Re: [multipathtcp] Multipath TCP Address advertisement 1/5 - Load Balancing

Yoshifumi Nishida <nishida@sfc.wide.ad.jp> Tue, 16 August 2016 17:47 UTC

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From: Yoshifumi Nishida <nishida@sfc.wide.ad.jp>
Date: Tue, 16 Aug 2016 10:47:29 -0700
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Subject: Re: [multipathtcp] Multipath TCP Address advertisement 1/5 - Load Balancing
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Hello Fabien, all,

On Thu, Jul 28, 2016 at 5:18 AM, Fabien Duchêne <fabien.duchene@uclouvain.be
> wrote:

> Hello,
>
> As agreed in Berlin during IETF96, I'm sending a series of emails to
> discuss the different contributions proposed
> inhttps://datatracker.ietf.org/doc/draft-duchene-mptcp-add-addr/
>
> To allow Multipath TCP to operate for servers residing behind unmodified
> layer 4 load balancers we propose to define the "B" flag in the
> MP_CAPABLE option.
>
> This flag can only be used during the three-way handshake. When this
> flag is set, it indicates that the source IP address of the segment
> containing this flag does not accept the establishment of additional
> subflows for this connection. Otherwise, the source IP address of this
> segment can be used as destination address to create additional subflows.
>
> There are two use cases for this flag :
>
> - servers behind a load balancer can use this flag in the SYN+ACK to
> indicate that the IP address of the load balancer should not be used to
> establish subflows. Those servers will typically announce one or more
> other addresses with the ADD_ADDR option.
> - clients behind firewalls or NAT can use this flag in the SYN. If set
> in the SYN, the flag MUST also be set in the third ACK to support
> stateless servers.
>

I basically agree with "don't try to establish subflows with this" feature.
But, I am wondering if we can use MP_PRIO for this. (I also think it's fine
to use MP_CAPABLE as well if needed)

If we use this feature in MP_CAPBLE, we can only use this feature in the
first subflow.
If we use MP_PRIO, we can apply this feature to any subflows.
In addition, if the node want to change the status for some reasons, it can
send another MP_PRIO to update it.

Thanks,
--
Yoshi