Re: [manet-dlep-rg] DLEP multicast address

["Stan Ratliff (sratliff)" <[e-mail]>]

On Nov 19, 2013, at 1:28 AM, Martin Duke <[e-mail]<mailto:[e-mail]>> wrote:

I don't think we want to rely just on TCP if we have OOB detection. Here are some cases where we need the peer discovery anyway:

1. The router is configured with the modem address but the modem does not have the router address.

In the general case, the TCP client needs the address/port of the TCP server.


2. The modem has the router IP address but not the port. (I believe the latest concept requires zero standard TCP ports, and the Peer Discovery can simply include the port number.)

I don't think we should even try to cover all bases of mod-configuration. Your either provide a-priori config, or you don't. If you do, and it's wrong, then shame on you. ;-)


3. The modem has the peer address, but powers up first; the TCP SYN gets no reply, backs off and times out.

"Heuristics for retrying the TCP session are left to the discretion of the implementation"… ;-)


Clearly it is much cleaner for the router to send a UDP packet where we control the frequency and timeout.

This looks like a backup for bad a-priori config, or to address timing issues. IMO, it increases complexity of the implementation, and doesn't provide a whole lot of value-add. But I could be missing something.

Regards,
Stan


On Thursday, November 14, 2013, Stan Ratliff (sratliff) wrote:
If you've already got the the peer's address via some out-of-band mechanism, then why "discover" him? I've tried to separate things out so that the *only* thing discovery does is… wait for it… 'discover'. It tells you the address/port of where you need to go connect up. Pretty much all other init gets pushed back into the new Peer Initialization message. About the only thing that makes sense to me in discovery is the software level of the peers - If, for instance, I'm at DLEP Version 19, and I discover a potential DLEP peer at Version 1, I *might not* want to connect up in the first place.

Regards,
Stan


On Nov 14, 2013, at 10:56 AM, Rick Taylor <[e-mail]<javascript:_e({},%20'cvml',%20'[e-mail]');>>
 wrote:

+1 - Good point, I think we need to suggest some final text for this whole discovery process soon or we will forget our rough consensus.

Rick (on his other email address)

________________________________
From: [e-mail] [[e-mail]] on behalf of Martin Duke [[e-mail]]
Sent: 14 November 2013 15:16
To: Taylor, Rick
Cc: [e-mail] Group ([e-mail]); Stan Ratliff (sratliff)
Subject: Re: [manet-dlep-rg] DLEP multicast address

I agree with almost all of what Stan and Rick said, but I don't think it would hurt to have a sentence like "A router MAY send unicast peer discovery messages to modems, regardless of logical distance, if it has obtained their IP address through an out-of-band process."
On Nov 14, 2013 2:13 AM, "Taylor, Rick" <[e-mail]> wrote:
> From: [e-mail] [mailto:manet-dlep-rg-
> [e-mail]] On Behalf Of Stan Ratliff (sratliff)
> Subject: Re: [manet-dlep-rg] DLEP multicast address
>
> +1. Henning's right; there's no need to go to the IEEE, IMO...
>
> Seems like the issue for us is how to scope discovery. Is it
>
> (a) a single-hop operation, exploiting link-local MCAST, or
> (b) a potentially multi-hop operation, utilizing some sort of site-local
> or other MCAST technique/address?
>
> I'm leaning to making it link-local (1-hop) myself. Note that does *NOT*
> preclude multi-hop DLEP operation over a TCP socket; it just means that
> multi-hop DLEP sessions would rely on a-priori configuration. There are
> *lots* of other issues that are going to confound, confuse, and otherwise
> screw-up multi-hop DLEP... ;-) Given the amount of characters typed over
> lesser issues, I don't know how far we want to go into multi-hop DLEP at
> this juncture. Suffice it to say my position is to write the spec in such
> a way as to avoid *precluding* it, but not to attempt to describe it.
> Multi-hop DLEP *can* work, given a careful network design (including a
> careful addressing policy). But I do not believe it will "generalize" down
> to something that warrants a section in the spec.

This is a big +1 from me.

Yes, we should specify that link-local multicast SHOULD be used (sent by the router periodically) and not forwarded.

Yes, we should add some text to say "Other discovery methods may be used, but then you start the standard TCP part of DLEP session establishment"

Yes, we should not preclude multi-hop links between router and modem, but also we should not get caught up in defining it - the draft IMHO should define the 1-hop behaviour only.

(When I say 'we' - I mean Stan and the other authors, it's just easier than translating all sentences into the passive voice and using 'one' instead, which just makes my prose increasingly Shakespearean which is unkind on those for whom English is a second language - this sentence being a case in point)

Rick

>
> Stan