Merge pull request #11050 from poettering/resolved-domain-route

resolved: beef up domain routing

18 files changed, 392 insertions, 95 deletions

diff --git a/src/libsystemd/sd-network/sd-network.c b/src/libsystemd/sd-network/sd-network.c
index 4b66a9220..d4b5e248c 100644
--- a/src/libsystemd/sd-network/sd-network.c
+++ b/src/libsystemd/sd-network/sd-network.c
@@ -204,6 +204,25 @@ _public_ int sd_network_link_get_route_domains(int ifindex, char ***ret) {
         return network_link_get_strv(ifindex, "ROUTE_DOMAINS", ret);
 }
 
+_public_ int sd_network_link_get_dns_default_route(int ifindex) {
+        char path[STRLEN("/run/systemd/netif/links/") + DECIMAL_STR_MAX(ifindex) + 1];
+        _cleanup_free_ char *s = NULL;
+        int r;
+
+        assert_return(ifindex > 0, -EINVAL);
+
+        xsprintf(path, "/run/systemd/netif/links/%i", ifindex);
+
+        r = parse_env_file(NULL, path, "DNS_DEFAULT_ROUTE", &s);
+        if (r == -ENOENT)
+                return -ENODATA;
+        if (r < 0)
+                return r;
+        if (isempty(s))
+                return -ENODATA;
+        return parse_boolean(s);
+}
+
 static int network_link_get_ifindexes(int ifindex, const char *key, int **ret) {
         char path[STRLEN("/run/systemd/netif/links/") + DECIMAL_STR_MAX(ifindex) + 1];
         _cleanup_free_ int *ifis = NULL;
diff --git a/src/network/networkd-link.c b/src/network/networkd-link.c
index d73e85cf2..e2851df31 100644
--- a/src/network/networkd-link.c
+++ b/src/network/networkd-link.c
@@ -3929,6 +3929,8 @@ int link_save(Link *link) {
                         resolve_support_to_string(link->network->llmnr));
                 fprintf(f, "MDNS=%s\n",
                         resolve_support_to_string(link->network->mdns));
+                if (link->network->dns_default_route >= 0)
+                        fprintf(f, "DNS_DEFAULT_ROUTE=%s\n", yes_no(link->network->dns_default_route));
 
                 if (link->network->dns_over_tls_mode != _DNS_OVER_TLS_MODE_INVALID)
                         fprintf(f, "DNS_OVER_TLS=%s\n",
diff --git a/src/network/networkd-network-gperf.gperf b/src/network/networkd-network-gperf.gperf
index 48d8ae52f..5d8aede59 100644
--- a/src/network/networkd-network-gperf.gperf
+++ b/src/network/networkd-network-gperf.gperf
@@ -58,6 +58,7 @@ Network.Address,                        config_parse_address,
 Network.Gateway,                        config_parse_gateway,                           0,                             0
 Network.Domains,                        config_parse_domains,                           0,                             0
 Network.DNS,                            config_parse_dns,                               0,                             0
+Network.DNSDefaultRoute,                config_parse_tristate,                          0,                             offsetof(Network, dns_default_route)
 Network.LLMNR,                          config_parse_resolve_support,                   0,                             offsetof(Network, llmnr)
 Network.MulticastDNS,                   config_parse_resolve_support,                   0,                             offsetof(Network, mdns)
 Network.DNSOverTLS,                     config_parse_dns_over_tls_mode,                 0,                             offsetof(Network, dns_over_tls_mode)
diff --git a/src/network/networkd-network.c b/src/network/networkd-network.c
index 62dc6a0bf..ccc1c3ce8 100644
--- a/src/network/networkd-network.c
+++ b/src/network/networkd-network.c
@@ -168,6 +168,7 @@ int network_load_one(Manager *manager, const char *filename) {
 
                 .lldp_mode = LLDP_MODE_ROUTERS_ONLY,
 
+                .dns_default_route = -1,
                 .llmnr = RESOLVE_SUPPORT_YES,
                 .mdns = RESOLVE_SUPPORT_NO,
                 .dnssec_mode = _DNSSEC_MODE_INVALID,
@@ -657,7 +658,6 @@ int config_parse_domains(
                          * routing domain, unconditionally. */
                         is_route = true;
                         domain = "."; /* make sure we don't allow empty strings, thus write the root domain as "." */
-
                 } else {
                         r = dns_name_normalize(domain, 0, &normalized);
                         if (r < 0) {
@@ -673,16 +673,12 @@ int config_parse_domains(
                         }
                 }
 
-                if (is_route) {
+                if (is_route)
                         r = strv_extend(&n->route_domains, domain);
-                        if (r < 0)
-                                return log_oom();
-
-                } else {
+                else
                         r = strv_extend(&n->search_domains, domain);
-                        if (r < 0)
-                                return log_oom();
-                }
+                if (r < 0)
+                        return log_oom();
         }
 
         strv_uniq(n->route_domains);
diff --git a/src/network/networkd-network.h b/src/network/networkd-network.h
index 3a72c5bd9..f6e62cdd7 100644
--- a/src/network/networkd-network.h
+++ b/src/network/networkd-network.h
@@ -260,17 +260,20 @@ struct Network {
         Hashmap *prefixes_by_section;
         Hashmap *rules_by_section;
 
