Monitoring of Internet connection

[VirginSnow at vfemail.net]

> Date: Wed, 6 Jun 2007 22:10:36 -0400
> From: "Ben Scott" <dragonhawk at gmail.com>

>   I'm looking to monitor the reliability of our Internet connection at
> $DAYJOB, from the inside out.  I'm familiar (in concept at least) with
> monitoring a bunch of hosts and services with a tool like Nagios, but
> here I'm only looking to monitor one link, and closely.
> 
>   I could just run ping in a screen(1) session, of course.  Indeed,
> that's what I'm often doing now.  But I'm thinking a more
> sophisticated approach is possible, and could yield more informative
> results.

You know me; I'd probably script something around ping -c $c -n $n -p
$randomstuff and wget in bash.

>   (Aside: Fellow IT geeks may be interested in the failure mode.  My
> local gateway (Linux box) is not getting an ARP reply for the peer
> gateway.  With a sniffer, I see our gateway sending ARP queries, but
> never an ARP response from the peer.  But I see the peer's ARP and our

Do you know if there's a switch between your gateway and the next
router?  Maybe someone on your WAN decided to use the same MAC as your
gateway, and you only see problems when they turn on their equipment
and sit there scratching their head.  Are you getting *all* the
TCP/UDP responses you should, or just a portion of them?  (I'd suspect
the latter.)  Remember ARP requests/responses can also be lost due to
collisions.  Have you tried decreasing your ARP reply timeout?  It
might also help to know what OS the peer router is running.  Have you
nmapped it yet?