DHCPD issue parameters

Wed Apr 18 00:11:44 UTC 2012

The version of DHCP i'm using is isc-dhcpd-V3.0.5-RedHat.

I'm not able to confirm if it works with the last version of dhcpd, I will
test it and see how it works.

In the meantime if everyone has some idea about it, don't hesitate.

-----Message d'origine-----
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Envoyé : mardi 17 avril 2012 02:00
À : dhcp-users at lists.isc.org
Objet : dhcp-users Digest, Vol 42, Issue 18

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Today's Topics:

   1. Re: DHCPD issue parameters (Cathy Almond)
   2. Re: DHCP Failover and dhcpd.leases (Glenn Satchell)
   3. Re: DHCPD issue parameters  (Teva AVRIL-TEIPOARII)

----------------------------------------------------------------------

Message: 1
Date: Mon, 16 Apr 2012 13:57:54 +0100
From: Cathy Almond <cathya at isc.org>
To: dhcp-users at lists.isc.org
Subject: Re: DHCPD issue parameters
Message-ID: <4F8C1752.1030906 at isc.org>
Content-Type: text/plain; charset=ISO-8859-1

On 14/04/12 13:32, Harald Sch?ner wrote:
> This is a misbehavior of the DHCP client, as it doesn't look at the
changed
> options during
> a renew of its lease.
> 
> This has been observed with many dhcp clients, even the isc one.

Hi Harald,

We're not aware of this misbehaviour occurring with the ISC DHCP client
- it observes the updated domain-name-servers in our tests.  What
version were you using when you encountered this?

Are you able to confirm that this doesn't work properly with a current
production version of DHCP client?  If so, we'd very much appreciate a
bug report with configuration files and other supporting information
(resulting client /etc/resolv.conf, wireshark tracing etc..)

Many thanks

Cathy

> On 13 April 2012 23:25, Teva AVRIL-TEIPOARII <teva at viti.pf> wrote:
> 
>>
>> Greetings,
>>
>> I've got a dhcpd server, which is working good. However i've got an
issue:
>> i've modified one parameter on the dhcpd.conf for one subnet (i've
changed
>> option domain-name-servers ip), i've restarted the dhcpd service.
>>
>> My issue is i've got an ip address, but not the update DNS-servers.
>>
>> Here below configuration of the dhcpd.conf before modification:
>>
>> shared-network test {
>> option domain-name "test.com";
>> option domain-name-servers 192.168.1.2, 192.168.1.3;
>> default-lease-time 360;
>> max-lease-time 360;
>>
>> subnet 192.168.10.0 netmask 255.255.255.0 {
>> option routers 192.168.10.254;
>> option subnet-mask 255.255.255.0;
>> option broadcast-address 192.168.10.255;
>> }
>>
>> pool {
>> range 192.168.10.1 192.168.10.253;
>> }
>> }
>>
>> And now after modification:
>>
>> shared-network test {
>> option domain-name "test.com";
>> option domain-name-servers 192.168.45.1, 192.168.1.3;
>> default-lease-time 360;
>> max-lease-time 360;
>>
>> subnet 192.168.10.0 netmask 255.255.255.0 {
>> option routers 192.168.10.254;
>> option subnet-mask 255.255.255.0;
>> option broadcast-address 192.168.10.255;
>> }
>>
>> pool {
>> range 192.168.10.1 192.168.10.253;
>> }
>> }
>>
>> And here below global parameters applied to all subnets:
>>
>>
>> ddns-update-style none;
>> authoritative;
>> log-facility local7;
>> update-static-leases on;
>>
>>
>>
>>
>> The result is that instead of having 192.168.45.1 and 192.168.1.3 as
>> primary
>> and secondary DNS, i still got 192.168.1.2 and 192.168.1.3 as primary and
>> secondary DNS.
>>
>> I've deleted dhcpd.leases , thinking that maybe the issue could come from
>> some leases not expired, but result is the same.
>>
>> I've performed a wireshark capture, and during the DORA process, i see
that
>> the DHCP server is sending the update DNS as it should. However on my PC
>> (on
>> Windows), i still see old DNS servers attributed (attribution is
automatic,
>> it's not in static on network configuration of the PC).
>>
>> I don't understand where this problem come from, if you have an idea,
>> please
>> let me know.
>>
>>
>>
>> _______________________________________________
>> dhcp-users mailing list
>> dhcp-users at lists.isc.org
>> https://lists.isc.org/mailman/listinfo/dhcp-users
>>
> 
> 
> 
> _______________________________________________
> dhcp-users mailing list
> dhcp-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users

------------------------------

Message: 2
Date: Tue, 17 Apr 2012 00:23:16 +1000
From: Glenn Satchell <glenn.satchell at uniq.com.au>
To: Users of ISC DHCP <dhcp-users at lists.isc.org>
Subject: Re: DHCP Failover and dhcpd.leases
Message-ID: <4F8C2B54.2030908 at uniq.com.au>
Content-Type: text/plain; charset=windows-1252; format=flowed

On 04/16/12 16:29, "K?ppers, Malte" wrote:
> Hi there and thanks a lot for your replies!
>
> There are just some questions left:
>
> -I guess thats ok then, so I can safely enable failover mode without
> losing leases?!

Yes.

> -How long does it take until the leases files are synchronized and equal
> on both servers? Until next update is pushed ?

As quickly as the leases can be copied over the network. FOr a small 
lease file it could be a few 10s of seconds, a large (few MB) might take 
a couple of minutes.

