[multipathtcp] draft-ford-mptcp-multiaddressed-02: Need ports in ADD address

[Magnus Westerlund <[e-mail]>]

Hi,

I just looked at draft-ford-mptcp-multiaddressed-02 and saw that the add
address option lacks a port number. I think that will not work for two
reasons.

1. First, there will a large amount of single flow TCP connections and
you will run into a synchronization issue and resource constrain issue
if you limit your interface port to be the same over all interfaces.

2. Your NAT traversal will fail as soon it encounters a NAT that is
unable to do port preservation. That is likelier and likelier to happen,
espeically for ISP place NATs where the load level is higher. Port
preservation will also fail as soon as two sub-flows goes over the same
NAT. Thus to enable MPTCP to work in cases where you use either an
explicit signalling protocol (UPnP, etc) or implicit methods, like STUN
to find out your external subflow address they will not be able to
preserver the port in the generic case. Thus there is need to be able to
indicate the listening port.

Cheers

Magnus Westerlund

IETF Transport Area Director
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