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Cisco IOS IP Addressing Services Configuration Guide, Release 12.4
- Part 1: IP Addressing
- Part 2: ARP
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Part 3: DHCP
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DHCP Features Roadmap
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DHCP Overview
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Configuring the Cisco IOS DHCP Server
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Configuring the DHCP Server On-Demand Address Pool Manager
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Configuring the Cisco IOS DHCP Relay Agent
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Configuring the Cisco IOS DHCP Client
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Configuring DHCP Services for Accounting and Security
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Configuring DHCP Enhancements for Edge Session Management
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- Part 4: DNS
- Part 5: NHRP
- Part 6: NAT
Table Of Contents
Configuring NAT for IP Address Conservation
Prerequisites for Configuring NAT for IP Address Conservation
NAT Requirements, Objectives, and Interfaces
Restrictions for Configuring NAT for IP Address Conservation
Information About Configuring NAT for IP Address Conservation
Benefits of Configuring NAT for IP Address Conservation
NAT Inside and Outside Addresses
Inside Source Address Translation
Inside Global Addresses Overloading
Address Translation of Overlapping Networks
Viruses and Worms That Target NAT
How to Configure NAT for IP Address Conservation
Configuring Inside Source Addresses
Configuring Static Translation of Inside Source Addresses
Configuring Dynamic Translation of Inside Source Addresses
Allowing Internal Users Access to the Internet
Configuring Address Translation Timeouts
Changing the Translation Timeout
Changing the Timeouts When Overloading Is Configured
Allowing Overlapping Networks to Communicate Using NAT
Configuring Static Translation of Overlapping Networks
Configuring Dynamic Translation of Overlapping Networks
Configuring the NAT Virtual Interface
Restrictions for NAT Virtual Interface
Enabling a Dynamic NAT Virtual Interface
Enabling a Static NAT Virtual Interface
Enabling Route Maps on Inside Interfaces
Enabling NAT Route Maps Outside-to-Inside Support
Configuring NAT of External IP Addresses Only
Forwarding Packets from Outside to Inside Local Address
Reenabling RTSP on a NAT Router
Configuring Support for ARP Ping
Limiting the Number of Concurrent NAT Operations
Configuration Examples for Configuring NAT for IP Address Conservation
Example: Configuring Static Translation of Inside Source Addresses
Example: Configuring Dynamic Translation of Inside Source Addresses
Example: Overloading Inside Global Addresses
Example: Translating Overlapping Address
Example: Enabling NAT Virtual Interface
Example: Avoiding Server Overload Using Load Balancing
Example: Enabling NAT Route Mapping
Example: Enabling NAT Route Maps Outside-to-Inside Support
Example: Configuring NAT Translation of External IP Addresses Only
Configuration Examples for NAT Static IP Support
Example: Configuring NAT Static IP Support
Example: Creating a RADIUS Profile for NAT Static IP Support
Configuration Examples for Limiting the Number of Concurrent NAT Operations
Example: Setting a Global NAT Rate Limit
Example: Setting NAT Rate Limits for a Specific VRF Instance
Example: Setting NAT Rate Limits for All VRF Instances
Example: Setting NAT Rate Limits for Access Control Lists
Example: Setting NAT Rate Limits for an IP Address
Feature Information for Configuring NAT for IP Address Conservation
Configuring NAT for IP Address Conservation
First Published: May 2, 2005Last Updated: December 16, 2010This module describes how to configure Network Address Translation (NAT) for IP address conservation and configure inside and outside source addresses. This module also provides information about the benefits of configuring NAT for IP address conservation.
NAT enables private IP internetworks that use nonregistered IP addresses to connect to the Internet. NAT operates on a router, usually connecting two networks, and translates the private (not globally unique) addresses in the internal network into legal addresses before packets are forwarded onto another network. NAT can be configured to advertise only one address for the entire network to the outside world. This ability provides additional security by effectively hiding the entire internal network behind that one address.
NAT is also used at the enterprise edge to allow internal users access to the Internet and to allow Internet access to internal devices such as mail servers.
Finding Feature Information
Your software release may not support all the features documented in this module. 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 Configuring NAT for IP Address Conservation" section.
