I have a two network interfaces machine, one is connected to the router and gets an automatic address via DHCP. The other has a static IP in a different subnet. I can ping both IP addresses, telnet to port 22 and see the "SSH prompt".. just fine. (trying them with switching the cable in my notebook)

Question: but when it comes to connecting to this machine via SSH I can only connect through the NIC that is connected via the router, not directly. It just timeouts when I try to connect directly. Why?

The firewall rules are the default, tried rebooting both sides, I only modified the "UseDNS to no" in the sshd_config on the machine.

  • What happens if you nmap the port where ssh hangs? – Thorsten Staerk Jan 14 '14 at 6:39
  • 2
    On which interface does your ssh daemon listen? Check config with cat /etc/ssh/sshd_config | grep Listen and check running daemon with netstat -putan | grep ssh. – chaos Jan 14 '14 at 7:15
  • 3
    What's the output of ssh -v user@domain (you might need to be prepared to supply more detailed log ssh -vv or -vvv if need be). You might also want to run sshd -d (-ddd) on the server on an alternative port, try connecting to that and then looking at the log from the SSH daemon. – peterph Jan 14 '14 at 8:12
  • @chaos if he gets SSH prompt, sshd is probably listening on that device as well. – peterph Jan 14 '14 at 8:13
  • First things first: are you sure you're connecting to the right machine (no alias in .ssh/config, no protocol-aware router in the middle)? If you are, then post the output of ssh -vv. – Gilles Jan 14 '14 at 21:05

I'm almost sure you have a route problem. Probably you either have none or two default routes.

Let's assume you have two networks, and, your router's IP and your machine's addresses and A manual configuration would be something like:

sudo ifconfig eth0 netmask up
sudo ifconfig eth1 netmask up
sudo route add default gw
sudo route add -net netmask

Although each scenario would require a slightly different command. [1]

Please make sure there's no other default route. Also, make sure you have ipv4_forward set to 1. [2]

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.