Table Of Contents

Configuring NAT for High Availability

Contents

Prerequisites for Configuring NAT for High Availability

Restrictions for Configuring NAT for High Availability

Information About Configuring NAT for High Availability

Stateful NAT

NAT Stateful Failover for Asymmetric Outside-to-Inside ALG Support

Interaction with HSRP

Translation Group

Address Resolution with ARP

How to Configure NAT for High Availability

Configuring the Stateful Failover of NAT

Restrictions for Configuring Stateful Failover of NAT

Configuring SNAT with HSRP

Configuring SNAT on the Primary (Active) Router

Configuring SNAT on the Backup (Standby) Router

Configuring NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support

Prerequisites for Configuring the NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support Feature

Benefits of Configuring Stateful Failover for Asymmetric Outside-to-Inside Support

How Stateful Failover for Asymmetric Outside-to-Inside Support Works

How Stateful Failover for ALGs Works

Configuring SNAT with HSRP

Configuring SNAT Primary/Backup

Configuring NAT Static Mapping Support for HSRP

Restrictions for Configuring Static Mapping Support for HSRP

Benefits of Configuring Static Mapping Support for HSRP

Enabling HSRP on the NAT Interface

Enabling Static NAT in an HSRP Environment

Configuration Example for NAT for High Availability

Configuring Stateful NAT: Examples

Configuration Examples for NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support

Configuring SNAT with HSRP: Example

Configuring SNAT Primary/Backup: Example

Configuring Static NAT in an HSRP Environment: Examples

Additional References

Related Documents

Standards

MIBs

RFCs

Feature Information for Configuring NAT for High Availability

Technical Assistance

Configuring NAT for High Availability

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This module contains procedures for configuring Network Address Translation (NAT) to support the increasing need for highly resilient IP networks. This network resiliency is required where application connectivity needs to continue unaffected by failures to links and routers at the NAT border.

Module History

This module was first published on May 2, 2005, and last updated on May 2, 2008.

Finding Feature Information in This Module

Your Cisco IOS software release may not support all features. To find information about feature support and configuration, use the "Feature Information for Configuring NAT for High Availability" section.

Contents

•Prerequisites for Configuring NAT for High Availability

•Restrictions for Configuring NAT for High Availability

•Information About Configuring NAT for High Availability

•How to Configure NAT for High Availability

•Configuration Example for NAT for High Availability

•Additional References

Prerequisites for Configuring NAT for High Availability

•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 tasks. For information about how to configure an access list, see the "IP Access List Sequence Numbering" document at the following URL:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122s/122snwft/release/122s14/fsaclseq.htm

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Note If you specify an access list to use with a NAT command, NAT does not support the commonly used permit ip any any command in the access list.

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Restrictions for Configuring NAT for High Availability

The Address Resolution Protocol (ARP) queries are always replied to by the Hot Standby Routing Protocol (HSRP) active router. If the active HSRP router fails upstream devices will point to the new HSRP active router and will not have an ARP entry pointing to the original active router, which may no longer be available.

Information About Configuring NAT for High Availability

To configure NAT for High availability, you should understand the following concepts:

•Stateful NAT

•NAT Stateful Failover for Asymmetric Outside-to-Inside ALG Support

•Interaction with HSRP

•Translation Group

•Address Resolution with ARP

Stateful NAT

Stateful NAT (SNAT) enables continuous service for dynamically mapped NAT sessions. Sessions that are statically defined receive the benefit of redundancy without the need for SNAT. In the absence of SNAT, sessions that use dynamic NAT mappings would be severed in the event of a critical failure and would have to be reestablished.

SNAT can be used with protocols that do not need payload translation.

NAT Stateful Failover for Asymmetric Outside-to-Inside ALG Support

NAT stateful failover for asymmetric outside-to-inside and Application Layer Gateway (ALG) support improves the ability to handle asymmetric paths by allowing multiple routing paths from outside-to-inside, and per-packet load balancing. This feature also provides seamless failover translated IP sessions with traffic that includes embedded IP addressing such as Voice over IP, FTP, and Domain Name System (DNS) applications.

Interaction with HSRP

SNAT can be configured to operate with the Hot Standby Routing Protocol (HSRP) to provide redundancy. Active and Standby state changes are managed by HSRP.

