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Asked: 2026-06-17T04:59:59+00:00

I am trying to sniff UDP packets using scapy sniff function, I send the

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I am trying to sniff UDP packets using scapy sniff function, I send the packets in the Looback interface, the sending code is simple as follows:

from socket import *

IPv4 = "127.0.0.1"
Port = 45943

ClientSock = socket(AF_INET, SOCK_DGRAM) 

while True:
    MESSAGE = raw_input()
    ClientSock.sendto(MESSAGE, (IPv4, Port))

However when i run (in another terminal tab after importing scapy):

a = sniff(iface="lo0", count = 5)

I get the following result:

>>> a.nsummary()
0000 Raw
0001 Raw
0002 Raw
0003 Raw
0004 Raw

whereas i am supposed to get UDP packets!, can any one point out to anything that i am missing here.
thanks

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1 Answer

  1. Editorial Team

    Unable to guess datalink type (interface=lo0 linktype=0)

    That message translates as “Scapy doesn’t understand the DLT_NULL link-layer header type, as used on the loopback device in *BSD and OS X, so it doesn’t support the loopback device on *BSD and OS X”.

    So you’re out of luck if you want to use Scapy on OS X to capture on the loopback device, unless and until Scapy is enhanced to handle DLT_NULL. (DLT_NULL is not that hard to handle, so presumably the only reason it’s not handled is that most of the people using it on a loopback device are doing so on Linux, where the link-layer header type value on the loopback device is DLT_EN10MB, i.e. Ethernet, so nobody’s bothered to fix it. I’ll see if I can get it working and, if so, send them a patch.)

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