The routing method and principle of the router Interconnect port in different network segments

The following figure: two Cisco routers connected two ports are not the same network, how to achieve the interconnection of two routers? It seems absolutely impossible at first sight, but it's doable, and I've turned this into reality. Here's how to configure, and how to explain.

This is about the routing principle, one of the roles of routers is routing, but there are two methods of routing, dynamic Routing and static routing. Dynamic routing is the use of routing algorithm, intelligent calculation of the way out, make routing decision. Static routing is relatively simple, generally a few commands on the OK.

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Let's take a look at a, if there is a packet, to go to B, through the dynamic routing protocol can do it? Obviously not. Because a thinks, he goes straight to 192.168.1.0/24 and 10.10.10.1/24 's network, to go to B, how to go? Router A cannot know---unless the administrator configures a route to him---but how to write this route? Static routing generally has 2 characters. One indicates the next hop address (the direct-attached end-to-end port address), and one indicates the local exit port. Similarly, we cannot simply point out the next hop address here, because even if you specify it, there is no---router does not know how to go with the address you specify.

Similarly, B's packet goes to a, and the same method is used to define a static route.

RA (config) #ip Route 10.10.20.1 255.255.255.0 FA 0/0

RB (config) #ip Route 10.10.10.1 255.255.255.0 FA 0/0

After such two static routes are configured, the two routers can pass packets to each other.

But what is---?

We know that the router is a 3-tier device, the role is to read the IP packet destination address, make routing judgments. But it doesn't matter how the packets come and how they get there. As soon as he gets the packet, the next task is routing judgment. Although the router is a 3-tier device, the transfer of data is still to be achieved by 2 layers. 3 layers make routing decision to 2 layer processing. The above two configurations can be achieved to help routers make routing decisions.

This example confirms the fact that packet transmission is ultimately dependent on the data link layer, and that the main function of the 3 layer is to implement router routing decisions.

This article from the "Turn Away-Wang June" blog, please be sure to keep this source http://johnwang.blog.51cto.com/474770/129069