Re: Announcing Peering-LAN prefixes to customers

[Andy Davidson <andy () nosignal org>]

Hi, Dominic --

On 20/12/2018, 17:49, Dominic Schallert <ds () schallert com> wrote:

> this might be a stupid question but today I was discussing with a colleague if
> Peering-LAN prefixes should be re-distributed/announced to direct customers/peers.
> My standpoint is that in any case, Peering-LAN prefixes should be filtered and not
> announced to peers/customers because a Peering-LAN represents some sort of
> DMZ and there is simply no need for them to be reachable by third-parties not being
> physically connected to an IXP themselves.

There are no stupid questions!  It is a good idea to not BGP announce and perhaps also to drop traffic toward peering 
LAN prefixes at customer-borders, this was already well discussed in the thread.  But there wasn’t a discussion on how 
we got to this point. Until the Cloudflare 2013 BGP speaker attack, that sought to flood Cloudflare’s transfer networks 
and exchange connectivity (and with it saturating IXP inter-switch links and IXP participant ports), it was common for 
IXP IPv4/6 peering LANs to be internet reachable and BGP transited. 

This facilitated troubleshooting (e.g. traceroutes showing peering lan interfaces in traceroutes instead of ‘starring 
out’) and PMTUD (e.g. see recommendation in https://www.ripe.net/ripe/mail/archives/ipv6-wg/2011-July/001839.html which 
actually asked for IXP peering LANs to be announced).

There are good reasons to announce but there are better reasons to filter.  The security benefits of filtering outweigh 
the upsides on today’s internet, but fashions and best practice may further evolve over time. 

Andy


-- 
Andy Davidson
Director, Asteroid International BV  www.asteroidhq.com
Director, Euro-IX - The European Internet Exchange Association  www.euro-ix.net