Subject: RE: 6to4 and 2002:PRIV:ATE [RE: A use for site local addresses?]

From: "Michel Py" <[email-masked]>
Date: Thu, 27 Mar 2003 08:55:16 -0800

>> Michel Py wrote:
>> If the routing table contains IGP or connected routes with
>> a mask of /64 as it should be the longest match route will
>> prevail over the 2002::/16 route associated with the tunnel
>> interface and traffic should flow.

> Pekka Savola wrote:
> You're making an assumption that all nodes implementing 6to4
> pseudo-intefarce take part in the IGP to get the more specific
> 2002:FOO routes,

Well, yes but these nodes are only routers. Hosts MUST NOT have any 6to4
pseudo-interfaces (or have it deactivated).

> or the topology is simple enough that there is only one subnet

No. The point is multiple subnets indeed.

> (and the site admin expects the default route to do the job).

Yes. Default route on a given subnet points to the router. The router
participates in the IGP and has specific routes.

> I do not believe this is realistically the case for what's
> being proposed.

For what reasons?

Michel.

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From: Pekka Savola <[email-masked]>
Date: Thu, 27 Mar 2003 19:00:03 +0200 (EET)

> pseudo-interfaces (or have it deactivated).

There is no such statement anywhere that I know of.  Please correct me if
I'm wrong.  Hosts indeed have 6to4 pseudo-interfaces.

> > I do not believe this is realistically the case for what's

See above.

-- 
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: Mika Liljeberg <[email-masked]>
Date: 27 Mar 2003 20:00:40 +0200

> I'm wrong.  Hosts indeed have 6to4 pseudo-interfaces.

You're right. However, I think it's just common sense that a host, which
sets up a 6to4 pseudo interface by default, should also automatically
disable it if a router is sending RAs with 2002:xyz:: prefixes.
Otherwise the host implementation is broken.

	MikaL

---

From: Pekka Savola <[email-masked]>
Date: Thu, 27 Mar 2003 20:22:48 +0200 (EET)

> Otherwise the host implementation is broken.

Maybe, maybe not.  In many cases, the node implementations include both 
host and router behaviour.  In such case, automatically disabling 
something may not be the best option.

This may be something worth fleshing out when/if we progress 6to4 to DS 
at some point :-)

---

From: "Tony Hain" <[email-masked]>
Date: Thu, 27 Mar 2003 10:32:55 -0800

Mika Liljeberg wrote:
> You're right. However, I think it's just common sense that a 
> host, which sets up a 6to4 pseudo interface by default, 
> should also automatically disable it if a router is sending 
> RAs with 2002:xyz:: prefixes. Otherwise the host 
> implementation is broken.

Not necessarily. As long as the RA based prefix has a lower metric than
the local pseudo interface, there is no reason to disable it. Depending
on the implementation, this might allow for a faster recovery when the
RA disappears.

Tony

---

From: Ole Troan <[email-masked]>
Date: Thu, 27 Mar 2003 18:34:44 +0000

>> Otherwise the host implementation is broken.

it should disable it for any received RA, i.e when it is on a native link.

> This may be something worth fleshing out when/if we progress 6to4 to DS 

a host connected to a native link should not automatically enable a
6to4 pseudo interface.

/ot

---

From: Brian E Carpenter <[email-masked]>
Date: Thu, 27 Mar 2003 19:46:00 +0100

> I'm wrong.  Hosts indeed have 6to4 pseudo-interfaces.

RFC 3056 mainly talks about routers and strongly implies what Michel says, 
but that MUST NOT is not in any RFC.

Some hosts can support such a pseudo-interface, but having it on by default
is a problem IMHO.

   Brian

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From: Mika Liljeberg <[email-masked]>
Date: 27 Mar 2003 20:48:16 +0200

> on the implementation, this might allow for a faster recovery when the

Nope. If your network uses 6to4 addressing, you probably want to send
off-link 6to4 destinations to your default router rather than the local
6to4 pseudo interface.

	MikaL

---

From: "Tony Hain" <[email-masked]>
Date: Thu, 27 Mar 2003 10:48:43 -0800

> it should disable it for any received RA, i.e when it is on a 

No, because this would force traffic to 6to4 sites through a relay. The
RA receiving interface should be the path to default, and the 6to4
interface should be used for those prefixes.

