Which Card Pings

[UnStable]

I've got a Linux box working as a router for my WinXP box. My linux box is also plugged into a router, with my roommate's comps. My Linux box uses 192.168.0.101 for eth0 (connected to the router) and 192.169.0.1 for eth1 (connected to the XP box). Whenever I try to ping a computer from my Linux box I can only ping outside my network or my XP machine because it's pinging from 192.168.0.1, so it can find the XP machine or outside addresses, but can't find any 192.168.0.100/102/103 (which are my roommate's comps). How can I go about changing which eth is responsible for ping requests?

I used the Mandrake Networking Autoconfiguration to setup the Linux machine as a router, if that is neccessary to know.

Also, how would I allow others to ping me? My roommates can't ping my linux computer even though they are all on the router.

-UnStable

[vttimwhite]

When your router is properly configured, it will send the ping (the echo request, actually) out the proper card. if you use the ROUTE command, you should see something that includes:

192.168.0.0 * 255.255.0.0 U 0 0 0 eth0
192.169.0.0 * 255.255.0.0 U 0 0 0 eth1

You don't say what your subnet mask is. That setting can make all the difference in the world. based on the addresses you say you're using, you need a 16-bit mask (255.255.0.0).

From your description, I can't quite tell how you're interconnected. It seems like there's an awful lot of routers there.

Are you pinging by name or by IP address?

It is also conceivable that the other computers are not using the appropriate default gateway. Realize that a Ping is an echo request answered by an echo reply. That means that it is possible that your request is making it out, but the reply can't make it back.

Some firewall configurations ignore the echo request. Are you using a firewall?

A little more detail might get you a specific answer...

[UnStable]

Ok, In my room I have an wall connection and 2 computers. I run my WinXp computer to my Linux computer, which runs into the wall. In another room in my apartment, all of the bedroom connections run into a box, which holds a hub that plugs into our cable modem. Here is the info of that stuff:

Router IP: 192.168.0.1
Roommate 1: 192.168.0.100
Roommate 2: 192.168.0.102
Roommate 3: 192.168.0.103
Myself (Linux box): 192.168.0.101


In my room my eth0 card is plugged into the wall. Here is the info on my eth1 card, which is plugged into my WinXP box:

IP: 192.168.0.1
WinXP IP: 192.168.0.110
WinXP Gateway: 192.168.0.1

All subnet masks (on all 5 comps) are 255.255.255.0.

All my roommates can ping each other, but not my Linux box. If I try to just "ping 192.168.0.xxx" I get no response, because it only looks at my WinXP machine. My linux computer can ping other computers if I put the command "ping 192.168.0.xxx -I eth0". This tells it to use eth0, and not eth1, to try to ping so it's checking our apartment LAN, instead of just my WinXP box. I was wondering if there is a way to make eth0 the default card that pings.

All Internet connections, FTPs, ect work on both my Linux box and WinXP box.

1. Can I change my default "pinger" from eth1 to eth0?

2. Is is possible for my linux machine to be blocking pings, so my roommates cannot ping me? And if so, how can I enable pings?

-UnStable

[vttimwhite]

1. Can I change my default "pinger" from eth1 to eth0?

Not directly, no. That decision is made when the computer looks at the routing table. I suppose you could create an alias command for PING that uses the -I eth0 switch, but that doesn't fix the problem really.

2. Is is possible for my linux machine to be blocking pings, so my roommates cannot ping me?

Yes. It is possible and it even seems likely at this point. Since all other services appear to work, you network is basically sound. Do you have a firewall running on the Linux machine? I suspect you do. PING is one of the ICMP protocol message types. Specifically, the echo request is ICMP message type 8 and the echo reply is type 0. Many firewalls block type 8 since it could turn into a Denial-Of-Service (DOS) attack.

I still suspect a routing table problem. Try using the TRACEROUTE command from the XP machine and see what happens, that might tell you where the breakdown is actually happening.

-vttimwhite