SNAT applies a more global context to the task of forwarding a particular datagram. Consideration is given to understanding the application state along with forwarding. Devices can take action to avoid potential failures that will have less impact on the flow and to the application that is transmitting data. Multiple NAT routers that share stateful context can work cooperatively and thereby increase service availability.

Translation Group

Two or more network address translators function as a translation group. One member of the group handles traffic requiring translation of IP address information. It also informs the backup translator of active flows as they occur. The backup translator can then use information from the active translator to prepare duplicate translation table entries, and in the event that the active translator is hindered by a critical failure, the traffic can rapidly be switched to the backup. The traffic flow continues since the same network address translations are used, and the state of those translations has been previously defined.

Address Resolution with ARP

A device in IP can have both a local address (which uniquely identifies the device on its local segment or LAN) and a network address (which identifies the network to which the device belongs). The local address is more properly known as a data link address because it is contained in the data link layer (Layer 2 of the OSI model) part of the packet header and is read by data-link devices (bridges and all device interfaces, for example). The local address is referred to as the MAC address, because the MAC sub-layer within the data link layer processes addresses for the layer.

To communicate with a device on Ethernet, for example, the Cisco IOS software first must determine the 48-bit MAC or local data-link address of that device. The process of determining the local data-link address from an IP address is called address resolution. The process of determining the IP address from a local data-link address is called reverse address resolution.

The software uses three forms of address resolution: Address Resolution Protocol (ARP), proxy ARP, and Probe (similar to ARP). The software also uses the Reverse Address Resolution Protocol (RARP). ARP, proxy ARP, and RARP are defined in RFCs 826, 1027, and 903, respectively. Probe is a protocol developed by the Hewlett-Packard Company (HP) for use on IEEE-802.3 networks.

ARP is used to associate IP addresses with media or MAC addresses. Taking an IP address as input, ARP determines the associated media address. Once a media or MAC address is determined, the IP address or media address association is stored in an ARP cache for rapid retrieval. Then the IP datagram is encapsulated in a link-layer frame and sent over the network. Encapsulation of IP datagrams and ARP requests and replies on IEEE 802 networks other than Ethernet is specified by the Subnetwork Access Protocol (SNAP).

How to Configure NAT for High Availability

This module describes three methods for configuring NAT for high availability:

•Configuring the Stateful Failover of NAT (optional)

•Configuring NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support (optional)

•Configuring NAT Static Mapping Support for HSRP (optional)

Configuring the Stateful Failover of NAT

The NAT Stateful Failover of Network Address Translation feature represents Phase 1 of the stateful failover capability. It introduces support for two or more network address translators to function as a translation group. A backup router running NAT provides translation services in the event the active translator fails. Protocols that do not need payload translations, such as HTTP and telnet, are supported by stateful NAT (SNAT).

This section contains the following procedures:

•Configuring SNAT with HSRP (optional)

•Configuring SNAT on the Primary (Active) Router (optional)

•Configuring SNAT on the Backup (Standby) Router (optional)

Restrictions for Configuring Stateful Failover of NAT

The following applications and protocols are not supported in Phase I:

•Application Level Gateway (ALG)

•FTP

•NetMeeting Directory (ILS)

•RAS

•SIP

•Skinny

•TFTP

•Asymmetrical routing

SNAT features are not backward compatible. See "Feature Information for Configuring NAT for High Availability" and "S.calability for Stateful NAT" for information on SNAT features and the releases in which they were introduced.

Configuring SNAT with HSRP

Perform this task to configure Stateful NAT using HSRP to provide router backup facilities.

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Note This task must be performed on both the active and the standby routers.

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SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. standby [group-name] ip [ip-address [secondary]]

5. exit

6. ip nat stateful id id-number {redundancy name mapping-id map-number}

7. ip nat pool name start-ip end-ip prefix-length prefix-length

8. ip nat inside source {route-map name pool pool-name mapping-id map-number} [overload]

