Configuring Network Object NAT

All NAT rules that are configured as a parameter of a network object are considered to be network object NAT rules. Network object NAT is a quick and easy way to configure NAT for a single IP address, a range of addresses, or a subnet. After you configure the network object, you can then identify the mapped address for that object.

This chapter describes how to configure network object NAT, and it includes the following sections:

note.gif

Noteblank.gif For detailed information about how NAT works, see Chapter27, “Information About NAT”

Information About Network Object NAT

When a packet enters the ASA, both the source and destination IP addresses are checked against the network object NAT rules. The source and destination address in the packet can be translated by separate rules if separate matches are made. These rules are not tied to each other; different combinations of rules can be used depending on the traffic.

Because the rules are never paired, you cannot specify that a source address should be translated to A when going to destination X, but be translated to B when going to destination Y. Use twice NAT for that kind of functionality (twice NAT lets you identify the source and destination address in a single rule).

For detailed information about the differences between twice NAT and network object NAT, see the “How NAT is Implemented” section.

Network object NAT rules are added to section 2 of the NAT rules table. For more information about NAT ordering, see the “NAT Rule Order” section.

Licensing Requirements for Network Object NAT

The following table shows the licensing requirements for this feature:

 

Model
License Requirement

All models

Base License.

Prerequisites for Network Object NAT

Depending on the configuration, you can configure the mapped address inline if desired or you can create a separate network object or network object group for the mapped address (the object network or object-group network command). Network object groups are particularly useful for creating a mapped address pool with discontinous IP address ranges or multiple hosts or subnets. To create a network object or group, see the “Configuring Objects and Groups” section.

For specific guidelines for objects and groups, see the configuration section for the NAT type you want to configure. See also the “Guidelines and Limitations” section.

Guidelines and Limitations

Context Mode Guidelines

Supported in single and multiple context mode.

Firewall Mode Guidelines

  • Supported in routed and transparent firewall mode.
  • In transparent mode, you must specify the real and mapped interfaces; you cannot use any.
  • In transparent mode, you cannot configure interface PAT, because the transparent mode interfaces do not have IP addresses. You also cannot use the management IP address as a mapped address.

IPv6 Guidelines

Does not support IPv6.

Additional Guidelines

  • You can only define a single NAT rule for a given object; if you want to configure multiple NAT rules for an object, you need to create multiple objects with different names that specify the same IP address, for example, object network obj-10.10.10.1-01, object network obj-10.10.10.1-02, and so on.
  • If you change the NAT configuration, and you do not want to wait for existing translations to time out before the new NAT configuration is used, you can clear the translation table using the clear xlate command. However, clearing the translation table disconnects all current connections that use translations.
note.gif

Noteblank.gif If you remove a dynamic NAT or PAT rule, and then add a new rule with mapped addresses that overlap the addresses in the removed rule, then the new rule will not be used until all connections associated with the removed rule time out or are cleared using the clear xlate command. This safeguard ensures that the same address is not assigned to multiple hosts.

  • Objects and object groups used in NAT cannot be undefined; they must include IP addresses.
  • You can use the same mapped object or group in multiple NAT rules.
  • The mapped IP address pool cannot include:

–blank.gif The mapped interface IP address. If you specify any interface for the rule, then all interface IP addresses are disallowed. For interface PAT (routed mode only), use the interface keyword instead of the IP address.

–blank.gif (Transparent mode) The management IP address.

–blank.gif (Dynamic NAT) The standby interface IP address when VPN is enabled.

–blank.gif Existing VPN pool addresses.

Default Settings

  • (Routed mode) The default real and mapped interface is Any, which applies the rule to all interfaces.
  • (8.3(1), 8.3(2), and 8.4(1)) The default behavior for identity NAT has proxy ARP disabled. You cannot configure this setting. (8.4(2) and later) The default behavior for identity NAT has proxy ARP enabled, matching other static NAT rules. You can disable proxy ARP if desired. See the “Routing NAT Packets” section for more information.
  • If you specify an optional interface, then the ASA uses the NAT configuration to determine the egress interface. (8.3(1) through 8.4(1)) The only exception is for identity NAT, which always uses a route lookup, regardless of the NAT configuration. (8.4(2) and later) For identity NAT, the default behavior is to use the NAT configuration, but you have the option to always use a route lookup instead. See the “Routing NAT Packets” section for more information.

Configuring Network Object NAT

This section describes how to configure network object NAT and includes the following topics:

Configuring Dynamic NAT

This section describes how to configure network object NAT for dynamic NAT. For more information, see the “Dynamic NAT” section.

