Table of Contents Link to heading

• First Hop Redundancy Protocols - FHRPs
• Hot Standby Router Protocol - HSRP
• Load Sharing
• HSRP Roles
• HSRP States
• Pre-emption
• Cisco IOS Configuration
  • Load Sharing Configuration
    • Single Subnet
    • Multiple Subnets
  • Verification
• Guidelines and Limitations for HSRP

First Hop Redundancy Protocols - FHRPs Link to heading

Hot Standby Router Protocol - HSRP Link to heading

• Cisco Proprietary (1994)
• It has two versions (v1 & v2)
• Hello interval 3 sec
• Hold interval 10 sec
• It uses UDP port number 1985
• It sends multicast hellos via 224.0.0.2 (v1) and 224.0.0.102 (v2)
• It support groups numbers from 0 to 255 (v1) and 0 to 4095 (v2)
• HSRP virtual MAC 0000.0c07.acxx (XX is group ID) (v1) and 0000.0C9F.Fxxx (v2)
• Default Priority is 100
• Default Preempt Disable
• Default decrement in priority using track 10
• It supports two types of authentication (MD-5 & Txt).
• It has built in track command

The active router sources hello packets from its configured IP address and the HSRP virtual MAC address while the standby router sources hellos from its configured IP address and the interface MAC address (BIA).

The routers send hello messages to each over their HSRP interface.

Load Sharing Link to heading

Two routers A and B and two HSRP groups. Router A is the active router for group A but is the standby router for group B. Similarly, router B is the active router for group B and the standby router for group A.

If both routers remain active, HSRP load balances the traffic from the hosts across both routers. If either router fails, the remaining router continues to process traffic for both hosts

HSRP Roles Link to heading

The active router handles routing packets, and the standby router takes over if the active router fails or meets preset conditions.

1. Active - A router which handles routing packets and gives the reply of ARP request of clients for gateway with the virtual MAC address.
   • Active Requirements:
     1. Higher Priority
     2. Higher IP
2. Stand by - Backup to active.
   • If the standby router no longer receives hellos from the active, it will transition to be the active router.

HSRP States Link to heading

1. Disabled
2. Init
3. Listening
4. Speaking
5. Stand by

Pre-emption Link to heading

• If pre-emption is enabled, when a higher priority router comes back online after a failure it will transition back to active.
• If pre-emption is not enabled (default), the lower priority router will remain active when the failed router comes back online.

Cisco IOS Configuration Link to heading

Load Sharing Configuration Link to heading

Single Subnet Link to heading

In the following example:

• R1 is HSRP Active for 10.10.10.1, R2 is Active for 10.10.10.254
• 50% of PCs use 10.10.10.1 as default gateway, other 50% use 10.10.10.254

Multiple Subnets Link to heading

In the following example:

• R1 is HSRP Active for 10.10.10.1, R2 is Active for 10.10.20.1

Verification Link to heading

To view HSRP information for all interfaces:

To view HSRP information for a specific interface (e.g., FastEthernet 1/0):

For a brief overview of HSRP information:

Guidelines and Limitations for HSRP Link to heading

• You must configure an IP address for the interface that you configure HSRP on and enable that interface before HSRP becomes active.
• You must configure HSRP version 2 when you configure an IPv6 interface for HSRP.  For IPv4, the virtual IP address must be in the same subnet as the interface IP address.
• We recommend that you do not configure more than one FHRP on the same interface.
• HSRP version 2 does not interoperate with HSRP version 1. An interface cannot operate both version 1 and version 2 because both versions are mutually exclusive. However, the different versions can be run on different physical interfaces of the same router.
• You cannot change from version 2 to version 1 if you have configured groups above the group number range allowed for version 1 (0 to 255).
• HSRP for IPv4 is supported with BFD. HSRP for IPv6 is not supported with BFD.
• Cisco NX-OS removes all Layer 3 configurations on an interface when you change the interface VRF membership, port channel membership, or when you change the port mode to Layer 2.
• If you configure virtual MAC addresses with vPC, you must configure the same virtual MAC address on both vPC peers.
• For mixed-chassis configurations where the vPC peer link is configured on an F-series module, configure the vPC peer gateway exclude option to exclude the Layer 3 backup route that traverses the vPC peer link.
• You cannot use the HSRP MAC address burned-in option on a VLAN interface that is a vPC member.
• If you have not configured authentication, the show hsrp command displays the following string: Authentication text “cisco”