What is HSRP?

 

What is HSRP?

Hot Standby Router Protocol (HSRP) is First hop redundancy protocol that provides default gateway redundancy.

If the active router fails, the standby router automatically takes over as the default gateway, minimizing network downtime.

  • standby 1 priority 120   R1 → Higher priority than R2 ( 100 )
  • standby 1 preempt → Allows R1 to become Active again after recovery R2 becomes Standby HSRP Timer

HSRP routers sends multicast Hello messages to determine which router is Active and whether it is still alive.

HSRP version 1 : Multicast IP 224.0.0.2 on UDP port 1985
HSRP version 2 : Multicast IP 224.0.0.102 on UDP port 1985

The Hold timer specifies how long a router waits without receiving Hellos before declaring the Active router down.

TimerDefault
Hello3 seconds
Hold10 seconds

Maximum HSRP Groups 

HSRP version 1 : up to 255 groups ( 0 - 255 ) 
HSRP version 2 : up to 4095 groups ( 0 - 4095 ) 
PC Hosts use one virtual IP address as their default gateway.
Behind that virtual gateway, there is one Active router and one Standby router per HSRP group.

HSRP 6 States

StateMeaning
Initial        HSRP is starting
Learn        Waiting to learn the virtual IP
Listen        Listening for HSRP messages
Speak        Sending HSRP hello packets
Standby        Backup router
Active        Forwarding traffic for the virtual gateway   

Real-World Example

Suppose an office has:

  • 200 computers
  • Router R1 (Primary)
  • Router R2 (Backup)

All PCs use a virtual IP as their default gateway instead of a physical router's IP.

If R1 fails, R2 automatically becomes the gateway.

Refer HSRP Lab 1

Design Lab Topology

                     





IP Addressing

DeviceInterfaceIP Address
R1G0/0192.168.10.2/24
R2G0/0192.168.10.3/24
Virtual IPHSRP192.168.10.1
PC1NIC192.168.10.100
PC2NIC192.168.10.101
Default Gateway-192.168.10.1

Step 1: Configure R1

enable

configure terminal

interface GigabitEthernet0/0

ip address 192.168.10.2 255.255.255.0

standby 1 ip 192.168.10.1   

standby 1 priority 120

standby 1 preempt

no shutdown

end

Explanation

  • standby 1 → HSRP Group 1
  • ip → Virtual IP address
  • priority 120 → Higher priority than R2
  • preempt → Allows R1 to become Active again after recovery

Step 2: Configure R2

enable
configure terminal

interface GigabitEthernet0/0

ip address 192.168.10.3 255.255.255.0

standby 1 ip 192.168.10.1  

standby 1 priority 100

standby 1 preempt

no shutdown

end

Election Result

RouterPriorityRole
R1120Active
R2100Standby

The router with the highest priority becomes the Active router.

Default priority is 100.

Verify HSRP

show standby

Sample output:

State is Active

Virtual IP address is 192.168.10.1

Active router is local

Standby router is 192.168.10.3

Priority 120

Another useful command:

show standby brief

Example:

Interface   Group  Priority State    Active      Standby            Virtual IP
Gi0/0       1      120      Active   local       192.168.10.3       192.168.10.1

Test Failover

On PC

ping 8.8.8.8 -t

Continuous ping to transmit high unmatched traffic to ISP router

On PC1 

ping 192.168.10.1 -t 

shutdown the interface Gi0/0 of R1 then R2 will take over.. 

Shut down R1

interface g0/0

shutdown

Immediately:

  • R1 becomes inactive.
  • R2 becomes Active.
  • The ping may lose only 1–2 packets before continuing.

Bring R1 Back

interface g0/0

no shutdown

Since preempt is enabled:

  • R1 (priority 120) becomes Active again.
  • R2 returns to Standby.


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