Scapy WTF???

handshake.py

# The goal of this script is to complete a three-way handshake with a netcat listener on port 8888. Tcpdump
# shows the SYN packet being sent but I'm getting a RST/ACK instead of a SYN/ACK packet from netcat. I've
# configured Iptables to drop any RST packets where the source and destination are the same as the server's
# IP address, but the output from iptables -L -nv shows the rule is not being hit. Any ideas what is going on?
#
# I think I've decided that scapy is good for processing pcaps or gathering stats while sniffing traffic but
# for actually sending packets, it sucks. I know I can create the socket with Python and use the stream with
# Scapy but I really don't want to do that.

# Suppress Scapy IPv6 warning
import logging
logging.getLogger("scapy.runtime").setLevel(logging.ERROR)

# Begin our Scapy script.
from scapy.all import *

server = '10.0.2.15'  # This is the local server where the script is running from. This breaks for some reason.
sport = 65535
dport = 8888
timeout= 5

def handshake(src, dst, sport, dport):
    ip = Ether()/IP(src=src, dst=dst)
    tcp = TCP(sport=sport, dport=dport, flags='S')
    print 'SYN\n---'
    print (ip/tcp).summary()

    print 'SYN_ACK\n-------'
    sa = srp1(ip/tcp, timeout=timeout)
    print sa.summary()

    print 'ACK\n---'
    tcp = TCP(sport=dport, dport=sport, flags="A", seq=sa[TCP].ack, ack=sa[TCP].seq+1)
    print (ip/tcp).summary()

    print 'SOCK\n----'
    sock = send(ip/tcp/'TEST', timeout=timeout)
    print sock.summary()

print('Send packet...')
handshake(server, server, sport, dport)

handshake_output.txt

Send packet...
SYN
---
Ether / IP / TCP 10.0.2.15:65535 > 10.0.2.15:8888 S
SYN_ACK
-------
Begin emission:
Finished to send 1 packets.
*
Received 1 packets, got 1 answers, remaining 0 packets
Ether / IP / TCP 10.0.2.15:8888 > 10.0.2.15:65535 RA / Padding
ACK
---
Ether / IP / TCP 10.0.2.15:8888 > 10.0.2.15:65535 A
SOCK
----
Begin emission:
*Finished to send 1 packets.

Received 1 packets, got 1 answers, remaining 0 packets
Ether / IP / TCP 10.0.2.15:65535 > 10.0.2.15:8888 R / Padding

iptables.txt

Chain INPUT (policy ACCEPT 26 packets, 2430 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 13 packets, 1113 bytes)
 pkts bytes target     prot opt in     out     source               destination         
    0     0 DROP       tcp  --  any    any     10.0.2.15            10.0.2.15            tcp flags:RST/RST

tcpdump.txt

18:51:14.934289 IP 10.0.2.15.65535 > 10.0.2.15.8888: Flags [S], seq 0, win 8192, length 0
18:51:14.934675 IP 10.0.2.15.8888 > 10.0.2.15.65535: Flags [R.], seq 0, ack 1, win 0, length 0
18:51:14.941400 IP 10.0.2.15.8888 > 10.0.2.15.65535: Flags [.], seq 1:5, ack 1, win 8192, length 4
18:51:14.941630 IP 10.0.2.15.65535 > 10.0.2.15.8888: Flags [R], seq 1, win 0, length 0

working_handshake.py

# Suppress Scapy IPv6 warning
import logging
logging.getLogger("scapy.runtime").setLevel(logging.ERROR)

# Begin our Scapy script.
from scapy.all import *

server = 'google.com'  # Using a non-local server made the script work.
port = 80
timeout = 5


def handshake(dst, port):
    ip = Ether()/IP(dst=dst)
    tcp = TCP(dport=port, flags='S')
    print 'SYN\n---'
    print (ip/tcp).summary()
    sa = srp1(ip/tcp, timeout=timeout)

    print '\nSYN_ACK\n-------'
    print sa.summary()

    print '\nACK\n---'
    tcp = TCP(sport=sa[TCP].dport, dport=sa[TCP].sport, flags="A", seq=sa[TCP].ack, ack=sa[TCP].seq+1)
    print (ip/tcp).summary()
    sock = srp1(ip/tcp, timeout=timeout)

    print '\nSOCK\n----'
    print sock.summary()


print('Send packet...')
handshake(server, port)

This worked for me between two VM's... are you sending it to a nc on the same host? if so, try between two different hosts.

import logging
logging.getLogger("scapy.runtime").setLevel(logging.ERROR)

from scapy.all import *

server = '192.168.187.136'
sport = random.randint(1024,65535)
dport = 8888
timeout = 5
my_seq = random.randint(1,50000)

def handshake(src, dst, sport, dport, my_seq):
ip = IP(dst=dst)
syn = ip/TCP(sport=sport, dport=dport, seq=my_seq, flags='S')
print 'SYN\n---'
print (ip/syn).summary()

print '\nSYN_ACK\n-------'
sa = sr1(syn, timeout=timeout)
print sa.seq

print '\nACK\n---'
my_ack = sa.seq + 1
my_seq = my_seq + 1
ack = TCP(sport=sport, dport=dport, seq=my_seq, ack=my_ack, flags='A')
send(ip/ack)
print (ip/ack).summary()

print '\nSOCK\n----'
my_seq = my_seq + 1
payload = "test"
push = TCP(sport=sport, dport=dport, seq=my_seq, ack=my_ack, flags='PA')
sock = send(ip/push/payload)
print (ip/push).summary()

print('Send packet...')
handshake(server, server, sport, dport, my_seq)