DHCP Failover and Performance

[Simon Hobson]

perl-list wrote:
>You might consider making your lease length a bit longer.  If you 
>are having 25 bindings/sec with only 100k clients, then you must 
>only have a 2 hour lease.  I would not run with less than an 8 hour 
>lease in any environment.  You might even consider longer than this 
>depending on what kind of clients they are.

But you do need to consider some corner cases.

Yes, you can reduce load considerably with longer leases - I'd 
personally suggest they should not be less than 4 days, and so cover 
a weekend. But you will still have peak loads :

1) If it's a "traditional" office environment, then there'll be a bit 
of a peak each morning as people switch on their machines. In general 
these should just be renewals as the machines will still have 
unexpired leases (note above about having leases that are longer than 
a weekend).

2) If you have a widespread outage (such as an area-wide power cut), 
then on power resumption you'll have a very significant peak.

I don't know if anyone has done any testing on this, but it's 
certainly conceivable that if you apply enough load to a server then 
it won't respond fast enough to satisfy clients. If that happens, 
then clients will re-try their requests and thus increase the load - 
so it's conceivable that there's a tipping where service drops very 
sharply when a certain tipping point is reached.

-- 
Simon Hobson

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