I need to make a port-IP diagram and so far the best way to do this seems to be through show arp after consoling into the brocade switch. The arp table is empty however, and the only way I have been able to add the connected devices has been by pinging them. I don't know all their IP addresses, so I am forced to ping through every possible IP on the network.

I tried pinging the broadcast address but it didn't work. (network is

There has GOT to be a smarter way to do this...

Any ideas?

  • 2
    A tool like nmap will ping all the hosts on the subnet in just a few seconds
    – Ron Trunk
    Commented Feb 9, 2021 at 20:16
  • 2
    Remember that the entries in an ARP table will expire and be removed after a period of time.
    – Ron Maupin
    Commented Feb 9, 2021 at 20:49
  • What both Rons says. If a device hasn't been active for a few minutes, it won't be visible in any ARP table. Use something like nmap -sP followed by arp -an, repeat once per hour for a few days depending on how often/when you expect devices to be switched on, collect the results. Commented Feb 10, 2021 at 6:48
  • can you run nmap through a console connection to the switch?
    – Frank
    Commented Feb 11, 2021 at 4:09
  • Did any answer help you? if so, you should accept the answer so that the question does not keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer.
    – Ron Maupin
    Commented Dec 23, 2021 at 16:35

2 Answers 2


To fill the ARP table, you have to generate ARP requests or replies.

  • 1
    Also, check the default gateway - it'll already know most of the MAC/IP pairs.
    – Zac67
    Commented Feb 9, 2021 at 20:37

The easiest way to find the IP-to-MAC associations is to look at the DHCP server's lease table. Of course, you won't configure all devices by DHCP but it's a good idea to set up reserved addresses for static device anyway.

Also, the (default) gateway's ARP table holds all IP-MAC pairs for those devices using the gateway. Likewise, the access switches have the MAC-port mappings.

If you combine these infos you'd likely get 95% of your network. Of course, an ARP sweep will find 100%. Obviously, you can run the ARP sweep on any device connected to the subnet.

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