如何使用 TRACERT 公用程式(windows)引自microsoft!
大家可以有用時先睇，呢個係一個好基本的指令！
TRACERT 診斷公用程式會傳送「網際網路控制訊息通訊協定」(ICMP) 回應封包給目的地，以確定到目的地所經的路徑。在這些封包中，TRACERT 會使用各種不同的 IP 執行時間 (Time-To-Live，TTL) 值。因為路徑上的每台路由器在轉送封包之前必須至少將封包的 TTL 遞減 1，所以 TTL 其實就是一個躍點計數器。當封包的 TTL 達到零 (0) 時，路由器會將 ICMP「超過時間」訊息傳回給來源電腦。
TRACERT 將 TTL 設為 1，來傳送第一個回應封包，之後每次傳輸都將 TTL 遞增 1，直到目的地回應或達到最大 TTL 為止。中介路由器傳回的 ICMP「超過時間」訊息會顯示出路徑。但是請注意，有些路由器會將 TTL 已經過期的封包悄悄丟棄，因此 TRACERT 不會察覺到這些封包。
TRACERT 會依序印出傳回 ICMP「超過時間」訊息的中介路由器清單。使用 tracert 命令時如果用 -d 選項，可以指示 TRACERT 不要對每個 IP 位址執行 DNS 查閱，使得 TRACERT 會報告路由器近端介面的 IP 位址。
在下列 tracert 命令及其輸出的範例中，封包通過 2 台路由器 (157.54.48.1 和 11.1.0.67) 後到達主機 11.1.0.1。在這個範例中，預設閘道是 157.54.48.1，而 11.1.0.0 網路上路由器的 IP 位址是 11.1.0.67。
命令：
C:\>tracert 11.1.0.1
命令的輸出：
Tracing route to 11.1.0.1 over a maximum of 30 hops
---------------------------------------------------
1 2 ms 3 ms 2 ms 157.54.48.1
2 75 ms 83 ms 88 ms 11.1.0.67
3 73 ms 79 ms 93 ms 11.1.0.1
Trace complete.
option
如何使用 TRACERT 的選項
您可以將 TRACERT 搭配許多命令列選項一起使用，雖然在進行標準疑難排解時通常用不到這些選項。
下列命令語法範例顯示所有可能的選項：
tracert -d -hmaximum_hops -jhost-list -wtimeout target_host
參數的功能：-d
指定不將位址解析成主機名稱
-h maximum_hops
指定用於搜尋目標的最大躍點數
-j host-list
指定沿著 host-list 的概略來源路由
-w timeout
對每個回覆，要等候 timeout 所指定的
毫秒數
target_host
指定目標主機的名稱或 IP 位址
p.s. linux 中相似功能的有 traceroute 或 tracepath.
Dhcp
實驗九 DHCP服務的配置與管理（2）
DHCP伺服器各選項的優先順序
在一個TCP/IP網路中，每一台主機都應該有一個IP位址以進行互相通信。IP位址的分配有兩種類型：靜態和動態。由管理員手工分配的IP位址是靜態位址，從DHCP伺服器獲得的IP位址是動態位址。
與靜態IP位址相比，使用動態IP位址有如下好處：
當網路中的電腦數目比較多時，可以減少網路系統管理員的工作負擔；
減少了由於手工輸入而導致的IP位址錯誤問題，從而消除了一個常見的網路故障來源；
可以解決網路中主機數目較多而IP位址不足的問題；
為可擕式用戶在不同子網間頻繁移動提供方便。
DHCP伺服器在為用戶端提供IP位址的同時，還可提供一些其他選項的配置，常用的有：
003選項：路由器（即預設閘道器）的IP地址
006選項：DNS伺服器的IP地址
015選項：DNS功能變數名稱
044選項：WINS伺服器的IP地址
046選項：NetBIOS名稱解析的類型
在DHCP控制台下的伺服器選項、作用域選項、類選項和保留客戶機選項中，都可以對這些選項的值進行設置。在一個網路中，如果要為不同的用戶端設置不同選項的值時，就必須清楚各個選項的優先順序。下面通過一組實驗來說明DHCP選項的優先順序。
（1） 在IP地址為192.168.1.139的DHCP伺服器上創建兩個作用域“192.168.1.0”和“172.16.0.0”，然後配置伺服器選項的“003路由器”的值為“192.168.1.1”。此時可以發現，在這兩個作用域中的作用域選項中都會自動繼承伺服器選項中“003路由器”的配置，從兩個作用域中獲得IP地址的用戶端同時獲得的預設閘道器地址為“192.168.1.1”。
（2） 在作用域“192.168.1.0”中配置作用域選項的“003路由器”的值為“192.168.1.2”，此時從作用域“192.168.1.0”獲得IP地址的用戶端同時獲得的預設閘道器地址為“192.168.1.2”。
（3） 在作用域“192.168.1.0”中為MAC地址是“00-10-b5-4d-8c-6f”的用戶端A新建保留，此時保留選項會自動繼承該作用域選項中“003路由器”的配置。重新配置保留客戶機選項中“003路由器”的值為“192.168.1.3”，則電腦A獲得的預設閘道器位址為“192.168.1.3”。
（4） 在DHCP伺服器上創建兩個用戶類“Manager”和“User”，然後在作用域“192.168.1.0”中的作用域選項中配置使用者類“Manager”的“003路由器”選項的值為“192.168.1.4”，配置使用者類“User”的“003路由器”選項的值為“192.168.1.5”，則屬於“Manager”類的用戶端獲得的預設閘道器地址為“192.168.1.4”，而屬於“User”類的用戶端獲得的預設閘道器地址為“192.168.1.5”。
此時將上述電腦A設置為屬於“Manager”類，則電腦A獲得的預設閘道器位址不是“192.168.1.4”，而是“192.168.1.3”。
綜上所述可以得出如下結論：
伺服器選項的配置對DHCP伺服器中所有的作用域都生效；
作用域選項的配置只對本作用域生效，作用域選項的優先順序高於伺服器選項；
類選項的配置只對屬於特定DHCP類的用戶端生效，類選項的優先順序高於作用域選項；
保留客戶機選項的配置只對設置了保留的用戶端生效，保留客戶機選項的優先順序高於類選項。
Win2000 DHCP實驗
>>考試題一、DHCP伺服器（保留地址）
