Unavailable Domains?

[Dean, Barry]

I have 3 domain names that I cannot resolve recursively from my DNS
servers. The problem exists inside my institution and not from outside.
I can resolve what I need just fine from a Broadband connection.
One domain is bjmu.edu.cn, I cannot resolve the MX records (or any
others for that matter). If I use "dig +norecurse ... ns" and start by
looking up ".", then "cn.", then "edu.cn." etc using "@server" and
trying each and every server at each level, it works.

I also have a problem with iop.kcl.ac.uk, again non-recursive queries
all along the chain work a treat, but as soon as you do "dig
iop.kcl.ac.uk" you get ";; connection timed out; no servers could be
reached" like the one above.

Finally I have an issue with ads.ahds.ac.uk, same error ";; connection
timed out; no servers could be reached".

This last one is complicated by the fact that just one of my DNS
servers, the outward facing dns0.liv.ac.uk is a slave for this one, so
it *can* resolve names in that domain.

I have contacted the hostmasters at the various places that master these
domains and they all confirm that they are working fine.

I have tried debug mode and query logging on a recursive name server and
get no useful clues, I just see the query and the fact that it times
out.

I have tried "+trace" on dig and that causes the queries to work!

I am completely stumped...

Is it my servers? If so what do I have to do to them?

Any clues would be welcomed as I am going out of my tree with this!

-- 
Barry Dean
Network Programmer
Computing Services Department
University of Liverpool
Email: B.Dean <at> liverpool.ac.uk, Web: http://pcwww.liv.ac.uk/~bvd/