【CCNP 4-3】Configuring Basic BGP Operations.ppt

前3个状态都跟TCP连接有关，所以BGP邻居排错时首先保证TCP连接能建立成功非常重要 BGP Synchronization Synchronization rule: Do not use or advertise to an external neighbor a route learned by IBGP until a matching route has been learned from an IGP Ensures consistency of information throughout the AS Safe to have it off only if all routers in the transit path in the AS are running full-mesh IBGP; off by default in Cisco IOS software release 12.2(8)T and later no synchronization Router(config-router)# Disables BGP synchronization so that a router will advertise routes in BGP without learning them in an IGP synchronization Router(config-router)# Enables BGP synchronization so that a router will not advertise routes in BGP until it learns them in an IGP Example: BGP Synchronization If synchronization is on, then: Routers A, C, and D would not use or advertise the route to until they receive the matching route via an IGP. Router E would not hear about . If synchronization is off (the default), then: Routers A, C, and D would use and advertise the route that theyreceive via IBGP; router E would hear about . If router E sends traffic for , routers A, C, and Dwould route the packets correctly to router B. Example: BGP Configuration BGP Example Configuration 1. RouterB(config)# router bgp 65000 2. RouterB(config-router)# neighbor remote-as 64520 3. RouterB(config-router)# neighbor remote-as 65000 4. RouterB(config-router)# neighbor update-source Loopback 0 5. RouterB(config-router)# neighbor next-hop-self 6. RouterB(config-router)# network mask 7. RouterB(config-router)# network 8. RouterB(config-router)# network 9. RouterB(config-router)# no synchronization BGP States When establishing a BGP session, BGP goes through the following states: Idle: Router is searching routing table to see whether a route exists to reach the neighbor. Connect: Router found a route to the neighbor and has completed the three-way TCP handshake. Open sent: Open message sent, with the parameters for the BGP session. Open