diff --git a/src/conf/network_conf.c b/src/conf/network_conf.c
index 18a7d575fd..e56e575e5e 100644
--- a/src/conf/network_conf.c
+++ b/src/conf/network_conf.c
@@ -582,33 +582,9 @@ virNetworkDefGetIpByIndex(const virNetworkDefPtr def,
  */
 int virNetworkIpDefPrefix(const virNetworkIpDefPtr def)
 {
-    if (def->prefix > 0) {
-        return def->prefix;
-    } else if (VIR_SOCKET_ADDR_VALID(&def->netmask)) {
-        return virSocketAddrGetNumNetmaskBits(&def->netmask);
-    } else if (VIR_SOCKET_ADDR_IS_FAMILY(&def->address, AF_INET)) {
-        /* Return the natural prefix for the network's ip address.
-         * On Linux we could use the IN_CLASSx() macros, but those
-         * aren't guaranteed on all platforms, so we just deal with
-         * the bits ourselves.
-         */
-        unsigned char octet
-            = ntohl(def->address.data.inet4.sin_addr.s_addr) >> 24;
-        if ((octet & 0x80) == 0) {
-            /* Class A network */
-            return 8;
-        } else if ((octet & 0xC0) == 0x80) {
-            /* Class B network */
-            return 16;
-        } else if ((octet & 0xE0) == 0xC0) {
-            /* Class C network */
-            return 24;
-        }
-        return -1;
-    } else if (VIR_SOCKET_ADDR_IS_FAMILY(&def->address, AF_INET6)) {
-        return 64;
-    }
-    return -1;
+    return virSocketAddrGetIpPrefix(&def->address,
+                                    &def->netmask,
+                                    def->prefix);
 }
 
 /* Fill in a virSocketAddr with the proper netmask for this
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index f778e9cd38..9f3a597a55 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1700,6 +1700,7 @@ virSocketAddrCheckNetmask;
 virSocketAddrEqual;
 virSocketAddrFormat;
 virSocketAddrFormatFull;
+virSocketAddrGetIpPrefix;
 virSocketAddrGetPort;
 virSocketAddrGetRange;
 virSocketAddrIsNetmask;
diff --git a/src/util/virsocketaddr.c b/src/util/virsocketaddr.c
index 3dfa3fb7ce..7ee450bb9e 100644
--- a/src/util/virsocketaddr.c
+++ b/src/util/virsocketaddr.c
@@ -754,4 +754,53 @@ virSocketAddrPrefixToNetmask(unsigned int prefix,
 
 error:
     return result;
+ }
+
+/**
+ * virSocketAddrGetIpPrefix:
+ * @address: network address
+ * @netmask: netmask for this network
+ * @prefix: prefix if specified instead of netmask
+ *
+ * Returns prefix value on success or -1 on error.
+ */
+
+int
+virSocketAddrGetIpPrefix(const virSocketAddrPtr address,
+                         const virSocketAddrPtr netmask,
+                         int prefix)
+{
+    if (prefix > 0) {
+        return prefix;
+    } else if (VIR_SOCKET_ADDR_VALID(netmask)) {
+        return virSocketAddrGetNumNetmaskBits(netmask);
+    } else if (VIR_SOCKET_ADDR_IS_FAMILY(address, AF_INET)) {
+        /* Return the natural prefix for the network's ip address.
+         * On Linux we could use the IN_CLASSx() macros, but those
+         * aren't guaranteed on all platforms, so we just deal with
+         * the bits ourselves.
+         */
+        unsigned char octet
+            = ntohl(address->data.inet4.sin_addr.s_addr) >> 24;
+        if ((octet & 0x80) == 0) {
+            /* Class A network */
+            return 8;
+        } else if ((octet & 0xC0) == 0x80) {
+            /* Class B network */
+            return 16;
+        } else if ((octet & 0xE0) == 0xC0) {
+            /* Class C network */
+            return 24;
+        }
+        return -1;
+    } else if (VIR_SOCKET_ADDR_IS_FAMILY(address, AF_INET6)) {
+        return 64;
+    }
+
+    /* When none of the three (address/netmask/prefix) is given, 0 is
+     * returned rather than error, because this is a valid
+     * expectation, e.g. for the address/prefix used for a default
+     * route (the destination of a default route is 0.0.0.0/0).
+     */
+    return 0;
 }
diff --git a/src/util/virsocketaddr.h b/src/util/virsocketaddr.h
index 8993f7b81d..1c9e54a441 100644
--- a/src/util/virsocketaddr.h
+++ b/src/util/virsocketaddr.h
@@ -116,6 +116,9 @@ int virSocketAddrGetNumNetmaskBits(const virSocketAddrPtr netmask);
 int virSocketAddrPrefixToNetmask(unsigned int prefix,
                                  virSocketAddrPtr netmask,
                                  int family);
+int virSocketAddrGetIpPrefix(const virSocketAddrPtr address,
+                             const virSocketAddrPtr netmask,
+                             int prefix);
 bool virSocketAddrEqual(const virSocketAddrPtr s1,
                         const virSocketAddrPtr s2);
 bool virSocketAddrIsPrivate(const virSocketAddrPtr addr);