why receiving duplicated frames using sockets in python?

Question

I make a simple client/server code to send/receive frames using sockets, but at the reception, i receive duplicated packets like this

> num seq= 4751 num seq= 4751 num seq= 4752 num seq= 4752 num seq= 4753
> num seq= 4753 num seq= 4754 num seq= 4754 num seq= 4755 num seq= 4755
> num seq= 4756 num seq= 4756 num seq= 4757 num seq= 4757 num seq= 4758
> num seq= 4758 num seq= 4759 num seq= 4759 num seq= 4760 num seq= 4760
> num seq= 4761 num seq= 4761 num seq= 4762 num seq= 4762 num seq= 4763
> num seq= 4763 num seq= 4764 num seq= 4764 num seq= 4765 num seq= 4765
> num seq= 4766 num seq= 4766 num seq= 4767 num seq= 4767 num seq= 4768
> num seq= 4768 num seq= 4769 num seq= 4769 num seq= 4770 num seq= 4770
> num seq= 4771 num seq= 4771 num seq= 4772 num seq= 4772 num seq= 4773
> num seq= 4773 num seq= 4774 num seq= 4774 num seq= 4775 num seq= 4775
> num seq= 4776 num seq= 4776 num seq= 4777 num seq= 4777 num seq= 4778

I couldn't understand why the packets are duplicated at reception !!??

this is the client code:

from socket import *
import binascii

#creation of the RAW socket
s=socket(AF_PACKET, SOCK_RAW)

# bind the socket to the interface
s.bind(("eth0",0))

# Ethernet header
src="\x01\x01\x01\x01\x01\x01"
dst="\x02\x02\x02\x02\x02\x02"
ethertype="74"  #type or length

# generate an infinite traffic 

i=0       # frame number

while True :
        payload=("0"*(100-len(str(i))))+str(i)
        cr=binascii.crc32(dst+src+ethertype+payload)
        res=''
        for j in range(4): # calculate the crc
            t=cr & 0xFF
            cr >>= 8
            res='%02X%s' % (t, res)
        s.send(dst+src+ethertype+payload+res)    # send the frame
        i+=1

And the server code is:

from scapy.all import *

def traiter(p) :

    k=str(p) #transform the frame to a string

    print "num seq=",int(k[14:112]) # print the sequence number

def main():

# intercept packet and send it to traiter

    sniff(iface="lo", prn=lambda x: traiter(x))

if __name__ == "__main__":
   sys.exit(main())

Answer 1

That's a normal behaviour: if source and destination are in the same machine, when you sniff on loopback interface, you capture exiting and entering packets! So packets are not actually duplicated.