From c3948d2f4fe02379c4cf77498d0de2feb834e9b9 Mon Sep 17 00:00:00 2001
From: Phil Pluckthun <phil@kitten.sh>
Date: Fri, 2 May 2025 14:57:41 +0100
Subject: [PATCH] fix: Ignore internal interfaces when probing routes (VPNs)
 (#7)

* Ignore internal assignments for probed routes

* Add changeset

* Determine internal interfaces with mac address as well
---
 .changeset/fair-cows-perform.md | 5 +++++
 src/index.ts                    | 6 +++++-
 src/network.ts                  | 6 +++++-
 3 files changed, 15 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/fair-cows-perform.md

diff --git a/.changeset/fair-cows-perform.md b/.changeset/fair-cows-perform.md
new file mode 100644
index 0000000..b890aca
--- /dev/null
+++ b/.changeset/fair-cows-perform.md
@@ -0,0 +1,5 @@
+---
+'lan-network': patch
+---
+
+When matching a probed route, ignore internal interfaces. The probed route will match a VPN (virtual) interface when using it to tunnel all traffic, but is unlikely to be considered the local network by users.
diff --git a/src/index.ts b/src/index.ts
index 81ee0d3..c255314 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -5,6 +5,7 @@ import {
   DEFAULT_ASSIGNMENT,
   interfaceAssignments,
   matchAssignment,
+  isInternal,
 } from './network';
 import type { GatewayAssignment } from './types';
 
@@ -26,7 +27,10 @@ export async function lanNetwork(): Promise<GatewayAssignment> {
   try {
     const defaultRoute = await probeDefaultRoute();
     // If this route matches a known assignment, return it without a gateway
-    if ((assignment = matchAssignment(assignments, defaultRoute))) {
+    if (
+      (assignment = matchAssignment(assignments, defaultRoute)) &&
+      !isInternal(assignment)
+    ) {
       return assignment;
     }
   } catch {
diff --git a/src/network.ts b/src/network.ts
index 2a292b9..59f59f6 100644
--- a/src/network.ts
+++ b/src/network.ts
@@ -45,6 +45,10 @@ const getSubnetPriority = (addr: string): number => {
   else return 0;
 };
 
+/** Determines if an assignment is internal (indicated by the flag or by a zeroed mac address) */
+export const isInternal = (assignment: NetworkAssignment) =>
+  assignment.internal || parseMacStr(assignment.mac).every(x => !x);
+
 export const interfaceAssignments = (): NetworkAssignment[] => {
   const candidates: NetworkAssignment[] = [];
   const interfaces = os.networkInterfaces();
@@ -62,7 +66,7 @@ export const interfaceAssignments = (): NetworkAssignment[] => {
     // Prioritise external interfaces, then sort by priority,
     // when priority is equal, sort by raw IP values
     const sortBy =
-      +a.internal - +b.internal ||
+      +isInternal(a) - +isInternal(b) ||
       priorityB - priorityA ||
       parseIpStr(b.address) - parseIpStr(a.address);
     return sortBy;
-- 
2.51.2