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Chapter 10 Device Discovery, Management, and Maintenance (Device Discovery…

- - - - The Cisco IOS File System (IFS) allows the administrator to navigate to different directories and list the files in a directory, and to create subdirectories in flash memory or on a disk.
        
        The show file systems command, which lists all of the available file systems on a Cisco 1941 router
        
        * indicates this is the current default file system
        # indicates this is a bootable disk
        
        The Flash File System
        
        Because flash is the default file system, the dir command lists the contents of flash.
        
        The NVRAM File System
- - - - Cisco Discovery Protocol (CDP) is a Cisco proprietary Layer 2 protocol that is used to gather information about Cisco devices which share the same data link
        
        The device sends periodic CDP advertisements to connected devices to share information about the type of device that is discovered, the name of the devices, and the number and type of the interfaces.
    - - CDP is enabled by default
        
        To verify the status of CDP and display information about CDP, enter the show cdp command
        
        To enable CDP globally for all the supported interfaces on the device, enter cdp run in the global configuration mode.
        
        CDP can be disabled for all the interfaces on the device with the no cdp run command in the global configuration mode
        
        To disable CDP on a specific interface, enter no cdp enable in the interface configuration mode
        
        To enable CDP on the specific interface again, enter cdp enable
    - - use the show cdp neighbors command in the privileged EXEC mode
    - - Use the show cdp interface command in the privileged EXEC mode to display the interfaces that are CDP enabled on a device
  - - - Cisco devices also support Link Layer Discovery Protocol (LLDP), which is a vendor-neutral neighbor discovery protocol similar to CDP.
    - - To verify the status of LLDP and display information about LLDP, enter the show lldp command
        
        To enable LLDP globally on a Cisco network device, enter the lldp run command in the global configuration mode
        
        To disable LLDP, enter the no lldp run command in the global configuration mode.
        
        LLDP can be configured on specific interfaces. However, LLDP must be configured separately to transmit and receive LLDP packets
        
        R1(config-if)# lldp transmit
        R1(config-if)# lldp receive
    - - show lldp neighbors | show lldp neighbors detail
- - - - The software clock on a router or switch starts when the system boots and is the primary source of time for the system.
        
        Typically, the date and time settings on a router or switch can be set using one of two methods:
        
        Manually configure the date and time
        
        R1# clock set 20:36:00 dec 11 2015
        
        Configure the Network Time Protocol (NTP)
        
        NTP uses UDP port 123
    - - NTP networks use a hierarchical system of time sources. Each level in this hierarchical system is called a stratum.
        
        The stratum level is defined as the number of hop counts from the authoritative source.
    - - Stratum 0
        
        An NTP network gets the time from authoritative time sources. These authoritative time sources, also referred to as stratum 0 devices, are high-precision timekeeping devices assumed to be accurate and with little or no delay associated with them.
      - Stratum 1
        
        The stratum 1 devices are directly connected to the authoritative time sources. They act as the primary network time standard.
      - Stratum 2 and Lower
        
        The larger the stratum number, the lower the stratum level. The max hop count is 15. Stratum 16, the lowest stratum level, indicates that a device is unsynchronized.
    - - Before NTP is configured on the network, the show clock command displays the current time on the software clock
        
        With the detail option (show clock detail), the time source is also displayed
        
        Use the ntp server ip-address command in global configuration mode to configure an IP as the NTP server
        
        To verify the time source is set to NTP, use the show clock detail command again.
      - Use the show ip ntp associations and show ntp status commands to verify
  - - - Syslog Operation
        
        On Cisco network devices, the syslog protocol starts by sending system messages and debug output to a local logging process internal to the device.
        
        Syslog messages may be sent across the network to an external syslog server.
        
        Alternatively, syslog messages may be sent to an internal buffer. Messages sent to the internal buffer are only viewable through the CLI of the device.
        
        Finally, the network administrator may specify that only certain types of system messages are sent to various destinations. For example, the device may be configured to forward all system messages to an external syslog server. However, debug-level messages are forwarded to the internal buffer and are only accessible by the administrator from the CLI.
        
        Popular destinations for syslog messages include:
        
        logging buffer (RAM inside a router or switch, use show logging command to view the events stored on ram)
      - Introduction to Syslog
        
        When certain events occur on a network, networking devices have trusted mechanisms to notify the administrator with detailed system messages
        
        The most common method of accessing system messages is to use a protocol called syslog.
        
        Syslog uses UDP port 514 to send event notification messages across IP networks to event message collectors
        
        The syslog logging service provides three primary functions:
        
        The ability to specify the destinations of captured syslog messages
        
        The ability to select the type of logging information that is captured
        
        The ability to gather logging information for monitoring and troubleshooting
      - Syslog Message Forma
        
        Cisco devices produce syslog messages as a result of network events. Every syslog message contains a severity level and a facility.