CCNA CHAPTER 12 BY jetarvind kumar madhukar

Release 16/07/2009 Jetking Infotrain Ltd.
NAT/PAT
Chapter 12

Chapter Objectives
 Explain Network Address Translation
 Explain Static NAT
 Explain Dynamic NAT
 Discuss Port Address Translation

Recall - I
 Frame relay is a technology used for connecting
devices on a WAN
 Frame relay networks are multi-access networks
where more than two devices can be attached to the
network
 A Virtual Circuit (VC) represents the path on which
the frame travels
 LMI enables the DCE and DTE to exchange
information, including the information about virtual
circuits

Recall - II
 The DLCI identifies a VC for the frame relay to
forward the frames to appropriate remote site when
multiple access list use the same access list
 Frame relay DLCI are locally significant, which
indicates that the addresses should be unique on
the local access link
 Frame relay networks use Asynchronous Transfer
Mode (ATM) in the core of the frame relay network

Network Address Translation (NAT)
 NAT-enabled router stores the details of private IP
addresses and the public IP address in a routing
table
 NAT overcomes the problem of lack of public IP
addresses
 It provides security from hackers by hiding
addresses
 Allows re-routing the requests to other servers in the
network if the request does not reach the destined
server

Explaining Network Address
Translation (NAT)
 NAT operates on a router connecting two networks
 NAT is transparent to the source and destination
computers
 NAT operates at the Network layer (Layer 3) of the
OSI Reference Model because routers work at this
layer
 NAT is useful for network administration

Working of NAT
 The inside network addresses are converted into
legal addresses before the packets are forwarded to
the other network
 Inside Local is the configured IP address assigned
to a host on the inside network

Working of NAT
 Inside Global is the IP address of an inside host as it
appears to the outside network, is the “Translated IP
Address”
 Addresses can be allocated from a globally unique
address space provided by the Internet Service Provider
(ISP) if the enterprise is connected to the global Internet

Outside Addressing

NAT Implementation
 NAT is implemented on a network that requires few
addresses to access the Global Internet
 NAT is implemented using two techniques:
 Static Address Translation
 Dynamic Address Translation

NAT Configuration Commands
 The NAT configuration commands include:
 Access-List
 ip nat pool
 ip nat inside source list pool
 ip nat outside source pool
 ip nat inside source static
 ip nat {inside | outside}
 ip nat inside destination list pool

NAT Overlapping Address Translation
 Assigning an IP address to a device in a network
and that address is a legal IP address of a device in
an outside network, it is referred as overlapping

Verifying NAT Operations
 The commands that help you to verify the NAT
operations are:
 show ip nat translations [verbose]
 show ip nat statistics

Static NAT
 Static NAT, also called inbound mapping, allows
connections initiated by external devices to
computers on the stub domain to take place in
specific circumstances
 Static NAT (inbound mapping) allows a computer on
the stub domain to maintain a specific address while
communicating with devices outside the network

Port Address Translation
 The Port Address Translation (PAT) is used to
translate internal addresses to only one or a few
external addresses
 The PAT feature is also referred as “overload”,
which is a subset of NAT functionality
 In a PAT implemented network, the address
translation device (router) assigns same IP address
to all the devices
 The source port number enables you to differentiate
the connections in the network

Port Address Translation
 Two devices in the network having the same source port
number, the router changes the port number of one
device to make it unique
 The total number of port numbers can theoretically be as
high as 65,536 per IP address

Concept of PAT

Summary - I
 NAT operates at the Network layer (Layer 3) of the
OSI Reference Model because this is the layer at
which routers work
 You can configure, verify and troubleshoot NAT and
PAT on an interface
 To configure Static NAT, you can configure the
router for IP routing and IP addressing

Summary - II
 To verify NAT use the following commands:
 show ip nat translations [verbose] -
Displays active translations
 show ip nat - Displays translation statistics
 To troubleshoot NAT, you can use the debug ip nat
[list | detailed] command. This command allows you
to trace the NAT operation by displaying a line of
output for each packet that gets translated

Summary - III
 To clear NAT translation use the following commands:
 clear ip nat translation - Clears all translation
entries
 clear ip nat translation inside global-ip
local-ip [ outsidelocal-ip globalip] - Clears a
simple translation entry containing an inside translation or
both an inside and outside translation
 clear ip nat translation outside local-ip
global-ip - Clears a simple translation entry containing
an outside translation
 clear ip nat translation protocol inside -
Enables you to clear an extended entry (in its various forms)

Summary - IV
 To monitor PAT, you can use the show ip pat
command to display PAT statistics and the currently
active translated sessions

CCNA CHAPTER 12 BY jetarvind kumar madhukar

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CCNA CHAPTER 12 BY jetarvind kumar madhukar