Overview Routing

After a device receives a packet through an interface, the device selects a route according to the destination of the route and then forwards the packet to another interface. This process is called routing. In network devices, routes are stored in a routing table database. The packets search the routing table to determine the next hop and output interface according to the destination of the packets. Routes are categorized into three types according to their sources.

• Direct route: The route is generated based on the interface address. After a user configures the IP address of an interface, the device generates a direct route of the network segment according to the IP address and mask.
• Static route: The route is manually configured by the user.
• Dynamic route: The route is discovered through the dynamic route discovery protocol. Based on whether the dynamic routing protocol is used within an autonomous domain, two types of dynamic routing protocols are available: Interior Gateway Protocol (IGP) and Exterior Gateway Protocol (EGP). Here an autonomous domain refers to a network which has a unified management organization and unified routing policy. A routing protocol that is used within an autonomous domain is an IGP. Common IGPs include Routing Information Protocol (RIP) and Open Shortest Path First (OSPF). EGPs are usually used for routing among multiple autonomous domains. A common EGP is BGP.

Routing supports load balancing, that is, multiple routes to the same destination. In forwarding packets, a device transmits packets in load balancing mode according to the routing table search result.