CCNP TSHOOT学习指南：全面解析与维护Cisco IP网络

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"《CCNP资料大全：故障排除与维护Cisco IP网络》（TSHOOT基础学习指南）是一本专门为CCNP TSHOOT考试642-832认证准备的学习材料。作者Amir Ranjbar拥有CCIENo.8669的资格，该书由Cisco Press出版，版权归属于Cisco Systems, Inc.，并强调了未经出版商书面许可，不得任何形式复制或传输书中的内容，包括但不限于影印、录音或通过任何信息存储和检索系统。本书于2010年首次印刷，版权页列出了图书的详细信息，如美国印制和图书馆编目号。在版权页下方有警告和免责声明，明确指出此书旨在为学习者提供关于故障排除与维护Cisco IP网络课程的知识参考，但不保证其完整性和准确性，并提示读者在使用时可能存在误差。书中内容覆盖了全面的基础学习，深入解析TSHOOT考试的核心概念和技术，可能涉及网络故障排查策略、路由器和交换机操作、网络安全问题、路由协议理解、QoS设置、网络性能监控以及网络维护等方面的知识。通过阅读这本书，学习者可以提升对Cisco网络架构的理解，掌握解决实际网络问题的技巧，以期在通过CCNP TSHOOT考试后能够更有效地管理和维护复杂的IP网络环境。值得注意的是，尽管本书旨在为备考提供支持，但实际的网络环境可能会不断变化，因此建议读者在学习过程中结合最新的技术更新和实践案例，确保知识的时效性和实用性。同时，由于考试内容可能会随技术发展而调整，持续关注官方更新和认证考试大纲是必不可少的。"

Figure 1-2. Fundamental Tools and Applications of Network Maintenance Toolkits

The basic components of a network maintenance toolkit are as follows:

• Command-line device management: Cisco IOS Software includes a powerful command-line

interface (CLI) that you can use to configure and monitor individual routers and switches. This

includes commands such as the show commands, the debug commands, Embedded Event Manager

(EEM) commands, and IP SLA commands. After an initial configuration through the serial console of

the device, the CLI is commonly accessed remotely through use of the Telnet or Secure Shell (SSH)

protocols. To be able to manage the devices during network outages, an out-of-band management

solution can be implemented to allow access to the CLI using the serial console at all times.

• Graphical user interface (GUI)-based device management: Cisco provides free GUI-based

device management tools for many Cisco routers and switches. Examples of such tools include Cisco

Configuration Professional (CCP), Secure Device Manager (SDM), Cisco Configuration Assistant

(CCA), and Cisco Network Assistant (CNA).

• Backup server: To create backups of the software and configurations of your routers and switches,

you need to provide a TFTP, FTP, HTTP, or Secure Copy Protocol (SCP) server. Many operating

systems include these services as optional add-ons, and many software packages offer those

services, too.

• Log server: Basic logging functionality can be provided by sending the router’s or switch’s log

messages to a syslog server using the syslog protocol. Syslog is a standard service on most UNIX-

based operating systems or could be provided by installing additional software on the operating

system of your choice.

• Time server: To synchronize clocks on all your network devices, it is useful to have a Network Time

Protocol (NTP) server on your network. You could even synchronize your router and switch clocks to

one of the many public time servers available on the Internet.

To ensure correct time stamps on logging and debug output and to support other time-based features such

as the use of certificates or time-based access, it is vital that the clocks of the network devices be properly

set and synchronized. The Network Time Protocol (NTP) can be used to synchronize the clock of a device to

the clock of an NTP server, which in turn is synchronized to another server higher up the NTP hierarchy. The

position of a device in the NTP hierarchy is determined by its stratum, which serves as an NTP hop count. A

stratum 1 server is a server that is directly connected to an authoritative time source such as a radio or

atomic clock. A server that synchronizes its clock to a stratum 1 server will become a stratum 2 time source,

and so on.

It is common to have a redundant set of servers in the core of the network that are synchronized to an

authoritative source or a service provider server, and to configure other devices to synchronize their clocks to

these central sources. In large networks, this hierarchy could even consist of multiple levels. You configure

time servers using the ntp server command. If multiple time servers are configured for redundancy, the NTP

protocol decides which server is most reliable and will synchronize to that server. Alternatively, a preferred

server can be appointed by use of the prefercommand option on the ntp server command. In addition to

defining timeservers, you can define your local time zone and configure the devices to adapt to daylight

savings time. Finally, after you have the time synchronized and the correct time zone has been configured,

you configure the router or switch to time stamp its log and debug entries.

Example 1-1 shows the clock of a device that is synchronized to a single time server with IP address

10.1.220.3. The time zone is configured to Pacific standard time (PST), which has an −8 hour offset to

universal time coordinated (UTC). The clock is configured to change to daylight savings time on the second

Sunday in March at 2:00 a.m. and back to standard time on the first Sunday in November at 2:00 a.m. The

logging for system logging is configured to use the local date and time in the time stamps and to include the

time zone in the time stamp. For log entries generated by debugs, the settings are similar, but milliseconds

are included in the time stamps for greater accuracy.

