North American Network Operators Group
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Re: Anycast 101

  • From: Iljitsch van Beijnum
  • Date: Tue Dec 21 09:01:06 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.