Use Cisco Feature Navigator to find information about platform support and Cisco 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
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Prerequisites for Configuring NAT for IP Address Conservation
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Prerequisites for Configuring NAT for IP Address Conservation
Access Lists
All access lists required for use with the tasks in this module should be configured prior to beginning the configuration task. For information about how to configure an access list, refer to the IP Access List Sequence Numbering document at the following URL:
http://www.cisco.com/en/US/docs/ios/sec_data_plane/configuration/guide/sec_ip_entry_numbrng.html
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NAT Requirements, Objectives, and Interfaces
Before configuring NAT in your network, it is important to understand on which interfaces NAT will be configured and for what purposes. The requirements listed below would help you to decide on how to configure and use NAT:
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Restrictions for Configuring NAT for IP Address Conservation
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Information About Configuring NAT for IP Address Conservation
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Benefits of Configuring NAT for IP Address Conservation
NAT allows organizations to resolve the problem of IP address depletion when they have existing networks and need to access the Internet. Sites that do not yet possess network information center (NIC)-registered IP addresses must acquire them, and if more than 254 clients are present or planned, the scarcity of Class B addresses becomes a serious issue. Cisco IOS NAT addresses these issues by mapping thousands of hidden internal addresses to a range of easy-to-get Class C addresses.
Sites that already have registered IP addresses for clients on an internal network may want to hide those addresses from the Internet so that hackers cannot directly attack the clients. With client addresses are hidden, a degree of security is established. Cisco IOS NAT gives LAN administrators complete freedom to expand Class A addressing, which is drawn from the reserve pool of the Internet Assigned Numbers Authority (RFC 1597). This expansion occurs within the organization without the concern for addressing changes at the LAN or Internet interface.
Cisco IOS software can selectively or dynamically perform NAT. This flexibility allows the network administrator to use a mix of RFC 1597 and RFC 1918 addresses or registered addresses. NAT is designed for use on a variety of routers for IP address simplification and conservation. In addition, Cisco IOS NAT allows the selection of internal hosts that are available for NAT.
A significant advantage of NAT is that it can be configured without requiring any changes to hosts or routers other than those few routers on which NAT will be configured.
Purpose of NAT
Two key problems facing the Internet are the depletion of IP address space and the scaling in routing. NAT is a feature that allows the IP network of an organization to appear, from the outside, to use a different IP address space than what it is actually using. Thus, NAT allows an organization with nonglobally routable addresses to connect to the Internet by translating those addresses into a globally routable address space. NAT also allows a graceful renumbering strategy for organizations that are changing service providers or voluntarily renumbering into classless interdomain routing (CIDR) blocks. NAT is described in RFC 1631.
Beginning with Cisco IOS Release 12.1(5)T, NAT supports all H.225 and H.245 message types, including FastConnect and Alerting as part of the H.323 version 2 specification. Any product that makes use of these message types will be able to pass through a Cisco IOS NAT configuration without any static configuration. Full support for NetMeeting Directory (Internet Locator Service) is also provided through Cisco IOS NAT.
How NAT Works
A router configured with NAT will have at least one interface to the inside network and one to the outside network. In a typical environment, NAT is configured at the exit router between a stub domain and the backbone. When a packet is leaving the domain, NAT translates the locally significant source address into a globally unique address. When a packet is entering the domain, NAT translates the globally unique destination address into a local address. If more than one exit point exists, each NAT must have the same translation table. If the software cannot allocate an address because it has run out of addresses, it drops the packet and sends an Internet Control Message Protocol (ICMP) host unreachable packet.
Uses of NAT
NAT can be used in the following scenarios:
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NAT Inside and Outside Addresses
The term inside in a NAT context refers to networks owned by an organization that must be translated. When NAT is configured, hosts within this network will have addresses in one space (knows as the local address space) that will appear to those outside the network as being in another space (known as the global address space).
Similarly, outside refers to those networks to which the stub network connects, and which are generally not under the control of the organization. Hosts in outside networks can also be subject to translation, and thus have local and global addresses.
NAT uses the following definitions:
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Inside Source Address Translation
You can translate your own IP addresses into globally unique IP addresses when communicating outside of your network. You can configure static or dynamic inside source translation as follows:
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In Cisco IOS Release 15.1(3)T and later releases, when you configure the traceroute command, NAT returns the same inside global IP address for all inside local IP addresses.
Figure 1 illustrates a router that is translating a source address inside a network to a source address outside the network.
Figure 1 NAT Inside Source Translation
The following process describes inside source address translation, as shown in Figure 1:
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Host 10.1.1.1 receives the packet and continues the conversation. The router performs Steps 2 through 5 for each packet.
Inside Global Addresses Overloading
You can conserve addresses in the inside global address pool by allowing the router to use one global address for many local addresses. When this overloading is configured, the router maintains enough information from higher-level protocols (for example, TCP or UDP port numbers) to translate the global address back to the correct local address. When multiple local addresses map to one global address, the TCP or UDP port numbers of each inside host distinguish between the local addresses.
Figure 2 illustrates NAT operation when one inside global address represents multiple inside local addresses. The TCP port numbers act as differentiators.
Figure 2 NAT Overloading Inside Global Addresses
The router performs the following process in overloading inside global addresses, as shown in Figure 2. Both host B and host C believe that they are communicating with a single host at address 2.2.2.2. They are actually communicating with different hosts; the port number is the differentiator. In fact, many inside hosts could share the inside global IP address by using many port numbers.
