CCNP Certification / BCMSN Exam Tutorial: HSRP MAC Addresses And Timers

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To earn your CCNP certification and pass on the BCMSN exam, you have got to understand that which HSRP does and also the configurable choices. While the operation of HSRP is quite easy (and covered in an earlier tutorial), you also need to learn how HSRP arrives in the MAC address for the virtual router – as well as how to configure a new MAC with this virtual router. This puts us in the position of developing a physical address for a router which doesn’t exist!

The outcome of show standby for a HSRP configuration is displayed below.

R2#show standby

Ethernet0 – Group 5

Local state is Standby

Hellotime 3 sec, holdtime 10 sec

Next hello sent in 0.776

Virtual IP address is 172.12.23.10 configured

Active router is currently 172.12.23.3, priority 100 expires in 9.568

Standby router is local

1 state changes, last state change 00:00:22

R3#show standby

Ethernet0 – Group 5

Local state is Active

Hellotime 3 sec, holdtime 10 sec

Next hello sent in 2.592

Virtual IP address is 172.12.23.10 configured

Active router is local

Standby router is 172.12.23.2 expires in 8.020

Virtual mac address is 0000.0c07.ac05

2 state changes, last state change 00:02:08

Although R2 is in Standby, r3 is in Active state. The hosts are employing the 172.12.123.10 address as their gateway, however, R3 is in fact managing the workload. R2 will require over if R3 becomes inaccessible.

An IP address has been assigned to the router during the HSRP configuration process, although not a MAC address. However, is a MAC address under the show standby output the router, signal on R3. Did the HSRP process arrive in a MAC of 00-00-0c-07-ac-05?

Well, most of the job is done before the configuration is begun. The MAC address 00-00-0c-07-ac-xx is reserved for HSRP, and xx is the group number in hexadecimal. That is a good skill so make sure you’re familiar with hex conversions. The band number is 5, that is called 05 using a two-bit hex character. In the event the group number was 17, 11’d be seen by us at the end of this MAC address – only just one unit of 16, 1 unit of 1.

The outcome of the show standby command tells us that the HSRP speakers have been currently sending Hellos every 3 minutes, using a holdtime. These values can be changed using the control that was standby, however HSRP speakers at the same group should have exactly the same timers. You can tie the time down to the millisecond, however, it is doubtful you’ll ever have to do that.

R3(config-if)#standby 5 timers?

<1-254> Hello interval in seconds

Celebrate hello interval in milliseconds

R3(config-if)#standby 5 timers 4?

<5-255> Hold time in seconds

R3(config-if)#standby Five timers 4 12

One other important HSRP ability is knowing how to alter the Active router assignment. I’ll show you how to configure HSRP interface tracking, in the part of my CCNP / BCMSN test tutorial, and the best way to do that!