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Network Management, image, image, image, image, image, image, image, image…

- - - - Structure:
        
        Standard branches: Common variables for all devices (defined by RFCs).
        
        Private branches: Vendor-specific variables (e.g., Cisco: 1.3.6.1.4.1.9).
      - Purpose: The SNMP manager uses the OID to get or set a specific piece of information from an agent.
  - - - SNMPv2c:
      - Uses a community string for weak security.
      - Improved with bulk retrieval and better error codes.
      - No authentication or encryption.
    - - SNMPv3:
      - Secure version.
      - Provides authentication, message integrity, and encryption.
  - - - NMS periodically asks devices for data.
        
        Used for monitoring (traffic, CPU) and creating graphs/baselines.
        
        Disadvantages: Delay in alerts and uses bandwidth.
    - - Agent immediately sends an unsolicited alert to the NMS.
        
        Used for critical events (link down, security failure).
        
        Advantage: Faster than polling and uses less bandwidth.
  - - - What: Plaintext passwords for SNMPv1 & v2c.
      - Types:
      - read-only (ro): Allows viewing MIB data only.
      - read-write (rw): Allows viewing and changing MIB data.
      - Purpose: Authenticate access to the device's MIB.
  - - - GET: Manager retrieves data from the device's MIB.
        SET: Manager changes configuration or triggers actions on the device (e.g., reboot).
    - - get-request: Get a specific value.
        
        get-next-request: Get the next value in a table.
        
        get-bulk-request: Get large data blocks (SNMPv2+).
    - - SNMP Agent: On devices, collects data and stores it in a MIB.
        SNMP Manager (NMS): Queries and controls the agents.
- - - - Syslog Server (external, for storage & reports)
      - Internal Buffer (RAM, viewable via CLI only)
      - Console Line
      - Terminal Line
  - - - What: Sends system messages and debug output from a device.
  - - - Problem: Log messages have no time by default.
      - Solution: Use the command service timestamps log datetime.
      - Result: Messages show the date and time, which is essential for tracking events.
- - - - Process exmaple:
        
        R1 discovers S1 connected on port G0/0/1. Using CDP detail, admin finds S1 IP: 192.168.1.2.
        From S1, discovers S2 connected via F0/1. From S2, no more devices found → network map complete.
- - - - NTP uses hierarchical “strata” levels to sync time across networks.
      - Stratum 0: Authoritative sources (atomic/GPS clocks, most accurate).
      - Stratum 1: Devices directly connected to stratum 0 — primary network time servers.
      - Stratum 2+: Get time from stratum 1 and can serve lower strata.
      - Lower stratum number = more accurate.
      - Max level: 15 hops; stratum 16 = unsynchronized.
      - Same-stratum servers can act as peers for backup or verification.
  - - - Commands
        
        show clock detail → Check current time and source.
        
        ntp server <IP> → Set NTP server (e.g., 209.165.200.225).
        
        show ntp associations → Shows NTP connections and stratum info.
        
        show ntp status → Verifies synchronization and current stratum.
  - - - Time synchronization is essential for accurate logs, troubleshooting, and security.
      - Devices can set time manually or using NTP (Network Time Protocol).
      - Manual setup is not reliable — time is lost after reboot.
      - NTP automatically syncs time from a server (private or public).
      - Uses UDP port 123 and ensures all network devices share the same time.
- - - - Important Info:
      - Size: Total and free memory.
      - Permissions: Read-only (ro), write-only (wo), read/write (rw).
      - Key Locations:
      - flash: Contains the IOS (bootable). Marked with * (default).
      - nvram: Stores startup-config.
      - tftp: Network storage.
- - - - Purpose: Install a new IOS version for bug fixes or new features.
      - Process: Copy the new image file from a TFTP server to the router's flash memory.
      - Example: Copy isr4200...bin from TFTP server at 2001:DB8:CAFE:100::99 to the router.
  - - - Backup IOS Image
      - Purpose: Quickly restore the OS if it gets corrupted or erased.
      - Process: Copy the image file from the router's flash to a TFTP server.
      - Example: Backup lsr4200...bin from router to TFTP server at 172.16.1.100.
  - - - Centralized File Management
      - Store IOS images and configs on a central TFTP server.
      - Benefits:
      - Controls the number of IOS images.
      - Manages revisions easily.
      - Maintains configuration files in one place.