diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index f0fbe83ac..1af4685af 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -359,6 +359,12 @@ func (m AddressMask) Prefix() int {
 	return p
 }
 
+// Equal returns whether m and other are equal. It exists for use by the cmp
+// library.
+func (m AddressMask) Equal(other AddressMask) bool {
+	return m == other
+}
+
 // Subnet is a subnet defined by its address and mask.
 type Subnet struct {
 	address Address