1、設置一台win2000 server為dhcp伺服器，ip地址為192.168.1.xx(其中xx為考生考試號碼的最後兩位)，並在該機上設置192.168.1.200-192.168.1.250的作用域，並且設置192.168.1.250為保留位址。
2、設置一台win2000 professional機器為dhcp客戶機，其ip位址自動從上面配置好的dhcp伺服器獲得。
3、設置該台客戶機的ip為保留的位址192.168.1.250，並設置該台主機的預設閘道器的位址為192.168.1.150。
實驗報告：
一、設置DHCP伺服器：
1、設置IP位址：
右擊“網上鄰居”-進入“本地連接”-“屬性”-TCP/IP屬性，設置IP：192.168.1.XX
2、安裝DHCP伺服器：
控制台-添加/刪除檔-Windows元件-網路服務-DHCP
3、配置DHCP伺服器：
（1）、開始-程式-管理工具-DHCP-添加伺服器，輸入伺服器IP：192.168.1.XX
（2）、右擊該電腦-新建作用域，名稱192.168.1.200-250，
（3）、起始IP：192.168.1.200，終止IP：192.168.1.250，子網路遮罩位數：24
（4）、右擊該作用域-啟動
4、設置保留位址：
（1）、在客戶機命令列中執行IPCONFIG/ALL，獲得MAC地址為：XX-XX-XX-XX-XX-XX
（2）、右擊保留-新建保留
保留名稱：客戶機
IP：192.168.1.250
MAC地址：XX-XX-XX-XX-XX-XX
二、客戶機設置：
1、右擊“網上鄰居”-進入“本地連接”-“屬性”-TCP/IP屬性，設置自動獲取IP和DNS；
2、命令列執行IPCONFIG/ALL，驗證OK
三、設置保留位址選項：
在DHCP中右擊保留位址（192.168.1.250）-配置選項-設置：
003路由器為：192.168.1.150（即預設閘道器）
四、客戶機驗證
>>考試題二、DHCP伺服器（用戶類）
1、設置一台win2000 server為dhcp伺服器，ip地址為192.168.1.xx(其中xx為考生考試號碼的最後兩位)，並在該機上設置192.168.1.200-192.168.1.250的作用域，並且設置預設閘道器為192.168.1.188，DNS伺服器為202.96.199.133。
2、為移動用戶設置一個名為MobieUser的用戶類，並設置其預設閘道器為192.168.1.88，DNS伺服器為192.168.1.133，其地址有效期為1個小時。
3、設置一台win2000 professional機器為dhcp客戶機，MobieUser的用戶類，其ip位址自動從上面配置好的dhcp伺服器獲得。
實驗報告：
一、設置DHCP伺服器：
1、設置IP位址：
右擊“網上鄰居”-進入“本地連接”-“屬性”-TCP/IP屬性，設置IP：192.168.1.XX
2、安裝DHCP伺服器：
控制台-添加/刪除檔-Windows元件-網路服務-DHCP
3、配置DHCP伺服器：
（1）、開始-程式-管理工具-DHCP-添加伺服器，輸入伺服器IP：192.168.1.XX
（2）、右擊該電腦-新建作用域，名稱192.168.1.200-250，
（3）、起始IP：192.168.1.200，終止IP：192.168.1.250，子網路遮罩位數：24
（4）、右擊該作用域-啟動
4、設置作用域選項：
（1）、在DHCP中右擊作用域選項-配置選項-設置：
003路由器為：192.168.1.188（即預設閘道器）
006 DNS伺服器為：202.96.199.133
二、創建並配置使用者類：
1、 在DHCP中右擊該電腦-定義使用者類，添加一個用戶類：MobieUser；
2、右擊作用域選項-配置選項-高級-選擇使用者類別MobieUser設置：
003路由器為：192.168.1. 88（即預設閘道器）
006 DNS伺服器為：192.168.1.133
051 租約：3600
三、客戶機設置：
1、右擊“網上鄰居”-進入“本地連接”-“屬性”-TCP/IP屬性，設置自動獲取IP和DNS；
2、 命令列執行ipconfig /setclassid “本地連接” MobieUser
3、 然後執行ipconfig/renew
4、 執行ipconfig/all，可查看結果OK
>>常規實驗題：準備兩台電腦A、B
1． 在電腦A上安裝DHCP服務（假設電腦A的IP位址為192.168.1.1）
2． 把電腦B設成自動獲得IP地址，即DHCP用戶端
3． 在電腦A上新建作用域，範圍為192.168.1.21-192.168.1.254
4． 在電腦B上測試看能不能獲得此範圍內的一個IP地址
5． 配置電腦A上的DHCP的伺服器選項，將003（預設閘道器）配為192.168.1.101，並到電腦B上測試效果
6． 配置電腦A上的DHCP作用域選項，將003配為192.168.1.102，並到電腦B上測試效果
7． 配置電腦A上的DHCP保留選項，為電腦B保留IP：192.168.1.104,到電腦B上測試效果
8． 配置電腦A上的DHCP使用者類選項,新建使用者類mobileuser(為移動用戶分配IP),並將mobileuser的003配置為192.168.1.103,把電腦B加入moblieuser使用者類,然後測試效果
DHCP伺服器各選項的優先順序
在一個TCP/IP網路中，每一台主機都應該有一個IP位址以進行互相通信。IP位址的分配有兩種類型：靜態和動態。由管理員手工分配的IP位址是靜態位址，從DHCP伺服器獲得的IP位址是動態位址。
與靜態IP位址相比，使用動態IP位址有如下好處：
當網路中的電腦數目比較多時，可以減少網路系統管理員的工作負擔；
減少了由於手工輸入而導致的IP位址錯誤問題，從而消除了一個常見的網路故障來源；
可以解決網路中主機數目較多而IP位址不足的問題；
為可擕式用戶在不同子網間頻繁移動提供方便。
DHCP伺服器在為用戶端提供IP位址的同時，還可提供一些其他選項的配置，常用的有：
003選項：路由器（即預設閘道器）的IP地址
006選項：DNS伺服器的IP地址
015選項：DNS功能變數名稱
044選項：WINS伺服器的IP地址
046選項：NetBIOS名稱解析的類型
在DHCP控制台下的伺服器選項、作用域選項、類選項和保留客戶機選項中，都可以對這些選項的值進行設置。在一個網路中，如果要為不同的用戶端設置不同選項的值時，就必須清楚各個選項的優先順序。下面通過一組實驗來說明DHCP選項的優先順序。
