qr code generator vb net open source NETWORK LAYER: LOGICAL ADDRESSING in Software

Drawer Code 39 Full ASCII in Software NETWORK LAYER: LOGICAL ADDRESSING

NETWORK LAYER: LOGICAL ADDRESSING
Generate Code 3 Of 9 In None
Using Barcode printer for Software Control to generate, create Code 3/9 image in Software applications.
Code-39 Scanner In None
Using Barcode scanner for Software Control to read, scan read, scan image in Software applications.
Figure 1910 A NAT implementation
Paint Code 39 Full ASCII In Visual C#
Using Barcode creation for .NET framework Control to generate, create Code39 image in .NET applications.
Drawing Code 39 Full ASCII In Visual Studio .NET
Using Barcode generation for ASP.NET Control to generate, create Code39 image in ASP.NET applications.
Site using private addresses 1721831
Code 3/9 Generator In .NET
Using Barcode creation for Visual Studio .NET Control to generate, create Code 3 of 9 image in .NET framework applications.
Code39 Maker In VB.NET
Using Barcode creation for .NET framework Control to generate, create Code 39 Extended image in .NET applications.
-----------------------------------,
Print Bar Code In None
Using Barcode printer for Software Control to generate, create bar code image in Software applications.
Encode EAN-13 Supplement 5 In None
Using Barcode generator for Software Control to generate, create EAN-13 Supplement 5 image in Software applications.
I I I I
Data Matrix 2d Barcode Generation In None
Using Barcode printer for Software Control to generate, create Data Matrix 2d barcode image in Software applications.
Paint Universal Product Code Version A In None
Using Barcode printer for Software Control to generate, create UPC A image in Software applications.
NAT router
Generate Code 39 In None
Using Barcode creator for Software Control to generate, create Code 3/9 image in Software applications.
Bar Code Creation In None
Using Barcode creation for Software Control to generate, create barcode image in Software applications.
___________________________________ J
Leitcode Generation In None
Using Barcode encoder for Software Control to generate, create Leitcode image in Software applications.
Code 39 Extended Drawer In None
Using Barcode generator for Microsoft Excel Control to generate, create Code-39 image in Office Excel applications.
Internet
EAN / UCC - 14 Creator In Visual C#.NET
Using Barcode drawer for VS .NET Control to generate, create USS-128 image in Visual Studio .NET applications.
Generate EAN 13 In Visual Studio .NET
Using Barcode drawer for Reporting Service Control to generate, create EAN-13 image in Reporting Service applications.
Address Translation
Painting Barcode In Objective-C
Using Barcode creator for iPhone Control to generate, create bar code image in iPhone applications.
Bar Code Encoder In None
Using Barcode printer for Word Control to generate, create barcode image in Microsoft Word applications.
All the outgoing packets go through the NAT router, which replaces the source address in the packet with the global NAT address All incoming packets also pass through the NAT router, which replaces the destination address in the packet (the NAT router global address) with the appropriate private address Figure 1911 shows an example of address translation
Data Matrix ECC200 Encoder In Objective-C
Using Barcode creation for iPad Control to generate, create DataMatrix image in iPad applications.
Barcode Recognizer In Visual Basic .NET
Using Barcode decoder for .NET framework Control to read, scan read, scan image in .NET framework applications.
Figure 1911 Addresses in a NAT
~--------------------------1
---------r---b
Destination: 1721831
Source: 1721831
I I I I
Source: 2002458
"-----------'-b
Internet Destination: 2002458
Translation Table
The reader may have noticed that translating the source addresses for outgoing packets is straightforward But how does the NAT router know the destination address for a packet coming from the Internet There may be tens or hundreds of private IP addresses, each belonging to one specific host The problem is solved if the NAT router has a translation table Using One IP Address In its simplest fonn, a translation table has only two columns: the private' address and the external address (destination address of the packet) When the router translates the source address of the outgoing packet, it also makes note of the destination address-where the packet is going When the response comes back from the destination, the router uses the source address of the packet (as the external address) to find the private address of the packet Figure 1912 shows the idea Note that the addresses that are changed (translated) are shown in color
SECTION 191
IPv4 ADDRESSES
Figure 1912 NAT address translation
--------------------------~
Destination: 258210 Source: 172 HUI
I I I
Destination: 258210 Source: 200245g
I I I I
Translation table Private External
258210 oEt----'
Destination: 1711831 Source: 258210
Destination: 2002451l Source: 258210
I I I I
------=:~=::::::::::::::=====----~~r___---:::---=========-
In this strategy, communication must always be initiated by the private network The NAT mechanism described requires that the private network start the communication As we will see, NAT is used mostly by ISPs which assign one single address to a customer The customer, however, may be a member of a private network that has many private addresses In this case, communication with the Internet is always initiated from the customer site, using a client program such as HTTP, TELNET, or FTP to access the corresponding server program For example, when e-mail that originates from a noncustomer site is received by the ISP e-mail server, the e-mail is stored in the mailbox of thecustomer until retrieved A private network cannot run a server program for clients outside of its network if it is using NAT technology Using a Pool of IP Addresses Since the NAT router has only one global address, only one private network host can access the same external host To remove this restriction, the NAT router uses a pool of global addresses For example, instead of using only one global address (2002458), the NAT router can use four addresses (2002458, 2002459, 20024510, and 20024511) In this case, four private network hosts can communicate with the same external host at the same time because each pair of addresses defines a connection However, there are still some drawbacks In this example, no more than four connections can be made to the same destination Also, no private-network host can access two external server programs (eg, HTTP and FfP) at the same time Using Both IP Addresses and Port Numbers To allow a many-to-many relationship between private-network hosts and external server programs, we need more information in the translation table For example, suppose two hosts with addresses 1721831 and 1721832 inside a private network need to access the HTTP server on external host
CHAPTER 19 NETWORK LAYER: LOGICAL ADDRESSING
25832 If the translation table has five columns, instead of two, that include the source and destination port numbers of the transport layer protocol, the ambiguity is eliminated We discuss port numbers in 23 Table 194 shows an example of such a table Table 194 Five-column translation table
Private Address Private Port External Address External Port Transport Protocol
TCP TCP
1721831 1721832
1400 1401
25832 25832
80 80
Note that when the response from HTTP comes back, the combination of source address (25832) and destination port number (1400) defines the-private network host to which the response should be directed Note also that for this translation to work, the temporary port numbers (1400 and 1401) must be unique
Copyright © OnBarcode.com . All rights reserved.