identifying which machine is using a specific IP address

[sebjenkins]

Hi,

I have a machine on my network that is hammering my firewall 4 times a minute with DoS attacks but when I look at my DHCP server, the IP address does not have a machine name next to it so I can't identify which machine is causing the problem !

Has anybody got any suggestions ?

Many thanks

 

[PalmTest]

Do a ping to the IP addres and the command ARP -A shows the MAC address.
Look through your switches to identify the interface.
Go visit the guy and ask him about his installed apps.

Suppose the MAC address is 00-11-22-33-44-55
To find a MAC address on a Cisco:
show mac-address-table | include 4455

Check if another switch is attached to the shown interface:
show cdp neighbors