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Enabling BGP Neighbor Soft-Reconfiguration
BGP soft-reconfiguration allows for faster and easier route changing.
Changing routing policies typically requires a reset of BGP sessions (the TCP connection) for the policies
to take effect. Such resets cause undue interruption to traffic due to hard reset of the BGP cache and the
time it takes to re-establish the session. BGP soft reconfig allows for policies to be applied to a session
without clearing the BGP Session. Soft-reconfig can be done on a per-neighbor basis and can either be
inbound or outbound.
BGP soft-reconfiguration clears the policies without resetting the TCP connection.
To reset a BGP connection using BGP soft reconfiguration, use the clear ip bgp command in EXEC
Privilege mode at the system prompt.
When you enable soft-reconfiguration for a neighbor and you execute the clear ip bgp soft in
command, the update database stored in the router is replayed and updates are reevaluated. With this
command, the replay and update process is triggered only if a route-refresh request is not negotiated
with the peer. If the request is indeed negotiated (after execution of clear ip bgp soft in), BGP
sends a route-refresh request to the neighbor and receives all of the peer’s updates.
To use soft reconfiguration (or soft reset) without preconfiguration, both BGP peers must support the soft
route refresh capability, which is advertised in the open message sent when the peers establish a TCP
session.
To determine whether a BGP router supports this capability, use the show ip bgp neighbors
command. If a router supports the route refresh capability, the following message displays: Received
route refresh capability from peer.
If you specify a BGP peer group by using the peer-group-name argument, all members of the peer
group inherit the characteristic configured with this command.
• Clear all information or only specific details.
EXEC Privilege mode
clear ip bgp {* | neighbor-address | AS Numbers | ipv4 | peer-group-name}
[soft [in | out]]
– *: Clears all peers.
– neighbor-address: Clears the neighbor with this IP address.
– AS Numbers: Peers’ AS numbers to be cleared.
– ipv4: Clears information for the IPv4 address family.
– peer-group-name: Clears all members of the specified peer group.
• Enable soft-reconfiguration for the BGP neighbor specified.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | peer-group-name} soft-reconfiguration inbound
BGP stores all the updates received by the neighbor but does not reset the peer-session.
Entering this command starts the storage of updates, which is required to do inbound soft
reconfiguration. Outbound BGP soft reconfiguration does not require inbound soft reconfiguration to
be enabled.
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Border Gateway Protocol IPv4 (BGPv4)