The situation is that I have to scan mac addresses of clients(portable ones) connected to multiple routers. I want to set up a server that can make an external request (or some networking tool to scan) all the routers to fetch the required data.
P.S.: I do know about nmap scan, but for that, the server also has to be connected to same router, and I can't fetch/scan from other routers.
MAC addresses are only seen or relevant on the LAN where the host is connected. Not all LAN protocols use MAC addresses, and of those that do (the IEEE LAN protocols), some use 48-bit MAC addresses, and some use 64-bit MAC addresses.
Routers strip off the frames, which contain the MAC addresses, and forward the packets encapsulated in the frames, creating new frames for the next interface. Any MAC addresses do not survive crossing a router.
You will need some type of agent on a LAN (stand-alone, or on the LAN hosts) in order to discover the LAN information. Some routers may work for this via something like SNMP (e.g. checking the router ARP table), but not all routers actually support that, or are configured to allow you to query SNMP.
