Getting an IP Address

[ejdrijin1]

Hi,

I have a Mac address of a device and would like to obtain his IP Address.

If I do a show ip arp the MAC address is not showing there.

Any ideas how I can obtain it?

Thanks in advanced!

[Madhukrishnan Gopinathan Nair]

Hi,

You can try few things here. 

Try to understand which vlan it is.  Use sh mac address-table <mac> it will show the vlan associated with that mac. Then if it is a DHCPd vlan, you can probably check in DHCP server to see if you can find the ip for that mac. 

Also check if DHCP snooping is enabled in the switches, then you can check the dhcp snooping table also to see.

HTH

Madhu

[Richard Burts · Accepted solution]

My guess is that the device is connected to a layer 2 switch and that you are doing show ip arp on that switch. But for the layer 2 switch the only things in its arp table are things that the management interface of the switch has accessed.

If you want to find the IP address used by the device I would suggest that you start by determining what port that device is connected to. Perhaps you already know where the device is connected or else you can look in the mac address table of the switch and find that mac address. Once you know where the device is connected check to find out what vlan is associated with that switch port. Then find out what device is doing the layer 3 routing for that vlan. Go to the device that is routing for the vlan and do show ip arp on that device. That is where you should fine the IP address associated with that mac address.

HTH

Rick

[ejdrijin1]

Thanks for your reply.

[Richard Burts]

You are quiet welcome. I am glad that my suggestion was helpful. Thank you for using the rating system to mark this question as answered. It helps other readers in the forum to identify discussions which have helpful information. I hope to see you continue to be active in the forum.

HTH

Rick