DHCP IP lookup from MAC address

Question

I have some computers I need to reinstall over the network, but for the install to work correctly, the computer need to have its MAC-address registered in the DNS/DHCP so that it'll be recognized and get the right IP and thus policies from AD.

Problem is that the computer often isnt registered in the DNS/DHCP for some reason, and that wont be noticed before a late stage in the reinstall-process, and thus it's wasting a lot of time to troubleshoot this way.

I'm wondering if it's some way to query a DNS-server with a MAC address, and see if its properly registered to a IP?

(I dont have access to AD).

Answer 1

AFAIK, there's no way to query a DHCP server with a MAC address, but you can use ping and the ARP table on your computer.

ping -b <broadcast address>
arp -a

will give you the MAC and IP addresses of all the hosts in the network.

Answer 2

Depending on the size of your network, it can be very quick to scan every possible machine.

device_hwaddr="XX:XX:XX:XX:XX"

# we ping every ip in the range 192.168.0.*
ip_last_number=0
while test $ip_last_number -ne 255; do
    ping -c 1 192.168.0.$ip_last_number >/dev/null 2>&1 &
    ip_last_number=$(($ip_last_number + 1))
done

# we search in the arp table if their is our device
echo $(arp|grep $device_hwaddr)

Answer 3

You can use the Reverse Address Resolution Protocol (RARP). It resolves IP addresses to a given MAC address via a broadcast. It's old (even obsolte via DHCP), but it should work.

Answer 4

Dynamic IPs usually are chosen from disjunctive range. For example static 192.168.0.0/25, dynamic 192.168.0.128/25. Depends on your configuration.

If you don't have access to DHCP server's configuration, I don't think there are other ways to check whether it's static or dynamic.

Answer 5

Is it only at install time that these machines need a certain IP address to set policy? If not, why aren't they getting the correct addresses at install time? Do they get assigned the correct IP later when they are deployed?

It would seem to me that creating static entries for each machine's MAC address in the DHCP server is the solution you're looking for. In your post it sounds like you can't do that yourself, but if it's necessary your sys-admin will probably do it for you. He can also probably allow you read-only access to all static address assignments (so you can check on them before installation).

Answer 6

I had the same problem: had a MAC address, but IP changed on me. Broadcast ping did not seem to work for me on WinXP, and our linux machines were on a different subnet...so brute force led me to:

for /l %i in (1,1,254) do ping -n 1 -l 1 -w 1 10.11.2.%i

Where 10.11.2.0 is my subnet. Then I could do:

arp -a

and look/grep for my known MAC address. (Note that windows uses - separator and linux uses : in MAC addresses).

You could extend this for a larger subnets too, with extra for loops.