ADSL problem... any ideas?

[Dave S]

Hey folks, wondered if anyone has ever heard of something like this?

A friend has an ADSL connection with a small network attached.

Some websites work great, others don't appear at all.  For example, Yahoo 
works, Google (any Google site I can think of) doesn't, various random 
websites I've made usually work, as well as some parts of Sourceforge, but 
Slashdot and BBC News doesn't.

I've checked the DNS resolution DHCP configuration, and pretty much everything 
on the network seems to be fine as far as I can see.  I can resolve any 
hostname (including non-working websites) using nslookup, and all machines on 
the network get correctly assigned IP addresses and other relevant details 
such as DNS servers via DHCP.  Everything looks like it should be fine, but 
it isn't!

This is with a "new" (well, not brand new but factory reset) D-Link wireless 
router (model DSL-6404T/UK) to replace an old broken router, but so far all 
machines are on wired connections so it can't be a wireless problem either.  
The wireless is switched off, actually.

I've been through all of the connection settings on the phone with the tech 
support people, and they all appear to be right.  Indeed, they must be pretty 
much there, because I can get to some websites completely fine.  So I managed 
to get to the D-Link website and find that this box isn't running the newest 
firmware - gonna sort that next week, as I couldn't download it from their 
FTP site (which didn't work), so need to take it with me on a memory stick 
from home!  :-S

But overall, this is a very weird problem, and I'm somewhat stumped.  I've 
never see it where some websites work and others don't, and I can't spot any 
sort of pattern that makes sense.  It's completely consistent (Google never 
works, Yahoo always does) but also seems completely random.

Any ideas anyone?  Where should I look that I may not already have looked?  
Could it be related to MTU or anything like that?  (I doubt it, and besides, 
I've already tried lowering that, and it didn't make any difference.)

Maybe the router is just borked, but it came from a relatively reliable source 
who said it was working fine, so I've no reason to think it would be.

Cheers,

~Dave