（1） 在IP地址為192.168.1.139的DHCP伺服器上創建兩個作用域“192.168.1.0”和“172.16.0.0”，然後配置伺服器選項的“003路由器”的值為“192.168.1.1”。此時可以發現，在這兩個作用域中的作用域選項中都會自動繼承伺服器選項中“003路由器”的配置，從兩個作用域中獲得IP地址的用戶端同時獲得的預設閘道器地址為“192.168.1.1”。
（2） 在作用域“192.168.1.0”中配置作用域選項的“003路由器”的值為“192.168.1.2”，此時從作用域“192.168.1.0”獲得IP地址的用戶端同時獲得的預設閘道器地址為“192.168.1.2”。
（3） 在作用域“192.168.1.0”中為MAC地址是“00-10-b5-4d-8c-6f”的用戶端A新建保留，此時保留選項會自動繼承該作用域選項中“003路由器”的配置。重新配置保留客戶機選項中“003路由器”的值為“192.168.1.3”，則電腦A獲得的預設閘道器位址為“192.168.1.3”。
（4） 在DHCP伺服器上創建兩個用戶類“Manager”和“User”，然後在作用域“192.168.1.0”中的作用域選項中配置使用者類“Manager”的“003路由器”選項的值為“192.168.1.4”，配置使用者類“User”的“003路由器”選項的值為“192.168.1.5”，則屬於“Manager”類的用戶端獲得的預設閘道器地址為“192.168.1.4”，而屬於“User”類的用戶端獲得的預設閘道器地址為“192.168.1.5”。
此時將上述電腦A設置為屬於“Manager”類，則電腦A獲得的預設閘道器位址不是“192.168.1.4”，而是“192.168.1.3”。
綜上所述可以得出如下結論：
伺服器選項的配置對DHCP伺服器中所有的作用域都生效；
作用域選項的配置只對本作用域生效，作用域選項的優先順序高於伺服器選項；
類選項的配置只對屬於特定DHCP類的用戶端生效，類選項的優先順序高於作用域選項；
保留客戶機選項的配置只對設置了保留的用戶端生效，保留客戶機選項的優先順序高於類選項。
Win2000 DHCP實驗
>>考試題一、DHCP伺服器（保留地址）
1、設置一台win2000 server為dhcp伺服器，ip地址為192.168.1.xx(其中xx為考生考試號碼的最後兩位)，並在該機上設置192.168.1.200-192.168.1.250的作用域，並且設置192.168.1.250為保留位址。
2、設置一台win2000 professional機器為dhcp客戶機，其ip位址自動從上面配置好的dhcp伺服器獲得。
3、設置該台客戶機的ip為保留的位址192.168.1.250，並設置該台主機的預設閘道器的位址為192.168.1.150。
實驗報告：
一、設置DHCP伺服器：
1、設置IP位址：
右擊“網上鄰居”-進入“本地連接”-“屬性”-TCP/IP屬性，設置IP：192.168.1.XX
2、安裝DHCP伺服器：
控制台-添加/刪除檔-Windows元件-網路服務-DHCP
3、配置DHCP伺服器：
（1）、開始-程式-管理工具-DHCP-添加伺服器，輸入伺服器IP：192.168.1.XX
（2）、右擊該電腦-新建作用域，名稱192.168.1.200-250，
（3）、起始IP：192.168.1.200，終止IP：192.168.1.250，子網路遮罩位數：24
（4）、右擊該作用域-啟動
4、設置保留位址：
（1）、在客戶機命令列中執行IPCONFIG/ALL，獲得MAC地址為：XX-XX-XX-XX-XX-XX
（2）、右擊保留-新建保留
保留名稱：客戶機
IP：192.168.1.250
MAC地址：XX-XX-XX-XX-XX-XX
二、客戶機設置：
1、右擊“網上鄰居”-進入“本地連接”-“屬性”-TCP/IP屬性，設置自動獲取IP和DNS；
2、命令列執行IPCONFIG/ALL，驗證OK
三、設置保留位址選項：
在DHCP中右擊保留位址（192.168.1.250）-配置選項-設置：
003路由器為：192.168.1.150（即預設閘道器）
四、客戶機驗證
>>考試題二、DHCP伺服器（用戶類）
1、設置一台win2000 server為dhcp伺服器，ip地址為192.168.1.xx(其中xx為考生考試號碼的最後兩位)，並在該機上設置192.168.1.200-192.168.1.250的作用域，並且設置預設閘道器為192.168.1.188，DNS伺服器為202.96.199.133。
2、為移動用戶設置一個名為MobieUser的用戶類，並設置其預設閘道器為192.168.1.88，DNS伺服器為192.168.1.133，其地址有效期為1個小時。
3、設置一台win2000 professional機器為dhcp客戶機，MobieUser的用戶類，其ip位址自動從上面配置好的dhcp伺服器獲得。
實驗報告：
一、設置DHCP伺服器：
1、設置IP位址：
右擊“網上鄰居”-進入“本地連接”-“屬性”-TCP/IP屬性，設置IP：192.168.1.XX
2、安裝DHCP伺服器：
控制台-添加/刪除檔-Windows元件-網路服務-DHCP
3、配置DHCP伺服器：
（1）、開始-程式-管理工具-DHCP-添加伺服器，輸入伺服器IP：192.168.1.XX
（2）、右擊該電腦-新建作用域，名稱192.168.1.200-250，
（3）、起始IP：192.168.1.200，終止IP：192.168.1.250，子網路遮罩位數：24
（4）、右擊該作用域-啟動
4、設置作用域選項：
（1）、在DHCP中右擊作用域選項-配置選項-設置：
003路由器為：192.168.1.188（即預設閘道器）
006 DNS伺服器為：202.96.199.133
二、創建並配置使用者類：
1、 在DHCP中右擊該電腦-定義使用者類，添加一個用戶類：MobieUser；
2、右擊作用域選項-配置選項-高級-選擇使用者類別MobieUser設置：
003路由器為：192.168.1. 88（即預設閘道器）
006 DNS伺服器為：192.168.1.133
051 租約：3600
三、客戶機設置：
1、右擊“網上鄰居”-進入“本地連接”-“屬性”-TCP/IP屬性，設置自動獲取IP和DNS；
2、 命令列執行ipconfig /setclassid “本地連接” MobieUser
3、 然後執行ipconfig/renew
4、 執行ipconfig/all，可查看結果OK
