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The following patch (now with fancy configuration options) modifies dhcp.c so, that once a pool reaches “adaptive-lease-time-threshold %” active leases, the server hands out only short min_lease_time leases - until the allocation drop down under the threshold, when it reverts back to default_lease_time.
Update: As of ISC DHCPD 3.0.6 this patch is now part of the main distribution.
diff -rc dhcp-3.0.3/includes/dhcpd.h dhcp-3.0.3-cc/includes/dhcpd.h *** dhcp-3.0.3/includes/dhcpd.h Sat Apr 30 01:10:57 2005 --- dhcp-3.0.3-cc/includes/dhcpd.h Tue Sep 13 13:42:24 2005 *************** *** 411,416 **** --- 411,418 ---- #define SV_LOG_FACILITY 44 #define SV_DO_FORWARD_UPDATES 45 #define SV_PING_TIMEOUT 46 + #define SV_ADAPTIVE_LEASE_TIME_THRESHOLD 47 + #define SV_UPDATE_CONFLICT_DETECTION 48 #if !defined (DEFAULT_PING_TIMEOUT) # define DEFAULT_PING_TIMEOUT 1 diff -rc dhcp-3.0.3/server/dhcp.c dhcp-3.0.3-cc/server/dhcp.c *** dhcp-3.0.3/server/dhcp.c Sat Apr 30 01:10:57 2005 --- dhcp-3.0.3-cc/server/dhcp.c Tue Sep 13 14:42:36 2005 *************** *** 1508,1513 **** --- 1508,1514 ---- int s1, s2; int val; int ignorep; + int poolfilled; /* If we're already acking this lease, don't do it again. */ if (lease -> state) *************** *** 2001,2006 **** --- 2002,2050 ---- } } + /* 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, + (struct client_state *)0, + packet -> options, + state -> options, + &lease -> scope, oc, MDL)) { + if (d1.len && d1.data [0] > 0 && d1.data [0] < 100) { + poolfilled = ((lease -> pool -> lease_count - + lease -> pool -> free_leases) * 100 ) / + lease -> pool -> lease_count; + log_info ("Adap-lease: %s%d, %s%d, %s%d, %s%d, %s%d", + "Total: ", lease -> pool -> lease_count, + "Free: ", lease -> pool -> free_leases, + "Ends: ", (int) (lease -> ends - cur_time), + "Fill: ",poolfilled, + "Threshold: ",d1.data [0]); + + if (poolfilled >= d1.data [0]) { + /* CC: if the client has a long lease already, + do not cut the running lease beyond what we + already committed. */ + if (lease -> ends - cur_time > min_lease_time) + min_lease_time = lease -> ends - cur_time; + if (lease_time > min_lease_time) { + log_info ("Pool over %s %s from %d to %d", + "threshold, reduce lease time for", + piaddr (lease -> ip_addr), + (int) lease_time, + (int) min_lease_time); + lease_time = min_lease_time; + } + } + } + data_string_forget (&d1, MDL); + } + if (lease_time < min_lease_time) { if (min_lease_time) lease_time = min_lease_time; diff -rc dhcp-3.0.3/server/dhcpd.conf.5 dhcp-3.0.3-cc/server/dhcpd.conf.5 *** dhcp-3.0.3/server/dhcpd.conf.5 Tue May 3 00:43:24 2005 --- dhcp-3.0.3-cc/server/dhcpd.conf.5 Tue Sep 13 14:24:36 2005 *************** *** 1629,1634 **** --- 1629,1653 ---- 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 lenght 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 diff -rc dhcp-3.0.3/server/stables.c dhcp-3.0.3-cc/server/stables.c *** dhcp-3.0.3/server/stables.c Thu Jun 10 19:59:58 2004 --- dhcp-3.0.3-cc/server/stables.c Tue Sep 13 11:42:49 2005 *************** *** 483,490 **** { "log-facility", "Nsyslog-facilities.", &server_universe, 44 }, { "do-forward-updates", "f", &server_universe, 45 }, { "ping-timeout", "T", &server_universe, 46 }, ! { "unknown-47", "X", &server_universe, 47 }, ! { "unknown-48", "X", &server_universe, 48 }, { "unknown-49", "X", &server_universe, 49 }, { "unknown-50", "X", &server_universe, 50 }, { "unknown-51", "X", &server_universe, 51 }, --- 483,490 ---- { "log-facility", "Nsyslog-facilities.", &server_universe, 44 }, { "do-forward-updates", "f", &server_universe, 45 }, { "ping-timeout", "T", &server_universe, 46 }, ! { "adaptive-lease-time-threshold", "B", &server_universe, 47 }, ! { "update-conflict-detection", "f", &server_universe, 48 }, { "unknown-49", "X", &server_universe, 49 }, { "unknown-50", "X", &server_universe, 50 }, { "unknown-51", "X", &server_universe, 51 },