[Bioclusters] alternative DHCP implementations?

Lars G. T. Jorgensen lars at binf.ku.dk
Wed Mar 30 07:55:55 EST 2005

Chris Dagdigian wrote:

> Agreed. It was just a shortcut. We already do allocation of IP based 
> on MAC address but that only works when you know the MAC address 
> information ahead of time.  This is rare especially on whitebox 
> cluster projects where people don't put the MAC on the product 
> packaging or on the chassis itself. Some vendors do a good job of 
> making the data easy to find and others simply don't bother.
> A dhcp server handing out dynamic-range leases in a predictable manner 
> is what allowed us to easily map MAC address to node position and 
> nodename simply by powering on the nodes for PXE boot in the order in 
> which they are racked and stacked. Once this was done we had the 
> MAC->Node mapping data we needed to generate the static allocation 
> entries.
> A workaround for non-predictable allocation is to simply power on the 
> cluster in the order in which you want things named, then parse the 
> dhcpd leases file for both the MAC address *and* the timestamp 
> representing the lease handout. That would allow you to map MAC -> 
> Node without having to care about hostnames for the first pass MAC 
> collection phase.  Then you build the static-by-mac entries into the 
> conf file and problem solved. If we stick with ISC DHCP this is a 
> possibility...

Or buy an switch with a bit of inteligence that can dump the machines 
MAC addresses based on ports.

> c
> Adam S. Moskowitz wrote:
>> Chris,
>>> We are thinking about trying to find a replacement DHCP server that 
>>> has a predictable method of allocating dynamic IP addresses (even if 
>>> only for the initial cluster deployment)
>> I think it's a bad idea to rely on such behavior. I don't remember what
>> the RFC says, but in general, unless the RFC guarantees an
>> implementation should behave a particular way, you are asking for
>> trouble to rely on specific behavior.
>> A great example of this is how round-robin DNS used to work and then how
>> it changed and lots of things broke.
>> DHCP isn't meant to do what you're asking it to do, so I strongly
>> suggest you not use it to solve that particular problem.
>> That said, DHCP supports a mechanism for binding specific IP addresses
>> to specific MAC addresses, even though the assignment is still done
>> dynamically. Yes, this is a bit more work, but at least it's guaranteed
>> behavior.
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Mvh|Regards, Lars
System Administrator, Phone: 3532 1349, Room: 318

Bioinformatics Centre, University of Copenhagen, 
Universitetsparken 15
DK-2100 Copenhagen

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