>>常規實驗題：準備兩台電腦A、B
1． 在電腦A上安裝DHCP服務（假設電腦A的IP位址為192.168.1.1）
2． 把電腦B設成自動獲得IP地址，即DHCP用戶端
3． 在電腦A上新建作用域，範圍為192.168.1.21-192.168.1.254
4． 在電腦B上測試看能不能獲得此範圍內的一個IP地址
5． 配置電腦A上的DHCP的伺服器選項，將003（預設閘道器）配為192.168.1.101，並到電腦B上測試效果
6． 配置電腦A上的DHCP作用域選項，將003配為192.168.1.102，並到電腦B上測試效果
7． 配置電腦A上的DHCP保留選項，為電腦B保留IP：192.168.1.104,到電腦B上測試效果
8． 配置電腦A上的DHCP使用者類選項,新建使用者類mobileuser(為移動用戶分配IP),並將mobileuser的003配置為192.168.1.103,把電腦B加入moblieuser使用者類,然後測試效果
0
意見
2008年2月28日 星期四
網路問題(English Version Only)
Network Troubleshooting Overview
These sections introduce you to the concepts and practice of network troubleshooting:
Introduction to Network Troubleshooting
Network Troubleshooting Framework
Troubleshooting Strategy
Network troubleshooting means recognizing and diagnosing networking problems with the goal of keeping your network running optimally. As a network administrator, your primary concern is maintaining connectivity of all devices (a process often called fault management). You also continually evaluate and improve your network's performance. Because serious networking problems can sometimes begin as performance problems, paying attention to performance can help you address issues before they become serious.
About Connectivity Problems
Connectivity problems occur when end stations cannot communicate with other areas of your local area network (LAN) or wide area network (WAN). Using management tools, you can often fix a connectivity problem before users even notice it. Connectivity problems include:
Loss of connectivity - When users cannot access areas of your network, your organization's effectiveness is impaired. Immediately correct any connectivity breaks.
Intermittent connectivity - Although users have access to network resources some of the time, they are still facing periods of downtime. Intermittent connectivity problems can indicate that your network is on the verge of a major break. If connectivity is erratic, investigate the problem immediately.
Timeout problems - Timeouts cause loss of connectivity, but are often associated with poor network performance.
About Performance Problems
Your network has performance problems when it is not operating as effectively as it should. For example, response times may be slow, the network may not be as reliable as usual, and users may be complaining that it takes them longer to do their work. Some performance problems are intermittent, such as instances of duplicate addresses. Other problems can indicate a growing strain on your network, such as consistently high utilization rates.
If you regularly examine your network for performance problems, you can extend the usefulness of your existing network configuration and plan network enhancements, instead of waiting for a performance problem to adversely affect the users' productivity.
