Description of each configuration of HSRP is required.[ASR9006 6.3.3]

[sjrcoel]

Hi, I'm studying HSRP, but I don't understand each item in the configuration of HSRP. Please explain.
Below is the one I've actually taken only the configuration from the HSRP-applied equipment that I've referenced to study. Please refer to it and explain it.

 

[Richard Burts · Accepted solution]

Here are explanations of the significant parts of the config

- "interface G0/0/1/18.359" this is the interface to which HSRP will be applied. It is a vlan interface connecting to a switch on a trunk for vlan 359

- "hsrp version 2" there was an earlier version of HSRP and this is the later version

- "hsrp 359" HSRP uses a concept of group to allow different interfaces to have a unique set of HSRP parameters. The group number is an arbitrary choice and in this case is based on the vlan number of the connection.

- "timers msec 200 1" establishes timers for HSRP actions

- "preempt delay 300" there are several concepts involved in this statement: if there are multiple participants in HSRP one is selected as "active" based on its priority value. If a new device joins the HSRP group and has a priority value higher than the existing active member, should it immediately become the new "active" member? Without preempt the new member is just a member and the existing active member continues. With preempt the new device becomes the new active member. delay 300 indicates that there should be a delay before the new device becomes the new active member. This is because there might be some volitility on the network and we might want some delay before changing the active member.

- "priority 110" selection of the active member is based on priority. The default value of priority is 100. So this priority establishes that this member should be the active member.

- address 38.109.9.1 this is the virtual ip address (VIP) shared by the members of the hsrp group. This will be the default gateway of the devices in the vlan connected to this interface.

- "track object" uses tracking of an object and if that object detects a failure it will lower the priority of this interface.

- "interface G0/1/18.359" this is the interface on the peer device on which HSRP will be active.

- "hsrp version 2" sane as the other interface.

- "timers" same as on the other interface.

- "preempt" this is similar to the other interface. If the priority of this interface becomes higher than the priority of the currently active interface then this interface will become the new "active" interface.

- address 38.109.9.1 this is the virtual ip address (VIP) shared by the members of the hsrp group. This will be the default gateway of the devices in the vlan connected to this interface.

So what does this mean? There are 2 devices connecting on vlan 359. The first device, according to the confit, will become the active HSRP device and the devices in vlan 359 will use it as their default gateway. If that interface should go "down" then immediately the interface on the other device will become the default gateway. If track on the primary device should detect some problem upstream then after a delay the primary device lowers its priority and  the standby device will become the primary. If the primary device comes back into service then it will preempt and immediately become the new active device.

[Richard Burts]

I am glad that our suggestions have been helpful. Thank you for marking this question as solved. This will help other participants in the community to identify discussions which have helpful information. This community is an excellent place to ask questions and to learn about networking. I hope to see you continue to be active in the community.

[Torbjørn]

hsrp 359 ! Enter HSRP configuration mode, sets HSRP group ID to 359
timers msec 200 1 ! Use hello timer of 200ms and a dead timer of 1s
preempt delay 100 ! Wait 100 seconds after boot before preempting(taking back active role)
priority 110 ! Use priority 110, where higher value is better. This router will be master.
address 38.109.9.1 ! This is the address that should be shared between the routers
track object IB 8 ! Track object IB 8 and decrement priority by 10 if it goes down

I am not 100% sure about the last line, as the syntax is a bit different to what I am used to in IOS-XE. You can find the configuration guide for HSRP on the ASR here: https://www.cisco.com/c/en/us/td/docs/routers/asr903/software/guide/ip/17-1-1/b-fhp-xe-17-1-asr900/m-hsrp-xe-asr900.html and a "fuller" config guide for HSRP here(for IOS-XE, I assume most things will be possible on the ASR as well): https://www.cisco.com/c/en/us/td/docs/routers/ios/config/17-x/ntw-servs/b-network-services/m_fhp-hsrp-0.html