Large RTT or Why doesn't my ping traffic get discarded?
Jason Iannone
jason.iannone at gmail.com
Thu Dec 22 12:35:43 UTC 2022
Thanks for engaging with this. I was intentionally brief in my explanation.
I have observed this behavior in congested networks for years and ignored
it as an obvious symptom of the congestion. What has always piqued my
curiosity though is just how long a ping can last.
In my case yesterday, I was at the airport at peak holiday travel and free
wifi usage time. I expect a bad experience. I don't expect a ping to return
5 seconds after originating it. I just imagine the network straining and
groaning to get my ping back to me. It's okay, man. Let it go.
On Thu, Dec 22, 2022 at 5:22 AM Masataka Ohta <
mohta at necom830.hpcl.titech.ac.jp> wrote:
> Jerry Cloe wrote:
>
> > Because there is no standard for discarding "old" traffic, only
> > discard is for packets that hop too many times. There is, however, a
> > standard for decrementing TTL by 1 if a packet sits on a device for
> > more than 1000ms, and of course we all know what happens when TTL
> > hits zero. Based on that, your packet could have floated around for
> > another 53 seconds.
>
> Totally wrong as the standard says TTL MUST be decremented at least
> by one on every hop and TTL MAY NOT be decremented further as is
> specified by the standard of IPv4 router requirements (rfc1812):
>
> When a router forwards a packet, it MUST reduce the TTL by at least
> one. If it holds a packet for more than one second, it MAY decrement
> the TTL by one for each second.
>
> As for IPv6,
>
> Unlike IPv4, IPv6 nodes are not required to enforce maximum packet
> lifetime. That is the reason the IPv4 "Time to Live" field was
> renamed "Hop Limit" in IPv6. In practice, very few, if any, IPv4
> implementations conform to the requirement that they limit packet
> lifetime, so this is not a change in practice.
>
> Masataka Ohta
>
>
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