Example 1-1. NTP Example

service time stamps debug datetime msec localtime show-timezone

service time stamps log datetime localtime show-timezone

clock timezone PST -8

clock summer-time PDT recurring 2 Sun Mar 2:00 1 Sun Nov 2:00

ntp server 10.1.220.3

For more details about the configuration of NTP, consult the “Configuring NTP” section of the Cisco IOS

Network Management Configuration Guide:

http://tinyurl.com/yezfkr3

Configuration and Documentation Tools

Many web-based (online) maintenance tools and resources can prove helpful during the planning and

implementation of network maintenance procedures. Cisco.com provides numerous tools to support your

network maintenance processes. Many of the tools are available only to registered users with a valid Cisco

service contract or to Cisco Channel Partners, however. Some useful and freely available tools are as follows:

• Dynamic Configuration Tool: This tool aids you in creating hardware configurations. It verifies

compatibility of the hardware and software you select, and it gives you a complete bill of materials

(BoM) that lists all the necessary part numbers. For more information,

seehttps://apps.cisco.com/qtc/config/html/configureHomeGuest.html.

• Cisco Feature Navigator: This tool enables you to quickly find the right Cisco IOS Software release

for the features you want to run on your network. For more information,

see http://tools.cisco.com/ITDIT/CFN/

• SNMP Object Navigator: The Simple Network Management Protocol (SNMP) Navigator translates

SNMP object identifiers (OIDs) into object names. This tool also enables you to download SNMP

Management Information Base (MIB) files and to verify the supported MIBs in a particular Cisco IOS

Software version. For more information, see http://tools.cisco.com/Support/SNMP/do/BrowseOID.do?

local=en.

• Cisco Power Calculator: This tool calculates the power-supply requirements for a particular Power

over Ethernet (PoE) hardware configuration. Access to this tool requires a Cisco.com account.

Good documentation is mostly the result of a good process. Good tools can prove extremely helpful in

supporting the documentation process, but it is most important that creating and updating documentation be

an integral part of your maintenance processes. The value of documentation heavily depends on how

accessible it is and how up-to-date it is. If you cannot find or cannot access the documentation when you

need it or if you cannot trust its information, the documentation has almost no value. Therefore, you must

ensure that any tool or application you use to support creation, retrieval, and updating of documentation

must be easy to access and easy to use. Examples of tools that can be used to access, create, and maintain

documentation include the following:

• Wiki: A wiki combines easy web-based access with intuitive editing capabilities. It is suitable as a

base documentation system. You can use a wiki as a framework to link various other existing

documentation systems.

• Issue tracking system: Other names for issue tracking systems include trouble ticket, support

ticket, or incident ticket system. An issue tracking system allows incoming support requests,

problems, or other incidents to be logged, tracked, and documented. By documenting progress,

communication, and escalation of incidents, an issue tracking system enables a team of people to

work on the same incidents in an efficient manner. You can also build a historical database of

problems, their treatments, and the resolutions.

Logging Services

Events that happen on a networking device such as router can be logged. There are different types of events,

and different events have different levels of significance or severity. Examples of events include interfaces

going up and down, configuration events, and routing protocol adjacencies being established. By default,

events are usually logged only to the device’s console; however, because the console is usually not easily

accessible, let alone monitored, it is worthwhile to collect and store the logs on a server, or at least in a

separate piece of memory of the router, to facilitate access to them during troubleshooting procedures.

Logging the messages to buffers on the router or switch is a minimal step that guarantees that logs are

available on the device, as long as it is not rebooted. On some devices and Cisco IOS Software versions,

logging to buffers is turned on by default. To enable buffer logging manually, you can use the logging

buffered command to specify that messages should be logged to a buffer in the device’s RAM. As an option,

you can specify the amount of RAM that should be allocated to this buffer. The buffer is circular, meaning that

when the buffer has reached its maximum capacity, the oldest messages will be discarded to allow the

logging of new messages. You can display the content of this logging buffer via the show loggingcommand.

Logging severity levels on Cisco Systems devices are as follows:

• (0) Emergencies

• (1) Alerts

• (2) Critical

• (3) Errors

• (4) Warnings

• (5) Notifications

• (6) Informational

• (7) Debugging

When logging is enabled, the severity level can be specified as an option. This causes the device to only log

messages with a severity at the configured level or lower numeric value. By default, messages of all severity

levels are logged to buffer.

You can also adjust the logging severity level of the console. By default, all messages from level 0 to 7 are

logged to the console; however, similar to buffer logging, you can configure the severity level as an optional

parameter on the logging console command.

Logging messages are best to be sent to a syslog server. Doing so allows you to store the logs of all your

network devices centrally. When logging messages are sent to a syslog server, logs are no longer lost when

the networking device crashes or reboots. You can configure one or more syslog servers by entering

the logging host command. By default, only messages of severity level 6 or lower are logged to the syslog

server. This can bechanged, similar to buffer or console logging, but unlike these other commands, the

severity is configured by entering the logging trap level command. This command applies to all configured

syslog hosts. Figure 1-3 shows three logging commands configured on a device and an explanation for each

command.

