I have a problem that's driving me insane.
I have a Thinkpad with 12.04 (hereafter, t-rex) and an iBook with OS X 10.4.11, freshly installed (hereafter, persephone).
I'm trying to share t-rex's internet connection, achieved via 3G USB modem, with persephone. I did the usual "new wired connection -> ipv4 -> shared with other computers" dance on t-rex, connected the two with a ethernet cable and expected it to work.
Little did I know, persephone obtains an IP, can ssh to t-rex, can ping t-rex and various external servers, can dig, can send and receive mail, albeit very slowly, but cannot browse with Safari nor curl, unless it is very short responses (301 redirect and stuff like that).
I CAN load pages from apache2 running on t-rex with no problem whatsoever - I suspect that if I set up a caching proxy on t-rex it would work fine. I just cannot load pages from external servers.
I tried toying around with the MTU (1400, then 700) with little hope and with no result.
The interesting bit is that if I remove the 3G modem and tether t-rex to my cellphone instead, everything works fine, so I'm assuming the problem is between the ethernet cable and the modem (and in fact both laptops work just fine when connected to the office's LAN).
[ iBook <-> Thinkpad ] works perfectly fine
[ iBook <-> Thinkpad <-> cellphone ] works fine
[ iBook <-> Thinkpad <-> 3G ] works only with small payloads
[ Other ubuntu box (11.04) <-> Thinkpad <-> 3G ] works fine
Any hints please?
Thanks a lot.