Merge pull request #15669 from andir/systemd-ipv6-pd-subnet-id

networkd: subnet id support for ipv6 prefix delegation

11 files changed, 329 insertions, 54 deletions

diff --git a/man/systemd.network.xml b/man/systemd.network.xml
index f9e8fa5c25..a5e64167e4 100644
--- a/man/systemd.network.xml
+++ b/man/systemd.network.xml
@@ -721,6 +721,16 @@
           </para></listitem>
         </varlistentry>
         <varlistentry>
+          <term><varname>IPv6PDSubnetId=</varname></term>
+          <listitem><para>Configure a specific subnet ID on the interface from a (previously) received prefix delegation.
+          You can either set "auto" (the default) or a specific subnet ID
+          (as defined in <ulink url="https://tools.ietf.org/html/rfc4291#section-2.5.4">RFC 4291</ulink>, section 2.5.4),
+          in which case the allowed value is hexadecimal, from 0 to 0x7fffffffffffffff inclusive.
+          This option is only effective when used together with <varname>IPv6PrefixDelegation=</varname>
+          and the corresponding configuration on the upstream interface.
+          </para></listitem>
+        </varlistentry>
+        <varlistentry>
           <term><varname>IPv6MTUBytes=</varname></term>
           <listitem><para>Configures IPv6 maximum transmission unit (MTU).
           An integer greater than or equal to 1280 bytes. When unset, the kernel's default will be used.
diff --git a/src/basic/in-addr-util.c b/src/basic/in-addr-util.c
index bfe855fb4b..9feee66343 100644
--- a/src/basic/in-addr-util.c
+++ b/src/basic/in-addr-util.c
@@ -177,47 +177,89 @@ int in_addr_prefix_next(int family, union in_addr_union *u, unsigned prefixlen)
         assert(u);
 
         /* Increases the network part of an address by one. Returns
-         * positive it that succeeds, or 0 if this overflows. */
+         * positive if that succeeds, or -ERANGE if this overflows. */
+
+        return in_addr_prefix_nth(family, u, prefixlen, 1);
+}
+
+/*
+ * Calculates the nth prefix of size prefixlen starting from the address denoted by u.
+ *
+ * On success 1 will be returned and the calculated prefix will be available in
+ * u. In the case nth == 0 the input will be left unchanged and 1 will be returned.
+ * In case the calculation cannot be performed (invalid prefix length,
+ * overflows would occur) -ERANGE is returned. If the address family given isn't
+ * supported -EAFNOSUPPORT will be returned.
+ *
+ *
+ * Examples:
+ *   - in_addr_prefix_nth(AF_INET, 192.168.0.0, 24, 2), returns 1, writes 192.168.2.0 to u
+ *   - in_addr_prefix_nth(AF_INET, 192.168.0.0, 24, 0), returns 1, no data written
+ *   - in_addr_prefix_nth(AF_INET, 255.255.255.0, 24, 1), returns -ERANGE, no data written
+ *   - in_addr_prefix_nth(AF_INET, 255.255.255.0, 0, 1), returns -ERANGE, no data written
+ *   - in_addr_prefix_nth(AF_INET6, 2001:db8, 64, 0xff00) returns 1, writes 2001:0db8:0000:ff00:: to u
+ */
+int in_addr_prefix_nth(int family, union in_addr_union *u, unsigned prefixlen, uint64_t nth) {
+        assert(u);
 
         if (prefixlen <= 0)
-                return 0;
+                return -ERANGE;
 
-        if (family == AF_INET) {
-                uint32_t c, n;
+        if (nth == 0)
+                return 1;
 
+        if (family == AF_INET) {
+                uint32_t c, n, t;
                 if (prefixlen > 32)
                         prefixlen = 32;
 
                 c = be32toh(u->in.s_addr);
-                n = c + (1UL << (32 - prefixlen));
-                if (n < c)
-                        return 0;
-                n &= 0xFFFFFFFFUL << (32 - prefixlen);
 
