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I have two laptops directly connected to each other and configured with the following network configuration:

PC1: 10.0.0.1/24

PC2: 10.0.0.2/24

Both Laptops run Linux Ubuntu and the Ethernet interfaces are configured using network-manager. I am not able to ping the peer laptop. I tried to analyze the problem using wireshark and I found the following:

When PC2 pings PC1, the ARP requests are received by PC1 and PC1 generates ARP reply but they never reach PC2. However, when PC1 pings PC2, ARP Request which are broadcast never reaches PC2. What would be the cause of this problem knowing that laptops used to ping and communicate with each normally?

Note: It is not a cable problem, I just switched PC1 to Windows and things started to work. So what would be the problem in Ubuntu that is preventing PC1 from correct forwarding?

  • Are you using the Orange Ethernet crossover cable? – WinEunuuchs2Unix Nov 10 '16 at 18:06
  • @WinEunuuchs2Unix I am using gray colored cable. Not sure if it is straight or crossover. But as far as I know, all network adapters these days have sensing mechanism to know if the peer is laptop or router, correct? – IoT Nov 10 '16 at 18:08
  • Yes I heard most could sense it properly. If you have access to an ohm-meter you can quickly check if they are straight or crossed. – WinEunuuchs2Unix Nov 10 '16 at 18:10
  • @WinEunuuchs2Unix check my edited question – IoT Nov 10 '16 at 18:37
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First confirm you have a good link between the boxes. You can check by looking for the link=yes setting returned from sudo lshw -c network run on both.

It's also worth checking if there is a crossover cable between them, or if they are straight, just plug both into a switch, hub, or router and see if you see the tx/rx lights going to both PCs. It's amazing how many devices I run into that don't support auto-crossover when a straight cable is plugged in.

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