ITE PC v4.0 Chapter 1

ITE PC v4.0 Chapter 1

Chapter 9: NAT for IPv4 Routing and Switching Essentials v6.0 Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 1 NAT Operation NAT Characteristics IPv4 Private Address Space 10.0.0.0 /8, 172.16.0.0 /12, and 192.168.0.0 /16 What is NAT? Process to translate network IPv4 address Conserve public IPv4 addresses Configured at the border router for translation

NAT Terminology Inside address Inside local address Inside global address Outside address Outside local address Outside global address Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential

2 NAT Operation Types of NAT Static NAT One-to-one mapping of local and global addresses Configured by the network administrator and remain constant. Dynamic NAT Uses a pool of public addresses and assigns them on a first-come, first-served basis Requires that enough public addresses for the total number of simultaneous user sessions Port Address Translation (PAT) Maps multiple private IPv4 addresses to a single public IPv4 address or a few addresses Also known as NAT overload Validates that the incoming packets were requested

Uses port numbers to forward the response packets to the correct internal device Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 3 NAT Operation NAT Advantages Advantages of NAT Conserves the legally registered addressing scheme Increases the flexibility of connections to the public network Provides consistency for internal network addressing schemes

Provides network security Disadvantages of NAT Performance is degraded End-to-end functionality is degraded End-to-end IP traceability is lost Tunneling is more complicated Initiating TCP connections can be disrupted Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 4

9.2 Configuring NAT Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 5 Configuring NAT Configuring Static NAT Configuring Static NAT Create the mapping between the inside local and outside local addresses ip nat inside source static local-ip global-ip Define which interfaces belong to the inside network and which belong to the outside network ip nat inside ip nat outside

Analyzing Static NAT Verifying Static NAT show ip nat translations show ip nat statistics clear ip nat statistics Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 6 Configuring NAT Configuring Dynamic NAT Dynamic NAT Operation The pool of public IPv4 addresses (inside global address pool) is available to any device on the inside network on a first-come, firstserved basis. With dynamic NAT, a single inside address is translated to a single outside address.

The pool must be large enough to accommodate all inside devices. A device is unable to communicate to any external networks if no addresses are available in the pool. Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 7 Configuring NAT Configuring Dynamic NAT (Cont.) Configuring Dynamic NAT Create the mapping between the inside local and outside local addresses ip nat pool name start-ip end-ip {netmask netmask | prefix-length prefix-length} Create a standard ACL to permit those addresses to be translated access-list access-list-number permit source

[source-wildcard] Bind the ACL to the pool ip nat inside source list access-list-number pool name Identify the inside and outside interfaces ip nat inside ip nat outside Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 8 Configuring NAT Configuring Dynamic NAT (Cont.) Analyzing Dynamic NAT Verifying Dynamic NAT show ip nat translations show ip nat translations verbose

clear ip nat statistics clear ip nat translations * Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 9 Configuring NAT Configuring Port Address Translations (PAT) Configuring PAT: Address Pool Create the mapping between the inside local and outside local addresses ip nat pool name start-ip end-ip {netmask netmask | prefixlength prefix-length} Create a standard ACL to permit those addresses to be translated access-list access-list-number permit source [sourcewildcard] Bind the ACL to the pool ip nat inside source list access-list-number pool name Identify the inside and outside interfaces

ip nat inside ip nat outside Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 10 Configuring NAT Configuring Port Address Translations (PAT) (Cont.) Configuring PAT: Single Address Define a standard ACL to permit those addresses to be translated access-list access-list-number permit source [sourcewildcard] Establish dynamic source translation, specify the ACL, exit interface, and overload option ip nat inside source list access-list-number interface type name overload Identify the inside and outside interfaces

ip nat inside ip nat outside Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 11 Configuring NAT Configuring Port Address Translations (PAT) (Cont.) Analyzing PAT Verifying PAT show ip nat translations show ip nat statistics slear ip nat statistics Presentation_ID

2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 12 9.3 Troubleshooting NAT Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 13 Troubleshooting NAT Troubleshooting NAT Configurations Troubleshooting NAT: show commands clear ip nat statistics clear ip nat translations *

show ip nat statistics Show ip nat translations Troubleshooting NAT: debug commands debug ip nat Presentation_ID 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 14

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