Re: A new spin on multihoming: multihoming classes.

[Daniel Senie <dts@senie.com>]

At 10:16 AM 9/9/01, Iljitsch van Beijnum wrote:
>On Sun, 9 Sep 2001, Peter Tattam wrote:
>
> > Also, because I believe that DNS is agnostic
> > towards routing, in practice if I assume you would MH SOA & NS entries, you
> > might find DNS lookups slow down if random NS entries were used to 
> locate DNS
> > information if one MH path was less optimal than another.  You might 
> not get
> > black holed, but DNS resolution for the site would end up being 
> degraded in the
> > presence of multihoming.
>
>For a single query this might be a problem. But unless I'm mistaken, BIND
>takes note of the round trip times it sees and (mostly) prefers the faster
>address over the slower one on subsequent queries.

Be a bit careful here, or you fall into a trap that some of the DNS load 
balancer vendors fall into. You care about the distance/latency between the 
RESOLVER and the target machine, NOT between the RESOLVER's Name Server and 
the target's name server. Several load balancer products ensure the latter 
case is not a problem, however, they do not address the issue of proximity 
of the name server doing the lookup on behalf of the user/service/whatever. 
The recursive name servers used when making requests are NOT required to be 
topologically close to the machine requesting the lookup.

I bring this up just so we don't go down any paths that could lead to bad 
assumptions about DNS resolution as a cure-all.


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Daniel Senie                                        dts@senie.com
Amaranth Networks Inc.                    http://www.amaranth.com