RH 7.2 and 3Com LAN Modem

[veronicay]

Hi,

I've just installed Red Hat Linux 7.2 on an old Pentium P120. The installation went fine, but I'm having great difficulty setting up networking. The machine is on a 10Base-T LAN with a 3Com OfficeConnect LANModem (combined hub/router/ISDN modem). All the machines on the LAN use the router to connect to the Internet. The PC is set to dual boot Linux/Win95, and in Win95 it has no problem seeing the LAN or connecting to the Internet.

When I initially installed RH, it didn't detect the NIC (a 3Com Etherlink III 3c509b). But when I booted Linux for the first time, it did detect the card and prompted me to configure it, which I did by copying the IP address etc. from the Windows configuration. After a lot of fiddling about, I think the basic hardware/driver configuration is OK -- there are no errors during boot, and eth0 is shown as mounting without error. The 3Com box has lights on the front showing connected NICs, and the relevant light duly lights up when I boot the machine. But it doesn't seem to be able to see anything else on the network. I can't ping the other machines or the router, and they can't ping the Linux box.

I've double-checked the configs -- the router has a built-in DNS, so I've set default gateway and DNS on the Linux box to 192.168.1.1 (the address of the router). The router also has DHCP, but I've switched it off and hard-coded the IP addresses of the PCs (in the 192.168.1.* range). These settings all work fine on the Windows boxes -- so what am I missing? I'm completely new to Linux and the howtos on linux.org are beyond me ... Some tips on how to diagnose where the problem is would be great!

[Stuka]

If you post the output of "ifconfig eth0" and "route" (both w/o the quotes), it would probably help verify that all your settings are correct.

[veronicay]

Originally posted by Stuka
If you post the output of "ifconfig eth0" and "route" (both w/o the quotes), it would probably help verify that all your settings are correct.

Thanks Stuka! Here goes:


ifconfig eth0:

eth0 Link encap:Ethernet HW addr 00:10:5A:5A:63:16
inet addr:192.168.1.3 Bcast:192.168.1.15 Mask:255.255.255.240
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX Packets 1159 errors:0 dropped:0 overruns:0 frame:0
TX Packets 124 errors:0 dropped:0 overruns:0 frame:0
collisions:0 txqueuelen:100
RX bytes: 0 (0.0 b) TX bytes:5208 (5.0kb)
Interrupt: 5 Base address: 0x220

route:

Kernel IP routing table

Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 * 255.255.255.240 U 0 0 0 eth0
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
default 192.168.1.1 0.0.0.0 UG 0 0 0 eth0


Hope this is some use ...

[Stuka]

Ah-ha! Found the problem, I'm 99% sure. This line Mask:255.255.255.240 is wrong. For 192.168.1.* addresses, the Mask: line should read 255.255.255.0. If the latest version of Linuxconf is like older ones, you should be able to fix that pretty easily - the line will be Subnet Mask, or something of the sort. Fix that, and you should be fine. If you want to verify that that line is correct, you can check the settings in Win95 - look for the subnet mask under Start->Control Panel->Network.

[veronicay]

Hi,

Well, all the PCs have the subnet set to 255.255.255.240. I don't know why, but hey, it works! (up till now...) I assume if I changed the Linux box to use 255.255.255.0, I would have to change the other PCs and the router as well? At any rate, changing the subnet on the Linux box alone doesn't make any difference -- it still can't ping or be pinged.

There's something else that puzzles me: the output from ifconfig says: bcast 192.168.1.15. Does this mean that the system is advertising itself as having this address?If so, that could be why the router won't talk to it. Excuse my ignorance if I'm complately off base here ...

[Stuka]

Well, the 255.255.255.240 mask is for a subdivided Class C network. My best guess is that the Windows boxes are getting info through a M$ networking thing, and they know how to get their ARP stuff done through that, but the Linux TCP/IP stack is trying through standard methods that aren't working. The broadcast address is based on the IP address and subnet mask, so that number is correct (it's the broadcast address for the whole 192.168.1.0/29 subnet). I would try changing ALL the machines over to a subnet mask of 255.255.255.0, and see if you can get 'em to work.

[veronicay]

Originally posted by Stuka
I would try changing ALL the machines over to a subnet mask of 255.255.255.0, and see if you can get 'em to work.

OK, thanks, I'll try that later (in use at present) ...

[veronicay]

Later ... damn, that didn't work. With the new subnet setting, the Windows PCs still see the network fine, but the Linux box can still only ping itself -- pinging anything else gives "Destination host unreachable". Any other suggestions??

Thanks!

[Stuka]

Can you post the new output from route & ifconfig?

[veronicay]

Originally posted by Stuka
Can you post the new output from route & ifconfig?

Sure ... much easier now I've found out how to pipe the output to a DOS-compatible floppy! <g>

ifconfig:

eth0 Link encap:Ethernet HWaddr 00:10:5A:5A:63:16
inet addr:192.168.1.3 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:14 errors:0 dropped:0 overruns:0 frame:0
TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:0 (0.0 b) TX bytes:420 (420.0 b)
Interrupt:5 Base address:0x220


route:

Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 * 255.255.255.0 U 0 0 0 eth0
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
default 192.168.1.1 0.0.0.0 UG 0 0 0 eth0