option dhcp-server-identifier

Ilkka Virta itvirta at iki.fi
Thu Oct 13 10:31:12 UTC 2016

On 12.10. 05:39, John Ratliff wrote:
> I have a pair of isc dhcp servers, version 4.3.1 on Debian 8 Jessie.
> I do not want to use the DHCP failover protocol. Instead, I want to use a
> virtual IP on the primary active server, and have the backup server
> shutdown. I have a cronjob to sync the lease file automatically, but
> failover will be strictly a manual process.

Just a thought:
I don't think you'll be able to sync new leases in real-time this way, 
i.e. there's a window between the server giving out the lease and the 
cron job running. (And with cron, you can't usually run more often than 
once per minute.) If the primary server crashes with unsynced leases, 
the client will still use the IP address, but the backup server will may 
happily give it to someone else. I think the failover protocol tries to 
work hard to prevent this.

Though of course the server tries to keep every client using the same IP 
address, so this may not be much of a problem.

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