Re: [multipathtcp] MPTCP backup flag attack via MP_PRIO message

[Alan Ford <[e-mail]>]

Hi Yoshi,

On Fri, 21 Jul 2017 at 22:37, Yoshifumi Nishida <[e-mail]>
wrote:

> Hi Alan,
>
> On Fri, Jul 21, 2017 at 12:45 AM, Alan Ford <[e-mail]> wrote:
>
>> Hi Yoshi,
>>
>> On 20 Jul 2017, at 22:22, Yoshifumi Nishida <[e-mail]>
>> wrote:
>>
>> On Thu, Jul 20, 2017 at 8:33 AM, Alan Ford <[e-mail]> wrote:
>>>
>>>
>>> So the main reason for this was to permit the signalling of backup for a
>>> subflow which was also signalled via ADD_ADDR. ADD_ADDR does not have a ‘B’
>>> bit in it, so the priority would be signalled separately.
>>>
>>
>> I think adding 'B' bit in ADD_ADDR has been proposed to be added in the
>> bis draft.
>> I have seen a few supports while haven't seen any oppositions.
>> Do we need more discussions on this?
>>
>>
>> Actually on further reflection (i.e. Christoph and Olivier reminding me
>> offline), this would be unnecessary, since MP_JOIN has a ‘B’ bit so it is
>> not required in ADD_ADDR.
>>
>> Given this I can see no reason to have the Address ID in MP_PRIO and feel
>> we can remove it.
>>
>> (The proposal for a bit in ADD_ADDR was, I believe, as a “do not even
>> attempt to establish to this address unless all other subflows fail - which
>> is different to the ‘B’ semantics in MP_PRIO and MP_JOIN)
>>
>
> Yes, I thought it's a valid use case.
> If we remove addr id from MP_PRIO, I think we will always need to
> establish a subflow to make it backup.
>

That has always been the case - MP_PRIO only affects running subflows. With
Address ID it could have affected policy on subflows that were later
established, but would not affect subflow establishment policy.

The proposal to signal a break-before-make backup flag has been suggested
but has not received sufficient traction to be adopted.

Regards,
Alan