Re: BFD for routes learned trough Route-servers in IXPs

[Nick Hilliard <nick () foobar org>]

Ryan Hamel wrote on 16/09/2020 03:01:
> Install a route optimizer that constantly pings next hops

or if you want a more reliable IXP experience, don't install a route 
optimiser and if you do, don't make it ping next-hops.

- you're not guaranteed that the icmp reply back to the route optimiser 
will follow the forward path.

- you are guaranteed that icmp is heavily deprioritised on ixp routers

- the busier the IXP, the busier the control planes of all the IXP 
routers you're going to ping, and the more likely they are to drop your 
ping packets. This will lead to greater route churn. If this approach is 
widely deployed it will lead to wider-scale routing oscillations due to 
control plane mismanagement.

- route optimisers are associated with serious bgp leakage issues. if 
you're doing this at an IXP, the danger is significantly magnified 
because bi-lat peering sessions rarely, if ever, implement prefix filtering.

It is true that IXPs occasionally see forwarding plane failures.  These 
tend to be pretty unusual these days.

Be careful about optimising edge cases like this.  You'll often end up 
introducing new failure modes which may be more serious and which may 
occur more regularly.

Nick