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Fw: Failover + non-expiring leases

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Alessandro Gherardi

Fw: Failover + non-expiring leases

Hi,

My goals are to configure dhcpd such that:

1. dhcpd dynamically assigns IP addresses to DHCP clients

2. When dhcpd assigns an IP address to a client it hasn't seen before, the lease never expires

3. For high-availability, dhcpd runs on 2 servers in a failover configuration.

I set both default-lease-time and max-lease-time to -1 (full dhcpd.conf's are below). My problem is that dhcpd never doles out a non-expiring lease. My expectation was that the very lease from the client would expire after MCLT, but the following leases would have never expire. Here's a reference:

https://lists.isc.org/pipermail/dhcp-users/2015-February/018577.html:

DHCP Failover cluster uses MCLT value as lease time
>> Is this is bug or a feature?
It's how the DHCP Failover protocol works, it gives out an MCLT lease
the first time a client gets a lease from the failover pair, that then
allows the peers to sync their leases databases in the background and
when the client renews it will get it's full 24h lease.

Here's dhcpd.conf on the primary:

ddns-update-style none;
default-lease-time -1;
max-lease-time -1;
authoritative;
log-facility local7;

#option ntp-servers 10.220.178.50,10.220.178.119;

failover peer "dhcp-failover" {
        primary;
        address 192.168.56.2;
        port 647;
        peer address 192.168.56.3;
        peer port 648;
        max-response-delay 30;
        max-unacked-updates 10;
        load balance max seconds 3;
        mclt 120;
        split 128;
}

omapi-port 7911;
omapi-key omapi_key;

key omapi_key {
algorithm hmac-md5;
secret ...;
}

subnet 192.168.56.0 netmask 255.255.255.0 {
        option routers 192.168.56.1;
        option broadcast-address 192.168.56.255;
        pool {
                failover peer "dhcp-failover";
                range 192.168.56.10 192.168.56.254;
        }
        default-lease-time -1;
        max-lease-time -1;
}

Here's dhcpd.conf on the secondary:

ddns-update-style none;
default-lease-time -1;
max-lease-time -1;
authoritative;
log-facility local7;

#option ntp-servers 10.220.178.50,10.220.178.119;

failover peer "dhcp-failover" {
        secondary;
        address 192.168.56.3;
        port 648;
        peer address 192.168.56.2;
        peer port 647;
        max-response-delay 30;
        max-unacked-updates 10;
        load balance max seconds 3;
}

omapi-port 7911;
omapi-key omapi_key;

key omapi_key {
algorithm hmac-md5;
secret ...;
}

Here's a snippet from /var/lib/dhcp/dhcpd.leases on the primary:

failover peer "dhcp-failover" state {
my state normal at 4 2016/03/17 15:32:28;
partner state normal at 4 2016/03/17 15:32:25;
}

lease 192.168.56.132 {
starts 4 2016/03/17 16:03:03;
ends 4 2016/03/17 16:05:03;
tstp 0 2152/04/23 22:32:18;
tsfp 4 2016/03/17 16:04:02;
atsfp 4 2016/03/17 16:04:02;
cltt 4 2016/03/17 16:03:03;
binding state active;
next binding state expired;
hardware ethernet 08:00:27:5c:f4:e5;
client-hostname "dhcpclient";
}

Any suggestions?

Thank you in advance.

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Alessandro Gherardi

Failover + infinite leases

Hi,

I'm trying to configure dhcpd to dole out infinite leases + failover.

I set both default-lease-time and max-lease-time to -1 (full dhcpd.conf's are below). The problem is that dhcpd never doles out infinite leases. I understand that, because of the failover protocol, the very first leave expires after MCLT. However, when the client renews, the server should return an infinite lease.

I downloaded and built dhcp-4.3.3-P1, and added some log statements in dhcp.c to try and understand what's going on. Here's the modified code:

#if defined (FAILOVER_PROTOCOL)
                /* Okay, we know the lease duration.   Now check the
                   failover state, if any. */
                if (lease -> pool && lease -> pool -> failover_peer) {
                        TIME new_lease_time = lease_time;
                        dhcp_failover_state_t *peer =
                            lease -> pool -> failover_peer;

                        /* Copy previous lease failover ack-state. */
                        lt->tsfp = lease->tsfp;
                        lt->atsfp = lease->atsfp;

/* cltt set below */

/* Lease times less than MCLT are not a concern. */
if (lease_time > peer->mclt) {

log_info("==> lease_time %ld MCLT %ld cur_time %ld tsfp %ld",
(long int)lease_time, (long int)peer->mclt, (long int)cur_time, (long int)lt->tsfp);

                                /* Each server can only offer a lease time
                                 * that is either equal to MCLT (at least),
                                 * or up to TSFP+MCLT. Only if the desired
                                 * lease time falls within TSFP+MCLT, can
                                 * the server allow it.
                                 */
                                if (lt->tsfp <= cur_time) {

log_info("==> setting new_lease_time to MCLT %ld", (long int)peer->mclt);

                                        new_lease_time = peer->mclt;
                                }
                                else if ((cur_time + lease_time) > (lt->tsfp + peer->mclt)) {
                                        new_lease_time = (lt->tsfp - cur_time) + peer->mclt;

log_info("==> new_lease_time %ld", (long int)new_lease_time);

}
}

Here's the output of dhcpd on the primary when a new client subscribes. I deleted the dhcpd.leases file from both primary and secondary before starting dhcpd and client:

