1. HSRP Redundancy & Failover:
When one router or switch fails the other redundant router or switch takes over so that the connectivity is not interfered.
Three protocol for redundancy are
HSRP
VRRP
GLBP
HSRP:
Hot Standby Router Protocol created in 1994
It is a Cisco proprietary protocol
Hello timer is 3 Sec
Holdon Timer is 10 Sec

2. HSRP VRRP: Virtual Router Redundancy Protocol created in 1999
Its Non proprietary
Works between various vendors and not limited to one.
Created by IETF
Hello Timer 1 sec
Holdon Timer 3 sec
GLBP:
Gateway Load Balance Protocol created in 2005
Cisco proprietary
Same Features as HSRP
Allows Load Balancing

3. HSRP
Scenario: Two Switches (Layer 3) A & B Switch A: Switch A has Vlan 50 as interface and its IP address is set to Shared Group 10 Switch B: Switch B has Vlan 50 as interface and its IP address is set to Virtual IP Address is

4. HSRP
Virtual IP Address & Virtual Mac Address: In Virtual Mac Address e.g C07.AC0A First 6 are vendor ID, 07AC is HSRP ID and 0A is Group 10 (HEX) It is generated on both Switches , so when the Active Switch fails the IP becomes available on Standby Switch. Clients don’t need to change any Gateway settings on their devices. Hello Messages are sent every 3 sec , Gateway is assumed Dead if no response is received in 10 secs. However we can tune the timers for fast processing.

5. HSRP
HSRP CONFIGURATION: A quick note : vlan 50 and int vlan 50 are different vlan 50 is only the segmentation of ports (layer 2) , int vlan 50 is routed interface for that vlan. SwitchA(Config)# int vlan 50  [int vlan 50 will take us into routed int] SwitchA(Config-if)# standby 10 ip  Note for above [10 is Group number, standby command is used to enable HSRP, Virtual IP / Phantom IP is ] Note: Every Switch will have default priority of 100 so to make switch active we higher the priority Switch A(config-if)# standby 10 priority 150  Exit Note: By default track interface decrement is 10.

6. HSRP
HSRP CONFIGURATION: On Switch B SwitchB(Config)# int vlan 50  [int vlan 50 will take us into routed int] SwitchB(Config-if)# standby 10 ip  Note for above [10 is Group number, standby command is used to enable HSRP, Virtual IP / Phantom IP is ] SwitchB(config-if)# standby 10 priority 100  Exit HSRP is Setup we can verify it by pinging to virtual ip and then we can disconnect Switch A and can see take over from Switch B. Thanks, Hyp3ri0n