+        /* All kinds of DNS configuration */
         struct in_addr_data *dns;
         unsigned n_dns;
-
-        char **search_domains, **route_domains, **ntp, **bind_carrier;
-
+        char **search_domains, **route_domains;
+        int dns_default_route;
         ResolveSupport llmnr;
         ResolveSupport mdns;
         DnssecMode dnssec_mode;
         DnsOverTlsMode dns_over_tls_mode;
         Set *dnssec_negative_trust_anchors;
 
+        char **ntp;
+        char **bind_carrier;
+
         LIST_FIELDS(Network, networks);
 };
 
diff --git a/src/resolve/resolvectl.c b/src/resolve/resolvectl.c
index 8a175ebef..4d533f851 100644
--- a/src/resolve/resolvectl.c
+++ b/src/resolve/resolvectl.c
@@ -67,6 +67,7 @@ typedef enum StatusMode {
         STATUS_ALL,
         STATUS_DNS,
         STATUS_DOMAIN,
+        STATUS_DEFAULT_ROUTE,
         STATUS_LLMNR,
         STATUS_MDNS,
         STATUS_PRIVATE,
@@ -1369,6 +1370,7 @@ struct link_info {
         char **domains;
         char **ntas;
         bool dnssec_supported;
+        bool default_route;
 };
 
 static void link_info_clear(struct link_info *p) {
@@ -1384,6 +1386,7 @@ static int status_ifindex(sd_bus *bus, int ifindex, const char *name, StatusMode
                 { "DNS",                        "a(iay)", map_link_dns_servers,        offsetof(struct link_info, dns)              },
                 { "CurrentDNSServer",           "(iay)",  map_link_current_dns_server, offsetof(struct link_info, current_dns)      },
                 { "Domains",                    "a(sb)",  map_link_domains,            offsetof(struct link_info, domains)          },
+                { "DefaultRoute",               "b",      NULL,                        offsetof(struct link_info, default_route)    },
                 { "LLMNR",                      "s",      NULL,                        offsetof(struct link_info, llmnr)            },
                 { "MulticastDNS",               "s",      NULL,                        offsetof(struct link_info, mdns)             },
                 { "DNSOverTLS",                 "s",      NULL,                        offsetof(struct link_info, dns_over_tls)     },
@@ -1439,6 +1442,14 @@ static int status_ifindex(sd_bus *bus, int ifindex, const char *name, StatusMode
         if (mode == STATUS_NTA)
                 return status_print_strv_ifindex(ifindex, name, link_info.ntas);
 
+        if (mode == STATUS_DEFAULT_ROUTE) {
+                printf("%sLink %i (%s)%s: %s\n",
+                       ansi_highlight(), ifindex, name, ansi_normal(),
+                       yes_no(link_info.default_route));
+
+                return 0;
+        }
+
         if (mode == STATUS_LLMNR) {
                 printf("%sLink %i (%s)%s: %s\n",
                        ansi_highlight(), ifindex, name, ansi_normal(),
@@ -1487,11 +1498,13 @@ static int status_ifindex(sd_bus *bus, int ifindex, const char *name, StatusMode
                        link_info.scopes_mask & SD_RESOLVED_MDNS_IPV4 ? " mDNS/IPv4" : "",
                        link_info.scopes_mask & SD_RESOLVED_MDNS_IPV6 ? " mDNS/IPv6" : "");
 
-        printf("       LLMNR setting: %s\n"
+        printf("DefaultRoute setting: %s\n"
+               "       LLMNR setting: %s\n"
                "MulticastDNS setting: %s\n"
                "  DNSOverTLS setting: %s\n"
                "      DNSSEC setting: %s\n"
                "    DNSSEC supported: %s\n",
+               yes_no(link_info.default_route),
                strna(link_info.llmnr),
                strna(link_info.mdns),
                strna(link_info.dns_over_tls),
@@ -2020,6 +2033,51 @@ static int verb_domain(int argc, char **argv, void *userdata) {
         return 0;
 }
 
