What I'm referring to is source based routing. It can be done with the new iproute stuff. What you do is use "ip rule" to match the ip address and use a different routing table. I use this on my gateway so that machines behind it can use the choice of ip to specify which external link to use. It's all external to the program. The don't route options would seem to be ok for contacting other machines on the local network but without the routing table you can't go through any gateways. Hope this helps, On Thu, Jan 15, 2004 at 05:05:50PM +0800, Xia Wei-Zhong-W20079 wrote: > Martijn > > Thanks for the information, but can you further describe how to config route to let it pay attention to the source ip address? > > Following your idea, I checked the SOL_DONTROUTE & MSG_DONTROUTE, and write a sample udp program that use MSG_DONTROUTE, > but still don't work. > > Searching the Internet, I find below article by Neil Brown, http://www.cs.helsinki.fi/linux/linux-kernel/2003-07/0711.html. > And I think what I am looking for is very similar to that describled in this article, that is applications have full control on sending which packet over which interface, > using no routing information at all. > > So is this possible on linux, for both udp & tcp, and in a not-very-complicated way? > > Thanks, Xia Weizhong > > -----Original Message----- > From: Martijn van Oosterhout [mailto:kleptog@svana.org] > Sent: 2004?1?15? 14:54 > To: Xia Wei-Zhong-W20079 > Cc: linux-net@vger.kernel.org > Subject: Re: route & bind > > > On Thu, Jan 15, 2004 at 02:40:49PM +0800, Xia Wei-Zhong-W20079 wrote: > > Hi > > > > This can be a silly question, but I still want to hear what you will say. > > > > For an IP host with multiple network interfaces, can I only use bind to send out packets? > > I mean by bind a socket to the local IP address of an interface. > > > > I test this on my linux box, seems it does not work. > > > > So what does the bind system call really do? and do you know any way other than > > setting up the routes to make the IP packet go through the correct interface? > > The bind system call sets the source IP address (and possibly the port) of the > outgoing packets. This will be the address used by the other end to send > replies. It has absolutly no affect on the routing unless the routing is > configured to pay attention to the source ip address. Which is definitly not > the default. > > If you don't use bind, the kernel will pick an IP address for you, usually > based upon the route used to send the packet. > > So the answer to your question is, use the routing tables to direct the > packets the way you want. If you want to have the source ip address affect > that, configure it that way. > > -- > Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > > (... have gone from d-i being barely usable even by its developers > > anywhere, to being about 20% done. Sweet. And the last 80% usually takes > > 20% of the time, too, right?) -- Anthony Towns, debian-devel-announce > - > : send the line "unsubscribe linux-net" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > (... have gone from d-i being barely usable even by its developers > anywhere, to being about 20% done. Sweet. And the last 80% usually takes > 20% of the time, too, right?) -- Anthony Towns, debian-devel-announce
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