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[master] Enabling dhcp-cache-threshold no longer causes unnecessary DNS updates

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Merges in rt37368.
This commit is contained in:
Thomas Markwalder 2014-11-24 07:36:13 -05:00
parent d9b2a590e8
commit f3a44c1037
4 changed files with 153 additions and 48 deletions
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5
RELNOTES
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@ -159,6 +159,11 @@ by Eric Young (eay@cryptsoft.com).
and no other value is available.
[ISC-Bugs #21323]
- DNS updates were being attempted when dhcp-cache-threshold enabled the use of
the existing lease and the forward DNS name had not changed. This has been
corrected.
[ISC-Bugs #37368]
Changes since 4.3.1b1
- Modify the linux and openwrt dhclient scripts to process information

3
includes/dhcpd.h
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@ -592,6 +592,9 @@ struct lease {
* update if we want to do a different update.
*/
struct dhcp_ddns_cb *ddns_cb;
/* Set when a lease has been disqualified for cache-threshold reuse */
unsigned short cannot_reuse;
};
struct lease_state {

178
server/dhcp.c
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@ -34,6 +34,9 @@
static void commit_leases_ackout(void *foo);
static void maybe_return_agent_options(struct packet *packet,
struct option_state *options);
static int reuse_lease (struct packet* packet, struct lease* new_lease,
struct lease* lease, struct lease_state *state,
int offer);
int outstanding_pings;
@ -2318,8 +2321,13 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
if (packet -> classes [i] ==
lease -> billing_class)
break;
if (i == packet -> class_count)
if (i == packet -> class_count) {
unbill_class (lease, lease -> billing_class);
/* Active lease billing change negates reuse */
if (lease->binding_state == FTS_ACTIVE) {
lease->cannot_reuse = 1;
}
}
}
/* If we don't have an active billing, see if we need
@ -2367,6 +2375,11 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
lease->billing_class != NULL &&
lease->binding_state != FTS_ACTIVE)
unbill_class(lease, lease->billing_class);
/* Lease billing change negates reuse */
if (lease->billing_class != NULL) {
lease->cannot_reuse = 1;
}
}
}
@ -2824,9 +2837,9 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
DHO_VENDOR_CLASS_IDENTIFIER);
if (oc != NULL &&
evaluate_option_cache(&d1, packet, NULL, NULL, packet->options,
NULL, &lease->scope, oc, MDL)) {
NULL, &lt->scope, oc, MDL)) {
if (d1.len != 0) {
bind_ds_value(&lease->scope, "vendor-class-identifier",
bind_ds_value(&lt->scope, "vendor-class-identifier",
&d1);
}
@ -2935,51 +2948,12 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
sizeof packet -> raw -> chaddr); /* XXX */
} else {
int commit = (!offer || (offer == DHCPACK));
int thresh = DEFAULT_CACHE_THRESHOLD;
/*
* Check if the lease was issued recently, if so replay the
* current lease and do not require a database sync event.
* Recently is defined as being issued less than a given
* percentage of the lease previously. The percentage can be
* chosen either from a default value or via configuration.
*
*/
if ((oc = lookup_option(&server_universe, state->options,
SV_CACHE_THRESHOLD)) &&
evaluate_option_cache(&d1, packet, lt, NULL,
packet->options, state->options,
&lt->scope, oc, MDL)) {
if (d1.len == 1 && (d1.data[0] < 100))
thresh = d1.data[0];
data_string_forget(&d1, MDL);
}
/*
* We check on ddns_cb to see if the ddns code has
* updated the lt structure. We could probably simply
* copy the ddns_cb pointer in that case but lets be
* simple and safe and update the entire lease.
*/
if ((lt->ddns_cb == NULL) &&
(thresh > 0) && (offer == DHCPACK) &&
(lease->binding_state == FTS_ACTIVE)) {
int limit;
int prev_lease = lease->ends - lease->starts;
/* it is better to avoid division by 0 */
if (prev_lease <= (INT_MAX / thresh))
limit = prev_lease * thresh / 100;
else
limit = prev_lease / 100 * thresh;
if ((lt->starts - lease->starts) <= limit) {
lt->starts = lease->starts;
state->offered_expiry = lt->ends = lease->ends;
commit = 0;
use_old_lease = 1;
}
/* If dhcp-cache-threshold is enabled, see if "lease" can
* be reused. */
use_old_lease = reuse_lease(packet, lt, lease, state, offer);
if (use_old_lease == 1) {
commit = 0;
}
#if !defined(DELAYED_ACK)
@ -5162,3 +5136,113 @@ void use_host_decl_name(struct packet* packet,
}
}
}
/*!
* \brief Checks and preps for lease resuse based on dhcp-cache-threshold
*