+static int verb_default_route(int argc, char **argv, void *userdata) {
+        _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
+        sd_bus *bus = userdata;
+        int r, b;
+
+        assert(bus);
+
+        if (argc >= 2) {
+                r = ifname_mangle(argv[1]);
+                if (r < 0)
+                        return r;
+        }
+
+        if (arg_ifindex <= 0)
+                return status_all(bus, STATUS_DEFAULT_ROUTE);
+
+        if (argc < 3)
+                return status_ifindex(bus, arg_ifindex, NULL, STATUS_DEFAULT_ROUTE, NULL);
+
+        b = parse_boolean(argv[2]);
+        if (b < 0)
+                return log_error_errno(b, "Failed to parse boolean argument: %s", argv[2]);
+
+        r = sd_bus_call_method(bus,
+                               "org.freedesktop.resolve1",
+                               "/org/freedesktop/resolve1",
+                               "org.freedesktop.resolve1.Manager",
+                               "SetLinkDefaultRoute",
+                               &error,
+                               NULL,
+                               "ib", arg_ifindex, b);
+        if (r < 0) {
+                if (sd_bus_error_has_name(&error, BUS_ERROR_LINK_BUSY))
+                        return log_interface_is_managed(r, arg_ifindex);
+
+                if (arg_ifindex_permissive &&
+                    sd_bus_error_has_name(&error, BUS_ERROR_NO_SUCH_LINK))
+                        return 0;
+
+                return log_error_errno(r, "Failed to set default route configuration: %s", bus_error_message(&error, r));
+        }
+
+        return 0;
+}
+
 static int verb_llmnr(int argc, char **argv, void *userdata) {
         _cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
         sd_bus *bus = userdata;
@@ -2407,6 +2465,7 @@ static int native_help(void) {
                "  reset-server-features        Forget learnt DNS server feature levels\n"
                "  dns [LINK [SERVER...]]       Get/set per-interface DNS server address\n"
                "  domain [LINK [DOMAIN...]]    Get/set per-interface search domain\n"
+               "  default-route [LINK [BOOL]]  Get/set per-interface default route flag\n"
                "  llmnr [LINK [MODE]]          Get/set per-interface LLMNR mode\n"
                "  mdns [LINK [MODE]]           Get/set per-interface MulticastDNS mode\n"
                "  dnsovertls [LINK [MODE]]     Get/set per-interface DNS-over-TLS mode\n"
@@ -2950,9 +3009,10 @@ static int native_main(int argc, char *argv[], sd_bus *bus) {
                 { "reset-server-features", VERB_ANY, 1,        0,            reset_server_features },
                 { "dns",                   VERB_ANY, VERB_ANY, 0,            verb_dns              },
                 { "domain",                VERB_ANY, VERB_ANY, 0,            verb_domain           },
+                { "default-route",         VERB_ANY, 3,        0,            verb_default_route    },
                 { "llmnr",                 VERB_ANY, 3,        0,            verb_llmnr            },
                 { "mdns",                  VERB_ANY, 3,        0,            verb_mdns             },
-                { "dnsovertls",            VERB_ANY, 3,        0,            verb_dns_over_tls      },
+                { "dnsovertls",            VERB_ANY, 3,        0,            verb_dns_over_tls     },
                 { "dnssec",                VERB_ANY, 3,        0,            verb_dnssec           },
                 { "nta",                   VERB_ANY, VERB_ANY, 0,            verb_nta              },
                 { "revert",                VERB_ANY, 2,        0,            verb_revert_link      },
diff --git a/src/resolve/resolved-bus.c b/src/resolve/resolved-bus.c
index fbe823da6..5b547ba7e 100644
--- a/src/resolve/resolved-bus.c
+++ b/src/resolve/resolved-bus.c
@@ -1530,6 +1530,10 @@ static int bus_method_set_link_domains(sd_bus_message *message, void *userdata,
         return call_link_method(userdata, message, bus_link_method_set_domains, error);
 }
 
+static int bus_method_set_link_default_route(sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        return call_link_method(userdata, message, bus_link_method_set_default_route, error);
+}
+
 static int bus_method_set_link_llmnr(sd_bus_message *message, void *userdata, sd_bus_error *error) {
         return call_link_method(userdata, message, bus_link_method_set_llmnr, error);
 }
@@ -1855,6 +1859,7 @@ static const sd_bus_vtable resolve_vtable[] = {
         SD_BUS_METHOD("GetLink", "i", "o", bus_method_get_link, SD_BUS_VTABLE_UNPRIVILEGED),
         SD_BUS_METHOD("SetLinkDNS", "ia(iay)", NULL, bus_method_set_link_dns_servers, 0),
         SD_BUS_METHOD("SetLinkDomains", "ia(sb)", NULL, bus_method_set_link_domains, 0),
+        SD_BUS_METHOD("SetLinkDefaultRoute", "ib", NULL, bus_method_set_link_default_route, 0),
         SD_BUS_METHOD("SetLinkLLMNR", "is", NULL, bus_method_set_link_llmnr, 0),
         SD_BUS_METHOD("SetLinkMulticastDNS", "is", NULL, bus_method_set_link_mdns, 0),
         SD_BUS_METHOD("SetLinkDNSOverTLS", "is", NULL, bus_method_set_link_dns_over_tls, 0),
diff --git a/src/resolve/resolved-dns-query.c b/src/resolve/resolved-dns-query.c
index 746ff1b8b..7a4f97754 100644
--- a/src/resolve/resolved-dns-query.c
+++ b/src/resolve/resolved-dns-query.c
@@ -682,22 +682,15 @@ int dns_query_go(DnsQuery *q) {
                         continue;
 
                 match = dns_scope_good_domain(s, q->ifindex, q->flags, name);
-                if (match < 0)
-                        return match;
-
-                if (match == DNS_SCOPE_NO)
+                if (match < 0) {
+                        log_debug("Couldn't check if '%s' matches against scope, ignoring.", name);
                         continue;
+                }
 
-                found = match;
-
-                if (match == DNS_SCOPE_YES) {
+                if (match > found) { /* Does this match better? If so, remember how well it matched, and the first one
+                                      * that matches this well */
+                        found = match;
                         first = s;
-                        break;
-                } else {
-                        assert(match == DNS_SCOPE_MAYBE);
-
-                        if (!first)
-                                first = s;
                 }
         }
 
@@ -725,10 +718,12 @@ int dns_query_go(DnsQuery *q) {
                         continue;
 
                 match = dns_scope_good_domain(s, q->ifindex, q->flags, name);
-                if (match < 0)
-                        goto fail;
+                if (match < 0) {
+                        log_debug("Couldn't check if '%s' matches agains scope, ignoring.", name);
+                        continue;
+                }
 
-                if (match != found)
+                if (match < found)
                         continue;
 
                 r = dns_query_add_candidate(q, s);
diff --git a/src/resolve/resolved-dns-scope.c b/src/resolve/resolved-dns-scope.c
index 35c3804db..972e661d7 100644
--- a/src/resolve/resolved-dns-scope.c
+++ b/src/resolve/resolved-dns-scope.c
@@ -30,15 +30,17 @@ int dns_scope_new(Manager *m, DnsScope **ret, Link *l, DnsProtocol protocol, int
         assert(m);
         assert(ret);
 
