Really, REALLY wierd networking issue...
 

My Hoary box isn't connecting correctly to the Internet. I have disabled ipv6, etc. Apparently I need to use an MTU of 1400, but can't find out how to. Can anyone tell me how?

Thanks.

and according to this you make it stick by editing your /etc/network/interfaces... ;)

Thanks.

ifconfig not only brings down the connection, but doesn't change the mtu to any effect (synaptic still doesn't work, etc). I'll try booting into ubuntu and changing the interfaces file.

(Now in Ubuntu)

It seems /etc/network/interfaces already has mtu 1400 at the bottom, which is odd. Yet, eth0 is still running at 1400. Any ideas?

Results of ifconfig:

My /etc/network/interfaces, sans comments:

Incidentally I'm running AOL Broadband with a Netgear DG632 router connected directly to my box. Also, I have no problems in Windows since changing the MTU. I'm very close to my telephone exchange (500 yards or so), and apparently this could affect the connection.

I use AOL in the UK as well and found the easiest solution was to change the MTU in my Linksys Router to 1400 to connect, it meant not having to "ifconfig" any of my boxes to connect as the router sorted it, I checked out the website for Netgear and they do make referance to the ability to do this with their routers,

"Instructions for changing MTU on other NETGEAR devices is found in the Reference Manuals." found here
not terribly helpful I know, but it solved my problem, and 2 of my friends as well.

also i had previously changed,

/etc/sysconfig/network-scripts/ifcfg-eth0

by adding

MTU=1400

to the end, this was in Mandrake tho and before I changed the MTU of my linksys router, but may be worth a try.

My router's already set to 1400, which is why I'm so perplexed at this problem. Could AOL's proxy server have something to do with this?

Doubtful it's the server as your windows seems to work ok, The only trouble I've had with their servers was with their SMTP server about a month ago, it threw a wobble and acted funny for a day or so.

I did notice the result of your ifconfig
Indicating your MTU still = 1500?. How are you modifying /etc/network/interfaces? VI as root? or sudo?
have you tried with the = character inserted? You are typing "sudo ifconfig eth0 mtu 1400"?
Noddy i know but just checking. Is that the ifconfig result you get after you've attempted to change the mtu?

ok, had a bit of a look and come up with 2 options,
first have a look here for a Debian based work around.
Or (make a backup first) modify
/etc/ppp/options
then find,
#mtu <n>
change to,
mtu 1400