Hello! A problem someone might be able to help me with:
I have 2 computers: one with Linux, the other with WinXP. The Linux one is set up as an internet gateway; eth0 is my cable connection, eth1 is my internal lan connection that runs to the XP box.
Everything was fine until I upgraded from Mandrake 9.0 to 9.2. Now I can't ping between the two boxes. I can still ping external internet addresses from the Linux box though.
The static network settings on the XP box haven't changed: IP 192.168.0.12/24, default gateway is 192.168.0.1. The linux box eth1 static address is 192.168.0.1/24.

The precise error I get when I try to ping 192.168.0.12 from the Linux box (as root) is:

#ping -c 8 192.168.0.12
PING 192.168.0.12 (192.168.0.12) 56(84) bytes of data.
From 192.168.0.1 icmp_seq=1 Destination Host Unreachable
From 192.168.0.1 icmp_seq=1 Destination Host Unreachable
From 192.168.0.1 icmp_seq=1 Destination Host Unreachable
From 192.168.0.1 icmp_seq=1 Destination Host Unreachable
From 192.168.0.1 icmp_seq=1 Destination Host Unreachable
From 192.168.0.1 icmp_seq=1 Destination Host Unreachable
ping: sendmsg: Operation not permitted
From 192.168.0.1 icmp_seq=2 Destination Host Unreachable
ping: sendmsg: Operation not permitted
From 192.168.0.1 icmp_seq=3 Destination Host Unreachable

--- 192.168.0.12 ping statistics ---
2 packets transmitted, 0 received, +8 errors, 100% packet loss, time 2038ms

I get "request timed out" when I try to ping from the XP box.

I've checked the network addresses/settings on both machines and can find nothing wrong with them. The problem occurred precisely after I did the linux upgrade, so I doubt it's a cabling problem.

Oh - one more thing - I have the internet connection sharing set up via the instructions I found at the following url: en.tldp.org/HOWTO/IP-Masquerade-HOWTO/
I basically just copied and pasted an iptables config thingey and set it to start up at boot. I'm still new to this stuff, I don't know how it all works.

Anyone have any suggestions as to what my problem is?

Thanks to anyone who takes the time to answer

Usually you get that error when there's filtering on your local system. Most likely iptables has been configured to block ICMP echo requests to your LAN from anywhere. You have to exclude the internal firewall interface from that rule (i.e. block ICMP echo requests to the LAN from everywhere, except internal interface).

iptables -L
This will list the active filter rules. Posting the result from that command here would help alot in the error tracking.

Ok thanks I'll get back with my findings

[edit] Yup, you were both right the iptables stuff was the problem. The install changed the location of the iptables binary, so my script couldn't find it anymore.
Everything working again! Yay!