Insufficient bandwidth or ISP connection lost?

This question has puzzled me for years but now I must provide an answer.

I am using ping to google dns [] from the router to know if the ISP has lost connection.

I notice ping loss occurs in both conditions:

  1. ISP connection is lost.
  2. The ISP bandwidth is insufficient [say 100 users connected on a 50 Mbps connection].

Is there a way to differentiate?
I can use tools like tcpdump etc if it is required.

Please help me out. is intended to be a DNS server. It is not a good way to test your connection as it often doesn't answer every ping.

To test your physical link to the ISP, use traceroute to find the IP of the ISP's first router on the other end of your line and ping that. Those routers are usually configured to answer pings.

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In my experience (and for my instance of it is pretty robust and reliable. I would just complement it with say and maybe and take all three going missing as indication of link loss.

That with fair sharing leaves 50/100 = 0.5 Mbps, which should well be enough for ICMP echo requests...

But the ping loss to all those IPs can also occur because I am trying to exceed the bandwidth committed by the ISP [see my example in the original post: 100 users, 50 Mbps].
How do I differentiate it from the ISP "outage"?


from SSH
ip r
you will get something similar to
default via A.B.C.D dev eth1 proto dhcp metric 100
so, the A.B.C.D is gateway addres, it is first hop, first node, first ... call it as you want, of your ISP
if you could ping A.B.C.D then your WAN interface is UP and your ISP is reachable