execute check for loaded kernel modules

clab/config.go

@@ -411,7 +411,9 @@ func (c *CLab) CheckTopologyDefinition(ctx context.Context) error {
 			return err
 		}
 	}
-
+	if err = c.verifyKernelModulesLoaded(); err != nil {
+		return err
+	}
 	if err = c.verifyLinks(); err != nil {
 		return err
 	}
@@ -451,6 +453,22 @@ func (c *CLab) verifyLinks() error {
 	return nil
 }
 
+// verifyKernelModulesLoaded makes sure the listed kernel modules are loaded
+func (c *CLab) verifyKernelModulesLoaded() error {
+	modules := []string{"ip_tables", "ip6_tables"}
+
+	for _, m := range modules {
+		isLoaded, err := utils.IsKernelModuleLoaded(m)
+		if err != nil {
+			return err
+		}
+		if !isLoaded {
+			log.Warnf("kernel module %s is not loaded", m)
+		}
+	}
+	return nil
+}
+
 // verifyDuplicateAddresses checks that every static IP address in the topology is unique.
 func (c *CLab) verifyDuplicateAddresses() error {
 	dupIps := map[string]struct{}{}