9. exit

10. show ip snat distributed verbose

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables higher privilege levels, such as privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Router(config)# interface ethernet 1/1	Enters interface configuration mode.
Step 4	standby [group-name] ip [ip-address [secondary]] Example: Router(config-if)# standby SNATHSRP ip 10.1.1.1	Enables the HSRP protocol.
Step 5	exit Example: Router(config-if)# exit	Returns to global configuration mode.
Step 6	ip nat stateful id id-number {redundancy name mapping-id map-number} Example: Router(config)# ip nat stateful id 1 redundancy snathsrp mapping-id 10	Specifies SNAT on routers configured for HSRP.
Step 7	ip nat pool name start-ip end-ip prefix-length prefix-length Example: Router(config)# ip nat pool snatpool1 10.1.1.1 10.1.1.9 prefix-length 24	Defines a pool of IP addresses.
Step 8	ip nat inside source {route-map name pool pool-name mapping-id map-number} [overload] Example: Router(config)# ip nat inside source route-map rm-101 pool snatpool1 mapping-id 10 overload	Enables stateful NAT for the HSRP translation group.
Step 9	exit Example: Router> exit	Returns to privileged EXEC mode.
Step 10	show ip snat distributed verbose Example: Router# show ip snat distributed verbose	(Optional) Displays active stateful NAT translations.

Configuring SNAT on the Primary (Active) Router

Perform this task to manually configure your primary SNAT router. When you have completed this task, perform the steps in the "Configuring SNAT on the Backup (Standby) Router" section.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip nat stateful id id-number primary ip-address peer ip-address mapping-id map-number

4. ip nat pool name start-ip end-ip {prefix-length prefix-length}

5. ip nat inside source route-map name pool pool-name mapping-id map-number [overload]

6. exit

7. show ip snat distributed verbose

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables higher privilege levels, such as privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip nat stateful id id-number primary ip-address peer ip-address mapping-id map-number Example: Router(config)# ip nat stateful id 1 primary 10.10.10.10 peer 10.22.22.22 mapping-id 10	Specifies stateful NAT on the primary router.
Step 4	ip nat pool name start-ip end-ip prefix-length prefix-length Example: Router(config)# ip nat pool SNATPOOL1 10.1.1.1 10.1.1.9 prefix-length 24	Defines a pool of IP addresses.
Step 5	ip nat inside source route-map name pool pool-name mapping-id map-number [overload] Example: Router(config)# ip nat inside source route-map rm-101 pool snatpool1 mapping-id 10 overload	Enables stateful NAT for the HSRP translation group.
Step 6	exit Example: Router> exit	Returns to privileged EXEC mode.
Step 7	show ip snat distributed verbose Example: Router# show ip snat distributed verbose	(Optional) Displays active stateful NAT translations.

Configuring SNAT on the Backup (Standby) Router

Perform this task to manually configure your backup (standby) SNAT router.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip nat stateful id id-number back-up ip-address peer ip-address mapping-id map-number

4. ip nat pool name start-ip end-ip prefix-length prefix-length

5. ip nat inside source route-map name pool pool-name mapping-id map-number [overload]

6. exit

7. show ip snat distributed verbose

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables higher privilege levels, such as privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ip nat stateful id id-number backup ip-address peer ip-address mapping-id map-number Example: Router(config)# ip nat stateful id 1 backup 10.2.2.2 peer 10.10.10.10 mapping-id 10	Specifies stateful NAT on the backup router.
Step 4	ip nat pool name start-ip end-ip prefix-length prefix-length Example: Router(config)# ip nat pool SNATPOOL1 10.1.1.1 10.1.1.9 prefix-length 24	Defines a pool of IP addresses.
Step 5	ip nat inside source route-map name pool pool-name mapping-id map-number [overload] Example: Router(config)# ip nat inside source route-map rm-101 pool snatpool1 mapping-id 10 overload	Enables stateful NAT for the HSRP translation group.
Step 6	exit Example: Router> exit	Returns to privileged EXEC mode.
Step 7	show ip snat distributed verbose Example: Router# show ip snat distributed verbose	(Optional) Displays active stateful NAT translations.

Configuring NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support

Stateful NAT Phase I required all sessions to pass through the primary NAT router that controlled the NAT translation entries unless the primary NAT router was unavailable. This requirement assured integrity of the translation information by guarding against the possibility of some packets relevant to NAT session control from traversing the backup without the primary being aware of it. Without synchronized IP sessions NAT eventually times out the IP session entries and the result is IP session states that are out of sequence.

This section contains the following procedures:

•Configuring SNAT with HSRP (required)

•Configuring SNAT Primary/Backup (required)

Prerequisites for Configuring the NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support Feature

Each router must have the same Network Address Translation (NAT) configurations.

