Hi GW,
Actually, I dont know how to explain it. There are 500 PCs
and 15 VLANs in my LAN. I can detect the IP address from mac
address if i console every of my switches. The problem is I want to find out
what is the IP address from one MAC address
given and it is not outside of my LAN or behind the router by using a
windows command line. I failed to get it.
There is no other way to find it out. That's the problem. If you use
DHCP you can access the DHCP server and maybe find it out there. The
only other real way to find it out is to ping the hosts (broadcast or
sent individual pings) which does the ARP resolution for you (unless you
use a tool that does only the ARP request for you) and check the answers.
I still don't understand the purpose of your search which would help to
find a solution. Because there is hardly anything you can do which would
help you (unless you use DHCP, then look there). MAC addresses are used
on layer 2 in the LAN. They are completely independent from IP
addresses. You can configure any host with any MAC address to use any IP
address. So it won't help you locating a host with a specific MAC
address nor with a specific IP address (on the contrary, I would say the
MAC address would be better to use as it is unique to the host and may
or may not be faked as easily).
Second, no device in your ethernet LAN is required to have an IP
address. It can easily communicate with other devices on Layer 2 even if
communication is somewhat limited in protocols. Transportation in your
ethernet LAN works only on the base of MAC addresses, there are actually
no IP addresses involved in the actual communication on the wire. IP
addresses are resolved beforehand with ARP, the routing is figured out
beforehand with help of the local routing tables (e.g. traffic for the
internet is sent to your gateway, i.e. to the MAC address of your gateway).
For all these reasons it is not reliably possible to find an IP address
from a MAC address. The other way round is possible under the assumption
that your other device does speak IP and wants to participate in IP
communication and therefore has to answer an ARP request to receive
traffic on IP layer (which is deductive reasoning in a sense for the
MAC->IP mapping). If it does not want to participate in IP you are lost
anyway. Therefore, there is no way to find it out.
So, the only easy way to find out about the hosts in your network is to
ping them, either by broadcast or in case they ignore you by a ping to
each individual IP address in your network. ARP resolution will take
place if the other hosts uses IP even if it does not echo your ping
request. (unless it is very mean and knows how to ignore you in particular)
Despite of that you are stuck in a layer 2 network and the only devices
that know MAC addresses information are your switchers and bridges and
other layer 2 devices which, however, do not consider IP addresses at all...
Gerald
