DHCP Failover cluster uses MCLT value as lease time

[Gordon Grubert]

Hi,

thx a lot to all for detailed explanations.

Best regards,
Gordon


On 16.02.2015 11:58, Glenn Satchell wrote:
> It's exactly as designed. The server hands out that initial lease without
> contacting the partner for performance reasons. This is from the
> dhcpd.conf man page:
>
> The mclt statement
>
>         mclt seconds;
>
>         The mclt statement defines the Maximum Client  Lead  Time.
>         It must be specified on the primary, and may not be speci-
>         fied on the secondary.  This is the  length  of  time  for
>         which  a  lease  may  be  renewed  by either failover peer
>         without contacting the other.
>
> The draft-ietf-dhc-failover document goes into great detail describing how
> failover works, how lease times are managed, and why this is done. It's
> not included with the current ISC distribution, but can be easily
> downloaded separately from sites such as
> https://tools.ietf.org/html/draft-ietf-dhc-failover-12
>
> The dhcpd man page also has information on failover.
>
> regards,
> -glenn
> --
> Glenn Satchell                                       |  Today is the past
> Uniq Advances Pty Ltd        http://www.uniq.com.au  |  that people in
> Mobile 0409 458 580                                  |  the future will
> Member System Admin Guild http://www.sage-au.org.au  |  dream about.
>
>
> On Mon, February 16, 2015 8:19 pm, Gordon Grubert wrote:
>> Hello,
>>
>> we are using a common dhcp failover cluster like described on
>>
>> https://kb.isc.org/article/AA-00502/0/A-Basic-Guide-to-Configuring-DHCP-Failover.html
>>
>> on debian 7 and an ldap-based storage backend (dhcp server version
>> 4.2.2).
>>
>> We have configured a global lease time of 24h but our clients will got
>> a lease time of 30 minutes. Then, we traced the connection on the
>> client and the server side. We found, that both the servers send DHCP
>> OFFER packages where the lease time value is set with the MCLT value of
>> the failover cluster. We could reproduces this by setting arbitrary
>> MCLT values.
>>
>> Sending DHCP RENEW requests one after another, the server beginns to
>> send the correct lease time of 24h. But every time, when the client
>> send the initial DISCOVER, he gets a lease time which is the MCLT value
>> of the cluster.
>>
>> Is this is bug or a feature?
>>
>>
>> Here, the basic part of our configuration
>> =========================================
>>
>> Primary
>> *******
>>
>> authoritative;
>> max-lease-time 86400;
>> default-lease-time 86400;
>> failover peer "dhcp-failover" {
>>       primary;
>>       address IP-PRI;
>>       port 519;
>>       peer address IP-SEC;
>>       peer port 520;
>>       max-response-delay 30;
>>       max-unacked-updates 10;
>>       load balance max seconds 3;
>>       mclt 1800;
>>       split 128;
>> }
>> subnet x.y.z.0 netmask 255.255.255.0 {
>>       option subnet-mask 255.255.255.0;
>>       option domain-name "DOMAINNAME";
>>       option routers x.y.z.1;
>>       option broadcast-address x.y.z.255;
>>       pool {
>>           range x.y.z.50 x.y.z.109;
>>           deny dynamic bootp clients;
>>           failover peer "dhcp-failover";
>>       }
>> }
>>
>>
>> Secondary
>> *********
>>
>> authoritative;
>> max-lease-time 86400;
>> default-lease-time 86400;
>> failover peer "dhcp-failover" {
>>       secondary;
>>       address IP-SEC;
>>       port 520;
>>       peer address IP-PRI;
>>       peer port 519;
>>       max-response-delay 30;
>>       max-unacked-updates 10;
>>       load balance max seconds 3;
>> }
>> subnet x.y.z.0 netmask 255.255.255.0 {
>>       option subnet-mask 255.255.255.0;
>>       option domain-name "DOMAINNAME";
>>       option routers x.y.z.1;
>>       option broadcast-address x.y.z.255;
>>       pool {
>>           range x.y.z.50 x.y.z.109;
>>           deny dynamic bootp clients;
>>           failover peer "dhcp-failover";
>>       }
>> }
>>
>> Best regards,
>> Gordon
>> _______________________________________________
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>> dhcp-users at lists.isc.org
>> https://lists.isc.org/mailman/listinfo/dhcp-users
>>
>
>
>
>
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