/64 or /124,/126,/127,/128 addresses?

[Alain Durand]

I would like to make some comments on this issue
from my 6bone experience with tunnels.

1) There is an interroperability issue now on the way people are doing
tunnels (which are by essence Point ot Point links).
Some implementations can use /128 addresses, end-point addresses may be taken
from any address spaces.
Some implementations do not allow anything longer that /127,
thus there is a technical need to number the tunnel with a /124,
/126 or /127 network.

2) If the tunnel need a network number, the question is now in which address
space this network is taken from? If it's a tunnel between an ISP and a
site,it's not a serious matter, if it's a tunnel between two ISPs,
then it's an issue: will this network be taken from address space A, B or
from a neutral "DMZ".
Taking addresses from the DMZ simplify renumbering (I buy Pedro's arguments)
but it's a real burden to delegate small chunk of this DMZ.
Using networks from address space A or B doens't help for renumbering
anymore than using /128 addresses.


3) In designing the G6 networks on the 6bone with pTLA & pNLAs, I have
dedicated a /64 network for all my ppp links, serial or tunnels.
This prooved very easy to extend to any number of links
If I had to use a /64 prefix for each tunnel, I will first waste a huge lot
of address space (maybe it's not an issue?) and, worse, to maintain
a good design in my addressing architecture, I will have to reserve a
large part of my site /48 prefix for the tunnels, a /52 or /56 prefix.
That's the reason why I like long prefixes, like /124 (easier to read
in hex. digits), and I even like /128 more!

4) Routers must be configured manually. We can not use stateless autoconf.
I found easier to number my routers starting from 1 than to build manually
an EUI64 for them. If ever one wants to reserve well known addresses,
I'd rather like to have 0x000 to 0xFFF reserved for manually configured
hosts and then from 0x1000 to, let's say 0x1FFF for well known addresses

5) If there a need of well known addresses for a point to point link?
Couldn't we say "well known addresses are reserved for non PtP links.

So my personal take is that /128 addresses for tunnels are the simplest
thing to use.

	- Alain.