==> lease_time 4294967295 MCLT 120 cur_time 1458325225 tsfp 0
==> setting new_lease_time to MCLT 120
DHCPDISCOVER from 08:00:27:5c:f4:e5 via eth1
DHCPOFFER on 192.168.56.132 to 08:00:27:5c:f4:e5 (dhcpclient) via eth1
==> lease_time 4294967295 MCLT 120 cur_time 1458325226 tsfp 0
==> setting new_lease_time to MCLT 120
DHCPREQUEST for 192.168.56.132 (192.168.56.2) from 08:00:27:5c:f4:e5 (dhcpclient) via eth1
DHCPACK on 192.168.56.132 to 08:00:27:5c:f4:e5 (dhcpclient) via eth1

==> lease_time 4294967295 MCLT 120 cur_time 1458325281 tsfp 1458325285
==> new_lease_time 124
DHCPREQUEST for 192.168.56.132 from 08:00:27:5c:f4:e5 (dhcpclient) via eth1
DHCPACK on 192.168.56.132 to 08:00:27:5c:f4:e5 (dhcpclient) via eth1

==> lease_time 4294967295 MCLT 120 cur_time 1458325332 tsfp 1458325342
==> new_lease_time 130
DHCPREQUEST for 192.168.56.132 from 08:00:27:5c:f4:e5 (dhcpclient) via eth1
DHCPACK on 192.168.56.132 to 08:00:27:5c:f4:e5 (dhcpclient) via eth1

I see this in the leases file:

lease 192.168.56.132 {
starts 5 2016/03/18 18:20:26;
ends 5 2016/03/18 18:22:26;
tstp 2 2152/04/25 00:49:41;
tsfp 5 2016/03/18 18:21:25;
atsfp 5 2016/03/18 18:21:25;
cltt 5 2016/03/18 18:20:26;
binding state active;
next binding state expired;
hardware ethernet 08:00:27:5c:f4:e5;
client-hostname "dhcpclient";
}

Since tstp is (basically) infinite but tsfp is always small, it appears that the secondary never acknowledges the infinite tsfp.

Any suggestions?

Thank you in advance.

dhcpd.conf on the primary:

ddns-update-style none;
default-lease-time -1;
max-lease-time -1;
authoritative;
log-facility local7;

omapi-port 7911;

Here's dhcpd.conf on the secondary:

ddns-update-style none;
default-lease-time -1;
max-lease-time -1;
authoritative;
log-facility local7;

omapi-port 7911;

Here's a snippet from /var/lib/dhcp/dhcpd.leases on the primary:

failover peer "dhcp-failover" state {
my state normal at 4 2016/03/17 15:32:28;
partner state normal at 4 2016/03/17 15:32:25;
}

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Alessandro Gherardi

Re: Failover + infinite leases

OK I found the issue. It's a bug in dhcpd, failover.c source file.

With reference to version 4.3.3-P1:

On line 5504, the pot_expire local variable is defined as a u_int32_t, which on my 64-bit Ubuntu is a 4-byte integer.

On line 5546, pot_expire is assigned lease->tstp, which is defined as a TIME, which is a time_t, which is an 8-byte integer.

This causes truncation and tsfp to NOT be set to the potential expiry time acknowledged by the partner.

To fix, define pot_expire as a TIME instead:

> diff dhcp-4.3.3-P1/server/failover.c ../dhcp-4.3.3-P1/server/failover.c
5504c5504
< u_int32_t pot_expire;
---
> TIME pot_expire;

From: Alessandro Gherardi <[hidden email]>
To: "[hidden email]" <[hidden email]>
Sent: Friday, March 18, 2016 12:41 PM
Subject: Failover + infinite leases

Hi,

I'm trying to configure dhcpd to dole out infinite leases + failover.

I downloaded and built dhcp-4.3.3-P1, and added some log statements in dhcp.c to try and understand what's going on. Here's the modified code:

                        /* Copy previous lease failover ack-state. */
                        lt->tsfp = lease->tsfp;
                        lt->atsfp = lease->atsfp;

/* cltt set below */

/* Lease times less than MCLT are not a concern. */
if (lease_time > peer->mclt) {

log_info("==> lease_time %ld MCLT %ld cur_time %ld tsfp %ld",
(long int)lease_time, (long int)peer->mclt, (long int)cur_time, (long int)lt->tsfp);

log_info("==> setting new_lease_time to MCLT %ld", (long int)peer->mclt);

log_info("==> new_lease_time %ld", (long int)new_lease_time);

}
}

Here's the output of dhcpd on the primary when a new client subscribes. I deleted the dhcpd.leases file from both primary and secondary before starting dhcpd and client:

I see this in the leases file:

Since tstp is (basically) infinite but tsfp is always small, it appears that the secondary never acknowledges the infinite tsfp.

Any suggestions?

Thank you in advance.

dhcpd.conf on the primary:

ddns-update-style none;
default-lease-time -1;
max-lease-time -1;
authoritative;
log-facility local7;

omapi-port 7911;

Here's dhcpd.conf on the secondary:

ddns-update-style none;
default-lease-time -1;
max-lease-time -1;
authoritative;
log-facility local7;

omapi-port 7911;

Here's a snippet from /var/lib/dhcp/dhcpd.leases on the primary:

failover peer "dhcp-failover" state {
my state normal at 4 2016/03/17 15:32:28;
partner state normal at 4 2016/03/17 15:32:25;
}

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dhcp-users mailing list
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