[AusNOG] As path prepend TPG and Vocus

[Matthew Moyle-Croft]

Have to remember some BGP basics:

1) longest prefix (eg. /24 in your case) will always win.
2) localpref will always win when comparing identical prefixes.
3) A network will always use localpref to prefer directly connected
customer routes.
4) ASPath length is not going to overcome the above.

What does "failover" mean to you? When there's a failure, look at what
Vocus and TPG have in their route tables and the timing. Also check, are
you actually withdrawing the routes during failure?

MMC

On Mon, 1 May 2023 at 18:09, Steven Waite <steven at waites.com.au> wrote:

> Good evening
>
> I hope everyone is well. We have a /23 block broken up between TPG /24 and
> Vocus /24 with the /23 advertise to both Vocus and TPG for failover. This
> worked will until recently as we noticed increasing failover times during
> maintenance and now takes around 10-15 minutes. Today I decided to try AS
> path prepending away from smallest prefix wins type of approach. I think
> Vocus and TPG ignores prepending as these are local routes thus the local
> route is preferred even with a lot of prepends. I would love to achieve the
> same thing via communities if it’s possible. Is someone able to share
> communities numbers that I should be using for Vocus/TPG please to
> advertise the primary route for a prefix?
>
> Many thanks Steve
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