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List:       linux-net
Subject:    Re: Routing problems etc.
From:       Keith Owens <kaos () ocs ! com ! au>
Date:       1999-08-29 3:08:55
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On Sat, 28 Aug 1999 19:47:28 -0700 (PDT), 
Martin Krzywinski <martink@physics.ubc.ca> wrote:
>  host on internet  ------ ISP ------- ISDN router --- host B
>
>No host on inet can connect to B: no route can be found. B can connect to
>internet, no problem. If B telnets to an external host, then this host
>can see B, but not otherwise. This happens even if B is the router. That
>is, no host on inet can see the router, unless communication from behind
>the router has already been initiated.

Sounds like the ISP is running masq, NAT or similar mapping of internal
addresses to external addresses.  With those setups, an internal host
is invisible unless it starts the connection, starting the connection
from inside adds an entry to the mapping table at the ISP.  No map
means the outside cannot see you.

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