[AusNOG] As path prepend TPG and Vocus

[McDonald Richards]

Vocus used to (and probably still do) have a script to prevent transit
theft/leakage that will also block more specific prefixes advertised by
downstream customers from other peering and transit. If you are advertising
the /23 to them and pre-pending it, it's likely still going to block /23 or
longer from other networks. If they don't, then hey, free transit...

They do have a looking glass at https://lg.vocus.network/ that you should
be able to use so you can observe what's happening to your prefix on their
network during a failure and work out why you are seeing long fail-over
times.

Macca


On Tue, May 2, 2023 at 9:01 AM Lincoln Dale <ltd at interlink.com.au> wrote:

> 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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