Re: [monit] Monitor network connection

[KevinF]

Emil Natan wrote:
> 
> On Wed, Mar 11, 2009 at 7:30 AM, Gilad Benjamini
> <address@hidden>wrote:
> Check connectivity to you gateway using ip address, check protocol dns to
> you dns server ...
> 

How might you do this if you don't know the gateway ahead of time?

I have a script that I run on a scheduled basis.  The idea is that I always
want to use my preferred interface, but when that is not possible, I have a
fall back interface to use.  If the preferred is working, I want the
fallback to turn off, if its not working, I want the fallback to come up. 
Since I am using monit to monitor the local (same box) DHCP and DNS
(non-authoritative) servers, I would like to somehow get this into monit.

The biggest problem is that this device is portable, and I never know what
network it will get plugged into.  The interface is designed to use DHCP
itself, so I will not know ahead of time what the gateway address is.  Once
we set this up, and connect our equipment, since there won't always be an IT
Engineer around, I don't want to then have to configure the monitoring... I
want it to "just work".

Here is the script I am using now:

<code>
#!/usr/bin/env bash

PREFINT=eth0
FAILINT=wlan0

GW=$(route -n | awk -v iface=$PREFINT '($4~/G/) && ($8~iface) {print $2}')
PREFADDR=$(ifconfig $PREFINT | awk '/inet addr/ {print $2}' | awk -F':'
'{print $2}')
FAILADDR=$(ifconfig $FAILINT | awk '/inet addr/ {print $2}' | awk -F':'
'{print $2}')

if [ ! -z $GW ];then
  ping -c 4 -w 2 -I $PREFINT -i 0.25 $GW > /dev/null
  if [ $? == 0 ]; then
    if [ ! -z $FAILADDR ];then
      ifdown $FAILINT
    fi
    exit 0
  fi
fi

if [ -z $FAILADDR ];then
  ifup $FAILINT
  ifdown $PREFINT && ifup $PREFINT
fi
</code>
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