BGP – Modifying the AD of Backdoor networks

As you may know that the backdoor feature of BGP changes the AD to 200. But is there a way to modify it?

There is a way, it’s not very intuitive. When you configure a network as a backdoor network you are creating a local-route that you don’t originate to others. To modify a local-route you can use the distance bgp command. Remember that bgp distance format it:

distance bgp (eBGP) (iBGP) (Local/Backdoor)

Below is a quick example where I use the route 10.1.4.0/24 as a backdoor route.

router bgp 5
no synchronization
bgp log-neighbor-changes
network 10.1.4.0 mask 255.255.255.0 backdoor
neighbor 10.1.45.4 remote-as 4
distance bgp 20 200 233
no auto-summary

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Redistribution RIP-OSPF Distance

Complex redistribution can be quite a challenging  task to encounter studying for the CCIE R&S lab. There doesn’t seem to be that many clearly define general rules out there. So I thought why not dissect each individual case that could cause tricky redistribution problems.

RIP and OSPF are a perfect example of two protocols that when they meet, something will go wrong by default. The reason that these two protocols are so prone to problems is for 1. RIP has no concept of an external routes and 2. OSPF has the same AD for internal and external routes.

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Welcome

Welcome to the first post of my new blog called kemot-net.com. I plan on posting about any interesting problems I encounter during my work projects or my studies. Generally I would focus on the main topics of computer networking such as routing, switching, quality of services and security. More posts to come so enjoy and please comment or contact me with any questions you may have.

Tom Kacprzynski