[nog] BGP communities

Marian Marinov mm at 1h.com
Sun Oct 23 18:01:18 EEST 2016

On 10/23/2016 11:08 AM, Vasil Kolev wrote:
> On Sat, 22 Oct 2016 19:53:42 +0300
> Marian Marinov <mm at 1h.com> wrote:
>> Basicaly I want to be abel to choose which upstream (from the ones
>> that my ISPs have) to use. This would allow me to reroute
>> destinations around certain routing issues in the world.
> For inbound traffic, this will work with adding communities that
> prepend, and is pretty standard. For outbound traffic, you can pick
> what to use, but not for everything, e.g. you can take the routes that
> go through a specific upstream, but without some magic (which isn't
> directly related to communities) you cannot pick a different upstream
> for some destination.
> Let's say the ISP has upstream A and B. is routed through A,
> is routed through B. The ASPATH for is "ISP A",
> for is "ISP B" and you can just match the second AS in the
> ASPATH and that's it. But there is no way with the usual stuff to say
> to the ISP to send traffic for through ISP A. There are
> tricks like having two separate links/peering sessions that go to
> different VRFs that have different upstreams, but most of these are
> weird, hard to setup and most ISPs don't bother.

Why not this:

my upstream has ISP A and B.

We have agreed to use communities 500 for A and 600 for B.
When I want my outgoing traffic to go trough ISP A, I simply start sending community 500 with my prefix.
When I want my outgoing traffic to go trough ISP B, I start sending community 600 with my prefix.

This way, I can choose the upstream I want to be routed trough. It seam straight forward.

What are your concerns?

Marian Marinov
Founder & CEO of 1H Ltd.
Jabber/GTalk: hackman at jabber.org
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