Quick Failover

Glenn Satchell Glenn.Satchell at uniq.com.au
Tue May 22 15:24:46 UTC 2007

>Date: Mon, 21 May 2007 23:08:51 +0100
>To: dhcp-users at isc.org
>From: Simon Hobson <dhcp1 at thehobsons.co.uk>
>Subject: Re: Quick Failover
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>Benjamin Wiechman wrote:
>>For a quick and dirty transition to a new dhcp server I should be able to do
>>the following correct?
>>1)       Shut down dhcpd on old machine
>>2)       Ensure that new server is listening on correct eth interface
>>3)       Copy dhcpd.conf, dhcpd.leases, and dhcpd.leases~ to new server
>>4)       Point my ip helper address at the new server
>>5)       Start dhcpd on new machine
>Yes (you don't need dhcpd.leases~)
>But I wouldn't call it "quick and dirty", it's quick but by no means dirty.
Except all the clients know the address of the old dhcp server, so when
they try to renew by directly contacting the dhcp server they will
fail. When the lease expires the client will fall back to DHCPDISCOVER
and broadcast for a dhcp server, they will find the new one, and it can
give them back the IP address they had before. Should be mostly
transparent tothe client though.

For totally seamless operation give the new dhcp server the same IP
address as the old one.

As Simon said this is pretty much the standard way to upgrade a server
to a new box.


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