> -Will I have to start the second server with a copy of the leases file?
> Or does a blank file work fine? Because while testing, I ran into the
> problem that if I wiped the leases files on both sides the
> both server got stuck in some ?waiting for update? state an neither
> primary nor secondary was handing out leases anymore. How can I wipe out
> the files safely if needed?

No. Start existing server with existing lease file. Start new server 
with empty lease file. New server will request a lease update from the 
other server.

This is covered in the section titled FAILOVER STARTUP in the dhcpd.conf 
man page.

If you wipe the lease files on both sides then both servers go into a 
state where they will wait before issuing new leases. Generally this is 
a bad thing to do, so you shouldn't wipe both lease files in production. 
Even though the servers have no concept of any leases after wiping the 
lease files, all the clients *do* have leases, but the servers are now 
out of synch with the clients, so the servers wait for the current 
leases to expire before handing out new leases. If the two systems get 
out of synch with each other (network error where they can't communicate 
for example) you can pick one system with the "best" lease file, and 
wipe out the other one, but really it's best to avoid that and let the 
systems heal themselves.

It's best to arrange for syslog from your dhcp servers to go to the same 
host so you can see messages from both together.

The other thing you'll see which may seem odd is initially a new client 
will get a lease that is half of the MCLT setting. Next time it renews 
it will get the full lease time.

regards,
-glenn

> Thanks in advance
>
> Regards
>
> Malte
>
>
>
> _______________________________________________
> dhcp-users mailing list
> dhcp-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users

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

------------------------------

Message: 3
Date: Mon, 16 Apr 2012 11:25:33 -1000
From: "Teva AVRIL-TEIPOARII" <teva at viti.pf>
To: <dhcp-users at lists.isc.org>
Subject: Re: DHCPD issue parameters 
Message-ID: <037301cd1c17$750ffce0$5f2ff6a0$@pf>
Content-Type: text/plain;	charset="us-ascii"

Hi,

What could be done so the DHCP client would look at the changed options
during a renew of its lease ?

It really seems something like this indeed:After 2 days off, i'm trying
again, and then DNS parameters has been updated, but now client has
192.168.45.1 as primary AND secondary DNS servers, instead of 192.168.45.1
and 192.168.1.3.

I've tested different computers, and result is the same for all of them now:
every client get 192.168.45.1 as DNS servers as primary and secondary.

I could understand that one client could misbehave DHCP Offer from the DHCP
server, however when all clients has the same behavior... Really weird...

If anyone has an idea, i'd be glad to read it.

Regards,

----------------------------------------------------------------------

Message: 1
Date: Sat, 14 Apr 2012 14:32:55 +0200
From: Harald Sch?ner <harald.schoener at mygate.net>
To: Users of ISC DHCP <dhcp-users at lists.isc.org>
Subject: Re: DHCPD issue parameters
Message-ID:
	<CAKd10K-Fj_M=2JQx1KY2+o6MDR63G-OjR92f5L8DktX1z0mJFQ at mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"

This is a misbehavior of the DHCP client, as it doesn't look at the changed
options during a renew of its lease.

This has been observed with many dhcp clients, even the isc one.

On 13 April 2012 23:25, Teva AVRIL-TEIPOARII <teva at viti.pf> wrote:

>
> Greetings,
>
> I've got a dhcpd server, which is working good. However i've got an issue:
> i've modified one parameter on the dhcpd.conf for one subnet (i've 
> changed option domain-name-servers ip), i've restarted the dhcpd service.
>
> My issue is i've got an ip address, but not the update DNS-servers.
>
> Here below configuration of the dhcpd.conf before modification:
>
> shared-network test {
> option domain-name "test.com";
> option domain-name-servers 192.168.1.2, 192.168.1.3; 
> default-lease-time 360; max-lease-time 360;
>
> subnet 192.168.10.0 netmask 255.255.255.0 { option routers 
> 192.168.10.254; option subnet-mask 255.255.255.0; option 
> broadcast-address 192.168.10.255; }
>
> pool {
> range 192.168.10.1 192.168.10.253;
> }
> }
>
> And now after modification:
>
> shared-network test {
> option domain-name "test.com";
> option domain-name-servers 192.168.45.1, 192.168.1.3; 
> default-lease-time 360; max-lease-time 360;
>
> subnet 192.168.10.0 netmask 255.255.255.0 { option routers 
> 192.168.10.254; option subnet-mask 255.255.255.0; option 
> broadcast-address 192.168.10.255; }
>
> pool {
> range 192.168.10.1 192.168.10.253;
> }
> }
>
> And here below global parameters applied to all subnets:
>
>
> ddns-update-style none;
> authoritative;
> log-facility local7;
> update-static-leases on;
>
>
>
>
> The result is that instead of having 192.168.45.1 and 192.168.1.3 as 
> primary and secondary DNS, i still got 192.168.1.2 and 192.168.1.3 as 
> primary and secondary DNS.
>
> I've deleted dhcpd.leases , thinking that maybe the issue could come 
> from some leases not expired, but result is the same.
>
> I've performed a wireshark capture, and during the DORA process, i see 
> that the DHCP server is sending the update DNS as it should. However 
> on my PC (on Windows), i still see old DNS servers attributed 
> (attribution is automatic, it's not in static on network configuration 
> of the PC).
>
> I don't understand where this problem come from, if you have an idea, 
> please let me know.
>
>
>
> _______________________________________________
> dhcp-users mailing list
> dhcp-users at lists.isc.org
> https://lists.isc.org/mailman/listinfo/dhcp-users
>

------------------------------

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