Benefits of Configuring Stateful Failover for Asymmetric Outside-to-Inside Support

The stateful failover asymmetric outside-to-inside enhancement provides the following benefits:

•Ability to support multiple routing paths from outside-to-inside

•Ability to handle per-packet load balancing of asymmetric routing from outside-to-inside

How Stateful Failover for Asymmetric Outside-to-Inside Support Works

Stateful failover for asymmetric outside-to-inside support enables two NAT routers to participate in a primary/backup design. One of the routers is elected as the primary NAT router and a second router acts as the backup router. As traffic is actively translated by the primary NAT router it updates the backup NAT router with the NAT translation state from NAT translation table entries. If the primary NAT router fails or is out of service, the backup NAT router will automatically take over. When the primary comes back into service it will take over and request an update from the backup NAT router. Return traffic is handled by either the primary or the backup NAT translator and NAT translation integrity is preserved.

When the backup NAT router receives asymmetric IP traffic and performs NAT of the packets, it will update the primary NAT router to ensure both the primary and backup NAT translation tables remain synchronized.

Figure 1 shows a typical configuration that uses the NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support feature.

Figure 1 Stateful NAT Asymmetric Outside-to-Inside Support

How Stateful Failover for ALGs Works

The stateful failover embedded addressing enhancement allows the secondary or backup NAT router to properly handle NAT and delivery of IP traffic. NAT inspects all IP traffic entering interfaces that have been configured with the NAT feature. The inspection consists of matching the incoming traffic against a set of translations rules and performs an address translation if a match occurs. The following are examples:

•Matching a source address range

•Matching a specific destination address range

•Matching a list of applications known to NAT that might require a specific source port for control plane negotiation, or embedded source IP addresses within the application protocol

Some of the applications and protocols that embed source port or IP address information include:

•H.323 Registration, Admission, and Status (RAS) Protocol

•DNS queries

•NetMeeting Internet Locator Server (ILS)

•Internet Control Message Protocol (ICMP)

•Simple Mail Transfer Protocol (SMTP)

•Point-to-Point Tunneling Protocol (PPTP)

•Network File System (NFS)

A complete list of current ALG protocols supported by Cisco IOS NAT can be found at

http://www.cisco.com/en/US/tech/tk648/tk361/tech_brief09186a00801af2b9.html

Configuring SNAT with HSRP

To configure your Hot Standby Router Protocol (HSRP) router with Stateful Network Address Translation (SNAT), use the following commands:

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. standby [group-name] ip [ip-address [secondary]]

5. exit

6. ip nat stateful id ip-address redundancy group-name mapping-id map-id

7. ip nat pool name start-ip end-ip prefix-length prefix-length

8. ip nat inside source route-map name pool pool-name mapping-id map-id [overload]

9. ip nat inside destination list number pool name mapping-id map-id

10. ip nat outside source static global-ip local-ip extendable mapping-id map-id

11. end

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	interface type number Example: Router(config)# interface ethernet 1/1	Enters interface configuration mode.
Step 4	standby [group-name] ip [ip-address [secondary]] Example: Router(config-if)# standby SNATHSRP ip 11.1.1.1 secondary	Enables the HSRP protocol.
Step 5	exit Example: Router(config-if)# exit	Returns to global configuration mode.
Step 6	ip nat stateful id ip-address redundancy group-name mapping-id map-id Example: Router(config)# ip nat stateful id 1 redundancy snathsrp mapping-id 10	Specifies SNAT on routers configured for HSRP.
Step 7	ip nat pool name start-ip end-ip prefix-length prefix-length Example: Router(config)# ip nat pool snatpool1 11.1.1.1 11.1.1.9 prefix-length 24	Defines a pool of IP addresses.
Step 8	ip nat inside source static route-map name pool pool-name mapping-id map-id [overload] Example: Router(config)# ip nat inside source static route-map rm-101 pool snatpool2 mapping-id 10 overload	Enables stateful NAT for the HSRP translation group.
Step 9	ip nat inside destination list number pool name mapping-id map-id Example: Router(config)# ip nat inside destination list 1 pool snatpool2 mapping-id 10	Enables the local SNAT router to distribute a particular set of locally created entries to a peer SNAT router.
Step 10	ip nat outside source static global-ip local-ip extendable mapping-id map-id Example: Router(config)# ip nat outside source static 1.1.1.1 2.2.2.2 extendable mapping-id 10	Enables stateful NAT for the HSRP translation group.
Step 11	end Example: Router(config)# end	Exits global configuration mode. •Use the end command to save your configuration and leave configuration mode.

