Re: [multipathtcp] Preparing for Prague meeting - things to delete or add to MPTCP protocol bis

[Christoph Paasch <[e-mail]>]

On 15/07/15 - 17:49:24, Olivier Bonaventure wrote:
> Christoph,
> >
> >On 15/07/15 - 16:48:40, Olivier Bonaventure wrote:
> >>>>>                                          +-+-+-+-+
> >>>>>
> >>>>>        Flags is a set of 4 flags:        |C|r|r|r|
> >>>>>
> >>>>>                                          +-+-+-+-+
> >>>>>
> >>>>>        C flag MUST be set to 1 when the address/port are checked.
> >>>>>
> >>>>>        "rrr" are for future assignment as additional flag bits.
> >>>>>
> >>>>>        r bits MUST each be sent as zero and MUST be ignored on receipt.
> >>>>>
> >>>>
> >>>>However, I'm stil not convinced by the usefulness of using the C bit
> >>>>that you propose. If a host knows that it cannot receive a SYN over a
> >>>>given address, then the best solution is to not advertise this address.
> >>>
> >>>[Med] Agree. An implementation that supports the "C" flag is likely to advertise addresses/ports for which pinholes have been created in NATs/FWs and address/ports that can be used to receive incoming packets successfully.
> >>
> >>
> >>>The issue with the implicit approach (i.e., no C-flag) is at the server side: should the server interpret the advertisement of an address/port as an indication that packets can be sent without experiencing reachability issues or not?
> >>
> >>This is what RFC6824 assumes today. ADD_ADDR is only a hint about the
> >>possibility of trying to reach this address. Anyway it will be a SYN and the
> >>host will wait for a SYN+ACK to confirm the reachability
> >
> >I think, concerning the reachability, what is rather interesting is to
> >advertise the secondary address without wanting the peer to even try
> >establishing a new subflow to this address. This advertisement is done in
> >case the "primary" subflow becomes unreachable. If it becomes unreachable,
> >then the peer can use the advertised address to create a new subflow.
> 
> You would then propose a kind of "Backup" flag in the ADD_ADDR option
> meaning that this address should only be used to create a subflow if the
> primary subflow fails ?

Yes, something along those lines.
When all other addresses are failing, then this "backup"-address can be used
for a new subflow.


Cheers,
Christoph