Hello All,

I need to configure 2 WAN interfaces for an Centos 3.8 server, the server already has two Interfaces eth0 and eth1 configured with LAN and WAN IPs.

eth0 Link encap:Ethernet HWaddr 00:25:90:D2:B3:81
inet addr:191.191.1.190 Bcast:191.191.1.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1276560 errors:0 dropped:0 overruns:0 frame:0
TX packets:797428 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:676799549 (645.4 Mb) TX bytes:108254374 (103.2 Mb)
Interrupt:11 Memory:dfe00000-dfe20000

eth1 Link encap:Ethernet HWaddr 00:25:90:D2:B3:80
inet addr:27.X.X.26 Bcast:27.X.X.31 Mask:255.255.255.248
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2185824 errors:0 dropped:0 overruns:0 frame:0
TX packets:2533231 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:340569314 (324.7 Mb) TX bytes:665885273 (635.0 Mb)
Interrupt:11 Memory:dfd00000-dfd20000


Now I attached an additional NIC and added the Interface eth2 with following configurations::

eth2 Link encap:Ethernet HWaddr 00:25:90:E4:38:C0
inet addr:123.X.X.130 Bcast:123.X.X.131 Mask:255.255.255.252
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)

Also the output of ip route ::

123.X.X.128/30 dev eth2 proto kernel scope link src 123.X.X.130
27.X.X.24/29 dev eth1 proto kernel scope link src 27.X.X.26
191.X.X.0/24 dev eth0 proto kernel scope link src 191.X.X.190
default via 27.X.X.25 dev eth1

I didn't added GATEWAY entry for eth2 device because As i assume it will change the default gw and my server can go unreachable.

So I just want to understand few things --

1) Do I need gateway entries for each WAN in ifcfg-ethX
2) IF yes then which Interface is going to be used for outgoing traffic
3) what happens when eth1 goes down, will eth2 be able to provide me uninterrupted connection even if default gw is for eth1

Thanks

Standard route tools do not allow multiple gateways and uninterrupted failover.
For that you need iproute2 tools and kernel modules. See here:

http://lartc.org/howto/index.html