load balancing (lbnamed) question

[Geoff Allen]

I'm trying to set up some load-balancing for a pair of mail
servers. I'm using lbnamed, but I don't think that's really the
issue. The lbnamed is working just fine. Rather, I have a few
questions related to the delegation of names to the load balancing
domain. We're using lbnamed rather than a round robin because we want
to robustly handle down hosts, in addition to distribute the load.

I've delegated the zone lb.wsu.edu to the host running lbnamed, and
have verified that lookups work fine.

The current setup has (in the wsu.edu zone):

mail         IN      A       134.121.1.8
             IN      MX      0 cheetah.it.wsu.edu.
             IN      MX      10 pegasus.it.wsu.edu.

where 134.121.1.8 is the address of cheetah.it.wsu.edu.

What I *want* is for mail.wsu.edu to point to mail.lb.wsu.edu to
balance out interactive and POP users, and to distribute the sendmail
load between cheetah, and a new machine, cougar. But I'm not sure how
to do it. I can't replace the above with the following because of the
restriction against having a CNAME and any other RR:

mail         IN      CNAME   mail.lb.wsu.edu.
             IN      MX      0 cheetah.it.wsu.edu.
             IN      MX      0 cougar.it.wsu.edu.

The equal-preference MX records would work to robustly distribute the
sendmail load, since mailers are supposed to try the whole list. And
since BIND will round-robin the MX records, there's even some
load-balancing.

If I reduce the above to just:

mail         IN      CNAME   mail.lb.wsu.edu.

and let mailers send to the host (i.e. do away with the MX records),
this seems to work in nslookup, but "normal" clients (ping, telnet,
and even sendmail) don't seem to be able to resolve the address. I'm
guessing this is because lbnamed returns a CNAME and an A and the
resolver is having problems with chained CNAMES (although RFC 1034
says chained CNAMES should be followed). It seems to be
resolver-dependent because it works with HP/UX but not with Tru64 Unix
or AiX.

If I deal directly with mail.lb.wsu.edu, I have no problems
whatsoever. It's only when I start trying to reference it from the
mail.wsu.edu zone that I have a problem. Is there a way to do what I
want (basically to point "real world" FQDNs at a delegated lbnamed
FQDN)? If so, how?

Thanks.

Geoff

-- 
Geoff Allen, geoff at wsu.edu, <http://www.wsu.edu/~geoff/>

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