Cisco CCNP Certification BCMSN Exam Tutorial The HSRP MAC Address
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Cisco CCNP Certification: BCMSN Exam Guide on HSRP MAC Addresses
Overview
Earning your CCNP certification requires mastering the BCMSN exam, including understanding the HSRP MAC address: how it's determined and how to modify it. This guide by Chris Bryant, CCIE
12933, will walk you through these concepts.
Understanding HSRP and MAC Addresses
To succeed on the BCMSN exam, you need a solid grasp of HSRP (Hot Standby Router Protocol), specifically how the virtual router's MAC address is generated and changed. We'll explore both aspects here.
Determining the HSRP Virtual Router MAC Address
Consider two routers running HSRP on a segment. We need to determine the MAC address of the HSRP virtual router. The key command for this is `show standby`, an essential tool for configuring and troubleshooting HSRP. Let’s compare the outputs from two routers:
Router R2 Output:
- Group: Ethernet0 - Group 5
- State: Standby
- Priority: 100
- Hellotime: 3 seconds
- Holdtime: 10 seconds
- Virtual IP: 172.12.23.10
- Active Router: 172.12.23.3
- Standby Router: Local
Router R3 Output:
- Group: Ethernet0 - Group 5
- State: Active
- Priority: 100
- Hellotime: 3 seconds
- Holdtime: 10 seconds
- Virtual MAC: 0000.0c07.ac05
In this scenario, Router R3 is active, processing data while R2 is on standby, ready to take over if needed.
How is the MAC Address Determined?
The MAC address for HSRP virtual routers typically follows a reserved format: 00-00-0c-07-ac-xx, where `xx` is the group number in hexadecimal. For example, Group 5 becomes `05`. Familiarity with hexadecimal conversion is important for the exam.
Changing the HSRP MAC Address
Occasionally, you may need to change the assigned MAC address for a virtual router. This is achieved with the `standby mac-address` command. Ensure the new MAC address isn’t already in use on your network.
```shell
R2(config-if)
standby 5 mac-address 0000.1111.2222
```Upon executing this command, the following occurs:
- The routers enter a Learn state briefly while the new MAC address is adopted.
Router R2 After Changing MAC Address:
- State: Active
- Priority: 150
- Hellotime: 4 seconds
- Holdtime: 12 seconds
- Virtual MAC: 0000.1111.2222
Troubleshooting Tip
If you encounter frequent state changes in your HSRP configuration, start by checking the physical layer. This is often a key troubleshooting step.
Best of luck on your BCMSN exam!
You can find the original non-AI version of this article here: Cisco CCNP Certification BCMSN Exam Tutorial The HSRP MAC Address.
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