OSPF Network Design Solutions
You will also want to duplicate some of the possible test patterns if you are testing a serial line by using either an all 1s or all 0s test pattern. When this is complete, look at the interface statistics. If errors have increased, then the media is causing problems and you will want to have it investigated further. Another way to generate a large network load is to specify a timeout value of 0. This tells the router not to wait for the echo reply before sending the next ping packet. You can really hammer your network this way so be careful.
TIPS: During your testing of serial interfaces, if you see the total number of errors exceeds two percent of the total number packets on the circuit, then you might have a deeper problem and you should respond accordingly. After you have run the extended ping tests, check if the input errors counter on the serial interface has increased as a result of the ping. If so, that means there is potentially a problem either in the WAN connection or the DSU. If the input errors counter does not increase, that means the DSU, cable, router interface card, and applique are okay. If this test was done as a result of high CRC and framing errors, then a clocking problem in the DSU might be the problem.
TIPS: On larger circuits, you might need to have more than one instance of ping running in order to stress it properly. Executing an Extended Ping in a Cisco Router Using an extended ping is very useful in determining the baseline operation of networks to determine what exactly is working and what is not.
TIPS: By selecting the extended command option with the display round trip time, you will be able to see any delays and the time interval between occurrences. It is a good idea to do a long extended ping sequence and plot the results in order to clearly see the change in round trip times. To execute an extended ping, go into the router’s Enable mode and enter the command ping. The options in brackets are default values. OSPF_Router# ping Protocol [ip]: Target IP address: 156.12.254.1 Repeat count [5]: Datagram size [100]: Timeout in seconds [2]: Extended commands [n]: yes Source address: Type of service [0]: Set DF bit in IP header? [no]: Validate reply data? [no]: Data pattern [0xABCD]: Loose, Strict, Record, Timestamp, Verbose[none]: record Number of hops [ 9 ]: Loose, Strict, Record, Timestamp, Verbose[RV]: Sweep range of sizes [n]: To fully utilize the configurable options of an extended ping, you need to understand what each option allows you to do. The following list describes the configurable options of an extended ping.
TIPS: When selecting the desired commands while performing an extended ping, remember the default setting is shown in brackets.
TIPS: In complex networks you will sometimes find instances in which the outgoing interface of the router from which you are running the ping will not have a route or be prevented by an access list to the destination. In these cases, you should use the extended ping’s source address field to set the ping’s source address to another IP address that is permitted. Understanding an Extended Ping with the Record Option When using the record option, the <*> indicates that the route is complete. Type escape sequence to abort. Sending 5, 100-byte ICMP Echoes to 56.12.254.1, timeout is 2 seconds: Packet has IP options: Total option bytes= 39, padded length=40 Record route: <*> 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 0.0.0.0 Reply to request 0 (72 ms). Received packet has options Total option bytes= 40, padded length=40 Record route: 56.0.16.35 56.0.17.98 56.12.254.1 56.0.17.97 56.0.16.39 56.0.16.35 <*> 0.0.0.0 0.0.0.0 0.0.0.0 End of list Reply to request 1 (76 ms). Received packet has options Total option bytes= 40, padded length=40 Record route: 56.0.16.67 56.0.17.98 56.12.254.1 56.0.17.97 56.0.16.39 56.0.16.35 <*> 0.0.0.0 0.0.0.0 0.0.0.0 End of list For additional information on using the ping and extended ping commands, refer to the Cisco IOS Configuration Fundamentals Command Reference. trace Command Trace is a common network diagnostic tool found on UNIX machines, Windows NT, Windows 95, and your Cisco router. Trace might help you uncover the cause of network difficulties. What Is trace? Trace is a network diagnostic tool that allows network engineers or users to trace and view the actual route an IP packet follows to the indicated host. The trace command provides a method for determining which path packets traverse between two devices. Because the Trace utility reveals IP routing decisions, it is useful in discovering if the routers erroneously converged on a path that traverses a low-bandwidth link or a heavily congested router or segment. How to Use trace The trace command discovers the route a router’s packets follow when traveling to their destinations. Network engineers could then use the results of the trace command to adjust routing protocol metrics to optimize the path between critical points.
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