> a host connected to a native link should not automatically 
> enable a 6to4 pseudo interface.

See above.

Tony

---

From: "Tony Hain" <[email-masked]>
Date: Thu, 27 Mar 2003 11:04:35 -0800

Mika Liljeberg wrote:
> > Not necessarily. As long as the RA based prefix has a lower metric 
> > than the local pseudo interface, there is no reason to disable it. 
> > Depending on the implementation, this might allow for a faster 
> > recovery when the RA disappears.
> 
> Nope. If your network uses 6to4 addressing, you probably want 
> to send off-link 6to4 destinations to your default router 
> rather than the local 6to4 pseudo interface.

You clearly missed the point about the lower metric.

Tony

---

From: Pekka Savola <[email-masked]>
Date: Thu, 27 Mar 2003 21:14:21 +0200 (EET)

> You clearly missed the point about the lower metric.

Note that "metric" is a bit vague term; it has significantly different
implications whether it's applied before or after the
longest-prefix-match.  Ie. whether it is used as a sequential number in
which to look for prefixes in different protocol-specific routing tables
or to compare among different routes of the same prefix and length.

In almost all cases, it's the latter.

---

From: Mika Liljeberg <[email-masked]>
Date: 27 Mar 2003 21:39:00 +0200

> In almost all cases, it's the latter.

Exactly my point. If the pseudo interface has a 2002::/16 on-link route,
longest prefix match will home in on it instead of the default route.

I guess you could set the 6to4 pseudo-interface up with a (high metric)
default route instead, in which case any other default route would take
precedence and effectively disable the pseudo interface.

	MikaL

---

From: "Tony Hain" <[email-masked]>
Date: Thu, 27 Mar 2003 11:43:27 -0800

Mika Liljeberg wrote:
> > longest-prefix-match.  Ie. whether it is used as a 
> sequential number 
> > in which to look for prefixes in different 
> protocol-specific routing 
> > tables or to compare among different routes of the same prefix and 
> > length.
> > 
> Exactly my point. If the pseudo interface has a 2002::/16 
> on-link route, longest prefix match will home in on it 
> instead of the default route.

You are missing the point that your scenario has a 2002::/16 on-link
route on the native interface as well. Default is not an issue here.

Tony

> 
> I guess you could set the 6to4 pseudo-interface up with a 
> (high metric) default route instead, in which case any other 
> default route would take precedence and effectively disable 
> the pseudo interface.
> 
> 	MikaL
>

---

From: Mika Liljeberg <[email-masked]>
Date: 27 Mar 2003 21:53:50 +0200

> route on the native interface as well. Default is not an issue here.

Nope. It has a 2002:ab:cd:xy::/64 on-link route on the native interface.
Any off-link 6to4 addresses will be routed to the pseudo interface.

	MikaL

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From: Markku Savela <[email-masked]>
Date: Thu, 27 Mar 2003 21:58:23 +0200

> From: Mika Liljeberg <[email-masked]>
> 

Ahem, I need to step in here... a router is advertising 6to4 prefix,
it will advertise it as (at least on ethernet):

  2002:xxx::/64 L=1, A=0 or 1

thus, it's longer and metrics don't apply... (unless there there are
two or more 6to4 prefixes announced).

---

From: Pekka Savola <[email-masked]>
Date: Thu, 27 Mar 2003 22:09:11 +0200 (EET)

> Any off-link 6to4 addresses will be routed to the pseudo interface.

.. unless it (must be a router, in practise) learns 2002::/16 from IGP,
which is probably what Tony meant.

This would be a horrible hack.  It is typically not possible or 
recommended to be able to able to override the administrative "distance" 
(or "metric") of connected routes.

You can work around this issue by advertising two /17's, though, to get 
the same effect.

---

From: Brian E Carpenter <[email-masked]>
Date: Thu, 27 Mar 2003 21:57:26 +0100

> two or more 6to4 prefixes announced).

Er, it's a /48, by definition. If it's a /64, that's already a subnet
prefix within the /48 site prefix.

   Brian