2 NICs on same subnet

[lucacarone]

Hi All,

I need help!
i'm with a problem and i didn't find a solution nowhere. In fact, i'm confused even how to find this my problem in the forums for example.

Well, i have a equipment with Linux Centos and 2ethernet ports. I enabled 2 ports, eth0 and eth1, and configured them with static ips (eth0 = 192.168.31.5 and eth1 = 192.168.31.9). Ok!

If i plug 2 ethernet cables, one for each, i can to ping my equipment by 2 ips, 192.168.31.5 and 192.168.31.9. But, if i remove the cable from eth1, i still can to ping in these 2 ips. After of this i can to disable the eth1 and 2 ips still will be available for me in the eth0 port.

I did a test, and if i configure the 2 ips in distinct subnets this problem doesn't occur.

Right now, if i to plug the cable in eth1 will not do difference, just eth0 port is working.

Someone know about this? Sorry,but my english is not so good...

Thanks!

[Irithori]

It doesnt work that way.

You need to create a "bond" device first, that consists of eth0 and eth1.
Once you have that, you can then create aliases on it to have multipe IPs in the same network.

http://www.kernel.org/doc/Documentat...ng/bonding.txt

[scathefire]

The reason you are able to ping 2 IPs regardless of if its plugged in may be a result of having forwarding enabled. With ip forwarding, even if the cable is unplugged to one NIC, the other will pass it through.

[Irithori]

Yes, and packets are only routed to one interface.
That explains the ping results.

[lucacarone]

The first thing: Thanks at all!

For scathefire
/etc/sysctl.conf:
net.ipv4.ip_forward = 0
It seems disabled.


For Irithori
Yes, i know bonding but i want know if this behavior is normal?

There is a method for disable this behavior?
Without bonding, I want that if I disconnect eth1 then i shouldn't ping 192.168.31.9!

[Kloschüssel]

Does pinging still work when you do:

$ ifdown eth1

and then unplug the cable from eth1?