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Routing Technology
When the IP subnet of a host to send IP packet to the same IP subnet to another host, it sent directly to the IP packet network, the other party will be able to receive. In order to give a different IP host on-line, it should be able to get to the purpose of choosing a subnet router, the IP packet sent to the router, by the router is responsible for IP packet to the destination.
If you do not find such a way By, host put IP packet sent to a group called the "default gateway (default gateway)" on the router. "Default gateway" is a per host configuration parameters, it is then in the same network to a router port IP address.
Router IP packet forwarding, only in accordance with the purpose of IP packet networks No. IP address section, select the appropriate port, the IP packet sent out. With the host, the router must then determine whether the port is the target subnet, and if so, on directly to the division through the port to the network, otherwise, have to choose a router to send packet. Router has its default gateway, used to send do not know where to send the IP packet.
In this way, through the router to know how to send the IP packet forwarding right away, I do not know the IP packet to the "default gateway" router, so a class transmission, IP packet will eventually be sent to destination, to send less than a destination IP packet networks are discarded.
At present, TCP / IP network, all through the interconnection with the router, Internet is the thousands of sub-Netcom over IP router interconnection with the international network. This network is called a router-based network (router based network), formed a router for the node "network of networks." In the "Internet Network", the router is not only responsible for IP packet forwarding, will also be responsible for liaison with other routers to jointly determine the "net inter-net" routing and maintenance of routing table.
Routing action includes two basic elements: routing and forwarding. Routing that is to determine the best path to reach their destinations by routing algorithm to achieve. As it relates to the different routing protocols and routing algorithm, it is necessary to relatively complicated. In order to determine the best path routing algorithm must be up and maintenance of routing information contained in the routing table, which relies on routing information used in routing algorithm and not the same.
Routing algorithm will collect information to fill in the different routing tables, according to the routing table can be the purpose of the network with the next stop (nexthop) tells the relationship between the router. Exchange of information between routers routing update, update the maintenance routing table to make it accurately reflect the network topology changes, measured by the router to decide in accordance with the best path. This is the routing protocol (routing protocol), such as Routing Information Protocol (RIP), Open Shortest Path First Protocol (OSPF) and Border Gateway Protocol (BGP) and so on.
Transponder that is good along the best path routing information packet transmission. Router first in the routing table to find, know how to identify whether the packet is sent to the next site (router or host), if the routers do not know how to send packet, usually the packet dropping; otherwise routing table on the basis of the corresponding table entry will be sent to a sub-site, if the purpose of the network connected directly with the router, the router packet put directly to the corresponding port. This is the route forward agreement (routed protocol).
Forward routing protocols and routing protocol is also independent of each other and cooperate with each other concept, the former using the latter to maintain routing table, while the latter wants to use the former to provide the function to release the data packet routing protocols.
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