Detailed Steps

 

Command
Purpose

Step 1

Network object:

object network obj_name

range ip_address_1 ip_address_2

 

Network object group:

object-group network grp_name

{ network-object { object net_obj_name | host ip_address } | group-object grp_obj_name }
 
 

hostname(config)# object network TEST

hostname(config-network-object)# range 10.1.1.1 10.1.1.70

 

hostname(config)# object network TEST2

hostname(config-network-object)# range 10.1.2.1 10.1.2.70

 

hostname(config-network-object)# object-group network MAPPED_IPS

hostname(config-network)# network-object object TEST

hostname(config-network)# network-object object TEST2

hostname(config-network)# network-object host 10.1.2.79

To specify the mapped addresses (that you want to translate to), configure a network object or network object group. A network object group can contain objects and/or inline addresses.

Note The object or group cannot contain a subnet.

If a mapped network object contains both ranges and host IP addresses, then the ranges are used for dynamic NAT, and then the host IP addresses are used as a PAT fallback.

See the “Guidelines and Limitations” section for information about disallowed mapped IP addresses.

For more information about configuring a network object or group, see the “Configuring Objects” section.

Step 2

object network obj_name

 

hostname(config)# object network my-host-obj1

Configures a network object for which you want to configure NAT, or enters object network configuration mode for an existing network object.

Step 3

{ host ip_address | subnet subnet_address netmask | range ip_address_1 ip_address_2 }

 

hostname(config-network-object)# subnet 10.1.1.0 255.255.255.0

If you are creating a new network object, defines the real IP address(es) that you want to translate.

Step 4

nat [ ( real_ifc , mapped_ifc ) ] dynamic mapped_obj [ interface ] [ dns ]

 

hostname(config-network-object)# nat (inside,outside) dynamic MAPPED_IPS interface

Configures dynamic NAT for the object IP addresses.

Note You can only define a single NAT rule for a given object. See the “Additional Guidelines” section.

See the following guidelines:

  • Interfaces—(Required for transparent mode) Specify the real and mapped interfaces. Be sure to include the parentheses in your command. In routed mode, if you do not specify the real and mapped interfaces, all interfaces are used; you can also specify the keyword any for one or both of the interfaces.
  • Mapped IP address—Specify the mapped IP address as:

–blank.gif An existing network object (see Step 1).

–blank.gif An existing network object group (see Step 1).

  • Interface PAT fallback—(Optional) The interface keyword enables interface PAT fallback. After the mapped IP addresses are used up, then the IP address of the mapped interface is used. For this option, you must configure a specific interface for the mapped_ifc. (You cannot specify interface in transparent mode).
  • DNS—(Optional) The dns keyword translates DNS replies. Be sure DNS inspection is enabled (it is enabled by default). See the “DNS and NAT” section for more information.

Examples

The following example configures dynamic NAT that hides 192.168.2.0 network behind a range of outside addresses 10.2.2.1 through 10.2.2.10:

hostname(config)# object network my-range-obj
hostname(config-network-object)# range 10.2.2.1 10.2.2.10
hostname(config)# object network my-inside-net
hostname(config-network-object)# subnet 192.168.2.0 255.255.255.0
hostname(config-network-object)# nat (inside,outside) dynamic my-range-obj
 

The following example configures dynamic NAT with dynamic PAT backup. Hosts on inside network 10.76.11.0 are mapped first to the nat-range1 pool (10.10.10.10-10.10.10.20). After all addresses in the nat-range1 pool are allocated, dynamic PAT is performed using the pat-ip1 address (10.10.10.21). In the unlikely event that the PAT translations are also use up, dynamic PAT is performed using the outside interface address.

hostname(config)# object network nat-range1
hostname(config-network-object)# range 10.10.10.10 10.10.10.20
 
hostname(config-network-object)# object network pat-ip1
hostname(config-network-object)# host 10.10.10.21
 
hostname(config-network-object)# object-group network nat-pat-grp
hostname(config-network-object)# network-object object nat-range1
hostname(config-network-object)# network-object object pat-ip1
 
hostname(config-network-object)# object network my_net_obj5
hostname(config-network-object)# subnet 10.76.11.0 255.255.255.0
hostname(config-network-object)# nat (inside,outside) dynamic nat-pat-grp interface
 

Configuring Dynamic PAT (Hide)

This section describes how to configure network object NAT for dynamic PAT (hide). For more information, see the “Dynamic PAT” section.

