Why can't I ping any computers on the same hub?

I'm having some interesting problems pinging machines, with the end goal to have Computer B SSH into Computer C. The specific error message I get from ping is "Destination Host Unreachable", and ssh returns "No Route To Host". To start, the following is my network topology:

Router (192.168.1.1)
   |
   |---- Computer A (192.168.1.2)
   |
   |---- Hub
          |
          |---- Computer B (192.168.1.3)
          |
          |---- Computer C (192.168.1.4)

Computer A is able to ping both Computers B and C, and vice-versa. However, Computer B cannot ping Computer C, and vice-versa. The IP addresses are shown above, and the network configuration for each machine is:

Gateway - 192.168.1.1
Netmask - 255.255.255.0

Why am I unable to have Computer B communicate with Computer C in this setup?

Breakthrough

Posted 2012-08-10T15:46:21.357

Reputation: 32 927

If you remove/replace the hub does the problem go away? Hubs are dumb (as in they don't do much) so I can't imagine it would be anything other than a bad hub if the problem goes away. – Tanner Faulkner – 2012-08-10T15:51:00.867

@r.tanner.f due to physical limitations, the hub has to stay. I do not believe the hub is bad, since all computers have full internet connectivity, and are able to access other machines on the network (i.e. Comp. B can see Comp. A). – Breakthrough – 2012-08-10T15:53:51.673

Firewall rules? (You can test it with the router unplugged and the FW temporarily turned off). Does it change if you change the cabling so that computer A and C are on the hub? (or A and B). – Hennes – 2012-08-10T15:57:14.790

@Hennes I have ruled out all factors related to the computers, as I've physically interchanged the computers and get the same result irregardless of the machine. Right now, A can ping C. If I move A to the hub, I cannot ping C anymore. – Breakthrough – 2012-08-10T15:58:54.803

As a sanity check, is there any way for me to force packets to be directed to the default gateway, even though Comp. B/C lie in the same subnet? – Breakthrough – 2012-08-10T15:59:59.140

Something like route add 192.168.1.3 255.255.255.255 192.168.1.1 1 Interface (or route add -host). The syntax depends on the used OS. But setting a direct route to the gateway is possible. – Hennes – 2012-08-10T16:05:40.457

1This "Hub", is it actually a switch? What's the make and model? – RedGrittyBrick – 2012-08-10T16:13:30.260

2@RedGrittyBrick no, it is indeed a hub. I don't have the make and model handy - at this point, I'm just going to run to the store and replace it with a switch (it's about time I did it regardless). I'll give an update when I make the switch (lol pun). – Breakthrough – 2012-08-10T16:26:29.667

@r.tanner.f looks like you were right, appears to be a bad hub. Just replaced it with a switch, and everything's working fine now. – Breakthrough – 2012-08-10T17:55:00.057

And looks like you (and firstly, r.tanner.f) were right. I replaced the hub with a switch, and was instantly able to connect between Computers B and C. For this reason, I'm going to assume that the hub was infact broken.

– Breakthrough – 2012-08-10T17:54:31.057

That's a weird one. I've never heard of a hub half breaking... Always thought they'd either be rock solid or just dead. Have to keep this in mind in the future. – Tanner Faulkner – 2012-08-10T17:58:52.907

Why can't I ping any computers on the same hub?

Answers