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Host 10.1.1.1 receives the packet and continues the conversation. The router performs Steps 2 through 5 for each packet.
Types of NAT
NAT operates on a router—generally connecting only two networks—and translates the private (inside local) addresses within the internal network into public (inside global) addresses before any packets are forwarded to another network. This functionality gives you the option to configure NAT so that it will advertise only a single address for your entire network to the outside world. Doing this effectively hides the internal network from the world, giving you some additional security.
NAT types include:
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Address Translation of Overlapping Networks
NAT is used to translate your IP addresses, if your IP addresses are not legal or officially assigned IP addresses. Perhaps you chose IP addresses that officially belong to another network. When an IP address is used both illegally and legally, it is called index overlapping. You can use NAT to translate inside addresses that overlap with outside addresses.
Figure 3 shows how NAT translates overlapping networks.
Figure 3 NAT Translating Overlapping Addresses
The router performs the following tasks when translating overlapping addresses:
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The router examines every DNS reply from everywhere, ensuring that the IP address is not in the stub network. If it is, the router translates the address.
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NAT Virtual Interface Design
The NVI feature allows NAT traffic flows on the virtual interface, eliminating the need to specify inside and outside domains. When a domain is specified, the translation rules are applied either before or after the route decisions depending on the traffic flow from inside to outside or outside to inside. The translation rules are applied only after the route decision for an NVI.
When a NAT pool is shared for translating packets from multiple networks connected to a NAT router, an NVI is created and a static route is configured that forwards all packets addressed to the NAT pool to the NVI. The standard interfaces connected to the various networks will be configured to identify that the traffic originating from and received on the interfaces needs to be translated.
Figure 4 shows a typical NVI configuration.
Figure 4 NAT Virtual Interface Typical Configuration
NAT Virtual Interface has the following benefits:
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TCP Load Distribution for NAT
Your organization may have multiple hosts that must communicate with a heavily used host. Using NAT, you can establish a virtual host on the inside network that coordinates load sharing among real hosts. DAs that match an access list are replaced with addresses from a rotary pool. Allocation is done on a round-robin basis, and only when a new connection is opened from the outside to the inside. Non-TCP traffic is passed untranslated (unless other translations are in effect). Figure 5 illustrates this feature.
Figure 5 NAT TCP Load Distribution
The router performs the following process when translating rotary addresses:
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The next connection request will cause the router to allocate 10.1.1.2 for the inside local address.
Route Map Overview
For NAT, a route map must be processed instead of an access list. A route map allows you to match any combination of access list, next hop IP address, and output interface to determine which pool to use. The ability to use route maps with static translations enables the NAT multihoming capability with static address translations. Multihomed internal networks can host common services such as the Internet and DNS, which are accessed from different outside networks. NAT processes route map-based mappings in lexicographical order. When static NAT and dynamic NAT are configured with route maps that share the same name, static NAT is given precedence over dynamic NAT. In order to ensure the precedence of static NAT over dynamic NAT, you can either configure the route map associated with static NAT and dynamic NAT to share the same name, or configure the static NAT route map name so that it is lexicographically lower than that of the dynamic NAT route map name.
Benefits of Using Route Maps for Address Translation are the following:
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Public Wireless LAN
A public wireless LAN provides users of mobile computing devices with wireless connections to a public network, such as the Internet.
RADIUS
RADIUS is a distributed client/server system that secures networks against unauthorized access. Communication between a network access server (NAS) and a RADIUS server is based on the UDP. Generally, the RADIUS protocol is considered a connectionless service. Issues related to server availability, retransmission, and timeouts are handled by the RADIUS-enabled devices rather than the transmission protocol.
RADIUS is a client/server protocol. The RADIUS client is typically a NAS, and the RADIUS server is usually a daemon process running on a UNIX or Windows NT machine. The client passes user information to designated RADIUS servers and acts on the response that is returned. RADIUS servers receive user connection requests, authenticate the user, and then return the configuration information necessary for the client to deliver service to the user. A RADIUS server can act as a proxy client to other RADIUS servers or other kinds of authentication servers.
Denial-of-Service Attacks
A denial-of-service (DoS) attack typically involves the misuse of standard protocols or connection processes with the intent to overload and disable a target, such as a router or web server. DoS attacks can come from a malicious user or from a computer infected with a virus or worm. When the attack comes from many different sources at once, such as when a virus or worm has infected many computers, it is known as a distributed denial-of-service (DDoS) attack. Such DDoS attacks can spread rapidly and involve thousands of systems.
