The use of two priorities enables the formation of flexible backup chains by which each physical router does not merely take a single place within the chain but takes a place for every physical WAN interface:
- The first physical router, the main router in the network, has a DSL and an ISDN interface for example, the second router (backup router) has a DSL and a UMTS interface.
- The first router receives the main priority 255. Consequently, it will become the main router with the value 50 as its backup priority.
- The second router receives the main priority 150 and the value 100 as its backup priority.
Under normal operating conditions, data traffic is processed by the DSL interface on the first router. If the router or this interface fails, the second router attempts (due to the next highest main priority) to establish the connection via its own DSL interface. If this does not succeed, then both devices will propagate their backup priority. Since the second router has the higher backup priority, the connection is established using its UMTS interface. Only when this interface is also unable to establish a connection will the ISDN interface on the first router (with the lower backup priority) be used.
Only keep alive connections return automatically!
The standard connection will only be automatically reestablished after a backup event if the hold time for the connection is configured properly:
- A hold time of 0 means that the connection will not be actively terminated. If the connection is terminated or interrupted due to interference, it will not be automatically established again. The connection will only be reestablished when communication is required of it.
- A hold time of 9999 means that the connection is permanently held open. If it is interrupted, then the connection will be actively opened up again. This behavior is known as keep alive.
Set the hold time to 9999 for connections to the Internet provider (in the corresponding name list) and backed-up VPN connections (in the VPN connection list) to ensure that the connection is automatically reestablished and resumes data transfer after interruption.
