A self IP address is an IP address on the BIG-IP^® system that you associate with a VLAN, to access hosts in that VLAN. By virtue of its netmask, a self IP address represents an address space, that is, a range of IP addresses spanning the hosts in the VLAN, rather than a single host address. You can associate self IP addresses not only with VLANs, but also with VLAN groups.

Self IP addresses serve two purposes:

• First, when sending a message to a destination server, the BIG-IP system uses the self IP addresses of its VLANs to determine the specific VLAN in which a destination server resides. For example, if VLAN internal has a self IP address of 10.10.10.100, with a netmask of 255.255.255.0, and the destination server’s IP address is 10.10.10.20 (with a netmask of 255.255.255.255), the BIG-IP system recognizes that the server’s IP address falls within the range of VLAN internal’s self IP address, and therefore sends the message to that VLAN. More specifically, the BIG-IP system sends the message to the interface that you assigned to that VLAN. If more than one interface is assigned to the VLAN, the BIG-IP system takes additional steps to determine the correct interface, such as checking the Layer2 forwarding table.
• Second, a self IP address can serve as the default route for each destination server in the corresponding VLAN. In this case, the self IP address of a VLAN appears as the destination IP address in the packet header when the server sends a response to the BIG-IP system.

You normally assign self IP addresses to a VLAN when you initially run the Setup utility on a BIG-IP system. More specifically, you assign one static self IP address and one floating self IP address to each of the default VLANs (internal and external). Later, using the BIG-IP Configuration utility, you can create self IP addresses for other VLANs that you create.

Self IP addresses reside in administrative partitions/folders and are associated with traffic groups. The self IP addresses that you create when you run the Setup utility reside in partition Common (that is folder /Common).

There are two types of self IP addresses that you can create:

• A static self IP address is an IP address that the BIG-IP^® system does not share with another BIG-IP system. Any self IP address that you assign to the default traffic group traffic-group-local-only is a static self IP address.
• A floating self IP address is an IP address that two BIG-IP systems share. Any self IP address that you assign to the default traffic group traffic-group-1 is a floating self IP address.

For each self IP address that you create for a VLAN, the BIG-IP^® system automatically assigns a media access control (MAC) address.

As an alternative, you can globally configure the BIG-IP system to assign the same MAC address to all VLANs. This feature is useful if your network includes a type of switch that does not keep a separate Layer 2 forwarding table for each VLAN on that switch.

When you configure the BIG-IP^® system to manage local area traffic, you can implement a feature known as a secure network address translation (SNAT). A SNAT is an object that causes the BIG-IP system to translate the original source IP address of a packet to an IP address that you specify. A SNAT ensures that the target server sends its response back through the BIG-IP system rather than to the original client IP address directly.

When you create a SNAT, you can configure the BIG-IP system to automatically choose a translation address. This ability of the BIG-IP system to automatically choose a translation address is known as SNAT automapping, and in this case, the translation address that the system chooses is always an existing self IP address. Thus, for traffic going from the BIG-IP system to a destination server, configuring SNAT automapping ensures that the source IP address in the header of a packet is a self IP address.

When you create an automapped SNAT, the BIG-IP system actually creates a SNAT pool consisting of the system’s internal self IP addresses, and then uses an algorithm to select and assign an address from that SNAT pool.

It is when you initially run the Setup utility on a BIG-IP^® system that you normally create any static and floating self IP addresses and assign them to VLANs. However, if you want to create additional self IP addresses later, you can do so using the BIG-IP Configuration utility.

1. On the Main tab, click Network > Self IPs .
2. Click Create.
   The New Self IP screen opens.
3. In the Name field, type a unique name for the self IP address.
4. In the IP Address field, type an IPv4 or IPv6 address.
   This IP address should represent the address space of the VLAN that you specify with the VLAN/Tunnel setting.
5. In the Netmask field, type the full network mask for the specified IP address.
6. From the VLAN/Tunnel list, select the VLAN to associate with this self IP address.
   • On the internal network, select the internal or high availability VLAN that is associated with an internal interface or trunk.
   • On the external network, select the external VLAN that is associated with an external interface or trunk.
7. From the Port Lockdown list, select Allow Default.
8. For the Traffic Group setting, choose one of the following actions:

   Action	Result
   Retain the default setting, traffic-group-local-only (non-floating).	The system creates a non-floating self IP address that becomes a member of traffic-group-local-only.
   Select the check box labeled Inherit traffic group from current partition / path.	The system creates a floating self IP address that becomes a member of traffic-group-1.
   Select a traffic group from the Traffic Group list.	The system creates a floating self IP address that becomes a member of the selected traffic group.

9. From the Service Policy list, retain the default value of None, or select a policy to associate with the self IP address.
   A service policy contains a timer policy, which defines custom timeouts for matched traffic types.
10. Click Finished.
    The screen refreshes, and displays the new self IP address.

1. On the Main tab, click Network > Self IPs .
2. Click Create.
   The New Self IP screen opens.
3. In the IP Address field, type an IPv4 or IPv6 address.
   This IP address should represent the address space of the VLAN group that you specify with the VLAN/Tunnel setting.
4. In the Netmask field, type the network mask for the specified IP address.

   For example, you can type 255.255.255.0.

5. From the VLAN/Tunnel list, select the VLAN group with which to associate this self IP address.
6. From the Port Lockdown list, select Allow Default.
7. For the Traffic Group setting, choose one of the following actions:

   Action	Result
   Retain the default setting, traffic-group-local-only (non-floating).	The system creates a non-floating self IP address that becomes a member of traffic-group-local-only.
   Select the check box labeled Inherit traffic group from current partition / path.	The system creates a floating self IP address that becomes a member of traffic-group-1.
   Select a traffic group from the Traffic Group list.	The system creates a floating self IP address that becomes a member of the selected traffic group.

8. Click Finished.
   The screen refreshes, and displays the new self IP address.