Subject: Re: [manet] I-D ACTION:draft-ietf-manet-iana-01.txt = WG Last Call

From: Alexandru Petrescu <[email-masked]>
Date: Fri, 04 May 2007 11:39:10 +0200

[MANET: this private discussion Ian and I had is with respect
  to the MANET IANA needs document.  I'm looking at why the necessity
  of site-local multicast address for IPv6 MANET protocols.  I've noticed
  no other routing protocol uses ff05 site scope multicast addresses, at
  least not by the specs - so it would be strange for MANET to use it.
  I've run into the idea of the probable need for a new scope, probably a
  "MANET scope" ff06.

  Any thoughts you may have on this, thanks.]

Ian Chakeres wrote:
> <snip>
> 
>> 
>> It's not what I asked.  I'm afraid no IPv6 routing protocol uses 
>> site-local ff05::x multicast addresses.  It would be strange for 
>> MANET routing protocols to use it.  Don't you agree?
> 
> MANET's are more heterogeneous and distributed, than other networks 
> with traditional routing protocols.

I'm afraid most MANETs that have been tested are very homogeneous in
terms of the type of link layer.  At least compared to the fixed networks.

> I think there will be a need to coordinate with MANET routers that 
> are not link-local.

I agree with that - MANET routers are often not on the same link.  But
that doesn't necessarily make them need multicast addresses with
site-local scope.

> Given existing routing protocols more fully synchronized attributes,
> I don't think they have as much need for a site-local multicast
> address.

Right, but I don't see why the less synchronized attributes in a MANET 
protocol will need a site-local multicast address scope.  I agree it 
needs a multicast address with larger scope than just link, but why 
_site_ scope; especially when  the concept of "site" is compromised by 
the depreciation of site-local addresses fec0.

OSPF has this notion of "area" that is semantically close to a "site", 
yet it doesn't use a site-scope multicast address (neither does RIPng). 
  BGP has "realm" and still not using site-scoped multicast addresses.

IANA and rfc4291 reserved the site-scoped ff05::2 "All Routers Address" 
but I think no routing protocol actually uses it.

Do I miss something.

Alex

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---

From: "Ian Chakeres" <[email-masked]>
Date: Fri, 4 May 2007 16:34:07 +0530

Comments inline.

<snip>

>From my understanding, site-local is the next larger scope than
link-local. I don't know how we might define a scope that is smaller
than site but larger than link. I think the boundary between them is
tight (1 hop vs. 1 or more hops).

---

From: Brian Haberman <[email-masked]>
Date: Fri, 04 May 2007 07:33:21 -0400

> tight (1 hop vs. 1 or more hops).

Not exactly.  Scope 4 can be used as well (e.g. "Admin Scope").

Take a look at RFC 4007 (http://tools.ietf.org/html/rfc4007) for some of
the technical discussions on the multicast scoping issues.

As for the issue itself, until I see a multicast routing protocol (or
unicast for that matter) that uses something other than link-local or
global addresses for exchanging information I don't see the benefit of
reserving a multicast address.

Regards,
Brian

---

From: "Joe Macker" <[email-masked]>
Date: Fri, 4 May 2007 10:51:14 -0400

>Take a look at RFC 4007 (http://tools.ietf.org/html/rfc4007) 
>for some of the technical discussions on the multicast scoping issues.
>
>As for the issue itself, until I see a multicast routing 
>protocol (or unicast for that matter) that uses something 
>other than link-local or global addresses for exchanging 
>information I don't see the benefit of reserving a multicast address.
>
Brian:

Most of the design interest I have seen for MANET site-scoping has come not
come from routing control plane usage (link-local seems fine to me) but
rather implementors wanting to apply SMF for some autconfiguration or
discovery protocol (outside of the routing control plane) within a
topological zone (e.g., autoconf).  There was some concern from previous ADs
that we support an approach to keep "site-intended" SMF application data
from leaking out when the application is MANET topological zone/site. There
are other ways to accomplish this.  We could debate whether an assignmnet is
needed at this time since global address forwarding is supported and PIM
gatewaying has been done. Use cases might come from the autoconf WG.  There
is certainly still an evolving area and there is a little bit of pre-app
definition going on.  I believe there is is no dependency related to the
present routing protocol designs in this regard just to be clear. Ian I am
not sure if you define a use case for DYMO.

There was some site-scoping language put in SMF because of ADs and others
concerns but the multicast applications that would use this are yet to be
defined (although some related proposals have shown up in the autoconf
community). I believe SMF site-boundary routing functionality will be useful
but perhaps it is redundant with standard practice definitions...