How do i get the default gateway in LINUX given the destination?

Question

I\'m trying to get the default gateway, using the destination 0.0.0.0

I used this command: netstat -rn | grep 0.0.0.0

And it return

Answer 1

works on any linux:

route -n|grep "UG"|grep -v "UGH"|cut -f 10 -d " "

Answer 2

You can get the default gateway using ip command like this:

IP=$(/sbin/ip route | awk '/default/ { print $3 }')
echo $IP

Answer 3

This simple perl script will do it for you.

#!/usr/bin/perl

$ns = `netstat -nr`;

$ns =~ m/0.0.0.0\s+([0-9]+.[0-9]+.[0-9]+.[0-9]+)/g;

print $1

Basically, we run netstat, save it to $ns. Then find the line that starts off with 0.0.0.0. Then the parentheses in the regex saves everything inside it into $1. After that, simply print it out.

If it was called null-gw.pl, just run it on the command like:

perl null-gw.pl

or if you need it inside a bash expression:

echo $(perl null-gw.pl)

Good luck.

Answer 4

netstat -rn | grep 0.0.0.0 | awk '{print $2}' | grep -v "0.0.0.0"

Answer 5

To get the NIC name that it's the default gateway use this command:

netstat -rn | grep UG | awk '{print $8}'

Answer 6

The ip route command from the iproute2 package can select routes without needing to use awk/grep, etc to do the selection.

To select the default route (from possibly many)

$ ip -4 route show default  # use -6 instead of -4 for ipv6 selection.
default via 172.28.206.254 dev wlp0s20f3 proto dhcp metric 600

To select the next hop for a particular interface

$ ip -4 route list type unicast dev eth0 exact 0/0  # Exact specificity
default via 172.29.19.1 dev eth0

In the case of multiple default gateways, you can select which one gets chosen as the next-hop to a particular destination address.

$ ip route get $(dig +short google.com | tail -1)
173.194.34.134 via 172.28.206.254 dev wlan0  src 172.28.206.66 
    cache

You can then extract the value using sed/awk/grep, etc. Here is one example using bash's read builtin.

$ read _ _ gateway _ < <(ip route list match 0/0); echo "$gateway"
172.28.206.254