Viruses and Worms That Target NAT
Viruses and worms are programs designed to attack computer and networking equipment. Although viruses are typically embedded in discrete applications and run only when executed, worms self-propagate and can quickly spread on their own. Although a specific virus or worm may not expressly target NAT, it might use NAT resources to propagate itself. The Rate Limiting NAT Translation feature can be used to limit the impact of viruses and worms that originate from specific hosts, access control lists, and VRF instances.
How to Configure NAT for IP Address Conservation
The tasks described in this section configure NAT for IP address conservation. At least one of the tasks must be performed. More than one of the tasks may be needed.
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Configuring Inside Source Addresses
Inside source address can be configured for static or dynamic translations. Perform one of the following tasks depending on your requirements:
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Configuring Static Translation of Inside Source Addresses
Configure static translation of inside source addresses when you want to allow one-to-one mapping between your inside local address and an inside global address. Static translation is useful when a host on the inside must be accessible by a fixed address from the outside.
Prior to Cisco IOS Release 15.1(1)T, if the static inside source address matched the inside global address, the output of the show ip aliases command displayed only the static inside source address. In Cisco IOS Release 15.1(1)T and later releases, if the static inside source address matches the inside global address, the output of the show ip aliases command displays both the addresses. The static inside source address is displayed as an interface address and the inside global address is displayed as a dynamic address.
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Configuring Dynamic Translation of Inside Source Addresses
Dynamic translation establishes a mapping between an inside local address and a pool of global addresses. Dynamic translation is useful when multiple users on a private network need to access the Internet. The dynamically configured pool IP address may be used as needed and is released for use by other users when access to the Internet is no longer required.
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Allowing Internal Users Access to the Internet
Perform this task to allow your internal users access to the Internet and conserve addresses in the inside global address pool using overloading of global addresses.
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Configuring Address Translation Timeouts
This section describes how to change the default translation timeout when overloading is configured and not configured. You can use the configuration that is applicable to your specific NAT configuration.
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Changing the Translation Timeout
By default, dynamic address translations time out after some period of nonuse. You can change the default values on timeouts, if necessary. When overloading is not configured, simple translation entries time out after 24 hours. Configure the ip nat translation timeout seconds commands to change the timeout value for dynamic address translations that do not use overloading.
Changing the Timeouts When Overloading Is Configured
If you have configured overloading, you have more control over translation entry timeouts, because each entry contains more context about the traffic using it. To change timeouts on extended entries, use the following commands as needed.
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Allowing Overlapping Networks to Communicate Using NAT
The tasks in this section are grouped because they perform the same action but are executed differently depending on the type of translation that is implemented—static or dynamic:
Perform the task that applies to the translation type that is implemented.
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Configuring Static Translation of Overlapping Networks
Configure static translation of overlapping networks if your IP addresses in the stub network are legitimate IP addresses belonging to another network and you want to communicate with those hosts or routers using static translation.
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What to Do Next
When you have completed the required configuration, go to the "Monitoring and Maintaining NAT" module.
Configuring Dynamic Translation of Overlapping Networks
Configure dynamic translation of overlapping networks if your IP addresses in the stub network are legitimate IP addresses belonging to another network and you want to communicate with those hosts or routers using dynamic translation.
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Configuring the NAT Virtual Interface
The NAT Virtual Interface (NVI) feature removes the requirement to configure an interface as either NAT inside or NAT outside. An interface can be configured to use or not use NAT.
This section contains the following procedure:
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Enabling a Dynamic NAT Virtual Interface
Perform this task to enable a dynamic NVI.
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Enabling a Static NAT Virtual Interface
Perform this task to enable a static NVI.
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Translating Rotary Addresses
Perform this task to configure server TCP load balancing by way of destination address rotary translation. The commands specified in the task allow you to map one virtual host to many real hosts. Each new TCP session opened with the virtual host will be translated into a session with a different real host.
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Enabling Route Maps on Inside Interfaces
Perform this task to use route maps for address translation decisions.
Prerequisites
All route maps required for use with this task should be configured before you begin the configuration task.
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Enabling NAT Route Maps Outside-to-Inside Support
The NAT Route Maps Outside-to-Inside Support feature enables the deployment of a NAT route map configuration that will allow IP sessions to be initiated from the outside to the inside. Perform this task to enable the NAT Route Maps Outside-to-Inside Support feature.
An initial session from inside-to-outside is required to trigger a NAT. New translation sessions can then be initiated from outside to the inside host that triggered the initial translation.
When route maps are used to allocate global addresses, the global address can allow return traffic, and the return traffic is allowed only if it matches the defined route map in the reverse direction. No additional entries are created to allow the return traffic for a route-map-based dynamic entry unless the reversible keyword is used with the ip nat inside source command.
