diff --git a/liteeth/common.py b/liteeth/common.py
index 272f946cf..540747f4c 100644
--- a/liteeth/common.py
+++ b/liteeth/common.py
@@ -16,17 +16,101 @@ eth_mtu = 1532
 eth_preamble = 0xD555555555555555
 buffer_depth = 2**log2_int(eth_mtu, need_pow2=False)
 
-def eth_phy_description(dw):
-	layout = [
-		("data", dw),
-		("error", dw//8)
-	]
-	return EndpointDescription(layout, packetized=True)
+class HField():
+	def __init__(self, byte, offset, width):
+		self.byte = byte
+		self.offset = offset
+		self.width = width
 
-def eth_mac_description(dw):
+mac_header_len = 14
+mac_header = {
+	"destination_mac_address":	HField(0,  0, 48),
+	"source_mac_address":		HField(6,  0, 48),
+	"ethernet_type":			HField(12, 0, 16)
+}
+
+arp_header_len = 28
+arp_header = {
+	"hardware_type":			HField( 0,  0, 16),
+	"protocol_type":			HField( 2,  0, 16),
+	"hardware_address_length":	HField( 4,  0, 8),
+	"protocol_address_length":	HField( 5,  0, 8),
+	"operation":				HField( 6,  0, 16),
+	"source_mac_address":		HField( 8,  0, 48),
+	"source_ip_address":		HField(14,  0, 32),
+	"destination_mac_address":	HField(18,  0, 48),
+	"destination_ip_address":	HField(24,  0, 32)
+}
+
+ipv4_header_len = 24
+ipv4_header = {
+	"version":					HField(0,  0, 4),
+	"ihl":						HField(0,  4, 4),
+	"dscp":						HField(1,  0, 6),
+	"ecn":						HField(1,  6, 2),
+	"total_length":				HField(2,  0, 16),
+	"identification":			HField(4,  0, 16),
+	"flags":					HField(6,  0, 3),
+	"fragment_offset":			HField(6,  3, 13),
+	"time_to_live":				HField(8,  0, 8),
+	"protocol":					HField(9,  0, 8),
+	"header_checksum":			HField(10,  0, 16),
+	"source_ip_address":		HField(12,  0, 32),
+	"destination_ip_address":	HField(16,  0, 32),
+	"options":					HField(20,  0, 32)
+}
+udp_header_len = 8
+udp_header = {
+	"source_port":				HField( 0,  0, 16),
+	"destination_port":			HField( 2,  0, 16),
+	"length":					HField( 4,  0, 16),
+	"checksum":					HField( 6,  0, 16)
+}
+
+# layouts
+def _layout_from_header(header):
+	_layout = []
+	for k, v in sorted(header.items()):
+		_layout.append((k, v.width))
+	return _layout
+
+def eth_phy_description(dw):
 	layout = [
 		("data", dw),
 		("last_be", dw//8),
 		("error", dw//8)
 	]
 	return EndpointDescription(layout, packetized=True)
+
+def eth_mac_description(dw):
+	layout = _layout_from_header(mac_header) + [
+		("data", dw),
+		("last_be", dw//8),
+		("error", dw//8)
+	]
+	return EndpointDescription(layout, packetized=True)
+
+def eth_arp_description(dw):
+	layout = _layout_from_header(arp_header) + [
+		("data", dw),
+		("last_be", dw//8),
+		("error", dw//8)
+	]
+	return EndpointDescription(layout, packetized=True)
+
+def eth_ipv4_description(dw):
+	layout = _layout_from_header(ipv4_header) + [
+		("data", dw),
+		("last_be", dw//8),
+		("error", dw//8)
+	]
+	return EndpointDescription(layout, packetized=True)
+
+def eth_udp_description(dw):
+	layout = _layout_from_header(udp_header) + [
+		("data", dw),
+		("last_be", dw//8),
+		("error", dw//8)
+	]
+	return EndpointDescription(layout, packetized=True)
+