Table Of Contents

Using Application Level Gateways with NAT

Finding Feature Information

Contents

Prerequisites for Using Application Level Gateways with NAT

Information About Configuring Application Level Gateways with NAT

Application Level Gateway

NAT Support for Application Level Gateways in Cisco IOS XE Software

NAT Support for SIP—Voice and Multimedia over IP Networks

NAT SIP Extended Methods

NAT SCCP Video Support

NAT Basic H.323 ALG Support

NAT H.323 RAS

NAT NetMeeting Directory (LDAP)

NAT DNS ALG Support

NAT ICMP ALG Support

NAT FTP ALG Support

NAT TFTP ALG Support

How to Configure Application Level Gateways with NAT

Configuring IPsec Through NAT

Benefits of Configuring NAT IPsec

IP Security

SPI Matching

Restrictions

Configuring IPsec ESP Through NAT

Enabling Preserve Port

Restrictions

Disabling SPI Matching on the NAT Device or Changing the Default Port

Prerequisites

Restrictions

Enabling SPI Matching on the Endpoints

Prerequisites

Restrictions

Deploying NAT Between an IP Phone and Cisco Call Manager

NAT Support of Skinny Client Control Protocol

Configuration Examples for Using Application Level Gateways with NAT

Configuring IPsec ESP Through NAT: Example

iEnabling the Preserve Port: Example

Enabling SPI Matching: Example

Configuring SPI Matching on the Endpoint Routers: Example

Deploying NAT Between an IP Phone and Cisco Call Manager: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Using Application Level Gateways with NAT

Using Application Level Gateways with NAT

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First Published: May 2, 2005

Last Updated: Novenber 25, 2009

Network Address Translation (NAT) performs translation service on any Transmission Control Protocol/User Datagram Protocol (TCP/UDP) traffic that does not carry source and/or destination IP addresses in the application data stream. These protocols include HTTP, Trivial File Transfer Protocol (TFTP), telnet, archie, finger, Network TimeProtocol (NTP), Network File System (NFS), remote login (rlogin), remote shell protocol (rsh), and remote copy protocol (rcp).

Specific protocols that do embed IP address information within the payload require support of an Application Level Gateway (ALG). Cisco IOS XE NAT requires a variety of ALGs to handle application data stream (Layer 7) protocol specific services such as translating embedded IP addresses and port numbers in the packet payload and extracting new connection/session information from control channels. NAT supports virtual routing and forwarding (VRF) for protocols that require an ALG.

The support for IPsec ESP Through NAT feature provides the ability to support multiple concurrent IP Security (IPsec) Encapsulating Security Payload (ESP) tunnels or connections through a Cisco IOS XE NAT device configured in Overload or Port Address Translation (PAT) mode.

Finding Feature Information

For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Using Application Level Gateways with NAT" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for Using Application Level Gateways with NAT

•Information About Configuring Application Level Gateways with NAT

•How to Configure Application Level Gateways with NAT

•Configuration Examples for Using Application Level Gateways with NAT

•Additional References

•Feature Information for Using Application Level Gateways with NAT

Prerequisites for Using Application Level Gateways with NAT

•Before performing the tasks in this module, you should be familiar with the concepts described in the "Configuring NAT for IP Address Conservation" module.

•All access lists required for use with the tasks in this module should be configured prior to beginning the configuration task.

•Before performing the tasks in this module, you should verify that Session Initiation Protocol (SIP) and H.323 have not been disabled. SIP and H.323 are enabled by default.

Information About Configuring Application Level Gateways with NAT

To configure ALGs with NAT, you should understand the following concepts:

•Application Level Gateway

•NAT Support for Application Level Gateways in Cisco IOS XE Software

Application Level Gateway

An application level gateway is an application that translates IP address information inside the payload of an applications packet.

Cisco IOS XE NAT performs translation service on any TCP/UDP traffic that does not carry source and/or destination IP addresses in the application layer data stream. Specific protocols or applications that do embed IP address information require support of an ALG.

See the NAT and Firewall ALG Support on Cisco ASR 1000 Series Routers matrix for a table that summarizes NAT and Firewall ALG feature support on Cisco ASR 1000 Series Aggregation Services Routers in Cisco IOS XE Release 2.1 and later releases.

NAT Support for Application Level Gateways in Cisco IOS XE Software

The following provides information on NAT support for ALGs in Cisco IOS XE software.