Guidelines

For a PAT pool:

  • If available, the real source port number is used for the mapped port. However, if the real port is not available, by default the mapped ports are chosen from the same range of ports as the real port number: 0 to 511, 512 to 1023, and 1024 to 65535. Therefore, ports below 1024 have only a small PAT pool that can be used. (8.4(3) and later, not including 8.5(1) or 8.6(1)) If you have a lot of traffic that uses the lower port ranges, you can now specify a flat range of ports to be used instead of the three unequal-sized tiers: either 1024 to 65535, or 1 to 65535.
  • (8.4(3) and later, not including 8.5(1) or 8.6(1)) If you use the same PAT pool object in two separate rules, then be sure to specify the same options for each rule. For example, if one rule specifies extended PAT and a flat range, then the other rule must also specify extended PAT and a flat range.

For extended PAT for a PAT pool (8.4(3) and later, not including 8.5(1) or 8.6(1)):

  • Many application inspections do not support extended PAT. See the “Default Settings” section in “Getting Started with Application Layer Protocol Inspection,” for a complete list of unsupported inspections.
  • If you enable extended PAT for a dynamic PAT rule, then you cannot also use an address in the PAT pool as the PAT address in a separate static NAT-with-port-translation rule. For example, if the PAT pool includes 10.1.1.1, then you cannot create a static NAT-with-port-translation rule using 10.1.1.1 as the PAT address.
  • If you use a PAT pool and specify an interface for fallback, you cannot specify extended PAT.
  • For VoIP deployments that use ICE or TURN, do not use extended PAT. ICE and TURN rely on the PAT binding to be the same for all destinations.

For round robin for a PAT pool:

  • (8.4(3) and later, not including 8.5(1) or 8.6(1)) If a host has an existing connection, then subsequent connections from that host will use the same PAT IP address if ports are available. Note : This “stickiness” does not survive a failover. If the ASA fails over, then subsequent connections from a host may not use the initial IP address.
  • (8.4(2), 8.5(1), and 8.6(1)) If a host has an existing connection, then subsequent connections from that host will likely use different PAT addresses for each connection because of the round robin allocation. In this case, you may have problems when accessing two websites that exchange information about the host, for example an e-commerce site and a payment site. When these sites see two different IP addresses for what is supposed to be a single host, the transaction may fail.
  • Round robin, especially when combined with extended PAT, can consume a large amount of memory. Because NAT pools are created for every mapped protocol/IP address/port range, round robin results in a large number of concurrent NAT pools, which use memory. Extended PAT results in an even larger number of concurrent NAT pools.

Detailed Steps

 

Command
Purpose

Step 1

(Optional)

Network object:

object network obj_name

{ host ip_address | range ip_address_1 ip_address_2 }

 

Network object group:

object-group network grp_name

{ network-object { object net_obj_name | host ip_address } | group-object grp_obj_name }
 
 

hostname(config)# object network PAT_POOL1

hostname(config-network-object)# range 10.5.1.80 10.7.1.80

 

hostname(config)# object network PAT_POOL2

hostname(config-network-object)# range 10.9.1.1 10.10.1.1

 

hostname(config)# object network PAT_IP

hostname(config-network-object)# host 10.5.1.79

 

hostname(config-network-object)# object-group network PAT_POOLS

hostname(config-network)# network-object object PAT_POOL1

hostname(config-network)# network-object object PAT_POOL2

hostname(config-network)# network-object object PAT_IP

Specify the mapped address(es) (that you want to translate to). You can configure a single address or, for a PAT pool, multiple addresses. Configure a network object or network object group. A network object group can contain objects and/or inline addresses. Alternatively, you can skip this step if you want to enter a single IP address as an inline value for the nat command or if you want to use the interface address by specifying the interface keyword.

For mapped addresses used as a PAT pool, all addresses in the object or group, including ranges, are used as PAT addresses.

Note The object or group cannot contain a subnet.

See the “Guidelines and Limitations” section for information about disallowed mapped IP addresses.

For more information about configuring a network object or group, see the “Configuring Objects” section.

Step 2

object network obj_name

 

hostname(config)# object network my-host-obj1

Configures a network object for which you want to configure NAT, or enters object network configuration mode for an existing network object.

Step 3

{ host ip_address | subnet subnet_address netmask | range ip_address_1 ip_address_2 }

 

hostname(config-network-object)# range 10.1.1.1 10.1.1.90

If you are creating a new network object, defines the real IP address(es) that you want to translate.

Step 4

nat [ ( real_ifc , mapped_ifc ) ] dynamic { mapped_inline_host_ip | mapped_obj | pat-pool mapped_obj [ round-robin ] [ extended ] [ flat [ include-reserve ]] | interface } [ interface ] [ dns ]

 

hostname(config-network-object)# nat (any,outside) dynamic interface

Configures dynamic PAT for the object IP addresses. You can only define a single NAT rule for a given object. See the “Additional Guidelines” section.

