Anycast 101

Fri Dec 17 11:33:40 UTC 2004

On 17-dec-04, at 11:23, Joe Shen wrote:

> is there any problem or anything must be taken
> care about when anycast is employed within a DNS
> server farm within MAN?

> What I mean is, if we want to employ anycast in a
> cache server farm which is located within a big OSPF
> network, is there anything problemetic ? or should we
> consider anycast only when root server is to be
> installed ?

Since OSPF generally converges orders of magnitude faster and it's 
easier to get OSPF to select the highest bandwidth/lowest latency path 
than BGP, this should be easier. The problem of how to revoke the 
anycast route when the service goes away is pretty much the same. The 
benefits (especially latency) are also likely to be less, though.

> Some people said, it's not needed to set up anycast in
> MAN because DNS system in such situation is very small
> ( less than 10 SUN servers ).

The only problem that is unsolvable without anycast is getting response 
times below 25 ms or so in every corner of the world. In all other 
cases it all depends on the pros and cons of different ways to get the 
job done.