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Configuring NAT of External IP Addresses Only
When you configure NAT of external IP addresses, NAT can be configured to ignore all embedded IP addresses for any application and traffic type. Traffic between a host and the traffic outside an enterprise's network flows through the internal network. A router configured for NAT translates the packet to an address that can be routed inside the internal network. If the intended destination is outside an enterprise's network, the packet gets translated back to an external address and is sent out.
Benefits of Configuring NAT of External IP Addresses Only are:
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Forwarding Packets from Outside to Inside Local Address
The NAT Default Inside Server feature helps forward packets from the outside to a specified inside local address. Traffic that does not match any existing dynamic translations or static port translations is redirected, and the packets are not dropped. For online games, outside traffic comes on a different UDP.
Dynamic mapping and interface overload can be configured for the PC traffic and also for the gaming device. If a packet is destined for the 806 interface from outside an enterprise's network and there no match in the NAT table for the fully extended entry or the static port entry, the packet is forwarded to the gaming device using a simple static entry.
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Reenabling RTSP on a NAT Router
The Real Time Streaming Protocol (RTSP) is a client/server multimedia presentation control protocol that supports multimedia application delivery. Some of the applications that use RTSP include Windows Media Services (WMS) by Microsoft, QuickTime by Apple Computer, and RealSystem G2 by RealNetworks.
When the RTSP protocol passes through a NAT router, the embedded address and port must be translated in order for the connection to be successful. NAT uses Network Based Application Recognition (NBAR) architecture to parse the payload and translate the embedded information in the RTSP payload.
RTSP is enabled by default. Use the ip nat service rtsp port port-number command to re-enable RTSP on a NAT router if this configuration has been disabled.
Configuring Static IP Support
Configuring support for users with static IP addresses enables those users to establish an IP session in a public wireless LAN environment.
The NAT Static IP Support feature extends the capabilities of public wireless LAN providers to support users configured with a static IP address. By configuring a router to support users with a static IP address, public wireless LAN providers extend their services to a greater number of potential users, which can lead to greater user satisfaction and additional revenue.
Users with static IP addresses can use services of the public wireless LAN provider without changing their IP address. NAT entries are created for static IP clients and a routable address is provided.
Perform this task to configure the NAT Static IP Support feature.
Prerequisites
Before configuring support for users with static IP addresses for NAT, you must first enable NAT on your router and configure a RADIUS server host. For additional information on NAT and RADIUS configuration, see the "Related Documents" section.
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Examples
The following is sample output from the show ip nat translations verbose command:
Router# show ip nat translations verbose--- 172.16.0.0 10.1.1.1 --- ---create 00:05:59, use 00:03:39, left 23:56:20, Map-Id(In): 1, flags: none wlan-flags: Secure ARP added, Accounting Start sent Mac-Address:0010.7bc2.9ff6 Input-IDB:Ethernet1/2, use_count: 0, entry-id:7, lc_entries: 0Configuring Support for ARP Ping
When the static IP client's NAT entry times out, the NAT entry and the secure ARP entry associations are deleted for the client. Reauthentication with the Service Selection Gateway (SSG) is needed for the client to reestablish WLAN services. The ARP Ping feature enables the NAT entry and the secure ARP entry to not be deleted when the static IP client exists in the network where the IP address is unchanged after authentication.
An ARP ping is necessary to determine static IP client existence and to restart the NAT entry timer.
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Limiting the Number of Concurrent NAT Operations
Limiting the number of concurrent NAT operations using the Rate Limiting NAT Translation feature provides users more control over how NAT addresses are used. The Rate Limiting NAT Translation feature can be used to limit the effects of viruses, worms, and denial-of-service attacks.
Because NAT is a CPU-intensive process, router performance can be adversely affected by denial-of-service attacks, viruses, and worms that target NAT. The Rate Limiting NAT Translation feature allows you to limit the maximum number of concurrent NAT requests on a router.
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Configuration Examples for Configuring NAT for IP Address Conservation
This section provides the following configuration examples:
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Example: Configuring Static Translation of Inside Source Addresses
The following example translates between inside hosts addressed from the 10.114.11.0 network to the globally unique 172.31.233.208/28 network. Further packets from outside hosts addressed from the 10.114.11.0 network (the true 10.114.11.0 network) are translated to appear to be from the 10.0.1.0/24 network.
ip nat pool net-208 172.31.233.208 172.31.233.223 prefix-length 28ip nat pool net-10 10.0.1.0 10.0.1.255 prefix-length 24ip nat inside source list 1 pool net-208ip nat outside source list 1 pool net-10!interface ethernet 0ip address 172.31.232.182 255.255.255.240ip nat outside!interface ethernet 1ip address 10.114.11.39 255.255.255.0ip nat inside!access-list 1 permit 10.114.11.0 0.0.0.255The following example shows NAT configured on the provider edge (PE) router with a static route to the shared service for the vrf1 and vrf2 VPNs. NAT is configured as inside source static one-to-one translation.