-        s = new0(DnsScope, 1);
+        s = new(DnsScope, 1);
         if (!s)
                 return -ENOMEM;
 
-        s->manager = m;
-        s->link = l;
-        s->protocol = protocol;
-        s->family = family;
-        s->resend_timeout = MULTICAST_RESEND_TIMEOUT_MIN_USEC;
+        *s = (DnsScope) {
+                .manager = m,
+                .link = l,
+                .protocol = protocol,
+                .family = family,
+                .resend_timeout = MULTICAST_RESEND_TIMEOUT_MIN_USEC,
+        };
 
         if (protocol == DNS_PROTOCOL_DNS) {
                 /* Copy DNSSEC mode from the link if it is set there,
@@ -457,9 +459,40 @@ int dns_scope_socket_tcp(DnsScope *s, int family, const union in_addr_union *add
         return dns_scope_socket(s, SOCK_STREAM, family, address, server, port, ret_socket_address);
 }
 
-DnsScopeMatch dns_scope_good_domain(DnsScope *s, int ifindex, uint64_t flags, const char *domain) {
+static DnsScopeMatch accept_link_local_reverse_lookups(const char *domain) {
+        assert(domain);
+
+        if (dns_name_endswith(domain, "254.169.in-addr.arpa") > 0)
+                return DNS_SCOPE_YES_BASE + 4; /* 4 labels match */
+
+        if (dns_name_endswith(domain, "8.e.f.ip6.arpa") > 0 ||
+            dns_name_endswith(domain, "9.e.f.ip6.arpa") > 0 ||
+            dns_name_endswith(domain, "a.e.f.ip6.arpa") > 0 ||
+            dns_name_endswith(domain, "b.e.f.ip6.arpa") > 0)
+                return DNS_SCOPE_YES_BASE + 5; /* 5 labels match */
+
+        return _DNS_SCOPE_MATCH_INVALID;
+}
+
+DnsScopeMatch dns_scope_good_domain(
+                DnsScope *s,
+                int ifindex,
+                uint64_t flags,
+                const char *domain) {
+
         DnsSearchDomain *d;
 
+        /* This returns the following return values:
+         *
+         *    DNS_SCOPE_NO         → This scope is not suitable for lookups of this domain, at all
+         *    DNS_SCOPE_MAYBE      → This scope is suitable, but only if nothing else wants it
+         *    DNS_SCOPE_YES_BASE+n → This scope is suitable, and 'n' suffix labels match
+         *
+         *  (The idea is that the caller will only use the scopes with the longest 'n' returned. If no scopes return
+         *  DNS_SCOPE_YES_BASE+n, then it should use those which returned DNS_SCOPE_MAYBE. It should never use those
+         *  which returned DNS_SCOPE_NO.)
+         */
+
         assert(s);
         assert(domain);
 
@@ -494,23 +527,35 @@ DnsScopeMatch dns_scope_good_domain(DnsScope *s, int ifindex, uint64_t flags, co
         switch (s->protocol) {
 
         case DNS_PROTOCOL_DNS: {
-                DnsServer *dns_server;
+                int n_best = -1;
 
                 /* Never route things to scopes that lack DNS servers */
-                dns_server = dns_scope_get_dns_server(s);
-                if (!dns_server)
+                if (!dns_scope_get_dns_server(s))
                         return DNS_SCOPE_NO;
 
                 /* Always honour search domains for routing queries, except if this scope lacks DNS servers. Note that
                  * we return DNS_SCOPE_YES here, rather than just DNS_SCOPE_MAYBE, which means other wildcard scopes
                  * won't be considered anymore. */
                 LIST_FOREACH(domains, d, dns_scope_get_search_domains(s))
-                        if (dns_name_endswith(domain, d->name) > 0)
-                                return DNS_SCOPE_YES;
+                        if (dns_name_endswith(domain, d->name) > 0) {
+                                int c;
+
+                                c = dns_name_count_labels(d->name);
+                                if (c < 0)
+                                        continue;
+
+                                if (c > n_best)
+                                        n_best = c;
+                        }
 
-                /* If the DNS server has route-only domains, don't send other requests to it. This would be a privacy
-                 * violation, will most probably fail anyway, and adds unnecessary load. */
-                if (dns_server_limited_domains(dns_server))
+                /* Let's return the number of labels in the best matching result */
+                if (n_best >= 0) {
+                        assert(n_best <= DNS_SCOPE_YES_END - DNS_SCOPE_YES_BASE);
+                        return DNS_SCOPE_YES_BASE + n_best;
+                }
+
+                /* See if this scope is suitable as default route. */
+                if (!dns_scope_is_default_route(s))
                         return DNS_SCOPE_NO;
 
                 /* Exclude link-local IP ranges */
@@ -528,25 +573,48 @@ DnsScopeMatch dns_scope_good_domain(DnsScope *s, int ifindex, uint64_t flags, co
                 return DNS_SCOPE_NO;
         }
 
