Using Links of 3G Cellular Interfaces as Backup Links to Connect to the Internet
Some enterprise branches require high network connectivity. A very short network disconnection may affect services of an enterprise branch, so a backup network solution is necessary for the branch. Wired links can be used as backup links; however, it takes a long time and costs too much to deploy wired links. When primary links are damaged by natural disasters, backup links connected to a fixed network may be also affected. 3G links provide larger bandwidth and wireless access. The 3G network is independent of the fixed network and is easy to deploy. Therefore, the network scheme "fixed network + 3G network" realizes highly reliable network backup for enterprises.
Figure 11-4 shows the 3G backup access scenario of the enterprise branch. A router that supports 3G access, for example, the Router in Figure 11-4, is deployed in the branch. The Router supports one or more types of fixed network interfaces, such as Ethernet, xDSL, and E1/T1 interfaces. These interfaces are called DSLAM interfaces.
- The fixed network interface and the 3G interface are configured as the primary interface and the backup interface respectively.
- IPSec is configured on the 3G interface and IPSec VPN is created between the headquarters and branch. IPSec ensures secure data exchanges between the headquarters and branch.
- The link connectivity detection function is enabled on the primary interface to check whether the link between the headquarters and branch is reachable. When a link fault is detected, the 3G interface is enabled to ensure the link connectivity between the headquarters and branch. The link connectivity detection function on the primary interface keeps working. When the primary link recovers, the Router disconnects the 3G link and switches traffic back to the primary link.
- Based on branch services and network requirements, you can associate the link connectivity detection function with static routes, policy-based routing (PBR), or Virtual Router Redundancy Protocol (VRRP), and use the 3G network to provide backup links.
