[Dnsmasq-discuss] [PATCH V2] Add a metric-order option that is a mix between strict-order and Default schedulers
DUPONCHEEL Sébastien
sebastien.duponcheel at corp.ovh.com
Tue Mar 13 14:36:21 GMT 2018
The default scheduler in dnsmasq query first all servers and then use the
fastest responding dns server for a short period and query all servers if a
timeout occurs.
The all-servers scheduler query fist the last fastest server and query all
others dns servers every time.
The strict-order scheduler query the first server that appear in resolv.conf
and if this server timeout dnsmasq try the next one.
strict-order is too slow and not resillient enougth to be use (ex: if only the
4th dns server in resolv.conf is reachable each dns request will take 20s).
"Default" and "all-servers" are fast and resilient but does not take care of
the server preferences defined in the resolv.conf.
This patch introduce a new scheduler that is an hybrid of the Default and the
strict-order schedulers.
Case study :
MyBox~# cat /etc/resolv.conf
# Behind VPN server
nameserver 169.254.254.1
# FAI or personal closed server
nameserver 91.121.161.184
# Open servers
nameserver 9.9.9.9
nameserver 8.8.8.8
nameserver 208.67.222.222
When my VPN is offline i want my router to use only my FAI or personal dns
server because i don't want to give my personnal datas to Quad9, Google,
OpenDNS or whatever.
But theses openservers are very good as backups if my personal dns server fail.
When i am using my VPN to do black magic stuffs like downloading debian dvd
images, i dont want my FAI to know what im doing by looking my dns requests or
sniffing my network traffic.
How the metric-order scheduler works ?
Dnsmasq read the resolv.conf and set a metric from 0 to N to each server in the
list.
The first query will be sent to all dns servers and dnsmasq will listen for
each answer and set the responding server's with the lowest metric as the
current server.
The next query will be sent first to the current server and sent to all other
servers with a lower metric than the current (supposed offline or unreachable).
When a query fail, the current server is cleared out and the query is resent
to all servers, a new current server is elected based on metric values.
If a server with a lowest metric turn online, it will answer to dns request
and will be elected as the new current server.
---
src/config.h | 14 +++++++++++++-
src/dbus.c | 6 +++---
src/dnsmasq.c | 5 +++++
src/dnsmasq.h | 9 +++++++--
src/forward.c | 40 +++++++++++++++++++++++++++++++++++++++-
src/network.c | 11 +++++++----
src/option.c | 3 +++
7 files changed, 77 insertions(+), 11 deletions(-)
diff --git a/src/config.h b/src/config.h
index b317071..722a7d7 100644
--- a/src/config.h
+++ b/src/config.h
@@ -123,6 +123,9 @@ HAVE_LOOP
HAVE_INOTIFY
use the Linux inotify facility to efficiently re-read configuration files.
+HAVE_METRIC_ORDER
+ include an hybrid scheduler that try to use the highest server in the resolv.conf file.
+
NO_ID
Don't report *.bind CHAOS info to clients, forward such requests upstream instead.
NO_IPV6
@@ -167,6 +170,7 @@ RESOLVFILE
#define HAVE_AUTH
#define HAVE_IPSET
#define HAVE_LOOP
+#define HAVE_METRIC_ORDER
/* Build options which require external libraries.
