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Dell EMC Configuration Guide for the S3100 Series 9.14.2.4

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Route-refresh and 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-reconfiguration allows for policies to be applied to a session without clearing the BGP Session. Soft-reconfiguration 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 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 configuration 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 filters. 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 configured with this command.

  • Enable soft-reconfiguration for the BGP neighbor specified.
    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-reconfiguration. Outbound BGP soft-reconfiguration does not require inbound soft-reconfiguration to be enabled.
  • Reset BGP connection using soft-reconfiguration.
    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 specified peer group.

Example of Soft-reconfigration of a BGP Neighbor

The example enables inbound soft-reconfiguration for the neighbor 10.108.1.1. All updates received from this neighbor are stored unmodified, regardless of the inbound policy. When inbound soft-reconfiguration 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
DellEMC(conf-router_bgp)# neighbor 10.108.1.1 soft-reconfiguration inbound
DellEMC(conf-router_bgp)# exit




                    
                    

                    

                        

                            

                                

                                    

    

        

            
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