Introduction to Python Network Programmingclnv.s3.amazonaws.com/2017/eur/pdf/DEVNET-1040.pdf ·...

Introduction to Python Network Programming for Network Architects and Engineers

Vince Kelly TSA

Session ID: DEVNET-1040

• Python Basics

• The Python Socket Module

• Security

• ‘Higher Layer’ Protocols & APIs: XMLRPC

• Higher Layer’ Protocols: REST & HTTP

• Conclusion

Agenda

© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public 4DEVNET-1040

Python Basics

• Working with the Command Line

• Python Basics: Working With files, Directories and Strings


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


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


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


‘Higher Layer’ Protocols & APIs

• Building A Spreadsheet Primer

• XMLRPC


‘Higher Layer’ Protocols: REST & HTTP

• REST and HTTP

• TCP Send a REST Request to Google

• ‘Screen Scraping’ using Python URLLIB

• APIC REST Interface

© 2017 Cisco and/or its affiliates. All rights reserved. Cisco Public

WHAT’S THE POINT of ALL THIS??

“Good Programmers write code, GREAT Programmers steal code”DEVNET-1040 10

© 2017 Cisco and/or its affiliates. All rights reserved. Cisco PublicDEVNET-1040 11

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)

Python Basics


Start python

Interpreter(python.exe)

Find & execute

this program (Program_xyz.py)

argv = [ ‘Program_xyz.py’, ‘www.cisco.com’, ‘192.168.10.1’ ]

Save whatever comes

after the program

name

as command line

argumentS(www.cisco.com,

192.168.10.1)

print argv[0]

‘Program_xyz.py’

print argv[1]

‘www.cisco.com’

print argv[2]

‘192.168.10.1’

Python Basics: Working with the Command Line

DEVNET-1040 12

http://www.cisco.com/


- 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

followCmd_Line.py

Python Basics: Working with the Command Line


Python Basics: Working With files, Directories and Strings


- 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

followFiles.py




followFile_Info.py

- Uses built-in getsize(), .stat() built-in methods

- Uses time.ctime() to return file creation, modification and last access



followEncrypt.py- Uses built-in codecs and os modules:

- Encodes user input with ROT-13

- Loops forever on user input



followDecrypt.py- Uses built-in codecs and os modules:

- Decodes user input using ROT-13




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


Network Communications


Operating System

App

Pytho

n

Enviro

nment

Web

Browse

r

Operating System

Data

Warehou

se

Pytho

n

Enviro

nment

Web

Service

s

SERVER

Operating System

App

Pytho

n

Enviro

nment

Web

Browse

r

CLIENT

CLIENT

Communications

Stack(s)

DEVNET-1040 22


IP

TCP UDP

XMLRPC

FTP

20,21

SNMP

161

Device Drivers

Pyth

on

So

cket

Lib

rary

“Higher Layer” Libraries

HTTP, etc.

NIC

B

U

STx

Buffers

Rx

Buffers

Framer/

Protocol

decode

Telnet

23

SMTP

25

DNS

53

TC

P/I

P P

RO

TO

CO

L S

TA

CK

LAYER 1

ACI APICFirefox

Browser

Web

80

Sockets: What Can We Get Just From the Python Standard Library Alone?

DEVNET-1040 23


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

Python Socket Library


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',


IP

TCP UDP

XMLRPC

FTP

20,21

SNMP

161

Device Drivers

Pyth

on

So

cket

Lib

rary

“Higher Layer” Libraries

HTTP, etc.

NIC

B

U

STx

Buffers

Rx

Buffers

Framer/

Protocol

decode

Telnet

23

SMTP

25

DNS

53

TC

P/I

P P

RO

TO

CO

L S

TA

CK

LAYER 1

ACI APICFirefox

Browser

Web

80

Sockets: Let’s Start with UDP

DEVNET-1040 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.

27DEVNET-1040


socket.getaddrinfo("192.168.252.253", 80, 0, 0, socket.SOL_TCP)

[ (2, 0, 6, '', ('192.168.252.253', 80)) ]

Family Protocol

Type

socket.getaddrinfo('2a04:4e42:5::223',80, 0, 0, socket.SOL_TCP)

[(23, 0, 6, '', ('2a04:4e42:5::223', 80, 0, 0))]

IPv6

TCP

Socket

Type

Canonical

Name

Socket Name: 2 Tuple

Socket Name: 6 Tuple

ScopeFlow LabelCanonical

Name

1 STREAM,

2 DATAGRAM,

3 RAW,

4 RDM,

5 SEQPACKET


But Before We Jump In, a B R I E F Primer on OOP versus POP…….


The ‘Big Five’ Questions to Answer:

1) What kind of network do we want to talk to? • What ‘address family’? IPv4 (AF_INET) or IPv6 (AF_INET6), etc.

2) What type of connection do we want? • Do we want a datagram service (UDP) or a connection oriented stream service (TCP)?

3) What kind of protocol do we need?• Answers 1 and 2 already narrowed this down

4) What IP address to use?

5) What UDP or TCP port number should we use?

30DEVNET-1040


import socket

c = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

Socket Objects

What Protocol Stack Version?

INET: use IPv4

INET6: use IPv6

What Part of the Protocol Stack Do You Want ?

SOCK_STREAM: use TCP

SOCK_DGRAM: use UDP

Python socket module’s METHOD

Retrieve (and use) the Python socket module

What do we mean by a ‘socket object’?

New socket object


Sockets

‘c’

Socket objectSocket object

- 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

client

import socket


c.connect((‘www.cisco.com’,80))


Sockets

server

import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

serverAddr = S.gethostname()

s.bind((serverAddr,12345))

s.listen(5)

NIC

10.255.88.76

while 1:

client, cleintAddr = s.accept()


Hello Server!!! TCP | IP

37DEVNET-1040

Sockets

server

import socket


serverAddr = ‘10.255.88.76’


s.listen(5)

NIC

10.255.88.76

‘c’

Socket object

client

import socket


NIC

192.168.19.5

‘client’

Socket object

while 1:

client, clientAddr = s.accept()c.send(‘Hello Server!!!’)

client 192.168.13.5

print “I just got a connection request from: “, clientAddr

client.close()

c.shutdown(socket.SHUT_RDWR))

c.connect((‘10.255.88.76’,80)


‘client’

Socket object3

‘client’

Socket object2

Hello Server!!! TCP | IP

38DEVNET-1040

Sockets

server

import socket


serverAddr = s.gethostname()


s.listen(5)

NIC

10.255.88.76

‘c’

Socket object

client

import socket


c.connect((‘www.cisco.com’,80))

NIC

192.168.19.5

‘client’

Socket object

while 1:

client, clientAddr = s.accept()c.send(‘Hello Server!!!’)

client 192.168.13.5

client2 10.23.11.254

17.255.10.1client3

print “I just got a connection request from: “, clientAddr

client.close()

c.shutdown(socket.SHUT_RDWR)


El-cheapo_UDP_server.py:

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'

Sockets


El-cheapo_UDP_client.py:

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) # get a message – up to to 1024 bytes - and where it came from

print '\r', data, addr # display the message

Sockets

Thank You


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44DEVNET-1040

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Introduction to Python Network Programmingclnv.s3.amazonaws.com/2017/eur/pdf/DEVNET-1040.pdf ·...

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Transcript of Introduction to Python Network Programmingclnv.s3.amazonaws.com/2017/eur/pdf/DEVNET-1040.pdf ·...