Subject: Prefix longer than /64

From: Mattias Webjörn Eriksson <[email-masked]>
Date: Mon, 14 Aug 2006 00:35:08 +0200 (CEST)

This might have been brought up and answered before,
my appologies.

It is possible to assign an address with a prefix longer than /64 to an 
interface, for instance 2001:16d8:ff97:4::1:2/112.

But, rfc4291 section 2.5.4 Global Unicast Addresses, states:

"All Global Unicast addresses other than those that start with binary 000 
have a 64-bit interface ID field (i.e., n + m = 64), formatted as 
described in Section 2.5.1. Global Unicast addresses that start with 
binary 000 have no such constraint on the size or structure of the 
interface ID field."

...Which means that a prefix longer than /64 is not valid.

rfc3627 suggests that one should use avoid using a prefix longer than /64,
meaning that it is "somewhat not invalid".

It seems to be some deployments with router link subnets with
prefixes longer than /64. 
(http://www.huque.com/~shuque/doc/penn-ipv6-plan.html).

Could someone enlighten me here, please?

Best regards
Mattias Webjorn Eriksson

--------------------------------------------------------------------
IETF IPv6 working group mailing list
[email-masked]
Administrative Requests: https://www1.ietf.org/mailman/listinfo/ipv6
--------------------------------------------------------------------

---

From: Jeroen Massar <[email-masked]>
Date: Mon, 14 Aug 2006 09:50:52 +0200

> interface, for instance 2001:16d8:ff97:4::1:2/112.

You can but then auto-configuration doesn't work any more.

The other question is why would you? that /64 is part of a /48 which is
assigned to you. That means you have 65536 /64's. Is that not enough?

Greets,
 Jeroen

---

From: Mattias Webjörn Eriksson <[email-masked]>
Date: Mon, 14 Aug 2006 11:46:39 +0200 (CEST)

> assigned to you. That means you have 65536 /64's. Is that not enough?

It certanly is enough.

But my question is about whether a prefix longer than /64 is valid 
according to the rfc:s, nothing else.

 	Med vänliga hälsningar/Best regards

 	Mattias W E

---

From: [email-masked]
Date: Mon, 14 Aug 2006 13:52:47 +0000

the RFC's are not consistent here.  certainly a /112 is valid.

--bill

---

From: "Templin, Fred L" <[email-masked]>
Date: Mon, 14 Aug 2006 08:48:09 -0700

I have come to consider an individual address as a /128 prefix,
which I have come to call a "fully-qualified prefix". I don't
know about other prefix lengths between /64 and /128, however.

Fred
[email-masked]  

-----Original Message-----
From: Mattias Webjörn Eriksson [mailto:[email-masked]] 
Sent: Sunday, August 13, 2006 3:35 PM
To: [email-masked]
Subject: Prefix longer than /64

Best regards
Mattias Webjorn Eriksson

---

From: Mattias Webjörn Eriksson <[email-masked]>
Date: Tue, 15 Aug 2006 11:15:57 +0200 (CEST)

I have found that there is at least one informational
rfc describeing these king of prefixes:
rfc3627: Use of /127 Prefix Length Between Routers Considered Harmful.
If this rfc would be out of spec, then it would be needless (why is it 
there?).

Otherwise, I conclude that IPv6 is classfull, having two classes:
namely /64 and /128 (routing, though is classless).

I still think this is ambiguous (rfc:s might not be, but my interpretation 
however is).

         Med vänliga hälsningar/Best Regards

         Mattias W E

---

From: Havard Eidnes <[email-masked]>
Date: Tue, 15 Aug 2006 11:39:56 +0200 (CEST)

> If this rfc would be out of spec, then it would be needless (why is it 

The abstract of the quoted RFC is telling -- /127 is a special case:

   Under certain situations, this may lead to one router claiming both
   addresses due to subnet-router anycast being implemented.

The quoted document says (among other things) that /126 doesn't
have this problem.

In IPv4 you also seldom find /31 as a subnet mask, and it's not
classful for that reason...

> namely /64 and /128 (routing, though is classless).

I think that would be a false conclusion.

Regards,

- Håvard

---

From: Mark Smith <[email-masked]>
Date: Tue, 15 Aug 2006 19:12:55 +0930

On Tue, 15 Aug 2006 11:15:57 +0200 (CEST)

> namely /64 and /128 (routing, though is classless).

