Re: [Autoconf] updated draft on aspects of multi-hop wireless communication

Thomas Heide Clausen <ietf@thomasclausen.org> Tue, 24 February 2009 22:04 UTC

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From: Thomas Heide Clausen <ietf@thomasclausen.org>
Date: Tue, 24 Feb 2009 23:06:03 +0100
To: Rex Buddenberg <budden@nps.navy.mil>
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Cc: "autoconf@ietf.org" <autoconf@ietf.org>, Emmanuel Baccelli <Emmanuel.Baccelli@inria.fr>
Subject: Re: [Autoconf] updated draft on aspects of multi-hop wireless communication
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On Feb 24, 2009, at 20:02 PM, Rex Buddenberg wrote:

> Charlie,
>
> Paul has a reality check point and its worthwhile understanding  
> this because missing the point has made both MANET and autoconf  
> harder than they need to be ... IMHO.  It's also made them less  
> relevant to what I think I see in the future.
> My background is analyzing information systems in DoD and emergency  
> services ... why are they not interoperable (or, in the rare  
> inverse instance, why are they interoperable)?
>
> In dealing with some DoD bureaucracy, I'm finding that they don't  
> understand the implications of the differences between LANs and  
> WANs.   And by MANET stating that every end system is also a  
> router, we equally obfuscate the point.
>

<SNIP>

I think there's a fundamental misunderstanding here. I'll try to  
clarify it, if I can...

In an OSPF-routed network, for all that OSPF cares about, every  
"system is [an OSPF] router".  That doesn't preclude that an OSPF  
router may have interfaces towards other entities, called hosts --  
but as such hosts do not take part in routing (and in the routing  
protocol), they're just not relevant when talking about OSPF.

In a MANET-routed network, all systems that the MANET routing  
protocols care about are.....MANET routers. That doesn't preclude  
that a MANET router may have interfaces towards other entities,  
called hosts -- but as such hosts do not take part in routing (and in  
the routing protocol), they're just not relevant when talking about  
MANETs.

In other words.....it's perfectly fine to hang an Ethernet hub or an  
802.11 access point or whatnot off of a MANET router, assign a prefix  
to that link, hang hosts on that link --  and use the MANET routing  
protocols to exchange that prefix such that these hosts are routable/ 
reachable. It's not just perfectly fine, that's what MANET routing  
protocols are build to do ;)

I'd actually make the exact opposite point of the one you're making,  
Rex: every end system is a host -- intermediate systems running MANET  
protocols are routers. Hosts are unaware of if they're hanging off a  
MANET, OSPF, ISIS or other router -- they just see a classic IP link  
and an IP hop and likely a default route. The MANET, OSPF, ISIS or  
other router deals with the "routing stuff", including  
characteristics of links to other routers. Hosts never see that. This  
is as it should be.

Occasionally, a system in a MANET may in the same physical box have a  
logical router and a host  present. This isn't that unusual either  
for non-MANET networks.

So when we talk about systems being routers in MANETs, then it's  
simply because the systems that "we care about" are the routers.  
Hosts are hanging off (some of) these routers just fine, over classic  
IP links -- over which the usual slew of protocols works just fine  
(fortunately -- so we do not have to care about that ;) ).

What MANETs are concerned with are MANET routers and their  
interconnect to other MANET routers. Interconnect from MANET routers  
to hosts is no different from interconnect from a host to, say, an  
OSPF router.

Does this help?

Thomas