SCTP sendmsgx

[Michael Tuexen]

> On 9. Mar 2020, at 11:01, Doug Hardie <bc979 at lafn.org> wrote:
> 
>> I am trying to get sctp_sendmsgx to work and not having a lot of success.  I have not been able to find any examples on the web of using it.  I have a client using sctp_sendmsg working fine.  I need to make use of the multihoming feature which requires sctp_sendmsgx.    I changed the call to sctp_sendmsgx, and changed the address count to 2.  However, all I get is an EINVAL response.  Looking through the code there are at least 2 different possible causes, but I can't distinguish between them. I do have two address structures in the address field.  Are there any examples of how to build a client with sctp_sendmsgx?
> 
> I am now making some progress.  If you are using the sctp_sendmsg function the sa_len or sin_len field is not used.  However, sctp_sendx does use it.  Leaving it at zero causes
Yepp, filling out the sa_len field is important.
> the problem.  sendx now sends a connection init to the remote host.  There is no server running there yet.  It hangs for quite some time and doesn't try the multihome address.  I seem to recall reading something about that so will investigate that tomorrow. 
What do you see on the wire? I would expect INIT chunks to be sent to the two addresses you provided.

Please note that sctp_sendx() is deprecated (like sctp_sendmsg()). Please consider using sctp_sendv().
See https://tools.ietf.org/html/rfc6458#section-9.12

Best regards
Michael
> 
> -- Doug
> 
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