From ecf17798e7a84129e136f1ce33d0282f614ec61b Mon Sep 17 00:00:00 2001
From: Hardik Dodiya <hardik.dodiya@sap.com>
Date: Wed, 2 Oct 2024 11:16:57 +0200
Subject: [PATCH] Set host bits to zero for PodCIDRs (#19)

---
 .../node_ipam_controller.go                   | 19 ++++++++++++++++++-
 .../node_ipam_controller_test.go              |  4 ++--
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/internal/metal-load-balancer-controller/node_ipam_controller.go b/internal/metal-load-balancer-controller/node_ipam_controller.go
index 32ffdf5..e779af7 100644
--- a/internal/metal-load-balancer-controller/node_ipam_controller.go
+++ b/internal/metal-load-balancer-controller/node_ipam_controller.go
@@ -6,6 +6,7 @@ package metal_load_balancer_controller
 import (
 	"context"
 	"fmt"
+	"net"
 
 	corev1 "k8s.io/api/core/v1"
 	"k8s.io/apimachinery/pkg/runtime"
@@ -37,7 +38,13 @@ func (r *NodeIPAMReconciler) Reconcile(ctx context.Context, req ctrl.Request) (c
 
 	for _, addr := range node.Status.Addresses {
 		if addr.Type == corev1.NodeInternalIP {
-			podCIDR := fmt.Sprintf("%s/%d", addr.Address, r.NodeCIDRMaskSize)
+			ip := net.ParseIP(addr.Address)
+			if ip == nil {
+				return ctrl.Result{}, fmt.Errorf("invalid IP address format")
+			}
+
+			maskedIP := zeroHostBits(ip, r.NodeCIDRMaskSize)
+			podCIDR := fmt.Sprintf("%s/%d", maskedIP, r.NodeCIDRMaskSize)
 
 			nodeBase := node.DeepCopy()
 			node.Spec.PodCIDR = podCIDR
@@ -58,6 +65,16 @@ func (r *NodeIPAMReconciler) Reconcile(ctx context.Context, req ctrl.Request) (c
 	return ctrl.Result{}, nil
 }
 
+func zeroHostBits(ip net.IP, maskSize int) net.IP {
+	if ip.To4() != nil {
+		mask := net.CIDRMask(maskSize, 32)
+		return ip.Mask(mask)
+	} else {
+		mask := net.CIDRMask(maskSize, 128)
+		return ip.Mask(mask)
+	}
+}
+
 // SetupWithManager sets up the controller with the Manager.
 func (r *NodeIPAMReconciler) SetupWithManager(mgr ctrl.Manager) error {
 	return ctrl.NewControllerManagedBy(mgr).
diff --git a/internal/metal-load-balancer-controller/node_ipam_controller_test.go b/internal/metal-load-balancer-controller/node_ipam_controller_test.go
index 0b44be4..373fad5 100644
--- a/internal/metal-load-balancer-controller/node_ipam_controller_test.go
+++ b/internal/metal-load-balancer-controller/node_ipam_controller_test.go
@@ -36,8 +36,8 @@ var _ = Describe("Node IPAM Controller", func() {
 			DeferCleanup(k8sClient.Delete, node)
 
 			Eventually(Object(node)).Should(SatisfyAll(
-				HaveField("Spec.PodCIDR", Equal("1a10:c0de::1/64")),
-				HaveField("Spec.PodCIDRs", ContainElement("1a10:c0de::1/64")),
+				HaveField("Spec.PodCIDR", Equal("1a10:c0de::/64")),
+				HaveField("Spec.PodCIDRs", ContainElement("1a10:c0de::/64")),
 			))
 
 		})