-        case DNS_PROTOCOL_MDNS:
+        case DNS_PROTOCOL_MDNS: {
+                DnsScopeMatch m;
+
+                m = accept_link_local_reverse_lookups(domain);
+                if (m >= 0)
+                        return m;
+
                 if ((s->family == AF_INET && dns_name_endswith(domain, "in-addr.arpa") > 0) ||
-                    (s->family == AF_INET6 && dns_name_endswith(domain, "ip6.arpa") > 0) ||
-                    (dns_name_endswith(domain, "local") > 0 && /* only resolve names ending in .local via mDNS */
+                    (s->family == AF_INET6 && dns_name_endswith(domain, "ip6.arpa") > 0))
+                        return DNS_SCOPE_MAYBE;
+
+                if ((dns_name_endswith(domain, "local") > 0 && /* only resolve names ending in .local via mDNS */
                      dns_name_equal(domain, "local") == 0 &&   /* but not the single-label "local" name itself */
                      manager_is_own_hostname(s->manager, domain) <= 0)) /* never resolve the local hostname via mDNS */
-                        return DNS_SCOPE_MAYBE;
+                        return DNS_SCOPE_YES_BASE + 1; /* Return +1, as the top-level .local domain matches, i.e. one label */
 
                 return DNS_SCOPE_NO;
+        }
+
+        case DNS_PROTOCOL_LLMNR: {
+                DnsScopeMatch m;
+
+                m = accept_link_local_reverse_lookups(domain);
+                if (m >= 0)
+                        return m;
 
-        case DNS_PROTOCOL_LLMNR:
                 if ((s->family == AF_INET && dns_name_endswith(domain, "in-addr.arpa") > 0) ||
-                    (s->family == AF_INET6 && dns_name_endswith(domain, "ip6.arpa") > 0) ||
-                    (dns_name_is_single_label(domain) && /* only resolve single label names via LLMNR */
+                    (s->family == AF_INET6 && dns_name_endswith(domain, "ip6.arpa") > 0))
+                        return DNS_SCOPE_MAYBE;
+
+                if ((dns_name_is_single_label(domain) && /* only resolve single label names via LLMNR */
                      !is_gateway_hostname(domain) && /* don't resolve "gateway" with LLMNR, let nss-myhostname handle this */
                      manager_is_own_hostname(s->manager, domain) <= 0))  /* never resolve the local hostname via LLMNR */
-                        return DNS_SCOPE_MAYBE;
+                        return DNS_SCOPE_YES_BASE + 1; /* Return +1, as we consider ourselves authoritative for
+                                                        * single-label names, i.e. one label. This is particular
+                                                        * relevant as it means a "." route on some other scope won't
+                                                        * pull all traffic away from us. (If people actually want to
+                                                        * pull traffic away from us they should turn off LLMNR on the
+                                                        * link) */
 
                 return DNS_SCOPE_NO;
+        }
 
         default:
                 assert_not_reached("Unknown scope protocol");
@@ -1322,3 +1390,56 @@ int dns_scope_remove_dnssd_services(DnsScope *scope) {
 
         return 0;
 }
+
+static bool dns_scope_has_route_only_domains(DnsScope *scope) {
+        DnsSearchDomain *domain, *first;
+        bool route_only = false;
+
+        assert(scope);
+        assert(scope->protocol == DNS_PROTOCOL_DNS);
+
+        /* Returns 'true' if this scope is suitable for queries to specific domains only. For that we check
+         * if there are any route-only domains on this interface, as a heuristic to discern VPN-style links
+         * from non-VPN-style links. Returns 'false' for all other cases, i.e. if the scope is intended to
+         * take queries to arbitrary domains, i.e. has no routing domains set. */
+
+        if (scope->link)
+                first = scope->link->search_domains;
+        else
+                first = scope->manager->search_domains;
+
+        LIST_FOREACH(domains, domain, first) {
+                /* "." means "any domain", thus the interface takes any kind of traffic. Thus, we exit early
+                 * here, as it doesn't really matter whether this link has any route-only domains or not,
+                 * "~."  really trumps everything and clearly indicates that this interface shall receive all
+                 * traffic it can get. */
+                if (dns_name_is_root(DNS_SEARCH_DOMAIN_NAME(domain)))
+                        return false;
+
+                if (domain->route_only)
+                        route_only = true;
+        }
+
+        return route_only;
+}
+
+bool dns_scope_is_default_route(DnsScope *scope) {
+        assert(scope);
+
+        /* Only use DNS scopes as default routes */
+        if (scope->protocol != DNS_PROTOCOL_DNS)
+                return false;
+
+        /* The global DNS scope is always suitable as default route */
+        if (!scope->link)
+                return true;
+
+        /* Honour whatever is explicitly configured. This is really the best approach, and trumps any
+         * automatic logic. */
+        if (scope->link->default_route >= 0)
+                return scope->link->default_route;
+
+        /* Otherwise check if we have any route-only domains, as a sensible heuristic: if so, let's not
+         * volunteer as default route. */
+        return !dns_scope_has_route_only_domains(scope);
+}
diff --git a/src/resolve/resolved-dns-scope.h b/src/resolve/resolved-dns-scope.h
index 04e93f8f7..f4b45c4f2 100644
--- a/src/resolve/resolved-dns-scope.h
+++ b/src/resolve/resolved-dns-scope.h
@@ -18,9 +18,10 @@ typedef struct DnsScope DnsScope;
 typedef enum DnsScopeMatch {
         DNS_SCOPE_NO,
         DNS_SCOPE_MAYBE,
-        DNS_SCOPE_YES,
+        DNS_SCOPE_YES_BASE, /* Add the number of matching labels to this */
+        DNS_SCOPE_YES_END = DNS_SCOPE_YES_BASE + DNS_N_LABELS_MAX,
         _DNS_SCOPE_MATCH_MAX,
-        _DNS_SCOPE_INVALID = -1
+        _DNS_SCOPE_MATCH_INVALID = -1
 } DnsScopeMatch;
 
 struct DnsScope {
@@ -28,6 +29,8 @@ struct DnsScope {
 
         DnsProtocol protocol;
         int family;
+
+        /* Copied at scope creation time from the link/manager */
         DnssecMode dnssec_mode;
         DnsOverTlsMode dns_over_tls_mode;
 
