2 network cards in one server on 2 networks.


I have three machines  A, B and C; and 2 hubs.
Machine B has 2 network cards and is attached to both
hubs, Machines A and C
are connected to different hubs respectively.

So the senario looks like.

 *                *
 *        A       *
 * *
 *                *
 *                     *
 *          B          *
 * eth0 *
 * eth1 *
 *                     *
 *                *
 *        C       *
 *  *
 *                *

I have installed Redhat 6.1 on machine B and given it
an IP address  I then ran linuxconf
and added the second ethernet device and
IP   Machines A and B can
ping each other happily. Then by swapping the IP
addresses in



ifconfig eth0 netmask up

ifconfig eth1 netmask up

and swapping the network cables on the network
devices. I can still ping A and B happily.

Figuring this proves both the network devices work.

I can not ping between machines B and C, I have tried
lots of different things but am obviously missing the

netstat -r gives me.

Destination    Gateway   GenMask        Flags  MSS Window  irtt   Iface  *  U       O  O        0     eth1  *  U       O  O        0     eth0      *      U       O  O        0     lo




all the ipx stuff is no.


all the ipx stuff is no.

I am aiming just to be able to ping machines A and C
from machine B. Then B from A and C at this point.

I looked in linuxconf and routing is enabled.
I then deleted everything from the route table

route del -net netmask dev eth0
route del -net netmask dev eth1

So when I do netstat -r I get.

Destination    Gateway   GenMask        Flags  MSS Window  irtt   Iface      *      U       O  O        0     lo

Of course I can't ping anything now.

I add
route add -net netmask gw
route add -net netmask gw

So doing a netstat -r again I get

Destination    Gateway                GenMask        Flags  MSS Window  irtt   Iface  UG       O  O        0     eth1  UG       O  O        0     eth0      *                  U        O  O        0     lo

I can pinging machine A( from machine
B( & ) is fine.

I still can't ping machine C( from
B( & ).

Any suggestions appreciated thanks.


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Could the obvious thing you are missing be that there is a bad (or misconfigured) ethernet card in the loop?  Does your hub have activity lights?  Check to see if they fash during ping attempts.  Compare the flashes seen on the working side to the non-working side.

Also, remember that 192.168.x.x are local internet addresses.  They can't be forwarded.  There are literally 100,000's of machines out there. Chaos would ensue . . .
It's not true that 192.168.x.x addresses can't be forwarded; just that they aren't _supposed_ to be forwarded outside of your local autonomous system (which can consist of many networks).  Internally, you can forward them at will, and it looks like that's what you'll want/need to do.

What type of machine is "C"?  If it's Linux or NT, could you post the "ifconfig" and "netstat -rn" output for it?  (I think W95/98 also has something similar, "ipconfig" or something?)

Is there anything else on the 192 hub that you can try pinging from both B and C?  How about pinging the broadcast address:

"ping [-b]"

(I think recent ping commands need a "-b" option to ping the broadcast address correctly.)  You should be able to see both machines, of course, but if you don't even get a response from yourself, you've got a problem.
william_holmesAuthor Commented:
Thanks guys the problem
is fixed.

my machine  A was running NT
machine C was running redhat 6

Turns out the linux machine had
hung it's networking. Never
thinking there would be a problem
there I never checked, just thinking
the problem was on Machine B.
Rebooted the linux Machine and
everything works, just nicely.
Boy have I learnt alot though : )
did you set a default route on A and C with B as the GW ?
that may solve your probleme.
to see that, execute route on either A and C and you must see for each machine a route for the local segment and your gw (B) to go out ( to go to the other segment ).

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