NAT Support for SIP—Voice and Multimedia over IP Networks

SIP is a protocol developed by the Internet Engineering Task Force (IETF) Multiparty Multimedia Session Control (MMUSIC) Working Group. The Cisco SIP functionality equips Cisco routers to signal the setup of voice and multimedia calls over IP networks. SIP provides an alternative to H.323 within the Voice over IP (VoIP) internetworking software.

Session Description Protocol (SDP) is a protocol that describes multimedia sessions. SDP may be used in SIP message bodies to describe multimedia sessions used for creating and controlling multimedia sessions with two or more participants.

The NAT Support for SIP feature allows SIP embedded messages passing through a router configured with NAT to be translated and encoded back to the packet. An ALG is used with NAT to translate the SIP messages.

NAT SIP Extended Methods

Cisco IOS XE NAT supports extended methods for SIP.

NAT SCCP Video Support

Cisco IOS XE NAT provides Skinny Call Control Protocol (SCCP) message translation support.

NAT Basic H.323 ALG Support

H.323 is a recommendation published by ITU-T defining a series of network elements and protocols for multimedia transmission through packet-based networks. H.323 defines a number of network elements used in the multimedia transmission:

•H.323 Terminal—This element is an end-point in the network providing two-way communication with another H.323 terminal or gateway.

•H.323 Gateway—This element provides a protocol conversion between H.323 terminals and other terminals that do not support H.323.

•H.323 Gatekeeper—This element provides services like address translation, network access control as well as bandwidth management and account for H.323 terminals and gateways.

The core protocols described by the H.323 specification are the following:

•H.225—This protocol describes call signaling methods used between any two H.323 entities to establish communication.

•H.225 Registration, Admission and Status (RAS)—The H.225 RAS protocol is used by H.323 end point and gateway for address resolution and admission control services.

•H.245—This protocol is used for exchanging the capabilities for multimedia communication and for opening and closing of logical channels for audio, video and data channels.

In addition to the above protocols, the H.323 specification describes the use of various IETF protocols like Real Time Transport (RTP) protocol and Audio (G.711, G.729 etc.) and Video (H.261, H.263 and H.264) Codecs.

Cisco IOS XE NAT requires a variety of ALGs to handle Layer 7 protocol specific services such as translating embedded IP addresses and port numbers in the packet payload and extracting new connection/session information from control channels. The H.323 ALG performs these specific services for H.323 messages.

NAT H.323 RAS

Cisco IOS XE NAT supports all H.225 and H.245 message types, including those sent in the Registration, Admission, and Status (RAS) protocol. RAS provides a number of messages that are used by software clients and VoIP devices to register their location, request assistance in call set up, and control bandwidth. The RAS messages are directed toward an H.323 gatekeeper.

Some RAS messages include IP addressing information in the payload, typically meant to register a user with the gatekeeper or learn about another user already registered. If these messages are not known to NAT, they cannot be translated to an IP address that will be visible to the public.

Previously, NAT did not support H.225 RAS messages. With this enhancement, H.225 RAS (v2 and v4) messages can be inspected for potential translation.

NAT NetMeeting Directory (LDAP)

Cisco IOS XE NAT provides ALG support for NetMeeting directory Lightweight Directory Access Protocol (LDAP) version 2 and version 3 messages.

Users have the ability to establish calls/connections between each other directly or through a NetMeeting directory. NetMeeting implements a series of LDAP messages for users to register themselves and perform look-ups of other NetMeeting users against the directory. These messages include IP address information.

To use a NetMeeting directory with a NAT device, NAT needs to understand these messages and perform standard NAT processing against the IP address information within the messages.

NAT DNS ALG Support

Cisco IOS XE NAT application awareness includes support for the Domain Name System (DNS). An ALG translates IP addresses and port numbers embedded in the DNS payload when a NAT mapping is processed.

NAT ICMP ALG Support

Cisco IOS XE NAT application awareness includes translation support for the Internet Control Message Protocol (ICMP). An ALG translates data embedded in the ICMP payload when a NAT mapping is processed.

NAT FTP ALG Support

Cisco IOS XE NAT application awareness includes support for the File Transfer Protocol (FTP). An FTP ALG performs translation for the IP addresses and TCP port information embedded in the payload of an FTP control session.

NAT TFTP ALG Support

Cisco IOS XE NAT application awareness includes support for the Trivial File Transfer Protocol (TFTP). A TFTP ALG creates a path for the TFTP data to traverse the NAT-enabled router.

