Fallback on 1320 if ICMP is blocked

2025-10-03 13:55:59 +00:00
parent 5b1dc295fe
commit ccc2f306b9
3 changed files with 26 additions and 32 deletions
--- a/internal/vpn/tunnelup.go
+++ b/internal/vpn/tunnelup.go
@@ -120,7 +120,13 @@ func updateToMaxMTU(ctx context.Context, vpnInterface string,
 	const pingTimeout = time.Second
 	vpnLinkMTU, err = pmtud.PathMTUDiscover(ctx, serverIP, vpnLinkMTU, pingTimeout, logger)
 	if err != nil {
-		return fmt.Errorf("path MTU discovering: %w", err)
+		if errors.Is(err, pmtud.ErrMTUNotFound) {
+			const conservativeMTU = 1300
+			vpnLinkMTU = conservativeMTU
+			logger.Debugf("using a conservative MTU of %d (%s)", conservativeMTU, err)
+		} else {
+			return fmt.Errorf("path MTU discovering: %w", err)
+		}
 	}

 	err = netlinker.LinkSetMTU(link, vpnLinkMTU)