Router bridging principle: Network Connection

Principle of router bridging: network connection. Recently, the principle of router bridging has been favored by many friends. Today, let's take a deeper look at the charm of the principle of router bridging! Virtual Server simulation, packet filtering, and so on, a new experience is waiting for you.

The simplest router bridging principle can be imagined as a single-line bus. Each computer can send packets to the bus to communicate with each other. However, as the number of computers in the network increases, this is not feasible and will cause many problems:
◆ Bandwidth resources are exhausted.
◆ Each computer wastes a lot of time processing unrelated broadcast data.
◆ The network becomes unmanageable, and any errors may paralyze the entire network.
◆ Each computer can listen to communications from other computers.

 

Router bridging Principle

Network segmentation can solve the problem of router bridging principles, but you must also provide a mechanism for computers in different network segments to communicate with each other, this usually involves transferring data between network segments in some ISO network protocol layers. Let's take a look at the network protocol layer and the router location. We can see that the router is at the network layer. This document assumes that the network layer protocol is IPv4, because it is the most popular protocol and involves a similar concept as other network layer protocols.

I. Routing and bridging

The bridge/switch between a route and a two-layer route is a high-level concept, which does not involve the physical details of the network. In a routable network, each host has the same network-layer address format, such as an IP address. The network layer address consists of the network address and host address. A bridge can only connect networks with the same or similar data link layer. Different routers can connect to any two networks, as long as the host uses the same network layer protocol.

2. Connecting the network layer and data link layer

The router bridging principle is the data link layer at the network layer. In order for them to communicate with each other, the "bonding" Protocol is required. ARP Address Resolution Protocol) is used to map network layer (Layer 3) addresses to data link layer (Layer 2) addresses. RARP (Reverse Address Resolution Protocol) is the opposite.

Although ARP has nothing to do with the network layer protocol, it is usually used to resolve IP addresses; the most common data link layer is Ethernet. Therefore, the following ARP and RARP examples are based on IP and Ethernet, but note that these concepts are the same for other protocols.

◆ Address Resolution Protocol

Router bridging principle: the network layer address is an abstract ing defined by the network administrator. It does not care about the underlying data link layer protocol. However, network interfaces can only communicate with each other based on Layer 2 addresses, and Layer 2 addresses are obtained from Layer 3 addresses through ARP. Instead of sending each packet, ARP requests are required to respond to ARP requests cached in the local ARP table. This reduces the number of ARP packets in the network. ARP is easy to maintain and is a simple protocol.

◆ Introduction

If interface A wants to send data to interface B and A only knows the IP address of B, it must first find the physical address of B, it sends the physical address of ARP Broadcast Request B containing the IP address of B. After receiving the broadcast, interface B responds to the physical address of.

 

Router bridging Principle

Note the principle of router bridging. Although all interfaces receive information, only B requests should be returned. This ensures that the response is correct and the expired information is avoided. It should be noted that when A and B are not in the same network segment, A sends ARP requests only to the next hop router rather than directly to B.

 

Router bridging Principle

To handle ARP packets, note the sender's <IP address, hardware address> on the local ARP table of the host to which ARP requests are received. Generally, when A wants to communicate with B, B may also need to communicate with.