+                t = nth << (32 - prefixlen);
+
+                /* Check for wrap */
+                if (c > UINT32_MAX - t)
+                        return -ERANGE;
+
+                n = c + t;
+
+                n &= UINT32_C(0xFFFFFFFF) << (32 - prefixlen);
                 u->in.s_addr = htobe32(n);
                 return 1;
         }
 
         if (family == AF_INET6) {
-                struct in6_addr add = {}, result;
+                struct in6_addr result = {};
                 uint8_t overflow = 0;
-                unsigned i;
+                uint64_t delta;  /* this assumes that we only ever have to up to 1<<64 subnets */
+                unsigned start_byte = (prefixlen - 1) / 8;
 
                 if (prefixlen > 128)
                         prefixlen = 128;
 
                 /* First calculate what we have to add */
-                add.s6_addr[(prefixlen-1) / 8] = 1 << (7 - (prefixlen-1) % 8);
+                delta = nth << ((128 - prefixlen) % 8);
 
-                for (i = 16; i > 0; i--) {
+                for (unsigned i = 16; i > 0; i--) {
                         unsigned j = i - 1;
+                        unsigned d = 0;
 
-                        result.s6_addr[j] = u->in6.s6_addr[j] + add.s6_addr[j] + overflow;
-                        overflow = (result.s6_addr[j] < u->in6.s6_addr[j]);
+                        if (j <= start_byte) {
+                                int16_t t;
+
+                                d = delta & 0xFF;
+                                delta >>= 8;
+
+                                t = u->in6.s6_addr[j] + d + overflow;
+                                overflow = t > UINT8_MAX ? t - UINT8_MAX : 0;
+
+                                result.s6_addr[j] = (uint8_t)t;
+                        } else
+                                result.s6_addr[j] = u->in6.s6_addr[j];
                 }
 
-                if (overflow)
-                        return 0;
+                if (overflow || delta != 0)
+                        return -ERANGE;
 
                 u->in6 = result;
                 return 1;
diff --git a/src/basic/in-addr-util.h b/src/basic/in-addr-util.h
index ae2dad0bb1..90d79a5ef5 100644
--- a/src/basic/in-addr-util.h
+++ b/src/basic/in-addr-util.h
@@ -36,6 +36,7 @@ bool in4_addr_equal(const struct in_addr *a, const struct in_addr *b);
 int in_addr_equal(int family, const union in_addr_union *a, const union in_addr_union *b);
 int in_addr_prefix_intersect(int family, const union in_addr_union *a, unsigned aprefixlen, const union in_addr_union *b, unsigned bprefixlen);
 int in_addr_prefix_next(int family, union in_addr_union *u, unsigned prefixlen);
+int in_addr_prefix_nth(int family, union in_addr_union *u, unsigned prefixlen, uint64_t nth);
 int in_addr_random_prefix(int family, union in_addr_union *u, unsigned prefixlen_fixed_part, unsigned prefixlen);
 int in_addr_to_string(int family, const union in_addr_union *u, char **ret);
 int in_addr_prefix_to_string(int family, const union in_addr_union *u, unsigned prefixlen, char **ret);
diff --git a/src/network/networkd-dhcp6.c b/src/network/networkd-dhcp6.c
index 29226b64bf..b3ebdc8cd7 100644
--- a/src/network/networkd-dhcp6.c
+++ b/src/network/networkd-dhcp6.c
@@ -25,6 +25,7 @@ static int dhcp6_lease_address_acquired(sd_dhcp6_client *client, Link *link);
 static Link *dhcp6_prefix_get(Manager *m, struct in6_addr *addr);
 static int dhcp6_prefix_add(Manager *m, struct in6_addr *addr, Link *link);
 static int dhcp6_prefix_remove_all(Manager *m, Link *link);
+static bool dhcp6_link_has_dhcpv6_prefix(Link *link);
 
 static bool dhcp6_get_prefix_delegation(Link *link) {
         if (!link->network)
@@ -35,6 +36,97 @@ static bool dhcp6_get_prefix_delegation(Link *link) {
                       RADV_PREFIX_DELEGATION_BOTH);
 }
 
