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I'm trying to test a number of Nortel Networks BayStack 470-48T switches. I can connect a machine per port, but it's a 48 port switch. I have two machines, and my plan was to plug one in and move the other 'down the line' testing each one as I went with a constant ping. Unfortunately, once a machine has been plugged into one port, the switch won't accept that machine on any other port. How can I make the switch clear its information on disconnect so I can quickly test each port?

corsiKa
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1 Answers1

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When your target machine responds to the ping, it's MAC address gets "registered" in the MAC address table of the switch to the port that the ping reply came from. When you move the target machine the switch still believes it to be connected to that port until the MAC address table cache expires. You could do two things to try and get around this:

  1. Establish a telnet session to the CLI of the switch and flush the MAC address table when you move the target machine.

  2. Reverse the test. Run the ping from the target machine to the "stationary" machine.

As an FYI: Switches populate their MAC address tables by examining the source MAC address of frames, not the destination address.

joeqwerty
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  • I can't seem to connect via CLI. I've tried serial to serial, and serial to straightthrough RJ45, and neither would connect over hyperterminal. And reversing the test because once the "mobile" machine has connected on one port, it won't acquire an IP address when it's on another port. – corsiKa Apr 30 '12 at 20:56
  • give it a static ip address for the purpose of the test. – joeqwerty Apr 30 '12 at 21:07
  • Tried that, no cigar. I suspect because it bound the mac address to a port already, it refuses to re bind. – corsiKa Apr 30 '12 at 21:08
  • OK, I thought that might force it to repopulate the MAC address table, I guess not though. What you could do, since the ping reply isn't coming back to the mobile machine, would be to continue running the reverse test from the mobile machine and at the same time run a packet capture on the stationary machine and look for the ICMP Echo Request from the mobile machine. The ICMP Echo Reply may not be getting back to the mobile machine but that shouldn't stop the ICMP Echo Request from getting to the stationary machine. – joeqwerty Apr 30 '12 at 21:12
  • Any recommendation on a freeware packet capture application that runs on win-xp? – corsiKa Apr 30 '12 at 21:21
  • Microsoft Network Monitor or Wireshark. – joeqwerty Apr 30 '12 at 21:23