mirror of https://github.com/tailscale/tailscale/
Revert "wgengine,net,ipn,disco: split up and define different types of MTU"
This reverts commit 059051c58a.
Signed-off-by: Val <valerie@tailscale.com>
pull/9519/head
Val
1 year ago
committed by
valscale
parent
059051c58a
commit
6cc5b272d8
@ -1,154 +1,33 @@
|
||||
// Copyright (c) Tailscale Inc & AUTHORS
|
||||
// SPDX-License-Identifier: BSD-3-Clause
|
||||
|
||||
package tstun
|
||||
|
||||
import (
|
||||
"tailscale.com/envknob"
|
||||
)
|
||||
|
||||
// The MTU (Maximum Transmission Unit) of a network interface is the largest
|
||||
// packet that can be sent or received through that interface, including all
|
||||
// headers above the link layer (e.g. IP headers, UDP headers, Wireguard
|
||||
// headers, etc.). We have to think about several different values of MTU:
|
||||
//
|
||||
// Wire MTU: The MTU of an interface underneath the tailscale TUN, e.g. an
|
||||
// Ethernet network card will default to a 1500 byte MTU. The user may change
|
||||
// this MTU at any time.
|
||||
//
|
||||
// TUN MTU: The current MTU of the tailscale TUN. This MTU is adjusted downward
|
||||
// to make room for the wireguard/tailscale headers. For example, if the
|
||||
// underlying network interface's MTU is 1500 bytes, the maximum size of a
|
||||
// packet entering the tailscale TUN is 1420 bytes. The user may change this MTU
|
||||
// at any time via the OS's tools (ifconfig, ip, etc.).
|
||||
//
|
||||
// User configured initial MTU: The MTU the tailscale TUN should be created
|
||||
// with, set by the user via TS_DEBUG_MTU. It should be adjusted down from the
|
||||
// underlying interface MTU by 80 bytes to make room for the wireguard
|
||||
// headers. This envknob is mostly for debugging. This value is used once at TUN
|
||||
// creation and ignored thereafter.
|
||||
//
|
||||
// User configured current MTU: The MTU set via the OS's tools (ifconfig, ip,
|
||||
// etc.). This MTU can change at any time. Setting the MTU this way goes through
|
||||
// the MTU() method of tailscale's TUN wrapper.
|
||||
//
|
||||
// Maximum probed MTU: This is the largest MTU size that we send probe packets
|
||||
// for.
|
||||
//
|
||||
// Safe MTU: If the tailscale TUN MTU is set to this value, almost all packets
|
||||
// will get to their destination. Tailscale defaults to this MTU in the absence
|
||||
// of path MTU probe information or user MTU configuration. We may occasionally
|
||||
// find a path that needs a smaller MTU but it is very rare.
|
||||
//
|
||||
// Peer MTU: This is the path MTU to a peer's current best endpoint. It defaults
|
||||
// to the Safe MTU unless we have path MTU probe results that tell us otherwise.
|
||||
//
|
||||
// Initial MTU: This is the MTU tailscaled creates the TUN with. In order of
|
||||
// priority, it is:
|
||||
//
|
||||
// 1. If set, the value of TS_DEBUG_MTU clamped to a maximum of 65536
|
||||
// 2. If TS_DEBUG_ENABLE_PMTUD is set, the maximum size MTU we probe, minus wg
|
||||
// overhead
|
||||
// 3. If TS_DEBUG_ENABLE_PMTUD is not set, the Safe MTU
|
||||
//
|
||||
// Current MTU: This the MTU of the tailscale TUN at any given moment
|
||||
// after TUN creation. In order of priority, it is:
|
||||
//
|
||||
// 1. The MTU set by the user via the OS, if it has ever been set
|
||||
// 2. If TS_DEBUG_ENABLE_PMTUD is set, the maximum size MTU we probe, minus wg
|
||||
// overhead
|
||||
// 4. If TS_DEBUG_ENABLE_PMTUD is not set, the Safe MTU
|
||||
|
||||
// TUNMTU is the MTU for the tailscale TUN.
|
||||
type TUNMTU uint32
|
||||
|
||||
// WireMTU is the MTU for the underlying network devices.
|
||||
type WireMTU uint32
|
||||
import "tailscale.com/envknob"
|
||||
|
||||
const (
|
||||
// maxTUNMTU is the largest MTU we will consider for the Tailscale
|
||||
// TUN. This is inherited from wireguard-go and can be surprisingly
|
||||
// small; on Windows it is currently 2048 - 32 bytes and iOS it is 1700
|
||||
// - 32 bytes.
|
||||
// TODO(val,raggi): On Windows this seems to derive from RIO driver
|
||||
// constraints in Wireguard but we don't use RIO so could probably make
|
||||
// this bigger.
