cmd/scion, snet: reduce range of IDs for SCMP requests

gateway/pathhealth/remotewatcher.go

@@ -17,7 +17,6 @@ package pathhealth
 import (
 	"context"
 	"fmt"
-	"math/rand"
 	"sync"
 	"time"
 
@@ -257,7 +256,7 @@ func (w *remoteWatcher) updatePaths(ctx context.Context) {
 
 func (w *remoteWatcher) selectID() (uint16, bool) {
 	for i := 0; i < 100; i++ {
-		id := uint16(rand.Uint32())
+		id := snet.RandomSCMPIdentifer()
 		if _, ok := w.pathWatchersByID[id]; !ok {
 			return id, true
 		}

pkg/snet/packet.go

@@ -15,6 +15,8 @@
 package snet
 
 import (
+	"math/rand"
+
 	"github.com/google/gopacket"
 
 	"github.com/scionproto/scion/pkg/addr"
@@ -192,6 +194,30 @@ func (m SCMPInternalConnectivityDown) length() int {
 	return 28 + len(m.Payload)
 }
 
+const (
+	// SCMPIdentifierStart and SCMPIdentiferEnd define the range for Identifiers
+	// that should be used for SCMPEchoRequest and SCMPTracerouteRequest,
+	// in preparation for a dispatcher-less snet.
+	// This range corresponds to the port range used for SCION/UDP by the
+	// dispatcher. Using the same range for Identifiers in SCMP requests will
+	// allow a router to dispatch SCMP requests based on the Identifier,
+	// without risk of interfering with unaware endpoints.
+	//
+	// WARNING: transitional, this will be removed in the dispatcher-less snet.
+	SCMPIdentifierStart = 32768
+	SCMPIdentifierEnd   = 65535
+)
+
+// RandomSCMPIdentifier returns a random SCMP identifier in the range
+// [SCMPIdentifierStart, SCMPIdentifierEnd].
+//
+// WARNING: This is a transitional helper function, which will be removed
+// in the dispatcher-less snet; then, the underlay port must be used as identifier.
+func RandomSCMPIdentifer() uint16 {
+	id := SCMPIdentifierStart + rand.Int31n(SCMPIdentifierEnd-SCMPIdentifierStart+1)
+	return uint16(id)
+}
+
 // SCMPEchoRequest is the SCMP echo request payload.
 type SCMPEchoRequest struct {
 	Identifier uint16

private/app/path/path.go

@@ -143,7 +143,7 @@ func filterUnhealthy(
 		DstIA:                  remote,
 		LocalIA:                cfg.LocalIA,
 		LocalIP:                cfg.LocalIP,
-		ID:                     uint16(rand.Uint32()),
+		ID:                     snet.RandomSCMPIdentifer(),
 		SCIONPacketConnMetrics: cfg.SCIONPacketConnMetrics,
 		Dispatcher:             cfg.Dispatcher,
 	}.GetStatuses(subCtx, nonEmptyPaths, pathprobe.WithEPIC(epic))

scion/ping/ping.go

@@ -18,7 +18,6 @@ package ping
 import (
 	"context"
 	"encoding/binary"
-	"math/rand"
 	"net"
 	"sync"
 	"time"
@@ -103,13 +102,13 @@ func Run(ctx context.Context, cfg Config) (Stats, error) {
 		return Stats{}, serrors.New("interval below millisecond")
 	}
 
-	id := rand.Uint64()
 	replies := make(chan reply, 10)
 
+	id := snet.RandomSCMPIdentifer()
 	svc := snet.DefaultPacketDispatcherService{
 		Dispatcher: cfg.Dispatcher,
 		SCMPHandler: scmpHandler{
-			id:      uint16(id),
+			id:      id,
 			replies: replies,
 		},
 	}
@@ -148,7 +147,7 @@ type pinger struct {
 	timeout  time.Duration
 	pldSize  int
 
-	id      uint64
+	id      uint16
 	conn    snet.PacketConn
 	local   *snet.UDPAddr
 	replies <-chan reply
@@ -224,7 +223,7 @@ func (p *pinger) send(remote *snet.UDPAddr) error {
 
 	binary.BigEndian.PutUint64(p.pld, uint64(time.Now().UnixNano()))
 	pkt, err := pack(p.local, remote, snet.SCMPEchoRequest{
-		Identifier: uint16(p.id),
+		Identifier: p.id,
 		SeqNumber:  uint16(sequence),
 		Payload:    p.pld,
 	})

scion/showpaths/showpaths.go

@@ -19,7 +19,6 @@ import (
 	"fmt"
 	"io"
 	"math"
-	"math/rand"
 	"net/netip"
 	"strconv"
 	"strings"
@@ -356,7 +355,7 @@ func Run(ctx context.Context, dst addr.IA, cfg Config) (*Result, error) {
 			DstIA:      dst,
 			LocalIA:    localIA,
 			LocalIP:    cfg.Local,
-			ID:         uint16(rand.Uint32()),
+			ID:         snet.RandomSCMPIdentifer(),
 			Dispatcher: cfg.Dispatcher,
 		}.GetStatuses(ctx, p, pathprobe.WithEPIC(cfg.Epic))
 		if err != nil {

scion/traceroute/traceroute.go

@@ -17,7 +17,6 @@ package traceroute
 
 import (
 	"context"
-	"math/rand"
 	"net"
 	"net/netip"
 	"time"
@@ -100,7 +99,7 @@ func Run(ctx context.Context, cfg Config) (Stats, error) {
 	if _, isEmpty := cfg.PathEntry.Dataplane().(path.Empty); isEmpty {
 		return Stats{}, serrors.New("empty path is not allowed for traceroute")
 	}
-	id := rand.Uint64()
+	id := snet.RandomSCMPIdentifer()
 	replies := make(chan reply, 10)
 	dispatcher := snet.DefaultPacketDispatcherService{
 		Dispatcher:  cfg.Dispatcher,
@@ -121,7 +120,7 @@ func Run(ctx context.Context, cfg Config) (Stats, error) {
 		replies:       replies,
 		errHandler:    cfg.ErrHandler,
 		updateHandler: cfg.UpdateHandler,
-		id:            uint16(id),
+		id:            id,
 		path:          cfg.PathEntry,
 		epic:          cfg.EPIC,
 	}