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Logging monitor

As explained in Acing the CCNA Exam: Volume 2 Advanced Networking and Security

logging monitor is a Cisco IOS command that enables logging of messages to monitored terminal lines and optionally sets their minimum severity threshold.

logging monitor enables real-time Syslog messages on Cisco IOS VTY lines used by Telnet or SSH sessions. It is enabled by default, but each VTY session must also run terminal monitor in privileged EXEC mode before messages appear. section 7.1.1

Key operational facts:

  • Disable VTY-line logging globally with no logging monitor. section 7.1.1
  • Enable monitoring for the current Telnet or SSH session with terminal monitor; repeat it after reconnecting, and have each simultaneous user run it independently. section 7.1.1
  • The default monitor threshold is debugging, so severity levels 0 through 7 are displayed; specifying a level includes that level and all numerically lower levels. section 7.2.2

Verify real-time VTY logging

SW1(config)# logging monitor SW1# terminal monitor After an interface state change, Syslog messages such as %LINK-3-UPDOWN and %LINEPROTO-5-UPDOWN appear in the active session. Without terminal monitor, the same VTY session displays no real-time messages. section 7.1.1

SW1(config)# interface g0/1
SW1(config-if)# shutdown                                                            #1
SW1(config-if)# do terminal monitor                                                 #2
SW1(config-if)# no shutdown                                                         #3
Sep 18 02:17:46.867: %LINK-3-UPDOWN: Interface FastEthernet0/3, changed state to up #4 
Sep 18 02:17:47.874: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to up                                                                 #4
#1 No Syslog messages are shown after disabling G0/1.
#2 Enables real-time logging for the session
#3 Reenables the interface
#4 Syslog messages are displayed.

Shows interface shutdown and reactivation commands alongside terminal monitor and the resulting Syslog output. section 7.1.1

How Acing the CCNA Exam: Volume 2 Advanced Networking and Security covers it

How deep it goes
Explains defaults, severity filtering, session scope, disabling, verification, and the required terminal monitor command.
Examples
Uses interface shutdown and reactivation to demonstrate displayed LINK and LINEPROTO Syslog messages.
What it assumes
Assumes Cisco IOS CLI access and Telnet or SSH connectivity while defining the per-session monitoring requirement.
What you can do after
Operate/configure VTY logging, enable it per session, filter severity levels, and verify resulting Syslog output.
How it connects
Connects VTY lines with Telnet, SSH, terminal monitor, Syslog, logging console, logging buffered, and logging trap.
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Related concepts

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 2 Advanced Networking and Security. The section links point to the parts of the book it draws on.