Understanding the network.pdf - Back to Home

timestamps debug> for debug messages. Timestamping logging
messages is important and should be enabled, because it provides the
time and date the event occurred. Timestamping is helpful for debug
messages as well, but in most cases is not required, and when
enabled just adds to the size of the debug message.
IOS Message Logging
Keeping up with what is going on with your router is important.
Logging provides this simple, but essential facility. In most cases, log
information is simply status data, such as changes in the router's
interface status, modifications to running configuration, and
debugging output. When things are operating smoothly, this data is
nice to have. When a problem comes up, however, this data can be
quite valuable. The IOS uses UNIX's syslog logging system to
generate IOS logging messages. The IOS provides four methods for
viewing logging information:
• Console—The router's console port
• Monitor—The router's system monitor, a VTY "console"
message display
• Trap—Syslog output to a remote syslog server running on UNIX
or NT
• Buffer—A place to store a list of logging events in the router's
DRAM
By default, all console and monitor methods are enabled, buffer is
disabled, and trap (while set up) needs to be configured to know
where to send its messages.
The trap and DRAM buffer logging methods provide a way to store
logging information. Of the two, the trap method is more useful for
logging because the messages are stored on a remote server. The
buffer approach stores the messages in DRAM, which is lost when the
router is shut down or rebooted. Storing messages in DRAM can also
affect the router's performance if your router is tight on shared DRAM
(which is why it is disabled by default). If your router has enough
memory to spare, saving logging information on the router will not
affect performance. It is helpful to have the messages accessible on
the router, especially when you are trying to debug a problem.
Before enabling local logging, check your router's memory usage (see
the general info section for command help) after the router has been