[AusNOG] As path prepend TPG and Vocus

[Lincoln Dale]

All of what MMC said. :)
I'd also add: check the prefixes you're announcing via various looking
glasses - Vocus and TPG both have ones, but you can go wider too and see
what others view you as too. Some nice visualizations from tools like
bgp.he.net where you can see their upstreams and how connectivity might
work.

Remember that in routing, the longest prefix always wins, and BGP path
selection doesn't even come into that.
Make sure that your upstreams are accepting your announcements. You cannot
announce a more-specific than a /24 and have the world accept it, but it
might be that the two /24s you're announcing aren't accepted either,
depending on what IRR policies are. You can at least verify that.
(I'd have done that but don't know your prefixes or ASNs as you didn't post
them.)

BGP route propagation does not take 10-15 minutes for an update or withdraw
to happen. It's way way quicker than that.


cheers,

lincoln.


On Tue, May 2, 2023 at 8:51 AM Matthew Moyle-Croft <mmc at mmc.com.au> wrote:

> 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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