Dear Tie, As I understand you have three machines of which each is in it's own logical segment. That means that you require a router in each segment to route packets from each subnet. Based on the networks you mentioned in your email you problem probably lays with routing between each subnet. Of course there is also the possibility of having rules locally on your machines active with iptables which can hence block traffic. You can list them by typing iptables -L and flush (empty) the rulesets by typing iptables -F. If you are not in charge of the routing between these segments then talk to someone who is and see what goes bad there but before that I would suggest checking the rules. In addition to that (as a plus) you can always run a tcpdump -i eth[X] and start flowing traffic (tsclient , ftp , etc) and see if the other end does indeed get the packets but simply can't route back to the originating machine. This is a ncie way of doing some access-list reconnaissance. In conclusion your problem could possibly be the access given to route between each of your three subnets. Warm Regards, Mario A. Spinthiras Nicosia , Cyprus Blog: <a href="http://www.spinthiras.net">http://www.spinthiras.net</a> Mail: <a href="mailto:mspinthiras@gmail.com">mspinthiras@gmail.com</a> Skype: smario125 <div class="gmail_quote">On Tue, Apr 1, 2008 at 5:46 AM, stin wang <<a href="mailto:stin.wang@gmail.com">stin.wang@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">I try to convert my work from windows to linux. first install Ubuntu is so easy , thanks god. now i can use Firefox, msn, and so on ,with proxy setting correctly but my question is my computer is used in subnet, configuration as follow pc1 ip <a href="http://172.18.20.87" target="_blank">172.18.20.87</a> mask <a href="http://255.255.255.224" target="_blank">255.255.255.224</a> gate <a href="http://172.18.20.94" target="_blank">172.18.20.94</a> the problem is described as follow: there are other two pcs pc2 <a href="http://172.18.20.98" target="_blank">172.18.20.98</a> <a href="http://255.255.255.224" target="_blank">255.255.255.224</a> <a href="http://172.18.20.126" target="_blank">172.18.20.126</a> pc3 <a href="http://172.18.20.225" target="_blank">172.18.20.225</a> <a href="http://255.255.255.224" target="_blank">255.255.255.224</a> <a href="http://172.18.20.253" target="_blank">172.18.20.253</a> i can ping <a href="http://172.18.20.98" target="_blank">172.18.20.98</a> <a href="http://172.18.20.225" target="_blank">172.18.20.225</a> in pc1 ,it's ok but i can't use ftp,vnc,or tsclient to pc2 or pc3, but it's ok for <a href="http://172.18.20.88" target="_blank">172.18.20.88</a> which is in the same gateway as pc1, what's wrong with it? how to figure out. or just ubuntu have some problem with subnet?? i use ubuntu 7.10 -- ---------------------------------------------- Tie Wang TianJin Climate Center TianJin Meteorological Bureau Tianjin, China, 300074 Email: <a href="mailto:stin.wang@gmail.com" target="_blank">stin.wang@gmail.com</a> Tel:+86-22-23333559 ---------------------------------------------- -- ubuntu-users mailing list <a href="mailto:ubuntu-users@lists.ubuntu.com">ubuntu-users@lists.ubuntu.com</a> Modify settings or unsubscribe at: <a href="https://lists.ubuntu.com/mailman/listinfo/ubuntu-users" target="_blank">https://lists.ubuntu.com/mailman/listinfo/ubuntu-users</a> </blockquote></div>