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net/tstun: add a debug envvar to override tun MTU.

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Signed-off-by: David Anderson <dave@natulte.net>
This commit is contained in:
David Anderson 2021-06-04 11:55:11 -07:00
parent 6ce77b8eca
commit df8a5d09c3
1 changed files with 13 additions and 6 deletions
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19
net/tstun/tun.go
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@ -11,6 +11,7 @@ import (
"os"
"os/exec"
"runtime"
"strconv"
"time"
"golang.zx2c4.com/wireguard/tun"
@ -18,20 +19,26 @@ import (
"tailscale.com/version/distro"
)
// minimalMTU is the MTU we set on tailscale's TUN
// interface. wireguard-go defaults to 1420 bytes, which only works if
// the "outer" MTU is 1500 bytes. This breaks on DSL connections
// (typically 1492 MTU) and on GCE (1460 MTU?!).
// tunMTU is the MTU we set on tailscale's TUN interface. wireguard-go
// defaults to 1420 bytes, which only works if the "outer" MTU is 1500
// bytes. This breaks on DSL connections (typically 1492 MTU) and on
// GCE (1460 MTU?!).
//
// 1280 is the smallest MTU allowed for IPv6, which is a sensible
// "probably works everywhere" setting until we develop proper PMTU
// discovery.
const minimalMTU = 1280
var tunMTU = 1280
func init() {
if mtu, _ := strconv.Atoi(os.Getenv("TS_DEBUG_MTU")); mtu != 0 {
tunMTU = mtu
}
}
// New returns a tun.Device for the requested device name, along with
// the OS-dependent name that was allocated to the device.
func New(logf logger.Logf, tunName string) (tun.Device, string, error) {
dev, err := tun.CreateTUN(tunName, minimalMTU)
dev, err := tun.CreateTUN(tunName, tunMTU)
if err != nil {
return nil, "", err
}