Re: [manet-dlep-rg] DLEP session establishment

["Taylor, Rick" <[e-mail]>]

My thoughts:

The principle of keeping the modem code as small and light as possible is good.  In general modems are not only getting bigger and smarter, they are also getting physically smaller and lower power.  Routers however are not getting so small so quickly, so even though there are full TCP stacks in many radios, we should not force a full server implementation on them.

So, Lets keep the 3-way handshake we have discussed, but make the router the advertiser/server:


   Router                                        Modem
   ===================================================

1) TCP Listen()

2) UDP Peer_Discovery ------------------------------->
     + Version TLV
     + TCP address:port

3)                                       TCP Connect()

4) <-------------------------------- Peer_Initialize()
                                      + Version TLV
                                      + Ident TLV
                                      + Mandatory TLVs

5) Peer_Initialize_Ack ------------------------------>
     + Status TLV
     + Ident TLV

I withdraw my suggestion about cookies.  As Teco has pointed out, just do security properly (TLS or IPSec or whatever).  Putting in a lightweight/half-baked authentication process in the protocol may lead some implementers to assume this provides security.

I have also suggested just Version TLV and TCP endpoint address in the UDP discovery packet to save space.  This should allow a listening modem to decide whether to start a session with a router before TCP connect.

At step 5, the router has the opportunity to send a negative ACK, by including an error Status TLV in the Peer_Inialize_Ack and then shutdown the connection.  This captures Teco's SHOULD condition "The router SHOULD NOT start a session with a modem that does not advertise mandatory metric TLVs"

Would it help to have a state machine in the draft?

Comments?

Rick Taylor
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