failover timeout

Ausmus, Matt mausmus at
Fri Apr 9 18:30:08 UTC 2010


Thank you for the response about how "partner-down" state works.  This
was one of the last questions I've been trying to find in the draft
document for dhcpd failover.  We're in the testing phase and getting
ready to rollout failover campus-wide and I like to have a full
knowledge of how systems work before rolling something out so I can
troubleshoot it effectively and know when it is working as intended.
I've also been translating how dhcpd failover works into plain English
for our internal wiki.  We document how how and why we configure devices
the way we do and also how processes work for whoever inherits our
network when or if we leave.  There's nothing worse than looking at how
something is setup and wondering what the psycho that set this up was
thinking about.

Again, thanks.

Matt Ausmus
Network Administrator
Chapman University
635 West Palm Street
Orange, CA  92868
mausmus at
"What the gods get away with, the cows don't."
-----Original Message-----
From: Glenn Satchell [mailto:glenn.satchell at] 
Sent: Thursday, April 08, 2010 9:30 PM
To: Users of ISC DHCP
Subject: Re: failover timeout

200k leases with one week duration. One week is 604800 seconds, so 200k 
leases renewing weekly would be about one every 3 seconds. Even if 
clients renew more often (typically 50% of lease time, or customers 
reboot CPE) this is still a very low number that would not require a 
very powerful computer. Given the high number of clients, failover or HA

of some sort would be a good recommendation.


On 04/09/10 00:39, Glenn Satchell wrote:
> 4,2.0 (currently alpha) has a configurable auto-partner-down feature.
> For all earlier releases the server stays in
> and *never* goes to partner down mode without manual action.
> Partner-down is the mode where the surviving server can allocate
> addresses previously given out by the failed server.
> Having said that it is pretty easy to write a script that monitors the
> other dhcp server, and uses omshell to switch to partner down when it
> detects that the other server has gone away. When the failed server
> comes back it will come out of partner-down mode and return to normal
> part of the startup negotiations.
> There was a post to the list by David Hankins on 25 Feb this year
> mentioning this which gives a lot more detail.
> regards,
> -glenn
> On 04/08/10 13:48, Abu Abdulla alhanbali wrote:
>> this is not what i mean. if the primary servers is down, how long
>> it take the secondary server to start assigning the IPs that are
>> reserved for the primary server. you can do this manually using the
>> omshell but i don't know if this will be done automatically or not.
>> On Wed, Apr 7, 2010 at 7:55 PM, Banana Flex<flex.banana at>
>> wrote:
>>> hi
>>> you can do a collaboration betwen two servers that send the same
>>> subnet, see the man page of dhcpd.conf for many information. you can
>>> also configure the timeout. 3 seconds is a good choice
>>> have fun
>>> Banana
>>> On Apr 7, 2010, at 5:41 AM, Abu Abdulla alhanbali wrote:
>>>> Hi,
>>>> i would like to know how long it will take the secondary DHCP
>>>> to start assigning IPs for all users (including the ranges
>>>> to the primary) in case the primary DHCP is down? is it a
>>>> configurable?
>>>> i would like also to ask if the DHCP can handle 200K users or above
>>>> assuming the H/W is capable and the lease time is big enough (more
>>>> than one week). is it recommended to run multiple instances or let
>>>> instance handle this number.
>>>> thanks
> _______________________________________________
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> dhcp-users at

Glenn Satchell                            |  Miss 9: What do you
Uniq Advances Pty Ltd, Sydney Australia   |  do at work Dad?
mailto:glenn.satchell at         |  Miss 6: He just tel:0409-458-580   |  types random stuff.

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