Category Archives: HSRP

Hot Standby Routing Protocol

HSRP Question

1. If active interface will down standby will be work as active, but if we would like to configure 3 interface for redundancy for HSRP then what will be the configuration we need to do and what will be interface status for all.

1. Use different groups for different HSRP instances. Active, standby and listen.

How Switches know .. who will be Active .. How they will compare .. Only When they talk to each other ..
If communication is stopped .. due to any reason ..
Then both will think they are alone .. there is no comparison of Priority and Both will declare themself as Active ..
” So Both will be Active ”

1. In VSS/VPC Technology.
2. Issues of ACTIVE/ACTIVE
1. physical link issue
2. one of the trunk interfaces are not forwarding desired vlan for which HSRP is configured
3. HSRP authentication Issue
option number 1 and 2 were observed in real environment. option 3 in lab environment
3. HSRP is using multicast address to communicate between Active and Standby. An Access list can block this address and the communications between the two nodes will stop.If communication between hsrp switches stop. It’s split brain scenario, Both switches will think he’s active.

3. Is it necessary to HSRP active router should be the STP root?

1. Not necessary because we can go HSRP load sharing of vlan on active switches or router but it’s better recommendation to have root bridge.

4. Can we configure HSRP on sub interfaces?
1. Yes, when we assign vlan or subnet to the Sub Interface .. then it will act as Gateway .. similar to Layer 3 Vlan.

5. Case #1: HSRP Standby IP Address Is Reported as a Duplicate IP Address
These error messages can appear:
Oct 17 13:15:41: %STANDBY-3-DUPADDR: Duplicate address on Vlan25, sourced by 0000.0c07.ac19
How to resolve the issue and what are the possibility of Duplicate IP address?

1. Same IP address configured on both active and standby devices, changing the IP at active or standby device will fix the issue.
2. Trace mac address mentioned in logs

6. Does Hsrp, VRRP and GLBP support ipv6?
1. Yes, version 2 for HSRP and GLBP but for VRRP only V3 supported IPv6.

7. How many routers can participate in one group? How many total groups can be formed?
1. Maximum group support 0-255 means total 256 group default is 0 and in one group max can be 16 router.

8. What is HSRP Coup message ?
1. Coup message is generated by this new highest priority router

First hop redundancy protocol (FHRP)

First Hop Redundancy Protocol (FHRP) IP routing redundancy is designed to allow for transparent fail-over at the first-hop IP router.

Concept of HSRP.


Configuration based on NX-OS

1. Enable Feature
3. One is active
4. Priority determine if Active/Passive. When using VPC both router will be active.
5. Uses UDP to detect failures designated routes.

HSRP / Load sharing – Creating more gateway

Sample configuration:
R1 Configuration:
interface FastEthernet0/0
ip address
standby 1 ip
standby 1 priority 110
standby 1 preempt
standby 1 track 1 decrement 20

R2 Configuration:
interface FastEthernet0/0
ip address
duplex half
standby 1 ip
standby 1 preempt

show standby bried

Common Failure scenario:
– R1 failure to down stream.
– R2 upstream interface f1/1.

1. Feature Enable
2. Group router share VIP
3. Elect master per group
4. Remaining routers is standby ready to take over during failure.
5. Requires the feature to be enabled.

Even though VRRP doesn’t support loadsharing natively, You can configure it in away to preform redundancy.

1. Path Redundancy for IP
2. L3 Router share load

Available load balancing method:
1. Round robin
2. Wighthed (Higher the more traffic)
3. Host dependent (Host based on one mac)


HSRP Question?

– Initial: This is the beginning state. It indicates HSRP is not running.
– Listen: The router knows both IP and MAC address of the virtual router but it is not the active or standby router.
– Speak: The router sends periodic HSRP hellos and participates in the election of the active or standby router.
– Standby: In this state, the router monitors hellos from the active router and it will take the active state when the current active router fails (no packets heard from active router)
– Active: The router forwards packets that are sent to the HSRP group

Troubleshooting HSRP, Documented by Cisco