+static bool dhcp6_has_preferred_subnet_id(Link *link) {
+        if (!link->network)
+                return false;
+
+        return link->network->router_prefix_subnet_id >= 0;
+}
+
+static int dhcp6_get_preferred_delegated_prefix(
+                Manager* manager,
+                Link *link,
+                const struct in6_addr *pd_prefix,
+                uint8_t pd_prefix_len,
+                struct in6_addr *ret_addr) {
+        int r;
+        union in_addr_union pd_prefix_union = {
+                .in6 = *pd_prefix,
+        };
+        int64_t subnet_id = link->network->router_prefix_subnet_id;
+
+        assert(pd_prefix_len <= 64);
+
+        uint8_t prefix_bits = 64 - pd_prefix_len;
+        uint64_t n_prefixes = UINT64_C(1) << prefix_bits;
+        _cleanup_free_ char *assigned_buf = NULL;
+
+        /* We start off with the original PD prefix we have been assigned and
+         * iterate from there */
+        union in_addr_union prefix = {
+                .in6 = *pd_prefix,
+        };
+
+        if (subnet_id >= 0) {
+                /* If the link has a preference for a particular subnet id try to allocate that */
+                if ((uint64_t)subnet_id >= n_prefixes)
+                        return log_link_debug_errno(link,
+                                        SYNTHETIC_ERRNO(ERANGE),
+                                        "subnet id %" PRIi64 " is out of range. Only have %" PRIu64 " subnets.",
+                                        subnet_id,
+                                        n_prefixes);
+
+                r = in_addr_prefix_nth(AF_INET6, &prefix, 64, subnet_id);
+                if (r < 0)
+                        return log_link_debug_errno(link,
+                                        r,
+                                        "subnet id %" PRIi64 " is out of range. Only have %" PRIu64 " subnets.",
+                                        subnet_id,
+                                        n_prefixes);
+
+                /* Verify that the prefix we did calculate fits in the pd prefix.
+                 * This should not fail as we checked the prefix size beforehand */
+                assert_se(in_addr_prefix_covers(AF_INET6, &pd_prefix_union, pd_prefix_len, &prefix) > 0);
+
+                Link* assigned_link = dhcp6_prefix_get(manager, &prefix.in6);
+
+                (void) in_addr_to_string(AF_INET6, &prefix, &assigned_buf);
+
+                if (assigned_link && assigned_link != link)
+                        return log_link_error_errno(link, SYNTHETIC_ERRNO(EAGAIN),
+                                       "The requested prefix %s is already assigned to another link: %s",
+                                       strnull(assigned_buf),
+                                       strnull(assigned_link->ifname));
+
+                *ret_addr = prefix.in6;
+
+                log_link_debug(link, "The requested prefix %s is available. Using it.",
+                               strnull(assigned_buf));
+                return 0;
+        } else {
+                for (uint64_t n = 0; n < n_prefixes; n++) {
+                        /* if we do not have an allocation preference just iterate
+                         * through the address space and return the first free prefix. */
+                        Link* assigned_link = dhcp6_prefix_get(manager, &prefix.in6);
+
+                        if (!assigned_link || assigned_link == link) {
+                                *ret_addr = prefix.in6;
+                                return 0;
+                        }
+
+                        r = in_addr_prefix_next(AF_INET6, &prefix, 64);
+                        if (r < 0)
+                                return log_link_error_errno(link,
+                                                r,
+                                                "Can't allocate another prefix. Out of address space?");
+                }
+
+                log_link_warning(link, "Couldn't find a suitable prefix. Ran out of address space.");
+        }
+
+        return -ERANGE;
+}
+
 static bool dhcp6_enable_prefix_delegation(Link *dhcp6_link) {
         Manager *manager;
         Link *l;
@@ -165,24 +257,27 @@ int dhcp6_lease_pd_prefix_lost(sd_dhcp6_client *client, Link* link) {
         return 0;
 }
 
