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Re: tlug: HAN IP addresses

tlug note from (John Little)
% How did you decide on local IP addresses? Is it possible that
% you could make a naming mistake that would adversly affect your
% ISP?


   There's an RFC on ranges of IP addresses for "private", non-internet
   connected addresses (see below), and I use an address within this
   range for my home network.

   This, of course, could confuse things even more than before (there
   could be hundreds of other people using your "private" address
   range instead of perhaps just one corporation using a non-private,
   legitimate IP range which you just happen to have picked on).

   The key is to prevent RIP packets from leaving your local network,
   so you need a gateway machine (the machine which is actually
   connected to your service provider) set up with two interfaces, IP
   forwarding turned off and outgoing RIP packets disabled. This
   ensures that your gateway machine is the only system visible to the
   ISP, but also allows you to have it connected to your home network.

   I have to admit to heresy here, in that my gateway machine is 
   running Solaris. Turning off IP forwarding is a single line in
   the /etc/inetinit file:-

		ndd -set /dev/ip ip_forwarding 0

   and preventing RIP packets getting out is a matter of creating an
   /etc/gateways file specifying:-

		noripout ipdptp0

   (no RIP packets to be sent on the point-to-point interface). This
   works fine for me. 



3. Private Address Space

   The Internet Assigned Numbers Authority (IANA) has reserved the
   following three blocks of the IP address space for private networks:        -      -     -

   We will refer to the first block as "24-bit block", the second as
   "20-bit block, and to the third as "16-bit" block.  Note that the
   first block is nothing but a single class A network number, while the
   second block is a set of 16 contiguous class B network numbers, and
   third block is a set of 255 contiguous class C network numbers.

   An enterprise that decides to use IP addresses out of the address
   space defined in this document can do so without any coordination
   with IANA or an Internet registry.  The address space can thus be
   used by many enterprises.  Addresses within this private address
   space will only be unique within the enterprise.

   As before, any enterprise that needs globally unique address space is
   required to obtain such addresses from an Internet registry.  An
   enterprise that requests IP addresses for its external connectivity
   will never be assigned addresses from the blocks defined above.

   In order to use private address space, an enterprise needs to
   determine which hosts do not need to have network layer connectivity
   outside the enterprise in the foreseeable future.  Such hosts will be
   called private hosts, and will use the private address space defined
   above.  Private hosts can communicate with all other hosts inside the
   enterprise, both public and private.  However, they cannot have IP
   connectivity to any external host.  While not having external network


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