Garrett Wollman writes:
> > When the program is run, if you ping the IP address from the
> > local machine, it sees packets. However, if you ping it from
> > a remote machine, it doesn't see packets.
>
> The ICMP never passes certain packets up to raw listeners. These
> include ECHO REQUEST, TIMESTAMP REQUEST, and SUBNET MASK REQUEST
> packets -- but not the corresponding replies! So, when you ping the
> local machine, you will see the ECHO REPLY packets on all raw
> listners, but not the initial ECHO REQUESTs. When you ping from a
> remote machine, you never see the ECHO REQUEST packets because the
> kernel takes care of them, and you never see the ECHO REPLY packets
> because they are addressed to the other machine.
Is this a FreeBSD-specific thing, or to other UNIX's have this
same peculiar behavior?
> It would be possible to pass all ICMP packets to the raw listeners,
> but it would require rewriting parts of icmp_input() (which would not
> be a bad idea) either to avoid modifying the packet in-place or to
> keep a copy of the original before responding -- either of which would
> slow down `ping' processing.
The existence of m_dup() makes the latter option a lot easier..
-Archie
___________________________________________________________________________
Archie Cobbs * Whistle Communications, Inc. * http://www.whistle.com
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