Subject: RE: (ngtrans) 6to4 gateway / 6to4 relay routerIPv4-compatibleIPv6 address interoperability concern ...

From: "Christian Huitema" <[email-masked]>
Date: Wed, 13 Jun 2001 08:41:22 -0700

May I point out that the 6to4 anycast draft already defines a "6to4
relay IPv6 anycast address" whose purpose is precisely to be able to
send a message to the 6to4 relay currently in use? This address is
precisely defined as 2002:ip:v4::, with "ip:v4" being the IPv4 6to4
relay anycast address.

In fact, I don't understand the purpose of
draft-durand-ngtrans-6to4-well-known-address-00.txt. Before we make it a
WG item, we must first find which exact problem we want to solve.
Clearly, it is not "finding the 6to4 anycast relay" from a random IPv4
location -- we already have a solution for that. The draft mentions
finding the "6to4 designated router", based on the assumption that
"there can only be one 6to4 router for inbound traffic." 

There are multiple problems with this definition. First, we need to
understand the scenarios in which a more specific anycast address is
needed in addition to the generic 6to4 anycast address. It cannot be for
the purpose of finding the nearest relay router -- the 6to4 anycast
address already does that. When I read Alain's draft, the motivation
seems to be, finding the border router of a site. Why exactly do we need
something different for 6to4? Until know, we had assumed that for the
IPv6 native nodes inside a site, there was no difference between a 6to4
prefix and a "native" prefix. Why exactly do we need one?

Then, the assumption of a unique egress gateway is wrong. We discussed
it before, and showed that it is indeed possible in a multi-homing
scenario to have several ingress routers for a domain -- just treat the
selected IPv4 address as an anycast address. It may not be very
practical with the current software release of the current routers, but
it is definitely a possibility. Assuming that there is only one
identifier for these routers is dubious, and over constraining.

Third, the choice of the "0000" subnet-id is poor. According to section
2.6.1 of the IP Version 6 Addressing Architecture
(draft-ietf-ipngwg-addr-arch-v3-05.txt), "2002:ip:v4::/48" is the
"required Anycast Address" for the entire site connected through the
6to4 router(s). This prefix will be matched by any IPv6 router in any
subnet in the site -- not just the 6to4 gateway.

-- Christian Huitema

> -----Original Message-----
> From: Brian E Carpenter [mailto:[email-masked]]
> Sent: Tuesday, June 12, 2001 7:15 AM
> To: Alain Durand
> Cc: [email-masked]
> Subject: Re: (ngtrans) 6to4 gateway / 6to4 relay
routerIPv4-compatibleIPv6
> address interoperability concern ...
> 
> Alain Durand wrote:
> >
> > At 05:09 PM 6/11/2001 -0500, Brian E Carpenter wrote:
> > > > This get us back to the discussion we had in Minneapolis.
> > > > We need a way to identify a 6to4 router by it's IPv6 address.
> > > > We already have the beginning of the prefix 2002:ip:v4::/48
> > > > and a proposal for the 64 bit token based on the link local
> > > > address. What is missing is how to form a subnet ID.
> > >
> > >I'd vote for zeros.
> > >
> > >    Brian
> >
> > Look at draft-durand-ngtrans-6to4-well-known-address-00.txt
> 
> Good enough. Can we make that a WG draft?
> 
>    Brian C

---

From: Alain Durand <[email-masked]>
Date: Wed, 13 Jun 2001 11:01:28 -0700

At 08:41 AM 6/13/2001 -0700, Christian Huitema wrote:

Third, the choice of the
"0000" subnet-id is poor. According to section

(draft-ietf-ipngwg-addr-arch-v3-05.txt), "2002:ip:v4::/48" is
the

"required Anycast Address" for the entire site connected
through the

6to4 router(s). This prefix will be matched by any IPv6 router in
any

2.6.1 Required Anycast
Address

The Subnet-Router anycast address is predefined.  Its
format is as

follows:

|
n
bits
|   128-n bits   |

+------------------------------------------------+----------------+

|
subnet
prefix
| 00000000000000 |

+------------------------------------------------+----------------+

The "subnet prefix" in an anycast address is the
prefix which

identifies a specific link.  This anycast address is
syntactically

the same as a unicast address for an interface on the link
with the

interface identifier set to zero.

Packets sent to the Subnet-Router anycast address will be
delivered

to one router on the subnet.  All routers are required
to support the

Subnet-Router anycast addresses for the subnets which they
have

interfaces.

The subnet-router anycast address is intended to be used
for

applications where a node needs to communicate with one of a
set of

routers on a remote subnet.

=> When I read this, my understanding was that this is
applicable to subnets only.

My understanding of subnets is that they are /64 prefixes and not site,
/48....

Of course, the bit patterns seems to imply otherwise...

Bob or Steve, could you please clarify my confusion?

-
Alain.