Large RTT or Why doesn't my ping traffic get discarded?
mohta at necom830.hpcl.titech.ac.jp
Thu Dec 22 11:19:27 UTC 2022
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.
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