Friday, January 21, 2011

Can't ping from Machine A to Machine B on the same VLAN

Switch: Netgear 7352PS Created a VLAN (id = 10), and assigned ports 13 through 24 to that vlan. Also configured PVID as 10 for all these ports.

Machine A: 172.31.192.111/24 Machine B: 172.31.192.110/24

I connected both A and B to ports 13 and 21 respectively. The ping between A and B is not working.

Am I missing something obvious here? Or better put, whats the best way to troubleshoot this?

  • Check to see if there is there a host based firewall on the PCs that is blocking ICMP. Drop a packet sniffer on the receiving machine and see if the ping is even getting to the target.

  • Do you see the mac address with the corresponding IP of the other machine on the current machines arp table? arp -a in Linux.

    RainDoctor : Right now, the ping from A to B is working. "arp -a" on A shows an entry for B. B to A is not working. Changed cables, and no arp entries. B is also connected to the switch console via serial.
    Kyle Brandt : Oh, ya, sounds like a firewall on B to me. A firewall that blocks ICMP would typically allow ICMP replies from pings, but not pings that it did not initiate.
    RainDoctor : Yeah, you are correct. XP firewall is the culprit. Thanks guys!
  • Sounds like it's an issue on the hosts (check network configuration, firewalls, etc.).

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