diff --git a/aurp/aurp.go b/aurp/aurp.go
new file mode 100644
index 0000000..e9dcebb
--- /dev/null
+++ b/aurp/aurp.go
@@ -0,0 +1,205 @@
+// Package aurp implements types for encoding and decoding AppleTalk
+// Update-Based Routing Protocol (AURP, RFC 1504) messages.
+package aurp
+
+import (
+	"bytes"
+	"encoding/binary"
+	"fmt"
+	"net"
+)
+
+// DomainHeader represents the header used to encapsulate both AppleTalk data
+// packets and AURP packets within UDP.
+type DomainHeader struct {
+	DestinationDI DomainIdentifier
+	SourceDI      DomainIdentifier
+	Version       uint16 // Should always be 0x0001
+	PacketType    uint16 // 2 = AppleTalk data packet, 3 = AURP packet
+}
+
+// Encode returns the encoded form of the header.
+func (dh *DomainHeader) Encode() ([]byte, error) {
+	var b bytes.Buffer
+	ddi, err := dh.DestinationDI.Encode()
+	if err != nil {
+		return nil, err
+	}
+	sdi, err := dh.SourceDI.Encode()
+	if err != nil {
+		return nil, err
+	}
+	b.Write(ddi)
+	b.Write(sdi)
+	binary.Write(&b, binary.BigEndian, dh.Version)
+	binary.Write(&b, binary.BigEndian, uint16(0x0000)) // Reserved
+	binary.Write(&b, binary.BigEndian, dh.PacketType)
+	return b.Bytes(), nil
+}
+
+// ParseDH parses a domain header, returning the DH and the remainder of the
+// input slice.
+func ParseDH(b []byte) (*DomainHeader, []byte, error) {
+	ddi, b, err := ParseDI(b)
+	if err != nil {
+		return nil, b, err
+	}
+	sdi, b, err := ParseDI(b)
+	if err != nil {
+		return nil, b, err
+	}
+	if len(b) < 6 { // sizeof(version + reserved + packettype)
+		return nil, b, fmt.Errorf("insufficient remaining input length %d < 6", len(b))
+	}
+	ver := binary.BigEndian.Uint16(b[:2])
+	if ver != 1 {
+		return nil, b, fmt.Errorf("unknown version %d", ver)
+	}
+	// Note: b[2:4] (reserved field) is ignored
+	pt := binary.BigEndian.Uint16(b[4:6])
+	if pt != 2 && pt != 3 {
+		return nil, b, fmt.Errorf("unknown packet type %d", pt)
+	}
+	b = b[6:]
+	return &DomainHeader{
+		DestinationDI: ddi,
+		SourceDI:      sdi,
+		Version:       ver,
+		PacketType:    pt,
+	}, b, nil
+}
+
+// DomainIdentifier is the byte representation of a domain identifier.
+type DomainIdentifier interface {
+	Encode() ([]byte, error)
+}
+
+// NullDI represents a null domain identifier.
+type NullDI struct{}
+
+// Encode returns the encoded form of the identifier.
+func (NullDI) Encode() ([]byte, error) {
+	return []byte{0x01, 0x00}, nil
+}
+
+// IPDI represents an IP address in a domain identifier.
+type IPDI net.IP
+
+// Encode returns the encoded form of the identifier.
+func (i IPDI) Encode() ([]byte, error) {
+	v4 := net.IP(i).To4()
+	if v4 == nil {
+		return nil, fmt.Errorf("need v4 IP address, got %v", i)
+	}
+	return append([]byte{
+			0x07,       // byte 1: length of the DI in bytes
+			0x01,       // byte 2: authority: 1 = IP address
+			0x00, 0x00, // bytes 3, 4: distinguisher: reserved
+		}, v4...), // bytes 5-8: the IP address
+		nil
+}
+
+// Authority represents the different possible authorities ("types") for domain
+// identifiers.
+type Authority byte
+
+// Various authorities.
+const (
+	// AuthorityNull is for null domain identifiers, suitable only when there is
+	// no need to distinguish the domains connected to a tunnel.