See the following guidelines:

  • Interfaces—(Required for transparent mode) Specify the real and mapped interfaces. Be sure to include the parentheses in your command. In routed mode, if you do not specify the real and mapped interfaces, all interfaces are used; you can also specify the keyword any for one or both of the interfaces.
  • Mapped IP address—You can specify the mapped IP address as:

–blank.gif An inline host address.

–blank.gif An existing network object that is defined as a host address (see Step 1).

–blank.gif pat-pool —An existing network object or group that contains multiple addresses.

–blank.gif interface —(Routed mode only) The IP address of the mapped interface is used as the mapped address. For this option, you must configure a specific interface for the mapped_ifc. You must use this keyword when you want to use the interface IP address; you cannot enter it inline or as an object.

  • For a PAT pool, you can specify one or more of the following options:

–blank.gif Round robin—The round-robin keyword enables round-robin address allocation for a PAT pool. Without round robin, by default all ports for a PAT address will be allocated before the next PAT address is used. The round-robin method assigns an address/port from each PAT address in the pool before returning to use the first address again, and then the second address, and so on.

(continued)

 

 

(continued)

–blank.gif Extended PAT—(8.4(3) and later, not including 8.5(1) or 8.6(1)) The extended keyword enables extended PAT. Extended PAT uses 65535 ports per service, as opposed to per IP address, by including the destination address and port in the translation information. Normally, the destination port and address are not considered when creating PAT translations, so you are limited to 65535 ports per PAT address. For example, with extended PAT, you can create a translation of 10.1.1.1:1027 when going to 192.168.1.7:23 as well as a translation of 10.1.1.1:1027 when going to 192.168.1.7:80.

–blank.gif Flat range—(8.4(3) and later, not including 8.5(1) or 8.6(1)) The flat keyword enables use of the entire 1024 to 65535 port range when allocating ports. When choosing the mapped port number for a translation, the ASA uses the real source port number if it is available. However, without this option, if the real port is not available, by default the mapped ports are chosen from the same range of ports as the real port number: 1 to 511, 512 to 1023, and 1024 to 65535. To avoid running out of ports at the low ranges, configure this setting. To use the entire range of 1 to 65535, also specify the include-reserve keyword.

  • Interface PAT fallback—(Optional) The interface keyword enables interface PAT fallback when entered after a primary PAT address. After the primary PAT address(es) are used up, then the IP address of the mapped interface is used. For this option, you must configure a specific interface for the mapped_ifc. (You cannot specify interface in transparent mode).
  • DNS—(Optional) The dns keyword translates DNS replies. Be sure DNS inspection is enabled (it is enabled by default). See the “DNS and NAT” section for more information.

Examples

The following example configures dynamic PAT that hides the 192.168.2.0 network behind address 10.2.2.2:

hostname(config)# object network my-inside-net
hostname(config-network-object)# subnet 192.168.2.0 255.255.255.0
hostname(config-network-object)# nat (inside,outside) dynamic 10.2.2.2
 

The following example configures dynamic PAT that hides the 192.168.2.0 network behind the outside interface address:

hostname(config)# object network my-inside-net
hostname(config-network-object)# subnet 192.168.2.0 255.255.255.0
hostname(config-network-object)# nat (inside,outside) dynamic interface
 

Configuring Static NAT or Static NAT-with-Port-Translation

This section describes how to configure a static NAT rule using network object NAT. For more information, see the “Static NAT” section.

Detailed Steps

 

Command
Purpose

Step 1

(Optional)

Network object:

object network obj_name

{ host ip_address | subnet subnet_address netmask | range ip_address_1 ip_address_2 }

 

Network object group:

object-group network grp_name

{ network-object { object net_obj_name | subnet_address netmask | host ip_address } | group-object grp_obj_name }
 
 

hostname(config)# object network MAPPED_IPS

hostname(config-network-object)# subnet 10.1.1.0 255.255.255.0

To specify the mapped addresses (that you want to translate to), configure a network object or network object group. A network object group can contain objects and/or inline addresses. Alternatively, you can skip this step if you want to enter the IP addresses as an inline value for the nat command or if you want to use the interface address (for static NAT-with-port-translation) by specifying the interface keyword.

See the “Guidelines and Limitations” section for information about disallowed mapped IP addresses.

For more information about configuring a network object or group, see the “Configuring Objects” section.

Step 2

object network obj_name

 

hostname(config)# object network my-host-obj1

Configures a network object for which you want to configure NAT, or enters object network configuration mode for an existing network object.

Step 3

{ host ip_address | subnet subnet_address netmask | range ip_address_1 ip_address_2 }

 

hostname(config-network-object)# subnet 10.2.1.0 255.255.255.0

If you are creating a new network object, defines the real IP address(es) that you want to translate.

