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Windows 2003 behaving oddly in Multicast network

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  • Windows 2003 behaving oddly in Multicast network


    We're recently changed our network design to have two core switches setup with VRRP and multicasting.

    We have a few legacy Windows 2003 machines which since the change have started acting a little odd. Theysuddenly stop seeing anything outside of their Vlan but can ping/talk to anything within their vlan.

    Hopping on to the box as local admin and clearing ARP and pinging out allows them to resume talking to other devices outside of their native VLan for a few hours and then it starts again.

    I'm convinced it is to do with enabling multicasting within the network and have added within the registry on the server for IMGPLevel (2) and IGMPVersion (4) under TCPIP Parameters.

    Has anyone come across anything similar?


  • #2
    Hosts suddenly being unable to communicate with other hosts outside their (V)LAN indicates a communication problem between the problematic hosts and the local gateway.

    It's very unlikely that this has anything at all to do with IGMP or multicasting on these hosts. VRRP does indeed communicate using link-local multicast addresses, but this communication does not involve any hosts, only the routers.

    However, VRRP creates virtual MAC addresses for the gateway(s), and since the problem can be temporarily resolved by flushing the ARP cache, you've pretty much narrowed it down to an ARP issue. If I had to guess, I'd say your VRRP setup isn't configured correctly, or you're using another standby protocol that relies on gratuitous ARPs rather than virtual MAC addresses.

    What is the MAC address associated with the gateway IP? Since you're using VRRP, it should be "00-00-5E-00-01-<something>", and should remain the same at all times