2 NIC on same subnet Linux Embedded

[hki]

Hi all, I'm working on an embedded Linux system 2.6.29.6-rt24 equipped with 2 NIC eth0 and eth1. I need to set them on the same subnet
eth0 = 192.168.1.87 sub 255.255.255.0
eth1 = 192.168.1.88 sub 255.2555.255.0

I tried temporary with
echo 1 > /proc/sys/net/ipv4/conf/all/arp_ignore
echo 2 > /proc/sys/net/ipv4/conf/all/arp_announce

but it doesn't' work!
all traffic (ping) come from eth0, if i disconnect eth0, then eth1 is not able to answer to ping


(the same command into a #! linux works properly..)

some suggestion?
Thanks

[Irithori]

Hi and welcome.

There are at least two ways.

First is to use bonding. http://www.kernel.org/doc/Documentat...ng/bonding.txt
You define a new interface bind0 with eth0 and eth1 as slaves.
This bind0 can then have alias IPs

The second is to use source based routing.
Aka: What comes in via eth0, comes out via eth0 and the same for eth1.
This code is untested. For details look here: Routing for multiple uplinks/providers

ip route add 192.168.1.0/24 dev eth0 src 192.168.1.87 
ip route add 192.168.1.0/24 dev eth1 src 192.168.1.88
ip route add default scope global nexthop via <YOUR_GW_IP> dev eth0 weight 1  nexthop via <YOUR_GW_IP> dev eth1 weight 1

In general, I prefer bonding where possible.
It seems more obvious too me and offers failover, but ymmv.

[hki]

I'm pretty newbie with Linux.. is it possible to test bonding in runtime without make system modifications? (my embedded box is an industrial automation device and I prefer void "hard" testing on it..)

[hki]

the strange thins is using "arp_ignore" and "arp_announce" it works properly on a crunchbang distro, the same settings in my embedded linux box, do not..why? Some settings to check?

[Irithori]

To play around, you can use the ifconfig (or ip) command together with ifenslave.
ifenslave potentially needs installation.

e.g.

modprobe bonding
ifconfig bond0 192.168.1.87 up
ifconfig bond0:0 192.168.1.88 up
ifenslave bond0 eth0
ifenslave bond0 eth1

ifconfig bond0:0 down
ifconfig bond0 down
ifenslave -d bond0 eth0 eth1

Debian has a short howto
http://wiki.debian.org/Bonding

Not sure about the difference in behaviour between crunchbang and your embedded linux.
Maybe different kernel versions and/or config.