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Source of routing information

2022-06-12 12:42:00 【51CTO】

The routing table contains several pieces of routing information , There are three ways to generate these routing information ： Device auto discovery 、 Manual configuration 、 Generated by dynamic routing protocol .

1. Direct link routing

We call the route information automatically discovered by the device as direct connection route （Direct Route）, After the network device starts , When the router interface status is UP when , The router can automatically find the route to the network directly connected to its interface .

Pictured 1 Shown , Router R1 Of GE 0/0/1 The status of the interface is UP when ,R1 According to GE 0/0/1 Interface IP Address 11.1.1.1/24 Deduce GE 0/0/1 The network address of the network where the interface is located is 11.1.1.0/24. therefore ,R1 Will be 11.1.1.0/24 Fill in your routing table as a routing item , The destination of this route / Mask as 11.1.1.0/24, The output interface is GE 0/0/1, Next jump IP The address is connected to the outgoing interface IP With the same address , namely 11.1.1.1, Because this route is a direct connection route , So its Protocol The attribute is Direct. in addition , For direct routing , Its cost The value of is always 0.

Similarly , Router R1 Another direct route will also be found automatically , The destination of the route / Mask as 172.16.0.0/24, The output interface is GE 0/0/0, The next hop address is 172.16.0.1,Protocol The attribute is Direct,Cost The value of is 0.

You can see R1、R2、R3 Once the router is powered on , port UP, The network segments connected to these ports will appear in the routing table .

The source of routing information _ Routing protocol

chart 1 Direct link routing

2. Static routing

To enable computers in the network to access any network segment , The router in the network must have a route to all network segments . The network segment directly connected to the router , The router can automatically discover and add it to the routing table . For networks without direct connection , Administrators need to manually add routes to these network segments . The routing information manually configured on the router is called static routing （Static Route）, It is suitable for small-scale networks or networks that do not change much .

Pictured 2 Shown , There are four network segments in the network , Each router is directly connected to two network segments , For network segments without direct connection , You need to add static routes manually . We need to add two static routes to each router . observe , The next hop of static routing , stay R1 Add to 12.1.1.0/24 Route of network segment , The next jump is 172.16.0.2, instead of R3 Of GE0/0/0 Interface 172.16.1.2. Many beginners are right “ Next jump ” There will be mistakes in understanding .

The source of routing information _ Static routing _02

chart 2 Manually configure static routing

3. Dynamic routing

Routers use dynamic routing protocols （RIP、OSPF） Obtaining routing information is called dynamic routing （Dynamic Route）, Dynamic routing is suitable for large-scale networks , It can automatically select the best path according to the changes of the network .

If the network is small , We can configure it manually “ tell ” The route of the network equipment to the non directly connected network . However , If the number of non directly connected networks is large , It will inevitably cost a lot of manpower to manually configure , This is often undesirable in reality , It's not even possible . in addition , Manually configured static routing has another obvious defect , That is, it does not have self adaptability . When the network fails or the network structure changes, resulting in the corresponding static route error or failure , These static routes must be modified manually , And this is often undesirable in reality , Or impossible .

in fact , Network devices can also obtain routing information by running routing protocols .“ Routing protocol ” and “ Dynamic routing protocol ” These two terms are actually the same thing , Because we have never been called “ Static routing protocol ” The routing protocol of （ We have static routing , But there is no static routing protocol ）. The route obtained by the network device through running the routing protocol is called dynamic route . If a network segment is added to the network 、 Deleted network segment 、 The network segment of an interface is changed , Or the network topology has changed （ The network interrupts a link or adds a link ）, The routing protocol can update the carcass routing information in the routing table in time .

It is important to note that , A router can run multiple routing protocols at the same time . Pictured 5-4 Shown ,R2 Routers are running at the same time RIP Routing protocols and OSPF Routing protocol . here , The router will create and maintain a IP Out of routing table , You will also create and maintain a separate RIP Routing table and a OSPF Routing table .RIP The routing table is used to store RIP All routes discovered by the protocol ,OSPF The routing table is used to store OSPF All routes discovered by the protocol .

RIP Routing tables and OSPF All routing items in the routing table will be added IP In the routing table , If RIP Routing tables and OSPF Each routing table has a routing item to a certain network segment , Then compare the routing protocol priority . chart 3 in ,R2 The router RIP Routing tables and OSPF The routing table has 24.6.10.0/24 Routing information of network segment , because OSPF The priority of the agreement is higher than RIP agreement ,OSPF In the routing table 24.6.10.0/24 Routing items are added to IP Routing table . The router is ultimately based on IP Routing table IP The forwarding of messages works .

The source of routing information _ Routing protocol _03