How to get the MAC address of the 'local' system given the IP address?

[Karl Auer]

On Fri, 2020-01-31 at 06:23 -0500, Little Girl wrote:
> Here's another way to get the LAN IP by using the ip command:
> ip route | grep kernel | cut -f1 -d'/'

These days, any interface can have multiple IP addresses, and (possibly
more importantly in this case) you can have multiple connections to
your LAN. I routinely have both wireless and wired connections going at
the same time, and not always to the same LAN!

That grep above will get you the networks your interfaces are in, not
the IP addresses on your interfaces. This gets you addresses:

ip route | grep kernel | tr -s " " | cut -d\  -f9

- run ip route
- select the lines containing "kernel"
- compress all spaces to single spaces
- take the ninth space-delimited field

However: You can have an address on an interface even if no routing is
going on at all, so it is better to use ip addr than ip route.

Here is my routing table now (edited for brevity):

kauer at kt:~$ ip route
default via 192.168.1.1 dev eth0 
default via 192.168.1.1 dev wlan0 
169.254.0.0/16 dev wlan0 
192.168.1.0/24 dev eth0  proto kernel src 192.168.1.119
192.168.1.0/24 dev wlan0  proto kernel src 192.168.1.142

Then I delete all the routes:

sudo route del default
sudo route del default
sudo route del -net 169.254.0.0/16 dev wlan0
sudo route del -net 192.168.1.0/24 dev eth0
sudo route del -net 192.168.1.0/24 dev wlan0

Then I have no routes:

kauer at kt:~$ ip route
kauer at kt:~$

But I still have addresses on my interfaces:

kauer at kt:~$ ifconfig | grep "inet addr" | cut -d: -f2 | cut -d\  -f1
192.168.1.119
127.0.0.1
192.168.1.142

Regards, K.

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Karl Auer (kauer at biplane.com.au)
http://www.biplane.com.au/kauer
http://twitter.com/kauer389

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