Figure 1-3. A Logging Command Example with Explanation

[View full size image]

For more detail about the configuration of logging and syslog services, consult the “Logging System

Messages” section of the Cisco IOS Network Management Configuration Guide:

http://tinyurl.com/yc8ftr6

Network Monitoring and Performance Measurement Tools

GUI- and CLI-based device management tools are used to examine individual devices, for example, at a time

you suspect a problem exists. However, the problem might not be noticed until a user complains. At that

point, when users have already noticed the failure, the problem has most likely had some impact on the

business. A network monitoring system continuously checks your network devices’ availability and status.

This enables you to detect possible problems as soon as they occur, and it might even allow you to diagnose

and resolve these problems before they even become apparent to end users. Most network monitoring

software incorporates various protocols such as SNMP, ICMP, and syslog so that you can monitor devices and

network events. In addition, Cisco IOS NetFlow technology can be leveraged, not just to monitor the devices,

but also to monitor the actual traffic on the network. Some network monitoring tools also incorporate

performance monitoring capabilities. There is a gray area between network monitoring and performance

measurement. While you monitor the network’s performance and look for faults and problems, you can also

use your data as input for capacity planning, SLA compliance measurements, or accounting purposes.

The three main motivations for measuring network performance are as follows:

• Capacity planning: By measuring average and peak loads on the network, you can create a

baseline of the traffic on your network and know the utilization of your network. By repeating the

measurements over time, you also recognize trends in the growth of the traffic and can predict when

you need to upgrade links or equipment before the growth starts causing congestion and

performance problems.

• Diagnosing performance problems: Performance problems are difficult to troubleshoot because

they are hard to quantify and are often intermittent in nature. A user might say, “Application x is

really slow lately.” But what does that mean? When exactly is the application slow? What is causing

this problem? Is it the client software faulty, or is it the server, or the network in between? Having a

good insight into the load on the network, specifically on the path between the client and the server,

helps you to determine whether network congestion might be causing the problems.

• SLA compliance: Whether you are guaranteeing a level of service to others through an SLA or

whether you have been promised a certain level of service by a provider, you need to have a way to

measure whether the service guarantees defined in the SLA are met.

You can measure network performance by first gathering statistics from the routers and switches. The

gathered statistics can then be stored in a database, graphed over time, and analyzed. This information can

be very useful for capacity planning and performance troubleshooting. Typical statistics to gather are the

packet and byte counters on interfaces and device CPU and memory utilization. For SLA compliance, on the

other hand, it is most useful to measure key indicators such as round-trip time (RTT), jitter, and packet loss.

The IP SLA feature that is available on many Cisco routers enables you to set up probes that measure these

key indicators along particular paths through your network. The statistics can then be read using Cisco IOS

commands or collected using SNMP. The raw data is stored in a database and can then be analyzed or

graphed. Cisco Internetwork Performance Monitor (IPM), which is part of the CiscoWorks LAN Management

Solution, can leverage the IP SLA functionality in the routers to provide detailed performance graphs. In

addition, various other network management software have the capability to collect statistics using SNMP

and graph the results. The open source Multi Router Traffic Grapher (MRTG) and other products based on it

are examples of this type of software.

Implementing Backup and Restore Services

An essential element of any network maintenance toolkit is a backup server from which device configurations

and Cisco IOS Software can be copied to and restored. The simplest and most commonly implemented

service is TFTP, which does not require any configuration on the network devices. The server is set up to

serve and receive files without any need for authentication or identification, other than specifying the name

of the configuration or software file itself. The fact that the protocol does not require any authentication and

that all content is sent across the network in clear text makes it a relatively unsecure mechanism. More

secure protocols such as FTP, SCP, and HTTP or HTTPS can also be used as a means of transferring

configurations and software. To use any of these more-secure protocols, you must specify the username and

password that are used to authenticate to the server. For all of these protocols, the credentials can be

specified as part of the Uniform Resource Locator (URL) that is used with the copycommand. The username

and password are specified by placing the username and password as username:password@ before the

server name or IP address in the URL. Example 1-3 shows how to copy the startup configuration using FTP to

a server with the IP address 10.1.152.1 and a file named RO1-test.cfg using the user name backup and

password san-fran.

Example 1-3. Performing Backup Using FTP with Username and Password

RO1# copy startup-config ftp://backup:san-fran@10.1.152.1/RO1-test.cfg

Address or name of remote host [10.1.152.1]?

Destination filename [RO1-test.cfg]?

Writing RO1-test.cfg !

2323 bytes copied in 0.268 secs (8668 bytes/sec)

For SCP, HTTP and HTTPS you would use a similar syntax, replacing the URL prefix ftp:// with scp://, http://

or https://, respectively. Specifying the username and password on the command line is somewhat

cumbersome and suffers from the fact that the password is displayed in clear text on the screen, which is

less desirable from a security standpoint. To circumvent this issue, the username and password can be

specified in the configuration, instead of on the command line, for the FTP, HTTP, and HTTPS

protocols. Example 1-4 shows how to store FTP and HTTP username and passwords in the configuration and

perform an FTP backup without having to type the username and password.

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