Ubuntu – SSH Connection Error: No route to host

opensshssh

There are three machines in this scenario:

  • Desktop A : user@1.23.x.x
  • Laptop A : user@1.23.y.y
  • Machine B : user@192.168.z.z

All the machines have Ubuntu 11.04 (Desktop A is a 64bit one) and have both openssh-server and openssh-client.

Now when I try to connect Desktop A to Laptop A or vice-versa by ssh user@1.23.y.y I get an error as 

port 22: No route to host

in both the cases.

I own both the machines, now if I try same commands from my friend's machine, i.e. via Desktop B, I can access both my Laptop and Desktop. But if I try to access Desktop B from my Laptop or by Desktop I get

port 22: Connection timed out

I even tried changing ssh port no. in ssh_config file but no success.

Note: that 'Laptop A' uses WiFi connection while 'Machine A' uses Ethernet Connection and 'Machine B' is on an entirely different network.

@Lekensteyn Here it is ->

Laptop A && Desktop A -> Router/Nano_Rcvr provided to me by ISP. So to one Router two Machines are connected and can be accessed at the same time.
here is my ifconfig output for both the machines :-
Laptop

wlan0

      Link encap:Ethernet  HWaddr X:X:X:X:00:bc  
      inet addr:1.23.73.111  Bcast:1.23.95.255  Mask:255.255.224.0
      inet6 addr: fe80::219:e3ff:fe04:bc/64 Scope:Link
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:108409 errors:0 dropped:0 overruns:0 frame:0
      TX packets:82523 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:44974080 (44.9 MB)  TX bytes:22973031 (22.9 MB)

Desktop

eth0

      Link encap:Ethernet  HWaddr X:X:X:X:c5:78  
      inet addr:1.23.68.209  Bcast:1.23.95.255  Mask:255.255.224.0
      inet6 addr: fe80::227:eff:fe04:c578/64 Scope:Link
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:10380 errors:0 dropped:0 overruns:0 frame:0
      TX packets:4509 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000 
      RX bytes:1790366 (1.7 MB)  TX bytes:852877 (852.8 KB)
      Interrupt:43 Base address:0x2000

Output of ip route show

      1.23.64.0/19 dev wlan0  proto kernel  scope link  src 1.23.73.111  metric 2 

      169.254.0.0/16 dev wlan0  scope link  metric 1000

Output of traceroute -n 1.23.73.111

       traceroute to 1.23.73.111 (1.23.73.111), 30 hops max, 60 byte packets
       1  1.23.68.209  3008.787 ms !H  3008.786 ms !H  3008.784 ms !H

Best Answer

The routes look fine. I'll assume that those IP addresses are private ones (LAN) and not public accessible.

Since you're connected in different ways to the network (wifi / wired), it's very likely that your router has separated wired / wireless networks. Try connecting both of them on a wired (or wireless) connection. Another possibility is that a firewall on the Ubuntu machines is blocking connections.

Otherwise, configure your router to use the same network (subnet) for wireless and wired connections. Also make sure that the router does not block client-to-client communication.

Your router is possibly dropping all unsolicited packets, that's why your friend gets a "connection timed out" message on your public IP address. Configure NAT port forwarding so that the public IP address + port combination forwards to your LAN address.

Example network:

YOUR NETWORK (A)
    Router A (public address: 198.51.100.1)
    Desktop A - 10.0.0.2
    Laptop  A - 10.0.0.3

YOUR FRIENDS NETWORK (B)
    Router B (public address: 203.0.113.1)
    Machine B - 192.168.0.2

On Router A, setup NAT forwarding:

To make your desktop accessible:
  forward the public port 22 to 10.0.0.2
To make your laptop accessible:
  forward the public port 2222 to 10.0.0.3

If you've a firewall (ufw, iptables, ...) on the machines set, allow incoming traffic to port 22 (Desktop A) and port 2222 (Laptop A).

The desktop can now be accessed using SSH with:

ssh user@198.51.100.1 -p 22

The laptop can now be accessed using SSH with:

ssh user@198.51.100.1 -p 2222

If you want to access your friends machine, apply these instructions to his machine + router.

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