ip nat pool outside 10.4.4.1 10.4.4.254 netmask 255.255.255.0ip nat outside source list 1 pool mypoolaccess-list 1 permit 172.16.18.0 0.0.0.255ip nat inside source static 192.168.121.33 10.2.2.1 vrf vrf1ip nat inside source static 192.169.121.33.10.2.2.2 vrf vrf2Example: Configuring Dynamic Translation of Inside Source Addresses
The following example translates between inside hosts addressed from either the 192.168.1.0 or 192.168.2.0 network to the globally unique 172.31.233.208/28 network:
ip nat pool net-208 172.31.233.208 172.31.233.223 prefix-length 9ip nat inside source list 1 pool net-208!interface ethernet 0ip address 172.31.232.182 255.255.255.240ip nat outside!interface ethernet 1ip address 192.168.1.94 255.255.255.0ip nat inside!access-list 1 permit 192.168.1.0 0.0.0.255access-list 1 permit 192.168.2.0 0.0.0.255The following example translates only traffic local to the provider edge device running NAT (NAT-PE):
ip nat inside source list 1 interface e 0 vrf vrf1 overloadip nat inside source list 1 interface e 0 vrf vrf2 overload!ip route vrf vrf1 0.0.0.0 0.0.0.0 192.168.1.1ip route vrf vrf2 0.0.0.0 0.0.0.0 192.168.1.1!access-list 1 permit 10.1.1.1.0 0.0.0.255!ip nat inside source list 1 interface e 1 vrf vrf1 overloadip nat inside source list 1 interface e 1 vrf vrf2 overload!ip route vrf vrf1 0.0.0.0 0.0.0.0 172.16.1.1 globalip route vrf vrf2 0.0.0.0 0.0.0.0 172.16.1.1 globalaccess-list 1 permit 10.1.1.0 0.0.0.255Example: Overloading Inside Global Addresses
The following example creates a pool of addresses named net-208. The pool contains addresses from 172.31.233.208 to 172.31.233.233. Access list 1 allows packets having the SA from 192.168.1.0 to 192.168.1.255. If no translation exists, packets matching access list 1 are translated to an address from the pool. The router allows multiple local addresses (192.168.1.0 to 192.168.1.255) to use the same global address. The router retains port numbers to differentiate the connections.
ip nat pool net-208 172.31.233.208 172.31.233.233 netmask 255.255.255.240ip nat inside source list 1 pool net-208 overload!interface serial 0ip address 172.31.232.182 255.255.255.240ip nat outside!interface ethernet 0ip address 192.168.1.94 255.255.255.0ip nat inside!access-list 1 permit 192.168.1.0 0.0.0.255Example: Translating Overlapping Address
In the following example, the addresses in the local network are being used legitimately by someone else on the Internet. An extra translation is required to access that external network. Pool net-10 is a pool of outside local IP addresses. The ip nat outside source list 1 pool net-10 statement translates the addresses of hosts from the outside overlapping network to addresses in that pool.
ip nat pool net-208 172.31.233.208 172.31.233.223 prefix-length 28ip nat pool net-10 10.0.1.0 10.0.1.255 prefix-length 24ip nat inside source list 1 pool net-208ip nat outside source list 1 pool net-10!interface serial 0ip address 172.31.232.192 255.255.255.240ip nat outside!interface ethernet0ip address 192.168.1.94 255.255.255.0ip nat inside!access-list 1 permit 192.168.1.0 0.0.0.255Example: Enabling NAT Virtual Interface
The following example shows how to configure NAT virtual interfaces without the use of inside or outside source addresses:
interface Ethernet 0/0ip vrf forwarding bankip address 192.168.122.1 255.255.255.0ip nat enable!interface Ethernet 1/0ip vrf forwarding parkip address 192.168.122.1 255.255.255.0ip nat enable!interface Serial 2/0ip vrf forwarding servicesip address 192.168.123.2 255.255.255.0ip nat enable!ip nat pool NAT 192.168.25.20 192.168.25.30 netmask 255.255.255.0 add-routeip nat source list 1 pool NAT vrf vrf1 overloadip nat source list 1 pool NAT vrf vrf2 overloadip nat source static 192.168.123.1 192.168.125.10 vrf services!access-list 1 permit 192.168.122.20access-list 1 permit 192.168.122.0 0.0.0.255!Example: Avoiding Server Overload Using Load Balancing
In the following example, the goal is to define a virtual address, connections to which are distributed among a set of real hosts. The pool defines the addresses of the real hosts. The access list defines the virtual address. If a translation does not already exist, TCP packets from serial interface 0 (the outside interface) whose destination matches the access list are translated to an address from the pool.
