diff --git a/errors.go b/errors.go
index 7275af0..ca86c8f 100644
--- a/errors.go
+++ b/errors.go
@@ -21,6 +21,7 @@ type errGeneric uint8
 const (
 	_             errGeneric = iota // non-initialized err
 	ErrPacketDrop                   // packet dropped
+	ErrBadCRC                       // incorrect checksum
 )
 
 func (err errGeneric) Error() string {
diff --git a/ethernet/definitions.go b/ethernet/definitions.go
index 80c50cd..63c9c57 100644
--- a/ethernet/definitions.go
+++ b/ethernet/definitions.go
@@ -1,9 +1,28 @@
 package ethernet
 
+import (
+	"strconv"
+)
+
 const (
 	sizeHeaderNoVLAN = 14
 )
 
+// AppendAddr appends the text representation of the hardware address to the destination buffer.
+func AppendAddr(dst []byte, hwAddr [6]byte) []byte {
+	for i, b := range hwAddr {
+		if i != 0 {
+			dst = append(dst, ':')
+		}
+		if b < 16 {
+			dst = append(dst, '0')
+		}
+		dst = strconv.AppendUint(dst, uint64(b), 16)
+	}
+	return dst
+}
+
+// BroadcastAddr returns the all 0xff's broadcast hardware/MAC/EUI/OUI address.
 func BroadcastAddr() [6]byte {
 	return [6]byte{0xff, 0xff, 0xff, 0xff, 0xff, 0xff}
 }
diff --git a/examples/xnet/main.go b/examples/xnet/main.go
index 6e68f19..d91b29d 100644
--- a/examples/xnet/main.go
+++ b/examples/xnet/main.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"encoding/hex"
 	"errors"
 	"flag"
@@ -17,6 +18,7 @@ import (
 
 	"github.com/soypat/lneto"
 	"github.com/soypat/lneto/dns"
+	"github.com/soypat/lneto/ethernet"
 	"github.com/soypat/lneto/http/httpraw"
 	"github.com/soypat/lneto/internal"
 	"github.com/soypat/lneto/internal/ltesto"
@@ -129,6 +131,8 @@ func run() (err error) {
 			pfbuf = fmt.Appendf(pfbuf[:0], "%-3s %3d", context, len(pkt))
 			pfbuf = append(pfbuf, ' ', '[')
 			pfbuf, err = pf.FormatFrames(pfbuf, frames, pkt)
+			pfbuf = bytes.ReplaceAll(pfbuf, stack.Addr().AppendTo(nil), []byte("us"))
+			pfbuf = bytes.ReplaceAll(pfbuf, ethernet.AppendAddr(nil, stack.HardwareAddress()), []byte("us"))
 			pfbuf = append(pfbuf, ']', '\n')
 			if err != nil {
 				return err
diff --git a/internet/definitions.go b/internet/definitions.go
index 010a896..583cfd3 100644
--- a/internet/definitions.go
+++ b/internet/definitions.go
@@ -6,6 +6,8 @@ import (
 	"math"
 	"net"
 	"slices"
+
+	"github.com/soypat/lneto"
 )
 
 // StackNode is an abstraction of a packet exchanging protocol controller. This is the building block for all protocols,
@@ -148,19 +150,20 @@ func (h *handlers) nodeByPortProto(port uint16, protocol uint16) *node {
 func (h *handlers) demuxByProto(buf []byte, offset int, proto uint16) (*node, error) {
 	node := h.nodeByProto(proto)
 	if node == nil {
-		return nil, nil
+		return nil, lneto.ErrPacketDrop
 	}
 	err := node.demux(buf, offset)
 	if h.tryHandleError(node, err) {
 		err = nil
 	}
+
 	return node, err
 }
 
 func (h *handlers) demuxByPort(buf []byte, offset int, port uint16) (*node, error) {
 	node := h.nodeByPort(port)
 	if node == nil {
-		return nil, nil
+		return nil, lneto.ErrPacketDrop
 	}
 	err := node.demux(buf, offset)
 	if h.tryHandleError(node, err) {
diff --git a/internet/pcap/format.go b/internet/pcap/format.go
index e006454..e8ec509 100644
--- a/internet/pcap/format.go
+++ b/internet/pcap/format.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/soypat/lneto"
+	"github.com/soypat/lneto/ethernet"
 	"github.com/soypat/lneto/tcp"
 )
 
