Re: [GROW] Comment on draft-iops-grow-bgp-session-culling

[Tore Anderson <[e-mail]>]

* Nick Hilliard <[e-mail]>

> Tore Anderson wrote:
> > My point here was that if the IXP is doing maintenance, it could shut
> > all ports to all members simultaneously, and thus get the exact same
> > effect as the «when someone yanks the physical connector» scenario
> > described in the draft.  
> 
> this doesn't work because 1. some ixp participants connect their
> routers via intermediate switches and if all ports are yanked
> simultaneously, they will blackhole traffic on their side and 2. any
> ixp with more than one switch in their peering fabric needs to be
> able to performance maintenance on part of their ixp without
> affecting the rest.

Maybe we're talking past each other.

I fully agree with you that this does not work sufficiently well, which
by extension means that the draft is wrong in suggesting that BGP
session culling is only needed «in topologies where upper layer fast
fault detection mechanisms are unavailable and the lower layer topology
is hidden».

In other words: in my opinion, BGP session culling should be considered
a BCP even in situations where link state signaling and/or BFD is used.
IP-transit providers should perform culling towards their customers
ahead of maintenance works. Direct peers, likewise.

IXPs aren't at all special regarding the fundamental need for session
culling, only in the method by which it is accomplished (i.e., using
layer-2 ACLs).

Tore