Subject: [manet] Fwd: Modem Dlep session with multiple routers

From: Eugene Reznik <[email-masked]>
Date: Tue, 12 Dec 2017 16:13:18 +0200

Hello,

My name is Evgeniy Reznik.
I am graduate student and I'm trying to implement Dlep modem.
The problem is that I do not understand clearly behavior of a modem.
Can you please help me with understanding rfc8175.

Suppose the modem supports only one Dlep connection (via one physical and
logical interface), the modem is connected to two routers on LAN and the
modem is in session with one router.

What should do the modem in case it receives peer discovery from second
router, while still being in session with the first router?
Should modem silently discard peer discovery or answer with peer offer
signal?
If modem answers with peer offer, then how modem rejects session
initialization?

I could not find any definition for this case in rfc.

Thank you in advance.
Regards, Evgeniy.

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From: Henning Rogge <[email-masked]>
Date: Tue, 12 Dec 2017 15:36:41 +0100

Hi,

I would guess there are two options...

first, just ignore any discovery or session initiation if you have a
session running.

second... if you ONLY support the delivery of metrics from radio to router
(no "request link characteristic", no flow control, no setting of IPs) you
could theoretically just run two DLEP sessions, no harm done if the router
cannot "write" any data.

Still, I would add a config option (with default "no") if you support the
second one.

Henning

On Tue, Dec 12, 2017 at 3:13 PM, Eugene Reznik <[email-masked]> wrote:

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From: Stan Ratliff <[email-masked]>
Date: Tue, 12 Dec 2017 10:58:08 -0500

+1 on what Henning said. And, I believe Rick mentioned this was
intentionally left a bit vague to allow for some innovation in the space -
to let implementations to do what's best in their environment. Some
examples of how you could handle the issue are:

1. If the modem only supports one DLEP peer session at a time, then
silently drop subsequent multicast discovery messages sent by the second
router.

2. In the case Henning describes - if there's no flow control or Link
Characteristic Request messages flowing, nothing stops the modem from
establishing 2 sessions and transmitting state information (Destination UP,
Destination DOWN, Destination UPDATE) to both routers. Since flow control
will be a DLEP extension, the modem can just refuse to support said option,
and flow control isn't an issue. LCR could also *theoretically* be handled
in that environment by always responding with the existing metrics
(effectively, when either of the routers ask for something like 'more
bandwidth', the modem responds with 'sorry, this is all I have').

3. If the modem has sufficient (whatever that means) a-priori configuration
to know, for instance, "Router 1 will only use a specific subset of DLEP
destinations, and Router 2 will use a second, non-overlapping subset of
DLEP destinations", then the modem could offer both flow control and LCR
support to the 2 routers simultaneously. Or, you could (again, via a-priori
configuration), designate one of the routers as "flow control and LCR
requests from this router will be honored; but not from other routers on
the segment".

And I'm sure there are more approaches that I haven't thought of.

Regards,
Stan