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

Applies To:

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  • 15.1.0, 15.0.1, 15.0.0, 14.1.3, 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.
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.
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.
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

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.
The virtual wire feature is not available on systems provisioned for Virtual Clustered Multiprocessing (vCMP).
  1. On the Main tab, click
    Virtual Wire
    This object appears on certain BIG-IP platforms only.
    The Virtual Wire screen opens.
  2. Click
  3. In the
    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
  7. In the
    field, type a name for the trunk, such as
  8. In the
    list, select the check boxes for the interfaces that you want to include in the trunk.
  9. From the
    list, select
    This enables the Link Aggregation Control Protocol (LACP) to monitor link availability within the trunk.
  10. Click
    If you do not see the
    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
    list, select a trunk name, such as
  13. In the Member 2 column, from the
    list, select another trunk name, such as
  14. In the VLAN Traffic Management Configuration column, for the
    Define VLANs
    list, use the default value of
  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
Naming convention
Virtual wire
VLAN group
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
  4. In the
    field, type a name, such as
  5. From the
    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
    , and an IPv6 address/prefix is
    . 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
  8. From the
    VLAN and Tunnel Traffic
    list, select the name of the virtual wire you previously created.
  9. Click

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.