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Introduction to Python Network Programming
for Network Architects and Engineers
Vince Kelly TSA
Session ID: DEVNET-1040
Agenda
•
Python Basics
•
The Python Socket Module
•
Security
•
‘Higher Layer’ Protocols & APIs: XMLRPC
•
Higher Layer’ Protocols: REST & HTTP
•
Conclusion
Python Basics
•
Working with the Command Line
•
Python Basics: Working With files, Directories and Strings
DEVNET-1040
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Sockets:
•
What Can We Get Just From the Python Standard Library Alone?
•
Python Socket Library
•
Starting Out With UDP
•
What Are Sockets?
•
B R I E F Primer on OOP versus POP
•
The ‘Big Five’ Questions to Answer
•
Socket Objects
•
Socket Names
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Sockets:
•
Moving on To TCP
•
Parsing Directories and Files with OS.Walk
•
Simple Message Passing Using TCP
•
Simple File Transfer Using TCP
•
Simple File Transfer With Directory Search Using TCP
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SECURITY
•
One-way Hash Creation
•
Display All Available Hash Algorithms
•
Generate a One-way Hash for a File
•
Verifying a File Has Not Been Tampered With – Step 1: Client Side, Server Side
•
Verifying a File Has Not Been Tampered With – Step 2 Client Side, Server Side
•
Establish Client/Server Connection Over SSL – Client Side, Server Side
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7
‘Higher Layer’ Protocols & APIs
•
Building A Spreadsheet Primer
•
XMLRPC
DEVNET-1040
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8
‘Higher Layer’ Protocols: REST & HTTP
•
REST and HTTP
•
TCP Send a REST Request to Google
•
‘Screen Scraping’ using Python URLLIB
•
APIC REST Interface
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9
WHAT’S THE POINT of ALL THIS??
“Good Programmers write code, GREAT Programmers steal code”
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Python Basics
Follow Along:
followCmd_line.py
Parsing command line
followFiles.py
Working with files, directories and strings
followFile_Info.py
Retrieves file size, creation, modified and accessed on a file
followFile_Encrypt.py
Encodes content and writes to disk
followFile_Decrypt.py
Decodes file and prints to screen
followPing.py
Detect what OS we are on, Make system call to execute ping (windows)
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11
Python Basics: Working with the Command Line
Start python
Interpreter
(python.exe)
Find & execute
this program
(Program_xyz.py)
Save whatever comes
after the program
name
as command line
argumentS
(www.cisco.com,
192.168.10.1)
argv = [ ‘Program_xyz.py’, ‘www.cisco.com’, ‘192.168.10.1’ ]
print argv[0]
‘Program_xyz.py’
print argv[1]
‘www.cisco.com’
DEVNET-1040
print argv[2]
‘192.168.10.1’
© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public
12
Python Basics: Working with the Command Line
followCmd_Line.py
-
Uses built-in SYS module: sys.argv() and len() built-in methods
Displays:
- The programs (empty) command line, number of arguments, etc
- Appends ‘Hello’ ‘World’ to the command line
- The programs (non-empty command line, number of arguments, etc
- Removes the last entry from the cmd line
- Example of Type Casting a string value entered by user into an integer
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Python Basics: Working With files, Directories and Strings
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Python Basics: Working With files, Directories and Strings
followFiles.py
-
Uses built-in os module: os.getcwd() built-in method and .lower() string method
Concatenates IP address, User Name and Password entered by user
Calls a function with the concatenated message as a parameter
Takes directory and file name from user (or defaults to CWD)
Opens file in append mode
Loops waiting forever on more input from user
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DEVNET-1040
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Python Basics: Working With files, Directories and Strings
followFile_Info.py
-
Uses built-in getsize(), .stat() built-in methods
Uses time.ctime() to return file creation, modification and last access
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Python Basics: Working With files, Directories and Strings
followEncrypt.py
-
Uses built-in codecs and os modules:
Encodes user input with ROT-13
Loops forever on user input
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Python Basics: Working With files, Directories and Strings
followDecrypt.py
-
Uses built-in codecs and os modules:
Decodes user input using ROT-13
Loops forever on user input
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19
Python Basics: Working With files, Directories and Strings
followPing.py
-
-
Uses built-in os module: os.name() returns the operating system ('posix', 'nt', 'mac',
'os2', 'ce', 'java', 'riscos‘)
Makes system call to execute ping and display the results
Displays warning if host doesn’t respond after timeout
Loops forever on user input
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20
Network Communications
SERVER
Data
Warehou
se
CLIENT
App
Pytho
n
Enviro
nment
Web
Service
s
Operating System
Web
Browse
r
Operating System
Pytho
n
Enviro
nment
Communications
Stack(s)
CLIENT
Pytho
n
Enviro
nment
App
Web
Browse
r
Operating System
DEVNET-1040
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Sockets: What Can We Get Just From the Python Standard Library Alone?