Configuring SNAT Primary/Backup

Use the following commands to enable the NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support feature:

SUMMARY STEPS

1. enable

2. configure terminal

3. ip nat stateful id id-number primary ip-address peer ip-address mapping-id map-number

4. ip nat pool name start-ip end-ip prefix-length prefix-length

5. ip nat inside source static route-map name pool pool-name mapping-id map-id [overload]

6. ip nat inside destination list number pool name mapping-id map-id

7. ip nat outside source static global-ip local-ip extendable mapping-id map-id

8. end

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 stateful id id-number primary ip-address peer ip-address mapping-id map-id Example: Router(config)# ip nat stateful id 1 primary 1.1.1.1 peer 2.2.2.2 mapping-id 10	Specifies stateful NAT on the primary router.
Step 4	ip nat pool name start-ip end-ip prefix-length prefix-length Example: Router(config)# parser config cache interface	Defines a pool of IP addresses.
Step 5	ip nat inside source static route-map name pool pool-name mapping-id map-id [overload] Example: Router(config)# ip nat inside source static route-map rm-101 pool snatpool2 mapping-id 10 overload	Enables stateful NAT of the inside source address to distribute a particular set of locally created entries to a peer SNAT router.
Step 6	ip nat inside destination list number pool name mapping-id map-id Example: Router(config)# ip nat inside destination list 1 pool snatpool2 mapping-id 10 overload	Defines the inside destination address that enables the local SNAT router to distribute locally created entries to a peer SNAT router.
Step 7	ip nat outside source Static global-ip local-ip extendable mapping-id map-id Example: Router(config)# ip nat outside source static 1.1.1.1 2.2.2.2 extendable mapping-id 10	Enables stateful NAT of the outside source address to distribute a particular set of locally created entries to a peer SNAT router.
Step 8	end Example: Router(config)# end	Exits global configuration mode. •Use the end command to save your configuration and leave configuration mode.

Configuring NAT Static Mapping Support for HSRP

When an Address Resolution Protocol (ARP) query is triggered for an address that is configured with NAT static mapping and owned by the router, NAT responds with the burned in MAC (BIA MAC) address on the interface to which the ARP is pointing. Two routers are acting as HSRP active and standby. Their NAT inside interfaces must be enabled and configured to belong to a group.

Both of the following tasks are required and must be performed on both the active and standby routers to configure NAT static mapping support for HSRP:

•Enabling HSRP on the NAT Interface (required)

•Enabling Static NAT in an HSRP Environment (required)

Restrictions for Configuring Static Mapping Support for HSRP

•Configuring static mapping support for HSRP provides NAT support in the presence of HSRP using static mapping configuration only.

•Static NAT mappings must be mirrored on two or more HSRP routers, because NAT state will not be exchanged between the routers running NAT in an HSRP group.

•Behavior will be unpredictable if both HSRP routers have the same static NAT and are not configured with the hsrp keyword linking them to the same HSRP group.

Benefits of Configuring Static Mapping Support for HSRP

•Using static mapping support for HSRP, failover is ensured without having to time out and repopulate upstream ARP caches in a high-availability environment, where HSRP router pairs have identical NAT configuration for redundancy.

•Static mapping support for HSRP allows the option of having only the HSRP active router respond to an incoming ARP for a router configured with a NAT address.

Enabling HSRP on the NAT Interface

Perform this task to enable HSRP on the NAT interface of both the active and standby routers.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. ip address ip-address mask

5. no ip redirects

6. ip nat {inside | outside}

7. standby [group-number] ip [ip-address [secondary]]

8. standby name [group-name]

9. end

10. show standby

11. show ip nat translations [verbose]

