Overview Static Routes

A static route is a self-defined route which is manually configured by a user. It specifies a path for transmitting IP packets which are targeted at a specified destination.

Compared with dynamic routing, static routing has higher security and lower device resource occupancy. The disadvantage is that when the network topology changes, manual configuration is required, and there is no automatic re-configuration mechanism.

Static routes do not occupy line bandwidth or occupy CPU to calculate and advertise routes periodically, improving the device and network performance.

Static routes can be used to ensure the security of a small-scale network, for example, in a network where there is only one path connecting to an external network. In a large-scale network, static routes can implement security control on services or links of certain types. A majority of networks adopt dynamic routing protocols but you can still configure some static routes for special purposes.

Static routes can be re-distributed to a dynamic routing protocol, but dynamic routes cannot be re-distributed to static routes. Note that improper static route configuration may cause routing loops.

The default route is a special route which can be a static route. In a routing table, the default route is a route to network 0.0.0.0 with the mask 0.0.0.0. You can use the show ip route command to check whether the route is valid. When the destination address of a received packet does not match any entry in the routing table, the packet takes the default route. If no default route is available and the destination is not in the routing table, the packet is discarded, and an ICMP packet is returned to the source end reporting that the destination address or network is not reachable. To prevent the routing table from becoming too large, you can set a default route. The packet that fails to find a matching routing table entry takes the default route for forwarding.

Null0 is a special route, with the route output interface as the Null0 interface. The Null0 interface is always in the UP status but it cannot forward packets. The packets that are sent to the interface will be discarded. If you configure a static route and specify the output interface for a certain network segment to Null0, the packets that are sent to the network segment will be discarded. Therefore, you can configure realize packet filtration by configuring Null0 static routes.