router: make room for multiple underlay impls phase 1

router/BUILD.bazel

@@ -10,6 +10,7 @@ go_library(
         "metrics.go",
         "serialize_proxy.go",
         "svc.go",
+        "underlay.go",
     ],
     importpath = "github.com/scionproto/scion/router",
     visibility = ["//visibility:public"],
@@ -69,6 +70,7 @@ go_test(
         "//private/underlay/conn:go_default_library",
         "//router/control:go_default_library",
         "//router/mock_router:go_default_library",
+        "//router/underlayproviders:go_default_library",
         "@com_github_golang_mock//gomock:go_default_library",
         "@com_github_gopacket_gopacket//:go_default_library",
         "@com_github_gopacket_gopacket//layers:go_default_library",

router/bfd/BUILD.bazel

@@ -14,6 +14,7 @@ go_library(
     deps = [
         "//pkg/log:go_default_library",
         "//pkg/private/serrors:go_default_library",
+        "//router/control:go_default_library",
         "@com_github_gopacket_gopacket//layers:go_default_library",
         "@com_github_prometheus_client_golang//prometheus:go_default_library",
     ],

router/bfd/session.go

@@ -16,15 +16,18 @@ package bfd
 
 import (
 	"context"
+	"crypto/rand"
 	"fmt"
 	"math"
+	"math/big"
 	"sync"
 	"time"
 
 	"github.com/gopacket/gopacket/layers"
 
 	"github.com/scionproto/scion/pkg/log"
 	"github.com/scionproto/scion/pkg/private/serrors"
+	"github.com/scionproto/scion/router/control"
 )
 
 const (
@@ -161,6 +164,33 @@ type Session struct {
 	testLogger log.Logger
 }
 
+// NewSession returns a new BFD session, configured as specified and updating the
+// given metrics. BFD packets are transmitted via the given Sender. Up to 10 incoming BFD packets
+// per session can be queued waiting for processing; excess traffic will be blocked.
+// A random discriminator is generated automatically. This can be used by the recipient to route
+// packets to the correct session.
+//
+// TODO(jiceatscion): blocking incoming traffic (*all of it*) when the BFD queue is full is
+// probably the wrong thing to do, but this is what we have been doing so far.
+func NewSession(s Sender, cfg control.BFD, metrics Metrics) (*Session, error) {
+
+	// Generate random discriminator. It can't be zero.
+	discInt, err := rand.Int(rand.Reader, big.NewInt(0xfffffffe))
+	if err != nil {
+		return nil, err
+	}
+	disc := layers.BFDDiscriminator(uint32(discInt.Uint64()) + 1)
+	return &Session{
+		Sender:                s,
+		DetectMult:            layers.BFDDetectMultiplier(cfg.DetectMult),
+		DesiredMinTxInterval:  cfg.DesiredMinTxInterval,
+		RequiredMinRxInterval: cfg.RequiredMinRxInterval,
+		LocalDiscriminator:    disc,
+		ReceiveQueueSize:      10,
+		Metrics:               metrics,
+	}, nil
+}
+
 func (s *Session) String() string {
 	return fmt.Sprintf("local_disc %v, remote_disc %v, sender %v",
 		s.LocalDiscriminator, s.getRemoteDiscriminator(), s.Sender)

router/cmd/router/BUILD.bazel

@@ -17,6 +17,7 @@ go_library(
         "//router/config:go_default_library",
         "//router/control:go_default_library",
         "//router/mgmtapi:go_default_library",
+        "//router/underlayproviders:go_default_library",
         "@com_github_go_chi_chi_v5//:go_default_library",
         "@com_github_go_chi_cors//:go_default_library",
         "@org_golang_x_sync//errgroup:go_default_library",

router/cmd/router/main.go

@@ -37,6 +37,7 @@ import (
 	"github.com/scionproto/scion/router/config"
 	"github.com/scionproto/scion/router/control"
 	api "github.com/scionproto/scion/router/mgmtapi"
+	_ "github.com/scionproto/scion/router/underlayproviders"
 )
 
 var globalCfg config.Config
@@ -64,6 +65,11 @@ func realMain(ctx context.Context) error {
 		DataPlane: router.DataPlane{
 			Metrics:                        metrics,
 			ExperimentalSCMPAuthentication: globalCfg.Features.ExperimentalSCMPAuthentication,
+			RunConfig: router.RunConfig{
+				NumProcessors:         globalCfg.Router.NumProcessors,
+				NumSlowPathProcessors: globalCfg.Router.NumSlowPathProcessors,
+				BatchSize:             globalCfg.Router.BatchSize,
+			},
 		},
 		ReceiveBufferSize:   globalCfg.Router.ReceiveBufferSize,
 		SendBufferSize:      globalCfg.Router.SendBufferSize,
@@ -131,12 +137,7 @@ func realMain(ctx context.Context) error {
 	})
 	g.Go(func() error {
 		defer log.HandlePanic()
-		runConfig := &router.RunConfig{
-			NumProcessors:         globalCfg.Router.NumProcessors,
-			NumSlowPathProcessors: globalCfg.Router.NumSlowPathProcessors,
-			BatchSize:             globalCfg.Router.BatchSize,
-		}
-		if err := dp.DataPlane.Run(errCtx, runConfig); err != nil {
+		if err := dp.DataPlane.Run(errCtx); err != nil {
 			return serrors.Wrap("running dataplane", err)
 		}
 		return nil