ip helper-address for PXE Boot only works with Unicast but not Multicast

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Aug 11th, 2008
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I have configured an IOS DHCP server on a 2960G switch and added the IP Helper-address for the DHCP server (2960G Switch) and also for the ghost server. So effectively I have 2 IP helper-addresses configured on the SVI's, first the DHCP server and second the Ghost server.

When we do a PXE boot it gets an IP from the switch and connects to the ghost server, but if we try a Multicast ghost session the PC's just hang on the Ghost screen. If we try a Unicast session then it works fine, but obviously we need to image around 30 PC's at a time so Multicast is preferable!

What have I missed out on the switch configs to allow Multicast?

Please, pleqase help!!!

Many thanks


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cowetacoit Mon, 08/11/2008 - 04:55
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is the PC and Ghost server on the same vlan/subnet? What device is doing your inter vlan routing?

bavingtonm Mon, 08/11/2008 - 05:07
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The PC's are in a different vlan to the servers. Theses particular pcs are using /24 subnet and the ghost server is on /24 subnet.

We have 2 x 3750G switches at the core which are using SVI's for intervlan routing. Each Vlan is in a different building and uses a 2960G switch, also with SVI, and has IOS DHCP server configured on it. This 2960G connects via fibre back to core 1, and below the 2960G in the cabinet are 4 more 3560G switches daisy chained together with copper and the last 3560G in the stackn has a fibre link back to core 2.

Any ideas?


bavingtonm Mon, 08/11/2008 - 05:46
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Thanks for the link.

Unfortunately the cores do not like the "IP multicast-routing" command.; When I do a "?" after "IP" there is no Multicast option.

The IOS release is version: 12.2.(35)SE5 I don't know if this matters?

Please help?

cowetacoit Mon, 08/11/2008 - 06:08
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You are probably running just the standard IP Base image. I'm not sure if the 3750's are the same, but with the 3560 you have to upgrade the image to Advanced ip services in order to use more advanced IOS features.


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