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  1. hi Rene
    at the beginning of the lab, i wasn’t able to issue the following commands

    SwitchA(config)#interface fa0/17
    SwitchA(config-if)#standby 1 ip

    the thing is SwitchA does not have the option standby under interface, not unless i convert this interface as a layer 3 int with command “no switchport”, then it has the option, but when i try to type the following command

    standby 1 ip

    then it give me the error that overlaps with vlan 1, and this is because the layer 3 interface does not belong to any vlan, can you please advice.

    or should i instead issue the standby under vlan 1 and then create a layer 3 interface for port f0/19 who is connected to the Router and need a layer 3 interface?

    thank you

  2. Rene,
    Hi. Couple questions/validations when you have time.

    1. I know it is best practice to have the HSRP hold timer be at least 3x’s the hello, but I did some lab testing and it appeared to work ok for instance with the hold time 2x’s the hello. Is this expected - is the idea just to have the hold time be large enough to not cause an unnecessary transition and that is what Cisco found to be best practice?
    2. What are the benefits of HSRP v2 over v1 - is it just the increased number of HSRP group numbers supported?
    3. If I have more than two routers that are part of the HSRP group do the remaining routers just stay in listen mode? Up to how many can I have?
    4. It appears that if the HSRP hello and hold timers are mismatched between two routers that are part of the same HSRP group that the router that is “active” dictates the timers that will be used? Is this always the case?

    Suggestion - might want to update the command syntax for the ip sla tracking for the “track 1 rtr 1 reachability” with the newer “track 1 ip sla 1 reachability” in the last part of the lesson.

    Many thanks

  3. 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!


  4. Hi Nilesh,

    Glad to hear you like it. When the active router disappears and the standby router takes over, a gratuitous ARP is sent so that all devices can update their MAC and/or ARP tables. Here’s what it looks like:

    Wireshark capture HSRP gratuitous ARP

    HSRP uses the 0000.0c07.acXX MAC address where XX is the HSRP group number.


  5. Hi Gareth,

    It’s not an ideal situation :smile: If you have a L2 switch in between then the virtual MAC address will flap between the two interfaces that connect to your HSRP routers.

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