They are both stating the

llukman.halimi · ‎04-14-2017

Can someone please explain to me how these timers work. In the book I am reading it says:

Active timer The active timer monitors the state of the active router. The timer resets each time a router in the standby group receives a Hello packet from the active router. This timer expires based on the hold time value that’s set in the corresponding eld of the HSRP hello message.

Standby timer The standby timer is used to monitor the state of the standby router. The timer resets anytime a router in the standby group receives a Hello packet from the standby router and expires based on the hold time value that’s set in the respective Hello packet.

But looking at Cisco's website: http://www.cisco.com/c/en/us/support/docs/ip/hot-standby-router-protocol-hsrp/10583-62.html

Active timer This timer is used to monitor the active router. This timer starts any time an active router receives a hello packet.

Standby timer this timer is used in order to monitor the standby router. The timer starts any time the standby router receives a hello packet.

What I am not understanding is why is it that on cisco's website it says anytime an active router receives a hello packet but in the book it is saying anytime a router in the standby group not the active router.

Same thing for the standby timer.

Reza Sharifi · ‎04-14-2017

They are both stating the same thing but I think the wording in the book is more complete as it says "each time a router in the standby group" because every time you configure HSRP, there is a standby group associated with it, e.g standby 10, standby 20, etc..

HTH

llukman.halimi · ‎04-14-2017

I know about the groups...my question was regarding the active timer the book says one of the standby router's receives a hello packet from the active router...Cisco says the active router is receiving not one of the standby router's

Do you understand what I am asking?

Reza Sharifi · ‎04-14-2017

Both active and stand-by send hello packets.

From active HSRP

Next hello sent in 0.112 secs

and from standby

Next hello sent in 1.008 secs

HSRP Router Communication

Routers that run HSRP communicate HSRP information between each other through HSRP hello packets. These packets are sent to the destination IP multicast address 224.0.0.2 on User Datagram Protocol (UDP) port 1985. IP multicast address 224.0.0.2 is a reserved multicast address that is used to communicate to all routers. The active router sources hello packets from its configured IP address and the HSRP virtual MAC address. The standby router sources hellos from its configured IP address and the burned-in MAC address (BIA). This use of source addressing is necessary so that HSRP routers can correctly identify each other.

Link

http://www.cisco.com/c/en/us/support/docs/ip/hot-standby-router-protocol-hsrp/10583-62.html

HTH

llukman.halimi · ‎04-14-2017

I don't think you are getting my question...thanks anyways maybe someone else can help me.

Jon Marshall · ‎04-14-2017

The wording is indeed unclear.

My understanding is that of the books ie. the active timer is used to monitor the active router so it is relevant to the other routers (ie not the active router) in the group. I can't tie that up with Cisco's own explanation which talks about the active router receiving a hello which doesn't make sense because it is not monitoring itself.

I checked with the RFC (2281) and it backs up what the book is saying so either the Cisco doc is wrong or it is one of those cryptically worded documents Cisco like to produce from time to time :)

Jon

llukman.halimi · ‎04-14-2017

Yes that is where I am confused Cisco's explanation makes no sense unless like you said they are making it really hard the way they are explaining it.

Jon Marshall · ‎04-14-2017

Their documentation is usually very good but there are times when it can be difficult to follow or just plain wrong and it certainly makes little sense to me compared to the other explanations.

That's all I can say really, unless someone else wants to add to this.

Jon

Ezeddean Yousif Almansouri · ‎04-15-2017

I agree with Jon, put simply the book is correct and the Cisco site quoted is wrong. A good place to go to to clear up misconceptions on how things actually work are to the RFC's like Jon did.

According to the RFC 2281;

5.4 Timers

   Each router maintains three timers, an Active timer, a Standby timer,
   and a Hello timer.

   The Active timer is used to monitor the active router.  The active
   timer is started anytime an authenticated Hello message is seen from
   the active router.  It is set to expire in the Holdtime seen in the
   Hello message.

   The Standby timer is used to monitor the standby router The Standby
   timer is started anytime an authenticated Hello message is seen from
   the standby router.  It is set to expire in the Holdtime seen in the
   Hello message.

Regards

http://www.faqs.org/rfcs/rfc2281.html

Active timer and standby timer for Hot Standby Router Protocol?

HSRP Router Communication