关于BGP同步对路由选择的影响

BGP Synchronization on the Impact of the Routing

BGP规定,BGP路由器不会将通过IBGP学习到路由发送给EBGP,除非这个路由在IGP中有获悉,即只有当IGP与IBGP都有到达某个网络的路由时,这个BGP路由才能发送给EBGP。本来这个规则是为了防止路由黑洞（向外部通告了一个本AS不可达的虚假的路由）。因此现在的ISP网络大都是在AS内实行全互联,且同时都运行BGP,这样就可以关闭同步。在BGP同步关闭的情况下,在当有两条路由信息同时发往一个目标时,且这两个路由信息都是始发路由的情况下,BGP会按照选路规则来判断哪一条才是最佳路由。

BGP requirements, BGP routers do not learn the route through IBGP sent to EBGP, unless the route in the IGP has learned that only when the IGP and IBGP has arrived when a network routing, the BGP routing to send to the EBGP. Actually, this rule is to prevent routing black hole （a present to the outside notice was not up to the false AS routing）. So now the ISP network are mostly implemented within the AS-wide interconnection, and also run BGP, so that you can turn off synchronization. BGP synchronization in closed cases, the same time when there are two routing information sent to a target, and routing information are the two cases originating routing, BGP routing rules will be judged according to what one is the most best route.