diff --git a/cmd/microcloud/main_init_test.go b/cmd/microcloud/main_init_test.go
index 4cc8360f9..ea637c40c 100644
--- a/cmd/microcloud/main_init_test.go
+++ b/cmd/microcloud/main_init_test.go
@@ -1,9 +1,11 @@
 package main
 
 import (
+	"net"
 	"testing"
 
 	lxdAPI "github.com/canonical/lxd/shared/api"
+	"github.com/stretchr/testify/assert"
 
 	"github.com/canonical/microcloud/microcloud/multicast"
 	"github.com/canonical/microcloud/microcloud/service"
@@ -226,3 +228,103 @@ func TestValidateSystemsMultiSystem(t *testing.T) {
 		t.Fatalf("sys4 with conflicting management IP and ipv6.ovn.ranges passed validation")
 	}
 }
+
+func newNetwork(ifaceName, ipStr string) *Network {
+	ip, subnet, _ := net.ParseCIDR(ipStr)
+	return &Network{
+		Interface: ifaceName,
+		IP:        ip,
+		Subnet:    subnet,
+	}
+}
+
+func TestValidateSystemsNetworkCollision(t *testing.T) {
+	tests := []struct {
+		name             string
+		systems          map[string]InitSystem
+		expectedWarnings []string
+	}{
+		{
+			name: "no collisions",
+			systems: map[string]InitSystem{
+				"system1": {
+					MicroCephPublicNetwork:    newNetwork("eth0", "10.0.1.0/24"),
+					MicroCephInternalNetwork:  newNetwork("eth1", "10.0.2.0/24"),
+					MicroCloudInternalNetwork: newNetwork("eth2", "10.0.3.0/24"),
+					OVNGeneveNetwork:          newNetwork("eth3", "10.0.4.0/24"),
+				},
+				"system2": {
+					MicroCephPublicNetwork:    newNetwork("eth0", "10.1.1.0/24"),
+					MicroCephInternalNetwork:  newNetwork("eth1", "10.1.2.0/24"),
+					MicroCloudInternalNetwork: newNetwork("eth2", "10.1.3.0/24"),
+					OVNGeneveNetwork:          newNetwork("eth3", "10.1.4.0/24"),
+				},
+			},
+			expectedWarnings: nil,
+		},
+		{
+			name: "single system interface collision",
+			systems: map[string]InitSystem{
+				"system1": {
+					MicroCephInternalNetwork:  newNetwork("eth0", "10.0.1.0/24"),
+					OVNGeneveNetwork:          newNetwork("eth0", "10.0.2.0/24"), // Same interface
+					MicroCloudInternalNetwork: newNetwork("eth1", "10.0.3.0/24"),
+				},
+			},
+			expectedWarnings: []string{
+				"- Ceph cluster network, OVN underlay sharing network interface \"eth0\"",
+			},
+		},
+		{
+			name: "cross-system subnet collision",
+			systems: map[string]InitSystem{
+				"system1": {
+					MicroCephInternalNetwork:  newNetwork("eth0", "10.0.1.0/24"), // Same subnet
+					OVNGeneveNetwork:          newNetwork("eth1", "10.0.2.0/24"),
+					MicroCloudInternalNetwork: newNetwork("eth2", "10.0.3.0/24"),
+				},
+				"system2": {
+					OVNGeneveNetwork:          newNetwork("eth3", "10.0.1.0/24"), // Same subnet for different network type
+					MicroCloudInternalNetwork: newNetwork("eth4", "10.0.4.0/24"),
+				},
+			},
+			expectedWarnings: []string{
+				"- Ceph cluster network, OVN underlay sharing subnet \"10.0.1.0/24\"",
+			},
+		},
+		{
+			name: "mixed interface and cross-subnet collision",
+			systems: map[string]InitSystem{
+				"system1": {
+					MicroCephInternalNetwork:  newNetwork("eth0", "10.0.1.0/24"), // Interface and subnet collision
+					OVNGeneveNetwork:          newNetwork("eth0", "10.0.1.0/24"), // Same interface and subnet
+					MicroCloudInternalNetwork: newNetwork("eth1", "10.0.2.0/24"),
+				},
+				"system2": {
+					OVNGeneveNetwork: newNetwork("eth2", "10.0.1.0/24"), // Same subnet globally
+				},
+			},
+			expectedWarnings: []string{
+				"- Ceph cluster network, OVN underlay sharing network interface \"eth0\"",
+				"- Ceph cluster network, OVN underlay sharing subnet \"10.0.1.0/24\"",
+			},
+		},
+		{
+			name: "ignore systems with missing networks",
+			systems: map[string]InitSystem{
+				"system1": { // Incomplete networks (skipped in checks)
+					OVNGeneveNetwork:          newNetwork("eth0", "10.0.1.0/24"),
+					MicroCloudInternalNetwork: newNetwork("eth1", "10.0.2.0/24"),
+				},
+			},
+			expectedWarnings: nil,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			warnings := detectCollisions(tt.systems)
+			assert.ElementsMatch(t, tt.expectedWarnings, warnings)
+		})
+	}
+}