White Papers

Enabling BGP Neighbor Soft-Reconguration
BGP soft-reconguration 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 eect. Such resets cause
undue interruption to trac due to hard reset of the BGP cache and the time it takes to re-establish the session. BGP soft reconguration
allows for policies to be applied to a session without clearing the BGP Session. Soft-reconguration can be done on a per-neighbor basis
and can either be inbound or outbound.
BGP soft-reconguration clears the policies without resetting the TCP connection.
To reset a BGP connection using BGP soft reconguration, use the clear ip bgp command in EXEC Privilege mode at the system
prompt.
When you enable soft-reconguration 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 re-evaluated. 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 reconguration (or soft reset) without preconguration, 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
congured with this command.
• Clear all information or only specic 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 clear.
• ipv4: Clears information for the IPv4 address family.
• peer-group-name: Clears all members of the specied peer group.
• Enable soft-reconguration for the BGP neighbor specied.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | peer-group-name} soft-reconfiguration inbound
BGP stores all the updates the neighbor receives but does not reset the peer-session.
Entering this command starts the storage of updates, which is required to do inbound soft reconguration. Outbound BGP soft
reconguration does not require inbound soft reconguration to be enabled.
Example of Soft-Recongration of a BGP Neighbor
The example enables inbound soft reconguration for the neighbor 10.108.1.1. All updates received from this neighbor are stored unmodied,
regardless of the inbound policy. When inbound soft reconguration is done later, the stored information is used to generate a new set of
inbound updates.
Dell>router bgp 100
neighbor 10.108.1.1 remote-as 200
neighbor 10.108.1.1 soft-reconfiguration inbound
212
Border Gateway Protocol IPv4 (BGPv4)