Re: [Autoconf] WC consensus call for RFC5889 modifications (Fwd: Forgotone [Was: RFC 5889)

"Charles E. Perkins" <charles.perkins@earthlink.net> Wed, 04 August 2010 19:37 UTC

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Date: Wed, 04 Aug 2010 12:38:03 -0700
From: "Charles E. Perkins" <charles.perkins@earthlink.net>
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To: Teco Boot <teco@inf-net.nl>
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Subject: Re: [Autoconf] WC consensus call for RFC5889 modifications (Fwd: Forgotone [Was: RFC 5889)
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Hello Teco,

On 8/4/2010 11:11 AM, Teco Boot wrote:

>>> You could say a host with one p2p link could set the default gateway automatically.
>>> But how can the opposite node learn the topology?
>>
>> Are we getting into solution space?
>
> No. We are getting out-of-scope.
> The document is about link with undetermined characteristics.
> P2P links are not in that category.

I definitely don't agree with this conclusion.
The links with undetermined characteristics can
support time-bounded P2P links.  There is no
reason to declare P2P links out of scope.

>> I didn't even say that a host had to have
>> a default router.
>
> Then, that host does not send packets.
> (Assuming empty routing table and /128 (v6) or /32 (v4) address prefix).

Bad assumption!

> (Host learning more specific routes via p2p links could be exception)

This isn't necessary.  Shall I make an example?

One trivial example would be to just run in
promiscuous mode, listen for addresses, and
pretend that some neighbor is a router.

I have other examples that are more normal :-)


>> Without presenting solutions, I cannot
>> convince you otherwise.  For this discussion,
>> suffice it to say that I am 100% certain your
>> statement is incorrect.
>
> I think I would call your solution topology exchange, thus routing.
> Just guessing, of course.

I am not claiming that the other solutions are
mine -- but there are numerous examples in the
literature.

As far as a host is concerned, topology
exchange isn't necessary -- unless you call
the simple fact of link establishment to be
"topology exchange".  And then our discussion
fails, because we have so little vocabulary.


>> In particular, I claim that hosts in an ad hoc
>> network often must adhere to the developed
>> address model.  Of course they don't run AODV
>> if they're not routers.
>
> OK, now were are there. How can the routers know the host is there?

If the host transmits a packet, the routers can know.

> When the host belongs to a subnet, with a "subnet router" as gateway
> to the rest of the network, I am OK. But this cannot happen, with the
> current addressing model.

Why not?

If I remember correctly, the current addressing model does
not legislate that all links have to be /128.  It just
says that SOME links appear to be /128, so that without
additional information, protocols may not make too many
assumptions about the connectivity properties of the link.

As many have pointed out, this world is not so black and
white.

>>> More detailed answer: in AODV, the subnet router is responsible for
>>> reachability for the subnet.
>>
>> Where's the subnet?
>
> Somewhere in the network. Optionally with hosts. And a router, connecting
> the subnet to the rest of the network.

Optionally.  And, a node can forward packets
based only on P2P routes.  Such a node is,
I claim, a router.  No subnets are needed.


>> Is there some weird magic that requires every
>> /128 subnet to have an AODV subnet router?
>> If not, then your conclusion is false.
>
> There is no magic.
> Point is: with /128, there are no hosts. Not on links with undetermined
> characteristics.

Teco -- this is just wrong.

Just because a network interface has undetermined
properties doesn't mean that the host utilizing
that network interface can't transmit or receive
packets.  Otherwise, what would be the point of
powering the interface?


>> Actually, I am further mystified -- especially
>> to think that point-to-point routes get so little
>> respect in this forum, and that anyone might
>> claim that hosts don't have routing tables.
>
> 1) P2P is out-of-scope, as we assume nothing for our links.

We do assume that hosts can transmit packets.
At least I do.  Hosts that can transmit packets
can support P2P links.  Why not??

> 2) hosts have routing tables.

Well, I'm glad you cleared that up.


> With IPv6, we could support hosts in our links with undetermined
> characteristics. Router sends RA with PIO (/64), with L-bit is 0.
> Nearby hosts can configure own address (SLAAC) and use the router
> as gateway. This only works for satellite hosts. This model is
> suggested multiple times (Templin, in't Velt, others).
> There was rough consensus not to support this addressing model.

What if the router sends out RA with /128, and hosts
receiving the RA configure P2P route table entries to
the router?  That would work.

But it's not the only way, of course.

Regards,
Charlie P.