Public BGP peering weighted

Answered Question
Mar 21st, 2008

We have a public AS that we are advertising using two BGP peers. How can we change the weight or administrative distance on one to make it less preferable to incoming traffic?

Correct Answer by Danilo Dy about 8 years 11 months ago

The sample will work for both (1 x Router or 2 x Router in iBGP)

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Overall Rating: 5 (2 ratings)
Danilo Dy Fri, 03/21/2008 - 07:29


To enfluence incoming traffic, use PREPEND. You can also use MED but not all ISP honors MED.

If its not enough, try advertising your prefix in two in your preferred ISP and in one in your less-preferred ISP.



gregwoodson Fri, 03/21/2008 - 07:35

Hey Dandy!

I appreciate the response. I cant seem to find good documentation anywhere regarding prepend or its use. This is what I dont understand at this point.


Danilo Dy Fri, 03/21/2008 - 07:45


Check this link

The link is HSRP and BGP, just focus on the prepend :) in your situation (R2 for example) you can PREPEND more....

set as-path prepend 100 100 100 100 nnn

...I think the maximum is 8 prepend

BTW, what is your setup? 2 x Router (each peer to different ISP) or 1 Router that peers to both ISP.



gregwoodson Fri, 03/21/2008 - 07:46

Currently it is 1 router that peers to both ISPs. Within the next couple weeks- it will be 2 routers (then 3) peered to 3 different spots.

Correct Answer
Danilo Dy Fri, 03/21/2008 - 07:51

The sample will work for both (1 x Router or 2 x Router in iBGP)

gregwoodson Fri, 03/21/2008 - 08:41

Thanks! I am implementing changes tonite. I will update on here if it fixed the issue.

Thanks again!

yuhuiyao Wed, 03/26/2008 - 06:06

for incoming traffic, you just have limited influence over the remote side's decision like AS prepend, or route origin (IGP/incomplete). MEDS will not work in multihomed scenario. If the remote side decides to use LP, it will override all your efforts.

The best way to control incoming traffic is to use different subnet mask to advertise the same route to different remote sides.


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