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  • Problem about IGMP querier on multicast router

    Hi, hope any guys can help me solve the problem, thx

    I am using a cisco 2821 for multcast routing, pim dense mode was enabled. Currently there are another core switch (procurve 5412) with the lowest IP address acting igmp querier (no ip multicast routing & no ip pim). I know that querier with the lowest IP address could win the querier election in the same vlan/subnet, but when I connect the 2821 to the same vlan as the core switch. the 2821 win the querier election. It's not the lowest IP address. Why it can win? It confuse me a lot.

  • #2
    Re: Problem about IGMP querier on multicast router

    It sounds like your switch is the querier until it detects the queries from your cisco device. At that point it stops being the querier. Check your IGMP config by running "show ip igmp config" on procurve while the 2811 is connected to the vlan that the switch is on. You are looking to see if the the ability for the procurve to become a querier is disabled. If it is try running the following command:

    "vlan <your vlan id> ip igmp querier"

    Below is a link to the documentation:

    http://ftp.hp.com/pub/networking/sof...12_XX-Book.pdf

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    • #3
      Re: Problem about IGMP querier on multicast router

      Thanks Ryan!

      Acutally I have enabled ip igmp querier on the specified VLAN on core switch. It has the lowest IP on the VLAN. But this can't make it as a querier.

      Seems need to enable ip pim-dense on the VLAN on core switch, then it will always win the querier election. Is it a necessary??

      I think let the core switch runs with dense mode will increse its loading such as learning the mroute table....the core switch will not be a DR (the 2821 takes it) so I don't think it need to enable pim dense.

      Please correct me if i have something wrong. thanks you all.

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      • #4
        Re: Problem about IGMP querier on multicast router

        Originally posted by DavidChoi View Post
        Thanks Ryan!

        Acutally I have enabled ip igmp querier on the specified VLAN on core switch. It has the lowest IP on the VLAN. But this can't make it as a querier.

        Seems need to enable ip pim-dense on the VLAN on core switch, then it will always win the querier election. Is it a necessary??

        I think let the core switch runs with dense mode will increse its loading such as learning the mroute table....the core switch will not be a DR (the 2821 takes it) so I don't think it need to enable pim dense.

        Please correct me if i have something wrong. thanks you all.
        Assuming that your VLAN that is configured on the procurve IGMP should be enabled by default. Because of this the procurve is automatically the querier which means that you don't have to have a multicast router configured for that VLAN. The problem is that you have two devices (procurve and cisco 2811) configured to be queriers. Even though your procurve has the lower IP, the second it recieves a query message it will quit being the querier for the VLAN and let the other device (cisco 2811) take over.


        Sounds like the procurve is a multi-layered switch (can do layer 3 functions):

        1. Make sure you have ip routing enabled on the procurve (to route between vlans)

        2. use either static or dynamic routes for every VLAN that you are going to route multicast traffic to

        3. enable IGMP on any VLAN that is going to participate in multicast forwarding

        4. Since you are going to use PIM dense mode, enable it globally and at the VLAN interface level.

        5. Disable IP multicasting on the cisco 2811l

        Try that out and let me know if it works or doesn't.

        Ryan

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