I don't think classful is the right way to express this. "classful" is
a loaded word from the IPv4 days, as it defines both an addressing
allocation method and a _forwarding_ algorithm. I think some of the
criticism of the /48 boundary has been based on misunderstanding what
classful addressing was also classful forwarding.

The /48, /64, /128 etc. boundaries in IPv6 are soft boundaries rather
than hard ones, and pretty much there primarily for operational and
administrative convenience. For example, the /64 boundary is basically
there so that an EUI-64 address can be used to generate a
semi-permanent and convenient node address (and also from what I
understand, to allow for routing goop, although we're never going to
"goop"). 

> I still think this is ambiguous (rfc:s might not be, but my interpretation 

To an extent I agree. I think if you look at from a slightly more
operational view point, rather than a technical / protocol one, the
convenience and simplicity of having fixed addressing boundaries makes
more sense.

Regards,
Mark.

---

From: Mattias Webjörn Eriksson <[email-masked]>
Date: Tue, 15 Aug 2006 13:12:30 +0200 (CEST)

> convenience and simplicity of having fixed addressing boundaries makes

This sounds resonable. All implementations I've tested so 
far happily accept assigning /112 prefix to interfaces.
My gut feeling is that the common practice and implementation is to allow
prefixes between /65 and /127.

Initially I was looking at it from an operational view point, as
I wanted to split a /64 (I had my reasons), but did not know if it was
allowed as per rfc. I found that rfc3513 says that all unicast addresses 
(except those that start with binary value 000) requires
an Interface ID to be 64 bit long, thus making /112 invalid.

Current specification says one thing and implementation says another.

 	Mattias W E

---

From: "Arturo Servin" <[email-masked]>
Date: Tue, 15 Aug 2006 14:02:51 +0100

Are there any guidelines, informational RFCs or best practices documents in
how organizations (ISPs, private Enterprises or government organizations)
should deploy IPv6?

Thanks in advance,
-as

---

From: Brian E Carpenter <[email-masked]>
Date: Tue, 15 Aug 2006 17:02:16 +0200

Arturo,

That is really closer to the scope of the v6ops WG. Have a look at the documents
listed in their charter:

http://www.ietf.org/html.charters/v6ops-charter.html

     Brian

---

From: Mohacsi Janos <[email-masked]>
Date: Tue, 15 Aug 2006 17:09:46 +0200 (CEST)

Hi,
 	There are several source on the Internet. Try 6NET deployment 
guide:
http://www.6diss.org/publications/manuals/deployment-guide.pdf
or IPv6 Task Force portal:
http://www.ipv6tf.org/

Janos Mohacsi
Network Engineer, Research Associate, Head of Network Planning
NIIF/HUNGARNET, HUNGARY
Key 00F9AF98: 8645 1312 D249 471B DBAE  21A2 9F52 0D1F 00F9 AF98

---

From: "Cesar Olvera" <[email-masked]>
Date: Tue, 15 Aug 2006 15:39:37 +0200

Arturo,

You can check:

Transition Scenarios for 3GPP Networks (RFC 3574)
Unmanaged Networks IPv6 Transition Scenarios (RFC 3750)
Evaluation of Transition Mechanisms for Unmanaged Networks (RFC 3904)
Scenarios and Analysis for Introducing IPv6 into ISP Networks (RFC 4029)
IPv6 Enterprise Network Scenarios (RFC 4057)
Analysis on IPv6 Transition in Third Generation Partnership Project
(3GPP) Networks (RFC 4215)
Basic Transition Mechanisms for IPv6 Hosts and Routers (RFC 4213)
Use of VLANs for IPv4-IPv6 Coexistence in Enterprise Networks (RFC 4554)

Further information at

Regards,

César Olvera

> From: Arturo Servin [mailto:[email-masked]]
> Sent: Tuesday, August 15, 2006 3:03 PM
> To: [email-masked]
> Subject: IPv6 Best Practices
>
>
>
>

**********************************************
The IPv6 Portal: http://www.ipv6tf.org

Bye 6Bone. Hi, IPv6 !
http://www.ipv6day.org

This electronic message contains information which may be privileged or confidential. The information is intended to be for the use of the individual(s) named above. If you are not the intended recipient be aware that any disclosure, copying, distribution or use of the contents of this information, including attached files, is prohibited.

---

From: Bob Hinden <[email-masked]>
Date: Tue, 15 Aug 2006 17:02:39 -0700

> how organizations (ISPs, private Enterprises or government  

Beside the IETF sources, you might also look at a book titled  
"Migrating to IPv6" by Marc Blanchet.  It's a good mix of theory and  
practice.

Bob