Step 4

nat [ ( real_ifc , mapped_ifc ) ] static { mapped_inline_ip | mapped_obj | interface } [ dns | service { tcp | udp } real_port mapped_port ] [ no-proxy-arp ]

 

hostname(config-network-object)# nat (inside,outside) static MAPPED_IPS service tcp 80 8080

Configures static NAT for the object IP addresses.

Note You can only define a single NAT rule for a given object. See the “Additional Guidelines” section.

See the following guidelines:

  • Interfaces—(Required for transparent mode) Specify the real and mapped interfaces. Be sure to include the parentheses in your command. In routed mode, if you do not specify the real and mapped interfaces, all interfaces are used; you can also specify the keyword any for one or both of the interfaces.
  • Mapped IP Addresses—You can specify the mapped IP address as:

–blank.gif An inline IP address. The netmask or range for the mapped network is the same as that of the real network. For example, if the real network is a host, then this address will be a host address. In the case of a range, then the mapped addresses include the same number of addresses as the real range. For example, if the real address is defined as a range from 10.1.1.1 through 10.1.1.6, and you specify 172.20.1.1 as the mapped address, then the mapped range will include 172.20.1.1 through 172.20.1.6.

–blank.gif An existing network object or group (see Step 1).

–blank.gif interface —(Static NAT-with-port-translation only; routed mode) For this option, you must configure a specific interface for the mapped_ifc. Be sure to also configure the service keyword.

Typically, you configure the same number of mapped addresses as real addresses for a one-to-one mapping. You can, however, have a mismatched number of addresses. For more information, see the “Static NAT” section.

  • DNS—(Optional) The dns keyword translates DNS replies. Be sure DNS inspection is enabled (it is enabled by default). See the “DNS and NAT” section for more information. This option is not available if you specify the service keyword.
  • Port translation—(Static NAT-with-port-translation only) Specify tcp or udp and the real and mapped ports. You can enter either a port number or a well-known port name (such as ftp).
  • No Proxy ARP—(Optional) Specify no-proxy-arp to disable proxy ARP for incoming packets to the mapped IP addresses. See the “Mapped Addresses and Routing” section for more information.

 

Examples

The following example configures static NAT for the real host 10.1.1.1 on the inside to 10.2.2.2 on the outside with DNS rewrite enabled.

hostname(config)# object network my-host-obj1
hostname(config-network-object)# host 10.1.1.1
hostname(config-network-object)# nat (inside,outside) static 10.2.2.2 dns
 

The following example configures static NAT for the real host 10.1.1.1 on the inside to 2.2.2.2 on the outside using a mapped object.

hostname(config)# object network my-mapped-obj
hostname(config-network-object)# host 10.2.2.2
 
hostname(config-network-object)# object network my-host-obj1
hostname(config-network-object)# host 10.1.1.1
hostname(config-network-object)# nat (inside,outside) static my-mapped-obj
 

The following example configures static NAT-with-port-translation for 10.1.1.1 at TCP port 21 to the outside interface at port 2121.

hostname(config)# object network my-ftp-server
hostname(config-network-object)# host 10.1.1.1
hostname(config-network-object)# nat (inside,outside) static interface service tcp 21 2121
 

Configuring Identity NAT

This section describes how to configure an identity NAT rule using network object NAT. For more information, see the “Identity NAT” section.

Detailed Steps

 

Command
Purpose

Step 1

(Optional)

object network obj_name

{ host ip_address | subnet subnet_address netmask | range ip_address_1 ip_address_2 }
 
 

hostname(config)# object network MAPPED_IPS

hostname(config-network-object)# subnet 10.1.1.0 255.255.255.0

For the mapped addresses (which will be the same as the real addresses), configure a network object. Alternatively, you can skip this step if you want to enter the IP addresses as an inline value for the nat command.

For more information about configuring a network object, see the “Configuring Objects” section.

Step 2

object network obj_name

 

hostname(config)# object network my-host-obj1

Configures a network object for which you want to perform identity NAT, or enters object network configuration mode for an existing network object.

Step 3

{ host ip_address | subnet subnet_address netmask | range ip_address_1 ip_address_2 }

 

hostname(config-network-object)# subnet 10.1.1.0 255.255.255.0

If you are creating a new network object, defines the real IP address(es) to which you want to perform identity NAT. If you configured a network object for the mapped addresses in Step 1, then these addresses must match.

Step 4

nat [ ( real_ifc , mapped_ifc ) ] static { mapped_inline_ip | mapped_obj } [ no-proxy-arp ] [ route-lookup ]

 

hostname(config-network-object)# nat (inside,outside) static MAPPED_IPS

Configures identity NAT for the object IP addresses.

