diff --git a/lilSYNner.py b/lilSYNner.py
index 779bf94..afaa319 100644
--- a/lilSYNner.py
+++ b/lilSYNner.py
@@ -1,22 +1,77 @@
+# lilSYNner
+
 import socket
+import sys
+import argparse
 
-s = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_TCP)
-s.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)
+parser = argparse.ArgumentParser(description='Send a SYN over ipv4.')
+parser.add_argument('--srcip', type=str, default='192.168.13.37', help='source address')
+args = parser.parse_args()
+if args.srcip:
+	print("setting src ip: "+str(args.srcip))
+	srcaddress = socket.inet_aton(args.srcip)
+else:
+	hname = socket.gethostname()
+	ip = socket.gethostbyname(hname)
+	print("src ip not specified, using: "+str(ip))
+	srcaddress = socket.inet_aton(ip)
+print("src ip bytes: "+str(srcaddress))
 
-version_ihl_typeofservice_totallength = b'\x45\x00\x00\x28'
-identification_flags_fragment_offset = b'\xab\xcd\x00\x00'
+sock = socket.socket(socket.AF_INET, socket.SOCK_RAW, socket.IPPROTO_TCP)
+sock.setsockopt(socket.IPPROTO_IP, socket.IP_HDRINCL, 1)
 
-ip_header  = b'\x45\x00\x00\x28'  # Version, IHL, Type of Service | Total Length
-ip_header += b'\xab\xcd\x00\x00'  # Identification | Flags, Fragment Offset
-ip_header += b'\x40\x06\xa6\xec'  # TTL, Protocol | Header Checksum
-ip_header += b'\x0a\x0a\x0a\x02'  # Source Address
-ip_header += b'\x0a\x0a\x0a\x01'  # Destination Address
+version = b'\x45'
+ihl = b'\x00'
+typeofservice = b'\x00'
+totallength = b'\x28'
+identification = b'\xab\xcd'
+flags = b'\x00'
+fragmentoffset = b'\x00'
+ttl = b'\x40'
+protocol = b'\x06'
+dstaddress = b'\xc0\xa8\x0b\x0b'  # 192.168.11.11
+#  dstaddress = b'\x0a\x0a\x0a\x01'  # 10.10.10.1
+#  headerchecksum = b'\xa6\xec'
+hh = int(version.hex(), 16)
+hh += int(ihl.hex(), 16)
+hh += int(typeofservice.hex(), 16)
+hh += int(totallength.hex(), 16)
+hh += int(flags.hex(), 16)
+hh += int(fragmentoffset.hex(), 16)
+hh += int(ttl.hex(), 16)
+hh += int(protocol.hex(), 16)
+hh += int(srcaddress.hex(), 16)
+hh += int(dstaddress.hex(), 16)
+print(hh)
+hh = (hh >> 3) + (hh & 0xffff)
+hh += hh >> 2
+headerchecksum = (hh + 0x10000 & 0xffff).to_bytes(2, byteorder=sys.byteorder)
+print("headerchecksum "+str(headerchecksum))
 
-tcp_header  = b'\x0d\x25\x00\x50'  # Source Port | Destination Port
-tcp_header += b'\x00\x00\x00\x00'  # Sequence Number
-tcp_header += b'\x00\x00\x00\x00'  # Acknowledgement Number
-tcp_header += b'\x50\x02\x71\x10'  # Data Offset, Reserved, Flags | Window Size
-tcp_header += b'\xe6\x32\x00\x00'  # Checksum | Urgent Pointer
+ip_header = version + ihl + typeofservice + totallength + identification + flags + fragmentoffset + ttl + protocol + headerchecksum + srcaddress + dstaddress
+
+
+srcport = b'\x0d\x25'  # 1337
+dstport = b'\x0b\x0b'  # 1111
+seqnum = b'\x00\x00\x00\x00'
+acknum = b'\x00\x00\x00\x00'
+dataoffset_reserved_flags_winsize = b'\x50\x02\x71\x10'
+urgentptr = b'\x00\x00'
+#  checksum = b'\xe6\x32'
+
+chh = int(srcport.hex(), 16)
+chh += int(dstport.hex(), 16)
+chh += int(dataoffset_reserved_flags_winsize.hex(), 16)
+chh += int(urgentptr.hex(), 16)
+chh = (chh >> 4) + (chh & 0xffff)
+chh += chh >> 4
+checksum = (chh + 0x10000 & 0xffff).to_bytes(2, byteorder=sys.byteorder)
+print("checksum "+str(checksum))
+
+tcp_header = srcport + dstport + seqnum + acknum + dataoffset_reserved_flags_winsize + checksum + urgentptr
 
 packet = ip_header + tcp_header
-s.sendto(packet, ('192.168.0.1', 0))
+print("sending SYN")
+sock.sendto(packet, (args.srcip, 0))
+
+res = int.from_bytes(srcaddress, byteorder=sys.byteorder)