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Today's Topics:
1. Re: Maximum Time difference between DHCP primary and DHCP
failover Server (Simon Hobson)
2. Re: Maximum Time difference between DHCP primary and DHCP
failover Server (Thomas Markwalder)
3. Re: Maximum Time difference between DHCP primary and DHCP
failover Server (Thomas Markwalder)
4. Re: Maximum Time difference between DHCP primary and DHCP
failover Server (kraishak)
5. Re: Maximum Time difference between DHCP primary and DHCP
failover Server (kraishak)
6. Re: Maximum Time difference between DHCP primary and DHCP
failover Server (Thomas Markwalder)
----------------------------------------------------------------------
Message: 1
Date: Tue, 19 Jan 2021 12:52:21 +0000
From: Simon Hobson <dh...@thehobsons.co.uk>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: Maximum Time difference between DHCP primary and DHCP
failover Server
Message-ID: <534adbf3-fe2d-4eb6-b319-f814dd443...@thehobsons.co.uk>
Content-Type: text/plain; charset=us-ascii
kraishak <kraishak....@gmail.com> wrote:
> Actually I want add validation script so that for the given two
> server address it can calculate the time difference and give me the results
> for proceeding to add failover peer on not.
Fair enough - seems a reasonable check to do. But I have a suggestion for an
alternative approach ...
> Can you also please comment or share your experience if you have any, about
> what could be the maximum network latency between the primary and failover
> DHCP servers that does not impact the server performance
I've not actually used failover, it's just not been appropriate to my needs.
But given the answer you've been given of "anything within 60s is OK", I don't
think you should have a problem.
I would tackle the issue from a different direction.
Put measures in place so that you can assume all your servers are time-synced,
and have monitoring in place so you can see if any of them aren't. That way,
you can assume DHCP failover will work (or at least, time won't be a reason for
it to fail) as long as you don't have any alarms in place.
Obviously NTP is good for keeping everything in sync, that's a problem solved
decades ago !
At my last job, I used Nagios to monitor all sorts of stuff. One of the things
it can monitor is NTP status - raising alerts if the monitored server isn't
synced with a source, or (from memory) if it's time differs from a configured
source by more than a settable amount. Monitoring was something I made a big
thing as I'd gone into an environment where even basics like time sync weren't
being done, and monitoring was of the "phone rings because a customer sees a
problem" style !
So with NTP working you don't have a time problem. With a monitoring system in
place, you'll know if there's a problem with that working.
If your monitoring system has a green status page, time differences aren't a
consideration for your DHCP deployment.
Simon
------------------------------
Message: 2
Date: Tue, 19 Jan 2021 08:03:52 -0500
From: Thomas Markwalder <tm...@isc.org>
To: dhcp-users@lists.isc.org
Subject: Re: Maximum Time difference between DHCP primary and DHCP
failover Server
Message-ID: <9c1ca129-847b-c28e-3194-e051fd2c7...@isc.org>
Content-Type: text/plain; charset=utf-8; format=flowed
This is going to vary largely on site dynamics. The primary challenge to
failover performance, is that it is a synchronous protocol.? Servers are
supposed to wait until their peers acknowledge that a least update has
been received prior to sending the corresponding response (i.e. DHCPACK)
to the client.
In other words, this adds the round trip latency to the response time
for a given client's DHCPREQUEST.? If DHCPREQUESTs are coming in too
fast, the server will fall behind and clients will stop getting
responses. If you need as sustained 10 DORAs a second, then 250ms
round-trip latency between the peers is going to be a deal breaker.
I'm sure others on this list will have plenty to share on the subject.
On 1/19/21 6:38 AM, kraishak wrote:
> Hi Thomas,
>
> Thanks for sharing information, Can you also please comment or share your
> experience if you have any, about what could be the maximum network latency
> between the primary and failover DHCP servers that does not impact the
> server performance
>
> Thanks in advance
> Kraishak
>
>
>
> --
> Sent from: http://isc-dhcp-users.2343191.n4.nabble.com/
> _______________________________________________
> ISC funds the development of this software with paid support subscriptions.
> Contact us at https://www.isc.org/contact/ for more information.
>
> dhcp-users mailing list
> dhcp-users@lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users
------------------------------
Message: 3
Date: Tue, 19 Jan 2021 08:05:38 -0500
From: Thomas Markwalder <tm...@isc.org>
To: dhcp-users@lists.isc.org
Subject: Re: Maximum Time difference between DHCP primary and DHCP
failover Server
Message-ID: <c1456760-0150-f18a-9158-89174463b...@isc.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Excuse the typo "least update" should be "lease update"
On 1/19/21 8:03 AM, Thomas Markwalder wrote:
> This is going to vary largely on site dynamics. The primary challenge
> to failover performance, is that it is a synchronous protocol. Servers
> are supposed to wait until their peers acknowledge that a least update
> has been received prior to sending the corresponding response (i.e.
