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▪ Python Tutorial - App#4: Collecting information from routers and storing it in a MySQL database.
▪ Python Tutorial - App#5: OSPF network discovery via SNMP. Building the OSPF topology.
▪ Python Tutorial - App#6: Basic network sniffer.
▪ Python Tutorial - App#7: Configuration file comparator.
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Python (2.7.3) programming course aimed not only at network professionals, but at anyone having little or no experience in coding or automation and a great desire to start learning Python from scratch. This hands-on training takes you from "Hello World!" to complex network applications in less than 15 hours.
This Python programming and network automation course is especially suitable for Network Professionals (CCNA, CCNP or CCIE level).
First, you will learn and practice every Python key concept, which is explained in one or more video lectures, followed by a short quiz.
Each video is filled with relevant examples, in a learn-by-doing fashion and the quizzes will help you consolidate the main ideas behind each Python topic.
After laying the foundation (and also exploring some advanced Python topics), you will dive right into the real-life network scenarios and apply your knowledge to build 7 great network tools.
Equipped with working files, network topologies and Python code samples (in .pdf and .py formats), you will be able to work alongside me on each lecture and each application. I will provide a virtual machine with all the Python modules already installed and also the full code for each application, so you can save time and start coding and testing on the spot.
We will use emulated routers in GNS3 to test our Python applications in a network environment, so you can see the actual results of running your code.
Join thousands of successful students who have decided to learn Python, upgrade their networking skills and boost their careers using this 100% hands-on course!
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Application
#6 - Basic Network Sniffer
This application is a basic
network sniffer, which captures some predefined protocols and saves info about
each network packet in an external file.
As with the other
applications in this course, the full code is available for download.
Based on what you have
learned so far in the course, it’s your job now to study, understand and test
the code against a network device, as you’ve seen me doing with the previous
applications.
Feel free to alter the code
in any way you want, add new protocols to be captured, more data to be exported
in the external file and so on. New functionality of any kind is welcome. Just
make sure to adapt your code to the contents of the packet in Scapy.
Also, please read the first
33 lines in the code carefully, as they are a good introduction to the code
that follows.
As you’ve probably guessed,
I used Scapy to build this sniffer, because this tool allows packet handling,
decoding and analysis in a very intuitive way.
Also, pay special attention
to the recommendations and settings that I made before starting to build the
user menu and so on. I am referring to these lines and the ones above them:
net_iface =
raw_input("* Enter the interface on which to run the sniffer (like
'eth1'): ")
subprocess.call(["ifconfig",
net_iface, "promisc"], stdout=None, stderr=None, shell=False)
Further more, please read the comments before every
code block, as they are good guidelines to what functionality is
covered by that piece of code.
As you can see at line 72,
the program asks the user what network interface is the capture process going
to be executed on. A good example is entering “eth1”.
net_iface =
raw_input("* Enter the interface on which to run the sniffer (like
'eth1'): ")
Then, at line 80, the user
is asked to enter the number of packets he wishes to be captured by the
sniffer:
pkt_to_sniff =
raw_input("Enter the number of packets to capture (0 is infinity): ")
At line 92, the program
requires the number of seconds to run the capture:
time_to_sniff =
raw_input("* Enter the number of seconds to run the capture: ")
At line 103, the program
asks the user for the protocol to filter the packets by:
proto_sniff =
raw_input("* Enter the protocol to filter by (arp|bootp|icmp|0 is all):
")
Lines 115 and 116 are
dedicated to choosing the file name and creating the file, by opening it for
writing (“w”):
file_name =
raw_input("* Please give a name to the log file: ")
sniffer_log =
open(file_name, "w")
At line 124, you can find
the function that takes care of the parameter extraction from each packet and
logging the packet info to the file: def packet_log(pkt)
The program implements a
counter for each packet, then records the source MAC address and destination
MAC address to the file, on a single row.
Finally, the sniffing
process is initialized by the sniff()
function in Scapy, at line 138, passing the values collected from the user as
arguments to this function.
pkt = sniff(iface=net_iface,
count=int(pkt_to_sniff), timeout=int(time_to_sniff), prn=packet_log)
Now, to test the program,
first you should have direct connectivity from the Debian VM to the router in
GNS3 (R1 - 192.168.2.101 was my test device):
root@debian:/home/debian/workingdir#
ping 192.168.2.101
PING 192.168.2.101
(192.168.2.101) 56(84) bytes of data.
64 bytes from 192.168.2.101:
icmp_req=1 ttl=255 time=429 ms
Let’s choose ICMP packets
for capturing purposes and after the capture is started, I am going to ping the
VM (192.168.2.100) from R1.
Please see the following way
to use the program menu as an example:
root@debian:/home/debian/workingdir#
python Sniffer.py
!
Make sure to run this program as ROOT !
*
Enter the interface on which to run the sniffer (like 'eth1'): eth1
Interface
eth1 was set to PROMISC mode.
Enter
the number of packets to capture (0 is infinity): 0
The
program will capture packets until the timeout expires.
*
Enter the number of seconds to run the capture: 10
The
program will capture packets for 10 seconds.
*
Enter the protocol to filter by (arp|bootp|icmp|0 is all): icmp
The
program will capture only ICMP packets.
*
Please give a name to the log file: udemy.txt
*
Starting the capture... Waiting for 10 seconds...
At this point, the program listens
for all the ICMP packets it receives in the next 10 seconds on eth1 (ping from R1 now!). The results
will be exported to the udemy.txt file.
And these are the results in
this case:
root@debian:/home/debian/workingdir#
cat udemy.txt
Packet
1: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
2: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Packet
3: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
4: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Packet
5: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
6: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Packet
7: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
8: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Packet
9: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
10: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Packet
11: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
12: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Packet
13: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
14: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Packet
15: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
16: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Packet
17: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
18: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Packet
19: SMAC: c0:01:24:c0:00:00 DMAC: 08:00:27:f2:9b:7c
Packet
20: SMAC: 08:00:27:f2:9b:7c DMAC: c0:01:24:c0:00:00
Thank you!