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables higher privilege levels, such as privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	interface type number Example: Router(config)# interface ethernet 1/1	Enters interface configuration mode.
Step 4	ip address ip-address mask Example: Router(config-if)# ip address 192.168.1.27 255.255.255.0	Sets the primary IP address on the interface.
Step 5	no ip redirects Example: Router(config-if)# no ip redirects	Disables the sending of redirect messages
Step 6	ip nat {inside | outside} Example: Router(config)# ip nat inside	Marks the interface as connected to the inside or outside.
Step 7	standby [group-number] ip [ip-address [secondary]] Example: Router(config-if)# standby 10 ip 192.168.5.30	Enables the HSRP protocol.
Step 8	standby [group-number] name [group-name] Example: Router(config-if)# standby 10 name HSRP1	Sets the HSRP group name.
Step 9	end Example: Router(config-if)# exit	Returns to privileged EXEC mode.
Step 10	show standby Example: Router# show standby	(Optional) Displays HSRP information
Step 11	show ip nat translations [verbose] Example: Router# show ip nat translations verbose	(Optional) Displays active NAT translations.

What to Do Next

Go to the next section and enable static NAT in the HSRP environment.

Enabling Static NAT in an HSRP Environment

To enable static mapping support with HRSP for high availability, perform this task on both the active and standby routers.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip nat inside source {list {access-list-number | access-list-name} pool pool-name} [overload] | static local-ip global- ip redundancy group-name}

4. ip nat outside source {list {access-list-number | access-list-name} pool pool-name} [overload] | static local-ip global- ip redundancy group-name}

5. exit

6. show ip nat translations [verbose]

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables higher privilege levels, such as 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 source {list {access-list-number | access-list-name} pool pool-name} [overload] | static local-ip global-ip redundancy group-name} Example: Router(config)# ip nat inside source static 192.168.5.33 10.10.10.5 redundancy HSRP1	Enables the router to respond to ARP queries using BIA MAC, if HSRP is configured on the NAT inside interface.
Step 4	ip nat outside source {list {access-list-number | access-list-name} pool pool-name} [overload] | static local-ip global-ip redundancy group-name} Example: Router(config)# ip nat outside source static 192.168.5.33 10.10.10.5 redundancy HSRP1	Enables the router to respond to ARP queries using BIA MAC, if HSRP is configured on the NAT outside interface.
Step 5	exit Example: Router(config-if)# exit	Returns to privileged EXEC mode.
Step 6	show ip nat translations [verbose] Example: Router# show ip nat translations verbose	(Optional) Displays active NAT translations.

Configuration Example for NAT for High Availability

This section provides the following configuration examples:

•Configuring Stateful NAT: Examples

•Configuration Examples for NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support

•Configuring Static NAT in an HSRP Environment: Examples

Configuring Stateful NAT: Examples

The following examples show configuring stateful NAT with HSRP and configuring stateful NAT primary and backup routers.

SNAT with HSRP Example

ip nat Stateful id 1

redundancy SNATHSRP

mapping-id 10

ip nat pool SNATPOOL1 10.1.1.1 10.1.1.9 prefix-length 24

ip nat inside source route-map rm-101 pool SNATPOOL1 mapping-id 10 overload

ip classless

ip route 10.1.1.0 255.255.255.0 Null0

no ip http server

ip pim bidir-enable

Configuring SNAT Primary/Backup Example

ip nat Stateful id 1

primary 10.88.194.17

peer 10.88.194.18

mapping-id 10

!

ip nat Stateful id 2

backup 10.88.194.18

peer 10.88.194.17

mapping-id 10

Configuration Examples for NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support

This section contains the following examples:

•Configuring SNAT with HSRP

•Enabling HSRP on the NAT Interface

Configuring SNAT with HSRP: Example

The following example shows how to configure SNAT with HSRP.

ip nat Stateful id 1

redundancy SNATHSRP

mapping-id 10

ip nat pool SNATPOOL1 11.1.1.1 11.1.1.9 prefix-length 24

ip nat inside source route-map rm-101 pool SNATPOOL1 mapping-id 10 overload

ip classless

ip route 11.1.1.0 255.255.255.0 Null0

no ip http server

ip pim bidir-enable

Configuring SNAT Primary/Backup: Example

The following example shows how to configure SNAT on the primary/backup router.

ip nat Stateful id 1

primary 10.88.194.17

peer 10.88.194.18

mapping-id 10

!

ip nat Stateful id 2

backup 10.88.194.18

peer 10.88.194.17

mapping-id 10

Configuring Static NAT in an HSRP Environment: Examples

The following example shows support for NAT with a static configuration in an HSRP environment. Two routers are acting as HSRP active and standby, and the NAT inside interfaces are HSRP enabled and configured to belong to the group HSRP1.

