Introduction

The following is a description of utilizing Network Boot Profiles in CapaInstaller

Network Boot Profiles offers a fine grained way of delivering a customized boot configuration to a specific subset of devices, based on their network cards MAC adress.

This functionality offers control over the following network boot options:

Direct the correct boot profiles to relevant groups of devices
Block boot replies to irrelevant groups of devices
Optimize download performance for specific devices during network boot

Requirements

Device selection

To add a new profile first choose what devices should be affected by the profile.

Managed Devices: consists of devices already enrolled in CapaInstaller.

Vendors: makes it possible to create a match for all devices with a specific vendor prefix to their network cards MAC adress.

Add a device
To add a specific subset of devices make a selection from the relevant list

Add a Vendor
To add all devices with network card MACs registered to a specific vendor, select from the list

All device recognition is MAC address based and the relevant network boot profile will only be offered to devices matching the selected criterias.

Configuration

Generally two types of configurations are available: Configurations aimed at specific network cards to improve performance with these or configurations disabling network boot responses to specific network adapters / devices.

Performance

Booting from the network requires a download of an initial boot image. CapaInstaller uses the TFTP standard for this initial download.

Trivial File Transfer Protocol

Trivial File Transfer Protocol (TFTP) is the network protocol used for downloading all files during network boots, including the boot image. TFTP is an inherently slow protocol because it requires one ACK packet for each block of data that is sent. The server will not send the next block in the sequence until the ACK packet for the previous block is received. As a result, on a slow network, the round-trip time can be very long. This can be improved by configuring TFTP windowing. TFTP windowing enables you to define how many data blocks it takes to fill up a transfer window. The data blocks are sent back to back until the window is filled, and then an ACK packet is sent. The result is fewer ACK packets and much faster download times for the client.

Variable window size: Allows the client and server to determine the largest workable window size, resulting in improved TFTP performance. Provides the ability to dynamically determine the optimal window size

Window size: Increasing this, increases the amount of blocks sent every transfer window, this might improve performance, but some network cards doesent react well to large windows sizes resulting in actual decreased performance. Consult the specifications for the specific network card or device to determine the maximum window size in bytes.

^{More about the TFTP Windowsize Option - RFC7440}

Block size: The size of each block sent every transfer window. Increasing this can improve performance, but some networks, devices or network cards may not support larger blocksizes depending on LAN MTU or the NICs largest memory block size.
_{More about the TFTP Blocksize Option - RFC2348}

No response

A configuration configured not to respond to network boot requests, offers the posibility to have network equipment listening to DHCP or BOOTP on the same subnet as computers that needs to be able to network boot, without affecting the operation of these devices. Typical examples are IP telephony gateways, certain routers or printers that should not be offered a network boot image download. This way you can control this funtionality directly in CapaInstaller instead of in the DHCP server configuration or by separating these on isolated subnets.

Profile Configuration