Manual Chapter : Using NAT44 to Translate IPv4 Addresses

Applies To:

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BIG-IP LTM

  • 15.0.1, 15.0.0, 14.1.0
Manual Chapter

Using NAT44 to Translate IPv4 Addresses

Overview: NAT44

For the BIG-IP system CGNAT module, NAT44 is the NAT type that maps IPv4 subscriber private addresses to IPv4 Internet public addresses. Translation addresses and ports are set in LSN pools. The CGNAT module performs NAT44 translations for all IP traffic.
Diagram of a NAT44 network
diagram of a NAT44 network

About CGNAT hairpinning

An optional feature on the BIG-IP system,
hairpinning
routes traffic from one subscriber's client to an external address of another subscriber's server, where both client and server are located in the same subnet. To each subscriber, it appears that the other subscriber's address is on an external host and on a different subnet. The BIG-IP system can recognize this situation and send, or hairpin, the message back to the origin subnet so that the message can reach its destination.
In order for hairpinning to function properly, the subscriber VLAN must be configured as an egress interface on the LSN pool. If the subscriber VLAN is not configured as an egress interface on the LSN pool, hairpinning fails.
At present hairpinning works with all BIG-IP CGNAT scenarios except NAT64.

Creating an LSN pool

The carrier-grade NAT (CGNAT) module must be enabled with the appropriate settings before you can create large-scale NAT (LSN) pools.
LSN pools are used by the CGNAT module to allow efficient configuration of translation prefixes and parameters.
  1. On the Main tab, click
    Carrier Grade NAT
    LSN Pools
    .
    The LSN Pool List screen opens.
  2. Click
    Create
    .
  3. In the
    Name
    field, type a unique name.
  4. In the Configuration area, for the
    Persistence Mode
    setting, select
    Address
    or
    Address Port
    .
  5. For the
    Member List
    setting, type an address and a prefix length in the
    Address/Prefix Length
    field, and click
    Add
    .
    If your pool uses deterministic mode, ensure that any address ranges you enter as a member do not overlap another member's prefix address ranges. For example, the address and prefix
    10.10.10.0/24
    overlaps
    10.10.10.0/23
    .
  6. Click
    Finished
    .

Creating a virtual server for an LSN pool

Virtual servers are matched based on source (client) addresses. Define a virtual server that references the CGNAT profile and the LSN pool.
  1. On the Main tab, click
    Carrier Grade NAT
    Virtual Servers
    .
    The Virtual Server List screen opens.
  2. Click
    Create
    .
    The New Virtual Server screen opens.
  3. In the
    Name
    field, type a unique name for the virtual server.
  4. From the
    Type
    list, select
    Performance (Layer 4)
    .
  5. For a network, in the
    Destination Address
    field, type an IPv4 or IPv6 address in CIDR format to allow all traffic to be translated.
    The supported format is address/prefix, where the prefix length is in bits. For example, an IPv4 address/prefix is
    0.0.0.0/0
    , and an IPv6 address/prefix is
    ::/0
    .
  6. In the
    Service Port
    field, type
    *
    or select
    * All Ports
    from the list.
  7. From the
    VLAN and Tunnel Traffic
    list, select
    Enabled on
    . Then, for the
    VLANs and Tunnels
    setting, move the VLAN or VLANs on which you want to allow the virtual servers to share traffic from the
    Available
    list to the
    Selected
    list.
  8. For the
    LSN Pool
    setting, select the pool that this server will draw on for translation addresses.
  9. In the Resources area of the screen, for the
    iRules
    setting, select the name of the iRule that you want to assign and using the Move button, move the name from the
    Available
    list to the
    Enabled
    list.
  10. Click
    Finished
    .
The custom CGNAT virtual server now appears in the CGNAT Virtual Servers list.

Configuring an ALG profile

An ALG profile provides the CGNAT module with protocol and service information to make specified packet modifications to the IP and TCP/UDP headers, as well as the payload during translation.
Edit only copies of the included ALG profiles to avoid unwanted propagation of settings to other profiles that use the included profiles as parents.
  1. On the Main tab, click
    Carrier Grade NAT
    ALG Profiles
    .
  2. In the ALG Profiles menu, click an ALG profile.
  3. Click
    Create
    .
    The New Profile screen opens.
  4. Type a name for the new profile.
  5. From the
    Parent Profile
    list, ensure that the correct parent profile is selected as the new profile.
  6. Select the
    Custom
    check box on the right.
  7. Configure the profile settings.
  8. Click
    Finished
    to save the new ALG profile.
You now have an ALG profile for use by CGNAT.

Configuring a CGNAT iRule

You create iRules to automate traffic forwarding for XML content-based routing. When a match occurs, an iRule event is triggered, and the iRule directs the individual request to an LSN pool, a node, or virtual server.
  1. On the Main tab, click
    Carrier Grade NAT
    iRules
    .
    The iRule List screen opens.
  2. Click
    Create
    .
  3. In the
    Name
    field, type a 1 to 31 character name, such as
    cgn_https_redirect_iRule
    .
  4. In the
    Definition
    field, type the syntax for the iRule using Tool Command Language (Tcl) syntax.
    For complete and detailed information about iRules syntax, see the F5 Networks DevCentral web site (
    http://devcentral.f5.com
    ).
  5. Click
    Finished
    .
You now have an iRule to use with a CGNAT virtual server.