476 CHAPTER 36: IPV6 BGP CONFIGURATIONTuning andOptimizing IPv6 BGPNetworksThis section describes configurations of IPv6 BGP timers, IPv6 BGP connection softreset and the maximum number of load balanced routes.■ IPv6 BGP timersAfter establishing an IPv6 BGP connection, two routers send keepalive messagesperiodically to each other to keep the connection. If a router receives no keepalivemessage from the peer after the holdtime elapses, it tears down the connection.When establishing an IPv6 BGP connection, the two parties compare theirholdtime values, taking the shorter one as the common holdtime. If the holdtimeis 0, neither keepalive massage is sent, nor holdtime is checked.■ IPv6 BGP connection soft resetAfter modifying a route selection policy, you have to reset IPv6 BGP connections tomake the new one take effect, causing a short time disconnection. The currentIPv6 BGP implementation supports the route-refresh feature that enables dynamicIPv6 BGP routing table refresh without needing to disconnect IPv6 BGP links.With this feature enabled on all IPv6 BGP routers in a network, when a routingpolicy modified on a router, the router advertises a route-refresh message to itspeers, which then send their routing information back to the router. Therefore, thelocal router can perform dynamic routing information update and apply the newpolicy without tearing down connections.If a router not supporting route-refresh exists in the network, you need toconfigure the peer keep-all-routes command on the router to save all routeupdates, and then use the refresh bgp ipv6 command to soft-reset IPv6 BGPconnections.Prerequisites Before configuring IPv6 BGP timers, you have:■ Enabled IPv6 function■ Configured IPv6 BGP basic functionsConfiguring IPv6 BGPTimersFollow these steps to configure IPv6 BGP timers:Specify a fake AS number fora peer/peer grouppeer { ipv6-group-name |ipv6-address } fake-asas-numberOptionalNot specified by defaultNeglect the AS_PATHattribute for best routeselectionbestroute as-path-neglect OptionalNot neglected by defaultConfigure to carry only thepublic AS number in updatessent to a peer/peer grouppeer { ipv6-group-name |ipv6-address } public-as-onlyOptionalBy default, BGP updates carryprivate AS numberSubstitute local AS numberfor the AS number of apeer/peer group indicated inthe AS_PATH attributepeer { ipv6-group-name |ipv6-address } substitute-asOptionalNot substituted by defaultTo do… Use the command… Remarks
