Re: [multipathtcp] q about remove addr behavior

[Yoshifumi Nishida <[e-mail]>]

Hi Christoph,

On Thu, Jun 22, 2017 at 12:14 AM, Christoph Paasch <[e-mail]>
wrote:

> Hello,
>
> On Jun 21, 2017, at 9:04 PM, Yoshifumi Nishida <[e-mail]>
> wrote:
> In the Chicago meeting, I remember Joseph mentioned an issue on linux
> which close all subflows that use an IP address when rem addr for it has
> been received.
>
> (page 13 in https://www.ietf.org/proceedings/98/slides/slides-98-mptcp-s
> essa-channel-bonding-of-low-rate-links-using-mptcp-for-airbo
> rne-flight-research-00.pdf)
>
> As far as I read 6824bis draft, this behavior seems not to be recommended.
> But, do we need more specific guidance here?
>
>
> true, in Linux we just close the subflow and do not send keepalives to
> check whether the subflow is really up or not.
>
> I'm not sure if sending keepalives is the right thing to do. Basically,
> when the peer tells us that this subflow should be removed, why shouldn't a
> host trust its peer and do as as it says ?
> The benefit of closing the subflow is that we can stop trying to send data
> on it and we free those resources. Lingering subflows is a serious problem
> on the server-side, when clients move away from a WiFi access-point.
>

I am guessing it depends on how implementations are using remove addr
feature. We should avoid mixing up addresses and flows.
Even if a subflow is removed, it won't be wise to send remove addr when the
other subflows use the address.
The draft seems to presume a case where an IF has gone, but this kind of
events might not be easy to be caught at the TCP layer.
--
Yoshi