+	AuthorityNull Authority = iota
+
+	// AuthorityIP is for
+	AuthorityIP
+)
+
+// ParseDI parses a DI from the front of b, and returns the DI and the remainder
+// of the input slice.
+func ParseDI(b []byte) (DomainIdentifier, []byte, error) {
+	if len(b) < 2 {
+		return nil, b, fmt.Errorf("insufficient input length %d for domain identifier", len(b))
+	}
+	// Now we know there is a length byte and authority byte, see if there is
+	// that much more data
+	lf := int(b[0])
+	if len(b) < 1+lf {
+		return nil, b, fmt.Errorf("input length %d < 1+specified length %d in domain identifier", len(b), lf)
+	}
+	switch Authority(b[1]) {
+	case AuthorityNull:
+		// That's it, that's the whole DI.
+		return NullDI{}, b[2:], nil
+
+	case AuthorityIP:
+		if lf != 7 {
+			return nil, b, fmt.Errorf("incorrect length %d for IP domain identifier", lf)
+		}
+		return IPDI(b[5:8]), b[8:], nil
+
+	default:
+		return nil, b, fmt.Errorf("unknown domain identifier authority %d", b[1])
+	}
+}
+
+// TrHeader represent an AURP-Tr packet header.
+type TrHeader struct {
+	ConnectionID uint16
+	Sequence     uint16 // Note: 65535 is succeeded by 1, not 0
+}
+
+// Header represents an AURP packet header.
+type Header struct {
+	CommandCode CmdCode
+	Flags       RoutingFlag
+}
+
+// CmdCode is the command code used in AURP packets.
+type CmdCode uint16
+
+// Various command codes.
+const (
+	CmdCodeRIReq     CmdCode = 0x0001
+	CmdCodeRIRsp     CmdCode = 0x0002
+	CmdCodeRIAck     CmdCode = 0x0003
+	CmdCodeRIUpd     CmdCode = 0x0004
+	CmdCodeRD        CmdCode = 0x0005
+	CmdCodeZoneReq   CmdCode = 0x0006 // has subcodes
+	CmdCodeZoneRsp   CmdCode = 0x0007 // has subcodes
+	CmdCodeOpenReq   CmdCode = 0x0008
+	CmdCodeOpenRsp   CmdCode = 0x0009
+	CmdCodeTickle    CmdCode = 0x000e
+	CmdCodeTickleAck CmdCode = 0x000f
+)
+
+// CmdSubcode is used to distinguish types of zone request/response.
+type CmdSubcode uint16
+
+// Various subcodes.
+const (
+	CmdSubcodeZoneInfo1         CmdSubcode = 0x0001
+	CmdSubcodeZoneInfo2         CmdSubcode = 0x0002 // only for responses
+	CmdSubcodeGetZonesNet       CmdSubcode = 0x0003
+	CmdSubcodeGetDomainZoneList CmdSubcode = 0x0004
+)
+
+// RoutingFlag is used in the flags field
+type RoutingFlag uint16
+
+const (
+	// Open-Req and RI-Req
+	RoutingFlagSUINA      RoutingFlag = 0x4000
+	RoutingFlagSUINDOrNRC RoutingFlag = 0x2000
+	RoutingFlagSUINDC     RoutingFlag = 0x1000
+	RoutingFlagSUIZC      RoutingFlag = 0x0800
+
+	// RI-Rsp and GDZL-Rsp
+	RoutingFlagLast RoutingFlag = 0x8000
+
+	// Open-Rsp
+	RoutingFlagRemappingActive   RoutingFlag = 0x4000
+	RoutingFlagHopCountReduction RoutingFlag = 0x2000
+	RoutingFlagReservedEnv       RoutingFlag = 0x1800
+
+	// RI-Ack
+	RoutingFlagSendZoneInfo RoutingFlag = 0x4000
+)
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..3706a21
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module gitea.drjosh.dev/josh/jrouter
+
+go 1.22.0
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..7905807
--- /dev/null
+++ b/main.go
@@ -0,0 +1,5 @@
+package main
+
+func main() {
+
+}