Large RTT or Why doesn't my ping traffic get discarded?

Wed Dec 21 17:28:29 UTC 2022

Keep in mind that ping reports round trip time, so there could be a device delaying the ping reply on the return trip. In these cases, it helps to have a traceroute from both ends, to detect asymmetrical routing and possibly return path congestion invisible in a traceroute from you end.
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From: NANOG <nanog-bounces+mel=beckman.org at nanog.org> on behalf of Mel Beckman <mel at beckman.org>
Sent: Wednesday, December 21, 2022 9:22 AM
To: Jason Iannone <jason.iannone at gmail.com>; North American Network Operators' Group <nanog at nanog.org>
Subject: Re: Large RTT or Why doesn't my ping traffic get discarded?

Sometimes this is usually due to high CPU time on the target device. If the device is under heavy load, the ICMP Echo process gets lowest priority. With a well-known name server like 4.2.2.2, this seems unlikely. It could be an intermediate hop or a routing loop, Do a traceroute to get more detailed per-hop statistics.

 -mel
________________________________
From: NANOG <nanog-bounces+mel=beckman.org at nanog.org> on behalf of Jason Iannone <jason.iannone at gmail.com>
Sent: Wednesday, December 21, 2022 9:10 AM
To: North American Network Operators' Group <nanog at nanog.org>
Subject: Large RTT or Why doesn't my ping traffic get discarded?

Here's a question I haven't bothered to ask until now. Can someone please help me understand why I receive a ping reply after almost 5 seconds? As I understand it, buffers in SP gear are generally 100ms. According to my math this round trip should have been discarded around the 1 second mark, even in a long path. Maybe I should buy a lottery ticket. I don't get it. What is happening here?

Jason

64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=392 ttl=54 time=4834.737 ms
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=393 ttl=54 time=4301.243 ms
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=394 ttl=54 time=3300.328 ms
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=396 ttl=54 time=1289.723 ms
Request timeout for icmp_seq 400
Request timeout for icmp_seq 401
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=398 ttl=54 time=4915.096 ms
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=399 ttl=54 time=4310.575 ms
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=400 ttl=54 time=4196.075 ms
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=401 ttl=54 time=4287.048 ms
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=403 ttl=54 time=2280.466 ms
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=404 ttl=54 time=1279.348 ms
64 bytes from 4.2.2.2<http://4.2.2.2>: icmp_seq=405 ttl=54 time=276.669 ms
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