> DHCPACK) to the client.
>
> In other words, this adds the round trip latency to the response time
> for a given client's DHCPREQUEST.? If DHCPREQUESTs are coming in too
> fast, the server will fall behind and clients will stop getting
> responses. If you need as sustained 10 DORAs a second, then 250ms
> round-trip latency between the peers is going to be a deal breaker.
>
> I'm sure others on this list will have plenty to share on the subject.
>
>
> On 1/19/21 6:38 AM, kraishak wrote:
>> Hi Thomas,
>>
>> Thanks for sharing information, Can you also please comment or share
>> your
>> experience if you have any, about what could be the maximum network
>> latency
>> between the primary and failover DHCP servers that does not impact the
>> server performance
>>
>> Thanks in advance
>> Kraishak
>>
>>
>>
>> --
>> Sent from: http://isc-dhcp-users.2343191.n4.nabble.com/
>> _______________________________________________
>> ISC funds the development of this software with paid support
>> subscriptions. Contact us at https://www.isc.org/contact/ for more
>> information.
>>
>> dhcp-users mailing list
>> dhcp-users@lists.isc.org
>> https://lists.isc.org/mailman/listinfo/dhcp-users
>
> _______________________________________________
> ISC funds the development of this software with paid support
> subscriptions. Contact us at https://www.isc.org/contact/ for more
> information.
>
> dhcp-users mailing list
> dhcp-users@lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users
------------------------------
Message: 4
Date: Tue, 19 Jan 2021 07:22:46 -0600 (CST)
From: kraishak <kraishak....@gmail.com>
To: dhcp-users@lists.isc.org
Subject: Re: Maximum Time difference between DHCP primary and DHCP
failover Server
Message-ID: <1611062566626-0.p...@n4.nabble.com>
Content-Type: text/plain; charset=us-ascii
Hi Simon,
Thanks for the information and suggested tools for monitoring the NTP
-Kraishak
--
Sent from: http://isc-dhcp-users.2343191.n4.nabble.com/
------------------------------
Message: 5
Date: Tue, 19 Jan 2021 07:38:34 -0600 (CST)
From: kraishak <kraishak....@gmail.com>
To: dhcp-users@lists.isc.org
Subject: Re: Maximum Time difference between DHCP primary and DHCP
failover Server
Message-ID: <1611063514753-0.p...@n4.nabble.com>
Content-Type: text/plain; charset=us-ascii
Hi Thomas,
The primary challenge to failover performance, is that it is a synchronous
protocol. Servers are
supposed to wait until their peers acknowledge that a least update has been
received prior to sending the corresponding response (i.e. DHCPACK)to the
client.
---> I have doubt about this topic, The dhcp failover protocol support lazy
update right?
server grants the leases for the client and updates the peer server after
client lease acknowledgment, This is how it can operate even if the peer
server is down, please correct if I am wrong
-Thanks
Kraishak
--
Sent from: http://isc-dhcp-users.2343191.n4.nabble.com/
------------------------------
Message: 6
Date: Tue, 19 Jan 2021 09:58:51 -0500
From: Thomas Markwalder <tm...@isc.org>
To: dhcp-users@lists.isc.org
Subject: Re: Maximum Time difference between DHCP primary and DHCP
failover Server
Message-ID: <a2108599-af4e-380f-7f1a-fb6bcefd8...@isc.org>
Content-Type: text/plain; charset=utf-8; format=flowed
Sorry, not enough coffee before answering emails, please disregard.
On 1/19/21 8:38 AM, kraishak wrote:
> Hi Thomas,
>
> The primary challenge to failover performance, is that it is a synchronous
> protocol. Servers are
> supposed to wait until their peers acknowledge that a least update has been
> received prior to sending the corresponding response (i.e. DHCPACK)to the
> client.
>
> ---> I have doubt about this topic, The dhcp failover protocol support lazy
> update right?
> server grants the leases for the client and updates the peer server after
> client lease acknowledgment, This is how it can operate even if the peer
> server is down, please correct if I am wrong
>
> -Thanks
> Kraishak
>
>
>
>
>
> --
> Sent from: http://isc-dhcp-users.2343191.n4.nabble.com/
> _______________________________________________
> ISC funds the development of this software with paid support subscriptions.
> Contact us at https://www.isc.org/contact/ for more information.
>
> dhcp-users mailing list
> dhcp-users@lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users
------------------------------
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