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

[Olivier Bonaventure <[e-mail]>]

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 ?


Olivier