arp -a command not working doesn't list devices

Question

First off, this is not a duplicate of this question because it wasn't answered properly. My question is this:

When I type into terminal (Kali Linux):

arp -a

And I know that there are 7 devices connected to the network, I get this:

Wireless_Broadband_Router.home (192.168.1.1) at f8:e4:fb:a1:a9:c8 [ether] on wlan0

Only the router shows up! where's everything else?

Solution

Dynamic ARP mappings expire automatically after a couple minutes. You'll only have dynamic ARP mappings for devices your machine has sent unicast packets to recently. Do a ping-scan of your subnet (or maybe just ping the subnet-broadcast address or the all-hosts multicast address) and then rerun arp -a.

Also note that I believe the arp command has been deprecated on modern Linux. The replacement is the ip command, such as ip neighbor show or abbreviated ip n show.

Comments

[Steampunkery]

how should I go about doing a ping-scan?

[Spiff]

@Nitroman Lots of tools can do ping scans, but a popular one is nmap, e.g. nmap -sn 192.168.1/24

[Steampunkery]

when I run ip n show I get this: 192.168.1.1 dev wlan0 lladdr f8:e4:fb:a1:a9:c8 REACHABLE ONLY THE ROUTER!!!!

[Steampunkery]

none of the other computers on the network show up.

[Spiff]

@Nitroman Did you do anything that would have populated the list first? Like the ping scan I talked about? Can you connect to the other devices on your subnet?

[Steampunkery]

no I didn't, should I?

[Spiff]

@Nitroman Well, you're not going to see other machines in your arp cache unless your machine has needed to talk to them (via IPv4) within the last two minutes.

[Steampunkery]

so I ran this command that I found online to do a ping sweep: for i in {1...254}; do ping -c 1 -W 1 192.168.1.$i | grep 'from'; done

[Steampunkery]

AND IT WORKS!!!!!