|
||||
maxTUNMTU TUNMTU = TUNMTU(MaxPacketSize)
|
||||
// safeTUNMTU is the default "safe" MTU for the Tailscale TUN that we
|
||||
// use in the absence of other information such as path MTU probes.
|
||||
safeTUNMTU TUNMTU = 1280
|
||||
maxMTU uint32 = 65536
|
||||
defaultMTU uint32 = 1280
|
||||
)
|
||||
|
||||
// MaxProbedWireMTU is the largest MTU we will test for path MTU
|
||||
// discovery.
|
||||
var MaxProbedWireMTU WireMTU = 9000
|
||||
|
||||
func init() {
|
||||
if MaxProbedWireMTU > WireMTU(maxTUNMTU) {
|
||||
MaxProbedWireMTU = WireMTU(maxTUNMTU)
|
||||
}
|
||||
}
|
||||
|
||||
// wgHeaderLen is the length of all the headers Wireguard adds to a packet
|
||||
// in the worst case (IPv6). This constant is for use when we can't or
|
||||
// shouldn't use information about the IP version of a specific packet
|
||||
// (e.g., calculating the MTU for the Tailscale interface.
|
||||
//
|
||||
// A Wireguard header includes:
|
||||
//
|
||||
// - 20-byte IPv4 header or 40-byte IPv6 header
|
||||
// - 8-byte UDP header
|
||||
// - 4-byte type
|
||||
// - 4-byte key index
|
||||
// - 8-byte nonce
|
||||
// - 16-byte authentication tag
|
||||
const wgHeaderLen = 40 + 8 + 4 + 4 + 8 + 16
|
||||
|
||||
// TUNToWireMTU takes the MTU that the Tailscale TUN presents to the user and
|
||||
// returns the on-the-wire MTU necessary to transmit the largest packet that
|
||||
// will fit through the TUN, given that we have to add wireguard headers.
|
||||
func TUNToWireMTU(t TUNMTU) WireMTU {
|
||||
return WireMTU(t + wgHeaderLen)
|
||||
}
|
||||
|
||||
// WireToTUNMTU takes the MTU of an underlying network device and returns the
|
||||
// largest possible MTU for a Tailscale TUN operating on top of that device,
|
||||
// given that we have to add wireguard headers.
|
||||
func WireToTUNMTU(w WireMTU) TUNMTU {
|
||||
if w < wgHeaderLen {
|
||||
return 0
|
||||
}
|
||||
return TUNMTU(w - wgHeaderLen)
|
||||
}
|
||||
|
||||
// DefaultTUNMTU returns the MTU we use to set the Tailscale TUN
|
||||
// MTU. It is also the path MTU that we default to if we have no
|
||||
// information about the path to a peer.
|
||||
//
|
||||
// 1. If set, the value of TS_DEBUG_MTU clamped to a maximum of MaxTunMTU
|
||||
// 2. If TS_DEBUG_ENABLE_PMTUD is set, the maximum size MTU we probe, minus wg overhead
|
||||
// 3. If TS_DEBUG_ENABLE_PMTUD is not set, the Safe MTU
|
||||
func DefaultTUNMTU() TUNMTU {
|
||||
if m, ok := envknob.LookupUintSized("TS_DEBUG_MTU", 10, 32); ok {
|
||||
return min(TUNMTU(m), maxTUNMTU)
|
||||
}
|
||||
|
||||
debugPMTUD, _ := envknob.LookupBool("TS_DEBUG_ENABLE_PMTUD")
|
||||
if debugPMTUD {
|
||||
return WireToTUNMTU(MaxProbedWireMTU)
|
||||
}
|
||||
|
||||
return safeTUNMTU
|
||||
}
|
||||
|
||||
// Temporary workaround for code on corp that uses this function name.
|
||||
// TODO(val): Remove as soon as corp OSS is updated.
|
||||
// DefaultMTU returns either the constant default MTU of 1280, or the value set
|
||||
// in TS_DEBUG_MTU clamped to a maximum of 65536.
|
||||
func DefaultMTU() uint32 {
|
||||
return uint32(DefaultTUNMTU())
|
||||
}
|
||||
|
||||
// DefaultWireMTU returns the default TUN MTU, adjusted for wireguard
|
||||
// overhead.
|
||||
func DefaultWireMTU() WireMTU {
|
||||
return TUNToWireMTU(DefaultTUNMTU())
|
||||
// DefaultMTU is the Tailscale default MTU for now.
|
||||
//
|
||||
// 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.
|
||||
tunMTU := defaultMTU
|
||||
if mtu, ok := envknob.LookupUintSized("TS_DEBUG_MTU", 10, 32); ok {
|
||||
mtu := uint32(mtu)
|
||||
if mtu > maxMTU {
|
||||
mtu = maxMTU
|
||||
}
|
||||
tunMTU = mtu
|
||||
}
|
||||
return tunMTU
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue