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WDS traverse vlans settings needed

Posted on 2011-09-20
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Last Modified: 2012-05-12
We have a WDS server sitting on what we'll call subnet A.  the hosts we want to distribute images to are on subnet B.  the DHCP server also sits on Subnet B--the WDS server is NOT a DCHP server.  Question:

We want our WDS server on subnet A to allow us to pxe boot and connect to it from subnet B where most of our servers, workstations, and the DHCP server reside.  I've seen some information out there that states we need some special DHCP settings for this.  I've seen other information that we need to make some changes to our switches with IP helper entries.  Which is it?  What is required to allow us to PXE boot and connet to our WDS server in this scenario?  If it's only IP Helper commands, then I assume they would be needed for any subnet we want to direct to the WDS server subnet?  Thanks!!
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Question by:patriots
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by:Craig Beck
ID: 36572756
You need an IP Helper configured on the VLAN where the clients connect, pointing to the WDS server.

You will also need to configure some options on your DHCP server to tell the clients which server they need to connect to, and what image to boot from once they have PXE booted.

Have a look at this...

http://www.microsoft.com/download/en/details.aspx?DisplayLang=en&id=9709
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vivigatt earned 250 total points
ID: 36573858
Actually, the IP-Helper needs to point to the DHCP server first.
Since your WDS server is not your DHCP server, I assume that the PXE service runs on the WDS server too.
So you need also an ip-helper to redirect UDP broadcasts on DHCP port to the WDS server (PE service does answer to DHCP DISCOVER packets which are sent on broadcast addresses). Hopefully, ip-helpers can be set to redirect broadcast packets to several hosts at the same time (I even have set once an IP-helper that was redirecting to a broadcast address!)

If the DHCP service runs on the same host that also runs the PXE service (and thus you have set the dhcp option 60 to "PXEClient"), you may need to forward packets on UDP 4011 to the DHCP/PXE server too

Maybe you can read my article:
http://www.experts-exchange.com/Networking/Misc/A_2978-PXEClient-what-is-it-for-Can-I-use-PXE-without-it.html
It gives some basic clues about PXE configuration.
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by:Craig Beck
Craig Beck earned 250 total points
ID: 36574210
@vivigatt - why does the IP Helper need to point to the DHCP server when the client is on the same subnet as the DHCP server?  I understand MS recommend it, but in practical terms that is not required.

When the client and the DHCP server is on the same subnet the client can send broadcast traffic to the DHCP server without an IP helper, so it isn't required.

You state... "Since your WDS server is not your DHCP server, I assume that the PXE service runs on the WDS server too. So you need also an ip-helper to redirect UDP broadcasts on DHCP port to the WDS server"

However, that does not make sense.  Why would you forward UDP broadcasts on the DHCP port to the WDS server?  The DHCP service isn't running on the WDS server (as the OP states).

In DHCP all you need to do is configure option 66 with the IP address of the WDS server and option 67 with the name of the bootfile which is on the WDS server (typically \boot\x86\wdsnbp.com)

The client will communicate with the WDS server directly on port 4011, so unless a firewall between the two VLANs is blocking that port there is no problem.  The only reason the IP Helper needs to be configured is to allow the client to download the PXE bootfile via TFTP.

So, in brief...

On your switch configure an IP Helper address on the VLAN where the client sits, pointing it at the IP address of the WDS server.
Configure options 66 and 67 on your DHCP server.

http://support.microsoft.com/kb/926172
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by:vivigatt
ID: 36577998
Read my article.

You are right, if dhcp server and clients are on the same subnet, no need for an IP helper for redirecting broadcasts to the dhcp server. However, a PXE service listens to dhcp broadcasts too. Check the specs... its also states that udp 4011 is to be used only if dhcp and pxe services run on the same host. Using dhcp options 67 and 67 make it useless to have a real pxe service. You would then just need a dhcp and tfto server.  
Onve again, read my article, it tries to explain all this. You may want to know where I got that knowledge. Well, I was the architect if a software that allowed to remote boot windows using pxe (and some other stuff)...
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