too many routes

Michael Dillon michael at
Thu Sep 11 20:01:45 UTC 1997

At 2:02 PM -0400 9/11/97, Jay R. Ashworth wrote:
>On Wed, Sep 10, 1997 at 09:11:55PM -0400, Sean M. Doran wrote:
>> Sanjay Dani <sanjay at> writes:
>> > There are backbone providers and there are providers of specialized
>> > ISP or hosting or security etc. services that need independent* IP
>> > address space and do not have to waste resources on building a private
>> > "backbone".
>> NAT.
>Perhaps I misunderstood Sanjay, Sean, but I believe his concern was
>that the addresses _not be the property of an upstream (ie: backbone)
>provider_ to provide flexibility of connection choice.
>NAT will not solve this problem; it resides at too low a level of the
>theoretical architecture, being used primarily to avoid renumbering of
>internetworks.  This isn't a network numbering problem, it's a routing

Please, let's think this through carefully before making such
pronouncements. If the problem to be solved is providing flexibility of
choice, then Sean is quite right and NAT (plus other renumbering
technologies) is the solution for most people. If you use NAT and
renumbering technologies then you don't give a darn what your IP address is
or who gave it to you as long as it is globally routable. You still have
flexibility of choice in that you can switch upstream providers on a whim
and use Paul Vixie's BSD tricks to multihome if that matters.

NAT may not be the solution to every problem but it certainly does provide
flexibility of choice which is one of the reasons many companies use it

You can't give everyone globally routable and portable address space on the
Internet. To do so would be tantamount to making everyone equal and
flattening the hierarchy of the network. But this creates an unmanageble
mess in which the network becomes a sort of amorphous blob with no
discernable internal structure like some sort of slime mode. What we are
trying to do is evolve the network into an organism that is strong and
resilient. This requires that the network have discernable internal
structure and that requires hierarchy and layering and a thick skin to
protect the organism from the outside world. Hierarchy means that some
addresses are better than others, i.e. portable, but it also allows us to
carve the network up into manageable pieces and then to manage it in a
reasonably stable and reliable way.

Routing problems involve how to design, manage and operate this internal
traffic distribution hierarchy and are essentially engineering problems,
not policy problems or social problems. I think that the desire for
portable address space is not a routing problem.

Michael Dillon                    voice: +1-650-482-2840
Senior Systems Architect            fax: +1-650-482-2844

"The People You Know.  The People You Trust."

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