Internet Addressing
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NETWORK ADDRESS TRANSLATION (NAT) Network address translation (NAT) allows a site to use a Network address translation (NAT) allows a site to use a set of private addresses for internal communication and a set of private addresses for internal communication and a set of global Internet addresses for communication with set of global Internet addresses for communication with another site. The site must have only one single another site. The site must have only one single connection to the global Internet through a router that connection to the global Internet through a router that runs NAT software. runs NAT software. The topics discussed in this section include: The topics discussed in this section include: Address Translation Address Translation Translation Table Translation Table NAT and ISP NAT and ISP NAT
description
ip
Transcript of Internet Addressing
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NETWORK ADDRESS TRANSLATION (NAT)
Network address translation (NAT) allows a site to use a Network address translation (NAT) allows a site to use a set of private addresses for internal communication and a set of private addresses for internal communication and a set of global Internet addresses for communication with set of global Internet addresses for communication with another site. The site must have only one single another site. The site must have only one single connection to the global Internet through a router that connection to the global Internet through a router that runs NAT software.runs NAT software.
The topics discussed in this section include:The topics discussed in this section include:
Address Translation Address Translation Translation Table Translation Table NAT and ISP NAT and ISP
NAT
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Address translation
Translation
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Table 26.2 Table 26.2 FiveFive--column translation tablecolumn translation table
How NAT Table is Created
On the FlyWhen an outgoing packet is received, an entry is made in the table if one does not exist alreadyRemove entry after an idle timeout ( 2-3 minutes )
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Other Types of NATs
The one used in the industry uses port mapping– NAPT Network Address Port Translation
NAPT includes additional fieldsBesides a pair of source and destination IP addresses, the mapping table contains a pair of source and destination protocol numbers and protocol port number used by the NAT box.
NAPT mapping Table
For the first TCP connection, the identifier is:Before Translation: (10.0.0.5, 21023, 128.6.9.20, 80)After NAT Translation: (G, 12001, 128.6.9.20, 80)
1201021128.10.19.8
2103210.0.2.6
1200380128.6.9.201238610.0.0.1
1200180128.6.9.202103210.0.0.5
NAT PortExternal Port
External Address
Private Port
Private Address
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Side Effects of NAT
NAT box needs access to IP data area– That’s where TCP/UDP port numbers are
Some applications (e.g. FTP) send port numbers in data area on TCP Packet.To support such applications NAT needs access and analyze TCP data area and may have to increase or decrease TCP Packet size.TCP will not work if sequence number is not adjusted when packet size is changed ( knowledge of TCP is pre requisite to understand this ! )NATs which support FTP are therefore very complex.
An ISP and NAT
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Upon completion you will be able to:
Next Generation: IPv6Next Generation: IPv6
• Understand the shortcomings of IPv4 • Know the IPv6 address format, address types, andabbreviations• Be familiar with the IPv6 header format
Objectives
IPv6
IPv6 has these advantages over IPv4: IPv6 has these advantages over IPv4: 1. 1. larger address space larger address space 2. 2. better header format better header format 3. 3. new optionsnew options4. 4. allowance for extensionallowance for extension5. 5. support for resource allocation support for resource allocation 6. 6. support for more securitysupport for more security
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IPV6
Even with careful assignment and NAT technology, the current 32 bit IP address space cannot accommodate projected growth of the internet beyond 2020128 bit address (instead of 32)Hexadecimal colon notation (instead of decimal)
IPv6 address
The dotted decimal colon notation used for IPv4 does not make addressing compact for IPv6
104.230.140.100.255.255.255.255.0.0.17.128.150.10.255.255
It requires fewer digits and fewer separators than dotted decimal notation
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Abbreviated address
Abbreviated address with consecutive zeros
It can be applied only once in any address
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CIDR address
Type of Addresses
Unicast AddressesAnycast AddressesMulticast Addresses
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Address structure
Type prefixes for IPv6 addressesType prefixes for IPv6 addresses
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Provider-based address
Address hierarchy
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Unspecified address
Loopback address
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Compatible address
Mapped address
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IPv6 datagram
Summary
Original Address StructureSubnettingCombating Address Depletion Problem
Dynamic Address AllocationCIDR, NAT, IPv6
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TRANSITION FROM IPv4 TO IPv6
Three strategies have been devised by the IETF to Three strategies have been devised by the IETF to provide for a smooth transition from IPv4 to IPv6.provide for a smooth transition from IPv4 to IPv6.
The topics discussed in this section include:The topics discussed in this section include:Dual Stack Dual Stack Tunneling Tunneling Header Translation Header Translation
Three transition strategies
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Dual stack
Automatic tunneling
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Configured tunneling
Header translation
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Reading Guidelines
Chapter 4, 5, 30 and 31– TCP/IP Protocol Suite, Second Edition,
Behrouz A. Forouzan
