Re: [multipathtcp] Preparing for Prague meeting - things to delete or add to MPTCP protocol bis

[Olivier Bonaventure <[e-mail]>]

Med,

>
> A change was proposed in
> (https://tools.ietf.org/html/draft-boucadair-mptcp-symmetric-02) to
> redefine IPVer field of ADD_ADDR as a set of flag bits (see below). This
> change applies also for ADD_ADDR2.


I think that replacing the IP version with a set of flags (at least in 
ADD_ADDR2 to prevent backward compatibility problems with the existing 
ADD_ADDR implementation) would make sense.

>                                          +-+-+-+-+
>
>        Flags is a set of 4 flags:        |C|r|r|r|
>
>                                          +-+-+-+-+
>
>        C flag MUST be set to 1 when the address/port are checked.
>
>        "rrr" are for future assignment as additional flag bits.
>
>        r bits MUST each be sent as zero and MUST be ignored on receipt.
>

However, I'm stil not convinced by the usefulness of using the C bit 
that you propose. If a host knows that it cannot receive a SYN over a 
given address, then the best solution is to not advertise this address. 
This will typically be the case when a host is behind a NAT or a 
firewall (I guess that at some point middlebox vendors will include 
software to parse ADD_ADDR and remove the ADD_ADDR that correspond to 
addresses that are not reachable accoring to their policies)


Olivier