HSRP Flashcards
What is HSRP?
Hot-standby routing protocol. A Cisco-proprietary FHRP.
What are the two router roles in HSRP?
Active and standby.
Do downstream devices know the real MAC/IP of the HSRP routers?
No, downstream devices only know the virtual MAC/IP shared by the routers.
What single command will add an interface to an HSRP group?
From interface config, “standby (group number) ip x.x.x.x”
What command can you use to troubleshoot your HSRP config?
From global config, “Show standby”
Can the virtual MAC/IP be shared by any physical MACs/IPs?
No, the virtual addresses must be unique.
HSRP is configured per ___.
VLAN.
The active router for a VLAN should also be the ___ for that VLAN.
Root bridge.
After initial configuration, what should not typically be occurring in the “show standby” output?
State changes, this usually indicates a problem.
What are the default timer values for HSRP?
Hello is three seconds, hold is ten seconds.
What is the hello timer?
Determines how often HSRP hello packets are sent.
What is the hold timer?
Determines how long the standby server will wait to hear a hello message before it takes over as the active server.
How is the virtual HSRP MAC generated?
By using the MAC address 00-00-0c-07-ac-xx, where “xx” equals the HSRP group number in hex.
Almost all HSRP configuration takes place in what config mode?
SVI configuration mode.
What value determines the active router?
Priority, higher is better.
What is the default HSRP priority?
100.
What command changes the router priority?
From SVI config, “standby __ priority __”
If two routers have equal priorities, which one wins the active router election?
The one with the higher IP.
Unless ___ is configured, priority changes will not affect the active router.
Preemption.
In HSRP, is preemption enabled by default?
No, it is not.
What is preemption delay?
Preemption delay is a feature that causes “new” active router to wait a certain amount of seconds after a priority change to take over as the active router.
How do you enable preemtption?
From SVI config, “standby __ preempt”
How do you enable preemption delay?
From SVI config, “standby __ preempt delay minimum (number of seconds)
List the HSRP states.
Disabled, initial, listen, speak, standby, active.
Describe the disabled state.
HSRP has not yet been configured on the router.
Describe the initial state.
HSRP has been configured, but is not running yet.
Describe the listen state.
Used for the election process. Occurs when the virtual IP is known, but the switch is waiting to hear hello packets from the other routers. Also occurs when a router has a lower priority than the standby router.
Describe the speak state.
The router is participating in the HSRP router election and is sending out hello packets.
Describe the standby state.
The router is next in line to become the active router.
Describe the active state.
Router is forwarding packets sent to the virtual IP.
Describe HSRP load balancing.
Create multiple HSRP groups with different IPs in the same subnet. Assign active router status to different devices, and manually set the default gateway for hosts.
Describe HSRP interface tracking.
Interface tracking allows an HSRP router to lower or raise its priority based on the status of an interface (down, up, etc.)
What is the standard interface tracking decrement value?
10.
For interface tracking to be effective, what must be enabled?
Preemption.
What can you track with interface tracking?
Interfaces, portchannels, loop-back addresses, etc.
How do you enable HSRP interface tracking?
From SVI config, “standby __ track (what you’re tracking) (decrement value)
If a standby doesn’t takeover as active when it should, what should you check first?
If preemption is enabled.
What two timers does HSRP use? Describe them.
Hold timer and hello timer. Hold timer refers to how long a router will wait to hear from the active router before taking over. The hello timer refers to how often the router will send its own hello packets.
Do timers have to match between all routers in an HSRP group?
No, but they should.
What are the default HSRP timers?
Hold timer of 10 seconds, hello timer of 3 seconds. Typically these defaults work well.
How do you change the HSRP default timers?
From SVI config, “standby __ timers (hello timer) (hold timer)
With HSRP authentication, what should you always use?
MD5 ecnryption.
What command will keep the HSRP keys from being viewed in the running config?
From global config, “service password-encryption”
What command enables HSRP authentication?
From SVI config, “standby __ authentication md5 key-string (password)”
HSRP authentication can also make use of what quality-of-life feature?
Key chains.