-static int dhcp6_pd_prefix_distribute(Link *dhcp6_link, Iterator *i,
+static int dhcp6_pd_prefix_distribute(Link *dhcp6_link,
                                       struct in6_addr *pd_prefix,
                                       uint8_t pd_prefix_len,
                                       uint32_t lifetime_preferred,
-                                      uint32_t lifetime_valid) {
+                                      uint32_t lifetime_valid,
+                                      bool assign_preferred_subnet_id) {
+        Iterator i;
         Link *link;
         Manager *manager = dhcp6_link->manager;
-        union in_addr_union prefix;
-        uint64_t n_prefixes, n_used = 0;
+        union in_addr_union prefix = {
+                .in6 = *pd_prefix,
+        };
+        uint64_t n_prefixes;
         _cleanup_free_ char *buf = NULL;
         _cleanup_free_ char *assigned_buf = NULL;
         int r;
+        bool pool_depleted = false;
 
         assert(manager);
         assert(pd_prefix_len <= 64);
 
-        prefix.in6 = *pd_prefix;
-
         r = in_addr_mask(AF_INET6, &prefix, pd_prefix_len);
         if (r < 0)
                 return r;
@@ -193,15 +288,8 @@ static int dhcp6_pd_prefix_distribute(Link *dhcp6_link, Iterator *i,
         log_link_debug(dhcp6_link, "Assigning up to %" PRIu64 " prefixes from %s/%u",
                        n_prefixes, strnull(buf), pd_prefix_len);
 
-        while (hashmap_iterate(manager->links, i, (void **)&link, NULL)) {
-                Link *assigned_link;
-
-                if (n_used == n_prefixes) {
-                        log_link_debug(dhcp6_link, "Assigned %" PRIu64 "/%" PRIu64 " prefixes from %s/%u",
-                                       n_used, n_prefixes, strnull(buf), pd_prefix_len);
-
-                        return -EAGAIN;
-                }
+        HASHMAP_FOREACH(link, manager->links, i) {
+                union in_addr_union assigned_prefix;
 
                 if (link == dhcp6_link)
                         continue;
@@ -209,35 +297,42 @@ static int dhcp6_pd_prefix_distribute(Link *dhcp6_link, Iterator *i,
                 if (!dhcp6_get_prefix_delegation(link))
                         continue;
 
-                assigned_link = dhcp6_prefix_get(manager, &prefix.in6);
-                if (assigned_link && assigned_link != link)
+                if (dhcp6_link_has_dhcpv6_prefix(link))
                         continue;
 
-                (void) in_addr_to_string(AF_INET6, &prefix, &assigned_buf);
-                r = dhcp6_pd_prefix_assign(link, &prefix.in6, 64,
+                if (assign_preferred_subnet_id != dhcp6_has_preferred_subnet_id(link))
+                        continue;
+
+                r = dhcp6_get_preferred_delegated_prefix(manager, link, &prefix.in6, pd_prefix_len,
+                                                        &assigned_prefix.in6);
+
+                if (assign_preferred_subnet_id && r == -EAGAIN) {
+                        /* A link has a preferred subnet_id but that one is
+                         * already taken by another link. Now all the remaining
+                         * links will also not obtain a prefix. */
+                        pool_depleted = true;
+                        continue;
+                } else if (r < 0)
+                        return r;
+
+                (void) in_addr_to_string(AF_INET6, &assigned_prefix, &assigned_buf);
+                r = dhcp6_pd_prefix_assign(link, &assigned_prefix.in6, 64,
                                            lifetime_preferred, lifetime_valid);
                 if (r < 0) {
-                        log_link_error_errno(link, r, "Unable to %s prefix %s/64 from %s/%u for link: %m",
-                                             assigned_link ? "update": "assign",
+                        log_link_error_errno(link, r, "Unable to assign/update prefix %s/64 from %s/%u for link: %m",
                                              strnull(assigned_buf),
                                              strnull(buf), pd_prefix_len);
-
-                        if (!assigned_link)
-                                continue;
-
                 } else
-                        log_link_debug(link, "Assigned prefix %" PRIu64 "/%" PRIu64 " %s/64 from %s/%u to link",
-                                       n_used + 1, n_prefixes,
+                        log_link_debug(link, "Assigned prefix %s/64 from %s/%u to link",
                                        strnull(assigned_buf),
                                        strnull(buf), pd_prefix_len);
-
-                n_used++;
-
-                r = in_addr_prefix_next(AF_INET6, &prefix, 64);
-                if (r < 0 && n_used < n_prefixes)
-                        return r;
         }
 