Solving Connectivity and Performance Problems
When you troubleshoot your network, you employ tools and knowledge already at your disposal. With an in-depth understanding of your network, you can use network software tools, such as "Ping", and network devices, such as "Analyzers", to locate problems, and then make corrections, such as swapping equipment or reconfiguring segments, based on your analysis.
Transcend® provides another set of tools for network troubleshooting. These tools have graphical user interfaces that make managing and troubleshooting your network easier. With "Transcend Applications", you can:
Baseline your network's normal status to use as a basis for comparison when the network operates abnormally
Precisely monitor network events
Be notified immediately of critical problems on your network, such as a device losing connectivity
Establish alert thresholds to warn you of potential problems that you can correct before they affect your network
Resolve problems by disabling ports or reconfiguring devices
See "Your Network Troubleshooting Toolbox" for details about each troubleshooting tool.
Network Troubleshooting Framework
The International Standards Organization (ISO) Open Systems Interconnect (OSI) reference model is the foundation of all network communications. This seven-layer structure provides a clear picture of how network communications work.
Protocols (rules) govern communications between the layers of a single system and among several systems. In this way, devices made by different manufacturers or using different designs can use different protocols and still communicate.
By understanding how network troubleshooting fits into the framework of the OSI model, you can identify at what layer problems are located and which type of troubleshooting tools to use. For example, unreliable packet delivery can be caused by a problem with the transmission media or with a router configuration. If you are receiving high rates of "FCS Errors" and "Alignment Errors", which you can monitor with Status Watch, then the problem is probably located at the physical layer and not the network layer. Figure 1 shows how to troubleshoot the layers of the OSI model.
Table 5 describes the data that the network management tools can collect as it relates to the OSI model layers.
Table 5 Network Data and the OSI Model Layers
Layer
Data Collected
TranscendcNCS Tool Used
Application
Presentation
Session
Transport
Protocol information and other Remote Monitoring (RMON) and RMON2 data
LANsentry Manager
Traffix Manager(for more detail)
Network
Routing information
Status Watch
LANsentry Manager(for more detail)
Traffix Manager(for more detail)
Data Link
Traffic counts and other packet breakdowns
Status Watch
LANsentry Manager(for more detail)
Physical
Error counts
Status Watch
Figure 1 OSI Reference Model and Network Troubleshooting
For information about network troubleshooting tools, see "Your Network Troubleshooting Toolbox".
Troubleshooting Strategy
How do you know when you are having a network problem? The answer to this question depends on your site's network configuration and on your network's normal behavior. See "Knowing Your Network" for more information.
If you notice changes on your network, ask the following questions:
Is the change expected or unusual?
Has this event ever occurred before?
Does the change involve a device or network path for which you already have a backup solution in place?
Does the change interfere with vital network operations?
Does the change affect one or many devices or network paths?
After you have an idea of how the change is affecting your network, you can categorize it as critical or noncritical. Both of these categories need resolution (except for changes that are one-time occurrences); the difference between the categories is the time that you have to fix the problem.
By using a strategy for network troubleshooting, you can approach a problem methodically and resolve it with minimal disruption to network users. It is also important to have an accurate and detailed map of your current network environment. Beyond that, a good approach to problem resolution is:
Recognizing Symptoms
Understanding the Problem
Identifying and Testing the Cause of the Problem
Solving the Problem
Recognizing Symptoms
The first step to resolving any problem is to identify and interpret the symptoms. You may discover network problems in several ways. Users may complain that the network seems slow or that they cannot connect to a server. You may pass your network management station and notice that a node icon is red. Your beeper may go off and display the message: WAN connection down.
User Comments
Although you can often solve networking problems before users notice a change in their environment, you invariably get feedback from your users about how the network is running, such as:
They cannot print.
They cannot access the application server.
It takes them much longer to copy files across the network than it usually does.
They cannot log on to a remote server.
When they send e-mail to another site, they get a routing error message.
Their system freezes whenever they try to Telnet.
Network Management Software Alerts
Network management software, as described in "Your Network Troubleshooting Toolbox", can alert you to areas of your network that need attention. For example:
The application displays red (Warning) icons.
Your weekly Top-N utilization report (which indicates the 10 ports with the highest utilization rates) shows that one port is experiencing much higher utilization levels than normal.
You receive an e-mail message from your network management station that the threshold for broadcast and multicast packets has been exceeded.
These signs usually provide additional information about the problem, allowing you to focus on the right area.
Analyzing Symptoms
When a symptom occurs, ask yourself these types of questions to narrow the location of the problem and to get more data for analysis:
To what degree is the network not acting normally (for example, does it now take one minute to perform a task that normally takes five seconds)?
On what subnetwork is the user located?
Is the user trying to reach a server, end station, or printer on the same subnetwork or on a different subnetwork?
Are many users complaining that the network is operating slowly or that a specific network application is operating slowly?
Are many users reporting network logon failures?
Are the problems intermittent? For example, some files may print with no problems, while other printing attempts generate error messages, make users lose their connections, and cause systems to freeze.
Understanding the Problem
Networks are designed to move data from a transmitting device to a receiving device. When communication becomes problematic, you must determine why data are not traveling as expected and then find a solution. The two most common causes for data not moving reliably from source to destination are:
The physical connection breaks (that is, a cable is unplugged or broken).
A network device is not working properly and cannot send or receive some or all data.
Network management software can easily locate and report a physical connection break (layer 1 problem). It is more difficult to determine why a network device is not working as expected, which is often related to a layer 2 or a layer 3 problem.
