A computer network (XXV) defined routing control, scope and routing algorithms

Routing control definition

1.IP address and routing control

The Internet is a network router connected to the combination formed. In order to allow the packets correctly to reach the target host, the router must be correctly forward on the way. This data transfer process performed in the right direction is called routing control or routing .
Routers forward data packets according to the routing control table (Routing Table).
Routing control table according to the obtained IP address and the comparison routing control table received packet should receive a target host router.

2. static routing and dynamic routing

Static and dynamic routing control sub-types.
Static Routing : A method of fixed routers and host information and route set in advance.
Setting static routing is typically done manually by the user.
Static Routing Disadvantages:
1. static routes to the manager a great deal of burden.
2. Once a router fails, basically it can not automatically bypass node failure occurs only after the administrator manually set to return to normal.
Dynamic Routing : Let routing protocols automatically provided a method of routing control information during operation.
The case of dynamic routing, the administrator must set the routing protocol, the complexity of its setting process and to set specific routing protocol types are directly related.
If there is a new network is added to the existing network, the setting to a dynamic routing as long as the newly added network router.
For more number of router network, dynamic routing is clearly a method can reduce the burden on administrators.
Once a fault occurs on the network, as long as there is a path around the other, then the data packet will automatically select this path, the router will automatically reset settings.
To be able to periodically such as routers exchange routing control information mutually necessary, will send messages to adjacent routers. These swap news network will bring a certain degree of load.
Whether static routing or dynamic routing, do not use only one of these, you can combine them to use.

3. Dynamic routing foundation

Neighbor router will send its known network connection information, and this information in turn passed like a baton as to other routers, until the entire network are aware, routing control table also finished up.

Range of routing control

1. A variety of organizations to access the Internet

Internet connected organizations around the world, including not only the language is not the same, and even religion completely different organization.

2. Autonomous System routing protocol

制定自己的路由策略，并以此为准在一个或多个网络群体中采用的小型单位叫做自治系统 (AS: Autonomous System) 或路由选择域 (Routing Domain) 。

在区域网络及ISP内部，由构造、管理和运维网络的管理员、运营者制定出路由控制相关方针，然后根据此方针进行具体路由控制的设定。
而接入到区域网络或ISP的组织机构，则必须根据管理员的指示进行路由控制设定。
自治系统（路由选择域）内部动态路由采用的协议是域内路由协议，即IGP。
自治系统之间的路由控制采用的是域间路由协议，即EGP。

3.IGP与EGP

路由协议大致分为两大类:
1.外部网关协议EGP。
2.内部网关协议IGP。
路由协议被分为EGP和IGP两个层次。
根据EGP在区域网络之间（或ISP之间 ）进行路由选择。EGP使用的是BGP (Border Gateway Protocol, 边界网关协议）协议。
根据IGP在区域网络内部（或ISP内部）进行主机识别。IGP中还可以使用 RIP (Routing Information Protocol, 路由信息协议）、 RIP2、 OSPF (Open Shortest Path First, 开放式最短路径优先）等众多协议。

路由算法

1.距离向量算法

Distance vector algorithm (DV) refers to a network or destination host a target position determined by the distance (Consideration) and direction. Wherein the means to go through the expense router
number.

Interchangeable target network information between a router and a direction of distances, and these control information is produced based on the routing table.
Since the only information about the distance and direction, when the network structure becomes exceptionally complex, until a steady routing information needs to consume a certain time, routing loops are also prone to problems.

2. Link State Algorithm

Link state routing algorithm is a method for generating a control table in the router based on knowledge of the overall state of the network connection.
In this method, each router must maintain the same information required for proper routing.
As long as a router maintain the same routing control information with other routers, it means that the routing information on the router is correct.
As long as each router synchronization routing information with other routers as quickly as possible, you can make routing information to reach a stable state.
Link state algorithm is how to pay the price to obtain routing information from a network proxy table. This process is quite complex.

3. The main routing protocol

Because EGP do not support CIDR, the Internet is no longer used as the external connection protocol.
Note: EGP here is not to distinguish between the EGP IGP and EGP, but rather refers to a specific protocol called EGP.