Subject: RE: AW: Guidelines for Numbering IPv6 Point-to-Point Links and Easing the Addressing Plans

From: "Chip Popoviciu \(cpopovic\)" <[email-masked]>
Date: Wed, 1 Mar 2006 16:39:30 -0500

Along these lines there are two other aspects that are worth
considering:

1. A single address with scope larger than link-local would indeed be
sufficient for a router as long as the network management policies and
tools do not need to reach specific interfaces for troubleshooting
purposes for example.

2. In the case of a Service Provider that offers VPN services, an
address with a scope larger than link-local is necessary for each VRF
for things such as PMTU discovery. In that case, it might be easier to
simply assign that address to the PE-CE link rather than create for
example a loopback for each VRF. 

In principle link-locals are sufficient for the PE-CE link however in
practice, all little details considered, people might end up assigning
more than that to the link. And in that sense, it will be better to use
a prefix set aside by the SP for its own infrastructure rather than what
is delegated to the customer (as Ole mentioned).

Regards,
Chip

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On
Behalf Of Fred Baker (fred)
Sent: Wednesday, March 01, 2006 11:30 AM
To: Bonness, Olaf
Cc: Ole Troan (otroan); [email-masked]; [email-masked]
Subject: Re: AW: Guidelines for Numbering IPv6 Point-to-Point Links and
Easing the Addressing Plans

My assumption as a routing geek is that the only reasonable use of a
numbered point to point link is to address an end station; it needs an
address to be useful in the network. But any router/router point-
to-point interface should be supportable using link-local addresses.  
A router needs one address reachable by its administration (eg non-
link-local), to be a member of any prefix on a LAN that it is serving,
and to be able to reach p/p-connected end stations it serves.

On Mar 1, 2006, at 5:41 AM, Bonness, Olaf wrote:

>>
>>    4.  Routing Aggregation of the Point-to-Point Links
>>
>>    Following this approach and assuming that a shorter prefix is
>>    typically delegated to a customer, in general a /48 [4], it is
>>    possible to simplify the routing aggregation of the point-to-point
>>    links.  Towards this, the point-to-point link may be numbered 
>> using
>>    the first /64 of a given /48.
>>
>> using the first (or any) subnet of a larger prefix, breaks the 
>> conceptual model of DHCP prefix delegation. the prefix is delegated 
>> to the requesting router and cannot be used to number the link 
>> between the delegating and requesting router.
>
> My assumption from a service provider point of view would be to use a 
> dedicated sub-preaefix (e.g. /48)of my own aggregate to address the 
> point-to-point links (e.g. /64)  to the custumers (in the case I have 
> to do this).
>
> cu
> 	Olaf

---

From: Tim Chown <[email-masked]>
Date: Thu, 2 Mar 2006 08:53:12 +0000

Are there also possibily PIM issues?  Would using only link locals cause 
problems for PIM-SM where the Register messages are sent to the RP from 
a link-local interface on a CPE acting as the DR?  For example, with the
Register Stop messages?   We ran into this a while ago, but I can't 
remember the specifics right now :)

I agree with Fred; from a management point of view, the less explicit 
numbering required the better, as that implies the least renumbering at 
a later date...

Tim

-- 
Tim/::1

---

From: JORDI PALET MARTINEZ <[email-masked]>
Date: Fri, 03 Mar 2006 01:31:16 +0800

As said, question of taste ... Both a prefix aside, or the same prefix are
good choices, and I'm not trying to describe the best practice, but a good
one (or alternatively add the aside prefix description and each reader to
choose).

Regards,
Jordi

> De: "Chip Popoviciu (cpopovic)" <[email-masked]>
> Responder a: <[email-masked]>
> Fecha: Wed, 1 Mar 2006 16:39:30 -0500
> Para: "Fred Baker (fred)" <[email-masked]>, "Bonness, Olaf"
> <[email-masked]>
> CC: "Ole Troan (otroan)" <[email-masked]>, <[email-masked]>,
> <[email-masked]>
> Conversación: AW: Guidelines for Numbering IPv6 Point-to-Point Links and
> Asunto: RE: AW: Guidelines for Numbering IPv6 Point-to-Point Links and Easing
> the Addressing Plans
> 
> 

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---

From: Stig Venaas <[email-masked]>
Date: Thu, 16 Mar 2006 09:57:57 +0100

> remember the specifics right now :)

The PIM-SM update, draft-ietf-pim-sm-v2-new-11.txt, points out that the 
source address of the PIM Register message must be reachable throughout 
the domain. I would assume that implementations would use a global 
address if the router has at least one global address.

If you use only link-locals on the link, then the CPE hopefully has a 
global address on the customer side that can be used as source address 
(or perhaps a loopback address)...

The problem you/we ran into, was that an RFC 1918 address was picked as 
source address... There might be similar issues with reachability of 
ULAs perhaps...

Stig

---

From: Pekka Savola <[email-masked]>
Date: Sun, 19 Mar 2006 16:57:31 +0200 (EET)

Hi,

I read this short doc.  I don't believe it's necessary, but if there's 
something important there, it could be added to the addcon draft.

I believe the /48 assignment suggestion below is technically 
incorrect.  The ISP router, when it gets a packet destined to anything 
except the first /64 will inccorrectly try to use Neighbor Discovery 
to find the address, instead of forwarding it to the customer router. 
This can't possibly work unless the customer router is using proxy-ND.

=======
    Moreover, it is possible to use the shorter prefix as the provider
    side numbering for the point-to-point link and keep the /64 for the
    customer side.  In our example, it will become:

    o  Point-to-point link at provider side: 2001:db8:aaaa::1/48

    o  Point-to-point link at customer side: 2001:db8:aaaa::2/64
========

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

---

From: Gert Doering <[email-masked]>
Date: Sun, 19 Mar 2006 16:05:11 +0100

Hi,

> This can't possibly work unless the customer router is using proxy-ND.

Depending on the type of link.  On "real" point-to-point links (PPP,
HDLC serials), I doubt that anyone is doing ND - because there is no
need to find out about the destination mac-level address.

OTOH on things like "ATM bridged encapsulation", you're completely
right.  You need a peer IPv6 address to route the /48 to.

Gert Doering
        -- NetMaster
-- 
Total number of prefixes smaller than registry allocations:  88685

SpaceNet AG                    Mail: [email-masked]
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