diff --git a/main.go b/main.go
index 414f469..5a58d4e 100644
--- a/main.go
+++ b/main.go
@@ -3,92 +3,52 @@ package main
 import (
 	"fmt"
 	"log"
-	"net"
 
+	"git.freifunk-franken.de/jkimmel/abbel/packet"
 	"git.freifunk-franken.de/jkimmel/abbel/tlv"
-	"golang.org/x/net/ipv6"
-	"inet.af/netaddr"
 )
 
 type options struct {
-	Group net.IP
+	Group string
 	Port  uint16
-	Ifs   []net.Interface
+	Ifs   []string
 }
 
 func parseOpts() (options, error) {
 	var opt options
 	var err error
 
-	opt.Group = net.ParseIP("ff02::1:6")
-	opt.Port = 6696
-	ifi, err := net.InterfaceByName("babel")
-	if err != nil {
-		return opt, err
+	opt = options{
+		Group: "ff02:0:0:0:0:0:1:6",
+		Port:  6696,
+		Ifs:   []string{"babel"},
 	}
-	opt.Ifs = []net.Interface{*ifi}
 
 	return opt, err
 }
 
-func readBabelPacket(up *ipv6.PacketConn, b []byte) ([]byte, netaddr.IP, error) {
-	n, rcm, src, err := up.ReadFrom(b)
-	if err != nil {
-		return nil, netaddr.IP{}, err
-	}
-
-	_ = rcm
-
-	b = b[:n]
-	if len(b) < 4 {
-		fmt.Println("packet too short:", len(b))
-	}
-	magic := b[0]
-	version := b[1]
-	length := uint16(b[2])<<8 + uint16(b[3])
-	b = b[4:]
-
-	if magic != 42 {
-		return nil, netaddr.IP{}, fmt.Errorf("Invalid magic number %d", magic)
-	}
-	if int(length) > len(b) {
-		fmt.Println("invalid length:", length)
-	}
-
-	fmt.Println(src, rcm, magic, version, length, n)
-	srcipport, err := netaddr.ParseIPPort(src.String())
-	return b, srcipport.IP(), err
-}
-
 func run(opt options) error {
-	var err error
-	uc, err := net.ListenUDP("udp6", &net.UDPAddr{Port: int(opt.Port)})
+	conn, err := packet.ListenPort(opt.Port)
 	if err != nil {
 		return err
 	}
-	defer uc.Close()
-	up := ipv6.NewPacketConn(uc)
-
-	if err := up.SetControlMessage(ipv6.FlagDst, true); err != nil {
-		return err
-	}
-
-	for ifi := range opt.Ifs {
-		if err := up.JoinGroup(&opt.Ifs[ifi], &net.UDPAddr{IP: opt.Group}); err != nil {
+	defer conn.Close()
+	for _, iface := range opt.Ifs {
+		if err = conn.JoinGroup(iface, opt.Group); err != nil {
 			return err
 		}
 	}
 
 	buf := [4096]byte{}
+	var s tlv.PacketDecoder
 	for {
-		b, src, err := readBabelPacket(up, buf[:])
+		b, src, ifindex, err := conn.ReadFrom(buf[:])
 		if err != nil {
 			fmt.Println("Skipping packet:", err)
 			continue
 		}
 
-		var s tlv.PacketDecoder
-		s.Reset(b, src)
+		s.Reset(b, src, ifindex)
 		for s.Scan() {
 			switch t := s.TLV().(type) {
 			case tlv.NextHop:
diff --git a/packet/packet.go b/packet/packet.go
new file mode 100644
index 0000000..37f4369
--- /dev/null
+++ b/packet/packet.go
@@ -0,0 +1,86 @@
+package packet
+
+import (
+	"fmt"
+	"net"
+
+	"golang.org/x/net/ipv6"
+	"inet.af/netaddr"
+)
+
+const (
+	BabelMagic            = 42
+	BabelVersion          = 2
+	BabelPacketHeaderSize = 4
+)
+
+type Conn struct {
+	v6pc *ipv6.PacketConn
+}
+
+func ListenPort(port uint16) (Conn, error) {
+	var c Conn
+
+	uc, err := net.ListenUDP("udp6", &net.UDPAddr{Port: int(port)})
+	if err != nil {
+		return c, err
+	}
+	c.v6pc = ipv6.NewPacketConn(uc)
+
+	return c, c.v6pc.SetControlMessage(ipv6.FlagDst, true)
+}
+
+func (c Conn) Close() error {
+	return c.v6pc.Close()
+}
+
+func (c Conn) JoinGroup(ifname string, addr string) error {
+	ifi, err := net.InterfaceByName(ifname)
+	if err != nil {
+		return err
+	}
+
+	ip, err := netaddr.ParseIP(addr)
+	if err != nil {
+		return err
+	}
+
+	return c.v6pc.JoinGroup(ifi, &net.UDPAddr{IP: ip.IPAddr().IP})
+}
+
+func (c Conn) ReadFrom(b []byte) (body []byte, src netaddr.IP, ifindex int, err error) {
+	n, rcm, _, err := c.v6pc.ReadFrom(b)
+	if err != nil {
+		return nil, netaddr.IP{}, 0, err
+	}
+
+	b = b[:n]
+	if len(b) < BabelPacketHeaderSize {
+		return nil, netaddr.IP{}, 0, fmt.Errorf("Packet too short: %d", len(b))
+	}
+
+	magic := b[0]
+	version := b[1]
+	length := uint16(b[2])<<8 + uint16(b[3])
+	b = b[4:]
+
+	if magic != BabelMagic {
+		return nil, netaddr.IP{}, 0, fmt.Errorf("Invalid magic number %d", magic)
+	}
+	if version != BabelVersion {
+		return nil, netaddr.IP{}, 0, fmt.Errorf("Unsupported version number %d", version)
+	}
+	if int(length) > len(b) {
+		return nil, netaddr.IP{}, 0, fmt.Errorf("Invalid length for packet of size %d: %d", n, length)
+	}
+
+	var ok bool
+	src, ok = netaddr.FromStdIPRaw(rcm.Src)
+
+	if !ok {
+		return nil, netaddr.IP{}, 0, fmt.Errorf("Invalid src address %q", rcm.Src)
+	}
+
+	return b, src, rcm.IfIndex, err
+
+}
diff --git a/tlv/tlv.go b/tlv/tlv.go
index 74a4523..3082a91 100644
--- a/tlv/tlv.go
+++ b/tlv/tlv.go
@@ -183,7 +183,7 @@ type PacketDecoder struct {
 }
 
 // Reset clears the parser state and sets a new byte slice to work on.
-func (s *PacketDecoder) Reset(b []byte, nexthop netaddr.IP) {
+func (s *PacketDecoder) Reset(b []byte, nexthop netaddr.IP, ifindex int) {
 	*s = PacketDecoder{}
 	s.tlvscanner.Reset(b)
 	switch {