[ipxe-devel] [PATCH] [device] Improve the seed of the pseudo-random number generator

Marcus Epperson mrepper at gmail.com
Wed Feb 13 01:15:36 UTC 2013

On Wed, Dec 12, 2012 at 8:33 AM, Bernhard Kohl <bernhard.kohl at nsn.com>wrote:

> When (re)starting a couple of virtual machines (about 10) on the same host
> it frequently happens that some of them use the same DHCP transaction ID.
> This problem can be solved by combining the current timer ticks and the
> least significant bits of the hardware address(es) to get a better
> randomness for the seed.

I ran into the same problem on a several thousand node Infiniband cluster
recently. We had hundreds of nodes booting with duplicate IPs because of
these PRNG-based XID collisions. I ended up reverting
12767d2202e620e32aef3fbdd2c4ad30c4e5ac22 to get back to MAC/GUID-based XIDs.

Your patch seems like the right way to fix it, but I probably won't have an
opportunity to test at large scale again anytime soon.

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