@@ -366,6 +370,10 @@ HAVE_SOCKADDR_SA_LEN
#undef HAVE_LOOP
#endif
+#ifdef NO_METRIC_ORDER
+#undef HAVE_METRIC_ORDER
+#endif
+
#if defined (HAVE_LINUX_NETWORK) && !defined(NO_INOTIFY)
#define HAVE_INOTIFY
#endif
@@ -454,7 +462,11 @@ static char *compile_opts =
#ifndef HAVE_INOTIFY
"no-"
#endif
-"inotify";
+"inotify "
+#ifndef HAVE_METRIC_ORDER
+"no-"
+#endif
+"metric-order";
#endif
diff --git a/src/dbus.c b/src/dbus.c
index 6a78b20..1621977 100644
--- a/src/dbus.c
+++ b/src/dbus.c
@@ -216,7 +216,7 @@ static void dbus_read_servers(DBusMessage *message)
domain = NULL;
if (!skip)
- add_update_server(SERV_FROM_DBUS, &addr, &source_addr, NULL, domain);
+ add_update_server(SERV_FROM_DBUS, &addr, &source_addr, NULL, domain, 0);
} while (dbus_message_iter_get_arg_type(&iter) == DBUS_TYPE_STRING);
}
@@ -393,7 +393,7 @@ static DBusMessage* dbus_read_servers_ex(DBusMessage *message, int strings)
else
p = NULL;
- add_update_server(flags | SERV_FROM_DBUS, &addr, &source_addr, interface, str_domain);
+ add_update_server(flags | SERV_FROM_DBUS, &addr, &source_addr, interface, str_domain, 0);
} while ((str_domain = p));
}
else
@@ -408,7 +408,7 @@ static DBusMessage* dbus_read_servers_ex(DBusMessage *message, int strings)
dbus_message_iter_get_basic(&string_iter, &str);
dbus_message_iter_next (&string_iter);
- add_update_server(flags | SERV_FROM_DBUS, &addr, &source_addr, interface, str);
+ add_update_server(flags | SERV_FROM_DBUS, &addr, &source_addr, interface, str, 0);
} while (dbus_message_iter_get_arg_type(&string_iter) == DBUS_TYPE_STRING);
}
diff --git a/src/dnsmasq.c b/src/dnsmasq.c
index ce44809..fe04ae8 100644
--- a/src/dnsmasq.c
+++ b/src/dnsmasq.c
@@ -225,6 +225,11 @@ int main (int argc, char **argv)
die(_("loop detection not available: set HAVE_LOOP in src/config.h"), NULL, EC_BADCONF);
#endif
+#ifndef HAVE_METRIC_ORDER
+ if (option_bool(OPT_METRIC_ORDER))
+ die(_("metric-order scheduler not available: set HAVE_METRIC_ORDER in src/config.h"), NULL, EC_BADCONF);
+#endif
+
if (daemon->max_port < daemon->min_port)
die(_("max_port cannot be smaller than min_port"), NULL, EC_BADCONF);
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 6773b69..39045b8 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -250,7 +250,8 @@ struct event_desc {
#define OPT_MAC_B64 54
#define OPT_MAC_HEX 55
#define OPT_TFTP_APREF_MAC 56
-#define OPT_LAST 57
+#define OPT_METRIC_ORDER 57
+#define OPT_LAST 58
/* extra flags for my_syslog, we use a couple of facilities since they are known
not to occupy the same bits as priorities, no matter how syslog.h is set up. */
@@ -525,6 +526,9 @@ struct server {
#ifdef HAVE_LOOP
u32 uid;
#endif
+#ifdef HAVE_METRIC_ORDER
+ u8 metric;
+#endif
struct server *next;
};
@@ -1282,7 +1286,8 @@ void add_update_server(int flags,
union mysockaddr *addr,
union mysockaddr *source_addr,
const char *interface,
- const char *domain);
+ const char *domain,
+ u8 metric);
void check_servers(void);
int enumerate_interfaces(int reset);
void create_wildcard_listeners(void);
diff --git a/src/forward.c b/src/forward.c
index cdd11d3..36c7d1a 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -239,6 +239,9 @@ static int forward_query(int udpfd, union mysockaddr *udpaddr,
struct all_addr *addrp = NULL;
unsigned int flags = 0;
struct server *start = NULL;
+#ifdef HAVE_METRIC_ORDER
+ struct server *last_server = NULL;
+#endif
#ifdef HAVE_DNSSEC
void *hash = hash_questions(header, plen, daemon->namebuff);
int do_dnssec = 0;
@@ -371,6 +374,16 @@ static int forward_query(int udpfd, union mysockaddr *udpaddr,
{
if (option_bool(OPT_ORDER))
start = daemon->servers;
+#ifdef HAVE_METRIC_ORDER
+ else if (option_bool(OPT_METRIC_ORDER))
+ {
+ forward->forwardall = 1;
+ if(!(start = daemon->last_server))
+ start = daemon->servers;
+ else
+ last_server = daemon->last_server;
+ }
+#endif
else if (!(start = daemon->last_server) ||
daemon->forwardcount++ > FORWARD_TEST ||
difftime(now, daemon->forwardtime) > FORWARD_TIME)
@@ -536,6 +549,10 @@ static int forward_query(int udpfd, union mysockaddr *udpaddr,
if (start == firstsentto)
break;
+#ifdef HAVE_METRIC_ORDER
+ if(option_bool(OPT_METRIC_ORDER) && (start->flags & SERV_FROM_RESOLV) && last_server && (last_server->flags & SERV_FROM_RESOLV) && (start->metric > last_server->metric))
+ start = daemon->servers;
+#endif
}
if (forwarded)
@@ -855,7 +872,19 @@ void reply_query(int fd, int family, time_t now)
}
}
if (!option_bool(OPT_ALL_SERVERS))
- daemon->last_server = server;
+#ifdef HAVE_METRIC_ORDER
+ if (!option_bool(OPT_METRIC_ORDER))
+#endif
+ daemon->last_server = server;
+#ifdef HAVE_METRIC_ORDER
+ if (option_bool(OPT_METRIC_ORDER) && (server->flags & SERV_FROM_RESOLV))
+ {
+ if (!daemon->last_server)
+ daemon->last_server = server;
+ else if (server->metric < daemon->last_server->metric)
+ daemon->last_server = server;
+ }
+#endif
}
/* We tried resending to this server with a smaller maximum size and got an answer.
