BGP学习精华.doc

BGP学习精华BGP FUNDAMENTALS l With the exception of the neighbor ebgp-multihop router configuration command,the commands for configuring EBGPIBGP are the same. l Within as AS,BGP peers dont need to be directly connected l router bgp command enables a BGP routing process and assigns to it a AS number l neighbor remote-as command adds an entry to the BGP neighbor table specifying that the peer identified by a particular IP address belongs to the specified AS. for EBGP ,neighbor IP address is usually the IP address directly connected. for IBGP, neighbor IP address can be the IP address of any of the routers interfaces. l To verify that BGP peers are up,use the show ip bgp neighbor, if it doesnt show that state=established,then the peers are not up. the remote router ID is the highest ip address or highest loopback interface on that router. the table version number increments by new incoming information l clear ip bgp to reset the bgp session after make a configuration change INTERNAL BGP 当BGP speaker收到同一个AS域中其他的BGP speaker发来的路由信息时，该BGP speaker 只通过EBGP向外部的BGP speaker发送收到的信息，所以在同一AS域中必须full meshed loopback interface: neighbor remote-as中的地址时，若该端口不能使用，则两个路由器将不能连通。使用loopback interface就没有这一顾虑。 router bgp 100 neighbor 190.225.22.2 remote-as 100 neighbor 190.225.22.2 update-source loopback 0 neighbor update-source是指明用于连接的是loopback端口，而不是物理端口。 EBGP peers之间通常是端对端互连的，必须依赖物理端口的连接，因此较少使用loopback EXTERNAL BGP ip multihop: BGP speaker之间不能直接连接时使用，这时可通过两者的loopback端口互连，并使用neighbor ebgp-multihop,但在配置中必须加上静态路由或起IGP，以保证两者能互通。 !Router A loopback interface 0 ip address 129.213.1.1 ! router bgp 100 neighbor 180.225.11.1 remote-as 300 neighbor 180.225.11.1 ebgp-multihop neighbor 180.225.11.1 update-source loopback 0 !Router B loopback interface 0 ip address 180.225.11.1 ! router bgp 300 neighbor 129.213.1.1 remote-as 100 neighbor 129.213.1.1 ebgp-multihop neighbor 129.213.1.1 update-source loopback 0 EBGP LOAD BALANCING 当两个AS之间通过多条链路连接时，使用neighbor ebgp-multiho