HSRP

• Hot Standby Router Protocol is an FHRP protocol
• HSRP uses a Virtual IP (VIP) and MAC address to allow for automated gateway failover
  • The hosts use the VIP as their default gateway address
  • If the active gateway fails, the standby gateway will take over
• Hello messages are sent ever 3 seconds by default by routes in the active, standby, or speak states
  • Only routers in the standby state listen for routers, and takes over if the span between hello messages exceeds the hold time (def. 10 seconds)
• VRRP (Virtual Router Redundancy Protocol) is identical to HSRP, except it uses vrrp instead of standby for its configuration

HSRP operations

1. Both routers have a normal physical IP address and MAC address on their HSRP interface
   1. Unique addresses area used on both routers
2. They both also have the HSRP VIP and MAC address configured on the interface
   1. The same addresses are used on both routers
3. When they come online, one is elected to HSRP active router, the other is standby
4. The active router owns the virtual IP and MAC address and responds to ARP requests
5. All traffic for the VIP goes through the active router
6. The routers send hello messages to each other over their HSRP interface
   1. If the standby router stops receiving hellos from the active, it will transition to be the active router
   2. It will take ownership of the VIP and MAC address and respond to ARP requests

HSRP Router States

1. There are 6 HSRP states
   1. Init
      1. When the link first comes up
   2. Learn
      1. The HSRP device is attempting to learn the VIP
   3. Listen
      1. The device has learned the VIP
      2. The device is listening for hello messages from other (active/standby) HSRP devices
      3. If a device is not elected to either active or standby, it remains in the Listen state
   4. Speak
      1. The device sends hello messages and participates in the Active router election
   5. Standby
      1. The device is actively listening to hello messages from the Active router
      2. The default hold time is 10 seconds, roughly 3x the hello time
   6. Active
      1. The device receives data for and manages the VIP
      2. Sends hello messages ever 3 seconds (by default)

Advanced Topics

1. Priority and Preemption
   1. Router priority can be set, with the higher value being preferred
      1. Default value is 100
   2. Preemption allows a router to take Active when it comes online
      1. Default, preemption is disabled because it can be more stable if there is a fault with the primary router
2. HSRP Version
   1. Version 2 introduced minor improvements
      1. Default version is 1
   2. Both routers must be on the same version
3. Standby Groups
   1. Multiple HSRP "Standby groups" can be configured on interface, allowing for "load balancing" between VLANs or different clients
      1. e.g., R1 is priority in standby 1 10.10.10.1/24, and R2 is priority in standby 2 10.10.20.1/24

HSRP Configuration

1. Configure both router interfaces with their IP and "standby IP" (Virtual IP)
   1. Example: VIP is 10.10.10.1

R1Config# int g0/1
	Config-if# ip address 10.10.10.2 255.255.255.0
	Config-if# no shut
	Config-if# standby 1 ip 10.10.10.1
	Config-if# standby 1 priority 110
    Config-if# standby 1 preempt
    Config-if# standby version 2
R2Config# int g0/1
	Config-if# ip address 10.10.10.3 255.255.255.0
	Config-if# no shut
	Config-if# standby 1 ip 10.10.10.1
	Config-if# standby 1 priority 90
	Config-if# standby version 2

2. Verification
   1. #sho standby

Metadata

OSI or TCP/IP Layer

CCNA Exam Topic

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