Concept Guide

Route-refresh and 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 change the BGP inbound policy locally, you need to process the updates received from a peer. The route-refresh capability allows
the local peer to reset inbound information dynamically by exchanging route-refresh requests to supporting peers. When an inbound policy
conguration is changed, then the Dell EMC Networking OS sends a refresh request message asking the peer to re-advertise updates.
Upon receiving the refresh request, the peer advertises the required information after applying the outbound lters. Route-refresh is
negotiated during the BGP session establishment and will be used only if both the BGP peers support this capability.
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.
• Enable soft-reconguration for the BGP neighbor specied.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | ipv6-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-reconguration. Outbound BGP soft-
reconguration does not require inbound soft-reconguration to be enabled.
• Reset BGP connection using soft-reconguration.
EXEC Privilege mode
clear ip bgp [vrf vrf-name] [* | neighbor-address | as-number | peer-group-name] {soft {in |
out}}
– *: Clears all peers.
– neighbor-address: Clears the IPv4 or IPv6 neighbor of this IP address.
– as-number: Clears the peers AS numbers.
– peer-group-name: Clears all members of the specied peer group.
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
DellEMC(conf)# router bgp 100
DellEMC(conf-router_bgp)# neighbor 10.108.1.1 remote-as 20
214
Border Gateway Protocol (BGP)