Clarification on multiple Boot servers in a subnet

Document ID : KB000027555
Last Modified Date : 14/02/2018
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Description:

Once a target computer has been registered to a Boot Server in a subnet is it possible to move the specified computer to an alternative Boot Server in the same subnet, either via a GUI function or from the Command Line Interface (CLI)

From the Inside Guides

Multiple Boot Servers in an IP Subnetwork

With a new scalability server, a boot server is also installed.

The new boot server does not take responsibility for target computers already assigned to another boot server in the sub network.

Each boot server is responsible for a specified set of target computers only. The DSM Manager determines the set of target computers.

All boot servers observe PXE requests in their sub network. But they immediately reply only to requests of machines belonging to their own set of target computers. Requests of other machines are answered only after a certain number of retries and after a certain amount of time. The number of retries and the time to wait can be configured. More than one boot server may send such a default response.

A target machine receiving one or more default responses will choose one of the replying Boot Servers and establish a connection. This usually is the Boot Server that replied first.

A new target (not yet assigned to a Boot Server) will be fetched by that Boot Server.

A target already assigned to a different boot server will be reassigned to the new boot server. If there is an activated or pending installation order for the target and the required OS image is not available at the new boot server, the installation order is cancelled.

The following configuration policy parameters in section DSM/ScalabilityServer/OSIM/ManagedPC/Server change the behavior of a boot server with respect to other boot servers in the IP sub network:

Figure 1

UseACL

0

If UseACL is set to "0", the boot server must be the only boot server in its IP sub network, because it answers all PXE requests immediately.

1

If UseACL is set to "1", the boot server immediately answers PXE requests of assigned targets only, that means, the boot server uses an Answer Control List (ACL).

PXE requests of other target machines will be answered only after a certain number of retries has been seen and after a certain amount of time has been elapsed since the first request.

2

If UseACL is set to "2", the boot server immediately answers PXE requests of assigned targets only, that means, the boot server uses an Answer Control List (ACL), but it does not answer to unknown targets!

Meaningful values:
"0" or "1" or "2"

Default Value:
"1"

DiscoveryRetriesBeforeAnswer

Number of retries before a boot server sends a default reply to the PXE request of a target not assigned to it.

Meaningful values:
"1" to "4"

Default value:
"3"

Only evaluated if "UseACL" is "1".

DiscoveryTimeoutBeforeAnswer

Number of seconds to wait before a Boot Server sends a default reply to the PXE request of a target not assigned to it.

Meaningful values:
"3" to "56"

Default value:
"10"

Only evaluated if "UseACL" is "1".

The following table shows corresponding DiscoveryRetriesBeforeAnswer and DiscoveryTimeoutBeforeAnswer values:

DiscoveryRetriesBeforeAnswer DiscoveryTimeoutBeforeAnswer
12
2 8
3 20
4 40

Any of the boot servers in a IP sub network can take responsibility of a PXE target. Therefore, it is recommended to store the needed OS and boot images on any of the Boot Servers in the sub network.

Solution:

The ability to have multiple boot servers allows greater fault tolerance in case a particular boot server is unavailable as well as generally assigning the Boot Server with the fastest response time for that specific computer. It is not intended that you can use this as a way to have specific Boot Servers for specific OS Images. In the current release there is no GUI or CLI method to move a target computer from one Boot Server to another in the same subnet. The system is designed to assign the correct boot server as per the settings in the configuration policy defined above.

Other Relevant Information:

There is one exception to this.

Once a new computer has been assigned to a particular Boot Server you can use the following procedure to change this assignment

  1. Copy the new computrs MAC address onto the clipboard.

  2. Delete the unmanaged computer from the scalability server.

  3. Right click on the All Computers group and select new computer.

  4. Follow the Computer pre-registration wizard pasting the MAC address copied in step 1. Tick the Use OS Installation Management box fill in the rest of the required details and when asked to specify the required scalability server, be sure to choose the Boot Server you require.

This will now have registered the agent machine to the required Boot Server. Unfortunately this cannot be used as a general resolution for already installed computers as you have to delete the old one and this will erase all installation history and other configurations that exist for this computer.