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Because synchronization is enabled, router running BGP can not learn routes from its EBGP peer

Publication Date:  2012-07-27 Views:  47 Downloads:  0
Issue Description
The Topology is as follow, C factory ROUTER A---(EBGP)---HUAWEI ROUTER---(IBGP)---C factory ROUTER B.
HUAWEI ROUTER enabled "undo synchronization" mode, the problem is that ROUTER A can not learn some routes from HUAWEI ROUTER, but these routes are already in HUAWEI ROUTER BGP routing-table and ip routing-table.
For the test, replace the HUAWEI ROUTER by another C factory ROUTER, the problem disappeared.            
Alarm Information

Null

Handling Process
There are two solutions for this issue:
1. Do not learn those routes from IGP but only  BGP.
2. Change the preference of those BGP routes, make them better than those IGP routes.

Root Cause
According to the BGP protocol, BGP router will only advertise the best routes to its BGP peers, what ever EBGP or IBGP peers,
and if the router enable synchronization mode or not. But there are some differences between vendor's solutions.
In HUAWEI's solution,a BGP route which is considered as a best route should match two rules. first, the nexthop of the BGP
route is reachable; second, the route must be better than any other routes no matter the routes learned by BGP or IGP routing protocols;
In C factory's solution, the same to HUAWEI's first opinion, but it only compares the route to which learned by BGP routing protocols.
Refer to this issue, HUAWEI ROUTER do not advertise some of its BGP routes to the EBGP peer, because they are better than BGP routes in IGP routing-table.
     
Suggestions
Since the existing VRP software such as 3.4, 5.0 do not support "synchronization" mode,  currently the NO.2 solution which mentioned above is recommended.

END