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mohammedmahmoud Thu, 08/30/2007 - 00:01
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When BGP tries to install the bestpath prefix into Routing Information Base (RIB) (the IP Routing table), RIB might reject the BGP route due to any of these reasons:

. Route with better administrative distance already present in IGP. For example, if a static route already exists in IP Routing table.

. Memory failure.

. The number of routes in VPN routing/forwarding (VRF) exceeds the route-limit configured under the VRF instance.

In such cases, the prefixes that are rejected for these reasons are identified by r RIB Failure in the show ip bgp command output and are not advertised to the peers. This feature was first made available in Cisco IOS Software Release 12.2(08.05)T.

NOTE Locally advertised BGP networks are not injected into the routing table via BGP (which is normal since the rule is for a route to advertised via BGP that it must reside first in the routing table), and this will be the only case where a route is valid and best but not in the routing table -> valid and best means the router will advertise it to its peers.


Mohammed Mahmoud.

Pavel Bykov Thu, 08/30/2007 - 03:39
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Additionally to Mohammed's post, BGP route is not installed in RIB when synchronization is ON and IGP does not have a route that BGP selects as BEST.

Harold Ritter Thu, 08/30/2007 - 05:21
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Is this an hypothetical question or is this an issue you encountered in your network. If the latter, please post the show ip bgp so we can better assist you.



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