Shulou(Shulou.com)06/01 Report--

Goal: getting started with the Internet

Time: 3 months (personal suggestion)

Master knowledge: the use and control of Switch and Router

Extended knowledge: basic use of NAT, security, and wireless.

Basic knowledge points:

The use of Switch, understand the working principle of Switch, a common broadcast domain, each port is an independent collision domain. A matching transmission of data is carried out based on the broadcast domain. According to the matching principle-MAC, the switch is determined to rely on its own MAC cache table query. If not, all ports are flooded until the response is recorded, the MAC cache table is added, and then the connection directly depends on the path distance of the cache table. If not, it will be discarded. The default aging time of the cache table is 300s. The independent collision domain is a guarantee of full-duplex, relying on CSMA/CA to avoid data transmission conflicts. The MAC matching principle is because the MAC of all physical devices is unique, it corresponds to IP, IP is variable, but MAC does not. During the matching process, you generally know the IP of the other party. ARP a packet to find the corresponding MAC, establish a local correspondence, and connect, so usually a ping packet will lose a packet.

To sum up, Switch layer 2 relies on broadcast domain for data transmission; MAC is the unique matching principle, and the corresponding information is found through ARP.

Extended use

A Switch is a broadcast domain, which is too wasteful, so we use the redundant broadcast domain to achieve the purpose of dividing the broadcast domain by dividing the VLAN. Broadcast domains cannot be transmitted by broadcast, but layer 2 is generally transmitted through broadcast, so different VLAN are isolated from each other, so the utilization rate is improved. At the same time, there is another problem. Switch has a MAC learning ability, which transmits information through broadcasts. Once flooded, it may cause broadcast storm / MAC address drift and other effects or even the risk of downtime, so we have a STP protocol, spanning Tree Protocol, through specific protocols and algorithms to build a tree-like path with only one trunk even if there are many forks.

Simple summary: Switch increases the availability by dividing VLAN, and avoids loops through STP protocol. For instructions and other information, see introduction to the Internet (2).

The use of Router, to understand the basic working principle of Router, Router is the path, different broadcast domains (VLAN) can not communicate with each other, so it needs Router to boot, its main application is three tables-routing table, topology table, adjacency table. Think about how to establish the routing table, through convergent routing learning, and there are two kinds of routing information, static route and dynamic route (here directly connected route does not think), static route is manually set, the path must be specified, once changed, it is necessary to reset, set up trouble, it is recommended to establish key locations of the network, but high reliability + fast. Dynamic routing is dynamically converged by protocols, such as RIPv1/2, OSPF, EIGRP, IS-IS, BGP, etc. (detailed explanation of the later experimental operation), which is simple to set up and strong expansibility.

Simple summary: Router ensures communication between different VLAN; Router guides the path through dynamic protocol and static path (manual)

Extended use

As far as the above Switch is concerned, it divides different VLAN on a Switch, but under normal circumstances, different VLAN cannot communicate, so if I want it to communicate, I must use Router. There are two ways, one is single-arm routing, by connecting to a router, the corresponding VLAN sub-port is established, and then pointed through the gateway. The gateway is mainly the manager of a broadcast domain address, and we point to the gateway through which the gateway broadcasts addressing to all addresses in this network segment. There is also a way to turn on routing using layer 3 VLAN or to use a routing protocol.

Simple summary: the communication between different VLAN depends on routing, and can be realized through one-arm routing and layer 3 switch. It is recommended to try.

Expand knowledge points

Simple understanding

NAT: literally speaking, it is a network address translation protocol, which can translate IP addresses into each other. It is created to save the IPv4 addresses to be used, so it generally translates multiple reserved addresses into one or more public addresses through PAT. For more information on how to use them, please see the later experiment.

Security: just take it literally to ensure that the transmission data will not be stolen and the transmission network will not be knocked down. At present, these two are all right. 3A authentication is generally used to ensure the connectivity of users, and to manage users, to filter some unwanted users and services through ACL, as well as firewall's distinction between internal and external networks, so as to achieve external protection and control requirements.

Wireless: according to the literal meaning of wireless connection, the network cable connection here is AP, but not a home router. In fact, there are some ways to generate WIFI. Create SSID and broadcast using 2.4G or 5G, corresponding to the upper port setting, it is recommended to try it yourself. The details will be explained in detail in the experiment.

PS: introductory books and experiments suggest using the CCNA Learning Guide and the CCNA experiment series with three cups of black tea

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