- A new dhcp server option 'adaptive-lease-time-threshold' has been added

which causes the server to substantially reduce lease-times if there are
  few (configured percentage) remaining leases.  Thanks to a patch submitted
  from Christof Chen. [ISC-Bugs #15409]

RELNOTES

@@ -162,6 +162,11 @@ and for prodding me into improving it.
   language.  Thanks to a patch written by Mattias Ronnblom, gotten to us
   via Robin Breathe.
 
+- A new dhcp server option 'adaptive-lease-time-threshold' has been added
+  which causes the server to substantially reduce lease-times if there are
+  few (configured percentage) remaining leases.  Thanks to a patch submitted
+  from Christof Chen.
+
 			Changes since 3.0.4
 
 - A warning that host statements declared within subnet or shared-network

includes/dhcpd.h

@@ -512,6 +512,7 @@ struct lease_state {
 #define SV_RESERVE_INFINITE		47
 #define SV_DDNS_CONFLICT_DETECT		48
 #define SV_LEASEQUERY			49
+#define SV_ADAPTIVE_LEASE_TIME_THRESHOLD	50
 
 #if !defined (DEFAULT_PING_TIMEOUT)
 # define DEFAULT_PING_TIMEOUT 1

server/dhcp.c

@@ -34,7 +34,7 @@
 
 #ifndef lint
 static char copyright[] =
-"$Id: dhcp.c,v 1.209 2006/07/25 13:26:00 shane Exp $ Copyright (c) 2004-2006 Internet Systems Consortium.  All rights reserved.\n";
+"$Id: dhcp.c,v 1.210 2006/07/31 23:17:24 dhankins Exp $ Copyright (c) 2004-2006 Internet Systems Consortium.  All rights reserved.\n";
 #endif /* not lint */
 
 #include "dhcpd.h"
@@ -2021,6 +2021,62 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
 			}
 		}
 
+		/* CC: If there are less than
+		   adaptive-lease-time-threshold % free leases,
+		     hand out only short term leases */
+
+		memset(&d1, 0, sizeof(d1));
+		if (lease->pool &&
+		    (oc = lookup_option(&server_universe, state->options,
+					SV_ADAPTIVE_LEASE_TIME_THRESHOLD)) &&
+		    evaluate_option_cache(&d1, packet, lease, NULL,
+					  packet->options, state->options,
+					  &lease->scope, oc, MDL)) {
+			if (d1.len == 1 && d1.data[0] > 0 &&
+			    d1.data[0] < 100) {
+				TIME adaptive_time;
+				int poolfilled, total, count;
+
+				if (min_lease_time)
+					adaptive_time = min_lease_time;
+				else
+					adaptive_time = DEFAULT_MIN_LEASE_TIME;
+
+				/* Allow the client to keep its lease. */
+				if (lease->ends - cur_time > adaptive_time)
+					adaptive_time = lease->ends - cur_time;
+
+				count = lease->pool->lease_count;
+				total = count - (lease->pool->free_leases +
+						 lease->pool->backup_leases);
+
+				poolfilled = (total > (INT_MAX / 100)) ?
+					     total / (count / 100) :
+					     (total * 100) / count;
+
+				log_debug("Adap-lease: Total: %d, Free: %d, "
+					  "Ends: %d, Adaptive: %d, Fill: %d, "
+					  "Threshold: %d",
+					  lease->pool->lease_count,
+					  lease->pool->free_leases,
+					  (int)(lease->ends - cur_time),
+					  (int)adaptive_time, poolfilled,
+					  d1.data[0]);
+
+				if (poolfilled >= d1.data[0] &&
+				    lease_time > adaptive_time) {
+					log_info("Pool over threshold, time "
+						 "for %s reduced from %d to "
+						 "%d.", piaddr(lease->ip_addr),
+						 (int)lease_time,
+						 (int)adaptive_time);
+
+					lease_time = adaptive_time;
+				}
+			}
+			data_string_forget(&d1, MDL);
+		}
+
 		if (lease_time < min_lease_time) {
 			if (min_lease_time)
 				lease_time = min_lease_time;

server/dhcpd.conf.5

@@ -28,7 +28,7 @@
 .\" see ``http://www.vix.com''.   To learn more about Nominum, Inc., see
 .\" ``http://www.nominum.com''.
 .\"
-.\" $Id: dhcpd.conf.5,v 1.78 2006/07/25 13:26:00 shane Exp $
+.\" $Id: dhcpd.conf.5,v 1.79 2006/07/31 23:17:24 dhankins Exp $
 .\"
 .TH dhcpd.conf 5
 .SH NAME
@@ -617,7 +617,7 @@ The
 statement
 .RS 0.25i
 .PP
-.B max-lease-misbalance \fIinteger\fR\fB;\fR
+.B max-lease-misbalance \fIpercentage\fR\fB;\fR
 .PP
 The \fBmax-lease-misbalance\fR statement tells the DHCP server what
 percentage of total free leases (as defined as the total number of
@@ -636,7 +636,7 @@ The
 statement
 .RS 0.25i
 .PP
-.B max-lease-ownership \fIinteger\fR\fB;\fR
+.B max-lease-ownership \fIpercentage\fR\fB;\fR
 .PP
 The \fBmax-lease-ownership\fR statement tells the DHCP server what
 percentage of total free leases either it or its peer are normally allowed to
@@ -1737,6 +1737,24 @@ force all clients that have been allocated addresses from this pool to
 obtain new addresses immediately when they next renew.
 .SH REFERENCE: PARAMETERS
 The
+.I adaptive-lease-time-threshold
+statement
+.RS 0.25i
+.PP
+.B adaptive-lease-time-threshold \fIpercentage\fR\fB;\fR
+.PP
+When the number of allocated leases within a pool rises above
+the \fIpercentage\fR given in this statement, the DHCP server decreases
+the lease length for new clients within this pool to \fImin-lease-time\fR
+seconds. Clients renewing an already valid (long) leases get at least the
+remaining time from the current lease. Since the leases expire faster,
+the server may either recover more quickly or avoid pool exhaustion
+entirely.  Once the number of allocated leases drop below the threshold,
+the server reverts back to normal lease times.  Valid percentages are
+between 1 and 99.
+.RE
+.PP
+The
 .I always-broadcast
 statement
 .RS 0.25i

server/stables.c

@@ -34,7 +34,7 @@
 
 #ifndef lint
 static char copyright[] =
-"$Id: stables.c,v 1.32 2006/07/19 17:14:55 dhankins Exp $ Copyright (c) 2004 Internet Systems Consortium.  All rights reserved.\n";
+"$Id: stables.c,v 1.33 2006/07/31 23:17:24 dhankins Exp $ Copyright (c) 2004 Internet Systems Consortium.  All rights reserved.\n";
 #endif /* not lint */
 
 #include "dhcpd.h"
@@ -234,6 +234,7 @@ static struct option server_options[] = {
 	{ "ping-timeout", "T",			&server_universe,  46, 1 },
 	{ "infinite-is-reserved", "f",		&server_universe,  47, 1 },
 	{ "update-conflict-detection", "f",	&server_universe,  48, 1 },
+	{ "adaptive-lease-time-threshold", "B",	&server_universe,  50, 1 },
 	{ NULL, NULL, NULL, 0, 0 }
 };