Re: Multiple connections from the same source address.

[Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>]

On Fri, Sep 08, 2017 at 09:03:31AM +0000, David Laight wrote:
> Can anyone think how to create multiple outgoing connections
> from the same subset of local IP addresses and the same port?
> 
> We bind() to the first IP address and port, then use
> SCTP_SOCKOPT_BINDX_ADD to add the second IP address.
> But even with IP_REUASADDR set you can't repeat that on
> a second socket.

When did you set IP_REUSEADDR? Checking the code, seems you have to set
it before any binding, because then the port entry will be created and
such flag will be initialized with that state.

> 
> It is possible to bind a second socket by reversing the
> order of the IP addresses (this might be deemed to be a bug!)

Interesting. It does seem like a bug. Probably related to the above
behavior.

> 
> If you bind to IN_ADDR_ANY then a second socket can be bound
> to the same port once the outgoing connection has been made
> (and the actual local address assigned).
> This works for TCP, but for SCTP you almost always need to
> constrain the local addresses advertised on the connection.
> 
> Ideas?
> 
> I've not tried binding to IN_ADDR_ANY and using bindx to
> add all the addresses.
> 
> 	David
> 
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