3com S7906E 설치 설명서

 

1-11 

Routing information synchronization between iBGP and IGP avoids giving wrong directions to routers 

outside of the local AS. 

If a non-BGP router works in an AS, it may discard a packet due to an unreachable destination. As 

shown in 

, Router E has learned a route of 8.0.0.0/8 from Router D via BGP. Then Router E 

sends a packet to 8.0.0.0/8 through Router D, which finds from its routing table that Router B is the next 

hop (configured using the peer next-hop-local command). Because Router D has learned the route to 

Router B via IGP, it forwards the packet to Router C through route recursion. Router C has no idea 

about the route 8.0.0.0/8, so it discards the packet.  

Figure 1-11 iBGP and IGP synchronization 

 

 

If synchronization is enabled in this example, only when the route 8.0.0.0/24 received from Router B is 

available in its IGP routing table, can Router D add the route into its BGP routing table and advertise the 

route to the eBGP peer. 

You can disable the synchronization feature in the following cases: 

z 

The local AS is not a transitive AS (AS20 is a transitive AS in the above figure). 

z 

Routers in the local AS are iBGP fully meshed. 

Route summarization can reduce the routing table size on a large network, and allow  BGP routers to 

advertise only summary routes rather than more specific routes. 

Currently, the system supports both manual and automatic route summarization. Manual route 

summarization allows you to determine the attribute of a summary route and whether to advertise the 

route. 

BGP route dampening is used to solve the issue of route instability such as route flaps, that is, a route 

comes up and disappears in the routing table frequently. 

When a route flap occurs, the routing protocol sends an update to its neighbor, and then the neighbor 

needs to recalculate routes and modify the routing table. Therefore, frequent route flaps consume large 

bandwidth and CPU resources and even affect network normal operation.