> Perhaps my choice of wording wasn't exactly correct. Make it "does not > function in this capacity unless modified." But there's a missed point: add > in packet analysis and you're doing NAT. The boasted transparency of Plan 9 > is a product of bringing most (or really all?) functions, including > networking, into a single framework. That single framework exists as an > application of networking, i.e. 9P, hence living in the application layer. > Descending to network layer is expulsion from the Plan 9 Eden.
I've tried to stay out of most of these, but I think this might help you get a better feel for it. First, don't get too hung up on application vs. network layers. The OSI protocols are largely forgotten for a reason. It's not bad as a conceptual model, but as soon as you try to force any predefined definitions of layers on real networks, you soon lose your grip on sanity. So how to think about it? First, it's *not* NAT, because there's no address translation going on. So when importing the router's /net, your messages are carried from your machine to the router as part of 9P Twrite messages. And your responses come back with Rread messages coming from the router to your machine. Notice here that the router doesn't get an IP datagram that it needs to pass on. Instead the router creates a TCP packet to carry the message. This is the fundamental difference. The encapsulation of the message in TCP/IP is done on the gateway, obviating the need for any translation and obviating the need for the router to care what is being sent from your machine. Using NAT, your machine does the encapsulating of the message in TCP/IP and passes that packet to the router. Because the encapsulating IP datagram carries the IP address of your machine,the router is required to translate the address, hence the name, NAT. Because the router isn't transparent in the sense that it doesn't pass what is sent from your machine unchanged, protocols like ftp are a nightmare. With 9P, there's no issue because what your machine sends (only the ftp messages) are not changed or even looked at by the router. So bottom line: importing /net is not NAT in any way. It's so much cleaner than NAT and it falls out for free from the structure of the system. There's not much better than getting functionality with no additional code that is better in many ways than the approaches that require special and kludgy code. BLS
