Table of Contents 1 System Maintaining and Debugging 1-1

Transcription

1 Table of Contents 1 System Maintaining and Debugging 1-1 System Maintaining and Debugging 1-1 Ping 1-1 Introduction 1-1 Configuring Ping 1-1 Ping Configuration Example 1-2 Tracert 1-4 Introduction 1-4 Configuring Tracert 1-4 System Debugging 1-5 Introduction to System Debugging 1-5 Configuring System Debugging 1-6 Ping and Tracert Configuration Example

2 1 System Maintaining and Debugging When maintaining and debugging the system, go to these sections for information you are interested in: System Maintaining and Debugging Ping Tracert System Debugging Ping and Tracert Configuration Example System Maintaining and Debugging Ping You can use the ping command and the tracert command to verify the current network connectivity, and use the debug command to enable debugging and thus to diagnose system faults based on the debugging information. Introduction You can use the ping command to verify whether a device with a specified address is reachable, and to examine network connectivity. The ping function is implemented through the Internet Control Message Protocol (ICMP): 1) The source device sends an ICMP echo request to the destination device. 2) The source device determines whether the destination is reachable based on whether it receives an ICMP echo reply; if the destination is reachable, the source device determines the link quality based on the numbers of ICMP echo requests sent and replies received, determines the distance between the source and destination based on the round trip time of ping packets. Configuring Ping Follow the step below to configure the ping function: To do Use the command Remarks Check whether a specified address in an IP network is reachable ping [ ip ] [ -a source-ip -c count -f -h ttl -i interface-type interface-number -m interval -n -p pad -q -r -s packet-size -t timeout -tos tos -v ] * host Available in any view 1-1

3 For a low-speed network, you are recommended to set a larger value for the timeout timer (indicated by the -t parameter in the command) when configuring the ping command. Ping Configuration Example Network requirements As shown in Figure 1-1, check whether an available route exists between Device A and Device C. If there is an available route exists between the two devices, get the detailed information of routes from Device A to Device C. Figure 1-1 Ping network diagram Configuration procedure # Use the ping command to display whether an available route exists between Device A and Device C. <DeviceA> ping PING : 56 data bytes, press CTRL_C to break Reply from : bytes=56 Sequence=1 ttl=254 time=205 ms Reply from : bytes=56 Sequence=2 ttl=254 time=1 ms Reply from : bytes=56 Sequence=3 ttl=254 time=1 ms Reply from : bytes=56 Sequence=4 ttl=254 time=1 ms Reply from : bytes=56 Sequence=5 ttl=254 time=1 ms --- ping statistics packet(s) transmitted 5 packet(s) received 0.00% packet loss round-trip min/avg/max = 1/41/205 ms # Get the detailed information of routes from Device A to Device C. <DeviceA> ping -r PING : 56 data bytes, press CTRL_C to break Reply from : bytes=56 Sequence=1 ttl=254 time=53 ms 1-2

4 Record Route: Reply from : bytes=56 Sequence=2 ttl=254 time=1 ms Record Route: Reply from : bytes=56 Sequence=3 ttl=254 time=1 ms Record Route: Reply from : bytes=56 Sequence=4 ttl=254 time=1 ms Record Route: Reply from : bytes=56 Sequence=5 ttl=254 time=1 ms Record Route: --- ping statistics packet(s) transmitted 5 packet(s) received 0.00% packet loss round-trip min/avg/max = 1/11/53 ms The principle of ping -r is as shown in Figure ) The source (Device A) sends an ICMP echo request with the RR option being empty to the destination (Device C). 2) The intermediate device (Device B) adds the IP address () of its outbound interface to the RR option of the ICMP echo request, and forwards the packet. 3) Upon receiving the request, the destination device copies the RR option in the request and adds the IP address () of its outbound interface to the RR option. Then the destination device sends an ICMP echo reply. 4) The intermediate device adds the IP address () of its outbound interface to the RR option in the ICMP echo reply, and then forwards the reply. 1-3

