Monitoring Troubleshooting an OSPF Network

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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.
  Protocol [ip]:. You can also select various other protocols such as decnet, sna, and ipx. Some protocols can only be used when pinging from router to router.
  Target IP address:. This is the destination IP address of the device you are trying to ping.
  Repeat count [5]:. You select the number of pings packets you want to send here; the default is five.
  Timeout in seconds [2]:. How many seconds will the router wait for the echo reply before timing out and going onto the next packet.
  Extended commands [n]:. At this point, you can accept the characteristics of the ping up until this point or not.
  Type of service [0]:. You can select various services here as well such as tcp, tftp, telnet, ftp, http, etc., to help troubleshoot specific problems.
  Validate reply data? [no]:. Do you want the ping packet’s checksum verified?
  Data Pattern [0xABCD]:. Other data patterns include 0xffff, 0x0000, 0x1010, or 0x0101. The last two data patterns can be used to duplicate a frame failure.
  Number of hops [9]:. How many hops should the ping travel to reach the desired destination?


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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OSPF Network Design Solutions
OSPF Network Design Solutions
ISBN: 1578700469
EAN: 2147483647
Year: 1998
Pages: 200
Authors: Tom Thomas

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