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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?

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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 Aug 10 '12 at 15:51
    
@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 Aug 10 '12 at 15:53
    
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 Aug 10 '12 at 15:57
1  
This "Hub", is it actually a switch? What's the make and model? –  RedGrittyBrick Aug 10 '12 at 16:13
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 Aug 10 '12 at 16:26

1 Answer 1

up vote 4 down vote accepted

Hub is not a Hub, it is a switch with different segment VLANs configured on each interface. Router is stripping the 8021Q tags and allowing routed communication back across to a single vlan.

If the router were replaced with a switch you wouldn't see the communication to and from A - B, A- C.

The reason why you are getting destination unreachable is because there is no ip on that vlan segment the ip of B on C's segment.

Hubs are multi-port repeaters. There is no way a simple hub can block this communication, this is not a hub but a misconfigured switch.

-- or Hub is busted.. lol.

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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 Aug 10 '12 at 17:54
    
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 Aug 10 '12 at 17:58

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