Hi Everyone.

I have a small network composed of 20 machines. The machines were previously installed with Windows XP, but now I am trying to get them networked with Linux.

A very strange thing that I see is that I can ping the Windows machines from the Linux machines and vice versa. I can also ping any Windows machine from any other Windows machine but I am unable to ping any linux machine from another Linux machine.
Here is an output that I got from the arp command

[root@lcbi1 molbill]# arp
Address HWtype HWaddress Flags Mask Iface
192.168.10.1 ether 00:04D:6D9:B5 C eth0
yibeltal ether 00:0E:7F:A5:10:E9 C eth0
cbi4 (incomplete) eth0

cbi4 is the linux machine, 192.168.10.1 is the router's address and yibeltal is the windows machine's name.

and here is an output from ifconfig. On all machines the subnet mask is 255.255.0.0 and the net adress is 192.168.0.0.
[root@lcbi1 molbill]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0E:7F:2A:08:F8
inet addr:192.168.49.150 Bcast:192.168.255.255 Mask:255.255.0.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:5060 errors:0 dropped:0 overruns:0 frame:0
TX packets:5337 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:2960048 (2.8 Mb) TX bytes:740862 (723.4 Kb)
Interrupt:20 Memory:fc500000-fc510000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:417 errors:0 dropped:0 overruns:0 frame:0
TX packets:417 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:41956 (40.9 Kb) TX bytes:41956 (40.9 Kb)

I am a newbie to Linux administration but I believe ip works the same in all machines. Does anyone have any idea what's wrong?

If the file of /proc/sys/net/ipv4/icmp_echo_ignore_all is 1. ICMP will be enjoined.So you will not ping the linux machine.You may edit the file.Make the file's content is "0".

I looked at the file but its content is 0. Anyother possible solutions?

Perhaps linux's fireware is a reason.Try to enter command "service iptables stop" or "service ipchains stop".
Perhaps you did not set Gateway for the linux machine.Try to enter command "man route".

what's the ping error message that you get when you ping another linux machine.

are you pinging hostnames or IP's

# iptables -A INPUT -s 192.168.0.0/255.255.0.0 -p icmp --icmp-type 8 -j ACCEPT
# iptables -A OUTPUT -d 192.168.0.0/255.255.0.0 -p icmp --icmp-type 0 -j ACCEPT

Those should allow a computer to be pinged from anything in the
192.168.0.0 range if everything else is set up correctly.