ISC Dhcp Failover behavior for INIT-REBOOT scenario

Glenn Satchell glenn.satchell at
Mon May 24 11:39:12 UTC 2010

Hi Ravi

I don't have an answer for you. I suggest that some testing and reading 
the source code may be the answer. A good place to start might be the 
file server/failover.c in the source distribution.


On 05/24/10 18:52, ravi kumar wrote:
> <Resending the mail, as there is no response>
> Can someone please throw light on ISC's implementation.
> regards
> Ravi
> On Thu, May 20, 2010 at 8:39 PM, ravi kumar <ravikumar.lrk at
> <mailto:ravikumar.lrk at>> wrote:
>     I would like to know the behavior of Dhcp Failover implementation in
>     INIT-REBOOT scenario. Is the following highlighted part taken care
>     of in Failover implementation ?
>     Also, would like to know if anyone has come across any Client, that
>     behaves in below specified manner : Request is sent during
>     INIT-REBOOT, though Client doesnot have valid lease.
>     <Copy-Paste from Dhcp Failover draft
>     [*draft-ietf-dhc-failover-12.txt*
>     <>]>
>     One troublesome issue is that of the DHCP client responsibility when
>         sending in DHCPREQUEST/INIT-REBOOT requests.  While the original
>     DHCP
>         RFC was written to require a DHCP client to have time left to run on
>         the lease for an IP address if the client is sending an INIT-REBOOT
>         request, it was sufficiently unclear that some client vendors didn't
>         realize this until recently.  Since the INIT-REBOOT request was sent
>         with the IP address in the dhcp-requested-address option and not in
>         the ciaddr (for perfectly good reasons), the similarity to the RENEW
>         and REBINDING case was lost on many people.
>     At present, the failover protocol does not assume that a client send-
>         ing in an INIT-REBOOT request necessarily has a valid lease on
>     the IP
>         address appearing in the dhcp-requested-address option in the INIT-
>         REBOOT request.
>         The implications of this are as follows: Assume that there is a DHCP
>         client that gets a lease from one server while that server is unable
>         to communicate with its failover partner.  Then, assume that after
>         that client reboots it is able only to communicate with the other
>         failover server.  If the failover servers have not been able to com-
>         municate with each other during this process, then the DHCP client
>         will get a new IP address instead of being able to continue to use
>         its existing IP address. This will affect no applications on the
>     DHCP
>         client, since it is rebooting.  However, it will use up an
>     additional
>         IP address in this marginal case.
>     regards
>     Ravi

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