BGP Backdoor


BGP backdoor command when used as an option at the end of the network command sets the network specified to an AD of 200 instead of 20. This allows for an IGP route to take precedence of over the received EBGP route.

If the link between R2 and R3 Fa0/0 goes down Loopback network of these two routers will lose connectivity even though there is a redundunt link between these two routers. The solution is to advertise these Loopbacks into BGP but then the traffic between networks 150.1.2.0/24 and 150.1.3.0/24 will start takinf sub-optimal path via R1 and not using direct path between R2 and R3 cause of the AD differene (EBGP=20 , EIGRP = 90)  There are few ways to fix it and one of them is BGP Backdoor

To Configure

R2(config)#router bgp 100
R6(config-router)#net 150.1.3.0 mask 255.255.255.0 backdoor

This sets the AD for the route 150.1.3.0/24 to an AD of 200 allowing the IGP route to be more preferred

Another solution to this would be to set the next hop of the received BGP route to the path desired however this does take away redundancy should the next hop fail

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About ccie4all
Hello, and welcome to the first post of my CCIE blog This blog has got one simple goal and that is to improve our skills in Cisco Networking field so we can become best engineers on a job market. Wordpress Blog https://ccie4all.wordpress.com/ information about the changes made to Gns3 BGP , MPLS and R&S CCIE labs. In order to access and download all provided materials and receive important updates from Gns3 BGP , MPLS and R&S CCIE labs under GNS3 tab in the main header please go ahead and subscribe to https://ccie4all.wordpress.com/ ! All other posts have not been affected and can be accessed at any given time. Enjoy ! Tom

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