* If dhcp-cache-threshold is enabled (i.e. greater than zero), this function
* determines if the current lease is young enough to be reused. If the lease
* can be resused the function returns 1, O if not. This function is called
* by ack_lease when responding to both DISCOVERs and REQUESTS.
*
* The current lease can be reused only if all of the following are true:
* a. dhcp-cache-threshold is > 0
* b. The current lease is active
* c. The lease "age" is less than that allowed by the threshold
* d. DNS updates are not being performed on the new lease.
* e. Lease has not been otherwise disqualified for reuse (Ex: billing class
* changed)
*
* Clients may renew leases using full DORA cycles or just RAs. This means
* that reusability must be checked when acking both DISCOVERs and REQUESTs.
* When a lease cannot be reused, ack_lease() calls supersede_lease() which
* updates the lease start time (among other things). If this occurs on the
* DISCOVER, then the lease will virtually always be seen as young enough to
* reuse on the ensuing REQUEST and the lease updates will not get committed
* to the lease file. The lease.cannot_reuse flag is used to handle this
* this situation.
*
* \param packet inbound packet received from the client
* \param new_lease candidate new lease to associate with the client
* \param lease current lease associated with the client
* \param options option state to search and update
*/
int
reuse_lease (struct packet* packet,
struct lease* new_lease,
struct lease* lease,
struct lease_state *state,
int offer) {
int reusable = 0;
/* To even consider reuse all of the following must be true:
* 1 - reuse hasn't already disqualified
* 2 - current lease is active
* 3 - DNS info hasn't changed */
if ((lease->cannot_reuse == 0) &&
(lease->binding_state == FTS_ACTIVE) &&
(new_lease->ddns_cb == NULL)) {
int thresh = DEFAULT_CACHE_THRESHOLD;
struct option_cache* oc = NULL;
struct data_string d1;
/* Look up threshold value */
memset(&d1, 0, sizeof(struct data_string));
if ((oc = lookup_option(&server_universe, state->options,
SV_CACHE_THRESHOLD)) &&
(evaluate_option_cache(&d1, packet, new_lease, NULL,
packet->options, state->options,
&new_lease->scope, oc, MDL))) {
if (d1.len == 1 && (d1.data[0] < 100))
thresh = d1.data[0];
data_string_forget(&d1, MDL);
}
/* If threshold is enabled, check lease age */
if (thresh > 0) {
int limit = 0;
int lease_length = 0;
long lease_age = 0;
/* Calculate limit in seconds */
lease_length = lease->ends - lease->starts;
if (lease_length <= (INT_MAX / thresh))
limit = lease_length * thresh / 100;
else
limit = lease_length / 100 * thresh;
/* Note new_lease->starts is really just cur_time */
lease_age = new_lease->starts - lease->starts;
/* Is the lease is young enough to reuse? */
if (lease_age <= limit) {
/* Restore expiry to its original value */
state->offered_expiry = lease->ends;
/* Restore bindings. This fixes 37368. */
if (new_lease->scope != NULL) {
if (lease->scope != NULL) {
binding_scope_dereference(
&lease->scope,
MDL);
}
binding_scope_reference(&lease->scope,
new_lease->scope, MDL);
}
/* We're cleared to reuse it */
log_debug("reuse_lease: lease age %ld"
" under %d%% limit, reusing it",
lease_age, limit);
reusable = 1;
}
}
}
/* If we can't reuse it and this is an offer disqualify reuse for
* ensuing REQUEST, otherwise clear the flag. */
lease->cannot_reuse = (!reusable && offer == DHCPOFFER);
return (reusable);
}

15
server/dhcpd.conf.5
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@ -2115,9 +2115,22 @@ update and write the database frequently resulting in a performance
impact on the server. The \fIdhcp-cache-threshold\fR
statement instructs the DHCP server to avoid updating leases too
frequently thus avoiding this behavior. Instead the server assigns the
same lease with no modifications except for CLTT (Client Last
same lease (i.e. reuses it) with no modifications except for CLTT (Client Last
Transmission Time) which does not require disk operations. This
feature applies to IPv4 only.
.PP
When an existing lease is matched to a renewing client, it will be reused
if all of the following conditions are true:
.nf
1. The dhcp-cache-threshold is larger than zero
2. The current lease is active
3. The percentage of the lease time that has elapsed is less than
dhcp-cache-threshold
4. The client information provided in the renewal does not alter
any of the following:
a. DNS information and DNS updates are enabled
b. Billing class to which the lease is associated
.fi
.RE
.PP
The