icmp problem

Danil V. Gerun news at 625.ru
Thu May 12 23:03:11 PDT 2005


Another possible solution came to my mind this morning :)
ICMP doesn't have ports like TCP and UDP do, but it does have the
contents of the ICMP packets ;)

What if the contents of the ICMP Echo Request, sent by the gateway to
the Internet, is for example equal to:
SHA1 (  original private src_ip + some (constant) garbage  )
It can be used like a NAT "port-table" by a "special" ping utility:
the real "private" sender gets all expected ICMP Replies.

Such ping utility might be found or created.
It would work with natd or with Netgraph (or with both :) ).

AW> I would guess, that ICMP packets do not have a port number (just a
AW> request/response id), so that the NAT cannot distinguish multiple
AW> ICMP packet sources (I mean: The response from the ICMP requestee
AW> cannot be mapped back to the appropriate ICMP requester).

AW> Hmm... I just think, that (if you have multiple ICMP requestees)
AW> the NAT could be able to map back the ICMP requester IP by the IP
AW> of the ICMP requestee. But I do not know, how your router works...

AW> Maybe your computer-pool could elect an ICMP-master, who
AW> coordinates all the ICMP traffic through the NAT.

AW> Bye
AW> Arne

Best regards, Danil V. Gerun.

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