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.

-- 
Network unreachable with Edgy
https://launchpad.net/bugs/58927

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