Non-Trivial (I think) Karmic Koala Upgrade-Related Networking Problem

[Chris Hiestand]

I was originally going to file a bug report, but I don't have enough information to file an actionable report, so I hoped you smart Ubuntu users might have an idea.

I have an Apple Mac Mini with an Apple USB ethernet adapter (driver=asix driverversion=14-Jun-2006 firmware=ASIX AX88772 USB 2.0) that I use to do NATing using iptables. eth0 (1gbps) is for the LAN, while eth1 (100 mbps, usb adapter) is on the WAN side.

It has been working more or less without a problem for the last couple years including at least one distribution upgrade. But when I upgraded from Jaunty 9.04 to Karmic 9.10 last night my WAN network connection ceased functioning. I apt-get removed network-manager because I don't use the GUI and all I need is a very simple configuration (plus while troubleshooting I read many complaints about it).

The crux of the problem is that I could not ping my WAN ISP gateway under my old, unchanged configuration. I could ping my static IP WAN/eth1 address, so the interface knew that it was set to the correct IP. But pings to the ISP gateway would go unreturned. Also, pings were not returned when I flushed iptables.

Here was how my /etc/network/interfaces file began:
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
  address 172.16.0.1
  netmask 255.240.0.0

auto eth1
iface eth1 inet static
  address  24.249.202.53
  netmask 255.255.255.240
  gateway 24.249.202.49

Another failed troubleshooting attempt was when I rebooted into the previous kernel (2.6.28-18) I had the same problem. Although now looking at my kernel image mtimes, I probably should have tried the one before that (2.6.28-17) since that was the one running before the upgrade. But really, how much difference should a security patch have made?

Strangely, I discovered that if I changed eth1 from static to dhcp my ISP would quickly assign an address and I'd be online, fully functional, except without my beloved static IP.

I tried "ifdown eth0" to attempt to bypass any bugs in a dual configuration - no help.

I tried connecting my laptop to my ISP with the static IP address - it worked perfectly. So the problem must be on the mac mini, and it is very likely a problem caused by Karmic Koala (9.10).

I spent hours on this problem and I could not get my ISP gateway to return a ping with a static eth1. So I decided to try swapping eth0 and eth1. That is, plugging the WAN cable into eth0, and the LAN cable into eth1, and reconfiguring my software to reverse the roles. eth0 is still my built-in 1000mbps port, and eth1 is still the 100mbps usb adapter:

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
  address 24.249.202.53
  netmask 255.255.255.240
  gateway 24.249.202.49

auto eth1
iface eth1 inet static
  address 172.16.0.1
  netmask 255.240.0.0


Unexpectedly (to me), it worked! Now through a static addressed eth0 I can ping my ISP gateway with no problem. Also, I can use my static LAN IP just fine.

So I again reversed eth0 and eth1 to see if perhaps there was another variable at play. Again, I could not ping my ISP gateway. So I switched back to implement the workaround - and it worked again. So the problem is reproducible, at least on my system.

I'm really at a loss for what's going on here. With a kernel driver date from 2006, it seems unlikely to be the network driver. But it seems that all I can do is rule things out. I'm not sure where to start looking for an explanation and fix. Yes, I read through my logs - and I can't find anything helpful.

Any help, or just something that verifies I'm not crazy would be greatly appreciated. Thanks.