To determine why a network device is not working properly, look first for:
Valid service - Is the device configured properly for the type of service it is supposed to provide? For example, has Quality of Service (QoS), which is the definition of the transmission parameters, been established?
Restricted access - Is an end station supposed to be able to connect with a specific device or is that connection restricted? For example, is a firewall set up that prevents that device from accessing certain network resources?
Correct configuration - Is there a misconfiguration of IP address, subnet mask, gateway, or broadcast address? Network problems are commonly caused by misconfiguration of newly connected or configured devices. See "Manager-to-Agent Communication" for more information.
Identifying and Testing the Cause of the Problem
After you develop a theory about the cause of the problem, test your theory. The test must conclusively prove or disprove your theory.
Two general rules of troubleshooting are:
If you cannot reproduce a problem, then no problem exists unless it happens again on its own.
If the problem is intermittent and you cannot replicate it, you can configure your network management software to catch the event in progress.
For example, with "LANsentry Manager", you can set alarms and automatic packet capture filters to monitor your network and inform you when the problem occurs again. See "Configuring Transcend NCS" for more information.
Although network management tools can provide a great deal of information about problems and their general location, you may still need to swap equipment or replace components of your network until you locate the exact trouble spot.
After you test your theory, either fix the problem as described in "Solving the Problem" or develop another theory.
Sample Problem Analysis
This section illustrates the analysis phase of a typical troubleshooting incident.
On your network, a user cannot access the mail server. You need to establish two areas of information:
What you know - In this case, the user's workstation cannot communicate with the mail server.
What you do not know and need to test -
Can the workstation communicate with the network at all, or is the problem limited to communication with the server? Test by sending a "Ping" or by connecting to other devices.
Is the workstation the only device that is unable to communicate with the server, or do other workstations have the same problem? Test connectivity at other workstations.
If other workstations cannot communicate with the server, can they communicate with other network devices? Again, test the connectivity.
The analysis process follows these steps:
1 . Can the workstation communicate with any other device on the subnetwork?
If no, then go to step 2.
If yes, determine if only the server is unreachable.
If only the server cannot be reached, this suggests a server problem. Confirm by doing step 2.
If other devices cannot be reached, this suggests a connectivity problem in the network. Confirm by doing step 3.
2 . Can other workstations communicate with the server?
If no, then most likely it is a server problem. Go to step 3.
If yes, then the problem is that the workstation is not communicating with the subnetwork. (This situation can be caused by workstation issues or a network issue with that specific station.)
3 . Can other workstations communicate with other network devices?
If no, then the problem is likely a network problem.
If yes, the problem is likely a server problem.
When you determine whether the problem is with the server, subnetwork, or workstation, you can further analyze the problem, as follows:
For a problem with the server - Examine whether the server is running, if it is properly connected to the network, and if it is configured appropriately.
For a problem with the subnetwork - Examine any device on the path between the users and the server.
For a problem with the workstation - Examine whether the workstation can access other network resources and if it is configured to communicate with that particular server.
Equipment for Testing
To help identify and test the cause of problems, have available:
A laptop computer that is loaded with a terminal emulator, TCP/IP stack, TFTP server, CD-ROM drive (to read the online documentation), and some key network management applications, such as LANsentry® Manager. With the laptop computer, you can plug into any subnetwork to gather and analyze data about the segment.
A spare managed hub to swap for any hub that does not have management. Swapping in a managed hub allows you to quickly spot which port is generating the errors.
A single port probe to insert in the network if you are having a problem where you do not have management capability.
Console cables for each type of connector, labeled and stored in a secure place.
Solving the Problem
Many device or network problems are straightforward to resolve, but others yield misleading symptoms. If one solution does not work, continue with another.
A solution often involves:
Upgrading software or hardware (for example, upgrading to a new version of agent software or installing Gigabit Ethernet devices)
Balancing your network load by analyzing:
What users communicate with which servers
What the user traffic levels are in different segments
Based on these findings, you can decide how to redistribute network traffic.
Adding segments to your LAN (for example, adding a new switch where utilization is continually high)
Replacing faulty equipment (for example, replacing a module that has port problems or replacing a network card that has a faulty jabber protection mechanism)
To help solve problems, have available:
Spare hardware equipment (such as modules and power supplies), especially for your critical devices
A recent backup of your device configurations to reload if flash memory gets corrupted (which can sometimes happen due to a power outage)
Use the Transcend NCS application suite Network Admin Tools to save and reload your software configurations to devices.
http://www.windowsnetworking.com/articles_tutorials/trouble/
http://support.3com.com/infodeli/tools/netmgt/tncsunix/product/091500/c1ovrvw.htm#18437
These sections introduce you to the concepts and practice of network troubleshooting:
Network Troubleshooting Framework
Troubleshooting Strategy
Network troubleshooting means recognizing and diagnosing networking problems with the goal of keeping your network running optimally. As a network administrator, your primary concern is maintaining connectivity of all devices (a process often called fault management). You also continually evaluate and improve your network's performance. Because serious networking problems can sometimes begin as performance problems, paying attention to performance can help you address issues before they become serious.
About Connectivity Problems
Connectivity problems occur when end stations cannot communicate with other areas of your local area network (LAN) or wide area network (WAN). Using management tools, you can often fix a connectivity problem before users even notice it. Connectivity problems include:
Loss of connectivity - When users cannot access areas of your network, your organization's effectiveness is impaired. Immediately correct any connectivity breaks.
