Overview:
Logging is essential to gaining visibility into your network
Study Notes:
- By default, system logging is enabled to the console at the debugging level
- Log messages are displayed in this format
Seq_no:timestamp: %facility-severity-MNEMONIC:description
- For example:
000052: Jan 20 08:50:18: %SYS-5-CONFIG_I: Configured from console by vty2 (172.16.0.25)
- Five types of logging
- Console logging - logs are visible to users who are consoled in
- Terminal logging - logs are visible to users who are connected via VTY lines
- Buffered logging - logs are written to the buffer whose size is configurable
- Syslog logging - logs are forwarded to an external syslog server
- SNMP logging - logs are forwarded to an external SNMP server via traps
- Eight levels of logging
- 0 - Emergencies
- 1 - Alerts
- 2 - Critical
- 3 - Errors
- 4 - Warnings
- 5 - Notifications
- 6 - Information
- 7 - Debugging
| Level Keyword | Level | Description | Syslog Definition |
| emergencies | 0 | System unstable | LOG_EMERG |
| alerts | 1 | Immediate action needed | LOG_ALERT |
| critical | 2 | Critical conditions | LOG_CRIT |
| errors | 3 | Error conditions | LOG_ERR |
| warnings | 4 | Warning conditions | LOG_WARNING |
| notifications | 5 | Normal but significant condition | LOG_NOTICE |
| informational | 6 | Informational messages only | LOG_INFO |
| debugging | 7 | Debugging messages | LOG_DEBUG |
- Logging rate limits can be set so as not to overwhelm the processor of the router with log messages
Sample logging configuration:
Router#config t Router(config)#logging on Router(config)#service timestamps log datetime [msec] [localtime] [show-timezone] Router(config)#service sequence-numbers Router(config)#logging buffered 16483 Router(config)#logging <ip.of.syslog.server> Router(config)#logging console <level> Router(config)#logging monitor <level> Router(config)#logging trap <level> Router(config)#logging history <level> Router(config)#logging history size <1 to 500> Router(config)#logging rate-limit <seconds> all except <level> Router(config)#end Router#terminal monitor Router#show running-config Router#show logging Router#show logging history
PacketTracer Lab: CCNA-7.3.d-Logging.pkt
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