Partner Down State
Gregory Sloop
gregs at sloop.net
Fri Nov 28 23:58:05 UTC 2014
Hi Greg
Thanks for your reply.
I am operating "Internet Systems Consortium DHCP Server 4.2.1-P1".
How can I use the features that you have mentioned in your reply ? Also regarding the second option what exactly do you mean by "lease rewind" ?
Regards,
Waqas Asghar
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Today's Topics:
1. Partner Down State (Waqas Asghar)
2. Re: Partner Down State (Gregory Sloop)
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Message: 1
Date: Fri, 28 Nov 2014 02:36:36 -0500
From: Waqas Asghar <waqas.asghar at aol.com>
To: dhcp-users at lists.isc.org
Subject: Partner Down State
Message-ID: <8D1D8F52CC643F5-7B8-28932 at webmail-vd010.sysops.aol.com>
Content-Type: text/plain; charset="us-ascii"
Hi
I am operating two ISC DHCP servers as active/backup.
However during an outage I would like to operate the backup server in "partner
down" state so that it can utilize all the IP's.Any suggestion how can I
manually place the backup server in partner down state.I have checked there is a
script that can be used but that's not working for me will appreciate it someone
can help me out here.
Regards,
Waqas Asghar
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Message: 2
Date: Thu, 27 Nov 2014 23:46:54 -0800
From: Gregory Sloop <gregs at sloop.net>
To: Users of ISC DHCP <dhcp-users at lists.isc.org>
Subject: Re: Partner Down State
Message-ID: <1386419988.20141127234654 at sloop.net>
Content-Type: text/plain; charset="iso-8859-15"
Hi
I am operating two ISC DHCP servers as active/backup.
However during an outage I would like to operate the backup server in "partner
down" state so that it can utilize all the IP's.Any suggestion how can I
manually place the backup server in partner down state.I have checked there is a
script that can be used but that's not working for me will appreciate it someone
can help me out here.
Regards,
Waqas Asghar
There's a new option in, IIRC, 4.2.0+ "auto partner down" that should do what
you want.
However, be *very* careful with it. There are reasons that the partners might
not be able to reach each other, and thus not really be down - and both servers
will then assume they have the whole IP block to lease from and will be issuing
duplicate leases all over the place. As you can imagine, this would be a very
bad(tm) situation. So, use it carefully and consider things carefully.
There's also another option that is also in 4.2.0+ that will allow the remaining
partner to "rewind" leases issued by the partner and "re-lease" them - thus
giving the remaining partner a lot more endurance. It's also a lot safer than
the "auto partner down" directive.
From the release notes for 4.2.0a1
---
- An optimization described in the failover protocol draft is now included,
which permits a DHCP server operating in communications-interrupted state
to 'rewind' a lease to the state most recently transmitted to its peer,
greatly increasing a server's endurance in communications-interrupted.
This is supported using a new 'rewind state' record on the dhcpd.leases
entry for each lease.
---
HTH
-Greg
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Best I can say, is read the docs.
See here:
https://kb.isc.org/article/AA-00333
...and the man page.
---
This is from a search on the web from the man page for ISC's dhcp server.
---
The auto-partner-down statement
auto-partner-down seconds;
This statement instructs the server to initiate a timed delay upon
entering the communications-interrupted state (any situation of being
out-of-contact with the remote failover peer). At the conclusion of
the timer, the server will automatically enter the partner-down
state. This permits the server to allocate leases from the partner's
free lease pool after an STOS+MCLT timer expires, which can be dan-
gerous if the partner is in fact operating at the time (the two
servers will give conflicting bindings).
Think very carefully before enabling this feature. The partner-down
and communications-interrupted states are intentionally segregated
because there do exist situations where a failover server can fail to
communicate with its peer, but still has the ability to receive and
reply to requests from DHCP clients. In general, this feature should
only be used in those deployments where the failover servers are
directly connected to one another, such as by a dedicated hardwired
link ("a heartbeat cable").
A zero value disables the auto-partner-down feature (also the
default), and any positive value indicates the time in seconds to
wait before automatically entering partner-down.
---
But really, I think you can dig from there - "man dhcpd" from a command prompt should not be too taxing, IMO.
If you know enough to setup a fail-over partner, you really should know enough to give a look at the man page, or even do a few google searches. [It's frustrating to feel like you're asking me to regurgitate a man page, or generate a full config file for you, when, as far as I can tell, you've not even attempted the same. If you'd tried and were unable to get it working, perhaps I'd feel different - though how you could fail in simply inserting something like "auto-partner-down 60" in your config, for example, is beyond me.]
Also, as I re-read your initial post; a follow-up. You can use OMAPI to put the remaining server in partner down mode, manually.
Here's a start: https://www.google.com/search?q=dhcpd+omapi+partner+down+mode
[However, the options I outlined may be more suitable. Inevitably, when one of the partners goes down, you'll be far from somewhere you can manually put one in partner-down mode and things will start to go wrong - so look at the docs and see what makes the most sense for your application.]
Lastly, I'm not sure what platform you're on, but it seems to me that something newer than 4.2.1 might be advisable. [But perhaps that's what supported by your distro.]
-Greg
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