Note You can only define a single NAT rule for a given object. See the “Additional Guidelines” section.

See the following guidelines:

  • Interfaces—(Required for transparent mode) Specify the real and mapped interfaces. Be sure to include the parentheses in your command. In routed mode, if you do not specify the real and mapped interfaces, all interfaces are used; you can also specify the keyword any for one or both of the interfaces.
  • Mapped IP addresses—Be sure to configure the same IP address for both the mapped and real address. Use one of the following:

–blank.gif Network object—Including the same IP address as the real object (see Step 1).

–blank.gif Inline IP address—The netmask or range for the mapped network is the same as that of the real network. For example, if the real network is a host, then this address will be a host address. In the case of a range, then the mapped addresses include the same number of addresses as the real range. For example, if the real address is defined as a range from 10.1.1.1 through 10.1.1.6, and you specify 10.1.1.1 as the mapped address, then the mapped range will include 10.1.1.1 through 10.1.1.6.

  • No Proxy ARP—Specify no-proxy-arp to disable proxy ARP for incoming packets to the mapped IP addresses. See the “Mapped Addresses and Routing” section for more information.
  • Route lookup—(Routed mode only; interface(s) specified) Specify route-lookup to determine the egress interface using a route lookup instead of using the interface specified in the NAT command. See the “Determining the Egress Interface” section for more information.

 

Example

The following example maps a host address to itself using an inline mapped address:

hostname(config)# object network my-host-obj1

hostname(config-network-object)# host 10.1.1.1

hostname(config-network-object)# nat (inside,outside) static 10.1.1.1

 

The following example maps a host address to itself using a network object:

hostname(config)# object network my-host-obj1-identity

hostname(config-network-object)# host 10.1.1.1

 

hostname(config-network-object)# object network my-host-obj1

hostname(config-network-object)# host 10.1.1.1

hostname(config-network-object)# nat (inside,outside) static my-host-obj1-identity

 

Monitoring Network Object NAT

To monitor object NAT, enter one of the following commands:

 

Command
Purpose

show nat

Shows NAT statistics, including hits for each NAT rule.

show nat pool

Shows NAT pool statistics, including the addresses and ports allocated, and how many times they were allocated.

show running-config nat

Shows the NAT configuration.

Note You cannot view the NAT configuration using the show running-config object command. You cannot reference objects or object groups that have not yet been created in nat commands. To avoid forward or circular references in show command output, the show running-config command shows the object command two times: first, where the IP address(es) are defined; and later, where the nat command is defined. This command output guarantees that objects are defined first, then object groups, and finally NAT. For example:

hostname# show running-config
...
object network obj1
range 192.168.49.1 192.150.49.100
object network obj2
object 192.168.49.100
object network network-1
subnet <network-1>
object network network-2
subnet <network-2>
object-group network pool
network-object object obj1
network-object object obj2
...
object network network-1
nat (inside,outside) dynamic pool
object network network-2
nat (inside,outside) dynamic pool

show xlate

Shows current NAT session information.

Configuration Examples for Network Object NAT

This section includes the following configuration examples:

Providing Access to an Inside Web Server (Static NAT)

The following example performs static NAT for an inside web server. The real address is on a private network, so a public address is required. Static NAT is necessary so hosts can initiate traffic to the web server at a fixed address. (See Figure 30-1).

Figure 30-1 Static NAT for an Inside Web Server

 
nat_objects-6.jpg

Step 1blank.gif Create a network object for the internal web server:

hostname(config)# object network myWebServ
 

Step 2blank.gif Define the web server address:

hostname(config-network-object)# host 10.1.2.27
 

Step 3blank.gif Configure static NAT for the object:

hostname(config-network-object)# nat (inside,outside) static 209.165.201.10
 

 

NAT for Inside Hosts (Dynamic NAT) and NAT for an Outside Web Server (Static NAT)

The following example configures dynamic NAT for inside users on a private network when they access the outside. Also, when inside users connect to an outside web server, that web server address is translated to an address that appears to be on the inside network. (See Figure 30-2).