TCP/IP PROTOCOL STACK
Python
Socket Library
ACI APIC
Firefox
Browser
XMLRPC
“Higher Layer” Libraries
HTTP, etc.
Web
80
FTP
20,21
Telnet
23
SMTP
25
SNMP
161
TCP
DNS
53
UDP
IP
Device Drivers
Tx
Buffers
LAYER 1
B
U
S
Framer/
Protocol
decode
Rx
Buffers
NIC
DEVNET-1040
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Python Socket Library
Follow Along:
followSocket_Examples.py
Displays local socket information
followSock_Scan1.py
Scans remote services
followDisplay_SocketProtocols.py
Displays basic IPv4 and IPv6 stack information
followUDP_Client.py
Basic UDP Client
followUDP_Server.py
Basic UDP Server
followUDP_ClientEncoded.py
Receives an encoded ROT-13 message and decodes it
followUDP_CountDownServer.py
Broadcasts an encoded message
DEVNET-1040
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gethostname()
return the current hostname
gethostbyname()
map a hostname to its IP number
'gethostbyname_ex()
IPv4 Only
gethostbyaddr()
-- map an IP number or hostname to DNS info
getservbyname()
map a service name and a protocol name to a port
number
getprotobyname()
map a protocol name (e.g. 'tcp') to a number
getaddrinfo()
getfqdn()
getnameinfo()
getservbyport()
socket.setdefaulttimeout()
set the default timeout value
socket.getdefaulttimeout()
get the default timeout value
'has_ipv6',
DEVNET-1040
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Sockets: Let’s Start with UDP
TCP/IP PROTOCOL STACK
Python
Socket Library
ACI APIC
Firefox
Browser
XMLRPC
“Higher Layer” Libraries
HTTP, etc.
Web
80
FTP
20,21
Telnet
23
SMTP
25
SNMP
161
TCP
DNS
53
UDP
IP
Device Drivers
Tx
Buffers
LAYER 1
B
U
S
Framer/
Protocol
decode
Rx
Buffers
NIC
DEVNET-1040
© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public
26
What Are Sockets?
•
Is an abstract concept that represents an end point. Programs use sockets to
communicate with other programs which may or may not be on the same
computer.
•
A socket is defined by IP address, the port it listens on and the protocol used
•
Client/Server sockets: represent endpoints of a conversation. Server sockets
just produce more client sockets e.g., Web Browser uses a client socket, Web
server uses a server socket to ‘listen’ on..
•
To create a client/server connection you:
•
•
•
Create/”spin up” a socket object. This contains all the methods needed to communicate
Bind to the port you want. If successful, the socket exists for the length of the session..
Client sockets are normally only used for one exchange (or a small set of
sequential exchanges). They are created and torn down frequently.
DEVNET-1040
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27
socket.getaddrinfo("192.168.252.253", 80, 0, 0, socket.SOL_TCP)
[ (2,
Family
0,
6,
'',
('192.168.252.253', 80)) ]
Socket
Protocol
Canonical
Type
Type
Name
socket.getaddrinfo('2a04:4e42:5::223',80, 0, 0, socket.SOL_TCP)
[(23,
IPv6
0,
6,
1 STREAM,
2 DATAGRAM,
'',
Socket Name: 6 Tuple
('2a04:4e42:5::223', 80,
Canonical
TCP
Socket Name: 2 Tuple
0,
Flow Label
0))]
Scope
Name
3 RAW,
4 RDM,
5 SEQPACKET
DEVNET-1040
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But Before We Jump In, a B R I E F Primer on OOP versus POP…….
DEVNET-1040
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29
The ‘Big Five’ Questions to Answer:
What kind of network do we want to talk to?
