diff --git a/src/libnm-glib-aux/nm-inet-utils.c b/src/libnm-glib-aux/nm-inet-utils.c
index 2ee73ad5e7..f4f418cf18 100644
--- a/src/libnm-glib-aux/nm-inet-utils.c
+++ b/src/libnm-glib-aux/nm-inet-utils.c
@@ -238,6 +238,42 @@ nm_ip6_addr_clear_host_address(struct in6_addr *dst, const struct in6_addr *src,
     return dst;
 }
 
+/**
+ * nm_ip6_addr_get_subnet_id:
+ * @addr: the IPv6 address
+ * @plen: the prefix length
+ *
+ * Given an IPv6 address and a prefix length, returns the subnet ID,
+ * defined as follows:
+ *
+ * |     plen bits   | (64 - plen) bits |          64 bits              |
+ * +-----------------+------------------+-------------------------------+
+ * |      prefix     |    subnet ID     |        interface ID           |
+ * +-----------------+------------------+-------------------------------+
+ *
+ * The prefix length must be a value between 0 and 64.
+ */
+guint64
+nm_ip6_addr_get_subnet_id(struct in6_addr *addr, guint8 plen)
+{
+    int     nbits = 64 - plen;
+    guint64 res   = 0;
+    guint64 tmp;
+    guint64 i;
+
+    g_return_val_if_fail(addr, 0);
+    g_return_val_if_fail(plen <= 64, 0);
+
+    for (i = 0; i < 2 && nbits > 0; i++, nbits -= 32) {
+        tmp = htonl(addr->s6_addr32[1 - i]);
+        tmp = tmp & ((1ULL << NM_MIN(32U, (guint) nbits)) - 1);
+        tmp = tmp << (32 * i);
+        res += tmp;
+    }
+
+    return res;
+}
+
 int
 nm_ip6_addr_same_prefix_cmp(const struct in6_addr *addr_a,
                             const struct in6_addr *addr_b,
diff --git a/src/libnm-glib-aux/nm-inet-utils.h b/src/libnm-glib-aux/nm-inet-utils.h
index 489d21dde2..999519f890 100644
--- a/src/libnm-glib-aux/nm-inet-utils.h
+++ b/src/libnm-glib-aux/nm-inet-utils.h
@@ -218,6 +218,8 @@ nm_ip4_addr_clear_host_address(in_addr_t addr, guint32 plen)
 const struct in6_addr *
 nm_ip6_addr_clear_host_address(struct in6_addr *dst, const struct in6_addr *src, guint32 plen);
 
+guint64 nm_ip6_addr_get_subnet_id(struct in6_addr *addr, guint8 plen);
+
 /*****************************************************************************/
 
 static inline int
diff --git a/src/libnm-glib-aux/tests/test-shared-general.c b/src/libnm-glib-aux/tests/test-shared-general.c
index 2f09a5490d..931c25c667 100644
--- a/src/libnm-glib-aux/tests/test-shared-general.c
+++ b/src/libnm-glib-aux/tests/test-shared-general.c
@@ -397,6 +397,53 @@ test_nm_ip4_addr_netmask_from_prefix(void)
 
 /*****************************************************************************/
 
+static void
+test_nm_ip6_addr_get_subnet_id(void)
+{
+#define check_subnet_id(_addrstr, _plen, _subnet_id)                              \
+    {                                                                             \
+        struct in6_addr addr;                                                     \
+                                                                                  \
+        addr = nmtst_inet6_from_string(_addrstr);                                 \
+        g_assert_cmpint(nm_ip6_addr_get_subnet_id(&addr, _plen), ==, _subnet_id); \
+    }
+
+    check_subnet_id("aaaa:bbbb:cccc:ffff::", 64, 0);
+    check_subnet_id("aaaa:bbbb:cccc:fffe::", 63, 0);
+    check_subnet_id("aaaa:bbbb:cccc:ffff::", 63, 1);
+    check_subnet_id("aaaa:bbbb:cccc:fffc::", 62, 0);
+    check_subnet_id("aaaa:bbbb:cccc:fffd::", 62, 1);
+    check_subnet_id("aaaa:bbbb:cccc:fffe::", 62, 2);
+    check_subnet_id("aaaa:bbbb:cccc:ffff::", 62, 3);
+    check_subnet_id("aaaa:bbbb:cccc:fff8::", 61, 0);
+    check_subnet_id("aaaa:bbbb:cccc:ffff::", 61, 7);
+    check_subnet_id("aaaa:bbbb:cccc:fff0::", 60, 0);
+    check_subnet_id("aaaa:bbbb:cccc:fff2::", 60, 2);
+    check_subnet_id("aaaa:bbbb:cccc:ffff::", 60, 15);
+    check_subnet_id("aaaa:bbbb:cccc:0000::", 48, 0);
+    check_subnet_id("aaaa:bbbb:cccc:f000::", 48, 61440);
+    check_subnet_id("aaaa:bbbb:cccc:ffff::", 48, 65535);
+    check_subnet_id("aaaa:bbbb:cccc:0000::", 46, 0);
+    check_subnet_id("aaaa:bbbb:cccc:0001::", 46, 1);
+    check_subnet_id("aaaa:bbbb:ccce:5555::", 46, 152917);
+    check_subnet_id("aaaa:bbbb:0000:0000::", 32, 0);
+    check_subnet_id("aaaa:bbbb:0000:0001::", 32, 1);
+    check_subnet_id("aaaa:bbbb:0001:0001::", 32, 65537);
+    check_subnet_id("aaaa:bbbb:ffff:ffff::", 32, 0xffffffff);
+    check_subnet_id("aaaa:bbb8:0000:0000::", 30, 0);
+    check_subnet_id("aaaa:bbb8:0000:0001::", 30, 1);
+    check_subnet_id("aaaa:bbb8:0001:0001::", 30, 65537);
+    check_subnet_id("aaaa:bbbb:0000:0000::", 30, 0x300000000ULL);
+    check_subnet_id("aaaa:bbbb:0001:0001::", 30, 0x300010001ULL);
+    check_subnet_id("aaaa:bbbb:0001:0001::", 8, 0xAABBBB00010001ULL);
+    check_subnet_id("abaa:bbbb:0001:0001::", 7, 0x1AABBBB00010001ULL);
+    check_subnet_id("abaa:bbbb:0001:0001::", 0, 0xABAABBBB00010001ULL);
+    check_subnet_id("abaa:bbbb:0001:0001:5555:5555:5555:5555", 0, 0xABAABBBB00010001ULL);
+    check_subnet_id("::", 0, 0);
+}
+
+/*****************************************************************************/
+
 static void
 test_unaligned(void)
 {
@@ -2864,6 +2911,7 @@ main(int argc, char **argv)
     g_test_add_func("/general/test_nm_ip4_addr_is_loopback", test_nm_ip4_addr_is_loopback);
     g_test_add_func("/general/test_nm_ip4_addr_netmask_from_prefix",
                     test_nm_ip4_addr_netmask_from_prefix);
+    g_test_add_func("/general/test_nm_ip6_addr_get_subnet_id", test_nm_ip6_addr_get_subnet_id);
     g_test_add_func("/general/test_unaligned", test_unaligned);
     g_test_add_func("/general/test_strv_cmp", test_strv_cmp);
     g_test_add_func("/general/test_strstrip_avoid_copy", test_strstrip_avoid_copy);