@@ -1131,7 +1160,16 @@ void reply_query(int fd, int family, time_t now)
send_from(forward->fd, option_bool(OPT_NOWILD) || option_bool (OPT_CLEVERBIND), daemon->packet, nn,
&forward->source, &forward->dest, forward->iface);
}
+#ifdef HAVE_METRIC_ORDER
+ if (!option_bool(OPT_METRIC_ORDER))
+#endif
free_frec(forward); /* cancel */
+#ifdef HAVE_METRIC_ORDER
+ else if (forward->forwardall > 1)
+ forward->forwardall--;
+ else
+ free_frec(forward);
+#endif
}
}
diff --git a/src/network.c b/src/network.c
index 0381513..9dd00a2 100644
--- a/src/network.c
+++ b/src/network.c
@@ -1385,7 +1385,8 @@ void add_update_server(int flags,
union mysockaddr *addr,
union mysockaddr *source_addr,
const char *interface,
- const char *domain)
+ const char *domain,
+ u8 metric)
{
struct server *serv, *next = NULL;
char *domain_str = NULL;
@@ -1444,6 +1445,9 @@ void add_update_server(int flags,
serv->domain = domain_str;
serv->next = next;
serv->queries = serv->failed_queries = 0;
+#ifdef HAVE_METRIC_ORDER
+ serv->metric = metric;
+#endif
#ifdef HAVE_LOOP
serv->uid = rand32();
#endif
@@ -1616,7 +1620,7 @@ int reload_servers(char *fname)
FILE *f;
char *line;
int gotone = 0;
-
+ u8 metric = 0;
/* buff happens to be MAXDNAME long... */
if (!(f = fopen(fname, "r")))
{
@@ -1683,8 +1687,7 @@ int reload_servers(char *fname)
else
continue;
#endif
-
- add_update_server(SERV_FROM_RESOLV, &addr, &source_addr, NULL, NULL);
+ add_update_server(SERV_FROM_RESOLV, &addr, &source_addr, NULL, NULL, metric++);
gotone = 1;
}
diff --git a/src/option.c b/src/option.c
index d358d99..84df76e 100644
--- a/src/option.c
+++ b/src/option.c
@@ -160,6 +160,7 @@ struct myoption {
#define LOPT_DHCPTTL 348
#define LOPT_TFTP_MTU 349
#define LOPT_REPLY_DELAY 350
+#define LOPT_METRIC_ORDER 351
#ifdef HAVE_GETOPT_LONG
static const struct option opts[] =
@@ -199,6 +200,7 @@ static const struct myoption opts[] =
{ "filterwin2k", 0, 0, 'f' },
{ "pid-file", 2, 0, 'x' },
{ "strict-order", 0, 0, 'o' },
+ { "metric-order", 0, 0, LOPT_METRIC_ORDER },
{ "server", 1, 0, 'S' },
{ "rev-server", 1, 0, LOPT_REV_SERV },
{ "local", 1, 0, LOPT_LOCAL },
@@ -380,6 +382,7 @@ static struct {
{ 'n', OPT_NO_POLL, NULL, gettext_noop("Do NOT poll %s file, reload only on SIGHUP."), RESOLVFILE },
{ 'N', OPT_NO_NEG, NULL, gettext_noop("Do NOT cache failed search results."), NULL },
{ 'o', OPT_ORDER, NULL, gettext_noop("Use nameservers strictly in the order given in %s."), RESOLVFILE },
+ { LOPT_METRIC_ORDER, OPT_METRIC_ORDER, NULL, gettext_noop("Try to use the highest nameserver that is given in %s."), RESOLVFILE },
{ 'O', ARG_DUP, "<optspec>", gettext_noop("Specify options to be sent to DHCP clients."), NULL },
{ LOPT_FORCE, ARG_DUP, "<optspec>", gettext_noop("DHCP option sent even if the client does not request it."), NULL},
{ 'p', ARG_ONE, "<integer>", gettext_noop("Specify port to listen for DNS requests on (defaults to 53)."), NULL },
--
2.7.4
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