Re: [manet-dlep-rg] TCP clients, servers, and discovery (WAS: Re: notes DLEP meeting @ IETF88)

[Teco Boot <[e-mail]>]

Op 15 nov. 2013, om 11:33 heeft Taylor, Rick <[e-mail]> het volgende geschreven:

> Okay, just to back it up a bit, and try to get some clarity in the debate.
> 
> As I understand it, we are all happy with:
> 
>    Server                                          Client
>    ======================================================
> 
> 1)  TCP Listen()
> 
> 2*) Peer_Discovery (UDP) ------------Multicast----------->
>      + Version
> 
> 3)  <--------------------------------------- TCP Connect()
> 
> 4)  <---------------------------------- Peer_Request (TCP)
>                                                 + Version
>                                       + optional extras 1
> 
> 5)  Peer_Accept (TCP) ----------------------------------->
>      + Status
>      + Version
>      + optional extras 2
> 
> *Step 2 may be replaced with a-priori configuration, mDNS, etc...
> 
> What we are arguing about is who should be the Client, and who should be the Server.
> 
> So, I am now calling for everyone's answer to the following question:
> 
> "Should the modem be the Client or the Server in the above diagram, and why?"

Modem should be the server:
 - modems are servers today, for link metrics, OA&M etc.
 - modems provide a service, so they act as server
 - modems are "thumb" devices and can be reach from anywhere in the Internet, if permitted. No need to configure the modem for it, except setting access rights. No need to fire an "ignition packet".
 - modems can easily handle many TCP sockets, either TCP server or TCP client
 - TCP server programming is not more difficult than TCP client


> 
> I have intentionally left 'optional extras' 1 and 2 undefined as they may be relevant in your answers.

The Ack in the 3-way handshake is missing. After 5, Server thinks the DLEP session is open, but Client is not aware of it yet. This is minor detail, perhaps indeed use as few packets as possible. Also less state.


> 
> I will give my answers in a separate email.
> 
> If anyone has a problem with the above diagram, now is your chance to shout!

Yes, TCP server socket must be opened before the Peer_Discovery. 
After connection, Peer_Discovery packets SHOULD continue to be sent, for the following reasons:
 - no relation between UDP and TCP sockets, more lightweight
 - for modems that support it, other routers may set up DLEP sessions also
 - better recovery in case of failures, router knows modem is still present (think of heartbeat=zero)
 - in line with other discovery protocols (CDP, LLDP, Bonjour etc).


Teco

> 
> Cheers,
> 
> Rick
> 
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