Resetting BGP sessions

When a BGP router configuration is changed, it is often necessary to reset the connections to the affected neighbors in order for the change to take effect. The user must reset the BGP connection for all:
  • Changes to BGP related route maps, prefix lists, aspath lists, and community-lists

  • Changes to the BGP-related timer specification

  • Changes to BGP-related weights

BGP supports two methods of clearing a BGP session:
  • A hard reset, which tears down the BGP session, removes BGP routes from the peer, and is the most disruptive.

  • A soft reset, which invalidates the BGP cache and requests a full advertisement from its BGP peer.

Initiate a hard or soft reset with the clear bgp commands. Clear sessions with all BGP neighbors by using an asterisk * instead of the peer IP address.

When a BGP route policy changes, the BGP table must be processed again to notify neighbors. If the BGP session supports route refresh capability, the peer refreshes the prefixes to the requesting router, allowing the inbound policy to process using the new policy changes. The route refresh capability is negotiated when the session is established.

If the BGP session does not support route refresh, use inbound soft reconfiguration so that updates to inbound route policies can be applied without performing a hard reset.
  • Inbound soft reconfiguration does not purge the Adj- RIB-In table after routes process into the Loc-RIB table.

  • The Adj-RIB-In table maintains the raw unedited routes received from neighbors and allows the inbound route policies to be processed again.

  • Enabling this feature can consume a significant amount of memory because the Adj-RIB-In table stays in memory.