moving to IPv6

Sat Nov 1 19:19:59 UTC 1997

I apologize that the quality of this message will be
somewhat limited by pressures of time and having to use a
really weird Microsoft keyboard that leaves me prone to
speeling mistakes, but I couldn't resist some of the
things being talked about in this thread.

Phil Howard <phil at charon.milepost.com> writes:

> The transition to IPv6 is clearly going to have some difficulties.  We are
> waiting on:
> 
> 1.  Network equipment, with translation
> translation 
> have to have translations
> routing software includes translation 

Bingo!

The thing that amazes me about people who are fans of IPv6
is that they have realized that NAT is THE fundamental
scaling technology for the Internet.

Translation of addresses, whether it is between IPv4 and
IPv4 or involves protocol translations as well (as is the
case in IPv4->IPv6->IPv4, or IPv6->IPv4->IPv6), is simply
the most practical and effective way of overcoming the two
principal scaling problems of the Internet, namely the
narrowness of the IPv4 address and the fact that deployed
routing protocols simply suck.

Observe that so long as a translatable subset of transport
layer options are used, there is absolutely no difference
between NAT between IPv4 addresses and protocol
translation between IPv4 and IPv6.   Moreover, in the
latter case, you are not restricted to IPv6s4 (who comes
up with these acronyms anyway?  Does anyone mind if I call
IPv4 IP?  If you do, well, tough.)

The technical goal is that end to end services will work,
period, in all cases.  This is possible provided that the
higher order protocols do not make invalid assumptions
about the transport layer.  Most importantly, just as CIDR
requires that protocol implementations respect that IP
addresses may change over time, NAT as THE new fundamental
scaling technology requires that protocol implementations
respect that IP addresses may change over space as well.

That is, so long as protocols do not assume that an IP
address is the same from the point of view of all
locations throughout the concatenated Internet, they will
do just fine with either NAT or protocol translation or
both.

Returning to the observation that NAT and protocol
translation are semantically equivalent from an end-to-end
perspective, we now need to consider whether simple
address translation or protocol translation is a better
idea.

> But just having [network routing software] translating IPv4 <-> IPv6s4 is not enough.
> We will need to manage the new IPv6 network. 

Deployed base is a strong engineering consderation in an
industry which is experiencing enormous growth.  NAT has
the advantage that reasonably designed existing
technologies ought not even notice that NAT is happening.

Protocol translation, on the other hand, requires, as you
say, new management techniques, which will generally
involve lots of learning time on the part of lots of
engineers and operators, wherever the new protocol is
deployed.

The fact is, that there may be a reason to deploy a new
protocol that makes this worthwhile, however, you should
also note that so long as a translation between transport
layers is straightforward, there is no reason why the new
protocol needs to be IPv6.

In fact, I welcome IPv6's fan base working on protocol
translation because there are also some more interesting
experimental protocols which could be deployed in
precisely the same fashion that do not suffer some of the
brokenesses of IPv6.  Most notably:

> Routing issues will become different in IPv6.

This is simply untrue.  Routing issues are EXACTLY the
same in IP and IPv6, the only difference is the width of
the addresses, which worsens the poor scaling properties
of IP with current routing protocols. 

The only attractive (and this is very very very
speculative) aspect of the IPv6 address scheme is that it
may be wide enough to experiment with something like using
a modified IS-IS that works on multiple hierarchical areas
encoded as fields in the IPv6 address, with the thought of
using that to supplant current interdomain routing
protocols.  I'm sure this thought will go over well with
the IPv6 crowd...

> If IPv6 allocations will have varying sizes like CIDR, then we might
> continue to have issues of size based route filtering.  

Please understand that the size-based filtering is done to
limit the number of prefixes carried, and that this is
completely independent of IP vs IPv6.  If the number of
prefixes must be kept to some maximum by filtering at,
say, the 19 bit mark, the same maximum will be maintained
even if the address space is much wider, and the
straightforward way of doing that is to retain filters at
the 19 bit mark.

> OTOH, with the
> right methods of allocating IPv6 space, no one should ever have to come
> back to get more space.  Eventually that should mean fewer routes as
> IPv4/IPv6s4 closes down.  Route filtering should be encouraged on IPv4
> space and prohibited on IPv6 space, at that point, IMHO.

Could you pleace elaborate?  I am completely lost by your
logic here.

	Sean.