DHCP failover and fixed-address

Simon Hobson dhcp1 at thehobsons.co.uk
Mon Mar 3 12:18:21 UTC 2008

Sebastian Hagedorn wrote:

>>FOr newer releases you may be thinking of reserved leases.
>Yes, that's what I meant.
>>While these
>>seem to work, the only way to enable them is by editting the leases
>>file or a complex omapi interface.
>So what advantage do they offer?

Well another feature that's been on and off the list of things to do 
is to allow the admin to override the primary ID selection. At 
present it is "select first value (client id, hardware)" - or use the 
client id if it's supplied, and fall back to MAC address of a client 
id wasn't supplied.

A proposed feature would allow the admin to override this - such as 
ignore client if altogether or use option 82 if supplied. The first 
is useful in multi-boot environments where some OSs supply a client 
ID and others don't, the second is useful if you want to assign IP 
address by physical switch port.

Combine this with the ability to reserve a lease to be kept for use 
with a specific "client" and it gives some powerful new capabilities 
that currently requires some long winded workarounds (such as having 
a class and a "single address" pool for each client). For example, 
you could use option-82 as your primary key, and reserve a lease for 
a particular port id - this gives you what is effectively a static 
address assignment to a switch port, while still keeping the normal 
lease state handling (including DNS insertion and removal).

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