+        /* If one of the link requests couldn't be fulfilled, signal that we
+           should try again with another prefix. */
+        if (pool_depleted)
+                return -EAGAIN;
+
         return 0;
 }
 
@@ -262,7 +357,6 @@ static int dhcp6_lease_pd_prefix_acquired(sd_dhcp6_client *client, Link *link) {
         union in_addr_union pd_prefix;
         uint8_t pd_prefix_len;
         uint32_t lifetime_preferred, lifetime_valid;
-        Iterator i = ITERATOR_FIRST;
 
         r = sd_dhcp6_client_get_lease(client, &lease);
         if (r < 0)
@@ -314,15 +408,47 @@ static int dhcp6_lease_pd_prefix_acquired(sd_dhcp6_client *client, Link *link) {
                 } else
                         log_link_debug(link, "Not adding a blocking route since distributed prefix is /64");
 
-                r = dhcp6_pd_prefix_distribute(link, &i, &pd_prefix.in6,
+                /* We are doing prefix allocation in two steps:
+                 * 1. all those links that have a preferred subnet id will be assigned their subnet
+                 * 2. all those links that remain will receive prefixes in sequential
+                 *    order. Prefixes that were previously already allocated to another
+                 *    link will be skipped.
+
+                 * If a subnet id request couldn't be fullfilled the failure will be logged (as error)
+                 * and no further attempts at obtaining a prefix will be made.
+
+                 * The assignment has to be split in two phases since subnet id
+                 * preferences should be honored. Meaning that any subnet id should be
+                 * handed out to the requesting link and not to some link that didn't
+                 * specify any preference. */
+
+                r = dhcp6_pd_prefix_distribute(link, &pd_prefix.in6,
                                                pd_prefix_len,
                                                lifetime_preferred,
-                                               lifetime_valid);
+                                               lifetime_valid,
+                                               true);
                 if (r < 0 && r != -EAGAIN)
                         return r;
 
-                if (r >= 0)
-                        i = ITERATOR_FIRST;
+                /* if r == -EAGAIN then the allocation failed because we ran
+                 * out of addresses for the preferred subnet id's. This doesn't
+                 * mean we can't fullfill other prefix requests.
+                 *
+                 * Since we do not have dedicated lists of links that request
+                 * specific subnet id's and those that accept any prefix we
+                 * *must* reset the iterator to the start as otherwise some
+                 * links might not get their requested prefix. */
+
+                r = dhcp6_pd_prefix_distribute(link, &pd_prefix.in6,
+                                               pd_prefix_len,
+                                               lifetime_preferred,
+                                               lifetime_valid,
+                                               false);
+                if (r < 0 && r != -EAGAIN)
+                        return r;
+
+                /* If the prefix distribution did return -EAGAIN we will try to
+                 * fullfill those with the next available pd delegated prefix. */
         }
 
         return 0;
@@ -878,3 +1004,17 @@ static int dhcp6_prefix_remove_all(Manager *m, Link *link) {
 