@@ -122,15 +123,7 @@ func (f *Formatter) formatField(dst []byte, pktStartOff int, field FrameField, p
 		} else if field.BitLength == 4*8 {
 			dst = netip.AddrFrom4([4]byte(f.buf)).AppendTo(dst)
 		} else if field.BitLength == 6*8 {
-			for i := range f.buf {
-				if i != 0 {
-					dst = append(dst, ':')
-				}
-				if f.buf[i] < 16 {
-					dst = append(dst, '0')
-				}
-				dst = strconv.AppendUint(dst, uint64(f.buf[i]), 16)
-			}
+			dst = ethernet.AppendAddr(dst, [6]byte(f.buf))
 		} else if field.BitLength == 16*8 {
 			dst = netip.AddrFrom16([16]byte(f.buf)).AppendTo(dst)
 		} else {
diff --git a/internet/stack-ip.go b/internet/stack-ip.go
index a4ec5ce..5e465ab 100644
--- a/internet/stack-ip.go
+++ b/internet/stack-ip.go
@@ -80,19 +80,21 @@ func (sb *StackIP) Demux(carrierData []byte, offset int) error {
 	}
 	dst := ifrm.DestinationAddr()
 	if sb.ip != ([4]byte{}) && *dst != sb.ip {
-		return errors.New("not meant for us") // Not meant for us.
+		sb.handlers.debug("ip:not-for-us")
+		return lneto.ErrPacketDrop // Not meant for us.
 	}
 
 	sb.validator.ResetErr()
 	ifrm.ValidateExceptCRC(&sb.validator)
 	if err = sb.validator.ErrPop(); err != nil {
+		sb.handlers.error("ip:Demux.validate")
 		return err
 	}
 	gotCRC := ifrm.CRC()
 	wantCRC := ifrm.CalculateHeaderCRC()
 	if gotCRC != wantCRC {
 		sb.handlers.error("StackIP:Demux:crc-mismatch", slog.Uint64("want", uint64(wantCRC)), slog.Uint64("got", uint64(gotCRC)))
-		return errors.New("IPv4 CRC mismatch")
+		return lneto.ErrBadCRC
 	}
 	off := ifrm.HeaderLength()
 	totalLen := ifrm.TotalLength()
@@ -104,8 +106,8 @@ func (sb *StackIP) Demux(carrierData []byte, offset int) error {
 	// nodeIdx := getNodeByProto(sb.handlers, uint16(proto))
 	if node == nil {
 		// Drop packet.
-		sb.handlers.info("iprecv:drop", slog.String("dstaddr", netip.AddrFrom4(*ifrm.DestinationAddr()).String()), slog.String("proto", ifrm.Protocol().String()))
-		return nil
+		sb.handlers.info("ip:demux.drop", slog.String("dstaddr", netip.AddrFrom4(*ifrm.DestinationAddr()).String()), slog.String("proto", ifrm.Protocol().String()))
+		return lneto.ErrPacketDrop
 	}
 	// Incoming CRC Validation of common IP Protocols.
 	var crc lneto.CRC791
@@ -118,7 +120,8 @@ func (sb *StackIP) Demux(carrierData []byte, offset int) error {
 		}
 		tfrm.CRCWrite(&crc)
 		if crc.Sum16() != tfrm.CRC() {
-			return errors.New("TCP CRC mismatch")
+			sb.handlers.error("ip:demux.tcpcrc")
+			return lneto.ErrBadCRC
 		}
 	case lneto.IPProtoUDP:
 		ifrm.CRCWriteUDPPseudo(&crc)
@@ -128,7 +131,8 @@ func (sb *StackIP) Demux(carrierData []byte, offset int) error {
 		}
 		ufrm.CRCWriteIPv4(&crc)
 		if crc.Sum16() != ufrm.CRC() {
-			return errors.New("UDP CRC mismatch")
+			sb.handlers.error("ip:demux.udpcrc")
+			return lneto.ErrBadCRC
 		}
 	}
 	sb.handlers.info("ipDemux", slog.String("ipproto", proto.String()), slog.Int("plen", int(totalLen)))
diff --git a/internet/stack-udpport.go b/internet/stack-udpport.go
index e64615f..ad60790 100644
--- a/internet/stack-udpport.go
+++ b/internet/stack-udpport.go
@@ -43,13 +43,13 @@ func (sudp *StackUDPPort) Demux(carrierData []byte, frameOffset int) error {
 	}
 	dst := ufrm.DestinationPort()
 	if dst != sudp.h.port {
-		return nil // Not meant for us.
+		return lneto.ErrPacketDrop // Not meant for us.
 	}
 	// TODO remote ip address handling.
 
 	src := ufrm.SourcePort()
 	if sudp.rmport != 0 && src != sudp.rmport {
-		return nil // Not from our target remote port.
+		return lneto.ErrPacketDrop // Not from our target remote port.
 	}
 	err = sudp.h.demux(carrierData, frameOffset+8)
 	if err != nil {