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  • 1.  Setting Multicast on Switch

    Posted Feb 28, 2007 11:00 AM
    Dose anyone know how to configure Multicast on Cisco catalyst switch 2960, or is configuration for this device even required, in order to use Ghost Console with different subnets? I found several documents on how to accomplish this and all of them explain different set of commands. On of those resources claims that this setting is already enabled on switch by default. I know command to configure router on all interfaces that process multicast traffic.

    ip multicast-routing

    interface ethernet0
    ip address
    <mask>
    ip pim sparse-dense-mode

    Is configuration on switch required to process multicast, or what would be minimum configuration in order to enable this setting? I know this is Symantec not Cisco forum, but I realize someone may have this issue in the past, and possibly easy answer.
    Highly appreciate any input.
    MC


  • 2.  RE: Setting Multicast on Switch

    Posted Feb 28, 2007 07:17 PM
    Since the 2960 is a "Layer2+" switch that is capable of doing some of the fancy Layer3 things with IP multicast, there are some things that you may need to configure.

    There are a couple of things to begin with; probably the most important is to understand the role that IGMP plays. IGMP is the fundamental core protocol used in IP multicast, and it's the one that the switches respond to. Machines subscribe to listen to multicast groups using IGMP subscription requests, which some switches are capable of listening to in order to figure out which switch ports to distribute multicast frames to.

    Generally, with more than one subnet, you'll need a multicast-capable router as well, and this router will be receiving the IGMP subscription requests. It will also periodically generally IGMP queries (which the switches also listen to) to ensure that if a machine fails without unsubscribing, its membership of the group times out. The kinds of switches that snoop IGMP subscriptions also need to snoop this refresh traffic.

    As for PIM, it only comes into play when you have a large enough network to need multiple routers - PIM is used between routers to exchange information about the sets of subscriptions they have for their attached networks. Mostly, the PIM traffic between routers contains a rolled-up summary of the IGMP subscriptions in the networks they serve.

    With that background, you also need to know the specific version of IOS your switch is running, so you can find the appropriate configuration guide. For the capable switches, the configuration guides generally devote a chapter to IGMP; for the 2960 running IOS 12.2(25)FX, you can see this at http://www.cisco.com/en/US/products/ps6406/products_configuration_guide_chapter09186a008055ff08.html
    which puts together a summary of the IGMP-related options.

    Separate to this is the question of the routing side; whichever device in your network that is providing the IP routing between the subnets will also need to be configured in a matching way to accept the IGMP subscriptions and generate IGMP queries.