How to Configure Application Level Gateways with NAT

This section contains the following procedures:

•Configuring IPsec Through NAT

•Deploying NAT Between an IP Phone and Cisco Call Manager

Configuring IPsec Through NAT

This section contains the following tasks related to configuring IPsec through NAT:

•Configuring IPsec ESP Through NAT (required)

•Enabling Preserve Port (optional)

•Disabling SPI Matching on the NAT Device or Changing the Default Port (required)

•Enabling SPI Matching on the Endpoints (required)

Benefits of Configuring NAT IPsec

•NAT enables customers to deploy private IP addresses within their network and perform translation to public IP addresses when connecting to the Internet or interconnecting with another corporate network.

•Normally ESP entries in the translation table are delayed from being transmitted until a reply is received from the destination. With predictable security parameter indexes (SPIs) and SPI matching, the delay can be eliminated since the SPI entries are matched. Some third-party concentrators require both the source and incoming ports to use port 500. Use of the preserve-port keyword with the ip nat service command preserves the ports rather than changing one, which is required with regular NAT.

IP Security

IP Security (IPsec) is a set of extensions to the IP protocol family in a framework of open standards for ensuring secure private communications over the Internet. Based on standards developed by the Internet Engineering Task Force (IETF), IPsec ensures confidentiality, integrity, and authenticity of data communications across the public network and provides cryptographic security services.

Secure tunnels between two peers, such as two routers, are provided and decisions are made as to which packets are considered sensitive and should be sent through these secure tunnels, and which parameters should be used to protect these sensitive packets by specifying characteristics of these tunnels. When the IPsec peer receives a sensitive packet, it sets up the appropriate secure tunnel and sends the packet through the tunnel to the remote peer.

IPsec using ESP can pass through a router running NAT without any specific support from it as long as Network Address Port Translation (NAPT) or address overloading are not configured.

There are a number of factors to consider when attempting an IPsec Virtual Private Network (VPN) connection that traverses a NAPT device that represents multiple private internal IP addresses as a single public external IP address. Such factors include the capabilities of the VPN server and client, the capabilities of the NAPT device, and whether more than one simultaneous connection is attempted across the NAPT device.

There are two possible methods for configuring IPsec on a router with NAPT:

•Encapsulate IPsec in a Layer 4 protocol such as TCP or UDP. In this case, IPsec is sneaking through NAT. The NAT device is unaware of the encapsulation.

•Add IPsec specific support to NAPT. IPsec works with NAT in this case as opposed to sneaking through NAT. The NAT Support for IPsec ESP—Phase II feature provides support for Internet Key Exchange (IKE) and ESP without encapsulation in tunnel mode through a Cisco IOS XE router configured with NAPT.

The recommended protocols to use when conducting IPsec sessions that traverse a NAPT device are TCP and UDP but not all VPN servers or clients support TCP or UDP.

SPI Matching

Security Parameter Index (SPI) matching is used to establish VPN connections between multiple pairs of destinations. NAT entries will immediately be placed in the translation table for endpoints matching the configured access list.

Restrictions

•NAT will translate only embedded IP version 4 addresses.

•The multicast gatekeeper discovery mechanism is not supported.

Configuring IPsec ESP Through NAT

IPsec ESP through NAT provides the ability to support multiple concurrent IPsec ESP tunnels or connections through a Cisco IOS XE NAT device configured in Overload or PAT mode.

Perform this task to configure IPsec ESP through NAT.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip nat [inside | outside] source static local-ip global-ip

4. exit

5. show ip nat translations

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip nat [inside | outside] source static local-ip global-ip Example: Router(config)# ip nat inside source static 10.10.10.10 172.16.30.30	Enables static NAT.
Step 4	exit Example: Router(config)# exit	Returns to privileged EXEC mode.
Step 5	show ip nat translations Example: Router# show ip nat translations	(Optional) Displays active NATs.

Enabling Preserve Port

This task is used for IPsec traffic using port 500 for the source and incoming ports. Perform this task to enable port 500 to be preserved for both source and incoming ports.

Restrictions

This task is required by certain VPN concentrators but will cause problems with other concentrators. Cisco VPN devices generally do not use this feature.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip nat service list access-list-number ike preserve-port

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip nat service list access-list-number ike preserve-port Example: Router(config)# ip nat service list 10 ike preserve-port	Specifies a port other than the default port.

Disabling SPI Matching on the NAT Device or Changing the Default Port

Security parameter index (SPI) matching is used to establish VPN connections between multiple pairs of destinations. NAT entries are immediately placed in the translation table for endpoints matching the configured access list.

The generation of SPIs that are predictable and symmetric is enabled. SPI Matching should be used in conjunction with NAT devices when multiple ESP connections across a NAT device are desired.

SPI Matching is enabled by default for listening on port 2000. This task may be used to either change the default port or disable SPI matching.

