The ARP table provides useful clues about IPv4 neighbors; however, it is not a complete list of all devices on the network. Separate cache logging and current availability.
Basic approach
ARP serves to map the IPv4 address to the link layer address on the same link. For traffic sent to a remote subnet, the client usually sees the MAC address of the next router, not the destination. Therefore, it can be expected that the MAC information of remote devices will remain empty.
Application steps
- Get the output of arp -a and see which adapter each record is listed under.
- Compare the recording with a known device on the same network; Note the scan time.
- Store accessible IP and service information for remote subnets instead of filling the MAC field with guesswork.
Practical example
It is normal that you can access a server behind a VPN but cannot see its MAC address. Copying the local gateway's MAC address to the server creates incorrect device matches in the inventory.
Interpret the result correctly
Old record may exist in cache; Incomplete registration does not prove that the device is turned off. Clearing the ARP table is not always necessary for diagnosis. First record the existing evidence and compare it with other sources without making changes.
Source and follow-up reading
Protocol or command details: RFC 826. The steps and example scenario are IPScans editorial narrative.