Re: [multipathtcp] API: which address to use

[William Herrin <[e-mail]>]

On Mon, Nov 9, 2009 at 5:49 AM, Pasi Sarolahti <[e-mail]> wrote:
> This problem was just discussed in the meeting. Could one possible solution
> to the getsockname semantics problem be to use a separate address family for
> multipath connections? It could be similarly structured to the traditional
> AF, but from the different AF the app would know the semantics are
> different.

Hi Pasi,

Not really, no.

Backwards compatibility is an issue, as you mentioned. So is a desire
to be able to use both IPv4 and IPv6 paths in a single multipath TCP
connection. If it's a legacy app then it's expecting getsockname to
return the same address family that it used to initiate the socket. If
you provide something else you could open a path for buffer overflows
or other mischief.

For applications which are aware of Multipath TCP, the underlying
address is quite literally the wrong question. The connection has
candidate addresses, active subflows and some form of shared
identifier but it doesn't have "a" local address. Getsockname and
getpeername should fail with EMULTIPATH.

Regards,
Bill Herrin

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