/127 between routers?

[Xavier Beaudouin]

Hi there,

Since I am the one that started this thread, I wanted to clarify why I am
asking that.

First, I wanted to quote Mark :

On Sat, 9 Jan 2010 12:51:28 +1030, Mark Smith

[...]

> What do they say? "Those who ignore history are doomed to repeat it."
> 
> Sometimes you need to make design decisions based on not so much the
> likelyhood of an event happening, but what the consequences are if it
> does. So you're probably right, a "hard classful" addressing structure
> in 128 or 256 bit IPv6 addresses probably wouldn't encounter any future
> issues - but dealing with the consequences if it does are likely to be
> near impossible. It's better to be safe than sorry.

I agree with Mark, we have for now "plenty" of address space, but really,
I don't want to make same error than we all did on IPv4.

Even with a /40 or /48 (that I have for my non profit organization), we
have lots of space, the core network I currently use has lots of point to
point interconnections. On IPv4, we can do that with /30 or even with Cisco
for example /31 (that, I assume very rare).

Now all my routing stuff is done by software, not for the cost, but for
the flexibility and also to provide my organization the possibility to give
some good stuff and be "vendor" free. Avoiding bug, race and so on (yeah
there is fscking bugs also on free/opensource solution I agree !).

Now with a single /48, we can have 65535 /64.
This is quite large... I know, but using a /64 for only 2 ip address, is,
I think a big waste of ressources...

I agree also that some TCAM / Hardware don't like prefix > /64. I noticed
that. So if I will use some hardware vendor thing, I will use /64 in case
to avoid software routing (in this case, I can be LIR, so a /32 will be
given to me).

Also use /127 or /126 between routers, is a good responsibility for all
IPv6 operators. Avoiding asking for to much prefixes in RIPE/ARIN/... is a
good way to be a good citizen...

To get some conclusion within this thread :

- if you use hardware that route that (switch/router): a /64 should be
used and will get good performance
- if you use software routers, you can use whatever you want : /64, /112,
/120, /126 and sometime /127 (but not recommended on Ethernet)
- if you use loopback, you can use /64 or /128 (depending if you use
hardware or software routers)
- if you need RA, you *have to* use /64

Anyway thank you everyone for your replies and your hints.

Sincerely,
Xavier

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