diff --git a/metropolis/node/allocs/net_protocols.go b/metropolis/node/allocs/net_protocols.go
new file mode 100644
index 0000000..360f763
--- /dev/null
+++ b/metropolis/node/allocs/net_protocols.go
@@ -0,0 +1,22 @@
+// Copyright The Monogon Project Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package allocs
+
+// These are netlink protocol numbers used internally for various netlink
+// resource (e.g. route) owners/manager.
+const (
+	// ProtocolOverlay is used by //metropolis/node/core/network/overlay
+	// when creating/removing routes pointing to the overlay interface.
+	ProtocolOverlay int = 129
+)
+
+// Netlink link groups used for interface classification and traffic matching.
+const (
+	// LinkGroupK8sPod is set on all host side PtP interfaces going to K8s
+	// pods.
+	LinkGroupK8sPod uint32 = 8
+	// LinkGroupOverlay is set on all interfaces which are part of the overlay
+	// network and thus exempt from SNATing of workload traffic.
+	LinkGroupOverlay uint32 = 9
+)