From: John Beckett 

"Geo"  wrote in message
news::
> I did have ICMP blocked, but it's enabled now.

Some really old notes I have say this:
-+-
Problem:

Open web page. Some of page may appear. Then nothing happens.

Cause: Your PC is on Ethernet and uses MTU = 1500 but there is a router
(e.g. using PPPoE) that forces lower MTU. The PMTU negotation fails because
the web server admin has blocked all ICMP (including those used for PMTU
fragmentation control).
-+-

Exactly the same would apply to any server providing a TCP service (e.g. a
newsgroup server).

When a TCP connection is established between hosts that are not on the same
segment, each host notifies the other of its MSS (maximum segment size =
1460 = 1500 bytes for standard Ethernet, less 40 for IP+TCP headers).

Each host then uses the smaller of the two values for the amount of data to
put in each datagram sent. The datagram include the DF (Don't Fragment)
flag in the IP header. That tells intermediate routers to not split up the
packet if it is too large. Instead, the router should return an ICMP
"need to fragment but DF is set" error to the sender.

The sender should then lower its packet size and repeat.

Probably, your news server was not lowering its packet size when some
weirdness at Randall's end (PPPoE?) enforced a lower MTU than Randall's
computer realised was required.

Randall could (given infinite time) find the setting to lower his
MTU to what his overall system, including router, is capable of.

Run 'ifconfig' to see the current value (MTU = 1500 for Ethernet, but
should be reduced if you know your router is using PPPoE or some framing
like IPSec, that reduces the amount of data that can be sent in a single
Ethernet frame).

John

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