telnet session. No command should be selected that
will cause the debug output to create additional traffic
that creates debug output. If this occurs, the telnet
session will rapidly saturate the link with traffic or the
router will exhaust one or more resources. A good rule to
follow to prevent this recursion of traffic is “Never debug any
activity on the port where the session is established”. The
output of the different debug commands varies. Some may
frequently generate many lines while others produce a line or
two of output every few minutes. Another IOS software service
that will enhance the usefulness of the debug output is
the timestamps command. This command will put a
timestamp on a debug message. This information provides
the time when the debug event occurred and the duration
of time between events. The following command configures a
timestamp that will show the hour:minute:second of the output,
the amount of time since the router was last powered up, and
when a reload command was executed: GAD(config)#service
timestamps debug uptime The no debug all command or
the undebug all command turn off all diagnostic output.
To disable a particular debug command, use the “no” form of the
command. For example, if debug for monitoring RIP was enabled
with the command debug ip rip, it can be disabled with
no debug ip rip. To view what is currently being
examined by a debug command, use show
debugging. Lab Activity Lab Exercise:
Troubleshooting Routing Issues with Debug This lab is to
utilize a systematic OSI troubleshooting process to diagnose
routing problems.
Content Summary An understanding
of the following key points should have been achieved:
- The show ip route command
- Determining the
gateway of last resort
- Determining the route source
and destination address
- Determining route
administrative distance
- Determining route metric
- Determining route next hop
- Determining last route
update
- Observing multiple paths to destination
- Using a structured approach to troubleshooting
- Testing by OSI layers
- Layer 1 troubleshooting
using indicators
- Layer 3 troubleshooting using
ping
- Layer 7 troubleshooting using Telnet
- Troubleshooting Layer 1 using show interfaces
- Troubleshooting Layer 2 using show interfaces
- Troubleshooting using show cdp
- Troubleshooting using traceroute
- Troubleshooting routing issues using show ip route
and show ip protocols
- Troubleshooting using
show controllers serial
- Troubleshooting using
debug commands