Monitoring Troubleshooting an OSPF Network

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OSPF debug Commands

The debug privileged EXEC commands can provide a wealth of information about the traffic and events being seen (or not seen) to include but not limited to, interface traffic, error messages generated by nodes on the network, protocol-specific diagnostic packets, and other useful troubleshooting data.

Exercise extreme care when using debug commands. Many of these commands are processor-intensive and can cause serious network problems (such as degraded performance or loss of connectivity) if they are enabled on an already heavily loaded router. When you finish using a debug command, remember to disable it with its specific no debug command (or use the no debug all command to turn off all debugging).

When to Use debug Commands

Only use debug commands to isolate problems, not to monitor normal network operation. Because the high overhead of debug commands can disrupt router operation, you should use debug commands only when you are looking for specific types of traffic or problems and have narrowed your problems to a likely subset of causes.

There are a quite a few debug commands available to you. The following is an example of only the IP-based debug commands that you might use.

    OSPF_Router# debug ip ?      bgp       BGP information      cache     IP cache operations      cgmp      CGMP protocol activity      dvmrp     DVMRP protocol activity      egp       EGP information      eigrp     IP-EIGRP information      error     IP error debugging      http      HTTP connections      icmp      ICMP transactions      igmp      IGMP protocol activity      igrp      IGRP information      mcache    IP multicast cache operations      mobile    Mobility protocols      mpacket   IP multicast packet debugging      mrouting  IP multicast routing table activity      ospf      OSPF information      packet    General IP debugging and IPSO security transactions      peer      IP peer address activity      pim       PIM protocol activity      policy    Policy routing      rip       RIP protocol transactions      routing   Routing table events      sd        Session Directory (SD)      security  IP security options      tcp       TCP information      udp       UDP based transactions 

The format of the output varies with each different debug command:

  Some debug commands generate a single line of output per packet, and others generate multiple lines of output per packet.
  Some debug commands generate large amounts of output, and others generate only occasional output.
  Some debug commands generate lines of text, and others generate information in field format.

How to Use debug Commands

Adhering to the following procedure minimizes the load created by using debug commands because the console port no longer has to generate character-by-character processor interrupts.

To minimize the negative impact on your router of using debug commands, follow this procedure:

1.  Use the no logging console global configuration command on your router. This command disables all logging to the console terminal.
2.  Telnet to a router port and enter the enable EXEC mode.
3.  Use the terminal monitor command to copy debug command output and system error messages to your current terminal display. This permits you to view debug command output remotely, without being connected through the console port.
4.  Open another Telnet session with the router and type the command undebug all in this second session but do not hit return. Then you start the debug session in the first session. When you are ready to stop the debug session go back to the second session and just press return to send the command. Eventually the router’s CPU will process the command and shut off debug.
If you intend to keep the output of the debug command, spool the output to a file. The procedure for setting up such a debug output file is described in Cisco’s Debug Command Reference publication. There are also certain programs that offer the capability to log everything displayed in your current Telnet session. The Windows Telnet application is a good example of a program with this capability.

Complete OSPF debug Commands

This book refers to specific debug commands that are useful when troubleshooting OSPF-specific related problems. Complete details regarding the function and output of debug commands are provided in Cisco’s Debug Command Reference publication.

debug is a useful command that has many different options available for its use. It also provides you with a lot of information on what is going on within a router. However, it also can hurt the routing processes and normal operation of the router, so use it wisely.

The following is a list of the different types of debug commands:

  debug ip ospf ?. Provides help for debug ip ospf commands
  debug ip ospf adj. Deals with OSPF adjacency events
  debug ip ospf events. Deals with OSPF events
  debug ip ospf flood. Deals with OSPF flooding
  debug ip ospf lsa-generation. Deals with OSPF lsa generation
  debug ip ospf packet. Deals with OSPF packets
  debug ip ospf retransmission. Deals with OSPF retransmission events
  debug ip ospf spf. Deals with OSPF spf
  debug ip ospf tree. Deals with OSPF database tree

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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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