Prerequisites

Cisco IOS XE software must be running on both the source router and the remote gateway enabling parallel processing.

Restrictions

SPI matching must be configured on the NAT device and both endpoint devices.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip nat service list access-list-number esp spi-match

4. no ip nat service list access-list-number esp spi-match

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip nat service list access-list-number esp spi-match Example: Router(config)# ip nat service list 10 esp spi-match	Specifies a port other than the default port. •This example shows how to enter ESP traffic matching list 10 into the NAT table, making the assumption that both devices are Cisco devices and are configured to provide matchable SPIs.
Step 4	no ip nat service list access-list-number esp spi-match Example: Router(config)# no ip nat service list 10 esp spi-match	Disables SPI matching.

Enabling SPI Matching on the Endpoints

Perform this task to enable SPI matching on both endpoints.

Prerequisites

Cisco IOS XE software must be running on both the source router and the remote gateway enabling parallel processing.

Restrictions

SPI matching must be configured on the NAT device and both endpoint devices.

SUMMARY STEPS

1. enable

2. configure terminal

3. crypto ipsec nat-transparency spi-matching

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	crypto ipsec nat-transparency spi-matching Example: Router(config)# crypto ipsec nat-transparency spi-matching	Enables SPI matching on both endpoints.

Deploying NAT Between an IP Phone and Cisco Call Manager

This section describes deploying Cisco's Skinny Client Control Protocol (SCCP) for a Cisco IP phone to Cisco Call Manager (CCM). The task in this section deploys NAT between an IP phone and CUCM.

NAT Support of Skinny Client Control Protocol

Cisco IP phones use the SCCP to connect with and register to CCM.

To be able to deploy Cisco IOS XE NAT between the IP phone and CCM in a scalable environment, NAT needs to be able to detect the SCCP and understand the information passed within the messages. Messages flow back and forth that include IP address and port information used to identify other IP phone users with which a call can be placed.

The SCCP client to CUCM communication typically flows from inside to outside. DNS should be used to resolve the CUCM IP address connection when the CCM is on the inside (behind the NAT device), or static NAT should be configured to reach the CCM in the inside.

When an IP phone attempts to connect to the CCM and it matches the configured NAT rules, NAT will translate the original source IP address and replace it with one from the configured pool. This new address will be reflected in the CUCM and be visible to other IP phone users.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip nat service skinny tcp port number

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip nat service skinny tcp port number Example: Router(config)# ip nat service skinny tcp port 20002	Configures the skinny protocol on the specified TCP port.

Configuration Examples for Using Application Level Gateways with NAT

This section provides the following configuration examples:

•Configuring IPsec ESP Through NAT: Example

•iEnabling the Preserve Port: Example

•Enabling SPI Matching: Example

•Configuring SPI Matching on the Endpoint Routers: Example

•Deploying NAT Between an IP Phone and Cisco Call Manager: Example

Configuring IPsec ESP Through NAT: Example

The following example shows NAT configured on the router with a static route. NAT is configured as inside source static 1- to-1 translations.

ip nat pool outside 192.0.2.1 192.0.2.14 netmask 255.255.255.0

ip nat outside source list 1 pool mypool

access-list 1 permit 192.0.2.3 0.0.0.255

ip nat inside source static 192.0.2.23 192.0.2.22 vrf gold

ip nat inside source static 192.0.2.21 192.0.2.2 vrf silver

iEnabling the Preserve Port: Example

The following example shows how to configure TCP port 500 of the third-party concentrator:

ip nat service list 10 ike preserve-port

Enabling SPI Matching: Example

The following example shows how to enable SPI matching:

ip nat service list 10 esp spi-match

Configuring SPI Matching on the Endpoint Routers: Example

The following example show how to enable SPI matching on the endpoint routers:

crypto ipsec nat-transparency spi-matching

Deploying NAT Between an IP Phone and Cisco Call Manager: Example

The following example shows how to configure the 20002 port of the CUCM:

ip nat service skinny tcp port 20002

Additional References

The following sections provide references related to using application level gateways with NAT.

Related Documents

Related Topic	Document Title
NAT commands: complete command syntax, command mode, defaults, usage guidelines, and examples	Cisco IOS IP Addressing Services Command Reference
IP Addressing Services configuration tasks	Cisco IOS XE IP Addressing Services Configuration Guide
NAT and Firewall ALG support	NAT and Firewall ALG Support on Cisco ASR 1000 Series Routers matrix

Standards

Standard	Title
None	—

MIBs

MIB	MIBs Link
None	To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs

RFCs

RFC	Title
No new or modified RFCS are supported, and support for existing RFCs has not been modified	—

Technical Assistance

Description

Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport

Feature Information for Using Application Level Gateways with NAT

Table 1 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

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Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.

