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To: joerg_wunsch@uriah.heep.sax.de
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Subject: Re: I seriously need some networking help
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Date: Sat, 13 Dec 1997 19:01:49 +0100
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> > What IP does it use?  If it uses the private one, you lose.  This does
> > break things like PMTU-D.
> 
> It doesn't, even if the IP source address is 10.*.  As long as the
> ICMP packet has the correct recipient address, it will arrive, and the
> (original) sender takes the appropriate actions -- it couldn't verify
> the validity of the ICMP packet's sender address anyway, be it 10.* or
> anything else.

No, in many cases packets with RFC 1918 source addresses will *not*
arrive - because they are blocked by packet filters meant to prevent
IP address forgery. I know for a fact that UNINETT (AS 224) blocks
such packets at its border routers.

Using RFC 1918 addresses for router links on the Internet is *not* a
good idea.

Steinar Haug, Nethelp consulting, sthaug@nethelp.no