From 9fca3640f9743862c4fa1f25e3cce5b026e7c2a5 Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Wed, 20 Nov 2019 22:11:52 +0000
Subject: [PATCH] Fix couple of issues with MTU calculations

---
 src/tuntap/tun.go       | 19 +++++++------------
 src/tuntap/tun_linux.go |  8 --------
 2 files changed, 7 insertions(+), 20 deletions(-)

diff --git a/src/tuntap/tun.go b/src/tuntap/tun.go
index ffee63b..c9a627a 100644
--- a/src/tuntap/tun.go
+++ b/src/tuntap/tun.go
@@ -170,22 +170,17 @@ func (tun *TunAdapter) _start() error {
 	nodeID := crypto.GetNodeID(&boxPub)
 	tun.addr = *address.AddrForNodeID(nodeID)
 	tun.subnet = *address.SubnetForNodeID(nodeID)
-	tun.mtu = current.IfMTU
-	ifname := current.IfName
-	iftapmode := current.IfTAPMode
 	addr := fmt.Sprintf("%s/%d", net.IP(tun.addr[:]).String(), 8*len(address.GetPrefix())-1)
-	if ifname != "none" {
-		if err := tun.setup(ifname, iftapmode, addr, tun.mtu); err != nil {
-			return err
-		}
-		if tun.MTU() != current.IfMTU {
-			tun.log.Warnf("Warning: Interface MTU %d automatically adjusted to %d (supported range is 1280-%d)", current.IfMTU, tun.MTU(), MaximumMTU(tun.IsTAP()))
-		}
-	}
-	if ifname == "none" || ifname == "dummy" {
+	if current.IfName == "none" || current.IfName == "dummy" {
 		tun.log.Debugln("Not starting TUN/TAP as ifname is none or dummy")
 		return nil
 	}
+	if err := tun.setup(current.IfName, current.IfTAPMode, addr, current.IfMTU); err != nil {
+		return err
+	}
+	if tun.MTU() != current.IfMTU {
+		tun.log.Warnf("Warning: Interface MTU %d automatically adjusted to %d (supported range is 1280-%d)", current.IfMTU, tun.MTU(), MaximumMTU(tun.IsTAP()))
+	}
 	tun.isOpen = true
 	go tun.handler()
 	tun.reader.Act(nil, tun.reader._read) // Start the reader
diff --git a/src/tuntap/tun_linux.go b/src/tuntap/tun_linux.go
index d3e9c85..b591832 100644
--- a/src/tuntap/tun_linux.go
+++ b/src/tuntap/tun_linux.go
@@ -27,14 +27,6 @@ func (tun *TunAdapter) setup(ifname string, iftapmode bool, addr string, mtu int
 	}
 	tun.iface = iface
 	tun.mtu = getSupportedMTU(mtu, iftapmode)
-	// The following check is specific to Linux, as the TAP driver only supports
-	// an MTU of 65535-14 to make room for the ethernet headers. This makes sure
-	// that the MTU gets rounded down to 65521 instead of causing a panic.
-	if iftapmode {
-		if tun.mtu > 65535-tun_ETHER_HEADER_LENGTH {
-			tun.mtu = 65535 - tun_ETHER_HEADER_LENGTH
-		}
-	}
 	// Friendly output
 	tun.log.Infof("Interface name: %s", tun.iface.Name())
 	tun.log.Infof("Interface IPv6: %s", addr)