EMC Networking OS, that penalty value is 1024. As time passes and the route does not ap, the
penalty value decrements or is decayed. However, if the route aps 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:
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Border Gateway Protocol (BGP)