Linux – ISC DHCP fails to sync leases between peers

I use ISC DHCP version 4.1.1 on Debian GNU/Linux on both servers.
I tried to solve the following problem using various versions of ISC DHCP but it remained the same.

My configuration for failover between two servers on different subnets is:

#-----------------------------------------------
# Primary Server
#-----------------------------------------------

authoritative;
default-lease-time 900;
max-lease-time 1800;         
option domain-name "foo.com";
option domain-name-servers 10.12.0.254;

failover peer "foo" {
    primary;
    address 10.12.0.254;
    port 647;
    peer address 10.10.10.12;
    peer port 647;
    max-response-delay 30;
    max-unacked-updates 10;
    load balance max seconds 3;
    mclt 1800;  
    split 128;
}

subnet 10.12.0.0 netmask 255.255.0.0 {
    pool {
        failover peer "foo";
        range 10.12.10.0 10.12.112.0;
        range 10.12.112.12 10.12.255.254;
        deny dynamic bootp clients;
    }
    option routers 10.12.0.254;
    option subnet-mask 255.255.0.0;
    option broadcast-address 10.12.255.255;
}

#-----------------------------------------------
# Secondary Server
#-----------------------------------------------

authoritative;
default-lease-time 900;
max-lease-time 1800;
option domain-name "foo.com";
option domain-name-servers 10.12.0.254;

failover peer "foo" {
        secondary;
        address 10.10.10.12;
        port 647;
        peer address 10.12.0.254;
        peer port 647;
        max-response-delay 30;
        max-unacked-updates 10;
        load balance max seconds 3;
}

subnet 10.12.0.0 netmask 255.255.0.0 {
        pool {
                failover peer "foo";
                range 10.12.10.0 10.12.112.0;
                range 10.12.112.12 10.12.255.254;
        deny dynamic bootp clients;
        }
    option routers 10.12.0.254;
    option subnet-mask 255.255.0.0;
    option broadcast-address 10.12.255.255;
}

subnet 10.10.10.0 netmask 255.255.255.240 {
}

IP helper (aka UDP helper) and DHCP relay is enabled on router that connects the network of the primary server with the network of the secondary server
I can ping and ssh from one server to the other and back.

When I start the dhcpd service on both servers they fail to balance their leases.

I paste a sample of the logs of both servers

Primary Server

Sep 19 10:31:11 primary dhcpd: failover peer foo: I move from recover to startup
Sep 19 10:31:11 primary dhcpd: failover peer foo: I move from startup to recover
Sep 19 10:31:11 primary dhcpd: Sent update request all message to foo
Sep 19 10:31:20 primary dhcpd: peer foo: disconnected
Sep 19 10:31:22 primary dhcpd: failover peer foo: peer moves from recover-done to recover-done
Sep 19 10:31:22 primary dhcpd: failover peer foo: peer moves from recover-done to recover-done
Sep 19 10:31:45 primary dhcpd: DHCPINFORM from 10.12.181.177 via eth1
Sep 19 10:31:45 primary dhcpd: DHCPACK to 10.12.181.177 (00:17:42:c0:e3:ce) via eth1
Sep 19 10:32:45 primary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c (PC1) via eth1: not responding (recovering)
Sep 19 10:32:46 primary dhcpd: DHCPINFORM from 10.12.181.177 via eth1
Sep 19 10:32:46 primary dhcpd: DHCPACK to 10.12.181.177 (00:17:42:c0:e3:ce) via eth1
Sep 19 10:32:49 primary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c (PC1) via eth1: not responding (recovering)
Sep 19 10:32:57 primary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c (PC1) via eth1: not responding (recovering)
Sep 19 10:33:13 primary dhcpd: DHCPDISCOVER from 00:19:99:95:41:99 (PC2) via eth1: not responding (recovering)
Sep 19 10:33:13 primary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c (PC1) via eth1: not responding (recovering)
Sep 19 10:33:17 primary dhcpd: DHCPDISCOVER from 00:19:99:95:41:99 (PC2) via eth1: not responding (recovering)
Sep 19 10:33:25 primary dhcpd: DHCPDISCOVER from 00:19:99:95:41:99 (PC2) via eth1: not responding (recovering)
Sep 19 10:33:41 primary dhcpd: DHCPDISCOVER from 00:19:99:95:41:99 (PC2) via eth1: not responding (recovering)

Secondary Server

Sep 19 10:31:11 secondary dhcpd: Update request all from foo: sending update
Sep 19 10:31:23 secondary dhcpd: Wrote 22 leases to leases file.
Sep 19 10:31:23 secondary dhcpd: failover peer foo: I move from recover-done to startup
Sep 19 10:31:23 secondary dhcpd: failover peer foo: I move from startup to recover-done
Sep 19 10:31:45 secondary dhcpd: DHCPINFORM from 10.12.181.177 via 10.12.0.1
Sep 19 10:31:45 secondary dhcpd: DHCPACK to 10.12.181.177 (00:17:42:c0:e3:ce) via eth0
Sep 19 10:32:45 secondary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c via 10.12.0.1: not responding (recover done)
Sep 19 10:32:46 secondary dhcpd: DHCPINFORM from 10.12.181.177 via 10.12.0.1
Sep 19 10:32:46 secondary dhcpd: DHCPACK to 10.12.181.177 (00:17:42:c0:e3:ce) via eth0
Sep 19 10:32:49 secondary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c via 10.12.0.1: not responding (recover done)
Sep 19 10:32:57 secondary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c via 10.12.0.1: not responding (recover done)
Sep 19 10:33:13 secondary dhcpd: DHCPDISCOVER from 00:19:99:95:41:99 via 10.12.0.1: not responding (recover done)
Sep 19 10:33:13 secondary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c via 10.12.0.1: not responding (recover done)
Sep 19 10:33:17 secondary dhcpd: DHCPDISCOVER from 00:19:99:95:41:99 via 10.12.0.1: not responding (recover done)
Sep 19 10:33:25 secondary dhcpd: DHCPDISCOVER from 00:19:99:95:41:99 via 10.12.0.1: not responding (recover done)
Sep 19 10:33:41 secondary dhcpd: DHCPDISCOVER from 00:19:99:95:41:99 via 10.12.0.1: not responding (recover done)
Sep 19 10:34:46 secondary dhcpd: DHCPDISCOVER from 00:1a:4b:45:3a:2f via 10.12.0.1: peer holds all free leases
Sep 19 10:34:51 secondary dhcpd: DHCPDISCOVER from 00:1a:4b:45:3a:2f via 10.12.0.1: peer holds all free leases
Sep 19 10:34:59 secondary dhcpd: DHCPDISCOVER from 00:1a:4b:45:3a:2f via 10.12.0.1: peer holds all free leases
Sep 19 10:35:16 secondary dhcpd: DHCPDISCOVER from 00:1a:4b:45:3a:2f via 10.12.0.1: peer holds all free leases
Sep 19 10:38:28 secondary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c via 10.12.0.1: not responding (recover done)
Sep 19 10:38:32 secondary dhcpd: DHCPDISCOVER from 00:16:d3:e5:3a:3c via 10.12.0.1: not responding (recover done)

I don't seem to have the load balance log lines so I don't think leases balancing is happening…

Sent update request all message to foo
Update request all from foo: sending update

Balancing process seems stuck on the two lines above

If I shut down the DHCPD daemon on one server the peer doesn't seem to take over even if it detects that other peer is down

How can I fix this problem?

Thank you in advance (and sorry for my bad English) 🙂