critical FYI secondary in partner-down

Randall C Grimshaw rgrimsha at syr.edu
Tue Aug 7 19:36:36 UTC 2012


It seems like an unexpected behavior for a server to issue leases that the clients cannot digest regardless of the mclt.

Randall Grimshaw rgrimsha at syr.edu<mailto:rgrimsha at syr.edu>

________________________________
From: dhcp-users-bounces+rgrimsha=syr.edu at lists.isc.org [dhcp-users-bounces+rgrimsha=syr.edu at lists.isc.org] on behalf of perl-list [perl-list at network1.net]
Sent: Tuesday, August 07, 2012 3:12 PM
To: Users of ISC DHCP
Subject: Re: critical FYI secondary in partner-down

The mclt as set on the primary affects the lease length available to the secondary when the primary fails.

________________________________
From: "Randall C Grimshaw" <rgrimsha at syr.edu>
To: "Users of ISC DHCP" <dhcp-users at lists.isc.org>
Sent: Tuesday, August 7, 2012 3:10:12 PM
Subject: RE: critical FYI secondary in partner-down

Since this is the secondary, mclt should not be set... but I did test this as the documentation standard 3600 as a test with no change.

Randall Grimshaw rgrimsha at syr.edu<mailto:rgrimsha at syr.edu>

________________________________
From: dhcp-users-bounces+rgrimsha=syr.edu at lists.isc.org [dhcp-users-bounces+rgrimsha=syr.edu at lists.isc.org] on behalf of perl-list [perl-list at network1.net]
Sent: Tuesday, August 07, 2012 2:29 PM
To: Users of ISC DHCP
Subject: Re: critical FYI secondary in partner-down

what is your mclt set to?

failover peer "dhcp" {
        primary;
        address x.x.x.x;
        port N;
        peer address x.x.x.x;
        peer port N;
        mclt 990;
        split 128;
        max-response-delay 60;
        max-unacked-updates 10;
        load balance max seconds 5;
}

mclt is only set on the primary and determines the length of leases when in failover on the non-primary ... from the 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 specified 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 longer you set this, the longer it will take for the running server to recover IP addresses after moving into PARTNER-DOWN state.   The shorter you set it, the more load your servers will experience when  they  are  not  communicating.    A
          value of something like 3600 is probably reasonable, but again bear in mind that we have no real operational experience with this.
From: "Randall C Grimshaw" <rgrimsha at syr.edu>
To: dhcp-users at lists.isc.org
Sent: Tuesday, August 7, 2012 2:21:48 PM
Subject: critical FYI secondary in partner-down

Internet Systems Consortium DHCP Server 4.1.1-P1 as distributed by Red Hat Enterprise Linux Server release 6.3 (Santiago) and possibly other versions.

To my great surprise when I brought up my secondary in partner-down mode, all of the leases issued had a zero duration. This was quite disruptive - All of my windows machines with dynamic leases failed.

The work-around is to change the server to primary. (but it took a bit of work and dented reputation to determine this)

FYI  FYI  FYI

has anyone else seen this?

Randall Grimshaw rgrimsha at syr.edu
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