How to resolve IBGP problems

[TCC_2]

Core Issue

Border Gateway Protocol (BGP) is an interdomain routing protocol used to exchange network reachability information with configured peers known as BGP neighbors. Interior BGP (IBGP) has certain behavior and follows certain rules to ensure that packet forwarding can take place correctly within the Autonomous System (AS) without any loops or black-holing. These are the most common problems with IBGP, mostly related to these rules and behavior:

• BGP neighbors are not in established state.
• A route is missing from the IP routing table due to an invalid route to next hop.
• An IBGP route is not installed in the IP routing table and is not advertised to other neighbors, due to a BGP synchronization rule failure.
• Routes learned from one IBGP neighbor are not advertised to another IBGP neighbor.
• IBGP routes are not redistributed into an Interior Gateway Protocol (IGP).

Resolution

For more information, refer to these documents:

• BGP neighbors are not in an established state       
• Route is missing from the routing table due to an invalid route to next hop        
• Route is missing from the routing table due to enabled synchronization       
• BGP does not advertise the network until IGP has propagated the route within the AS        
• BGP does not advertise iBGP-learned routes to eBGP peers        
• BGP router does not advertise the routes learned from one iBGP neighbor to another       
• Unable to redistribute iBGP learnt routes into an IGP such as EIGRP, OSPF, and IS-IS       
• How to address BGP problems

Type of Route Missing from Routing Table

All routes / All routes from specific neighbor

Valid Route to BGP Next Hop

Valid route to next hop does not exist

show ip bgp neighbors {neighbor  address}

State is active