DrayTek Vigor 3900/2960 - WAN-WAN transit over WAN2
When you are setting two sites, one as a redundant site for failover, in a datacentre, it is important to configure all of your external interfaces properly. Recommended settings for this are that you have a separate subnet at each site so that data can be routed over the WAN as and when required, rather than a single subnet that sends and receives all packets over the WAN unknowingly. In this example we are going to have two subnets:
The primary site where the live system is housed. The system has two WANs - 220.127.116.11 to the internet and 10.10.11.254 to the redundant subnet
The secondary (redundant) site which has two WANs also - 18.104.22.168 to the internet and 10.10.10.254 to the primary site.
So we must connect the two subnets via WAN2 on our two routers, in this case a DrayTek 3900 for the primary site, and a DrayTek 2960 for the redundant site.
So on the DrayTek Vigors, we will set the WAN2 to be both in the same subnet, so that they have their own small LAN for comms. In this example we will set them to be 172.16.0.1 & 2 with a subnet of ./24 so taht they can ping each other easily. Then we set the gateway of each WAN2 to be the other WAN2 IP. So taht the forst router will have an IP of 172.16.0.1/24 with gateway 22.214.171.124.
This should give us a direct link from one router to the other.