Re: BGP AFI or SAFI for advertising BFD status

[William Herrin <bill () herrin us>]

On Sun, Dec 22, 2024 at 4:15 AM Nick Hilliard <nick () foobar org> wrote:
> There are two main target situations: firstly, when a router unexpectedly
> drops off an ixp platform, this won't be explicitly signaled to the other routers
> on the fabric, which can mean that packets to that device will be black-holed
> until all the others bgp hold timers kick in.

Hi Nick,

I'm missing something.

Wouldn't the route server send withdrawals and updates to the rest of
the participants as soon as its hold timer with the lost router
expires?

Could this not be accelerated by the IXP asking the participants to
keep low keepalive and hold timers with the route server?

How would your solution help when two participants at an IXP have
chosen -not- to bilaterally peer, thus needing the route server to
intermediate? They're going to agree to build BFD sessions even though
they don't want BGP sessions? That... doesn't make sense.


> The second situation would be to deal with forwarding plane incongruence
> on IXPs, i.e. where router A can reach RS, router B can reach RS, router A
> cannot reach router B due to a problem on the IXP fabric itself. Thankfully
> this style of problem has become quite unusual over the last several years.

Doesn't seem like it would solve the bouncy link problem.

Absent bouncy links, simply having a reasonable time out for arp and
ND will assure the router quickly finds its neighbor unreachable,
which is applied as backpressure into BGP.

Regards,
Bill Herrin



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