[lwip-devel] [bug #21107] LwIP doesn't reset the TTL in ICMP Echo Replies

[Simon Goldschmidt]

Follow-up Comment #4, bug #21107 (project lwip):

> If I don't do any mistake, this problem is already fixed by Jonathan...

Is it? From reading the code, ICMP_TTL is passed to ip_output_if, but is not
used there, since it is only used if 'dest != IP_HDRINCL', and dest _is_
IP_HDRINCL in this case! In my opinion, the header must be completely filled
in icmp_input(), so the patch in buf #19580 in fact didn't fix the problem...
Or am I wrong?

> Oops, typo. I meant "Recalculate the IP Checksum".

Ah, OK. It's right that icmp_input() has to calculate the checksum, if
ip_output_if is called with dest == IP_HDRINCL, the checksum isn't
re-calculated! But the checksum can still be adjusted (which is much faster),
instead of being completely recalculated!

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