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Configure BGP Soft-Reconfiguration

Whenever there is a change in the policy, the BGP session has to be cleared for the new policy to take effect. Clearing a BGP session causes cache invalidation and results in a tremendous impact on the operation of networks. Which is not delightful event!

Soft reconfiguration allows policies to be configured and activated without clearing the BGP session. Soft reconfiguration can be done on a per-neighbor basis.

When soft reconfiguration is used to generate inbound updates from a neighbor, it is called inbound soft reconfiguration.
When soft reconfiguration is used to send a new set of updates to a neighbor, it is called outbound soft reconfiguration.

Performing inbound reconfiguration enables the new inbound policy to take effect. Performing outbound reconfiguration causes the new local outbound policy take effect without resetting the BGP session. As a new set of updates is sent during outbound policy reconfiguration, a new inbound policy of the neighbor can also take effect.

In order to generate new inbound updates without resetting the BGP session, the local BGP speaker should store all the received updates without modification, regardless of whether it is accepted or denied by the current inbound policy. This is memory intensive and should be avoided. On the other hand, outbound soft reconfiguration does not have any memory overhead. One could trigger an outbound reconfiguration in the other side of the BGP session to make the new inbound policy take effect.

To allow inbound reconfiguration, BGP should be configured to store all received updates. However, outbound reconfiguration does not require preconfiguration.

To configure BGP soft configuration, perform the following task in router configuration mode:

Router#config

Router(config)#router bgp [ASN]

Router(config-bgp)#neighbor x.x.x.x soft-reconfiguration inbound

To clear bgp session from router CLI

Router#clear ip bgp x.x.x.x (neighbor IP) soft inbound

Well, if you want to reset entire BGP sessions

Router#clear ip bgp *

Our implementation of BGP supports BGP Versions 2, 3, and 4. If the neighbor does not accept default Version 4, dynamic version negotiation is implemented to negotiate down to Version 2.

If you specify a BGP peer group by using the peer-group-name argument, all members of the peer group will inherit the characteristic configured with this command.

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