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[lwip-devel] [patch #5952] Integration of AutoIP module

From: Dominik Spies
Subject: [lwip-devel] [patch #5952] Integration of AutoIP module
Date: Fri, 22 Jun 2007 07:33:51 +0000
User-agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 1.1.4322)

Follow-up Comment #28, patch #5952 (project lwip):

Simons patch for the caclic inclusion problem is okay for me, I tested it and
it works fine for me.
So, the rand problem.
RFC3927 says:

The pseudo-random number generation algorithm MUST be chosen so that
   different hosts do not generate the same sequence of numbers.  If the
   host has access to persistent information that is different for each
   host, such as its IEEE 802 MAC address, then the pseudo-random number
   generator SHOULD be seeded using a value derived from this
   information.  This means that even without using any other persistent
   storage, a host will usually select the same IPv4 Link-Local address
   each time it is booted, which can be convenient for debugging and
   other operational reasons.  Seeding the pseudo-random number
   generator using the real-time clock or any other information which is
   (or may be) identical in every host is NOT suitable for this purpose,
   because a group of hosts that are all powered on at the same time
   might then all generate the same sequence, resulting in a never-
   ending series of conflicts as the hosts move in lock-step through
   exactly the same pseudo-random sequence, conflicting on every address
   they probe.

Why I used only 4 Byte of the MAC-Address for srand has no reason. I saw that
somewhere and just did it the same way. The cut 2 Bytes of the "Manufacturerer
Bytes" should not be a problem. What should be avoided is cut bytes from the
end what could result in same seed for a series of devices.

To just increment the LL-Address by adding MAC[4], MAC[5] and the number of
tries is not a good solution. I think the chance for conflicts is to high
when many devices from one series is used.


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