5 Tracert 5) Upon receiving the reply, the source device adds the IP address () of its inbound interface to the RR option. Finally, you can get the detailed information of routes from Device A to Device C: <-> {; } <->. Introduction By using the tracert command, you can trace the Layer 3 devices involved in delivering an IP packet from source to destination to check whether a network is available. This is useful for identification of failed node(s) in the event of network failure. Figure 1-2 Tracert diagram The tracert function is implemented through ICMP, as shown in Figure 1-2: 1) The source (Device A) sends a packet with a TTL value of 1 to the destination (Device D). The UDP port of the packet is a port number that will not be used by any application of the destination. 2) The first hop (Device B) (the Layer 3 device that first receives the packet) responds by sending a TTL-expired ICMP error message to the source, with its IP address encapsulated. In this way, the source device can get the address () of the first Layer 3 device. 3) The source device sends a packet with a TTL value of 2 to the destination device. 4) The second hop (Device C) responds with a TTL-expired ICMP error message, which gives the source device the address () of the second Layer 3 device. 5) The above process continues until the ultimate destination device is reached. No application of the destination uses this UDP port. Therefore, the destination replies a port unreachable ICMP error message with the destination IP address ) When the source device receives the port unreachable ICMP error message, it knows that the packet has reached the destination, and it can get the addresses of all the Layer 3 devices involved to get to the destination device (,, ). Configuring Tracert Follow these steps to configure tracert: To do Use the command Remarks Enter system view system-view 1-4

6 To do Use the command Remarks Enable sending of ICMP timeout packets Enable sending of ICMP destination unreachable packets ip ttl-expires enable ip unreachables enable Disabled by default. Disabled by default. Display the routes from source to destination tracert [ -a source-ip -f first-ttl -m max-ttl -p port -q packet-numbe -w timeout ] * host Available in any view System Debugging Introduction to System Debugging The device provides various debugging functions. For the majority of protocols and features supported, the system provides corresponding debugging information to help users diagnose errors. The following two switches control the display of debugging information: Protocol debugging switch, which controls protocol-specific debugging information. Screen output switch, which controls whether to display the debugging information on a certain screen. As Figure 1-3 illustrates, suppose the device can provide debugging for the three modules 1, 2, and 3. Only when both the protocol debugging switch and the screen output switch are turned on can debugging information be output on a terminal. Figure 1-3 The relationship between the protocol and screen debugging switch 1-5

7 Configuring System Debugging Output of the debugging information may reduce system efficiency. The debugging commands are usually used by administrators in diagnosing network failure. After completing the debugging, disable the corresponding debugging function, or use the undo debugging all command to disable all the debugging functions. Output of debugging information is related to the configurations of the information center and the debugging commands of each protocol and functional module. Displaying the debugging information on a terminal (including console or VTY) is a common way to output debugging information. You can also output debugging information to other destinations. For the detailed configurations, refer to Information Center Commands. By default, you can output debugging information to a terminal by following these steps: To do Use the command Remarks Enable the terminal monitoring of system information Enable the terminal display of debugging information Enable debugging for a specified module Display the enabled debugging functions terminal monitor terminal debugging debugging { all [ timeout time ] module-name [ option ] } display debugging [ interface interface-type interface-number ] [ module-name ] Optional The terminal monitoring on the console is enabled by default and that on the monitoring terminal is disabled by default. Available in user view Disabled by default Available in user view Disabled by default Available in user view Optional Available in any view You must configure the debugging, terminal debugging and terminal monitor commands first to display the detailed debugging information on the terminal. For the detailed description on the terminal debugging and terminal monitor commands, refer to Information Center Commands. Ping and Tracert Configuration Example Network requirements As shown in Figure 1-4, Device A failed to telnet Device C. Now it is required to determine whether an available route exists between Device A and Device C. If no such a route exists, you need to locate the failed nodes in the network. 1-6

8 Figure 1-4 Ping and tracert network diagram Configuration procedure # Use the ping command to display whether an available route exists between Device A and Device C. <DeviceA> ping PING : 56 data bytes, press CTRL_C to break --- ping statistics packet(s) transmitted 0 packet(s) received % packet loss # No such a route exists. Use the tracert command to determine failed nodes. <DeviceA> system-view [DeviceA] ip ttl-expires enable [DeviceA] ip unreachables enable [DeviceA] tracert traceroute to () 30 hops max,40 bytes packet, press CTRL_C to bre ak 1 14 ms 10 ms 20 ms 2 * * * 3 * * * 4 * * * 5 <DeviceA> The above output shows that no available route exists between Device A and Device C; an available router exists between Device A and Device B; an error occurred on the connection between Device B and Device C. In this case, you can use the debugging ip icmp command to enable ICMP debugging on Device A and Device C to check whether the devices send or receive the specified ICMP packets, or you can use the display ip routing-table command to display whether a route exists between the two devices. 1-7