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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.

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
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This isn't a problem with SSH, it's a problem with your network config. You're looking in the wrong place. No route to host means that your machine can't work out how to route traffic of any kind to the other machine. Look again at the network config, make sure that's in order before you try and fix ssh. – EightBitTony Jul 21 '11 at 10:22
I posted same Q in Stackoverflow and they told me to put it in superuser. If you know how solve this prob can u gimme resources to look for the answer. – dewbot Jul 21 '11 at 10:34
Okay is machine B on a different Network but is connected to the same router? Im guessing all the IPS are internal not external, What are the actual networks these machines are on as 1.23.x.x isnt a valid internal range so i'm guessing you put that just for this question? It would help to have the actual addresses your using. Ping results etc... – Stephen Martin Jul 21 '11 at 10:52
well my friend's router is nt same as mine. His ISP is also completely diff. Check out the Edits which I have added you will get a better idea about it – dewbot Jul 21 '11 at 11:10
Does the problem go away if you boot your MacBook back into Mac OS X? – Spiff Jul 21 '11 at 12:20
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1 Answer

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These kinds of partial-connectivity problems with wireless involved usually come down to broken multicast handling causing ARPs not to get through reliably.

See the troubleshooting steps I recommended in this Answer: WiFi Network is fine for Macbook Pro and Win XP, but Win Vista "Limited Connectivity"

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well I can't understand most ;) of the part except WPA/WPA2 one. See my ISP is Tikona Digital Networks. So if some one wants to use WiFi Tikona provides a WiFi Dialer which is available only for Windows. So couple of days ago I figured out how to use WiFi Connection from Ubuntu n I wrote a blog too on it dewbot.posterous.com/… check it. Tht might help u about understanding my connection. Otherwise I tried changing WPA2 to WEP but its not working. I cant even establish the connection. – dewbot Jul 21 '11 at 12:35
So you're using a public Wi-Fi hotspot network or something? Or your ISP doesn't let you change the settings of your Wi-Fi router? My Answer assumed you have the ability to reconfigure your own Wi-Fi router. – Spiff Jul 23 '11 at 5:28
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