Figure 30-2 Dynamic NAT for Inside, Static NAT for Outside Web Server

 

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Step 1blank.gif Create a network object for the dynamic NAT pool to which you want to translate the inside addresses:

hostname(config)# object network myNatPool
hostname(config-network-object)# range 209.165.201.20 209.165.201.30
 

Step 2blank.gif Create a network object for the inside network:

hostname(config)# object network myInsNet
hostname(config-network-object)# subnet 10.1.2.0 255.255.255.0
 

Step 3blank.gif Enable dynamic NAT for the inside network:

hostname(config-network-object)# nat (inside,outside) dynamic myNatPool
 

Step 4blank.gif Create a network object for the outside web server:

hostname(config)# object network myWebServ
 

Step 5blank.gif Define the web server address:

hostname(config-network-object)# host 209.165.201.12
 

Step 6blank.gif Configure static NAT for the web server:

hostname(config-network-object)# nat (outside,inside) static 10.1.2.20
 

 

Inside Load Balancer with Multiple Mapped Addresses (Static NAT, One-to-Many)

The following example shows an inside load balancer that is translated to multiple IP addresses. When an outside host accesses one of the mapped IP addresses, it is untranslated to the single load balancer address. Depending on the URL requested, it redirects traffic to the correct web server. (See Figure 30-3).

Figure 30-3 Static NAT with One-to-Many for an Inside Load Balancer

 

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Step 1blank.gif Create a network object for the addresses to which you want to map the load balancer:

hostname(config)# object network myPublicIPs
hostname(config-network-object)# range 209.165.201.3 209.265.201.8
 

Step 2blank.gif Create a network object for the load balancer:

hostname(config)# object network myLBHost
 

Step 3blank.gif Define the load balancer address:

hostname(config-network-object)# host 10.1.2.27
 

Step 4blank.gif Configure static NAT for the load balancer:

hostname(config-network-object)# nat (inside,outside) static myPublicIPs
 

 

Single Address for FTP, HTTP, and SMTP (Static NAT-with-Port-Translation)

The following static NAT-with-port-translation example provides a single address for remote users to access FTP, HTTP, and SMTP. These servers are actually different devices on the real network, but for each server, you can specify static NAT-with-port-translation rules that use the same mapped IP address, but different ports. (See Figure 30-4.)

Figure 30-4 Static NAT-with-Port-Translation

 

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Step 1blank.gif Create a network object for the FTP server address:

hostname(config)# object network FTP_SERVER
 

Step 2blank.gif Define the FTP server address, and configure static NAT with identity port translation for the FTP server:

hostname(config-network-object)# host 10.1.2.27
hostname(config-network-object)# nat (inside,outside) static 209.165.201.3 service tcp ftp ftp
 

Step 3blank.gif Create a network object for the HTTP server address:

hostname(config)# object network HTTP_SERVER
 

Step 4blank.gif Define the HTTP server address, and configure static NAT with identity port translation for the HTTP server:

hostname(config-network-object)# host 10.1.2.28
hostname(config-network-object)# nat (inside,outside) static 209.165.201.3 service tcp http http
 

Step 5blank.gif Create a network object for the SMTP server address:

hostname(config)# object network SMTP_SERVER
 

Step 6blank.gif Define the SMTP server address, and configure static NAT with identity port translation for the SMTP server:

hostname(config-network-object)# host 10.1.2.29
hostname(config-network-object)# nat (inside,outside) static 209.165.201.3 service tcp smtp smtp
 

 

DNS Server on Mapped Interface, Web Server on Real Interface (Static NAT with DNS Modification)

For example, a DNS server is accessible from the outside interface. A server, ftp.cisco.com, is on the inside interface. You configure the ASA to statically translate the ftp.cisco.com real address (10.1.3.14) to a mapped address (209.165.201.10) that is visible on the outside network. (See Figure 30-5.) In this case, you want to enable DNS reply modification on this static rule so that inside users who have access to ftp.cisco.com using the real address receive the real address from the DNS server, and not the mapped address.

When an inside host sends a DNS request for the address of ftp.cisco.com, the DNS server replies with the mapped address (209.165.201.10). The ASA refers to the static rule for the inside server and translates the address inside the DNS reply to 10.1.3.14. If you do not enable DNS reply modification, then the inside host attempts to send traffic to 209.165.201.10 instead of accessing ftp.cisco.com directly.

Figure 30-5 DNS Reply Modification

 

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Step 1blank.gif Create a network object for the FTP server address:

hostname(config)# object network FTP_SERVER
 

Step 2blank.gif Define the FTP server address, and configure static NAT with DNS modification:

hostname(config-network-object)# host 10.1.3.14
hostname(config-network-object)# nat (inside,outside) static 209.165.201.10 dns
 

 

DNS Server and Web Server on Mapped Interface, Web Server is Translated (Static NAT with DNS Modification)

Figure 30-6 shows a web server and DNS server on the outside. The ASA has a static translation for the outside server. In this case, when an inside user requests the address for ftp.cisco.com from the DNS server, the DNS server responds with the real address, 209.165.20.10. Because you want inside users to use the mapped address for ftp.cisco.com (10.1.2.56) you need to configure DNS reply modification for the static translation.

