8:35 a.m.
Hi Paolo,
On 13/11/2019 17:18, Paolo Abeni wrote:
On Wed, 2019-11-13 at 16:48 +0100, Matthieu Baerts wrote:
> <On 12/11/2019 09:21, Paolo Abeni wrote:
>> AFAICS DSS, MP_CAPABLE and MP_JOIN are mutually esclusive, and the
>> bigger is DSS with 64 bytes ack/seq and csum with a total of 28 bytes -
>> which fit the TCP option space.
>>
>> Additional MPTCP options (ADD/DEL_ADDR/PRIO/FAIL/FASTCLOSE/...) can
>> indeed run out of space, but that failure is not fatal (do not break
>> the connection nor causes fallback) and is handled gracefully - no
>> WARN, just omit the option. Additionally we could increment some MIB
>> counter.
>
> When you say that the option is omitted, do you mean that the option is
> sent in the new (dedicated?) ACK packet or dropped/never sent? :)
With the current code, prior to this series, the ADD/DEL_ADDR option
exceeding the TCP option space is dropped/never sent. This series do
not change such behavior.
Indeed, it was already the case. Thank you for your quick reply!
Should we already add the MIB counter? And/or add a TODO in the code?
We are not there yet but missing an ADD_ADDR can have bad consequences.
And it would be unexpected for the userspace to drop it, especially with
MPTCPv1 which should make it reliable :)
Inserting a (duplicate) ack to try to fit such option looks doable,
but
also out-of-scope for this change.
Agreed. We should add this in a TODO list of "things for later" :) (or a
TODO in the code?)
Cheers,
Matt
--
Matthieu Baerts | R&D Engineer
matthieu.baerts(a)tessares.net
Tessares SA | Hybrid Access Solutions
www.tessares.net
1 Avenue Jean Monnet, 1348 Louvain-la-Neuve, Belgium