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CCNA 4 v3.1 Module 1Scaling IP Addresses

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Objectives

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Private Addressing

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NAT

• A NAT-enabled device typically operates at the border of a stub network.

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NAT Terms

• Inside Local Addresses – An IP address assigned to a host inside a network. This address is likely to be a RFC 1918 private address.

• Inside Global Address – A legitimate IP address assigned by the NIC or service provider that represents one or more inside local IP address to the outside world.

• Outside Local Address - The IP address of an outside host as it known to the hosts in the inside network.

• Outside Global Address - The IP address assigned to a host on the outside network. The owner of the host assigns this address.

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NAT Features

• Static NAT is designed to allow one-to-one mapping of local and global addresses.

Outside

10.0.0.10 DA

179.9.8.10

Inside

Internet

179.9.8.1010.0.0.10

179.9.8.8010.0.0.2

Inside Global IP Address

Inside Local IP Address

NAT Table10.0.0.2

http://179.9.8.10

DA

10.0.0.10

777

NAT Features

• Dynamic NAT is designed to map a private IP address to a public address.

Outside

10.0.0.10

Inside

Internet

179.9.8.1010.0.0.10

179.9.8.8010.0.0.2

Inside Global IP Address

Inside Local IP Address

NAT Table10.0.0.2

SA

10.0.0.2

SA

179.8.9.80

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PAT Features

• PAT uses unique source port numbers on the inside global IP address to distinguish between translations.

SA

10.0.0.3:2333

Outside

Inside

Internet

10.0.0.2

SA

10.0.0.2:1456

SA

179.9.8.80:1345

10.0.0.3

179.9.8.80:233310.0.0.3:2333

179.9.8.80:145610.0.0.2:1456

Inside Global IP Address

Inside Local IP Address

NAT Table

126.23.2.2:80126.23.2.2:80

202.6.3.2:80202.6.3.2:80

Outside Global IP Address

Outside Local IP Address

SA

179.9.8.80:2333

202.6.3.2

126.23.2.2

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NAT Benefits

• Eliminates re-assigning each host a new IP address when changing to a new ISP

• Eliminates the need to re-address all hosts that require external access, saving time and money

• Conserves addresses through application port-level multiplexing

• Protects network security

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Configuring Static NAT Translations

• Static translation are entered directly into the configuration and are permanent in the translation table

Router(config)#ip nat inside source static

10.6.1.20 171.69.68.10

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Inside/Outside interface

• An interface on the router can be defined as inside or outside

• Translations occur only from inside to outside interfaces or vice versa—never between the same type of interface

NATInside InterfaceInside

Interface

Inside Network Outside Network

ip nat inside ip nat outsideInside Host Outside Host

Router(config-if)#ip nat inside

Outside InterfaceOutside Interface

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Configuring Static NAT

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Dynamic Translations

• Dynamic translation specify the pool of global addresses that inside addresses can be translated into

Router(config)#ip nat pool nat-pool

179.9.8.80 179.9.8.95 netmask 255.255.255.240

• Dynamic translations use access lists to identify IP addresses that NAT should create translations for

Router(config)#ip nat inside source list 1 pool nat-pool

Router(config)#access-list 1 permit 10.0.0.0 0.0.255.255

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Configuring Dynamic NAT

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Configuring PAT

• Establishes overload translation, specifying the IP address to be overloaded as that assigned to an outside interface

Router(config)#ip nat inside source list 1

interface serial0/0 overload

• Establishes overload translation, specifying the IP address to be overloaded as that assigned to a pool name

Router(config)# ip nat pool nat-pool2 179.9.8.20

netmask 255.255.255.240

Router(config)#ip nat inside source list 1

pool nat-pool2 overload

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Configuring PAT

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Clearing the NAT Translation Table

• Clears all dynamic address translation entries

Router#clear ip nat translation *

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Verifying NAT and PAT Configuration

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Troubleshooting NAT and PAT

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Issues With NAT

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DHCP

• DHCP works by providing a process for a server to allocate the IP information to clients.

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• Clients lease the information from the server for an administratively defined period.

DHCP

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BOOTP and DHCP Differences

• DHCP defines mechanisms through which clients can be assigned an IP address for a finite lease period. This lease period allows for re-assignment of the IP address to another client later, or for the client to get another assignment, if the client moves to another subnet. Clients may also renew leases and keep the same IP address.

• DHCP provides the mechanism for a client to gather other IP configuration parameters, such as WINS and domain name.

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Major DHCP Features

• Automatic Allocation

• Manual Allocation

• Dynamic Allocation

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DHCP Operation

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The Order of DHCP Messages Transmitting

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Configuring DHCP

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Configuring DHCP While Excluding IP

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Verifying DHCP

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Troubleshooting DHCP

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DHCP Relay

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Summary