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#1 2020-09-18 14:13:33

schwim
Member
From: Western NC, US
Registered: 2015-09-29
Posts: 297
Website

arp -a only showing me on network

Hi there everyone!

I'm trying to map everything on my local network.  A person on Tom's hardware told me I can do that with arp -a.  When I run that, however, I get only me on the network:

schwim@schwim-vm-bll:~$ arp -a
? (192.168.8.1) at 14:35:8b:1b:26:00 [ether] on enp0s3
schwim@schwim-vm-bll:~$

My router is assigning all devices to the 192.168.8 range so I expected to see everything but I'm not.  Is there anything I need to do to get the command to detect other devices if I'm running this from a virtual machine using a bridged network?

Thanks for your time!


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#2 2020-09-18 16:51:33

rbh
Member
From: Sweden/Vasterbotten/Rusfors
Registered: 2016-08-11
Posts: 685

Re: arp -a only showing me on network

schwim wrote:

I'm trying to map everything on my local network.  A person on Tom's hardware told me I can do that with arp -a.

"arp -a" lists all known ip's with their ether adresses on your lan segment.

If you ping your gateway and after run "arp -a", the ip of the gateway will be listed also.

To find all ip-devises, use nmap (cli) or zenmap (gui frontende for nmap).

Last edited by rbh (2020-09-18 16:52:07)


// Regards rbh

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#3 2020-09-18 18:42:11

Sun For Miles
Member
Registered: 2017-04-12
Posts: 191

Re: arp -a only showing me on network

I would just expand a bit on rbh' answer.

"Known IP" can be defined as IP and MAC address combination that is still being held in ARP/neighbor cache on the machine, which means that there was some kind of communcation between host and target mahine within the ARP cache time limit.

Nmap is frequently used tool for discovering availability of the machines using various protocols. You can use ssimple ICMP availability scan that just pings the subnet, or specific protocol and port combinations. When you do the namp scan of your local subnet, you can then hit "arp -a" and see that there are all the machines you were expecting, because there was recent communication with them.

Linux arp timeout settings is kind of a messy topic, but thse commands might give you a hint:

# check for arp timeout of the interface
cat /proc/sys/net/ipv4/neigh/IF_NAME/gc_stale_time

# modern way of checking the arp table
ip -s neighbor list

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