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Multicasting OS images across VLANs

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  • Multicasting OS images across VLANs

    We are trying to get multicast image deployment working using Microsoft's System Center Configuration Manager 2007 R2, and are having problems multicasting an operating system image across VLANs.

    The server is in a server-specific VLAN, while the client machines (a lab of 18 computers) are in a separate VLAN.

    We CAN multicast across the VLANs, but there seems to be a (random) limit on how many machines we can do at once. Anything up to 5 machines is generally successful. Once we get above that number, however, we start running into problems.

    The multicast will usually start off OK. We get a failure (the Config Manager client gives a 0x80091007 bad hash error) sometime after the multicast download has started. The multicast download will generally get at least part of the way through before failing.

    All switches are Cisco - there is a 3750 stack which the server is directly connected to, which then connects to a 2950 acting as a distribution switch, which is connected to a second 2950 which the client computers are connected to.

    ip multicast-routing has been enabled on the 3750, and the relevant VLAN interfaces have "ip pim dense-mode" enabled. Multicasting across the VLANs wouldn't work at all without doing this, so we've got at least part of the way there!

    As a test, we moved all the client machines to the same VLAN as the server, and the multicast went perfectly. This is unfortunately not a feasible solution for our production environment.

    I've been reading up on Cisco multicast documentation, but it doesn't make it very easy to decipher what the problem might be.

    It seems like we must be missing some relatively simple piece of config on the 3750 - can anyone give me any pointers?

    Please let me know if you need further information.

  • #2
    Re: Multicasting OS images across VLANs

    I'm no closer to finding out what the problem is here, despite much troubleshooting.

    I've been playing about some more, without any real success. I've had a few successful runs, but these have often been immediately followed by a failure, with no changes to any of the configuration.

    Learning as I go, I've change pim to sparse-mode only on the two VLAN interfaces, and added ip pim rp-address <router> to the configuration.]

    While the multicast is successfully running (i.e. machines in the lab are receiving the image file via multicast), a show ip mroute includes the following sections that are relevant:
    (*,, 00:01:51/00:01:08, RP, flags: SJC
    Incoming interface: Null, RPF nbr
    Outgoing interface list:
    Vlan888, Forward/Sparse, 00:01:30/00:01:29, H
    Vlan430, Forward/Sparse, 00:01:51/00:02:32, H

    (,, 00:01:51/00:02:58, flags: T
    Incoming interface: Vlan430, RPF nbr
    Outgoing interface list:
    Vlan888, Forward/Sparse, 00:01:30/00:01:29, H

    where is the Config Mgr server. When the multicast fails, the Outgoing interface list: changes to Null instead of the correct Vlan888.

    What troubleshooting/debugging steps can I take next?