Figure 30-6 DNS Reply Modification Using Outside NAT

 

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Step 1blank.gif Create a network object for the FTP server address:

hostname(config)# object network FTP_SERVER
 

Step 2blank.gif Define the FTP server address, and configure static NAT with DNS modification:

hostname(config-network-object)# host 209.165.201.10
hostname(config-network-object)# nat (outside,inside) static 10.1.2.56 dns
 

 

Feature History for Network Object NAT

Table 30-1 lists each feature change and the platform release in which it was implemented.

 

Table 30-1 Feature History for Network Object NAT

Feature Name
Platform Releases
Feature Information

Network Object NAT

8.3(1)

Configures NAT for a network object IP address(es).

We introduced or modified the following commands: nat (object network configuration mode), show nat, show xlate, show nat pool.

Identity NAT configurable proxy ARP and route lookup

8.4(2)

In earlier releases for identity NAT, proxy ARP was disabled, and a route lookup was always used to determine the egress interface. You could not configure these settings. In 8.4(2) and later, the default behavior for identity NAT was changed to match the behavior of other static NAT configurations: proxy ARP is enabled, and the NAT configuration determines the egress interface (if specified) by default. You can leave these settings as is, or you can enable or disable them discretely. Note that you can now also disable proxy ARP for regular static NAT.

When upgrading to 8.4(2) from 8.3(1), 8.3(2), and 8.4(1), all identity NAT configurations will now include the no-proxy-arp and route-lookup keywords, to maintain existing functionality.

We modified the following commands: nat static [ no-proxy-arp ] [ route-lookup ].

PAT pool and round robin address assignment

8.4(2)

You can now specify a pool of PAT addresses instead of a single address. You can also optionally enable round-robin assignment of PAT addresses instead of first using all ports on a PAT address before using the next address in the pool. These features help prevent a large number of connections from a single PAT address from appearing to be part of a DoS attack and makes configuration of large numbers of PAT addresses easy.

We modifed the following commands: nat dynamic [ pat-pool mapped_object [ round-robin ]].

Round robin PAT pool allocation uses the same IP address for existing hosts

8.4(3)

When using a PAT pool with round robin allocation, if a host has an existing connection, then subsequent connections from that host will use the same PAT IP address if ports are available.

We did not modify any commands.

This feature is not available in 8.5(1) or 8.6(1).

Flat range of PAT ports for a PAT pool

8.4(3)

If available, the real source port number is used for the mapped port. However, if the real port is not available, by default the mapped ports are chosen from the same range of ports as the real port number: 0 to 511, 512 to 1023, and 1024 to 65535. Therefore, ports below 1024 have only a small PAT pool.

If you have a lot of traffic that uses the lower port ranges, when using a PAT pool, you can now specify a flat range of ports to be used instead of the three unequal-sized tiers: either 1024 to 65535, or 1 to 65535.

We modifed the following commands: nat dynamic [ pat-pool mapped_object [ flat [ include-reserve ]]].

This feature is not available in 8.5(1) or 8.6(1).

Extended PAT for a PAT pool

8.4(3)

Each PAT IP address allows up to 65535 ports. If 65535 ports do not provide enough translations, you can now enable extended PAT for a PAT pool. Extended PAT uses 65535 ports per service, as opposed to per IP address, by including the destination address and port in the translation information.

We modifed the following commands: nat dynamic [ pat-pool mapped_object [ extended ]].

This feature is not available in 8.5(1) or 8.6(1).

Automatic NAT rules to translate a VPN peer’s local IP address back to the peer’s real IP address

8.4(3)

In rare situations, you might want to use a VPN peer’s real IP address on the inside network instead of an assigned local IP address. Normally with VPN, the peer is given an assigned local IP address to access the inside network. However, you might want to translate the local IP address back to the peer’s real public IP address if, for example, your inside servers and network security is based on the peer’s real IP address.

You can enable this feature on one interface per tunnel group. Object NAT rules are dynamically added and deleted when the VPN session is established or disconnected. You can view the rules using the show nat command.

Note Because of routing issues, we do not recommend using this feature unless you know you need this feature; contact Cisco TAC to confirm feature compatibility with your network. See the following limitations:

  • Only supports Cisco IPsec and AnyConnect Client.
  • Return traffic to the public IP addresses must be routed back to the ASA so the NAT policy and VPN policy can be applied.
  • Does not support load-balancing (because of routing issues).
  • Does not support roaming (public IP changing).

We introduced the following command: nat-assigned-to-public-ip interface (tunnel-group general-attributes configuration mode).