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Q&A : ZLM and ZDM ProxyDHCP (PXE)

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Posted: 24 Jul 2007
 

Here's an excellent set of questions and answers from Novell Technical Services about ZENworks Linux and Desktop Management and PXE. (For the record, the term "PXE server" is actually a misnomer -- but a very popular one. The correct term for it is "ProxyDHCP server.") This should clear up many common misconceptions. Enjoy!

Q: With ZLM 7.2 installed, is the server acting as a ProxyDHCP (PXE) server?

A: Yes and no. All services are installed and ready, but the ProxyDHCP service will not start automatically. This avoids having multiple ProxyDHCP servers installed on a segment. So, if the ProxyDHCP server is activated (/etc/init.d/novell-proxydhcp start) the server will act as a ProxyDHCP server. (/etc/init.d/novell-proxydhcp install will cause the daemon to start each time the server reboots)

Q: Do all the same rules apply, one ProxyDHCP server for each DHCP server?

A: Yes, all the old rules apply. One ProxyDHCP server per DHCP server is a good rule, but the principle is to have exactly one ProxyDHCP server respond to each client. Obviously, if no ProxyDHCP server responds, then nothing ProxyDHCP-related will work. If multiple ProxyDHCP servers respond, then the results may be unpredictable (meaning it most likely will not work).

Q: Is a ProxyDHCP server needed for each VLAN?

A: Not necessarily, but that is a good rule of thumb. ProxyDHCP servers follow the same rules as DHCP servers and benefit from the same configuration. So if there is a single DHPC server for multiple VLANs, then there should be a single ProxyDHCP server. To have a single ProxyDHCP server for multiple VLANs, knowledge of how to configure your VLANs and switches with DHCP/bootp helpers/bridges is needed. Different vendors use different terms and methods like IPHelper and IPForwarding.

Q: We want a single ZLM 7.2 server. What are the configuration and install options?

A: This question is larger than PXE services, so this answer may not cover all issues that need to be considered when installing ZLM. In many instances, a single ZLM server may be sufficient, but you may want to consider a few things, especially if you have multiple sites.

PXE services will download several megabytes of data to enable imaging to occur, and then the images tend to be on the order of a few gigabytes. You may not want to have all this traffic originating from a single server or crossing certain networks segments (WLANs or other lower-speed segments). In this case you may want to deploy other imaging/PXE servers in strategic locations.

Q: How many NICs will bind to ZLM?

A: One. The server can have more than one NIC, but the service will only bind to a single interface, and then use internal routing to service the others.

Q: What about ZDM and ZLM interoperating ProxyDHCP servers?

A: This is the exact scenario where we designed server referrals. It is a technical requirement that each client only "see" a single ProxyDHCP server, regardless of whether they are imported into a ZDM or ZLM management zone.

The best solution is to use VLAN management configuration to ensure that each client can see a PXE server from his "home zone" and no others. For the cases where this is not possible, ZLM has the ability to perform PXE server referrals.

Where a client will see a PXE server from ZDM and ZLM, the user must:

  1. Disable the ZDM PXE services (just the proxyDHCP service/daemon)
  2. In ZLM's ZCC, enter a referral entry for a ZDM imaging server.

Now when any ZDM client requests PXE services, the ZLM server will recognize that it does not belong to his set of managed devices, and will refer him to the ZDM server.

This will work for any reasonable number of overlapping management zones.

Again, this is not the preferred method, but it will work when needed. For more information about PXE see this section of the documentation.


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