diff --git a/challenge/day23/a.go b/challenge/day23/a.go
index 0572513..0afda1b 100644
--- a/challenge/day23/a.go
+++ b/challenge/day23/a.go
@@ -23,6 +23,11 @@ const (
 )
 
 func a(challenge *challenge.Input) int {
+	inputs, outputs := bootNetwork(challenge)
+	return <-NewRouter(inputs, outputs).RouteTraffic()
+}
+
+func bootNetwork(challenge *challenge.Input) ([]chan int, []<-chan int) {
 	program := <-challenge.Lines()
 	computers := make([]*intcode.CPU, networkSize)
 	inputs := make([]chan int, networkSize)
@@ -37,7 +42,7 @@ func a(challenge *challenge.Input) int {
 
 		go func(i int) {
 			// Boot the nic and assign the ID
-			fmt.Printf("[%2d] booting...\n", i)
+			fmt.Printf("[%3d] booting...\n", i)
 			go computers[i].Run()
 			inputs[i] <- i
 			startup.Done()
@@ -45,6 +50,5 @@ func a(challenge *challenge.Input) int {
 	}
 
 	startup.Wait()
-
-	return <-NewRouter(inputs, outputs).RouteTraffic()
+	return inputs, outputs
 }
diff --git a/challenge/day23/b.go b/challenge/day23/b.go
new file mode 100644
index 0000000..d23776c
--- /dev/null
+++ b/challenge/day23/b.go
@@ -0,0 +1,24 @@
+package day23
+
+import (
+	"fmt"
+
+	"github.com/nlowe/aoc2019/challenge"
+	"github.com/spf13/cobra"
+)
+
+var B = &cobra.Command{
+	Use:   "23b",
+	Short: "Day 23, Problem B",
+	Run: func(_ *cobra.Command, _ []string) {
+		fmt.Printf("Answer: %d\n", b(challenge.FromFile()))
+	},
+}
+
+func b(challenge *challenge.Input) int {
+	inputs, outputs := bootNetwork(challenge)
+	r := NewRouter(inputs, outputs)
+	r.trackNat = true
+
+	return <-r.RouteTraffic()
+}
diff --git a/challenge/day23/router.go b/challenge/day23/router.go
index 10569a9..32b6acf 100644
--- a/challenge/day23/router.go
+++ b/challenge/day23/router.go
@@ -1,12 +1,17 @@
 package day23
 
 import (
+	"context"
 	"fmt"
 	"reflect"
+	"runtime"
+	"time"
+
+	"golang.org/x/sync/semaphore"
 )
 
 const (
-	addressAnswer    = 255
+	addressNAT       = 255
 	routerBufferSize = 16
 )
 
@@ -21,7 +26,11 @@ type router struct {
 	ins  []chan int
 	outs []<-chan int
 
-	bufs []chan packet
+	bufs        []chan packet
+	idleTracker *semaphore.Weighted
+
+	trackNat      bool
+	lastNATPacket packet
 }
 
 func NewRouter(in []chan int, out []<-chan int) *router {
@@ -34,6 +43,8 @@ func NewRouter(in []chan int, out []<-chan int) *router {
 		ins:  in,
 		outs: out,
 		bufs: bufs,
+
+		idleTracker: semaphore.NewWeighted(int64(len(in))),
 	}
 }
 
@@ -41,6 +52,9 @@ func (r *router) RouteTraffic() <-chan int {
 	answer := make(chan int)
 	go r.runPacketAggregator(answer)
 	go r.runTransmitter()
+	if r.trackNat {
+		go r.runNATHandler(answer)
+	}
 
 	return answer
 }
@@ -61,13 +75,22 @@ func (r *router) runPacketAggregator(answer chan int) {
 		x := <-r.outs[sender]
 		y := <-r.outs[sender]
 
-		if dst == addressAnswer {
-			answer <- y
-			return
+		parsed := packet{sender, dst, x, y}
+
+		if dst == addressNAT {
+			if !r.trackNat {
+				fmt.Printf("[NAT] write answer (non-tracking): %d\n", y)
+				answer <- y
+				return
+			}
+
+			r.lastNATPacket = parsed
+			fmt.Printf("[NAT] intercept {%d,%d} from %d\n", x, y, sender)
+			continue
 		}
 
