On Mar 16, 2011, at 2:04 AM, <[email protected]> <[email protected]> wrote:
> This reminds me of a related concept, using the TTL really as 'Time To Live'
> (in today's IP, it's more of a 'Remaining Hop Count). According to RfC 791, a
> router that buffers a packet by n seconds must decrease its TTL by n. I doubt
> that many routers implement this properly.
There is, of course, a fundamental bug in that, noted in RFC 970.
RFC 1812, which I edited, contains this text (that I didn't write):
In this specification, we have reluctantly decided to follow the
strong belief among the router vendors that the time limit
function should be optional. They argued that implementation of
the time limit function is difficult enough that it is currently
not generally done. They further pointed to the lack of
documented cases where this shortcut has caused TCP to corrupt
data (of course, we would expect the problems created to be rare
and difficult to reproduce, so the lack of documented cases
provides little reassurance that there haven't been a number of
undocumented cases).
The corresponding field in IPv6 (RFC 2460) picks up this bit of wisdom:
Hop Limit 8-bit unsigned integer. Decremented by 1 by
each node that forwards the packet. The packet
is discarded if Hop Limit is decremented to
zero.
I think that you will find that every router implements the hop limit properly,
and implements the TTL as modified by RFC 1812 properly.
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