© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-1 Managing IP Traffic with ACLs Scaling the Network with NAT and PAT

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-2 Outline Overview Introducing NAT and PAT Translating Inside Source Addresses Overloading an Inside Global Address Verifying the NAT and PAT Configuration Troubleshooting the NAT and PAT Configuration Summary

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-3 Network Address Translation An IP address is either local or global. Local IP addresses are seen in the inside network.

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-4 Port Address Translation

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-5 Translating Inside Source Addresses

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-6 Configuring Static Translation Establishes static translation between an inside local address and an inside global address Router(config)# ip nat inside source static local-ip global-ip Marks the interface as connected to the inside Router(config-if)# ip nat inside Marks the interface as connected to the outside Router(config-if)# ip nat outside

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-7 Enabling Static NAT Address Mapping Example

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-8 Configuring Dynamic Translation Establishes dynamic source translation, specifying the ACL that was defined in the prior step. Router(config)# ip nat inside source list access-list-number pool name Defines a pool of global addresses to be allocated as needed. Router(config)# ip nat pool name start-ip end-ip {netmask netmask | prefix-length prefix-length} Defines a standard IP ACL permitting those inside local addresses that are to be translated. Router(config)# access-list access-list-number permit source [source-wildcard]

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-9 Dynamic Address Translation Example

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-10 Overloading an Inside Global Address

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-11 Configuring Overloading Establishes dynamic source translation, specifying the ACL that was defined in the prior step Router(config)# ip nat inside source list access-list-number interface interface overload Defines a standard IP ACL that will permit the inside local addresses that are to be translated Router(config)# access-list access-list-number permit source source-wildcard

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-12 Overloading an Inside Global Address Example

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-13 Clearing the NAT Translation Table Clears a simple dynamic translation entry that contains an inside translation or both an inside and outside translation Router# clear ip nat translation inside global-ip local-ip [outside local-ip global-ip] Clears all dynamic address translation entries Router# clear ip nat translation * Clears a simple dynamic translation entry that contains an outside translation Router# clear ip nat translation outside local-ip global-ip Clears an extended dynamic translation entry Router# clear ip nat translation protocol inside global-ip global-port local-ip local-port [outside local-ip local-port global-ip global-port]

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-14 Displays translation statistics Router# show ip nat statistics Displays active translations Router# show ip nat translations Router# show ip nat translation Pro Inside global Inside local Outside local Outside global Router# show ip nat statistics Total active translations: 1 (1 static, 0 dynamic; 0 extended) Outside interfaces: Ethernet0, Serial2.7 Inside interfaces: Ethernet1 Hits: 5 Misses: 0 … Displaying Information with show Commands

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-15 Sample Problem: Cannot Ping Remote Host

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-16 Solution: New Configuration

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-17 Using the debug ip nat Command Router# debug ip nat NAT: s= > , d= [6825] NAT: s= , d= > [21852] NAT: s= > , d= [6826] NAT*: s= , d= > [23311] NAT*: s= > , d= [6827] NAT*: s= > , d= [6828] NAT*: s= , d= > [23313] NAT*: s= , d= > [23325]

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-18 Translation Not Installed in the Translation Table? Verify that: The configuration is correct. There are not any inbound ACLs denying the packets entry to the NAT router. The ACL referenced by the NAT command is permitting all necessary networks. There are enough addresses in the NAT pool. The router interfaces are appropriately defined as NAT inside or NAT outside.

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-19 Summary NAT enables private IP internetworks that use non-registered IP addresses to connect to the Internet. PAT, a feature of NAT, enables several internal addresses to be translated to only one or a few external addresses. You can translate your own IP addresses into globally unique IP addresses when you are communicating outside of your network. Overloading is a form of dynamic NAT that maps multiple unregistered IP addresses to a single registered IP address (many-to-one) by using different ports, known also as PAT. Once NAT is configured, the clear and show commands can be used to verify that it is operating as expected. The debug command can be used to troubleshoot NAT connectivity problems.

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—4-20