Router troubleshooting methods

1. Serial Port troubleshooting

When a connectivity problem occurs in the serial port, in order to eliminate the serial port fault, the show interface serial command is generally used to analyze its screen output report content and locate the problem. The start of the serial port report provides the interface status and line protocol status. Possible Combinations of interfaces and line protocols are as follows:

1) serial port running and line protocol running are all working conditions. The serial port and line protocol have been initialized and are switching protocol survival information.

2) serial port running and line protocol disabling. This display indicates that the router is connected to the device that provides the carrier detection signal, indicating that the carrier signal appears between the local and remote modem, however, the Protocol survival information at both ends of the connection is not correctly exchanged. Possible faults occur in vro configuration problems, modem Operation Problems, lease line interference or remote router faults, Digital Modem clock problems, two serial ports connected through the link are not on the same subnet, this report will appear.

3) Both the serial port and line protocol are closed, which may be due to line faults, cable faults, or modem faults of the Telecommunications Department.

4) the serial port management is disabled and the line protocol is disabled. In this case, the shutdown command is entered in the interface configuration. Run the no shutdown command to enable management shutdown.

When both interfaces and line protocols are running, although basic communication on the serial port link is established, many potential faults may still occur due to information packet loss and information packet errors. During normal communication, the interface input or output information package should not be lost, or the loss volume is very small and will not increase. If the loss of information packets increases regularly, the traffic transmitted through this interface exceeds the traffic that can be processed by the interface. The solution is to increase the line capacity. Find information packages that are lost due to other causes, and check that the input and output in the output report of the show interface serial command keep the queue status. When the number of information packets in the keep queue reaches the maximum allowed value, the size of the keep queue settings can be increased.

2. Ethernet interface troubleshooting

Typical Ethernet interface faults: excessive bandwidth utilization, frequent collision conflicts, and incompatible use ?? Type. You can use the show interface ethernet command to view the throughput and touch of this interface? H conflict, information packet loss, and ?? Type.

You can check the network utilization by checking the interface throughput. If the percentage of the network broadcast information package is high, the network performance starts to decline. The information package from the optical fiber network to the Ethernet segment may overwhelm the Ethernet port. In this case, the Internet can adopt the optimization interface, that is, the Ethernet interface uses the no ip route-cache command to disable fast conversion, adjust the buffer zone and maintain the queue.

When two interfaces try to transfer information to the ethernet cable at the same time, what will happen? H. Ethernet requires few conflicts, and different network requirements are different. Generally, the cause of the conflict is found to be three or five times per second. Touch? H conflict produces congestion, touch? The reason for the H conflict is usually that the cables are too long, over-utilized, or "deaf" nodes. Ethernet cables should be considered in Physical Design and Management of Cable Laying systems. Over-standard cables may cause more conflicts.

If the interface and line Protocol report the running status, and the node's physical connection is in good condition, but cannot communicate. The problem may also be caused by incompatibility between the two nodes ?? Type. The solution is to use the same configuration ?? Type. ?? Two devices in the same network of the same type communicate with each other. You can use sub-interfaces on the router interface and specify different encapsulation types for each sub-interface.

3. troubleshooting of Asynchronous Communication Ports

During the operation of the Interconnection Network, the asynchronous communication port provides reliable services for users, but is also a fault-prone part. The main problem is that when the LAN-based traffic is transmitted through an asynchronous link, the amount of lost information packets is minimized.

The common external factors of asynchronous communication port faults are: poor performance of dial-up links, connection quality of telephone network switches, and modem settings. Check the modem used at both ends of the link: there are not many problems connecting to the remote PC port modem, because the modem is usually initialized every time a new dial is generated, most communication programs can send the appropriate setting string before issuing the dialing command. There are many problems with connecting to the vro port. The Modem usually waits for a connection from the remote modem. Before connecting, the specified string is not received. If the modem loses its settings, you should use one method to initialize the remote modem. A simple method is to use a modem that can be configured through the front panel. Another method is to connect the modem to the asynchronous interface of the router, establish reverse telnet, and send the setting command to configure the modem.

The show interface async and show line commands are the most widely used tools for diagnosing asynchronous communication port faults. In the show interface async command output report, the only condition that the interface status report is closed is that the encapsulation type is not set for the interface. The line protocol status is displayed the same as that of the serial port. The show line command displays the interface receiving and transmission speed settings, and the EIA status. The show line command can be considered as an extension of the show interface async interface command. The EIA signal and network status output by the show line command:

NoCTS noDSR dtr rts: the modem is not connected to an asynchronous interface.

CTS noDSR dtr rts: the modem and the asynchronous interface are normally connected, but the remote modem is not connected.

Cts dsr dtr rts: Remote modem dial-up access and establish a connection.

To determine the asynchronous communication port failure, perform the following steps: Check the cable line quality, check the modem parameter settings, and check the modem connection speed; check whether rxspeed and txspeed match the modem configuration. Use the show interface async command and the show line command to check the port communication status. Check the EIA Status display from the Report of the show line command; check interface encapsulation; check information package loss and buffer loss.

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