Logging

4.3.c i Local logging, syslog, debugs, conditional debugs

Local logging, syslog

General information on “Local logging, syslog”:

• Logging, syslog is enabled by default
• Messages are stored in the RAM by default
• The severity can be defined (each level includes all severities above (numerically lower))
• Because of this, there’s a maximum buffer size (4096 bytes by default), which can be increased/decreased
• If the buffer size gets exceeded, the oldest messages will be removed
• Syslogs can also be stored on a remote server or file in the flash memory
• When connected by console, logging messages are displayed automatically
• If connected by Telnet/SSH, displaying of logging messages must be enabled first

Logging severity levels:

• Severity-0: Emergencies
• Severity-1: Alerts
• Severity-2: Critical
• Severity-3: Errors
• Severity-4: Warnings
• Severity-5: Notifications
• Severity-6: Informational
• Severity-7: Debugging

Mnemonic:

Every Alley Cat Eats Warm Noodles In Doors

Log message format:

seq no:timestamp: %facility-severity-MNEMONIC:description

“Local logging, syslog” CLI configuration commands:

## Disabling/Enabling logging for console/VTY lines globally
Router(config)# [no] logging console
Router(config)# [no] logging monitor

## Defining the logging severity for console/VTY lines
Router(config)# logging console <severity>
Router(config)# logging monitor <severity>

## Defining the logging buffer size
Router(config)# logging buffered <size>

## Defining a syslog server (both commands do the same)
Router(config)# logging <syslog-srv-ip>
Router(config)# logging host <syslog-srv-ip>

## Setting logging to write messages to a file in the flash memory
Router(config)# logging file flash:<filename>

## Enabling logging on the VTY line (needs to be done after every login)
Router# terminal monitor

“Local logging, syslog” CLI show commands:

## Showing all log messages
Router# show logging

Debugs, conditional debugs

General information on “Debugs, conditional debugs”:

• Debugging is used to find out what’s exactly happening within the system
• Debugging can be enabled for all kinds of information or only specific features
• Enabling debugging for all kinds of information can cause the system to slow down heavily and make it unreachable
• Debugging features can also be filtered to get only specific information (eg. debugs of a specific interface)
• When connected by console, debug messages are displayed automatically
• If connected by Telnet/SSH, displaying debug messages must be enabled first

“Debugs, conditional debugs” CLI configuration commands:

## Enabling debugging for specific features and conditions
Router# debug [all | specific feature]
Router# debug condition [condition]

## Disabling debugging for specific features and conditions
Router# undebug [all | specific feature]
Router# undebug condition [condition]

“Debugs, conditional debugs” CLI show commands:

## Showing enabled debug parameters and conditions
Router# show debug
Router# show debug condition

4.3.c ii Timestamps

General information on “Logging Timestamps”:

• Timestamps are important to record when something has occurred
• By default, logs don’t have a timestamp and therefor it cannot be determined when something has happened
• There are two ways a timestamp can be configured:
  1. Timestamp with time since uptime
  2. Timestamp with actual date/time
• Additionally sequence numbers can be configured (disabled by default)
• This is especially useful when several messages occur at the same time to see the exact sequence in which the messages occurred

“Logging Timestamps” CLI show commands:

## Enabling the timestamp service globally (with time since uptime)
Router(config)# service timestamps [log | debug] uptime

## Enabling the timestamp service globally (with actual date/time)
Router(config)# service timestamps [log | debug] datetime [msec | year | localtime  | show-timezone]

## Enabling the sequence numbers service globally
Router(config)# service sequence-numbers