Send dhcp-users mailing list submissions to
dhcp-users@lists.isc.org
To subscribe or unsubscribe via the World Wide Web, visit
https://lists.isc.org/mailman/listinfo/dhcp-users
or, via email, send a message with subject or body 'help' to
dhcp-users-requ...@lists.isc.org
You can reach the person managing the list at
dhcp-users-ow...@lists.isc.org
When replying, please edit your Subject line so it is more specific
than "Re: Contents of dhcp-users digest..."
Today's Topics:
1. fixed-address within range (Thomas R)
2. Re: fixed-address within range (Chuck Anderson)
3. Shriking ranges that are already in use?? (project722)
4. Re: Shriking ranges that are already in use?? (Simon Hobson)
5. Re: Shriking ranges that are already in use?? (project722)
6. Re: Shriking ranges that are already in use?? (Simon Hobson)
----------------------------------------------------------------------
Message: 1
Date: Mon, 8 Jan 2018 10:13:03 -0700 (MST)
From: Thomas R <thomas.reifenr...@web.de>
To: dhcp-users@lists.isc.org
Subject: fixed-address within range
Message-ID: <1515431583621-0.p...@n4.nabble.com>
Content-Type: text/plain; charset=us-ascii
Hello,
I have about 35 fixed IP addresses in a subnet. But I don't want to
configure 35 different IP Ranges so that the fixed IP addresses are not in
the range. Is there an easier way to prevent the fixed IP addresses from
being assigned to other DHCP clients when they are not online?
The hosts must keep their fixed IP addresses. The addresses are spread
across the range.
I have read various statements. Some say that if the host is assigned a
fixed address, it will no longer be assigned by DHCP. The other statement is
that fixed IP addresses must not be within the range.
What's true?
In total I have about 800 fixed IP addresses in different subnets. Building
the right range for this is extremely complex.
With a Windows DHCP server, a fixed IP address may be in the range. There
must be a solution for the ISC DHCP server, right?
best regards,
Thomas
--
Sent from: http://isc-dhcp-users.2343191.n4.nabble.com/
------------------------------
Message: 2
Date: Mon, 8 Jan 2018 12:20:59 -0500
From: Chuck Anderson <c...@wpi.edu>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: fixed-address within range
Message-ID: <20180108172059.gl1...@angus.ind.wpi.edu>
Content-Type: text/plain; charset=us-ascii
The solution in ISC DHCP is to use Reserved Leases rather than Fixed Addresses.
https://lists.isc.org/pipermail/dhcp-users/2007-August/004396.html
On Mon, Jan 08, 2018 at 10:13:03AM -0700, Thomas R wrote:
> Hello,
>
> I have about 35 fixed IP addresses in a subnet. But I don't want to
> configure 35 different IP Ranges so that the fixed IP addresses are not in
> the range. Is there an easier way to prevent the fixed IP addresses from
> being assigned to other DHCP clients when they are not online?
> The hosts must keep their fixed IP addresses. The addresses are spread
> across the range.
>
> I have read various statements. Some say that if the host is assigned a
> fixed address, it will no longer be assigned by DHCP. The other statement is
> that fixed IP addresses must not be within the range.
>
> What's true?
>
> In total I have about 800 fixed IP addresses in different subnets. Building
> the right range for this is extremely complex.
>
> With a Windows DHCP server, a fixed IP address may be in the range. There
> must be a solution for the ISC DHCP server, right?
>
> best regards,
>
> Thomas
>
>
>
>
>
> --
> Sent from: http://isc-dhcp-users.2343191.n4.nabble.com/
> _______________________________________________
> dhcp-users mailing list
> dhcp-users@lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users
------------------------------
Message: 3
Date: Mon, 8 Jan 2018 11:25:48 -0600
From: project722 <project...@gmail.com>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Shriking ranges that are already in use??
Message-ID:
<CAPBQMZBuyuOUJBJu82=voejrppkvbfyud7awarhycc1uakp...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hey all,
We have a few scopes in DHCP that were made according to inaccurate
projections. Now we are being forced to shrink these ranges.
