Kickstart files and MAC-addresses

[Grant Huddlestone]

Stumbled across something interesting last week that took me a while to understand.

I have a number of VMs that use PXE-boot to install Centos7.

I serve custom kickstart files from a local tftp server. Part of the kickstart file has an %include section that points to a local http server by a domain name (not IP address).

Some of the anaconda installs would not start and give an error message about the domain name not resolving in the kickstart file. This appeared to be random and was consistent across reboots for the affected server. It never started the anaconda install.

I looked at firewalls, dns server and many other possible contributing factors until I noticed something,

The install would only fail for VMs that had network adapters with MAC-addresses that started with the letter 'F'.

Not only that, if any network adapter attached to the VM started with F the anaconda installation would fail, it didn't have to be the one that was associated with the network that the http server was connected to.

Note: It is expected behaviour that the NIC is cycled just before the anaconda installation starts.

 

[LnxBil]

Wow. Nice findings.

In order to prevent this, you can set or better limit the range of generated MAC addresses via the MAC prefix setting (datacenter->options).

 

[Stoiko Ivanov]

The one thing this reminds me of would be the distinction between unicast and multicast mac-addresses (however there the second hex-digit needs to be even (so FE:XX:XX:XX:XX:XX should work) - https://en.wikipedia.org/wiki/MAC_address#Unicast_vs._multicast

I hope this helps!