combining lease files

project722 project722 at
Wed Aug 29 14:40:39 UTC 2018

Thanks. So would this syntax be correct on the secondary?

failover peer "dhcp-failover" {
        secondary; # declare this to be the secondary server
        address <server IP address>;
        port 647;
        peer address <A-master>;
        peer address <B-master>;
        peer port 647;
        max-response-delay 30;
        max-unacked-updates 10;
        load balance max seconds 5;

On Wed, Aug 29, 2018 at 9:35 AM Bob Harold <rharolde at> wrote:

> On Wed, Aug 29, 2018 at 10:14 AM project722 <project722 at> wrote:
>> Thanks for the feedback guys!
>> So, in this scenario I'll have 2 masters temporarily - B will become a
>> new master and sync to A-failover, and A-master will still be in the
>> picture as well? If I try this approach, then, I will have to add the
>> subnets for server B to A-failover, then enable failover between B and
>> A-failover? Wouldn't A-master have a problem with A-failover having subnets
>> in its conf file that A-master doesn't?
>> Also, I'm starting to think aboout ip helper addresses. Seems like the
>> flow would be:
>> Add an IP helper address on the router for server B's subnets to also
>> point to A-failover
>> Once they are completely in sync then remove the IP helper for server B
>> altogether and add another for A-master
>> Does that sound about right?
> That is correct.  A DHCP server can be master for some subnets with
> failover 1, and others with failover 2, and still others with no failover.
> A DHCP failover server can be failover for some subnets with master 3,
> others with master 4, and other subnets that are not using failover.  The
> only limitation is that I don't think a server can be master for some
> subnets and failover for others.
> p.s. Here at U of Michigan we currently have 8 pairs, and have some
> experience moving subnets around  :)  The trick is to verify that the dhcp
> forwarding on the routers is really working and that there is no firewall
> rule or acl somewhere blocking it.
> --
> Bob Harold
>> On Wed, Aug 29, 2018 at 8:36 AM Bob Harold <rharolde at> wrote:
>>> On Wed, Aug 29, 2018 at 9:33 AM Sten Carlsen <stenc at> wrote:
>>>> On 29/08/2018 14.28, project722 wrote:
>>>> Hey All,
>>>> We are consolidating all subnets on server B and moving to an exisitng
>>>> failover pair we have, In order to decom server B. I'll need to take the
>>>> leases file from server B and combine whats there with the leases file on
>>>> both servers in the failover pair. (doing this to make the failover pair
>>>> aware of what leases are already out there that were assigned by server B)
>>>> I am not sure, but I think one other way could be to make server B part
>>>> of a failover pair with one of the existing failover servers for a period
>>>> of time. That way the remaining server will have all the information
>>>> transferred from server B. Later that configuration could be changed to
>>>> have the other remaining failover server act as the peer, that way the
>>>> servers would transfer the data, probably with less risk.
>>>> Others should confirm or reject this idea.
>>>> I'm thinking just a simple cat on both files should be fine to combine
>>>> the data. And, all 3 servers are running the same verison of dhcp
>>>> ( and RHEL so I don't expect and formatting problems.
>>>> However, since failover pairs have more transitional states with the
>>>> "binding state" variable, is it possible I will run into any issues doing
>>>> this? Is there a better, more preferred way of doing this instead of
>>>> merging the leases file?
>>> The benefit of a failover pair is that we can upgrade/repair/replace one
>>> server at a time without any interruption in service.
>>> Let's call the failover pair A-master and A-failover.
>>> The recommended method is to configure server B as master and the
>>> A-failover server as failover for server B's subnets also.  Give it some
>>> time (watch the failover messages in the logs) to sync the data from B to
>>> A-failover.  Then move the subnets from B to A-master, and A-master will
>>> sync the data from A-failover.
>>> --
>>> Bob Harold
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