014 BGP soft-reconfiguaration

BGP soft reconfiguration inbound
    Whenever we do some changes in the BGP 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.
     Soft reconfiguration allows policies to be configured and activated without clearing the BGP session. Soft reconfiguration can be done on a per-neighbor basis.
    There are two types of soft reconfiguration

1. inbound soft reconfiguration
2. outbound soft reconfiguration

Inbound soft reconfiguration:

• Soft reconfiguration can be used to generate inbound updates from a neighbor.
• Performing inbound reconfiguration enables the new inbound policy to 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.
• To allow inbound reconfiguration, BGP should be configured to store all received updates.

Outbound soft reconfiguration:

• Soft reconfiguration can be used to send a new set of updates to a neighbor.
• 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.
• 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. Outbound reconfiguration does not require pre-configuration.
   

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.

BGP Peer – Soft Reconfiguration
Router(config-router)# neighbor X.X.X.X soft-reconfiguration inbound

• Use to configure BGP soft configuration.
• Use this command in router configuration mode.
• The X.X.X.X stands for ip-address.

Verification
show ip bgp neighbor X.X.X.X received-routes

• Use to display all received routes (both accepted and rejected) from the specified neighbor.
• Displays information only about IPv4 address-family sessions unless the all keyword is entered.
• Prefix activity is displayed based on the number of prefixes that are advertised and withdrawn.
• Policy denials display the number of routes that were advertised but then ignored based the function or