best practice for moving subnets?

[Bjarne Blichfeldt]

Tom Schmitt wrote:
> 
> Hi,
> 
> I want to move a few subnets from one dhcpd failoverpair to another dhcpd
> failoverpair and was asked if I could do that without causing the dynamic
> clients to loose their connection to the network (or their ip address).
> 
> My question: Is there a best practice for such a task?

I think I would :

add the subnets to the new failoverpair
change helper addresses
change the config for the relevant subnets on the old pair to include :
	# 1 = DHCPDISCOVER
             if option dhcp-message-type = 1 {
                        deny booting;
              }
            deny after 4 2010/12/28 16:00:00;
or something suitable.

The thing is, even if you change helper address, the clients will continue to use the old dhcp serves if there are
network connectivity.
Only discoveries are sent as broadcast make use of the helper address. DHCPINFORM, DHCPREQUEST will be sent directly to the previous
used dhcp sever.


Regards,
Bjarne Blichfeldt



> 
> The straight forward approach, simply deleting the config on the first pair
> and adding it on the other and then changing the ip-helper-addresses on the
> router, would cause all the dynamic clients to request new IP addresses which
> means loosing their existing network sessions.
> 
> The second strategy that comes to my mind (shutting down all dhcpd, cutting
> all leases from these subnets out of the leasedatabases from the old pair and
> add them to the leasedatabases of the new pair. Then start all four dhcpd with
> the new config again) would mean a long downtime of all dhcpd which seemes to
> be not acceptable.
> 
> Is there any other strategy you could suggest?
> 
> Tom.
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