ip nat pool real-hosts 192.168.15.2 192.168.15.15 prefix-length 28 type rotaryip nat inside destination list 2 pool real-hosts!interface serial 0ip address 192.168.15.129 255.255.255.240ip nat outside!interface ethernet 0ip address 192.168.15.17 255.255.255.240ip nat inside!access-list 2 permit 192.168.15.1Example: Enabling NAT Route Mapping
The following example shows the use of route mapping with static NATs:
interface Ethernet3ip address 172.18.1.100 255.255.255.0ip nat outsidemedia-type 10BaseT!interface Ethernet4ip address 192.168.1.100 255.255.255.0ip nat outsidemedia-type 10BaseT!interface Ethernet5ip address 110.1.1.100 255.255.255.0ip nat insideip policy route-map isp1media-type 10BaseT!router ripnetwork 172.18.0.0network 192.168.1.0!ip nat inside source static 10.1.1.2 192.168.1.21 route-map isp2ip nat inside source static 10.1.1.2 172.18.1.21 route-map isp1ip nat inside source static 10.1.1.1 192.168.1.11 route-map isp2ip nat inside source static 10.1.1.1 172.18.1.11 route-map isp1access-list 101 permit ip 10.1.1.0 0.0.0.255 172.16.0.0 0.255.255.255access-list 102 permit ip 10.1.1.0 0.0.0.255 192.168.0.0 0.255.255.255!route-map isp2 permit 10match ip address 102set ip next-hop 192.168.1.1!route-map isp1 permit 10match ip address 101set ip next-hop 172.18.1.1Example: Enabling NAT Route Maps Outside-to-Inside Support
The following example shows how to configure route map A and route map B to allow outside-to-inside translation for a destination-based NAT:
ip nat pool POOL-A 10.1.10.1 10.1.10.126 netmask 255.255.255.128ip nat pool POOL-B 10.1.20.1 10.1.20.126 netmask 255.255.255.128ip nat inside source route-map MAP-A pool POOL-A reversibleip nat inside source route-map MAP-B pool POOL-B reversible!ip access-list extended ACL-Apermit ip any 10.1.10.128 0.0.0.127ip access-list extended ACL-Bpermit ip any 10.1.20.128 0.0.0.127!route-map MAP-A permit 10match ip address ACL-A!route-map MAP-B permit 10match ip address ACL-BThe following example shows how to configure route map R1 to allow outside-to-inside translation for static NAT:
ip nat inside source static 10.1.1.1 10.2.2.2 route-map R1 reversible!ip access-list extended ACL-Apermit ip any 10.1.10.128 0.0.0.127route-map R1 permit 10match ip address ACL-AExample: Configuring NAT Translation of External IP Addresses Only
The following example shows how to translate the packet to an address that is able to be routed inside the internal network:
interface ethernet 3ip address 10.1.1.1 255.255.255.0ip nat outsideno ip mroute-cachemedia-type 10BaseT!interface Ethernet4ip address 192.168.15.1 255.255.255.0ip nat insideno ip mroute-cachemedia-type 10BaseT!router ripnetwork 10.0.0.0Network 192.168.15.0!ip nat outside source static network 10.1.1.0 192.168.251.0/24 no-payload!ip route 10.1.1.0 255.255.255.0 Ethernet4ip route 10.1.1.0 255.255.255.0 Ethernet3Configuration Examples for NAT Static IP Support
This section provides the following configuration examples:
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Example: Configuring NAT Static IP Support
The following example shows how to enable static IP address support for the router at 192.168.196.51:
interface ethernet 1ip nat insideip nat allow-static-hostip nat pool net-208 172.16.1.1 172.16.1.10 netmask 255.255.255.0 accounting WLAN-ACCTip nat inside source list 1 pool net-208access-list 1 deny ip 192.168.196.51Example: Creating a RADIUS Profile for NAT Static IP Support
The following example shows how to create a RADIUS profile for use with the NAT Static IP Support feature:
aaa new-model
!
aaa group server radius WLAN-RADIUS
server 172.16.88.1 auth-port 1645 acct-port 1645
server 172.16.88.1 auth-port 1645 acct-port 1646
!
