Manual Chapter : Overview Configuring the BIG-IP system as a Layer 2 device with wildcard VLANs

Applies To:

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  • 15.0.1, 15.0.0, 14.1.2, 14.1.0, 14.0.1, 14.0.0
Manual Chapter

Overview: Configuring the BIG-IP system as a Layer 2 device with wildcard VLANs


To deploy a BIG-IP® system without making changes to other devices on your network, you can configure the system to operate strictly at Layer 2. By deploying a virtual wire configuration, you transparently add the device to the network without having to create self IP addresses or change the configuration of other network devices that the BIG-IP device is connected to.

A virtual wire logically connects two interfaces or trunks, in any combination, to each other, enabling the BIG-IP system to forward traffic from one interface to the other, in either direction. This type of configuration is typically used for security monitoring, where the BIG-IP system inspects ingress packets without modifying them in any way.

Important: The virtual wire feature is not available on systems provisioned for Virtual Clustered Multiprocessing (vCMP).

Sample configuration

This illustration shows a virtual wire configuration on the BIG-IP system. In this configuration, a VLAN group contains two VLANs tagged with VLAN ID 4096. Each VLAN is associated with a trunk, allowing the VLAN to accept all traffic for forwarding to the other trunk. Directly connected to a Layer 2 or 3 networking device, each interface or trunk of the virtual wire is attached to a wildcard VLAN, which accepts all ingress traffic. On receiving a packet, an interface of a virtual wire trunk forwards the frame to the other trunk and then to another network device.

Optionally, you can create a forwarding virtual server that applies a security policy to ingress traffic before forwarding the traffic to the other trunk.

Key points

There are a few key points to remember about virtual wire configurations in general:

  • An interface accepts packets in promiscuous mode, which means there is no packet modification.
  • The system bridges both tagged and untagged data.
  • Source MAC address learning is disabled.
  • Forwarding decisions are based on the ingress interface.
  • Neither VLANs nor MAC addresses change.
Note: VLAN double tagging is not supported in a virtual wire configuration.

About memory consumption

When you use the BIG-IP Layer 2 Transparency feature, the BIG-IP device switches the traffic at Layer 2, in the absence of any virtual server on the system that matches the traffic. In this case, the device maintains a "connection" state with a default age of 300 seconds. If the number of these connections is large, the BIG-IP device can experience high memory consumption.

To alleviate this, F5 recommends that you take one of the following actions:

  • Configure one or more matching virtual servers to handle all traffic.
  • If you are unaware of all traffic patterns, configure a wildcard virtual server instead, of type Forwarding (IP) or Performance (Layer 4). This enables the device to perform a connection close operation much more quickly and therefore mitigate high memory consumption.
  • Configure a lower threshold for the BigDB variable tm.l2forwardidletimeout.

Create BIG-IP objects for Layer 2 transparency

To configure the BIG-IP system as an inline device operating in Layer 2 transparency mode, you first need to create a virtual wire configuration object. Creating a virtual wire object causes the BIG-IP system to automatically perform these actions:

  • Create trunks for accepting all VLAN traffic, with Link Aggregation Protocol (LACP) enabled.
  • Set the trunk members (interfaces) to virtual wire mode.
  • Create two VLANs with tag 4096 that allow all Layer 2 ingress traffic.
  • Create a VLAN group to logically connect the VLANs.
Important: The virtual wire feature is not available on systems provisioned for Virtual Clustered Multiprocessing (vCMP).
  1. On the Main tab, click Network > Virtual Wire .
    This object appears on certain BIG-IP platforms only.
    The Virtual Wire screen opens.
  2. Click Create.
  3. In the Name field, type a name for the virtual wire object.
  4. On the right side of the screen, click the double-arrow symbol to expand the Shared Objects panel.
  5. Click within the Trunks heading area.
    This displays a list of existing trunks, and displays the + symbol for creating a trunk.
  6. Click the + symbol.
  7. In the Name field, type a name for the trunk, such as trunk_external or trunk_internal.
  8. In the Interfaces list, select the check boxes for the interfaces that you want to include in the trunk.
  9. From the LACP list, select Enabled.
    This enables the Link Aggregation Control Protocol (LACP) to monitor link availability within the trunk.
  10. Click Commit.
    If you do not see the Commit button, try using a different browser.
    This creates the trunk that you can specify as an interface when you complete the creation of the virtual wire object.
  11. Repeat steps 6 through 10 to create a second trunk.
  12. In the Member 1 column, from the Interfaces/Trunks list, select a trunk name, such as trunk_external.
  13. In the Member 2 column, from the Interfaces/Trunks list, select another trunk name, such as trunk_internal.
  14. In the VLAN Traffic Management Configuration column, for the Define VLANs list, use the default value of No.
  15. Click Done Editing.
  16. Click Commit Changes to System.
After you perform this task, the BIG-IP system contains a virtual wire object, two trunks, two VLANs, and a VLAN group.

Naming conventions for virtual wire-related objects

For virtual wire-related configuration objects, the BIG-IP system manages object naming in specific ways. See the following table for details.

Object type System-named? Naming convention
Virtual wire No User-defined
Trunk No User-defined
VLAN Yes virtual-wire-name_vlan_4096_member_number_xx
VLAN group Yes Same name as the virtual wire object

Create a listener for bi-directional traffic

You create a virtual server when you want the BIG-IP system to listen for client-side and server-side ingress traffic at Layer 2, without performing any packet modifications such as address translation.
  1. Log in to the BIG-IP Configuration utility using the system's management IP address.
  2. On the Main tab, click Local Traffic > Virtual Servers .
    If your BIG-IP system user account restricts you to using TMSH (TMOS Shell) only, skip this step.
  3. Click Create.
  4. In the Name field, type a name, such as my_virtual_wire_vs.
  5. From the Type list, select Forwarding (Layer 2).
  6. In the Destination Address field, type the IP address in CIDR format. The supported format is address/prefix, where the prefix length is in bits. For example, an IPv4 address/prefix is or, and an IPv6 address/prefix is ffe1::0020/64 or 2001:ed8:77b5:2:10:10:100:42/64. When you use an IPv4 address without specifying a prefix, the BIG-IP system automatically uses a /32 prefix.
  7. In the Service Port field, type a port number or select a service name from the Service Port list.
  8. From the VLAN and Tunnel Traffic list, select the name of the virtual wire you previously created.
  9. Click Finished.

Configuration results

When you complete the Layer 2 transparency mode configuration, the BIG-IP system contains these objects:
  • Two trunks that represent Member 1 and Member 2 interfaces of the virtual wire. Each interface of a trunk has its forwarding mode set to Virtual Wire .

  • A tagged VLAN for the Member 1 trunk with a tag of 4096, assigning the Member 1 trunk to the VLAN.

  • A tagged VLAN for the Member 2 trunk with a tag of 4096, assigning the Member 2 trunk to the VLAN.

  • A VLAN group with the transparency mode set to Virtual Wire , where the VLAN group name matches the name of the virtual wire object.

  • A virtual server that listens for both client-side and server-side traffic. The virtual server forwards the client-side traffic to the Member 2 trunk and forwards the server-side traffic to the Member 1 trunk.