Introduction to dynamic route backup

The dynamic route backup function employs DCC to dynamically maintain dialup links. It can provide backup for dialup links based on routes.

The dynamic route backup function combines the backup function and the routing function. It provides reliable connections and standard dial-on-demand services.

1. Dynamic route backup features

   The dynamic route backup function is mainly used to back up dynamic routes. Moreover, it can also back up static routes and directly connected routes.

   The dynamic route backup function is suitable for scenarios with multiple interfaces and multiple routers. It is not dedicated to a specific interface or link.

   With dynamic route backup enabled, the backup link will be activated automatically when the primary link fails. The primary-backup switchover does not incur dialup delay (the route convergence time is not counted in).

   The dynamic route backup function is routing protocol-independent. It can collaborate with the RIPv1, RIPv2, OSPF, IS-IS, and BGP. However, some routing protocols (such as BGP) use the optimal routes by default. Therefore, with BGP employed, when the backup link is activated due to a failure of the primary link to the monitored network segment, the device will learn routes to the monitored network segment through BGP. When the primary link recovers, the device will learn routes to the monitored network segment through BGP too. However, the routes that the primary link learns might be less optimal than what the backup link learns. As a result, the routes backup link learns remain activated, dynamic route monitoring fails, and the backup link-to-primary link switchover fails.

   To address this problem, do the following:

   • Make sure the IP address assigned to the backup link is greater than that assigned to the primary link.

   • Make sure the same route can be learned by multiple links (which can be achieved through load balancing configuration).

2. How dynamic route backup works

   The dynamic route backup function is implemented using dynamic route backup groups. In a dynamic route backup group, the backup link is activated when the primary link leading to the monitored network segment fails.

   Dynamic route backup operates in the following steps:

   • The system monitors whether the routes to the monitored network segment are updated and checks whether at least one route to the monitored network segment exists.

   • If at least one route to the monitored network segment exists, and the route is originated from an interface with dynamic route backup disabled, the primary link is considered operating correctly.

   • If no route exists, the primary link is considered to be shut down and unavailable, and the backup link will be activated.

   • After the backup link is activated successfully, the data is transferred across it. During this process, the system periodically checks the primary link status.

   • When the primary link recovers, the backup link can be brought down either immediately or when the timer expires, depending on the related configuration.