Comment 3 for bug 58927

I have the same problem now with edgy (upgraded from dapper around knot3), in dapper this used to work fine. On my home network dhcp fails with "Message too long".

DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 6
send_packet: Message too long

I tried to look at the traffic with wireshark but not even a single packet was sent. This felt a bit weird, but the reason was simple: interface mtu was set to 64, so a single dhcp query packet was too large. If I set the interface mtu by hand (ifconfig eth0 mtu 1400) and then tried to obtain an address it worked fine but it reset the mtu back to 64, which is not good. However, everything was working as expected because dhclient was asking for interface mtu and the crappy adsl-router returned mtu=64 (confirmed with wireshark).

It is not possible to change the mtu-value returned by the adsl-router, so dhcp must be set to not ask the mtu (edit /etc/dhcp3/dhclient.conf and remove "interface mtu" from "request" line). This way default mtu will be used and the network works fine.

I assume this config change for dhcp was done after dapper as my network used to work fine then? If the setting is left as it is now (dhcp3-client version 3.0.4-6ubuntu5), there will be many with non-working networks. Those A-Link Roadrunners (model 44E for me, but I doubt the problem exists only for a single model) are very common here at least as ISPs have been giving them for new customers.