High Availability Techniques

First Hop Redundancy Protocol [FHRP]

IP network gateway redundancy is a standard high availability solution. The First Hop Redundancy Protocol features – Host Standby Router Protocol [HSRP], Virtual Router Redundancy Protocol [VRRP] and Global Load Balancing Protocol [GLBP].

Host Standby Router Protocol [HSRP]

  • HSRP is Cisco proprietary protocol.
  • HSRP does not supports preemption by default.
  • HSRP has two versions;
    • HSRPv1
    • HSRPv2
 HSRPv1HSRPv2
Group RangeDoes not support millisecond timer valuesSupports millisecond timer values
Multicast Address0 to 2550 to 4095
MAC Address range000.0C07.ACxx
(xx represents the HSRP group number)
000.0C9F.Fxxx
(xx represents the HSRP group number)
Differences between HSRPv1 and HSRPv2

Virtual Router Redundancy Protocol [VRRP]

  • VRRP is an industry standard, RFC 5798.
  • VRRP has two versions
    • VRRPv2: Supports IPv4
    • VRRPv3: Supports IPv6

HSRP and VRRP enables two or more devices work together in a group and sharing a single IP address called virtual IP address. The virtual IP address is configured in each devices as its default gateway. An active router is chosen to handle all requests to the virtual IP address.

VRRP and HSRP operates similarly but have below differences:

  • VRRP active router called master router;
  • all other routers are known as backup routers.
  • MAC Address of VIP Gateway uses the 0000.5E00.01xx
    • xx reflects the group ID in HEX.
  • VRRP uses multicast address 224.0.0.18

Global Load Balancing Protocol [GLBP]

  • Provides gateway redundancy and load-balancing capability to network segments.
  • GLBP supports four active AVFs and one AVG per GLBP group.
  • A router can be a AVG and AVF at the same time.
  • GLBP uses round robin load balancing traffic method as default.

GLBP Roles:

  • Active Virtual Gateway [AVG]
    • Participating router elect one AVG per GLBP group to initial ARP requests for the VIP.
  • Active Virtual Forwarder [AVF]
    • routes traffic received from assigned hosts. A unique MAC Address is created and assigned by the AVG to the AVFs.

GLBP Three methods of Load Balancing Traffics:

  • Round Robin – uses each virtual forwarder MAC address to sequentially reply for the virtual IP address.
  • Weighed – defines weighs to each device in the GLBP group to define the ration of load balancing between devices.
  • Host Dependent – Uses the host MAC Address to decide to which virtual forwarder MAC address to redirect the packet.

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