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Table 1 Feature Information for Using Application Level Gateways with NAT

Feature Name	Releases	Feature Configuration Information
NAT VRF-Aware ALG Support	Cisco IOS XE Release 2.5	Cisco IOS XE NAT supports virtual routing and forwarding (VRF) for protocols that require an Application Level Gateway (ALG), such as SIP, H.323, and SCCP/Skinny.
NAT: SIP ALG Enhancement for T.38 Fax Relay	Cisco IOS XE Release 2.4.1	Cisco IOS XE NAT provides translation support for SIP ALG support of T.38 Fax Relay over IP.
NAT Netmeeting Directory (LDAP)	Cisco IOS XE Release 2.4	Cisco IOS XE NAT provides ALG support for NetMeeting directory Lightweight Directory Access Protocol (LDAP) messages. The following section provides information about this feature: •NAT NetMeeting Directory (LDAP)
NAT H.323 RAS	Cisco IOS XE Release 2.4	Cisco IOS XE NAT supports all H.225 and H.245 message types, including those sent in the Registration, Admission, and Status (RAS) protocol. RAS provides a number of messages that are used by software clients and VoIP devices to register their location, request assistance in call set up, and control bandwidth. The RAS messages are directed toward an H.323 gatekeeper. The following section provides information about this feature: •NAT H.323 RAS
NAT: SIP Extended Methods	Cisco IOS XE Release 2.4	Cisco IOS XE NAT supports extended methods for SIP. The following section provides information about this feature: •NAT SIP Extended Methods
NAT: SCCP for Video	Cisco IOS XE Release 2.4	Cisco IOS XE NAT provides Skinny Call Control Protocol (SCCP) message translation support. The following section provides information about this feature: •NAT SCCP Video Support
NAT Support for SIP	Cisco IOS XE Release 2.1	NAT Support for SIP adds the ability to deploy Cisco IOS XE NAT between VoIP solutions based on SIP. The following section provides information about this feature: •NAT Support for SIP—Voice and Multimedia over IP Networks
NAT Basic H.323 ALG Support	Cisco IOS XE Release 2.1	Cisco IOS XE NAT requires a variety of ALGs to handle Layer 7 protocol specific services such as translating embedded IP addresses and port numbers in the packet payload and extracting new connection/session information from control channels. The H.323 ALG performs these specific services for H.323 messages. The following section provides information about this feature: •NAT SCCP Video Support
NAT DNS ALG Support	Cisco IOS XE Release 2.1	Cisco IOS XE NAT supports translation of DNS packets. The following section provides information about this feature: •NAT DNS ALG Support
NAT ICMP ALG Support	Cisco IOS XE Release 2.1	Cisco IOS XE NAT supports translation of ICMP packets. The following section provides information about this feature: •NAT ICMP ALG Support
NAT FTP ALG Support	Cisco IOS XE Release 2.1	Cisco IOS XE NAT supports translation of FTP packets. The following section provides information about this feature: •NAT FTP ALG Support
NAT TFTP ALG Support	Cisco IOS XE Release 2.1	Cisco IOS XE NAT supports translation of TFTP packets. The following section provides information about this feature: •NAT TFTP ALG Support
NAT Support of IP Phone to Cisco Call Manager	Cisco IOS XE Release 2.1	This feature adds NAT support in deploying Cisco's Skinny Client Control Protocol (SCCP) for a Cisco IP phone to Cisco Unified Communications Manager (CUCM) communication. The following section provides information about this feature: •Deploying NAT Between an IP Phone and Cisco Call Manager
NAT Support for IPsec ESP— Phase II feature	Cisco IOS XE Release 2.1	The NAT Support for IPsec ESP— Phase II feature provides support for Internet Key Exchange (IKE) and ESP without encapsulation in tunnel mode through a Cisco IOS XE router configured with NAPT. The following sections provide information about this feature: •Configuring IPsec Through NAT •Configuring IPsec ESP Through NAT: Example
Support for IPsec ESP Through NAT	Cisco IOS XE Release 2.1	IPsec ESP Through NAT provides the ability to support multiple concurrent IP Security (IPsec) Encapsulating Security Payload (ESP) tunnels or connections through a Cisco IOS XE Network Address Translation (NAT) device configured in Overload or Port Address Translation (PAT) mode. The following section provides information about this feature: •Configuring IPsec ESP Through NAT

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