1)
•
What ‘address family’? IPv4 (AF_INET) or IPv6 (AF_INET6), etc.
What type of connection do we want?
2)
•
Do we want a datagram service (UDP) or a connection oriented stream service (TCP)?
What kind of protocol do we need?
3)
•
Answers 1 and 2 already narrowed this down
4)
What IP address to use?
5)
What UDP or TCP port number should we use?
DEVNET-1040
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30
Socket Objects
Retrieve (and use) the Python socket module
import socket
Python socket module’s METHOD
c = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
New socket object
What Protocol Stack Version?
What Part of the Protocol Stack Do You Want ?
INET:
SOCK_STREAM:
use TCP
SOCK_DGRAM:
use UDP
use IPv4
INET6: use IPv6
What do we mean by a ‘socket object’?
DEVNET-1040
© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public
31
Sockets
client
import socket
c = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
Socket object
Socket object
c.connect((‘www.cisco.com’,80))
‘c’
-
Gets instantiated/’spun up’ (on each side) through the
python socket module
-
Handles setting up the session
-
Handles sending & receiving data
-
Handles Error recovery
-
Handles ending/tearing down the session
DEVNET-1040
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32
Sockets
server
import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serverAddr = S.gethostname()
s.bind((serverAddr,12345))
s.listen(5)
while 1:
client, cleintAddr = s.accept()
10.255.88.76
NIC
DEVNET-1040
© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public
36
Sockets
server
import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serverAddr = ‘10.255.88.76’
client
s.bind((serverAddr,12345))
import socket
s.listen(5)
c = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client
192.168.13.5
c.connect((‘10.255.88.76’,80)
while 1:
c.send(‘Hello Server!!!’)
Socket object
client, clientAddr = s.accept()
Socket object
c.shutdown(socket.SHUT_RDWR))
‘c’
print “I just got a connection request from: “, clientAddr
‘client’
client.close()
10.255.88.76
192.168.19.5
Hello Server!!!
TCP | IP
NIC
NIC
DEVNET-1040
© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public
37
Sockets
server
import socket
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serverAddr = s.gethostname()
client
s.bind((serverAddr,12345))
import socket
s.listen(5)
c = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
c.connect((‘www.cisco.com’,80))
Socket object3
c.send(‘Hello Server!!!’)
Socket object
while 1:
Socket object2
client
192.168.13.5
client2
10.23.11.254
client3
17.255.10.1
client, clientAddr = s.accept()
Socket object
c.shutdown(socket.SHUT_RDWR)
‘c’
‘client’
‘client’
‘client’
print “I just got a connection request from: “, clientAddr
client.close()
10.255.88.76
192.168.19.5
Hello Server!!!
TCP | IP
NIC
NIC
DEVNET-1040
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38
El-cheapo_UDP_server.py:
Sockets
import socket,sys
sp = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sp.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
count = 0
port = 5678
dest = ('<broadcast>', port)
print 'Sending message...'
while True:
msg = 'Hello World'
sp.sendto(msg, dest)
# send message out on port 5678 to address 'ffffff'
DEVNET-1040
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39
El-cheapo_UDP_client.py:
Sockets
import socket,time
s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
# spin up socket object
s.setsockopt(socket.SOL_SOCKET, socket.SO_BROADCAST, 1)
# tell it to use broadcasts
s.bind(('',5678))
# 'glue' this program onto any address using port 5678
print "waiting..."
data,addr = s.recvfrom(1024)
print '\r', data, addr
# get a message – up to to 1024 bytes - and where it came from
# display the message
DEVNET-1040
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40
Thank You
Q&A
Complete Your Online Session Evaluation
•
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Session Evaluations after each
session
•
Complete 4 Session Evaluations &
the Overall Conference Evaluation
(available from Thursday) to receive
your Cisco Live T-shirt
•
All surveys can be completed via
the Cisco Live Mobile App or the
Communication Stations
Don’t forget: Cisco Live sessions will be available
for viewing on-demand after the event at
CiscoLive.com/Online
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Continue Your Education
•
Demos in the Cisco campus
•
Walk-in Self-Paced Labs
•
Lunch & Learn
•
Meet the Engineer 1:1 meetings
•
Related sessions
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44
Thank You