I have two PCs in the same LAN: "A1" and "A2". There is another PC in a different LAN: "B". A TCP server is listening on machine "B", port 80. From machine "A1", I can connect successfully to machine "B". If I try to connect from machine "A2", I can see three outgoing TCP-SYN packets, but no response. The SYNs don't reach machine "B".

Windows firewall is turned off on machine "A2". If I start the TCP server on machine "A1", I'm able to connect to it from machine "A2".

What am I doing wrong? Thank you for your help.

  • check the network settings on a1 and a2 whats different? probably subnet mask in this case. – tony roth Apr 5 '13 at 16:42
  • IP address of "A1" is x.y.z.245, IP address of "A2" is x.y.z.238, subnet mask is the same:, default gateway is the same too: x.y.z.200 (the value of x, y, and z is not important) – kol Apr 5 '13 at 16:49
  • What about the firewall on machine A2 for outgoing connections? What's doing the routing / NAT'ing between the two LANs? – Rhys Evans Apr 5 '13 at 17:04
  • oh btw thanks for telling us that (the value of x, y, and z is not important)... – tony roth Apr 5 '13 at 17:14
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    @kol you seem to write better then most english speaking people! Ok do a route print on a1 and a2 is there a difference? – tony roth Apr 8 '13 at 13:49

Finally, I could figure out the problem: only part of the IP range of subnet "A" (the part which contained the address of "A1", but not that of "A2") has been allowed to connect to subnet "B".

I greatly appreciate all the help I got in the comments!

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