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

Another perl thing:

$return = (split(" ", `ip route | grep default`))[2];<br>

Note: use these backticks before ip and after default

Answer 2

#!/bin/bash

##################################################################3
# Alex Lucard
# June 13 2013
#
# Get the gateway IP address from the router and store it in the variable $gatewayIP
# Get the Router mac address and store it in the variable gatewayRouter
# Store your routers mac address in the variable homeRouterMacAddress
#

# If you need the gateway IP uncomment the next line to get the gateway address and store it in the variable gateWayIP
# gatewayIP=`sudo route -n | awk '/^0.0.0.0/ {print $2}'` 

homeRouterMacAddress="20:aa:4b:8d:cb:7e" # Store my home routers mac address in homeRouterMac.
gatewayRouter=`/usr/sbin/arp -a`

# This if statement will search your gateway router for the mac address you have in the variable homeRouterMacAddress
if `echo ${gatewayRouter} | grep "${homeRouterMacAddress}" 1>/dev/null 2>&1`
then
  echo "You are home"
else
  echo "You are away"
fi

Answer 3

use command below:

route -n | grep '^0\.0\.\0\.0[ \t]\+[1-9][0-9]*\.[1-9][0-9]*\.[1-9][0-9]*\.[1-9][0-9]*[ \t]\+0\.0\.0\.0[ \t]\+[^ \t]*G[^ \t]*[ \t]' | awk '{print $2}'

Answer 4

The following command returns the default route gateway IP on a Linux host using only bash and awk:

printf "%d.%d.%d.%d" $(awk '$2 == 00000000 && $7 == 00000000 { for (i = 8; i >= 2; i=i-2) { print "0x" substr($3, i-1, 2) } }' /proc/net/route)

This should even work if you have more than one default gateway as long as their metrics are different (and they should be..).

Answer 5

If you know that 0.0.0.0 is your expected output, and will be at the beginning of the line, you could use the following in your script:

IP=`netstat -rn | grep -e '^0\.0\.0\.0' | cut -d' ' -f2`

then reference the variable ${IP}.

It would be better to use awk instead of cut here... i.e.:

IP=`netstat -rn | grep -e '^0\.0\.0\.0' | awk '{print $2}'`

Answer 6

For a list of all default gateways, use mezgani's answer, duplicated (and slightly simplified) here:

/sbin/ip route | awk '/^default/ { print $3 }'

If you have multiple network interfaces configured simultaneously, this will print multiple gateways. If you want to select a single known network interface by name (e.g. eth1), simply search for that in addition to filtering for the ^default lines:

/sbin/ip route |grep '^default' | awk '/eth1/ {print $3}'

You can make a script that takes a single network-interface name as an argument and prints the associated gateway:

#!/bin/bash
if [[ $# -ne 1 ]]; then
    echo "ERROR: must specify network interface name!" >&2
    exit 1
fi
# The third argument of the 'default' line associated with the specified
# network interface is the Gateway.
# By default, awk does not set the exit-code to a nonzero status if a
# specified search string is not found, so we must do so manually.
/sbin/ip route | grep '^default' | awk "/$1/ {print \$3; found=1} END{exit !found}"

As noted in the comments, this has the advantage of setting a sensible exit-code, which may be useful in a broader programmatic context.