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I'd like to get my Ubuntu 11.04 server to route packet between its two network interfaces.

The two ethernet interfaces (eth0, eth1) work apparently well as such. Both have static IP addresses ( & and both are reachable from their respective network. All IP services as well as the Samba server are reachable from both sides.

sysctl -p returns "net.ipv4.ip_forward=1" and I can even ping the interface "on the other side" from both networks. In other words: I can ping from all PCs on the network and from all systems on the net. But I cannot reach any other address on the respective "other side"

I've already read numerous "how to" articles and Forum threads on this very topic of setting up Ubuntu as a router, but I just don't find the final solution to my problem.

Here are also some further information on the setup.

Kernel IP routing table shows:

Destination Gateway     Genmask     Flags   Metric  Ref Use Iface
default     UG  100 0   0   eth0 *   U   0   0   0   eth1 *   U   0   0   0   eth0

interfaces shows:

iface eth0 inet static

iface eth1 inet static

I do not need any NAT or DHCP. There is no firewall running (no ufw, no iptables settings). Both networks have their own firewall protected internet connection and the connected devices get their IP addresses from the respective internet routers. I just want to be able to reach for example printers on one network from clients on the other.

What am I missing? Does anyone have any idea?

Many thanks in advance!

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closed as off-topic by Seth Jun 23 '14 at 23:04

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This describes a problem that can't be reproduced that seemingly went away on its own or was only relevant to a very specific period of time. It's off-topic as it's unlikely to help future readers." – Seth
If this question can be reworded to fit the rules in the help center, please edit the question.

I've noticed that IP forwarding seems to fail if network manager is managing the interfaces involved in the forwarding. Maybe someone else could explain why?

try adding:

# interfaces not to manage with Network Manager

to your /etc/NetworkManager/NetworkManager.conf where you replace the mac addresses above with the ones of your network cards.

or disabling network manager entirely if you don't need it.

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