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

"Charles E. Perkins" <> Wed, 04 August 2010 19:37 UTC

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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

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

>>> 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.

Charlie P.