Anycast 101

Tue Dec 21 13:59:28 UTC 2004

On 20-dec-04, at 17:32, Paul Vixie wrote:

>>> 1. There should always be non-anycast alternatives

>> I believe there is a strong consensus about that. And therefore a
>> strong agreement that ".org" is seriously wrong.

> i believe that icann/afilias/ultradns would be very receptive to input
> from the ietf-dnsop wg on this topic.  but it's not cut and dried -- if
> you have two widely anycast'd servers plus one non-anycast server "just
> in case something bad happens to anycast" you're doing two questionable
> things: (1) treating anycast as new/unstable/experimental which it's 
> not,
> and (2) limiting your domain's availability to the strength of that one
> non-anycast server.

??? How are things worse with two anycasted addresses and one 
non-anycasted address vs two anycasted addresses?

I think there is one thing that isn't very controversial: two addresses 
isn't really enough. Let's start with that. I'd rather have 5 or 8 
anycasted addresses than 2 anycasted addresses. (Although I think at 
least 8 addresses, half of which are anycast, would be best.)

> if .ORG's NS RRset were to be changed to include non-anycast nodes, 
> i'd hope
> for 11 of them, or however many underlying servers there actually are.
> but at that point, the only thing anycast would buy you is ddos 
> resistance
> and the ability to have more than 13 physical servers... which is all 
> the
> root server system wants from anycast, but maybe not all that afilias 
> and
> ultradns and icann want from anycast in .ORG.

If we as a community feel we need DDoS resistance for the root and 
TLDs, we should consider more options than just anycast.

Anycast can increase the number of physical servers, but this is also 
possible with more traditional clustering techniques or anycasting that 
stays outside BGP.

What I find surprising is that every IP address gets to query the 
roots, despite the fact that most addresses don't have any need to do 
this or know how to do it properly. It would make perfect sense to me 
that people would have to sign up for "root service" before they get to 
talk to the root servers. This way, all unknown addresses can be 
filtered out. (Or more practical, rate limited.) Obviously something 
like this would face deployment issues, but if we're serious about DDoS 
issues these kinds of options are the ones we should consider.

Another way to approach this would be for larger ISPs to connect to one 
or more roots using private peering. This gives those operators both 
the means and an incentive to keep such links free of clutter.

Remember that DDoS is only a force of nature for end sites. In large 
networks it's just part of the general traffic that can be filtered or 
rate limited without too much trouble as long as it can be identified.