For instance, all of our /25's will need to become /27's. We have a
legitimate concern that the gateway for the new /27's may already/will
probably be leased out from the original /25.
What can we do to make this a smooth transition and are there any other
considerations that we need to be aware of?
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<https://lists.isc.org/pipermail/dhcp-users/attachments/20180108/823e4efa/attachment-0001.html>
------------------------------
Message: 4
Date: Mon, 8 Jan 2018 18:11:34 +0000
From: Simon Hobson <dh...@thehobsons.co.uk>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: Shriking ranges that are already in use??
Message-ID: <3f7f4360-73e9-42ee-bddc-a9a5818ef...@thehobsons.co.uk>
Content-Type: text/plain; charset=us-ascii
project722 <project...@gmail.com> wrote:
> We have a few scopes in DHCP that were made according to inaccurate
> projections. Now we are being forced to shrink these ranges.
>
> For instance, all of our /25's will need to become /27's. We have a
> legitimate concern that the gateway for the new /27's may already/will
> probably be leased out from the original /25.
>
> What can we do to make this a smooth transition and are there any other
> considerations that we need to be aware of?
First off, ignore the spaced that will be freed up by the shrinking (for now).
Then in advance, you will want to shorten your max lease time. If your max
lease time is (say) 14 days then you cannot guarantee any step is complete
until 14 days after you make the change. But if you shorten it, then you will
only have to wait out the full time once, and then it will be the shorter time
you have to wait. For long lease times, you can balance load/stability vs
convenience by a stepped reduction - eg reduce from 14 days to 7 days, wait 7
days, reduce to 3 days, wait 4 days, reduce to 1 day, wait 2 days. Now you will
have no leases valid for more than 1 day - you can go shorter if needed.
Make sure that all your routers will have an address in the shrunk ranges.
Eg, if you have used 172.16.0.0/25 and put the router at 172.16.1.254 then that
will not be within 172.16.0.0/27. But if you've used 172.16.0.1 then that will
be OK. If you need to change the router address, add the new one as a secondary
address and change the routers option in the DHCP config.
Also change any fixed addresses and all your ranges so that they will fit
within the new reduced size subnet.
Wait 1 day (or whatever time you have set) and now all your clients will have
suitable addresses and be using the right router address.
You can now change the subnet mask in the DHCP config and wait another day (or
time you set). After this, all the clients will be using the new shrunk subnet.
You can now remove the old address from the router (if it changed), and the
freed up space is now available to use.
------------------------------
Message: 5
Date: Mon, 8 Jan 2018 12:50:40 -0600
From: project722 <project...@gmail.com>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: Shriking ranges that are already in use??
Message-ID:
<CAPBQMZCYgkh3ya-zAZi7jrJnw=Do=__vCih4s=f=+umcbgs...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Thanks Simon for the very detailed write up. So, if I am understanding you
correctly, lets say we used 172.16.0.0/25 and set a router address of
172.16.0.1. Next we wanted to shrink that to 172.16.0.0/27. Will I need to
use a secondary router in the option router line in this case? I'm a bit
confused on this part. When would we need to actually use a secondary
router and what would the option line look like? Something like this:
option routers 172.16.0.1 172.16.0.2;
If we do this what determines which router address gets assigned to the
client? ( I'm assuming it can only have one)
On Mon, Jan 8, 2018 at 12:11 PM, Simon Hobson <dh...@thehobsons.co.uk>
wrote:
> project722 <project...@gmail.com> wrote:
>
> > We have a few scopes in DHCP that were made according to inaccurate
> projections. Now we are being forced to shrink these ranges.
> >
> > For instance, all of our /25's will need to become /27's. We have a
> legitimate concern that the gateway for the new /27's may already/will
> probably be leased out from the original /25.
> >
> > What can we do to make this a smooth transition and are there any other
> considerations that we need to be aware of?
>
> First off, ignore the spaced that will be freed up by the shrinking (for
> now).
