I have a client which is having issues very symptoms very similar to MTU packet size issues (unreliable browsing, Terminal Server sessions failing etc)
This client has a laptop and a 3G card, and sits out on a boat way past great barrier island. They can only get GPRS service, but has been working fine for the last year or so.
I setup my laptop to replicate their settings (Clean install of Windows XP) VMC 7.03.0004 (latest) and a 3G Card locked to GPRS with APN of web.vodafone.net.nz and internet.
Unusual results. I can ping 184.108.40.206 usually with up to a 1500 MTU from a broadband connection (Clear's DNS servers.)
From the GPRS connection I can only send a ping -f -l 64 and get a reply.
If I send a do not fragment and packet size of 65 and above it does not get a reply - BUT ALSO does not recieve a packet needs to be fragmented.
The maxmum packet I can sent with a fragmentation error is 1476, which seems right from what google says (but most dialup connections are 576 MTU)
My gateway when on Vodafone is 220.127.116.11 I can send packets of up to 1476, but they get eaten after this. Seems to be a GPRS problem, and perhaps even only on this gateway.
I called Vodafone Data support, but the only guy which knew had gone home for the day.
Questions - Whats the MTU meant to be for Vodafone GPRS??? Surely it isn't 64!!!