pinging same host on the internet from two different LAN stations

[Karl O. Pinc]

On 07/28/2005 04:37:38 AM, Daniel Hartmeier wrote:

> Assuming Windows ping is not doing that, you'll have to provide an
> alternative way to decide which client to send replies to. There's
> ICMP
> sequence numbers, but they can and will overlap for concurrent ping
> invokations. The ICMP echo reply quotes the ICMP payload of the query.
> But most ping tools will use a constant payload, so that's no
> distinguishing criterion. The NAT device could tamper with the payload
> and insert its own ID there, but that's modifying the packet in an
> intrusive and unexpected way.
> 
> I'm curious how any NAT device would do that correctly without relying
> on unique/random ICMP ids.

I cannot speak to how anything is implemented anywhere, but it seems to
me that the NAT device could substitute it's own ICMP ID,
which it saves in a state table associated with the sending
IP.  When the ICMP reply returns it would then put the original
ICMP id back.  This scheme swaps ICMP IDs in a fashion analogous
to the swapping of ports in TCP/UDP NAT port mapping.

I imagine this would require another kind of pf translation
declaration.

Regards,

Karl <kop at meme.com>
Free Software:  "You don't pay back, you pay forward."
                  -- Robert A. Heinlein

P.S.  I remain anxious to hear whether I'd be wasting
my time pursuing inbound traffic bandwidth management.
The thread is:
http://marc.theaimsgroup.com/?t=112139406900001&r=1&w=2