7On Sat, 14 May 2005 02:28:57 +0300, Christos TZOTZIOY Georgiou <[EMAIL PROTECTED]> wrote: >On Wed, 11 May 2005 22:48:31 -0400, rumours say that "Terry Reedy" ><[EMAIL PROTECTED]> might have written: > >>> and what if both computers >>> wanted to participate on the port 6000 fun? > >>Recently, I had one family member use my purchased account to logon to and >>play an online action game, which sends a constant stream of update info. >>Then, curious what would happen, I logged on, from a different computer but >>through the same router, with a temporary guest account. Somewhat to my >>surprise, it worked -- without touching the computer (XP) or router >>settings. And kept working the whole weekend. So there is a way to tag >>update packets so they can be reliably separated into two streams (and vice >>versa). Solipsis should be able to do the same. > >In your case, it's the internal address that originated the connection-- >so the router can distinguish the streams: > >(int1, port1)->(ext_host, port0) >maps to (router_ext, port2)->(ext_host, port0) > >(int2, port3)->(ext_host, port0) >maps to (router_ext, port4)->(ext_host, port0) > >Every TCP/UDP packet includes srcip, srcport, dstip, dstport, so an >internal "dictionary" makes the translations to and fro (the router >changes the srcip, srcport whenever a packet passes through). The >internal computer knows not that the router mangled the packets, and the >external computer knows nothing about the internal computer address. > >However, if both of your internal computers listen to port 6000 for >example, there is no easy way for the router to know to which one it >should forward an *incoming* request for connection to port 6000-- all >it knows is that some external computer connected to its external >interface ip address at some specific port. In this case, *typically* >you would map port (router_ext, 6000) to (int1, 6000) and (router_ext, >6001) to (int2, 6000). The internal computers would both think that >some computer is doing a connect at their port 6000.
Combinations of marginally smart routers and non-broken protocols can deal with even this situation automatically, without user configuration or intervention. Traffic to (router_ext, N) from (ext, M) can be switched to (int1, N) or (int2, N) by simply noticing which of int1 or int2 has recently sent traffic from N to (ext, M). If both have, you can still generally figure it out, by rewriting the source port automatically on the router. Many routers support the former of these, and a sizable portion support the latter. Of course, if your protocol includes port numbers in the application areas of the packets it sends, the router usually can't properly rewrite the packet, so things go pear shaped. Jp -- http://mail.python.org/mailman/listinfo/python-list
