limitations of the protocol

Glenn Satchell Glenn.Satchell at
Fri Jun 26 15:01:37 UTC 2009

>Date: Fri, 26 Jun 2009 16:33:06 +0530
>Subject: limitations of the protocol
>From: loganathan Govindaraj <loganosc at>
>To: dhcp-users at
>X-BeenThere: dhcp-users at
>  Hi  all
>  under the section limitation of the protocol in
> draft-ietf-dhc-failover-07.txt
> " A subset of the address pool is reserved for secondary server  use.  In
> order to handle the failure case where both servers
>  are able to communicate with DHCP clients, but unable to communicate with
> each other, a subset of the IP address pool must
>   be set aside as a private address pool for the secondary server.  The
> secondary can use these to service newly arrived
>    DHCP clients during such a period.  The required size of this private
> pool is based only on the arrival rate of new DHCP clients and the length of
> expected downtime, and is not influenced in any way by the total number of
> DHCP clients support by the server pair.".
> Can one some one clarify whether the above mentioned process is
> automatically done by the fail over protocol ?
> if so how
> Logan

It's automatic. What that statement really means is that you need to
over-allocate the ip address range. Say you have 100 devices, then
allocate more than 100 ip addresses.

The number of extras is determined by the arrival rate of new requests
and the duration. So if you get a new request every 5 minutes, and
expect 1 hour of downtime then you need 12 extra IPs in your range to
cover the expected 12 requests during that 1 hour.

That's all, nothing too complex is meant by this.


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