Basic introduction Chinese name: default routing mbth: default routing function: forwarding all packets of unknown destination Other names: introduction, purpose, working process, advantages and disadvantages, application and configuration examples of default routing. Brief introduction Default route, also known as default route, is a special static route, and the destination address and mask are configured as all zeros (0.0.0.0.0.0). When all the routes in the routing table fail, the preset route will be used to make the message have a final forwarding location. A preset route usually directs messages to another router in the same way. If other routes match, the corresponding message is forwarded according to the routing rules, otherwise, the message is forwarded to the preset route of the router. Repeat this process until the packet reaches its destination. The default route of a device is usually called the default gateway, which usually provides functions such as packet filtering, firewall or proxy server. Purpose To enable ospf to broadcast the default route 0.0.0.0? Enter the ospf domain, even if the route is 0.0.0.0? It does not exist in the local ip routing table, and this command form will also broadcast the preset route. If the keyword always is not used and the preset route is dithering, ospf needs to send an update to the ospf domain every time the preset jitter occurs. If the preset route is unstable, using the keyword always will reduce the operation on the ospf database and keep the ospf database stable. In the process of work, each router uses the longest matching principle to obtain the best route in the process of routing packets. Match the next-hop gateway of the destination IP address with the longest subnet mask. The destination address of the default route in IPv4 is 0.0.0.0/0, which is often referred to as the 40 path. The subnet mask is /0, which actually points to all destination networks and can be used as the shortest matching choice. This route will be used when no other route match can be found. Similarly, in IPv6, the default route is specified as:: /0. Administrators usually configure the default route to the network router in the host. Therefore, packets sent outside the local area network (usually to the Internet or WAN) will be forwarded to the router directly connected to the network provider. Advantages and Disadvantages The default route can be a static route set by the administrator or an automatic result of some dynamic routing protocols. Advantages: It can greatly reduce the routing table entries, thus greatly reducing the processing burden of the router. Disadvantages: If the configuration is incorrect, it may lead to self-loop or non-optimal routing. In the process of network maintenance and management, we often encounter problems such as network communication congestion, router memory and CPU capacity can not meet too much data processing and data transmission. Although increasing the bandwidth of network communication links and improving the performance of routers (or re-selecting high-grade routers) is one aspect to solve this kind of problem, it is far from enough, and we should also consider reducing data processing and data transmission. Among them, the rational use of the preset route is one of the measures. Configuration example IP:130.89.102.10 Next hop IP address: 130.89. 102.254 Configure static routing command: routeadd/kloc-.