Router Troubleshooting Encyclopedia

Troubleshooting Router Interface

Serial Port Trouble Shooting

Serial port connectivity problems, in order to eliminate the serial port fault, usually from show interface serial command, analysis of its screen output report content, to find out where the problem lies. The beginning of the serial port report provides the state of the interface and the status of the line protocol. There are several possible combinations of interfaces and line protocols:
1. Serial port operation, line protocol operation, this is the complete working conditions. The serial and line protocols have been initialized and are exchanging the surviving information of the protocol.

2. Serial port operation, line protocol shutdown, this display indicates that the router is connected with a device that provides carrier detection signals, indicating that the carrier signal appears between the local and remote modems, but does not properly exchange protocol survival information at both ends of the connection. Possible failures occur in router configuration issues, modem operation problems, leased line disturbances or remote router failures, digital modem clock problems, and two serial ports connected through the link are not on the same subnet, and this report appears.

3. Both serial and line protocols are closed, which may be a line failure in the telecommunications department, a cable failure, or a modem failure.

4. Serial port management shutdown and line protocol shutdown, this situation is in the interface configuration entered the shutdown command. Turn on administrative shutdown by entering the no shutdown command.

While the interface and line protocols are running, although the basic communication of serial link is established, there may be many potential failure problems due to packet loss and packet error. interface input or output packets should not be lost during normal communication, or the amount lost is very small and will not increase. If there is a regular increase in packet loss, it indicates that traffic transmitted over this interface exceeds the amount of traffic that the interface can handle. The solution is to increase the line capacity. Look for other causes of packet loss, view the input output in the output report of the show interface serial command to maintain the status of the queue. When you find that the number of packets in the queue reaches the maximum allowable value of the information, you can increase the size of the queue settings.
Troubleshooting Ethernet Interfaces

The typical fault problem of Ethernet interface is: Excessive utilization of bandwidth and frequent collision conflicts; using incompatible frame types. Use the Show interface Ethernet command to view throughput, collision violations, packet loss, and frame type content for this interface.

1. The bandwidth utilization of the network can be detected by looking at the throughput of the interface. If the percentage of network broadcast packets is high, network performance begins to decline. Packets that are converted to Ethernet segments may overwhelm the Ethernet port. On the internet this can be done by optimizing the interface, which uses the no IP route-cache command on the Ethernet interface, disables fast conversion, and adjusts the buffer and maintains the queue's settings.

2. A collision occurs when two interfaces attempt to transmit information packets to the Ethernet cable at the same time. Ethernet requires a very small number of conflicts, different network requirements are different, generally found that conflicts 35 times per second should find the cause of the conflict. Collision conflicts are caused by congestion, which is usually caused by the cable being too long, excessive utilization, or "deaf" nodes. The Ethernet network should be considered in the physical design and cabling system management, and the Ultra specification cabling may cause more conflicts to occur.

3. If the interface and the line protocol report a running state, and the node's physical connection is intact, it cannot communicate. The cause of the problem may also be that two nodes use incompatible frame types. The solution to the problem is to reconfigure the use of the same

The frame type. If two devices of the same network with different frame types are required to communicate with each other, you can use sub-interfaces at the router interface and specify different package types for each sub-interface.

Troubleshooting Asynchronous communication Ports

In the operation of Interconnection network, the task of asynchronous communication port is to provide reliable service for users, but it is also a fault-prone site. The general external factors of asynchronous communication port fault are: Poor dial-up link performance, connection quality problem of telephone network switch, modem settings. Check the modems used at both ends of the link: there are not too many problems connecting to the remote PC port modem, because the modem is typically initialized each time a new dial is generated, and most communication programs can send the appropriate settings string before dialing commands are issued, and there are more problems connecting the router ports. This modem usually waits for a connection from a remote modem and does not receive the settings string until it is connected. If the modem loses its settings, a method should be used to initialize the remote modem. An easy way to do this is to use a modem that is configurable through the front panel, and another way is to connect the modem to the router's asynchronous interface, establish a reverse telnet, and send a settings command to configure the modem.

Show Interface async command, show line command is the most used tool for diagnosing asynchronous communication port failures. Show interface Async command output report, the only case where the interface status report is closed is that the interface does not have a package type set. The line protocol status display is the same as the Serial Line protocol display. Show line command displays interface reception and transmission speed settings as well as EIA status display. The show line command can be considered an extension of the interface command (show interface async). View the EIA signal output from the show line command to determine the network status.

To determine the asynchronous communication port failure The following steps are generally available: Check the cable quality, check the modem's parameter settings, check the modem's connection speed, check rxspeed and txspeed for the modem configuration, and the show Interface Async command and Show line command to view the communication status of the port; Check the EIA status display from the report Line command, check the interface encapsulation, check packet loss, and buffer loss.