3.1.1 Failover Speed (was: Re: 4.1.0a1 Failover sync speed)

John Wobus jw354 at cornell.edu
Thu May 29 17:38:14 UTC 2008

On May 29, 2008, at 11:03 AM, Michael Kaegler wrote:
>>  >This may have been true once, but we tested this: setup a subnet 
>> with
>>> a "range" and assigned '.4 fixed. We joined two
>>> machines, neither of which were the MAC assigned '.4, and no other
>>> machines were on the subnet at all. The first was assigned .5, the
>>> second just generated a 'no addresses available' error.
>> Umm, not necessarily. dhcpd sends a ping before offering the address 
>> to
>> make sure it is free. If it gets a response then it will abandon that
>> address and not attempt to re-use it until it has no other available
>> leases.
> We included that in our test by having no other devices in the subnet 
> (other than a router at .1; the DHCP server was out of the subnet with 
> an ip-helper). The '.4 address would not have gotten a ping response, 
> and so if the server was going to assign it, it would have.
>> Best practise says that you should not have fixed-address devices
>> inside your dynamic ranges.
> Not an option at the moment, random addresses were allocated from all 
> over the subnet in the old system. We'd have literally hundreds of 
> pool statements (x140 subnets. Unworkable.)
> But like I said, this is tested working. Despite what you're both 
> saying, practical testing has shown that an address in a pool will not 
> be handed out if there is a fixed-address statement for it.
> -porkchop
> -- 
> Michael "Porkchop" Kaegler, Sr. Network Analyst
> (845) 575-3061 Marist College, Poughkeepsie, NY

I recommend you check the ISC source or get the developer's word before
trusting the daemon will continue to do what you found in your tests.
Did you find leases in the lease file for the dynamic/fixed addresses?  
What state were they in?
Folks on this list are trying to head off a disaster for you down the 
road if
production does not continue to work in the manner that your tests did.
The list hasn't received word that the ISC server has been modified to 
work the way
you found it does, and the list periodically gets postings from those 
who expected it to
work as you describe and were chagrinned at the result.

If the ISC server is indeed now designed to work as you describe, there 
will be
admins who are happier.  My own site doesn't worry about the issue even 
numerous pools because we generate our config with a script that keeps 
and fixed addresses separate.

John Wobus

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