HSRP (Hot Standby Routing Protocol)

Lessons Discussion
21

Hi Abdelrahman,

Yes that shouldn’t be a problem.

Rene

22

Hi Rene
why you said that HSRP v1 support up to 255 group but said the opposite when you talked about vrrp (said vrrp support up to 255 but HSRP up to 16)?

23

Hi Hakam,

Where did you see that? I’ll check it.

HSRPv1 should support group number 0-255 and HSRPv2 supports 0-4095. VRRP supports group numbers 1-255, it is limited to 16 addresses per group though.

Rene

1 Like
24

You configured the VLAN 1 interface on SW 1 & 2 in your HSRP example. Is that the only way to configure HSRP? Could you have used the Gi0/1 interfaces on SW1 & SW2? If yes, - what would the implications have been? In your VRRP and GLBP lesson you are configuring interfaces fa0/17 and fa0/19 ( not vlans )

25

What exactly is “preemption”? What does it mean? What does it do?

26

Jason,
Preemption refers to having a HSRP partner with the highest priority automatically take over the processing of gateway traffic. With HSRP this is off by default, whereas with VRRP it is on by default.

Let’s say you have two routers, A (priority 100) and B (priority 105), configured using HSRP and you have enabled preemption. Now, let’s say that Router A is the only one powered on. Once Router B powers up and initializes HSRP, it will send what is called a “Coup” message to Router A saying that it wants to take over being the gateway because it has a higher priority. Upon receiving the Coup message, Router A responds by sending a “Resign” message acknowledging that it agrees with this. The two routers will then exchange roles of Active and Standby.

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27

You can configure HSRP, VRRP and GLBP on L3 interfaces. This includes router interfaces and SVI interfaces.

On a multilayer switch you can also do this on the interfaces but you’ll have to convert them from L2 to L3 with the “no switchport” command first.

28

Rene,

Can you explain to me what will be the MAC address at each router for a request from client to internet in HSRP environment.

29

Shree,
This depends on which HSRP is being used, version 1 or version 2.

For version 1, the gateway’s MAC would appear to be: 00:00:0c:07:ac:XX (where XX is the HSRP group number you have configured).

For version 2, the gateway’s MAC would appear to be: 00:00:0c:9f:fX:XX (again, where X is the configured HSRP group)

30

Hi Rene

I find it difficult to follow the lesson because I have to scroll up the screen many times to examine the topology diagram while reading your text. It would be nice if you give us a button to make the topology diagram (or any reference diagram) pop up on a separate window, so I don’t have to scroll up and down.
Thank you.

31

Hi Saw,

You should be able to do this from your browser. If you do a right mouse click on any image, you can select “open in new tab”.

This works in Google chrome and it should be the same in Firefox.

Give it a try :slight_smile:

Rene

32

Hi Sir
yes, it works, thank you.

33

Hi Rene,

could you please explain the following command with respect to HSRP:

“forwarding-threshold lower lower-value upper upper-value”

Cant really find a proper explanation for it and dont really understand what it is good for.

Thanks

Florian

34

Hello Florian!

Let’s begin with Cisco’s explanation and we’ll go from there. Cisco says that this command:

Sets the priority level used to select the active router in an HSRP group. The level range is from 0 to 255. The default is 100. Optionally, sets the upper and lower threshold values used by vPC to determine when to fail over to the vPC trunk. The lower-value range is from 1 to 255. The default is 1. The upper-value range is from 1 to 255. The default is 255.

(See http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/unicast/configuration/guide/l3_cli_nxos/l3_hsrp.html)

An example of this command is the following:
switch1(config-if-hsrp)# priority 60 forwarding-threshold lower 40 upper 50

(Please note, when I refer to “switch” in the following paragraphs, I am referring to an L3 switch.)

Keep in mind that the forwarding-threshold keyword is used as part of the priority command. The priority command is used to determine which router will be the active router. The addition of the forwarding-threshold keyword is used in conjunction with vPC (Virtual Port Channel). vPC is a feature that is available on the Cisco Nexus series switches and allows the creation of a “Virtual” port channel where the physical ports of the port channel can span two switches that are functioning as an HSRP group. In such a virtual port channel, under normal conditions, vPS forwards traffic to both the active and standby switches with ports participating in the vPC.

The purpose of the forwarding-threshold keyword and its configuration parameters is to determine when a switch participating in HSRP/vPC is considered “down” so that the ports in the vPC will forward traffic only to the “good” switch. If the standby router priority falls below the lower threshold, HSRP sends all standby router traffic accross the vPC trunk to forward through the active HSRP router. HSRP maintains this scenario until the standby HSRP router priority increases above the upper threshold.

Keep in mind that the priority of an interface on a switch can dynamically change based on the Object Tracking functionality of HSRP. Take a look at this for more information: http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/unicast/configuration/guide/l3_cli_nxos/l3_hsrp.html#17650

I hope this has been helpful!

Laz

35

Hi Laz,

thanks for your help! Ok, i thought this command is also used when HSRP is configured without vPC, but thats not the case.

Regards

Florian

36

Hello Florian.

Glad I could be of help. Actually, during my research I learned a lot too!

Laz

37

hi
Rene

have you got tutorial/lab for this one

thanks Ronak

38

Ron,
Try this on the GNS3Vault sister site:

http://gns3vault.com/network-services/hot-standby-routing-protocol/

39

19 posts were merged into an existing topic: HSRP (Hot Standby Routing Protocol)

40

Hi,

I have 2 router and both has a port-channel and then port channel has 3 sub interface. port-channel on both routers have 3 sub-interface which is for a different vlan coming from switch.

now i want to config hsrp between 2 routers. My doubt is :

do I config port channel this way

standby 1 ip <>
standby 2 ip <>
standby 3 ip <>

OR DO I config 3 sub-interface this way

standby 1 ip <> on first sub-interface
standby 2 ip <> on first sub-interface
standby 3 ip <> on first sub-interface

I am also getting a warning " address is not within a subnet on this interface "
"
is it just a warning or hsrp wont work in this case ?