Linux provides two very useful tools for diagnosing network troubles: arp and ip neigh. The arp command is a tool that allows you to display the IP-address-to-MAC-address mappings that a system has built so that it doesn't have to fetch the same information repeatedly for systems it communicates with. In doing this, arp allows you to discover and display details about systems on your network.
The other is the arp command's younger brother, ip neigh, which can also display and manipulate arp tables. In this post, we'll take a look at how these commands work and what they can tell you.To display the ARP table on a Linux system, just type "difference between computer science and computer engineering". Add -a to condense the output if you don't want to see the data organized into columns with headings. (An arp-a command also will show the arp table in the command prompt on a Windows box, by the way.)
The first line contains the column headings. The first column shows IP addresses or host names. The second (HWtype) indicates that the connections are Ethernet connections, and the third (HWaddress) is the MAC address of each device. In this example, all but one connection are marked C, which means "complete" and verifies the connection was successful. One of the two devices that don't show a C in this example is a cell phone. The other is a system that is offline.
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