Subject: [Autoconf] MANET-Arch (was: Updated Problem Statement. Review requested)

From: Shubhranshu <[email-masked]>
Date: Tue, 24 Apr 2007 19:05:28 +0530

----- Original Message ----- 
From: "Alexandru Petrescu" <[email-masked]>
To: "Shubhranshu" <[email-masked]>

> This is something I consider open to question in the MANET Architecture
> document (draft-ietf-autoconf-manetarch-01).  I don't think it's neither
> useful nor necessary to assign _a_ unique prefix (shorter than /128) per
> node in a MANET network.  We can discuss that separately.  I think the
> prefixes are assigned to subnets, not necessarily to routers.  I mean
> both should be possible (assign a prefix per node, and per subnets).
> 

The architecture allows for a prefix length shorter than /128.
It allows a prefix to be allocated to a router and hosts attached
to it that form a subnet.

There had been a very long discussion on architecture aspect. I 
 recall we had a very good consensus on the MANET-Architecture during
IETF-67 Autoconf WG meeting and I believe the draft-ietf-autoconf-manetarch-01 
captures them reasonably well. 

<snip>
> In this context, would you consider that MANET networks are only for
> 802.11b 11Mb/s? (where it was experimented presumably the most).
> 

No.

> The second thing (link-layer triggers) seems to be mentioned in the
> MANETarch document, section 7 cross-layering; but not enough precise
> IMHO, simply because it doesn't say which trigger.
> 

 OK.
In the current ID version, the Cross-layering section seems much more 
general. Not sure if authors/others think it is somehow related to the 
manet-architecture and could be kept in the next version as well ? IMO, providing
trigger details seems to be out of scope of this document.

- Shubhranshu
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---

From: Alexandru Petrescu <[email-masked]>
Date: Tue, 24 Apr 2007 16:32:41 +0200

Shubhranshu wrote:
> ----- Original Message ----- From: "Alexandru Petrescu" 
> <[email-masked] <mailto:[email-masked]>>
>  To: "Shubhranshu" <[email-masked] 
> <mailto:[email-masked]>>
> 
>> This is something I consider open to question in the MANET 
>> Architecture document (draft-ietf-autoconf-manetarch-01).  I don't 
>> think it's neither useful nor necessary to assign _a_ unique prefix
>> (shorter than /128) per node in a MANET network.  We can discuss
>> that separately.  I think the prefixes are assigned to subnets, not
>> necessarily to routers.  I mean both should be possible (assign a
>> prefix per node, and per subnets).
>> 
> 
> The architecture allows for a prefix length shorter than /128. It 
> allows a prefix to be allocated to a router and hosts attached to it 
> that form a subnet.

On a router there can be two different prefixes.  Something like P1 is
2002:c3d4:6df5:1000::/64 and P2 is 2002:c3d4:6df5:2000::/64.

That router has two interfaces and each prefix is valid on one of these
interface.

There is no _one_ common prefix assigned to the router.  The common
prefix of P1 and P2 is 2002:c3d4:6df5::/48 and is assigned to another
router.

Figure 6 of MANETarch document suggests that in order for P:1:: and
P:2:: to be assigned to an interface then P:: must be delegated to that
router:
> If the MANET router is delegated a prefix p::, this prefix can be 
> assigned to the classic IP link(s), and hosts can be assigned 
> addresses from within this prefix, and configured with this prefix as
>  illustrated in Figure 6.

Or, I believe it is very possible that P:1::/64 and P:2::/64 be assigned
to one router; then P:3::/64 and P:4::/64 to another router and the
common _one_ P::/48 assigned to a yet another router.

Additionally, I don't see anything MANET-specific that requires that
when P:1::/64 and P:2::/64 are assigned to a MANET router's interfaces
then the entire P::/48 (the _one_ prefix) must be assigned to that
router's interface.

That's why I believe saying that _one_ prefix is assigned to a MANET
router is generally little valid.  One can easily say that _one_ prefix
is assigned to a subnet, generally.  But one can't say so easily and
generally that one prefix is assigned to a router - there are at least
two prefixes between which the router routes.

Moreover, MANETarch goes on:
> However it is worth noting that prefix lengths shorter than /128 
> (IPv6) or /32 (IPv4) are possible on the MANET interfaces

All interfaces of all routers (MANET or others) usually have prefix
lenghts shorter than /128.  This is true for IPv4 as well.  I don't
understand why this paragraph sounds like this were an exception ('it is
worth noting that prefixes... are possible') - it's the standard way,
not an exception.

> Link-local Multicast/Broadcast Scope On a MANET interface, a 
> link-local multicast or broadcast reaches MANET interfaces of 
> neighboring nodes,

A link-local multicast _what_?  A packet that is sent to multicast
address with link scope?

> regardless of their configured addresses.  A link-local multicast or 
> broadcast on a MANET interfaces is a "neighborcast" and is not 
> forwarded, nor is it assumed to be received by all nodes within a 
> MANET.

"Neighborcast" is a new term, ack.

Ok, it is not received by all nodes within a MANET (what's a MANET? - a
link or a set of links connected by routers? because the terminology
section of this document calls a MANET a set of MANET routers that is
reachable via one or more hops.)  But is received by all nodes that have
subscribed to that multicast address' group.

> The MANET addressing model presented in this section makes a clear 
> separation between the role of router and host in a MANET, 
> recognizing that:
> 
> o  MANET interfaces are seen only by the router, assumed to be MANET 
> aware, and running appropriate protocols;

Can a real interface be a MANET interface?  In that case the host in
that box also sees the MANET interface, not only the router in that box.

But the entire concept of MANET interface in this draft is a bit weird
to me, because it sounds like the MANET interface can not be a real
interface.

>  IETF-67 Autoconf WG meeting and I believe the 
> draft-ietf-autoconf-manetarch-01 captures them reasonably well.

That's fine if there's consensus on this document.

[...]

Alex

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