[c-nsp] Basic inbound BGP path preferencing query

Steve Housego Steve.Housego at itps.co.uk
Tue Jan 27 09:52:04 EST 2015

You could always use an as-path prepend,

Announce yours routes with the same prefix from both connections

route 1 would show as AS123 AS5089 AS-XX
route 2 would show as AS123 AS123 AS174 AS-XX

This allows more traffic to come in via route 1, whilst still utilising
route 2, (you can also add multiple pre-prends if required). For example
AS174 will prefer customer routes so traffic from as174 to your as123
should always come in that path. Any of AS174¹s peerings may prefer that
route if they don¹t also peer with AS5089 for example.

This obviously only works per entire subnet rather than individual IP¹s
but it still allows you to utilise both links un-equally (if that¹s a
word? :).


-----Original Message-----
From: Joshua Riesenweber <joshua.riesenweber at outlook.com>
Reply-To: "joshua.riesenweber at outlook.com" <joshua.riesenweber at outlook.com>
Date: Tuesday, 27 January 2015 01:28
To: "cisco-nsp at puck.nether.net" <cisco-nsp at puck.nether.net>
Subject: [c-nsp] Basic inbound BGP path preferencing query
Resent-From: Steve Housego <Steve.Housego at it-ps.com>

>Hi all,
>I'm looking for a bit of insight from someone with more BGP experience
>than me. (I've tried searching around the 'net trying to find an elegant
>I have the common enterprise configuration of 2x WAN links multi-homed
>with 2x ISPs. I have a single /24 public IP allocation being advertised
>out both links, and are using MEDs  to preference one link.
>I'd like to load balance across both links, unfortunately, one link is
>lower-bandwidth and has a smaller data quota from the ISP.One simple
>solution is upgrading to a /23. Then I can preference a unique /24 subnet
>over each link, and assign the large bandwidth-consuming devices to that
>particular subnet on my better WAN link.
>My only hesitation is that configuration potentially uses more IP
>addresses than I need. Does anyone have any tips on preferencing certain
>IP addresses inbound through one link if I am only advertising a single
>If there's a better way of doing this your ideas are welcome.
>cisco-nsp mailing list  cisco-nsp at puck.nether.net
>archive at http://puck.nether.net/pipermail/cisco-nsp/


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