Hi Antony, Thanks for your reply. Please see inline: > On Saturday 10 April 2004 7:54 pm, Jee J.Z. wrote: > > > Dear all, > > > > I am trying to setup three PCs and do some simple filter+nat jobs. The > > situation is specified below: > > > > 1.PC1 has one NIC with a global IP connected to a Switch; > > 2.PC2 has two NICs, eth0 with a global IP connected to the Switch and eth1 > > with an internal IP (192.168.0.1/24) directly connected to PC3's eth1; > > 3.PC3 has two NICs, eth0 with a global IP connected to the Switch and eth1 > > with an internal IP (192.168.0.2/24) directly connected to PC2's eth1. > > !? Why !? > > (Either, why are PC2 and PC3 connected, or, why are both PC2 and PC3 connected > to the switch?) > > > I am trying to send packets from PC1 to PC3, via PC1/eth0(global > > IP)-->PC2/eth0(global IP)-->PC2/eth1(192.168.0.1)-->PC3/eth1(192.168.0.2). > > Actually, PC3/eth0 is not in used in the case. > > So, what's PC3/eth0 for? You are right. PC3/eth0 is a redundancy in this setup. That's why I tried disabling PC3/eth0. I am just curious that when more than one NIC are activated, which one will the PC choose to send packets? I guess one of them should be a default NIC, right? How do I know or set one as default? > I think your problem is a routing table (almost certainly the one on PC3, but > possibly the one on PC2). Right. I am quite new to setting up routing tables. That should be the reason... :( > Look at the routing table of each machine the packets are going through, and > then the replies trying to get back again, and see if (a) there is a path, > and (b) it makes sense. Both PC2 and PC3's routing look like: Destination Gateway Genmask Flags Metric Ref Iface 192.168.0.0 0.0.0.0 255.255.255.0 U 0 0 eth1 144.32.xxx.0 0.0.0.0 255.255.254.0 U 0 0 eth0 127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 lo 0.0.0.0 144.32.xxx.yyy 0.0.0.0 UG 0 0 eth0 I haven't added anything to the routing tables, and not quite sure what rules I should add. I have ever tried adding a default gateway, but it doesn't seem to work. I know I must be missing something obvious. Could you show me your thoughts? > I think once you've done this you will find the source of your problem, but I > really do recommend you think about your network setup, and the path you are > trying to get packets to take, and ask yourself "why do it like this?" Once getting rid of PC3/eth0, four NICs remained are involved: PC1/eth0-->PC2/eth0-->(filter,nat)-->PC2/eth1-->PC3/eth1. Then any problems? > For your benefit I have specifically selected the sig on this email :) Thank you!:) > Regards, > > Antony. > > -- > 90% of networking problems are routing problems. > 9 of the remaining 10% are routing problems in the other direction. > The remaining 1% might be something else, but check the routing anyway. > > Please reply to the list; > please don't CC me. > > >
