On Fri, Jun 22, 2007 at 11:47:11AM +0100, Ian O'Connell wrote:
> >> desk to a network engineer i was informed that ping times and
> >> latency are entirely unrelated....
> >
> >Guess what, they were right.
> So ping isn't a tool for determining network latency then?
>
Actually - much as I *hate* to agree with Paul, he's right !
ping is a tool for measuring the length of time it takes for an ICMP
echo request to elicit an ICMP echo response and for that response to
return to your machine.
It can be used as a tool to test end-to-end connictivity of a link, to
test that ICMP packets can make their way across the IP network. However
ICMP is a very different protocol to TCP (and indeed UDP and other
protocols which function over the IP layer).
So, while ping _can_ tell you that there is a functioning network in
place, and indeed that end-to-end connectivity exists for ICMP packets,
and even how long the return path for ICMP packets is. It cannot be
considered a useful measure of latency on the link, as ICMP may (or
indeed may not) be subject to the same QoS restrictions as other
traffic.
P
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