I'm worried that it takes so many words to describe what this does.
Configuration options are no good unless people can see what problem
they solve and understand when to use them.

I confess I'm not sure I understand when anyone would use this, and why.
It's not security, because it doesn't guarantee that low-metric servers
will not get used. It's not performance, because it will use a server
that's earlier in /etc/resolv.conf even if it's slower (maybe much
slower) than another server.

It doesn't provide any determinism on which server is used. (That would
be a bad idea anyway.)

I'm sceptical, but willing to be convinced.

Anyone else have thoughts?

Cheers,

Simon.



On 14/03/18 12:50, DUPONCHEEL Sébastien wrote:
> 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 },
> 


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