[SOLVED] Problem using 2 NIC cards, same subnet

mbrose1994 · 03-10-2011, 06:12 PM

I have a private network in our lab.

One particular node talks via CISCO switch to the other nodes on eth1. And, this node has to talk via crossover cable to one machine on eth0. All the nodes are configured in the same 192.168.50.x address scheme.

Of course when I toggle the NIC cards the active NIC works fine. The issue is when both are up, which ever NIC card came up first is the default. Then the other NIC card is somehow invisible, ie, does not work.

I have ip_forwarding on. I edited the network-scripts/cfg-eth[0,1] files as seemed correct. But no luck.

I did lots of google'ing looking for solutions, nothing addresses this issue so far. Most of the route and ip threads deal with NAT issues and separate subnets.

I thought eth1 could use the CISCO switch for its gateway. But, a wireshark capture shows NO ip address for the switch. The packet breakout only shows its MAC and a "mfg address" that is the first 3 bytes of the MAC. As best I can tell, does not have a dotted quad address.

Any guidance will be appreciated.

M

timetraveler · 03-10-2011, 06:38 PM

You want to have traffic destined for 192.168.50.x to go to both nics?

hogar.strashni · 03-10-2011, 08:28 PM

I guess that layout of your network looks like this:

Code:

 _________                                   _________
|         |---------<CISCO switch>----------|         |
| machine |                                 | machine |
|    1    |---------------------------------|    2    |
|_________|         crossover cable         |_________|

I'm sorry if I'm underestimating your knowledge, but switch is by default second layer device. This means it is transparent for 3. layer => it doesn't have IP address. Unless it is IP switch. Is it? If I'm right that would be your first thing to fix. What did you mean, by "gateway" in "I thought eth1 could use the CISCO switch for its gateway."? It seems to me I'm not the only one who thinks you could be more verbose about what you are trying to accomplish with this network architecture.

mbrose1994 · 03-11-2011, 12:00 AM

Quote:

Originally Posted by timetraveler

You want to have traffic destined for 192.168.50.x to go to both nics?

Not exactly.

Let me lay more details.

The node with 2 NIC cards has ip addresses: eth0 192.168.50.X5, eth1 192.168.50.X25.

I need traffic targeted to nodes 192.168.50.<X1-X4> via eth0 (192.168.50.X5).
Nodes X1-X5 all hang off the switch. It is not an ip switch, so no ip address (thanks hogar.strashni).

Traffic out the other NIC card, eth1 (192.168.50.X25), is targeted to a node with ip 192.168.50.X10.
Node X10 is connected via cross-over cable from node X25 NIC card.

_________
| eth0 X5>|--<switch>--|Nodes X1-X4|
| machine |
| 2 NICs |
|eth1 X25>|-crossover--|Node X10|
|_________|

Above is my situation to make work.

Thanks again for your responses.

M

mesiol · 03-11-2011, 12:50 AM

Hi,

to get such a configuration work, you should split your network or configure a network brigde. You will not get it work if all nodes are part of the same subnet but requires routing to find one of the hosts.