failover compatibility

[Glenn Satchell]

The client can continue to use the IP address until the lease expires.
SOme non-conforming clients continue to use it.

Most clients will try to renew when the lease is at the 50% time, and
continue retrying until the expiry time. Then it falls back to doing a
broadcast to find new dhcp servers.

As a way to mitigate the migration, you could increase your lease time a
few days before the upgrade, so all the clients will be more tolerant of
any outage.

It's only clients whose leases expire that will drop off the new. Renewing
clients will just keep on trying until they get a response or the lease
expires.

You can get an idea of the impact by counting the number of clients doing
a dhcp discover in a given period, say 5 minutes.

Being on the same box actually works in your favour. Only need to upgrade
the dhcp packages - config and lease files will stay in place.

regards,
-glenn

On Wed, September 5, 2012 4:26 pm, Campbell.ColinD at police.qld.gov.au wrote:
> Hi,
>
> Again, thanks. My method will have to be a little different since oldx
> and newx are the same box but I get the idea. The IP addresses will be
> the same as we're allocating through a WAN so using ip-helpers.
>
> One last, probably dumb question, if I may. What does a client do if no
> DHCP servers are available? Does it keep its address or drop it and go
> off the air?
>
> Colin
> --
> Colin Campbell
> Security Specialist
> Public Safety Network Management Centre
> p: (07) 3008 4851
> f: (07) 3008 4799
> e: campbell.colind at police.qld.gov.au
>
>
>> -----Original Message-----
>> From:
> dhcp-users-bounces+campbell.colind=police.qld.gov.au at lists.isc.org
>>
> [mailto:dhcp-users-bounces+campbell.colind=police.qld.gov.au at lists.isc.o
> rg]
>> On Behalf Of Glenn Satchell
>> Sent: Wednesday, 5 September 2012 4:20 PM
>> To: Users of ISC DHCP
>> Subject: RE: failover compatibility
>>
>> (b) copy the leases file is preferable. Do this after shutting down
> dhcpd.
>>
>> The clients hold the lease information too, so they need to match up.
>>
>> It's been a while since I've done this, but essentially you need to
> copy
>> each one.
>>
>> 1. Shut down old1
>> 2. Copy dhcpd.conf and dhcpd.leases to new1.
>> 3. Start new1
>> 4. Shut down old2
>> 5. Copy dhcpd.conf and dhcpd.leases to new2
>> 6. Start new 2
>>
>> May need to swap steps 3 and 4.
>>
>> Are you using new dhcp servers? Will they have the same or new IPs? If
> the
>> new servers are running on new ip addresses then all clients will need
> to
>> wait for their lease to expire, then they will go back to discover the
> new
>> dhcp servers. On the other hand if the new servers have the same IP
>> addresses as the old servers then the clients will contact them
> directly
>> to renew existing leases. Either works ok as long as the leases file
> is
>> copied to the new server so that it can issue the same IP address the
>> client had before.
>>
>> regards,
>> -glenn
>>
>> On Wed, September 5, 2012 2:30 pm, Campbell.ColinD at police.qld.gov.au
> wrote:
>> > Hi,
>> >
>> > Thanks for that. That brings a new quandary.
>> >
>> > I can't upgrade both servers simultaneously. I have to do one at a
> time.
>> > In doing so, I plan on shutting one down, upgrading it, restoring
> the
>> > configs, shutting down the other old server and doing something with
> the
>> > leases on the new server. That something could be:
>> >
>> > a) let the new server create a new leases file, or
>> > b) copy the leases file from the still-active old server
>> >
>> > Is (a) or (b) preferable? If neither, what is the correct procedure?
>> >
>> > Colin
>> > --
>> > Colin Campbell
>> > Security Specialist
>> > Public Safety Network Management Centre
>> > p: (07) 3008 4851
>> > f: (07) 3008 4799
>> > e: campbell.colind at police.qld.gov.au
>> >
>> >
>> >> -----Original Message-----
>> >> From:
>> > dhcp-users-bounces+campbell.colind=police.qld.gov.au at lists.isc.org
>> >>
>> >
> [mailto:dhcp-users-bounces+campbell.colind=police.qld.gov.au at lists.isc.o
>> > rg]
>> >> On Behalf Of Glenn Satchell
>> >> Sent: Wednesday, 5 September 2012 2:11 PM
>> >> To: Users of ISC DHCP
>> >> Subject: Re: failover compatibility
>> >>
>> >> No. The failover protocol changed somewhere in the 3.1 to 4.x
> range.
>> >> Details would be in the RELNOTES file distributed with the source.
>> >>
>> >> Essentially you need to shutdown and upgrade both failover hosts at
>> > the
>> >> same time. You can pre-check the format of dhcpd.conf and
> dhcpd.leases
>> >> using dhcpd -t and dhcpd -T to see if there are any issues wit the
> new
>> >> version. In general, the files *should* be compatible with all
> newer
>> >> versions.
>> >>
>> >> regards,
>> >> -glenn
>> >>
>> >> On Wed, September 5, 2012 8:24 am,
> Campbell.ColinD at police.qld.gov.au
>> > wrote:
>> >> > Hi,
>> >> >
>> >> > Will a 3.0.5 server form a failover pair with a 4.x server? This
>> > would
>> >> > be a temporary arrangement during a server pair upgrade.
>> >> >
>> >> > Colin
>> >> > --
>> >> > Colin Campbell
>> >> > Security Specialist
>> >> > Public Safety Network Management Centre
>> >> > p: (07) 3008 4851
>> >> > f: (07) 3008 4799
>> >> > e: campbell.colind at police.qld.gov.au
>> >> >
>> >> >
>> >> >
>> >
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