Multi-Homed Hosts

[Kevin Darcy]

Ricky Salmon wrote:

> Using Bind 8, is there a way on the entries for a multi-homed host to set a
> "preference" or "weight" to one of the records?  I haven't found it in any
> documentation or in the "Cricket Book" (DNS & Bind from O'Reilly) and i'm
> hoping there is some obscure undocumented feature...  It seems logical it
> would be life an MX preference, but that does seem to apply in this case....

Ultimately, when all clients use SRV records, you'll be able to "weight" those
records, but that's many years away, if it happens at all. Until then there is
no general solution. The problem is that, even if you could configure a
particular RRset to be weighted a particular way on the master, how could you
propagate that weighting information to the slaves? If the weighting is
implemented as a master-file directive (I wrote an ugly hack implementing this
a while back), then the slave never sees it, since zone transfers just transfer
*records*, not directives. If the weighting is implemented as a named.conf
construct (e.g. extending "rrset-order"), then the slaves don't see that
either. You'd end up having to resort to some out-of-band mechanism to
propagate the zone files and/or named.conf files. Or, you'd end up having to
make a protocol change so that the weighting information is actually contained
in the zone transfer. But is that protocol change likely to implemented any
sooner than SRV, which has been out, in some form or another, for years?

A very limited form of weighting can be achieved with "sortlist", but this
weighting is determined by the IP address of the DNS client. It's not a general
solution.


- Kevin