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resolved: add 100ms initial jitter to all LLMNR requests

This commit is contained in:
Lennart Poettering 2014-08-05 17:01:33 +02:00
parent aea2429d6e
commit 6e06847294
3 changed files with 35 additions and 1 deletions
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5
src/resolve/resolved-dns-scope.c
View File

@ -549,6 +549,11 @@ void dns_scope_process_query(DnsScope *s, DnsStream *stream, DnsPacket *p) {
return;
}
/* Note that we always immediately reply to all LLMNR
* requests, and do not wait any time, since we
* verified uniqueness for all records. Also see RFC
* 4795, Section 2.7 */
r = manager_send(s->manager, fd, p->ifindex, p->family, &p->sender, p->sender_port, reply);
}

27
src/resolve/resolved-dns-transaction.c
View File

@ -490,6 +490,33 @@ int dns_transaction_go(DnsTransaction *t) {
}
}
if (t->scope->protocol == DNS_PROTOCOL_LLMNR && !t->initial_jitter) {
usec_t jitter;
/* RFC 4795 Section 2.7 suggests all queries should be
* delayed by a random time from 0 to JITTER_INTERVAL. */
t->initial_jitter = true;
random_bytes(&jitter, sizeof(jitter));
jitter %= LLMNR_JITTER_INTERVAL_USEC;
r = sd_event_add_time(
t->scope->manager->event,
&t->timeout_event_source,
clock_boottime_or_monotonic(),
now(clock_boottime_or_monotonic()) + jitter, LLMNR_JITTER_INTERVAL_USEC,
on_transaction_timeout, t);
if (r < 0)
return r;
t->n_attempts = 0;
t->state = DNS_TRANSACTION_PENDING;
log_debug("Delaying LLMNR transaction for " USEC_FMT "us.", jitter);
return 0;
}
log_debug("Cache miss!");
/* Otherwise, we need to ask the network */

4
src/resolve/resolved-dns-transaction.h
View File

@ -54,6 +54,8 @@ struct DnsTransaction {
DnsTransactionState state;
uint16_t id;
bool initial_jitter;
DnsPacket *sent, *received;
DnsAnswer *cached;
int cached_rcode;
@ -96,7 +98,7 @@ DnsTransactionState dns_transaction_state_from_string(const char *s) _pure_;
#define LLMNR_TRANSACTION_TIMEOUT_USEC (1 * USEC_PER_SEC)
/* LLMNR Jitter interval, see RFC 4795 Section 7 */
#define LLMNR_TRANSACTION_JITTER_INTERVAL_USEC (100 * USEC_PER_MSEC)
#define LLMNR_JITTER_INTERVAL_USEC (100 * USEC_PER_MSEC)
/* Maximum attempts to send DNS requests, across all DNS servers */
#define DNS_TRANSACTION_ATTEMPTS_MAX 8