Add create subnet operation
diff --git a/openstack/networking/v2/subnets/errors.go b/openstack/networking/v2/subnets/errors.go
index b15101b..9299927 100644
--- a/openstack/networking/v2/subnets/errors.go
+++ b/openstack/networking/v2/subnets/errors.go
@@ -1 +1,13 @@
 package subnets
+
+import "fmt"
+
+func err(str string) error {
+	return fmt.Errorf("%s", str)
+}
+
+var (
+	ErrNetworkIDRequired = err("A network ID is required")
+	ErrCIDRRequired      = err("A valid CIDR is required")
+	ErrInvalidIPType     = err("An IP type must either be 4 or 6")
+)