Advice on IP Helper Configuration for SCCM 2007 Infrastructure
"will be serviced locally assuming it can find those services on the local VLAN" Although this is what usually happens, it doesn't technically have to happen. When clients PXE boot, they (actually the NIC) send a boradcast request for the PXE server. IPHelpers merely forward this broadcast request on without any decision making process, they always do this. Thus, both the local PXE server and any remote ones pointed to by the IPHelper will see the PXE boradcast request from the client. The client will then choose the PXE server that responds to it first (if you're familar with the DHCP boradcast request process, this should should familiar because its identical). Thus, yes the local PXE server should get selected, but its possible it doesn't respond in a timely manner for a variety of reason and thus the PXE request gets serviced by the remote PXE server. Q1: Yes, there's no other way to do it with IPHelpers because as just mentioned, the process for locating each by the client is nearly identical. This is perfectly acceptable though because when the client broadcasts its request, it is marked as a DHCP or PXE request so the servers know to respond to the correct type of request. Q2: Not really, but there's nothing really wrong with it provided you are comfortable with what I laid out above (which was a worst case scenario). WHat SP are you running for ConfigMgr? If SP2, have you installed the hotfixes relating to PSP reliability (http://social.technet.microsoft.com/wiki/contents/articles/4505.list-of-public-kb-articles-and-hotfixes-for-configuration-manager-2007-sp2-en-us.aspx)? If not SP2, why not?Jason | http://blog.configmgrftw.com | Twitter @JasonSandys
July 27th, 2012 9:40am

This may be a network related question but it does relate to an SCCM 2007 R3 environment and takes into account the reliability we've experienced with the PXE Service Point. We've had to reinstall WDS and the PXE Service Point a few times already but that's another discussion. We're looking for guidance on the best IP helper/forwarder configuration for the following placement of services: Main Site Server A: Windows Server hosting DHCP - Home to secondary scopes for remote sites (resilience)Server B: Windows Server hosting DHCP - Home to more secondary scopes for other remote sites (resilience)Server C: SCCM Primary - PXE Service Point Remote Site Server Y: Windows Server hosting DHCP - Home to primary scope for the local siteServer Z: SCCM Secondary - PXE Service Point (currently NOT servicing PXE requests) Current IP Helper Configuration for the Remote Site Router Server A (Main Site - DHCP)Server B (Main Site - DHCP)Server C (Main Site - SCCM - PXE) Proposed Remote Site Router IP Helper Configuration to Support the local PXE Server Herein lies the question. I've assumed that the IP helper configuration needn't change. My reasoning is that DHCP and PXE will be serviced locally assuming it can find those services on the local VLAN, if it can't then then IP helper on the router will send the requests off to the main site. The reason for including the main site PXE server in the list is so that when the local PXE Service Point fails the clients can still find a server for when the local PCs are first powered on, i.e. so they don't sit waiting forever for a network boot server. Q1: Is the above reasonable or is it best practice to include the local DHCP and PXE servers in the IP Helper config on the local router, i.e. top of the list?Q2: Is the addition of a remote site PXE server in the IP Helper list common? It's purely to help with the PXE Service Point issues that we're seeing, we'd ensure that in SCCM any advertisements relating to OS deployment would be configured for local distribution points only, we don't want images being deployed across the WAN. Any guidance would be much appreciated.
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July 28th, 2012 5:51am

"will be serviced locally assuming it can find those services on the local VLAN" Although this is what usually happens, it doesn't technically have to happen. When clients PXE boot, they (actually the NIC) send a boradcast request for the PXE server. IPHelpers merely forward this broadcast request on without any decision making process, they always do this. Thus, both the local PXE server and any remote ones pointed to by the IPHelper will see the PXE boradcast request from the client. The client will then choose the PXE server that responds to it first (if you're familar with the DHCP boradcast request process, this should should familiar because its identical). Thus, yes the local PXE server should get selected, but its possible it doesn't respond in a timely manner for a variety of reason and thus the PXE request gets serviced by the remote PXE server. Q1: Yes, there's no other way to do it with IPHelpers because as just mentioned, the process for locating each by the client is nearly identical. This is perfectly acceptable though because when the client broadcasts its request, it is marked as a DHCP or PXE request so the servers know to respond to the correct type of request. Q2: Not really, but there's nothing really wrong with it provided you are comfortable with what I laid out above (which was a worst case scenario). WHat SP are you running for ConfigMgr? If SP2, have you installed the hotfixes relating to PSP reliability (http://social.technet.microsoft.com/wiki/contents/articles/4505.list-of-public-kb-articles-and-hotfixes-for-configuration-manager-2007-sp2-en-us.aspx)? If not SP2, why not?Jason | http://blog.configmgrftw.com | Twitter @JasonSandys
July 28th, 2012 9:15am

Thanks Jason, I'm proposing that the IP forwarder/helpers for the scenario we have will be configured as follows: Server Y (Local Site - DHCP)Server Z (Local Site - SCCM PXE)Server A (Main Site - DHCP)Server B (Main Site - DHCP)Server C (Main Site - SCCM PXE) We're running SP2 on ConfigMgr but it the PSP seems to work fine for a while and then suddenly something triggers it and the WDS service to fail. The error type is consistent, 16389 errors on the PSP and the WDS service failing to start. The Microsoft blog post for cleaning up and reinstating the PSP & WDS works, albeit for a week or two.
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July 29th, 2012 5:01pm

Have you installed the hotfix for the PSP though?Jason | http://blog.configmgrftw.com | Twitter @JasonSandys
July 29th, 2012 5:48pm

I was told the site servers were hotfixed, on further investigation there are only a few updates applied and none relate to the PXE SP or WDS service. I should have checked for myself ;-) I'll give them a try, many thanks Jason!
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July 30th, 2012 11:07am

ConfigMgr hotfixes aren't in the WSUS catalog so there is no way to download and apply them automatically or from Windows Update so maybe just a bad assumption about the servers being hotfixed.Jason | http://blog.configmgrftw.com | Twitter @JasonSandys
July 30th, 2012 11:53am

I've picked up this issue, which others have spent time looking at, and was told that all KB articles and hotfixes in relation to the PXE SP and WDS had been explored. I'd normally check for myself had I not been reassured this had been done, if we'd logged a call then I know full well the first question Microsoft would have asked. Anyway moving on there are two KB's which appear to offer some hope. I'll let you know how we get on, thanks again.
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July 31st, 2012 2:22am

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