BIND > returning hosts based on client requests

[Kevin Darcy]

Jim Reid wrote:

> >>>>> "Dan" == Hubbard, Dan <dhubbard at websense.com> writes:
>
>     Dan> We would like to change our DNS so it returns a different
>     Dan> hostname based on where the request is coming from. Many
>     Dan> Global Load Balancing solutions base this on IANA #'s. Any
>     Dan> ideas on how to set this up with BIND ? We would like to add
>     Dan> a list of possible networks with the corresponding hostname
>     Dan> that would be returned if the query came from that netblock.
>
> I think you meant "return a different IP address" rather than
> "hostname". The way to do this in BIND is with a sortlist{} clause in
> the options{} statement. This can get the name server to return a
> sorted list of IP addresses for some host based on the order that is
> "best" for the client making the request. There are also commercial
> products like Distributed Director from Cisco which do something
> similar.

And I'll toss in the usual disclaimer about intermediate caching servers
-- assuming they're not all configured with the same sortlists --
"round-robining" the answers out of their caches and mucking up one's
careful sortlist plans. One can minimize this by reducing the TTL's to
low values, but that's wasteful and rude. Then again, that's what a lot
of the commercial products do, so it must be OK, right?

Sigh. One of these days I'll come up with an RR type for encoding
"preferred RRset sort order" so that even caching servers can know the
order in which the master wants them to give out answers for a given
RRset.


- Kevin