Active Router Configuration

interface BVI10 

 ip address 192.168.5.54 255.255.255.255.0 

 no ip redirects 

 ip nat inside 

 standby 10 priority 105 preempt 

 standby 10 name HSRP1 

 standby 10 ip 192.168.5.30 

 standby 10 track Ethernet2/1 

! 

! 

 ip default-gateway 10.0.18.126 

 ip nat inside source static 192.168.5.33 10.10.10.5 redundancy HSRP1 

 ip classless 

 ip route 10.10.10.0 255.255.255.0 Ethernet2/1 

 ip route 172.22.33.0 255.255.255.0 Ethernet2/1 

 no ip http server 

Standby Router Configuration

interface BVI10 

 ip address 192.168.5.56 255.255.255.255.0 

 no ip redirects 

 ip nat inside 

 standby 10 priority 100 preempt 

 standby 10 name HSRP1 

 standby 10 ip 192.168.5.30 

 standby 10 track Ethernet3/1 

! 

 ip default-gateway 10.0.18.126 

 ip nat inside source static 192.168.5.33 3.3.3.5 redundancy HSRP1 

 ip classless 

 ip route 10.0.32.231 255.255.255 Ethernet3/1 

 ip route 10.10.10.0 255.255.255.0 Ethernet3/1 

 no ip http server 

Additional References

The following sections provide references related toNAT for high availability.

Related Documents

Related Topic	Document Title
NAT configuration tasks	"Configuring NAT for IP Address Conservation" module
Using NAT with MPLS VPNs	"Integrating NAT with MPLS VPNs" module
NAT maintenance	"Monitoring and Maintaining NAT" module
NAT commands: complete command syntax, command mode, command history, usage guidelines, and examples	Cisco IOS IP Addressing Services Command Reference

Standards

Standards	Title
None

MIBs

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

RFCs

RFCs	Title
RFC 903	Reverse Address Resolution Protocol
RFC 826	Ethernet Address Resolution Protocol: Or converting network protocol addresses to 48.bit Ethernet address for transmission on Ethernet hardware
RFC 1027	Using ARP to implement transparent subnet gateways

Feature Information for Configuring NAT for High Availability

Table 1 lists the features in this module and provides links to specific configuration information. Only features that were introduced or modified in Cisco IOS Releases 12.2(4) or later appear in the table.

Not all commands may be available in your Cisco IOS software release. For details on when support for a specific command was introduced, see the command reference documentation.

For information on a feature in this technology that is not documented here, see the "Configuring Network Address Translation Features Roadmap."

Cisco IOS software images are specific to a Cisco IOS software release, a feature set, and a platform. Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.

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

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Table 1 Feature Information for Configuring NAT for High Availability 

Feature Name	Releases	Feature Configuration Information
NAT—Static Mapping Support with HSRP for High Availability	12.2(4)T 12.2(4)T2 Cisco IOS XE Release 2.1	Static mapping support for HSRP allows the option of having only the HSRP active router respond to an incoming ARP for a router configured with a NAT address. The following sections provide information about this feature: •"Configuring NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support" section •"Configuring Static NAT in an HSRP Environment: Examples" section
NAT Stateful Failover of Network Address Translation	12.2(13)T	The NAT Stateful Failover of Network Address Translation feature represents Phase 1 of the stateful failover capability. It introduces support for two or more network address translators to function as a translation group. The following sections provide information about this feature: •"Configuring the Stateful Failover of NAT" section •"Configuring Stateful NAT: Examples" section
NAT Stateful Failover for Asymmetric Outside-to-Inside ALG Support	12.3(7)T	The NAT Stateful Failover for Asymmetric Outside-to-Inside and Application Layer Gateway (ALG) Support feature improves the ability to handle asymmetric paths by allowing multiple routing paths from outside-to-inside, and per-packet load balancing. This feature also provides seamless failover translated IP sessions with traffic that includes embedded IP addressing such as Voice over IP, FTP, and Domain Name System (DNS) applications. The following sections provide information about this feature: •"Configuring NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support" section •"Configuration Examples for NAT Stateful Failover for Asymmetric Outside-to-Inside and ALG Support" section

Technical Assistance

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Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.

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