Intermittent connectivity - Although users have access to network resources some of the time, they are still facing periods of downtime. Intermittent connectivity problems can indicate that your network is on the verge of a major break. If connectivity is erratic, investigate the problem immediately.
Timeout problems - Timeouts cause loss of connectivity, but are often associated with poor network performance.
About Performance Problems
Your network has performance problems when it is not operating as effectively as it should. For example, response times may be slow, the network may not be as reliable as usual, and users may be complaining that it takes them longer to do their work. Some performance problems are intermittent, such as instances of duplicate addresses. Other problems can indicate a growing strain on your network, such as consistently high utilization rates.
If you regularly examine your network for performance problems, you can extend the usefulness of your existing network configuration and plan network enhancements, instead of waiting for a performance problem to adversely affect the users' productivity.
Solving Connectivity and Performance Problems
When you troubleshoot your network, you employ tools and knowledge already at your disposal. With an in-depth understanding of your network, you can use network software tools, such as "Ping", and network devices, such as "Analyzers", to locate problems, and then make corrections, such as swapping equipment or reconfiguring segments, based on your analysis.
Transcend® provides another set of tools for network troubleshooting. These tools have graphical user interfaces that make managing and troubleshooting your network easier. With "Transcend Applications", you can:
Baseline your network's normal status to use as a basis for comparison when the network operates abnormally
Precisely monitor network events
Be notified immediately of critical problems on your network, such as a device losing connectivity
Establish alert thresholds to warn you of potential problems that you can correct before they affect your network
Resolve problems by disabling ports or reconfiguring devices
See "Your Network Troubleshooting Toolbox" for details about each troubleshooting tool.
Network Troubleshooting Framework
The International Standards Organization (ISO) Open Systems Interconnect (OSI) reference model is the foundation of all network communications. This seven-layer structure provides a clear picture of how network communications work.
Protocols (rules) govern communications between the layers of a single system and among several systems. In this way, devices made by different manufacturers or using different designs can use different protocols and still communicate.
By understanding how network troubleshooting fits into the framework of the OSI model, you can identify at what layer problems are located and which type of troubleshooting tools to use. For example, unreliable packet delivery can be caused by a problem with the transmission media or with a router configuration. If you are receiving high rates of "FCS Errors" and "Alignment Errors", which you can monitor with Status Watch, then the problem is probably located at the physical layer and not the network layer. Figure 1 shows how to troubleshoot the layers of the OSI model.
Table 5 describes the data that the network management tools can collect as it relates to the OSI model layers.
Table 5 Network Data and the OSI Model Layers
Layer
Data Collected
TranscendcNCS Tool Used
Application
Presentation
Session
Transport
Protocol information and other Remote Monitoring (RMON) and RMON2 data
LANsentry Manager
Traffix Manager(for more detail)
Network
Routing information
Status Watch
LANsentry Manager(for more detail)
Traffix Manager(for more detail)
Data Link
Traffic counts and other packet breakdowns
Status Watch
LANsentry Manager(for more detail)
Physical
Error counts
Status Watch
Figure 1 OSI Reference Model and Network Troubleshooting
For information about network troubleshooting tools, see "Your Network Troubleshooting Toolbox".
Troubleshooting Strategy
How do you know when you are having a network problem? The answer to this question depends on your site's network configuration and on your network's normal behavior. See "Knowing Your Network" for more information.
If you notice changes on your network, ask the following questions:
Is the change expected or unusual?
Has this event ever occurred before?
Does the change involve a device or network path for which you already have a backup solution in place?
Does the change interfere with vital network operations?
Does the change affect one or many devices or network paths?
After you have an idea of how the change is affecting your network, you can categorize it as critical or noncritical. Both of these categories need resolution (except for changes that are one-time occurrences); the difference between the categories is the time that you have to fix the problem.
By using a strategy for network troubleshooting, you can approach a problem methodically and resolve it with minimal disruption to network users. It is also important to have an accurate and detailed map of your current network environment. Beyond that, a good approach to problem resolution is:
Recognizing Symptoms
Understanding the Problem
Identifying and Testing the Cause of the Problem
Solving the Problem
Recognizing Symptoms
The first step to resolving any problem is to identify and interpret the symptoms. You may discover network problems in several ways. Users may complain that the network seems slow or that they cannot connect to a server. You may pass your network management station and notice that a node icon is red. Your beeper may go off and display the message: WAN connection down.
User Comments
Although you can often solve networking problems before users notice a change in their environment, you invariably get feedback from your users about how the network is running, such as:
They cannot print.
They cannot access the application server.
It takes them much longer to copy files across the network than it usually does.
They cannot log on to a remote server.
When they send e-mail to another site, they get a routing error message.
Their system freezes whenever they try to Telnet.
Network Management Software Alerts
Network management software, as described in "Your Network Troubleshooting Toolbox", can alert you to areas of your network that need attention. For example:
The application displays red (Warning) icons.
Your weekly Top-N utilization report (which indicates the 10 ports with the highest utilization rates) shows that one port is experiencing much higher utilization levels than normal.
You receive an e-mail message from your network management station that the threshold for broadcast and multicast packets has been exceeded.
These signs usually provide additional information about the problem, allowing you to focus on the right area.
Analyzing Symptoms
When a symptom occurs, ask yourself these types of questions to narrow the location of the problem and to get more data for analysis:
To what degree is the network not acting normally (for example, does it now take one minute to perform a task that normally takes five seconds)?
On what subnetwork is the user located?
