Analysis of IP Route Selection Process experts (1)

This article describes the process of IP Route Selection. This is a basic knowledge. This article describes the specific precautions from a specific case, I hope this article will be helpful for you to select a route later.

For example, the current network. Host a and host B are connected in two different network segments through routers. Now, if host a needs to communicate with host B, how can host a locate host B? I will use this example to explain in detail the entire process of IP route selection. Here, I will introduce Cisco routers as an example.

Assume that the user of host a uses the Ping command to check the connectivity of host B. Although this network architecture is relatively simple, the steps in the route selection process are not missing. Perform the following steps:

Step 1: After you PING 172.1680.8 on host a, host a has an Internet Control Packet Protocol (ICMP. This Protocol creates a response packet that contains only letters in its data domain.

Step 2: The Internet control protocol will send this load (that is, the newly created packet) to the Internet Protocol (IP ). Then the Internet Protocol creates a packet. The data packets created by the Internet Protocol contain more data packets than those created by the Internet control protocol. This package contains the IP address of host a, the IP address of the destination host, and the protocol field with the value of 01h. When the data packet arrives at host B, the content tells the other party that the payload should be forwarded to the Internet Control Packet protocol for processing.

Step 3: The IP protocol determines whether the destination IP address belongs to a remote network or a local network. According to the IP address planning rules, host a and host are already different networks. At this time, the data packets created by the Internet Protocol (IP) will be sent to the default gateway. In the network attribute configuration of host a, in addition to its own logical IP address, it also has the default gateway address. A gateway address is a gateway used for communication between hosts in different networks. Only through the gateway can the data packets of host a be sent to host B of different networks.

Step 4: confirm the MAC address of the corresponding router interface. Assume that the default gateway of host a (IP Address: 172.1660.6) is configured as 172.1660.1. If the data packet of host a is sent to this default gateway, you must know the physical address of the corresponding router interface, that is, the MAC address. Only in this way can data packets be transmitted to the data link layer of the next layer and frames are generated according to certain rules. Then host a can send the data packet to the router interface connected to the 172.1660.0 network. On the local LAN, hosts can communicate with each other only through hardware addresses. Therefore, to send data packets to a specific gateway, host a must know the MAC address of the gateway. This process is inevitable. To achieve this, host a first checks its ARP cache to check whether the IP address of a default gateway has been resolved to the hardware address of the corresponding interface. If a corresponding record exists in the ARP cache table, it indicates that it has been successfully parsed. In this case, the data packet is released, transmitted to the data link layer, and a frame is generated. The hardware address of the target party will also be uploaded to the data link layer together with the data packet. Generally, on host a, you can run the ARP command to view the table corresponding to the current IP address and MAC address of the host. For example. The default gateway set on my computer is 192.168.0.254, followed by a 16-character hardware address corresponding to the default gateway.

Step 5: generate a frame. When the data packet and the destination hardware address are transmitted to the data link layer, the LAN drive is used to provide media access services for data transmission over Ethernet. A data frame is about to be generated, and some control information is used to encapsulate this data packet. The data frame contains the hardware addresses of the target and source. And ethernet fields. This Ethernet field is mainly used to describe the network layer protocol used to deliver the data link layer of this data packet Island. At the end of the frame, it is a field called the frame verification sequence. It is the region where the Cyclic Redundancy verification calculation value is loaded. That is to say, in this frame, it mainly includes the destination MAC address (corresponding to the MAC address of the router interface) and source MAC address (the MAC address of host) ethernet fields, data packets, and frame verification sequences. Note: the destination address here is not the address of host B, but the default gateway address closest to host. During the first communication, host a does not know the MAC address of host B. Once the frame is encapsulated, the frame will be delivered to the physical layer. If the enterprise network is composed of twisted pair wires, it will be sent to the physical media one by one.

The above five steps are mainly completed on host. After these five steps are completed, the preliminary work of the IP route selection process is completed. The next step is to watch the vro performance.