tmark at isc.org
Wed Oct 12 09:56:44 UTC 2016
On 10/11/16 10:39 PM, 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.
> It seems that the running server always sends packets from the primary IP
> on the NIC, and sets the dhcp-server-identifier option to this IP. So when
> a DHCP client tries to renew, if the server has changed, it takes quite a
> while before the client realizes this. If I could change the packet and
> the dhcp-server-identifier to be the virtual IP, the clients wouldn't have
> this problem.
> Is there a way to configure this in isc-dhcp?
> dhcp-users mailing list
> dhcp-users at lists.isc.org
You should be able to use the "server-identifier" configuration
parameter to fix the value used to the desired IP address. From
"The server-identifier statement
The server-identifier statement can be used to define the value
that is sent in the DHCP Server Identifier option for a given
scope. The value specified must be an IP address for the DHCP
server, and must be reachable by all clients served by a particu-
The use of the server-identifier statement is not recommended -
the only reason to use it is to force a value other than the
default value to be sent on occasions where the default value
would be incorrect. The default value is the first IP address
associated with the physical network interface on which the
The usual case where the server-identifier statement needs to be
sent is when a physical interface has more than one IP address,
and the one being sent by default isn't appropriate for some or
all clients served by that interface. Another common case is when
an alias is defined for the purpose of having a consistent IP
address for the DHCP server, and it is desired that the clients
use this IP address when contacting the server.
Supplying a value for the dhcp-server-identifier option is equiva-
lent to using the server-identifier statement."
ISC Software Engineering
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