         return 0;
 }
+
+static bool dhcp6_link_has_dhcpv6_prefix(Link *link) {
+        Iterator i;
+        Link *l;
+
+        assert(link);
+        assert(link->manager);
+
+        HASHMAP_FOREACH(l, link->manager->dhcp6_prefixes, i)
+                if (link == l)
+                        return true;
+
+        return false;
+}
diff --git a/src/network/networkd-network-gperf.gperf b/src/network/networkd-network-gperf.gperf
index a2dd5479b2..8484669ad9 100644
--- a/src/network/networkd-network-gperf.gperf
+++ b/src/network/networkd-network-gperf.gperf
@@ -250,6 +250,7 @@ BridgeVLAN.PVID,                             config_parse_brvlan_pvid,
 BridgeVLAN.VLAN,                             config_parse_brvlan_vlan,                                 0,                             0
 BridgeVLAN.EgressUntagged,                   config_parse_brvlan_untagged,                             0,                             0
 Network.IPv6PrefixDelegation,                config_parse_router_prefix_delegation,                    0,                             0
+Network.IPv6PDSubnetId,                      config_parse_router_prefix_subnet_id,                     0,                             0
 IPv6PrefixDelegation.RouterLifetimeSec,      config_parse_sec,                                         0,                             offsetof(Network, router_lifetime_usec)
 IPv6PrefixDelegation.Managed,                config_parse_bool,                                        0,                             offsetof(Network, router_managed)
 IPv6PrefixDelegation.OtherInformation,       config_parse_bool,                                        0,                             offsetof(Network, router_other_information)
diff --git a/src/network/networkd-network.c b/src/network/networkd-network.c
index 1b4083febf..a3a1b070e0 100644
--- a/src/network/networkd-network.c
+++ b/src/network/networkd-network.c
@@ -415,6 +415,7 @@ int network_load_one(Manager *manager, OrderedHashmap **networks, const char *fi
                 .dhcp_server_emit_router = true,
                 .dhcp_server_emit_timezone = true,
 
+                .router_prefix_subnet_id = -1,
                 .router_emit_dns = true,
                 .router_emit_domains = true,
 
diff --git a/src/network/networkd-network.h b/src/network/networkd-network.h
index 362ef6508f..64d6ef0553 100644
--- a/src/network/networkd-network.h
+++ b/src/network/networkd-network.h
@@ -178,6 +178,7 @@ struct Network {
 
         /* IPv6 prefix delegation support */
         RADVPrefixDelegation router_prefix_delegation;
+        int64_t router_prefix_subnet_id;
         usec_t router_lifetime_usec;
         uint8_t router_preference;
         bool router_managed;
diff --git a/src/network/networkd-radv.c b/src/network/networkd-radv.c
index d9267dd805..f5f8ec65ed 100644
--- a/src/network/networkd-radv.c
+++ b/src/network/networkd-radv.c
@@ -864,3 +864,40 @@ int config_parse_router_preference(const char *unit,
 
         return 0;
 }
+
+int config_parse_router_prefix_subnet_id(const char *unit,
+                const char *filename,
+                unsigned line,
+                const char *section,
+                unsigned section_line,
+                const char *lvalue,
+                int ltype,
+                const char *rvalue,
+                void *data,
+                void *userdata) {
+        Network *network = userdata;
+        uint64_t t;
+        int r;
+
+        assert(filename);
+        assert(lvalue);
+        assert(rvalue);
+        assert(data);
+
+        if (isempty(rvalue) || streq(rvalue, "auto")) {
+                network->router_prefix_subnet_id = -1;
+                return 0;
+        }
+
+        r = safe_atoux64(rvalue, &t);
+        if (r < 0 || t > INT64_MAX) {
+                log_syntax(unit, LOG_ERR, filename, line, r,
+                                "Subnet id '%s' is invalid, ignoring assignment.",
+                                rvalue);
+                return 0;
+        }
+
+        network->router_prefix_subnet_id = (int64_t)t;
+
+        return 0;
+}
diff --git a/src/network/networkd-radv.h b/src/network/networkd-radv.h
index 8bf697aff0..b115243ef5 100644
--- a/src/network/networkd-radv.h
+++ b/src/network/networkd-radv.h
@@ -58,6 +58,7 @@ RADVPrefixDelegation radv_prefix_delegation_from_string(const char *s) _pure_;
 
