Overlapping Protocols: Backdoors
This example shows how the backdoor command can be used to change the EBGP distance to have IGP routes favored over EBGP routes for specific network numbers. Figure 11-5 illustrates the topology for this example.
Figure 11-5. BGP Backdoor Routes
In Figure 11-5, AS2 is running an IGP (OSPF) on the private link between it and AS1, and it is running EBGP with AS3. RTC, in AS1, will receive advertisements about 192.68.10.0/24 from AS3 via EBGP with a distance of 20 and from AS2 via OSPF with a distance of 110. Because the lower distance is preferred, RTC will use the BGP link to AS3 to reach 192.68.10.0/24. ...
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