Total Networking Failure after upgrade to 12.04LTS

Tom H tomh0665 at
Sat Jul 27 15:49:04 UTC 2013

On Sat, Jul 27, 2013 at 10:03 AM, Hal Burgiss <hal at> wrote:
> After a server upgrade from 10.04LTS to 12.04LTS, which otherwise seemed
> very normal, networking is non-functional. Nothing works (ping, dns, ssh,
> etc). Cannot ping any address, even on the LAN, and the system is not
> pingable from other systems on the LAN.
> The system in question is a 3 yr old Dell PowerEdge R510 server with duel
> NIC's, both are Broadcom NetXtreme. This system has no history of problems,
> and is used as a file server and internal DNS server for an office LAN. The
> original configuration bonded the 2 NIC's. The system is typically managed
> remotely via ssh (and thus I have no good way of copy/pasting screen
> output). There are no gui tools installed -- its a server. There is no
> unusual routing or networking configuration (other than the bonding). No
> VPN. Just a very typical single default gateway type set up.
> After the upgrade to 12.04, there just is no functional networking of any
> kind.
> What's been tried:
> - pinging localhost and the local network ip address on the NIC both work
> normally. pinging anything else, including the default gateway by ip
> address, fails with "network unreachable".
> - take firewall up / down
> - remove bonding (pretty sure this was problematic after the upgrade) +
> reboot
> - tried NIC's one at a time individually -- identical behavior
> - manually reconfigured NIC's with ifconfig and route commands to make sure
> there wasn't a config file change that was problematic.
> - manually compared the output of ifconfig and route to another similar
> working
> system (10.04LTS) in the same rack (no difference other than the ip address)
> - tried setting NIC's to dhcp (times out)
> - turning off apparmor (desperation)
> - disabled ipv6 with sysctl (more deperation)
> Other factoids:
> - Boot sequence looks normal, NIC's are recognized and are shown as "ready".
> No errors reported.
> - No errors in kern.log or syslog, ever.
> - No errors shown by ifconfig.
> - Very strangely ifconfig will show both TX and RX steadily incrementing. I
> can ping and watch both values change, but pings timeout.
> - When the firewall is up, it shows normally looking volume of packets in
> both the INPUT and OUTPUT chains. iptables apparently sees incoming traffic.
> Symptoms are the same with firewall up or down.
> - tcpdump will show arp traffic only, and nothing else. But interestingly it
> shows a lot of packets "dropped by kernel".
> 'tcpdump -vv -X' output summary will look something like:
> 15 packets captured
> 369 packets received by filter
> 350 packets dropped by kernel
> I haven't found anything except arp traffic by tcpdump. So does anyone know
> what causes "packets dropped by kernel" other than maybe iptables? Or is
> this an artifact of something else being wrong, like dns not working? Or
> other ideas of what to try?

Any configs?

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