Aerohive WLAN故障排查全攻略：从L1到L7层问题解决

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"Aerohive WLAN Troubleshooting Guide Coleman.pdf"是一份全面的无线局域网(WLAN)故障排查手册，适用于那些希望解决L1层至L7层的各种问题的专业人士，特别是认证无线网络管理员(CWNA)的学习者准备参加CWNA-107考试的人员。该文档涵盖了关键的无线网络技术领域，包括但不限于： 1. L1层问题：这部分着重于底层物理层的问题，如无线信号强度、信号干扰和设备兼容性，涉及到天线配置、射频环境分析以及基本的网络连接设置。 2. L2层问题：涉及数据包传输和介质访问控制(MAC)层的故障，可能包括帧丢失、错误帧和重传，网络设备间的通信问题，以及Wi-Fi标准（如802.11n, ac, ax）的兼容性和效率。 3. 安全问题：讲解如何诊断和解决WLAN的安全问题，例如加密问题、非法接入点(rogue APs)、认证失败以及WPA/WPA2等协议的管理与配置。 4. 漫游功能：讨论无缝漫游过程中的故障，包括漫游速度、切换时间、以及客户端在不同AP间切换时可能出现的问题。 5. 信道优化：提供关于如何选择和调整Wi-Fi信道以避免干扰，提升网络性能的策略，如智能信道选择算法和动态信道分配。 6. L3到L7层问题：探讨网络层和应用层的问题，如IP路由、QoS设置、网络服务质量(QoS)问题以及高级应用服务的故障排查。此外，这份指南还介绍了常用的故障排除工具和技术，如网络监控软件、Wireshark抓包分析、无线扫描器以及Aerohive公司的特定诊断工具。它旨在帮助读者通过系统性的方法，从底层硬件到高层应用，有效地识别并解决复杂的无线网络问题。 "Aerohive WLAN Troubleshooting Guide Coleman.pdf"是一本实用的参考书籍，适合无线网络维护工程师、网络管理员和准备升级认证的从业人员使用，它强调了理论知识与实践技能的结合，是提升无线网络故障处理能力的宝贵资源。

Five Tenets of WLAN Troubleshooting

networking issue or an application issue. As shown in Figure 1, TCP/IP

problems should be investigated at layers 3–4, whereas most application

issues exist between layers 5 and 7.

FIGURE1 OSI model

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data-Link

1 Physical

IP address, routing

Wi-Fi: RF problems, bad WLAN design,

drivers, misconﬁgured supplicant

RADIUS, Active Directory, DNS,

DHCP, NTP, and user applications

TCP/UDP ports, ﬁrewalls

Wi-Fi: 802.1X, PSK, 802.11 encryption, VLANs

roaming problems

Most Wi-Fi Problems Are Client Issues

As previously mentioned, whenever you troubleshoot a WLAN, you should

start at the Physical layer. Additionally, 70 percent of the time the problem

will reside on the WLAN client. If there are any client connectively problems,

WLAN Troubleshooting 101 dictates that you disable and re-enable the

WLAN network adapter. The driver for the WLAN network interface card

(NIC) is the interface between the 802.11 radio and the operating system (OS)

of the client device. For whatever reason, the WLAN driver and the OS of the

device may not be communicating properly. A simple disable/re-enable of the

WLAN NIC will reset the driver. Always eliminate this potential problem

before investigating anything else. Additionally, rst-generation radio drivers

and rmware are notorious for possible bugs. Always make sure the WLAN

client population has the latest available drivers installed. Another change

that is quick and easy to make is to recongure the client conguration pro-

le. Most client supplicants allow the user to dene a WLAN conguration

prole or connection parameters. Sometimes troubleshooting a problem is as

easy as deleting the old prole and conguring a new prole.

As mentioned earlier, client-side security issues usually evolve around

improperly congured supplicant settings. This could be something as simple

as a mistyped WPA2-Personal passphrase or as complex as 802.1X/EAP

digital certicate problems.

Layer 1 Troubleshooting

Proper WLAN Design Reduces Problems

A huge percentage of WLAN support phone calls are a symptom of a lack of

WLAN design. Proper capacity and coverage planning, spectrum analysis,

and a validation site survey will eliminate the majority of WLAN support

tickets in regard to performance. Proper WLAN design will minimize prob-

lems such as co-channel interference (CCI) in advance. Additionally, many

WLAN security holes can be eliminated in advance with proper WLAN

security planning. If 802.1X/EAP is deployed, one of the biggest chal-

lenges is how to provision the root CA certicates for mobile devices such as

smartphones and tablets. A well-thought-out security strategy for employee

WLAN devices, BYOD devices, and guest WLAN access is essential. Proper

WLAN planning and design in advance will reduce time spent troubleshoot-

ing WLAN problems at a later juncture.

WLAN Always Gets the Blame

Despite all your best WLAN troubleshooting practices and best efforts,

you should resign yourself to the fact the WLAN will always get the blame.

Experienced WLAN administrators know the WLAN will be blamed for

problems that have nothing to do with the WLAN. This is another reason that

troubleshooting up the OSI stack is important. If the problem is not a layer 1 or

layer 2 issue, then Wi-Fi is not the culprit. However, put yourself in the shoes

of the end user who is connected to the WLAN. 802.11 technology exists at

the access layer. The whole point of an AP is to provide a wireless portal to a

preexisting network infrastructure. Your employees and guests who connect

to the WLAN expect seamless wireless mobility, and they have no concept

of problems that exist at layers 3–7. A WLAN end user is not aware that the

DHCP server is out of leases. A WLAN end user is not aware the Internet ser-

vice provider (ISP) is experiencing difculty and the WAN link is down. The

WLAN end user just knows that they cannot access

www.facebook.com

through

the WLAN and therefore they point the nger at the Wi-Fi network.

Layer 1 Troubleshooting

As discussed in the beginning of this booklet, most networking problems

usually exist at the Physical layer. In the following sections, we will delve

deeper into layer 1 problems often caused by bad WLAN design or RF inter-

ference. We will also discuss layer 1 issues such as radio driver issues, rm-

ware bugs, and issues related to Power over Ethernet (PoE).

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