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List:       nanog
Subject:    Re: Large RTT or Why doesn't my ping traffic get discarded?
From:       Jason Iannone <jason.iannone () gmail ! com>
Date:       2022-12-22 12:35:43
Message-ID: CAGL1wDSPCOWdDUKK1mxMn1kKkrJnm8GhdXKp_9FE4eQs41nkSQ () mail ! gmail ! com
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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@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
>
>

[Attachment #3 (text/html)]

<div dir="ltr"><div>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.</div><div><br></div><div>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&#39;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&#39;s okay, man. Let it go.<br></div></div><br><div \
class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Dec 22, 2022 at 5:22 AM \
Masataka Ohta &lt;<a \
href="mailto:mohta@necom830.hpcl.titech.ac.jp">mohta@necom830.hpcl.titech.ac.jp</a>&gt; \
wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px \
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Jerry Cloe wrote:<br> \
<br> &gt; Because there is no standard for discarding &quot;old&quot; traffic, \
only<br> &gt; discard is for packets that hop too many times. There is, however, \
a<br> &gt; standard for decrementing TTL by 1 if a packet sits on a device for<br>
&gt; more than 1000ms, and of course we all know what happens when TTL<br>
  &gt; hits zero. Based on that, your packet could have floated around for<br>
  &gt; another 53 seconds.<br>
<br>
Totally wrong as the standard says TTL MUST be decremented at least<br>
by one on every hop and TTL MAY NOT be decremented further as is<br>
specified by the standard of IPv4 router requirements (rfc1812):<br>
<br>
      When a router forwards a packet, it MUST reduce the TTL by at least<br>
      one.   If it holds a packet for more than one second, it MAY decrement<br>
      the TTL by one for each second.<br>
<br>
As for IPv6,<br>
<br>
      Unlike IPv4, IPv6 nodes are not required to enforce maximum packet<br>
      lifetime.   That is the reason the IPv4 &quot;Time to Live&quot; field was<br>
      renamed &quot;Hop Limit&quot; in IPv6.   In practice, very few, if any, \
                IPv4<br>
      implementations conform to the requirement that they limit packet<br>
      lifetime, so this is not a change in practice.<br>
<br>
                                                                        Masataka \
Ohta<br> <br>
</blockquote></div>



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