Questions about anycasting setup

Fri Mar 9 08:11:31 UTC 2012

Bill,

woody at pch.net (Bill Woodcock) wrote:

> >   2. We plan to use this anycasting based setup for DNS during initial few
> >   months. Assuming low traffic for DNS say ~10Mbps on average (on 100Mbps
> >   port) and transit from just single network (datacenter itself) - is this
> >   setup OK for simple software based BGP like Quagga or Bird? 
> 
> Yes, and in fact, that's how nearly all large production anycast networks are built???  Each anycast instance contains its own BGP speaker, which announces its service prefix to adjacent BGP-speaking routers, whether those be your own, or your transit-provider's.  Doing exactly as you describe is, in fact, best-practice.

Well, let's say, using Quagga/BIRD might not really be best practice for
everybody... (e.g., *we* are using Cisco equipment for this)

Using anycasting for DNS is, to my knowledge, best practice nowadays.

> >   3. IPv6! - Is /32 is standard? We have only one /32
> >   allocation from ARIN and thus if using /32 seems like hard deal - we have
> >   to likely get another /32 just for anycasting? or we can use /48 without
> >   issues? Also, is /48 a good number for breaking /32 so that we can do /48
> >   announcements from different datacenters in simple uni casting setup?
> 
> A /48 is quite reasonable.  Announcing a whole /32 just for your anycast service would be wasteful.

Why? It's simply another prefix, no matter how big. It might look
wasteful, but if *that* is the allocation you *have*, it's the
one you ought to use.

One should be careful - people do filter on allocation lengths, so
breaking out a /48 out of a /32 allocation and advertising it on its
own can lead to it being filtered.

Elmar.