aaa accounting network WLAN-ACCT start-stop group WLAN-RADIUS
aaa session-id common
ip radius source-interface Ethernet3/0
radius-server host 172.31.88.1 auth-port 1645 acct-port 1646
radius-server key cisco
Configuration Examples for Limiting the Number of Concurrent NAT Operations
This section provides the following configuration examples:
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Example: Setting a Global NAT Rate Limit
The following example shows how to limit the maximum number of allowed NAT entries to 300:
ip nat translation max-entries 300Example: Setting NAT Rate Limits for a Specific VRF Instance
The following example shows how to limit the VRF instance named "vrf1" to 150 NAT entries:
ip nat translation max-entries vrf vrf1 150Example: Setting NAT Rate Limits for All VRF Instances
The following example shows how to limit each VRF instance to 200 NAT entries:
ip nat translation max-entries all-vrf 200The following example shows how to limit the VRF instance named "vrf2" to 225 NAT entries, but limit all other VRF instances to 100 NAT entries each:
ip nat translation max-entries all-vrf 100ip nat translation max-entries vrf vrf2 225Example: Setting NAT Rate Limits for Access Control Lists
The following example shows how to limit the access control list named "vrf3" to 100 NAT entries:
ip nat translation max-entries list vrf3 100Example: Setting NAT Rate Limits for an IP Address
The following example shows how to limit the host at IP address 10.0.0.1 to 300 NAT entries:
ip nat translation max-entries host 10.0.0.1 300Where to Go Next
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Additional References
Related Documents
Cisco IOS commands
NAT commands: complete command syntax, command mode command history, defaults, usage guidelines, and examples
Application Level Gateways
IP Access List Sequence Numbering
IP Access List Sequence Numbering document
NAT on a Stick technology note
NAT maintenance
"Monitoring and Maintaining NAT" module
RADIUS attributes overview
"RADIUS Attributes Overview and RADIUS IETF Attributes" module
Using Hot Standby Router Protocol (HSRP) and Stateful NAT (SNAT) for high availability
Using NAT with MPLS VPNs
"Integrating NAT with MPLS VPNs" module
Standards
MIBs
None
To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:
RFCs
Technical Assistance
Feature Information for Configuring NAT for IP Address Conservation
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 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.
Note
Table 1 Feature Information for Configuring NAT for IP Address Conservation
Configuring Support for ARP Ping in a Public Wireless LAN
12.4(6)T
The ARP Ping feature enables the NAT entry and the secure ARP entry to not be deleted when the static IP client exists in the network where the IP address is unchanged after authentication.
The following section provides information about this feature:
NAT Ability to Use Route Maps with Static Translation
12.2.(4)T
The NAT Ability to Use Route Maps with Static Translation feature provides a dynamic translation command that can specify a route map to be processed instead of an access list. A route map allows you to match any combination of access list, next-hop IP address, and output interface to determine which pool to use. The ability to use route maps with static translations enables NAT multihoming capability with static address translations.
The following section provides information about this feature:
NAT Default Inside Server
12.3(13)T
The NAT Default Inside Server feature provides for the need to forward packets from the outside to a specified inside local address.
The following section provides information about this feature:
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NAT Route Maps Outside-to-Inside Support
12.2(33)SXI5
12.3(14)TThe NAT Route Maps Outside-to-Inside Support feature enables the deployment of a NAT route map configuration that will allow IP sessions to be initiated from the outside to the inside.
The following sections provide information about this feature:
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NAT RTSP Support Using NBAR
12.3(7)T
The Real Time Streaming Protocol (RTSP) is a client/server multimedia presentation control protocol that supports multimedia application delivery. Applications that use RTSP include Windows Media Services (WMS) by Microsoft, QuickTime by Apple Computer, and RealSystem G2 by RealNetworks.
The following section provides information about this feature:
NAT Static and Dynamic Route Map Name-Sharing
15.0(1)M
The NAT Static and Dynamic Route Map Name-Sharing feature provides the ability to configure static and dynamic NAT to share the same route map name, while enforcing precedence of static NAT over dynamic NAT.
The following section provides information about this feature:
NAT Static IP Support
12.3(7)T
The NAT Static IP Support feature provides support for users with static IP addresses, enabling those users to establish an IP session in a public wireless LAN environment.
The following sections provide information about this feature:
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NAT Translation of External IP Addresses Only
12.2(4)T
12.2(4)T2
15.0(1)SYou can use the NAT Translation of External IP Addresses Only feature, NAT can be configured to ignore all embedded IP addresses for any application and traffic type.
The following sections provide information about this feature:
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NAT Virtual Interface
12.3(14)T
The NAT Virtual Interface feature removes the requirement to configure an interface as either Network Address Translation (NAT) inside or NAT outside. An interface can be configured to use NAT or not use NAT.
The following sections provide information about this feature:
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Rate Limiting NAT Translation
12.3(4)T
15.0(1)SThe Rate Limiting NAT Translation feature provides the ability to limit the maximum number of concurrent Network Address Translation (NAT) operations on a router. In addition to giving users more control over how NAT addresses are used, the Rate Limiting NAT Translation feature can be used to limit the effects of viruses, worms, and denial-of-service attacks.
The following sections provide information about this feature:
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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.
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