 CONFIG_PARSER_PROTOTYPE(config_parse_router_prefix_delegation);
 CONFIG_PARSER_PROTOTYPE(config_parse_router_preference);
+CONFIG_PARSER_PROTOTYPE(config_parse_router_prefix_subnet_id);
 CONFIG_PARSER_PROTOTYPE(config_parse_prefix);
 CONFIG_PARSER_PROTOTYPE(config_parse_prefix_flags);
 CONFIG_PARSER_PROTOTYPE(config_parse_prefix_lifetime);
diff --git a/src/test/test-socket-util.c b/src/test/test-socket-util.c
index 05c375d79b..024e12a799 100644
--- a/src/test/test-socket-util.c
+++ b/src/test/test-socket-util.c
@@ -173,6 +173,45 @@ static void test_in_addr_prefix_next(void) {
         test_in_addr_prefix_next_one(AF_INET6, "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ff00", 120, NULL);
 }
 
+static void test_in_addr_prefix_nth_one(unsigned f, const char *before, unsigned pl, uint64_t nth, const char *after) {
+        union in_addr_union ubefore, uafter, t;
+
+        assert_se(in_addr_from_string(f, before, &ubefore) >= 0);
+
+        t = ubefore;
+        assert_se((in_addr_prefix_nth(f, &t, pl, nth) > 0) == !!after);
+
+        if (after) {
+                assert_se(in_addr_from_string(f, after, &uafter) >= 0);
+                assert_se(in_addr_equal(f, &t, &uafter) > 0);
+        }
+}
+
+static void test_in_addr_prefix_nth(void) {
+        log_info("/* %s */", __func__);
+
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.0.0", 24, 0, "192.168.0.0");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.0.0", 24, 1, "192.168.1.0");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.0.0", 24, 4, "192.168.4.0");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.0.0", 25, 1, "192.168.0.128");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.255.0", 25, 1, "192.168.255.128");
+        test_in_addr_prefix_nth_one(AF_INET, "192.168.255.0", 24, 0, "192.168.255.0");
+        test_in_addr_prefix_nth_one(AF_INET, "255.255.255.255", 32, 1, NULL);
+        test_in_addr_prefix_nth_one(AF_INET, "255.255.255.255", 0, 1, NULL);
+
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 8, 1, "4500::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 7, 1, "4600::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 64, 1, "4400:0:0:1::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 64, 2, "4400:0:0:2::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 64, 0xbad, "4400:0:0:0bad::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400:0:0:ffff::", 64, 1, "4400:0:1::");
+        test_in_addr_prefix_nth_one(AF_INET6, "4400::", 56, ((uint64_t)1<<48) -1, "44ff:ffff:ffff:ff00::");
+        test_in_addr_prefix_nth_one(AF_INET6, "0000::", 8, 255, "ff00::");
+        test_in_addr_prefix_nth_one(AF_INET6, "0000::", 8, 256, NULL);
+        test_in_addr_prefix_nth_one(AF_INET6, "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff", 128, 1, NULL);
+        test_in_addr_prefix_nth_one(AF_INET6, "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff", 0, 1, NULL);
+}
+
 static void test_in_addr_to_string_one(int f, const char *addr) {
         union in_addr_union ua;
         _cleanup_free_ char *r = NULL;
@@ -691,6 +730,7 @@ int main(int argc, char *argv[]) {
         test_in_addr_is_null();
         test_in_addr_prefix_intersect();
         test_in_addr_prefix_next();
+        test_in_addr_prefix_nth();
         test_in_addr_to_string();
         test_in_addr_ifindex_to_string();
         test_in_addr_ifindex_from_string_auto();
diff --git a/test/fuzz/fuzz-network-parser/directives.network b/test/fuzz/fuzz-network-parser/directives.network
index 2b95192672..178bd9aaae 100644
--- a/test/fuzz/fuzz-network-parser/directives.network
+++ b/test/fuzz/fuzz-network-parser/directives.network
@@ -186,6 +186,7 @@ NTP=
 DHCP=
 Domains=
 IPv6PrefixDelegation=
+IPv6PDSubnetId=
 VLAN=
 DHCPServer=
 BindCarrier=