Operation Manual – IPv4 RoutingH3C S3610&S5510 Series Ethernet Switches Chapter 5 BGP Configuration5-33Note:z The maximum keepalive interval should be one third of the holdtime and no lessthan 1 second. The holdtime is no less than 3 seconds unless it is set to 0.z The intervals set with the peer timer command are preferred to those set with thetimer command.z Use of the peer keep-all-routes command saves all routing updates from the peerregardless of whether any filtering policy is configured. The system uses theseupdates to rebuild the routing table after a soft reset.z Performing BGP soft reset can refresh the routing table and apply the new policywithout tearing down BGP sessions.z BGP soft reset requires all routers in the network have the route-refresh capability. Ifnot, you need use the peer keep-all-routes command to keep all routinginformation from a BGP peer to perform soft reset.5.7 Configuring a Large Scale BGP NetworkIn a large-scale BGP network, configuration and maintenance become difficult due tolarge numbers of BGP peers. In this case, configuring peer groups makes managementeasier and improves route distribution efficiency. Peer group includes IBGP peer group,where peers belong to the same AS, and EBGP peer group, where peers belong todifferent ASs. If peers in an EBGP group belong to the same external AS, the EBGPpeer group is a pure EBGP peer group, and if not, a mixed EBGP peer group.Configuring BGP community can also help simplify routing policy management, and acommunity has a much larger management scope than a peer group by controllingrouting policies of multiple BGP routers.To guarantee the connectivity between IBGP peers, you need to make them fullymeshed. But it becomes unpractical when there are large numbers of IBGP peers.Configuring route reflectors or confederation can solve it. In a large-scale AS, both ofthem can be used.5.7.1 Configuration PrerequisitesBefore configuring this task, you have made peering nodes accessible to each other atthe network layer.
