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disco,net/tstun,wgengine/magicsock: probe peer MTU

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Automatically probe the path MTU to a peer when peer MTU is enabled, but do not
use the MTU information for anything yet.

Updates #311

Signed-off-by: Val <valerie@tailscale.com>
This commit is contained in:
Val
2023-10-05 20:05:19 +02:00
committed by valscale
parent b4e587c3bd
commit 893bdd729c
7 changed files with 91 additions and 40 deletions
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68
wgengine/magicsock/endpoint.go
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@ -35,6 +35,16 @@ import (
"tailscale.com/util/ringbuffer"
)
var mtuProbePingSizesV4 []int
var mtuProbePingSizesV6 []int
func init() {
for _, m := range tstun.WireMTUsToProbe {
mtuProbePingSizesV4 = append(mtuProbePingSizesV4, pktLenToPingSize(m, false))
mtuProbePingSizesV6 = append(mtuProbePingSizesV6, pktLenToPingSize(m, true))
}
}
// endpoint is a wireguard/conn.Endpoint. In wireguard-go and kernel WireGuard
// there is only one endpoint for a peer, but in Tailscale we distribute a
// number of possible endpoints for a peer which would include the all the
@ -374,7 +384,7 @@ func (de *endpoint) addrForPingSizeLocked(now mono.Time, size int) (udpAddr, der
udpAddr = de.bestAddr.AddrPort
pathMTU := de.bestAddr.wireMTU
requestedMTU := pingSizeToPktLen(size, udpAddr.Addr())
requestedMTU := pingSizeToPktLen(size, udpAddr.Addr().Is6())
mtuOk := requestedMTU <= pathMTU
if udpAddr.IsValid() && mtuOk {
@ -666,21 +676,41 @@ func (de *endpoint) startDiscoPingLocked(ep netip.AddrPort, now mono.Time, purpo
st.lastPing = now
}
txid := stun.NewTxID()
de.sentPing[txid] = sentPing{
to: ep,
at: now,
timer: time.AfterFunc(pingTimeoutDuration, func() { de.discoPingTimeout(txid) }),
purpose: purpose,
res: res,
cb: cb,
// If we are doing a discovery ping or a CLI ping with no specified size
// to a non DERP address, then probe the MTU. Otherwise just send the
// one specified ping.
// Default to sending a single ping of the specified size
sizes := []int{size}
if de.c.PeerMTUEnabled() {
isDerp := ep.Addr() == tailcfg.DerpMagicIPAddr
if !isDerp && ((purpose == pingDiscovery) || (purpose == pingCLI && size == 0)) {
de.c.dlogf("[v1] magicsock: starting MTU probe")
sizes = mtuProbePingSizesV4
if ep.Addr().Is6() {
sizes = mtuProbePingSizesV6
}
}
}
logLevel := discoLog
if purpose == pingHeartbeat {
logLevel = discoVerboseLog
}
go de.sendDiscoPing(ep, epDisco.key, txid, size, logLevel)
for _, s := range sizes {
txid := stun.NewTxID()
de.sentPing[txid] = sentPing{
to: ep,
at: now,
timer: time.AfterFunc(pingTimeoutDuration, func() { de.discoPingTimeout(txid) }),
purpose: purpose,
res: res,
cb: cb,
size: s,
}
go de.sendDiscoPing(ep, epDisco.key, txid, s, logLevel)
}
}
// sendDiscoPingsLocked starts pinging all of ep's endpoints.
@ -982,13 +1012,13 @@ func (de *endpoint) noteConnectivityChange() {
// pingSizeToPktLen calculates the minimum path MTU that would permit
// a disco ping message of length size to reach its target at
// addr. size is the length of the entire disco message including
// disco headers. If size is zero, assume it is the default MTU.
func pingSizeToPktLen(size int, addr netip.Addr) tstun.WireMTU {
// disco headers. If size is zero, assume it is the safe wire MTU.
func pingSizeToPktLen(size int, is6 bool) tstun.WireMTU {
if size == 0 {
return tstun.DefaultWireMTU()
return tstun.SafeWireMTU()
}
headerLen := ipv4.HeaderLen
if addr.Is6() {
if is6 {
headerLen = ipv6.HeaderLen
}
headerLen += 8 // UDP header length
@ -999,12 +1029,12 @@ func pingSizeToPktLen(size int, addr netip.Addr) tstun.WireMTU {
// create a disco ping message whose on-the-wire length is exactly mtu
// bytes long. If mtu is zero or less than the minimum ping size, then
// no MTU probe is desired and return zero for an unpadded ping.
func pktLenToPingSize(mtu tstun.WireMTU, addr netip.Addr) int {
func pktLenToPingSize(mtu tstun.WireMTU, is6 bool) int {
if mtu == 0 {
return 0
}
headerLen := ipv4.HeaderLen
if addr.Is6() {
if is6 {
headerLen = ipv6.HeaderLen
}
headerLen += 8 // UDP header length
@ -1053,7 +1083,7 @@ func (de *endpoint) handlePongConnLocked(m *disco.Pong, di *discoInfo, src netip
}
if sp.purpose != pingHeartbeat {
de.c.dlogf("[v1] magicsock: disco: %v<-%v (%v, %v) got pong tx=%x latency=%v pktlen=%v pong.src=%v%v", de.c.discoShort, de.discoShort(), de.publicKey.ShortString(), src, m.TxID[:6], latency.Round(time.Millisecond), pingSizeToPktLen(sp.size, sp.to.Addr()), m.Src, logger.ArgWriter(func(bw *bufio.Writer) {
de.c.dlogf("[v1] magicsock: disco: %v<-%v (%v, %v) got pong tx=%x latency=%v pktlen=%v pong.src=%v%v", de.c.discoShort, de.discoShort(), de.publicKey.ShortString(), src, m.TxID[:6], latency.Round(time.Millisecond), pingSizeToPktLen(sp.size, sp.to.Addr().Is6()), m.Src, logger.ArgWriter(func(bw *bufio.Writer) {
if sp.to != src {
fmt.Fprintf(bw, " ping.to=%v", sp.to)
}
@ -1071,9 +1101,9 @@ func (de *endpoint) handlePongConnLocked(m *disco.Pong, di *discoInfo, src netip
// Promote this pong response to our current best address if it's lower latency.
// TODO(bradfitz): decide how latency vs. preference order affects decision
if !isDerp {
thisPong := addrQuality{sp.to, latency, pingSizeToPktLen(sp.size, sp.to.Addr())}
thisPong := addrQuality{sp.to, latency, tstun.WireMTU(pingSizeToPktLen(sp.size, sp.to.Addr().Is6()))}
if betterAddr(thisPong, de.bestAddr) {
de.c.logf("magicsock: disco: node %v %v now using %v mtu %v", de.publicKey.ShortString(), de.discoShort(), sp.to, thisPong.wireMTU)
de.c.logf("magicsock: disco: node %v %v now using %v mtu=%v tx=%x", de.publicKey.ShortString(), de.discoShort(), sp.to, thisPong.wireMTU, m.TxID[:6])
de.debugUpdates.Add(EndpointChange{
When: time.Now(),
What: "handlePingLocked-bestAddr-update",