@@ -104,5 +107,6 @@ int dns_scope_ifindex(DnsScope *s);
 int dns_scope_announce(DnsScope *scope, bool goodbye);
 
 int dns_scope_add_dnssd_services(DnsScope *scope);
-
 int dns_scope_remove_dnssd_services(DnsScope *scope);
+
+bool dns_scope_is_default_route(DnsScope *scope);
diff --git a/src/resolve/resolved-dns-server.c b/src/resolve/resolved-dns-server.c
index 3e69741b8..b85eb7527 100644
--- a/src/resolve/resolved-dns-server.c
+++ b/src/resolve/resolved-dns-server.c
@@ -580,26 +580,6 @@ void dns_server_warn_downgrade(DnsServer *server) {
         server->warned_downgrade = true;
 }
 
-bool dns_server_limited_domains(DnsServer *server) {
-        DnsSearchDomain *domain;
-        bool domain_restricted = false;
-
-        /* Check if the server has route-only domains without ~., i. e. whether
-         * it should only be used for particular domains */
-        if (!server->link)
-                return false;
-
-        LIST_FOREACH(domains, domain, server->link->search_domains)
-                if (domain->route_only) {
-                        domain_restricted = true;
-                        /* ~. means "any domain", thus it is a global server */
-                        if (dns_name_is_root(DNS_SEARCH_DOMAIN_NAME(domain)))
-                                return false;
-                }
-
-        return domain_restricted;
-}
-
 static void dns_server_hash_func(const DnsServer *s, struct siphash *state) {
         assert(s);
 
@@ -906,6 +886,16 @@ void dns_server_unref_stream(DnsServer *s) {
         dns_stream_unref(ref);
 }
 
+DnsScope *dns_server_scope(DnsServer *s) {
+        assert(s);
+        assert((s->type == DNS_SERVER_LINK) == !!s->link);
+
+        if (s->link)
+                return s->link->unicast_scope;
+
+        return s->manager->unicast_scope;
+}
+
 static const char* const dns_server_type_table[_DNS_SERVER_TYPE_MAX] = {
         [DNS_SERVER_SYSTEM] = "system",
         [DNS_SERVER_FALLBACK] = "fallback",
diff --git a/src/resolve/resolved-dns-server.h b/src/resolve/resolved-dns-server.h
index 6e73f32df..3c4627bca 100644
--- a/src/resolve/resolved-dns-server.h
+++ b/src/resolve/resolved-dns-server.h
@@ -122,8 +122,6 @@ bool dns_server_dnssec_supported(DnsServer *server);
 
 void dns_server_warn_downgrade(DnsServer *server);
 
-bool dns_server_limited_domains(DnsServer *server);
-
 DnsServer *dns_server_find(DnsServer *first, int family, const union in_addr_union *in_addr, int ifindex);
 
 void dns_server_unlink_all(DnsServer *first);
@@ -153,3 +151,5 @@ void dns_server_reset_features_all(DnsServer *s);
 void dns_server_dump(DnsServer *s, FILE *f);
 
 void dns_server_unref_stream(DnsServer *s);
+
+DnsScope *dns_server_scope(DnsServer *s);
diff --git a/src/resolve/resolved-link-bus.c b/src/resolve/resolved-link-bus.c
index b1581740d..96093fff5 100644
--- a/src/resolve/resolved-link-bus.c
+++ b/src/resolve/resolved-link-bus.c
@@ -107,6 +107,31 @@ static int property_get_domains(
         return sd_bus_message_close_container(reply);
 }
 
+static int property_get_default_route(
+                sd_bus *bus,
+                const char *path,
+                const char *interface,
+                const char *property,
+                sd_bus_message *reply,
+                void *userdata,
+                sd_bus_error *error) {
+
+        Link *l = userdata;
+
+        assert(reply);
+        assert(l);
+
+        /* Return what is configured, if there's something configured */
+        if (l->default_route >= 0)
+                return sd_bus_message_append(reply, "b", l->default_route);
+
+        /* Otherwise report what is in effect */
+        if (l->unicast_scope)
+                return sd_bus_message_append(reply, "b", dns_scope_is_default_route(l->unicast_scope));
+
+        return sd_bus_message_append(reply, "b", false);
+}
+
 static int property_get_scopes_mask(
                 sd_bus *bus,
                 const char *path,
@@ -346,6 +371,31 @@ clear:
         return r;
 }
 
+int bus_link_method_set_default_route(sd_bus_message *message, void *userdata, sd_bus_error *error) {
+        Link *l = userdata;
+        int r, b;
+
+        assert(message);
+        assert(l);
+
+        r = verify_unmanaged_link(l, error);
+        if (r < 0)
+                return r;
+
+        r = sd_bus_message_read(message, "b", &b);
+        if (r < 0)
+                return r;
+
+        if (l->default_route != b) {
+                l->default_route = b;
+
+                (void) link_save_user(l);
+                (void) manager_write_resolv_conf(l->manager);
+        }
+
+        return sd_bus_reply_method_return(message, NULL);
+}
+
 int bus_link_method_set_llmnr(sd_bus_message *message, void *userdata, sd_bus_error *error) {
         Link *l = userdata;
         ResolveSupport mode;
@@ -550,6 +600,7 @@ const sd_bus_vtable link_vtable[] = {
         SD_BUS_PROPERTY("DNS", "a(iay)", property_get_dns, 0, 0),
         SD_BUS_PROPERTY("CurrentDNSServer", "(iay)", property_get_current_dns_server, offsetof(Link, current_dns_server), 0),
         SD_BUS_PROPERTY("Domains", "a(sb)", property_get_domains, 0, 0),
+        SD_BUS_PROPERTY("DefaultRoute", "b", property_get_default_route, 0, 0),
         SD_BUS_PROPERTY("LLMNR", "s", bus_property_get_resolve_support, offsetof(Link, llmnr_support), 0),
         SD_BUS_PROPERTY("MulticastDNS", "s", bus_property_get_resolve_support, offsetof(Link, mdns_support), 0),
         SD_BUS_PROPERTY("DNSOverTLS", "s", property_get_dns_over_tls_mode, 0, 0),
@@ -559,6 +610,7 @@ const sd_bus_vtable link_vtable[] = {
 
         SD_BUS_METHOD("SetDNS", "a(iay)", NULL, bus_link_method_set_dns_servers, 0),
         SD_BUS_METHOD("SetDomains", "a(sb)", NULL, bus_link_method_set_domains, 0),
+        SD_BUS_METHOD("SetDefaultRoute", "b", NULL, bus_link_method_set_default_route, 0),
         SD_BUS_METHOD("SetLLMNR", "s", NULL, bus_link_method_set_llmnr, 0),
         SD_BUS_METHOD("SetMulticastDNS", "s", NULL, bus_link_method_set_mdns, 0),
         SD_BUS_METHOD("SetDNSOverTLS", "s", NULL, bus_link_method_set_dns_over_tls, 0),
diff --git a/src/resolve/resolved-link-bus.h b/src/resolve/resolved-link-bus.h
index 6b8092fdb..671725101 100644
--- a/src/resolve/resolved-link-bus.h
+++ b/src/resolve/resolved-link-bus.h
@@ -13,6 +13,7 @@ int link_node_enumerator(sd_bus *bus, const char *path, void *userdata, char ***
 
 int bus_link_method_set_dns_servers(sd_bus_message *message, void *userdata, sd_bus_error *error);
 int bus_link_method_set_domains(sd_bus_message *message, void *userdata, sd_bus_error *error);
+int bus_link_method_set_default_route(sd_bus_message *message, void *userdata, sd_bus_error *error);
 int bus_link_method_set_llmnr(sd_bus_message *message, void *userdata, sd_bus_error *error);
 int bus_link_method_set_mdns(sd_bus_message *message, void *userdata, sd_bus_error *error);
 int bus_link_method_set_dns_over_tls(sd_bus_message *message, void *userdata, sd_bus_error *error);
diff --git a/src/resolve/resolved-link.c b/src/resolve/resolved-link.c
index 2cfb848a8..44f70acea 100644
--- a/src/resolve/resolved-link.c
+++ b/src/resolve/resolved-link.c
@@ -30,16 +30,19 @@ int link_new(Manager *m, Link **ret, int ifindex) {
         if (r < 0)
                 return r;
 
-        l = new0(Link, 1);
+        l = new(Link, 1);
         if (!l)
                 return -ENOMEM;
 
-        l->ifindex = ifindex;
-        l->llmnr_support = RESOLVE_SUPPORT_YES;
-        l->mdns_support = RESOLVE_SUPPORT_NO;
-        l->dnssec_mode = _DNSSEC_MODE_INVALID;
-        l->dns_over_tls_mode = _DNS_OVER_TLS_MODE_INVALID;
-        l->operstate = IF_OPER_UNKNOWN;
+        *l = (Link) {
+                .ifindex = ifindex,
+                .default_route = -1,
+                .llmnr_support = RESOLVE_SUPPORT_YES,
+                .mdns_support = RESOLVE_SUPPORT_NO,
+                .dnssec_mode = _DNSSEC_MODE_INVALID,
+                .dns_over_tls_mode = _DNS_OVER_TLS_MODE_INVALID,
+                .operstate = IF_OPER_UNKNOWN,
+        };
 
         if (asprintf(&l->state_file, "/run/systemd/resolve/netif/%i", ifindex) < 0)
                 return -ENOMEM;
@@ -60,6 +63,7 @@ int link_new(Manager *m, Link **ret, int ifindex) {
 void link_flush_settings(Link *l) {
         assert(l);
 
+        l->default_route = -1;
         l->llmnr_support = RESOLVE_SUPPORT_YES;
         l->mdns_support = RESOLVE_SUPPORT_NO;
         l->dnssec_mode = _DNSSEC_MODE_INVALID;
@@ -297,6 +301,27 @@ clear:
         return r;
 }
 
+static int link_update_default_route(Link *l) {
+        int r;
+
+        assert(l);
+
+        r = sd_network_link_get_dns_default_route(l->ifindex);
+        if (r == -ENODATA) {
+                r = 0;
+                goto clear;
+        }
+        if (r < 0)
+                goto clear;
+
+        l->default_route = r > 0;
+        return 0;
+
+clear:
+        l->default_route = -1;
+        return r;
+}
+
 static int link_update_llmnr_support(Link *l) {
         _cleanup_free_ char *b = NULL;
         int r;
@@ -613,6 +638,10 @@ static void link_read_settings(Link *l) {
         r = link_update_search_domains(l);
         if (r < 0)
                 log_warning_errno(r, "Failed to read search domains for interface %s, ignoring: %m", l->name);
+
+        r = link_update_default_route(l);
+        if (r < 0)
+                log_warning_errno(r, "Failed to read default route setting for interface %s, proceeding anyway: %m", l->name);
 }
 
 int link_update(Link *l) {
@@ -1109,7 +1138,8 @@ static bool link_needs_save(Link *l) {
 
         if (l->llmnr_support != RESOLVE_SUPPORT_YES ||
             l->mdns_support != RESOLVE_SUPPORT_NO ||
-            l->dnssec_mode != _DNSSEC_MODE_INVALID)
+            l->dnssec_mode != _DNSSEC_MODE_INVALID ||
+            l->dns_over_tls_mode != _DNS_OVER_TLS_MODE_INVALID)
                 return true;
 
         if (l->dns_servers ||
@@ -1119,6 +1149,9 @@ static bool link_needs_save(Link *l) {
         if (!set_isempty(l->dnssec_negative_trust_anchors))
                 return true;
 
+        if (l->default_route >= 0)
+                return true;
+
         return false;
 }
 
@@ -1161,6 +1194,9 @@ int link_save_user(Link *l) {
         if (v)
                 fprintf(f, "DNSSEC=%s\n", v);
 
+        if (l->default_route >= 0)
+                fprintf(f, "DEFAULT_ROUTE=%s\n", yes_no(l->default_route));
+
         if (l->dns_servers) {
                 DnsServer *server;
 
@@ -1242,7 +1278,8 @@ int link_load_user(Link *l) {
                 *dnssec = NULL,
                 *servers = NULL,
                 *domains = NULL,
-                *ntas = NULL;
+                *ntas = NULL,
+                *default_route = NULL;
 
         ResolveSupport s;
         const char *p;
@@ -1265,7 +1302,8 @@ int link_load_user(Link *l) {
                            "DNSSEC", &dnssec,
                            "SERVERS", &servers,
                            "DOMAINS", &domains,
-                           "NTAS", &ntas);
+                           "NTAS", &ntas,
+                           "DEFAULT_ROUTE", &default_route);
         if (r == -ENOENT)
                 return 0;
         if (r < 0)
@@ -1282,6 +1320,10 @@ int link_load_user(Link *l) {
         if (s >= 0)
                 l->mdns_support = s;
 
+        r = parse_boolean(default_route);
+        if (r >= 0)
+                l->default_route = r;
+
         /* If we can't recognize the DNSSEC setting, then set it to invalid, so that the daemon default is used. */
         l->dnssec_mode = dnssec_mode_from_string(dnssec);
 
diff --git a/src/resolve/resolved-link.h b/src/resolve/resolved-link.h
index 81ab2056a..f95ea37a4 100644
--- a/src/resolve/resolved-link.h
+++ b/src/resolve/resolved-link.h
@@ -51,6 +51,8 @@ struct Link {
         LIST_HEAD(DnsSearchDomain, search_domains);
         unsigned n_search_domains;
 
+        int default_route;
+
         ResolveSupport llmnr_support;
         ResolveSupport mdns_support;
         DnsOverTlsMode dns_over_tls_mode;
diff --git a/src/resolve/resolved-resolv-conf.c b/src/resolve/resolved-resolv-conf.c
index 5fcd59d87..5205071d3 100644
--- a/src/resolve/resolved-resolv-conf.c
+++ b/src/resolve/resolved-resolv-conf.c
@@ -217,6 +217,8 @@ clear:
 }
 
 static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
+        DnsScope *scope;
+
         assert(s);
         assert(f);
         assert(count);
@@ -226,13 +228,12 @@ static void write_resolv_conf_server(DnsServer *s, FILE *f, unsigned *count) {
                 return;
         }
 
-        /* Check if the DNS server is limited to particular domains;
-         * resolv.conf does not have a syntax to express that, so it must not
-         * appear as a global name server to avoid routing unrelated domains to
-         * it (which is a privacy violation, will most probably fail anyway,
-         * and adds unnecessary load) */
-        if (dns_server_limited_domains(s)) {
-                log_debug("DNS server %s has route-only domains, not using as global name server", dns_server_string(s));
+        /* Check if the scope this DNS server belongs to is suitable as 'default' route for lookups; resolv.conf does
+         * not have a syntax to express that, so it must not appear as a global name server to avoid routing unrelated
+         * domains to it (which is a privacy violation, will most probably fail anyway, and adds unnecessary load) */
+        scope = dns_server_scope(s);
+        if (scope && !dns_scope_is_default_route(scope)) {
+                log_debug("Scope of DNS server %s has only route-only domains, not using as global name server", dns_server_string(s));
                 return;
         }
 
diff --git a/src/systemd/sd-network.h b/src/systemd/sd-network.h
index c8b7226bc..cc6bca9f5 100644
--- a/src/systemd/sd-network.h
+++ b/src/systemd/sd-network.h
@@ -151,6 +151,9 @@ int sd_network_link_get_search_domains(int ifindex, char ***domains);
 /* Get the route DNS domain names for a given link. */
 int sd_network_link_get_route_domains(int ifindex, char ***domains);
 
+/* Get whether this link shall be used as 'default route' for DNS queries */
+int sd_network_link_get_dns_default_route(int ifindex);
+
 /* Get the carrier interface indexes to which current link is bound to. */
 int sd_network_link_get_carrier_bound_to(int ifindex, int **ifindexes);