Adding interfaces to /etc/network/interfaces

[anjanesh]

If I try to add a new interface (eth1) to /etc/network/interfaces, I get

 * Reconfiguring network interfaces...                                                                                                                                           SIOCSIFADDR: No such device
eth1: ERROR while getting interface flags: No such device
SIOCSIFNETMASK: No such device
SIOCSIFBRDADDR: No such device
eth1: ERROR while getting interface flags: No such device
eth1: ERROR while getting interface flags: No such device
Failed to bring up eth1.

I had to comment out the previous eth0 and recreate the new one with eth0

auto lo
iface lo inet loopback

#auto eth0
#iface eth0 inet static
#address 192.168.10.243
#netmask 255.255.255.0
#network 192.168.10.1
#broadcast 192.168.10.255
#gateway 192.168.10.1

auto eth0
iface eth0 inet static
address 192.168.1.243
netmask 255.255.255.0
network 192.168.1.1
broadcast 192.168.1.255
gateway 192.168.1.1

How do I add 2 interfaces and get anyone of them to work, as available ?

[terazen]

Do you have an eth1 or just eth0 and you want 2 ip addresses? If you only have 1 nic then something like this may work.

auto eth0
iface eth0 inet static
address 1.1.1.10
netmask 255.255.255.0
gateway 1.1.1.1

auto eth0:0
iface eth0:0 inet static
address 1.1.1.20
netmask 255.255.255.0
gateway 1.1.1.1

[anjanesh]

Oh...ok, so an additional ethx would mean additional NIC ?
Yes, one NIC but may change ISPs via the routers quite often resulting in different gateways.
Thanks

[terazen]

What do you mean by "changing isp's quite often"? Why would a default gateway change on the server instead of letting the router make the decision of which WAN connection to use? I'm not sure I understand.

[anjanesh]

Why would a default gateway change on the server instead of letting the router make the decision of which WAN connection to use?

Two different routers - one for each ISP. Thats how its setup in office. The network guy will switch to another router when one is down.

[terazen]

Ah, I'm not sure how to setup something like that through the server's network setup. There are options if your network guy can setup the routers differently though.

Option 1: Setup the 2 routers so that the lan interface ip information is the same on both (only 1 of the lan interfaces can be connected at one time). That way the default gateway would always stay the same when he/she moves the cable over. The network person would know if this is possible.

Option 2: Connect the 2 routers to each other and let a routing protocol do the failover automatically.

Option 3: Connect a router to both internet connections (or both routers) and let it do the failover when one of the internet connections goes down.

I can't think of any way to do it solely through the server setup.