From: Marcelo Ricardo Leitner > Sent: 08 September 2017 15:50 > 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. Indeed, otherwise it has no effect. The point is that (IIRC) IP_REUSEADDR only lets you bind the same port number to 2 sockets - the IP addresses have to be different. Code that does this for TCP (like the old ftp data connection) only worked because the address it was binding was IN_ADDR_ANY and the existing socket had a local IP address. It always had to retry because two sockets couldn't be bound to the port and IN_ADDR_ANY either. > > 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. More likely the duplicate check is in some generic code that doesn't look at the extra addresses. David -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
