I have this same problem: I must usually do a manual "sudo dhclient" to get an IP address after boot, on Ubuntu Dapper, though it seems to be intermittent. This is annoying because I have to attach a monitor and keyboard to my server to do this.
Bug #34505 seems similar. Bug #19740 (rejected) also seems similar though it may contain several different problems. -- Ethernet interface not working after reboot https://launchpad.net/bugs/42608 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
