Re: Arista “IP-SLA” / Active Probing

[William Herrin <bill () herrin us>]

On Fri, Dec 22, 2023 at 12:13 PM David Zimmerman via NANOG
<nanog () nanog org> wrote:
> I've had a variant of this on our transit routers for enterprise purposes
> for a few years.  We run DFZ and originate 0/0 and ::/0 internally, but

Hi David,

There are several variants on Alex's problem. One is that there's an
upstream failure reflected in the BGP table but Alex doesn't see it
because he's only taking a default route. Your solution, or one like
it, should work for that. In a nutshell:

1. Take a full table
2. Filter everything but a selection of representative routes
3. Set static default routes tied to addresses within the representative routes.

If the representative routes disappear from the table, the static
defaults become invalid and leave the local routing table as well.

Or perhaps he has the reverse problem where he wants to advertise his
route only if the representative routes are there so that when his
anycast node has network problems it drops itself off the Internet and
allows others to take over.


Another variant is that BGP reports having the entire Internet table
but the packets don't get there. The upstream suffers from anything
between high packet loss to a misbegotten filtering rule that black
holes all his packets. He'd like to do some active polling via static
routes to the upstream and drop both advertised and received routes
when the polling indicates a path failure.

I thought the latter was what he was asking for, but on a second
read-through I see he talked about taking a default route via BGP
rather than a full table.

Regards,
Bill Herrin


--
William Herrin
bill () herrin us
https://bill.herrin.us/