-		fmt.Printf("[%2d] send {%d,%d} to %d\n", sender, x, y, dst)
-		r.bufs[dst] <- packet{sender, dst, x, y}
+		fmt.Printf("[%3d] send {%d,%d} to %d\n", sender, x, y, dst)
+		r.bufs[dst] <- parsed
 	}
 }
 
@@ -86,9 +109,43 @@ func (r *router) runTransmitterFor(id int) {
 		select {
 		case in <- -1:
 		case p := <-packets:
-			fmt.Printf("[%2d] got {%d,%d} from %d\n", id, p.x, p.y, p.from)
+			_ = r.idleTracker.Acquire(context.Background(), 1)
+			fmt.Printf("[%3d] got {%d,%d} from %d\n", id, p.x, p.y, p.from)
 			in <- p.x
 			in <- p.y
+			r.idleTracker.Release(1)
+		}
+
+		// Give other goroutines some time to run
+		runtime.Gosched()
+	}
+}
+
+func (r *router) runNATHandler(answer chan int) {
+	last := -1
+	for {
+		// Give the adapters some time to send some traffic, especially if we just
+		// kick-started node 0
+		time.Sleep(50 * time.Millisecond)
+
+		if r.lastNATPacket.to != addressNAT || !r.idleTracker.TryAcquire(int64(len(r.ins))) {
+			// Yield back to the scheduler
+			runtime.Gosched()
+			continue
 		}
+
+		if r.lastNATPacket.y == last {
+			fmt.Printf("[NAT] write answer (tracking) %d\n", last)
+			answer <- r.lastNATPacket.y
+			return
+		}
+
+		fmt.Printf("[NAT] network idle enough, sending {%d,%d} from %d to [  0]\n", r.lastNATPacket.x, r.lastNATPacket.y, r.lastNATPacket.from)
+		r.bufs[0] <- r.lastNATPacket
+		last = r.lastNATPacket.y
+
+		// Don't try to immediately steal the semaphore back
+		r.idleTracker.Release(int64(len(r.ins)))
+		runtime.Gosched()
 	}
 }
diff --git a/go.mod b/go.mod
index 4a910b1..d926bc0 100644
--- a/go.mod
+++ b/go.mod
@@ -20,6 +20,7 @@ require (
 	github.com/stretchr/testify v1.4.0
 	github.com/zalando/go-keyring v0.0.0-20191212171435-ac5f1d08068b // indirect
 	github.com/zellyn/kooky v0.0.0-20190514172626-f2bb24889ec7
+	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e
 	golang.org/x/sys v0.0.0-20191128015809-6d18c012aee9 // indirect
 	golang.org/x/text v0.3.2 // indirect
 	gopkg.in/yaml.v2 v2.2.7 // indirect
diff --git a/go.sum b/go.sum
index 8c782a2..0d6d30b 100644
--- a/go.sum
+++ b/go.sum
@@ -169,7 +169,10 @@ golang.org/x/net v0.0.0-20190522155817-f3200d17e092/go.mod h1:HSz+uSET+XFnRR8LxR
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/sync v0.0.0-20180314180146-1d60e4601c6f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20181108010431-42b317875d0f/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4 h1:YUO/7uOKsKeq9UokNS62b8FYywz3ker1l1vDZRCRefw=
 golang.org/x/sync v0.0.0-20181221193216-37e7f081c4d4/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e h1:vcxGaoTs7kV8m5Np9uUNQin4BrLOthgV7252N8V+FwY=
+golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20180905080454-ebe1bf3edb33/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20181107165924-66b7b1311ac8/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
diff --git a/intcode/cpu.go b/intcode/cpu.go
index da52a8a..dbef7b7 100644
--- a/intcode/cpu.go
+++ b/intcode/cpu.go
@@ -106,7 +106,7 @@ func (c *CPU) write(mode, offset, value int) {
 
 func (c *CPU) debugState() string {
 	view := strings.Builder{}
-	view.WriteString("...")
+	view.WriteString("... ")
 
 	for i := c.pc - 10; i < c.pc+10; i++ {
 		if i == c.pc {
diff --git a/main.go b/main.go
index d5cb33a..2239ea7 100644
--- a/main.go
+++ b/main.go
@@ -86,7 +86,7 @@ func init() {
 		day20.A, day20.B,
 		day21.A, day21.B,
 		day22.A, day22.B,
-		day23.A,
+		day23.A, day23.B,
 	)
 
 	flags := rootCmd.PersistentFlags()