DD-WRT:Dual WAN with one as standby backup

article need of major revision - one with dual wan as backup another simple round equalization

This tutorial explains how you can assign one (or more) of the LAN ports as an extra WAN port. There is another tutorial Dual-WAN for simple round-robin load equalization which explains how you can load balance between the two WAN connections. In this case I did not want to load balance; but rather create a standby WAN connection.

Justification
I needed to configure backup WAN as standby as it is not an unlimited connection. I pay for the backup connections by Giga-Bytes used. My primary WAN connection is of unlimited type. I intend to switch to backup only when the primary one goes down.

Assumptions
I have assumed static IP addresses for both the WAN interfaces. Making them dynamic will require some changes (hint: ) Also, I am assuming DNSMasq is used for DHCP and DNS. JFFS should be enabled if you want to save the WAN-connection switch scripts. Also, I am assuming that you have already configured the first WAN connection (tied to vlan1) using nvram or web interface.

Create an extra VLAN
First you need to create an extra VLAN. In this case we want to to remove the port 4 from vlan0 and add it to the new vlan2

You can confirm or perform the setting using the dd-wrt web interface

http://your_router_ip/Vlan.asp

Now you have created an extra VLAN (vlan2).

Bring up the vlan2 interface
I found it easier to configure the interface using ifconfig in the startup script. Somehow nvram bindings for backup WAN interface IP address did not work. ifconfig does the job though.

Replace 10.10.2.209 with your WAN2 IP address

You can also perform this operation via the web interface

http://your_router_ip/Diagnostics.asp

Of course you will need a reboot for this to be effective.

Configure NAT on vlan2
We want to make sure packets leaving vlan2 are NATed

Again, the same Diagnostics.asp page can be used on the web interface.

Create scripts to do the connection switch
We switch the internet connection by switching the default route and DNS servers.

Here we will create two scripts in /jffs to switch from one WAN connection to the other.

Script to switch to wan1
Put this in :

Used kill -9; because not sure why -1 (HUP) didnt work.

Obviously 10.10.1.10 and 10.10.1.11 are DNS servers for WAN1 and 10.10.1.1 is the default gateway. Replace these values with your own settings for WAN1.

Script to switch to wan2
And put this in :

Obviously 10.10.2.10 and 10.10.2.11 are DNS servers for WAN2 and 10.10.2.1 is the default gateway. Replace these values with your own settings for WAN2.

You can switch connection by running the respective script.

Connect the cable

Connect the backup WAN cable to the ethernet port marked as "4" and reboot.

More to come

 * 1) Automation of connection switching with email notification
 * 2) Web interface to monitor and switch connection