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18 - Day 29 - First Hop Redundancy Protocol (FHRP).md

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Day 29 - First Hop Redundancy Protocol (FHRP)

Reviewed: No

1. Introduction to FHRPs:

  • Purpose:
    • FHRPs ensure that hosts in a network have a redundant default gateway in case the primary gateway fails.
    • FHRPs allow multiple routers to back up a single gateway IP address, so if the primary router fails, another router takes over without any disruption.
  • Common FHRPs for CCNA:
    • HSRP (Hot Standby Router Protocol) - Cisco proprietary.
    • VRRP (Virtual Router Redundancy Protocol) - Open standard.
    • GLBP (Gateway Load Balancing Protocol) - Cisco proprietary.

2. How FHRPs Work:

  • Virtual IP and MAC Addresses:
    • FHRPs use a Virtual IP (VIP) address that is shared between routers. Hosts on the network use this VIP as their default gateway.
    • A Virtual MAC Address is also used to respond to ARP requests.
  • Router Roles:
    • Active Router (HSRP)/Master Router (VRRP):
      • This router handles all traffic for the VIP.
    • Standby Router (HSRP)/Backup Router (VRRP):
      • This router takes over if the active router fails.
  • ARP and Gratuitous ARP:
    • ARP Requests: Sent by hosts to find out the MAC address corresponding to the VIP.
    • Gratuitous ARP: Sent by the standby router when it takes over to update the MAC address tables in switches, ensuring traffic is directed correctly.

3. Specific FHRPs Overview:

  • HSRP (Hot Standby Router Protocol):
    • Cisco Proprietary: Runs only on Cisco devices.
    • Versions:
      • HSRP Version 1: Uses multicast address 224.0.0.2.
      • HSRP Version 2: Uses multicast address 224.0.0.102, adds support for IPv6 and more groups.
    • Virtual MAC Address Format:
      • Version 1: 0000 0c07 acXX (XX is the group number in hexadecimal).
      • Version 2: 0000 0c9F FXXX (XXX is the group number in hexadecimal).
    • Preemption: Can be enabled to allow a router with a higher priority to take over as the active router when it comes back online. Command: standby <group-number> preempt
  • VRRP (Virtual Router Redundancy Protocol):
    • Open Standard: Can be used on any device that supports it.
    • Roles:
      • Master: Equivalent to the active router.
      • Backup: Equivalent to the standby router.
    • Multicast Address: 224.0.0.18.
    • Virtual MAC Address Format: 0000 5e00 01XX (XX is the group number in hexadecimal).
  • GLBP (Gateway Load Balancing Protocol):
    • Cisco Proprietary: Runs only on Cisco devices.
    • Load Balancing: Can load balance traffic across multiple routers in the same subnet.
    • Roles:
      • AVG (Active Virtual Gateway): Manages the assignment of virtual MAC addresses to routers (AVFs).
      • AVF (Active Virtual Forwarder): Forwards traffic for a portion of the hosts in the subnet.
    • Multicast Address: 224.0.0.102 (same as HSRP v2).
    • Virtual MAC Address Format: 0007 b400 XXXXYY (XXXX is the group number and YY is the AVF number in hexadecimal). fhrp

4. Basic Configuration of HSRP:

  • Commands:

    • standby version 2: Configures HSRP version 2.
    • standby <group-number> ip <virtual-ip>: Sets the virtual IP address for the HSRP group.
    • standby <group-number> priority <value>: Sets the priority for the router (default is 100).
    • standby <group-number> preempt: Enables preemption, allowing a router with a higher priority to take over as the active router.

  • Example Configuration for R1:

    interface GigabitEthernet0/0
 standby version 2
 standby 1 ip 172.16.0.254
 standby 1 priority 200
 standby 1 preempt

  • Example Configuration for R2:

    interface GigabitEthernet0/0
 standby version 2
 standby 1 ip 172.16.0.254

5. Summary and Key Points:

  • HSRP, VRRP, and GLBP are the three FHRPs to know for the CCNA.
  • HSRP and GLBP are Cisco proprietary, while VRRP is an open standard.
  • HSRP uses terms like Active and Standby, while VRRP uses Master and Backup.
  • GLBP can load balance within a single subnet, while HSRP and VRRP cannot.
  • Preemption allows a router with a higher priority to take over as the active router.
  • Gratuitous ARP is used to update MAC address tables when the active router changes.

Commands Used in Day 29:

  1. Configure HSRP Version 2:standby version 2
  2. Set the Virtual IP Address:standby <group-number> ip <virtual-ip>
  3. Set Priority:standby <group-number> priority <value>
  4. Enable Preemption:standby <group-number> preempt
  5. Verify HSRP Configuration:show standby