Ping maximum delay is so high

[s76602061]

When ping time is around 10, maximum delay time is almost same as average but when ping time is around 10,000, maximum delay time is 88 ms even though average is 1 ms like below. Could you tell me what is the reason for this?

Success rate is 100 percent (10000/10000), round-trip min/avg/max = 1/1/88 ms

[pwwiddicombe]

10,000 for a ping time is pretty severe - you have periodic heavy congestion on a WAN link, presumably?  If it's LAN, then you probably have links flapping or periodic outages.

Now, frequently the FIRST ping will be longer, as the path endpoints are being discovered - don't worry about that.

[devils_advocate]

I think 10000 is the amount of ICMP packets sent, not the round trip time.

I suspect he is asking why the average shows 1ms when sending 10k packets yet the maximum is 88ms.

[devils_advocate]

It depends on how many packets had a round trip time (RTT) above 1ms.

Say you sent 10 ICMP packets and the round trip time of them all was 1ms.

1+1+1+1+1+1+1+1+1+1 = 10
10/10 = 1 
The average would be 1ms.

Say you sent 10 ICMP packets and the round trip time of all of them was 1ms but one was 88ms.

1+1+1+1+1+1+1+1+1+88  = 97
97/10 = 9.7
The average should be 9.7ms

Sending 10000 ICMP packets follows the same logic but as the number to divide by is larger, it will depend on how many packets were above 1ms.

If 9999 packets were 1ms and only a single packet was 88ms, then the average would still be 1ms.

Getting a higher RTT for a single packet when sending a small number of packets will give a bigger average then sending a large number of packets. 

I think....hopefully my maths is right on this one :)

[s76602061]

thank you, I would like to know why maximum delay is suddenly up to 88 ms even though between connect LAN segment when ping times is too many (around 10,000 times). 

[Joseph W. Doherty]

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Posting

Lots of possible reasons.

There could have been transient congestion or the ping target is just slow to respond.  Understand, ping was intended to help verify a destination is "alive", not as a high precision network latency test tool.  Hosts may treat ping reply priority with low priority (inflating the RTT).

BTW, that's also why IP SLA often has destinations configured to support increased RTT accuracy.

[s76602061]

Thanks! I will consider to check latency by IP SLA.