Forum Replies

  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. tkalis says:

    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. 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.


  4. Hello Gareth.

    If for whatever reason hellos cannot be exchanged, then both routers will think that they are the active router. Therefore they will both assume the virtual IP address. This will cause an IP address conflict as there will be two same addresses on the same subnet. The network would then behave as it would if you had two gateways with the same IP address. Until the hellos can be exchanged again, this would be the case.

    I hope this has been helpful!


  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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