>
>
> Then in advance, you will want to shorten your max lease time. If your max
> lease time is (say) 14 days then you cannot guarantee any step is complete
> until 14 days after you make the change. But if you shorten it, then you
> will only have to wait out the full time once, and then it will be the
> shorter time you have to wait. For long lease times, you can balance
> load/stability vs convenience by a stepped reduction - eg reduce from 14
> days to 7 days, wait 7 days, reduce to 3 days, wait 4 days, reduce to 1
> day, wait 2 days. Now you will have no leases valid for more than 1 day -
> you can go shorter if needed.
>
> Make sure that all your routers will have an address in the shrunk ranges.
> Eg, if you have used 172.16.0.0/25 and put the router at 172.16.1.254
> then that will not be within 172.16.0.0/27. But if you've used 172.16.0.1
> then that will be OK. If you need to change the router address, add the new
> one as a secondary address and change the routers option in the DHCP config.
>
> Also change any fixed addresses and all your ranges so that they will fit
> within the new reduced size subnet.
>
> Wait 1 day (or whatever time you have set) and now all your clients will
> have suitable addresses and be using the right router address.
>
> You can now change the subnet mask in the DHCP config and wait another day
> (or time you set). After this, all the clients will be using the new shrunk
> subnet.
>
> You can now remove the old address from the router (if it changed), and
> the freed up space is now available to use.
>
> _______________________________________________
> dhcp-users mailing list
> dhcp-users@lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<https://lists.isc.org/pipermail/dhcp-users/attachments/20180108/3e222971/attachment-0001.html>
------------------------------
Message: 6
Date: Mon, 8 Jan 2018 19:24:06 +0000
From: Simon Hobson <dh...@thehobsons.co.uk>
To: Users of ISC DHCP <dhcp-users@lists.isc.org>
Subject: Re: Shriking ranges that are already in use??
Message-ID: <60de81c0-53db-45ef-8622-25ec7a916...@thehobsons.co.uk>
Content-Type: text/plain; charset=us-ascii
On 8 Jan 2018, at 18:50, project722 <project...@gmail.com> wrote:
> Thanks Simon for the very detailed write up. So, if I am understanding you
> correctly, lets say we used 172.16.0.0/25 and set a router address of
> 172.16.0.1. Next we wanted to shrink that to 172.16.0.0/27. Will I need to
> use a secondary router in the option router line in this case?
No, because 172.16.0.1 is a valid address in the 172.16.0.0/27 subnet.
Had you used (say) 172.16.1.254 then that would NOT be valid in the
172.16.0.0/27 subnet - and so you'd need to change it. Since you can't "just
change it" without breaking clients for a while, it's best to add the new
address as a secondary address on the router* so that clients with old leases
will carry on working until they get new settings via DHCP.
* Ah, reading it over I see the confusion. It's not about adding a second
router address in the DHCP config, it's about adding it on the router itself.
On a Linux box something like :
> ip addr add 172.16.0.1/25 dev eth0
on a Cisco box something like :
> int gi0/0
> ip address 172.16.0.1 255.255.255.128 secondary
That way, clients still configured to use 172.16.1.254 will continue working,
when things get their new config then they'll switch to using 172.16.0.1. When
everything has been reconfigured, you can remove the 172.16.1.254 address from
the router and make 172.16.0.1 the primary (and probably, only) IPv4 address.
I did miss one step BTW - when all the clients have been reconfigured, the
router will need reconfiguring - if it originally had 172.16.0.1/25 then it
will need changing to 172.16.0.1/27.
Reconfiguring the network is never something you could call fun - I've done it
a couple of times :-( Assume that you'll have missed something - a device you
didn't realise was manually configured, a device configured to talk to a PC at
a particular address (common when third parties install things like access
control systems or multi-funcion copier/scanners), and so on.
Given the number of outfits I've come across who just still don't understand
IPv4 basics, I hate to think how they'll cope with IPv6 8-0
------------------------------
Subject: Digest Footer
_______________________________________________
dhcp-users mailing list
dhcp-users@lists.isc.org
https://lists.isc.org/mailman/listinfo/dhcp-users
------------------------------
End of dhcp-users Digest, Vol 111, Issue 8
******************************************