Is the user trying to reach a server, end station, or printer on the same subnetwork or on a different subnetwork?
Are many users complaining that the network is operating slowly or that a specific network application is operating slowly?
Are many users reporting network logon failures?
Are the problems intermittent? For example, some files may print with no problems, while other printing attempts generate error messages, make users lose their connections, and cause systems to freeze.
Understanding the Problem
Networks are designed to move data from a transmitting device to a receiving device. When communication becomes problematic, you must determine why data are not traveling as expected and then find a solution. The two most common causes for data not moving reliably from source to destination are:
The physical connection breaks (that is, a cable is unplugged or broken).
A network device is not working properly and cannot send or receive some or all data.
Network management software can easily locate and report a physical connection break (layer 1 problem). It is more difficult to determine why a network device is not working as expected, which is often related to a layer 2 or a layer 3 problem.
To determine why a network device is not working properly, look first for:
Valid service - Is the device configured properly for the type of service it is supposed to provide? For example, has Quality of Service (QoS), which is the definition of the transmission parameters, been established?
Restricted access - Is an end station supposed to be able to connect with a specific device or is that connection restricted? For example, is a firewall set up that prevents that device from accessing certain network resources?
Correct configuration - Is there a misconfiguration of IP address, subnet mask, gateway, or broadcast address? Network problems are commonly caused by misconfiguration of newly connected or configured devices. See "Manager-to-Agent Communication" for more information.
Identifying and Testing the Cause of the Problem
After you develop a theory about the cause of the problem, test your theory. The test must conclusively prove or disprove your theory.
Two general rules of troubleshooting are:
If you cannot reproduce a problem, then no problem exists unless it happens again on its own.
If the problem is intermittent and you cannot replicate it, you can configure your network management software to catch the event in progress.
For example, with "LANsentry Manager", you can set alarms and automatic packet capture filters to monitor your network and inform you when the problem occurs again. See "Configuring Transcend NCS" for more information.
Although network management tools can provide a great deal of information about problems and their general location, you may still need to swap equipment or replace components of your network until you locate the exact trouble spot.
After you test your theory, either fix the problem as described in "Solving the Problem" or develop another theory.
Sample Problem Analysis
This section illustrates the analysis phase of a typical troubleshooting incident.
On your network, a user cannot access the mail server. You need to establish two areas of information:
What you know - In this case, the user's workstation cannot communicate with the mail server.
What you do not know and need to test -
Can the workstation communicate with the network at all, or is the problem limited to communication with the server? Test by sending a "Ping" or by connecting to other devices.
Is the workstation the only device that is unable to communicate with the server, or do other workstations have the same problem? Test connectivity at other workstations.
If other workstations cannot communicate with the server, can they communicate with other network devices? Again, test the connectivity.
The analysis process follows these steps:
1 . Can the workstation communicate with any other device on the subnetwork?
If no, then go to step 2.
If yes, determine if only the server is unreachable.
If only the server cannot be reached, this suggests a server problem. Confirm by doing step 2.
If other devices cannot be reached, this suggests a connectivity problem in the network. Confirm by doing step 3.
2 . Can other workstations communicate with the server?
If no, then most likely it is a server problem. Go to step 3.
If yes, then the problem is that the workstation is not communicating with the subnetwork. (This situation can be caused by workstation issues or a network issue with that specific station.)
3 . Can other workstations communicate with other network devices?
If no, then the problem is likely a network problem.
If yes, the problem is likely a server problem.
When you determine whether the problem is with the server, subnetwork, or workstation, you can further analyze the problem, as follows:
For a problem with the server - Examine whether the server is running, if it is properly connected to the network, and if it is configured appropriately.
For a problem with the subnetwork - Examine any device on the path between the users and the server.
For a problem with the workstation - Examine whether the workstation can access other network resources and if it is configured to communicate with that particular server.
Equipment for Testing
To help identify and test the cause of problems, have available:
A laptop computer that is loaded with a terminal emulator, TCP/IP stack, TFTP server, CD-ROM drive (to read the online documentation), and some key network management applications, such as LANsentry® Manager. With the laptop computer, you can plug into any subnetwork to gather and analyze data about the segment.
A spare managed hub to swap for any hub that does not have management. Swapping in a managed hub allows you to quickly spot which port is generating the errors.
A single port probe to insert in the network if you are having a problem where you do not have management capability.
Console cables for each type of connector, labeled and stored in a secure place.
Solving the Problem
Many device or network problems are straightforward to resolve, but others yield misleading symptoms. If one solution does not work, continue with another.
A solution often involves:
Upgrading software or hardware (for example, upgrading to a new version of agent software or installing Gigabit Ethernet devices)
Balancing your network load by analyzing:
What users communicate with which servers
What the user traffic levels are in different segments
Based on these findings, you can decide how to redistribute network traffic.
Adding segments to your LAN (for example, adding a new switch where utilization is continually high)
Replacing faulty equipment (for example, replacing a module that has port problems or replacing a network card that has a faulty jabber protection mechanism)
To help solve problems, have available:
Spare hardware equipment (such as modules and power supplies), especially for your critical devices
A recent backup of your device configurations to reload if flash memory gets corrupted (which can sometimes happen due to a power outage)
Use the Transcend NCS application suite Network Admin Tools to save and reload your software configurations to devices.
http://www.windowsnetworking.com/articles_tutorials/trouble/
http://support.3com.com/infodeli/tools/netmgt/tncsunix/product/091500/c1ovrvw.htm#18437
0
意見
2008年2月24日 星期日
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