Appendix 7 - L2 Mode Without Virtual Wire Support

True layer 2 topology support in SSL Orchestrator is a function of a Broadcom chipsets available in iSeries i5000 appliances and above. This chipset is not available in i2000, i4000, Bourne-series platforms, Viprion, or vCMP instances (regardless of platform). It is possible, however, to modify SSLO to support a software-based layer 2 configuration. In a layer 2 topology, the client and server sides of the F5, while on separate physical interfaces, share the same IP subnet. A VLAN group is required to bridge the interfaces, allowing ARP and other routing protocol traffic to flow through, while the SSLO listeners process TCP and UDP traffic. The Transparent Nexthop setting, included in the SSLO license, then copies the layer 2 headers across the proxy environment. The following steps detail that configuration for SSLO 5.0.


In preparation for a layer 2 topology environment, the following prerequisites are required:

  • The BIG-IP must have defined, separate VLANs for the client-side and server-side networks. These VLAN's must be on the same IP subnet.
  • The BIG-IP must NOT have self-IPs configured on these VLANs.

Configure the software-based layer 2 topology

  1. Delete (or do not create) client-side and server-side VLAN self-IPs on the BIG-IP.

  2. Create a VLAN group combining the client-side and server-side VLANs, with Transparent mode, and “Bridge All Traffic” enabled. At this point the client should be able to ping the gateway and access server side (i.e. Internet resources), all flowing through the VLAN group. The next step is to enable SSLO processing.


    Do not switch between Translucent and Transparent mode in the VLAN group settings. Translucent mode performs a bit-flip on the destination MAC passing through the VLAN group, which is both incompatible with SSLO, and can be incorrectly cached by upstream routing devices.

  3. Enable VIP traffic processing in the presence of a VLAN group. By default, a VLAN group will take precedence over LTM virtual servers. The following TMSH commands allow the SSLO virtual servers to capture TCP and UDP traffic, while ARP and other routing protocol traffic flows through the VLAN group.

    tmsh modify sys db vlangroup.forwarding.override value disable
    tmsh save sys config
  4. Process an SSLO outbound proxy topology workflow. Follow these steps to configure SSLO processing for outbound traffic. Full details on the SSL Orchestrator configuration are available in the respective deployment guide

    1. Topology Properties
      • Protocol: Any
      • Topology: L3 Outbound
    2. System Settings - nothing required, additional logging optional.
    3. SSL Configurations - define as required for outbound SSL inspection.
    4. Services List - add security services as required.
    5. Service Chain - add service chains as required.
    6. Security Policy - create an outbound security policy as required.
    7. Interception Rules
      • Rule Type: Default
      • VLANs: client-side VLAN
    8. Deploy
  5. Disable strictness on the new topology. Click the lock icon (to unlock) on the Topology tab.

  6. In the BIG-IP UI, under Local Traffic -> Virtual Servers, edit the -in-t-, -in-u-, and -ot-virtual servers. In the Transparent Nexthop setting, apply the VLAN group. If enabled, also add this setting to any FTP, SMTP, IMAP or POP3 virtual servers.


    Editing the topology settings or Interception Rules in the SSLO UI will override the Transparent Nexthop settings in the LTM virtual servers.

  7. Optionally create any required SSLO L3 inbound topology workflows, disable strictness on the topology, then apply the Transparent Nexthop settings to the respective LTM virtual servers.

    1. Topology Properties

      • Protocol: TCP

      • Topology: L3 Outbound


        This is not a typo. For "inbound topology" the "L3 Outbound" topology must be selected.

    2. SSL Configurations – define as required for outbound SSL inspection.

    3. Services List – add new security services as required, or re-use existing services.

    4. Service Chain – add new service chains, or re-use existing service chains.

    5. Security Policy – create an inbound security as required. Inbound traffic generally does not require categorization or additional intercept/bypass rules, so it is usually sufficient to strip the inbound security policy down to just the ‘All’ rule that intercepts and sends to the define service chain.

    6. Interception Rules

      • Source: (or as required)
      • Destination: (this is an L2 configuration, so nothing else makes sense)
      • Port: 443 (or as required)
      • VLANs: ingress VLAN
      • L7 Profile Type: HTTP (or as required)
      • L7 Profile: /Common/http (or as required)
    7. Deploy

Verify correct SSLO traffic processing

Perform any or more of the following steps:

  • Validate that the client is able to access resources on the other side of the BIG-IP. If remote resources are accessible, inspect the server certificate in the browser to view the issuer.

  • Monitor the APM log in debug mode. This will indicate if SSLO is processing traffic.

  • Monitor the inbound or outbound interfaces of an inline service. All traffic to is should be decrypted, so a simple tcpdump would display clear text traffic:

    tcpdump -lnni eth1-Xs0

Testing a software L2 solution

An L2 deployment topology (software or hardware) basically works like this:

  • A VLAN group defines a "bridged" interface through which all traffic passes across the BIG-IP. Normally this would override any VIP listeners, except that the vlangroup.forwarding.override DB key (set to disabled) overrides this behavior allowing more specific virtual servers to process traffic.
  • In an L2 topology, both sides of the F5 are on the same subnet, such that the client can ARP and ping the gateway (next hop), which naturally passes through the VLAN group bridge.
  • In an L2 SSLO topology, There are no client/server-facing self-IPs on the F5. A client-facing TCP virtual server processes all TCP traffic. Traffic arriving at the TCP VIP contains the true destination IP and the MAC address of the next hop (gateway).
  • SSLO handles encryption and shuffles decrypted traffic through the service chain. Virtual wire and Transparent Nexthop both function to then insert (copy) the L2 headers from the client-side packets to the server-side. Traffic arriving at the next hop correctly contains the true destination IP and MAC of the next hop.

The primary differences between hardware L2 (virtual wire) and software L2 (Transparent Nexthop) are:

  1. The type and number of L2 headers copied, and
  2. The type of VLAN group and objects created to support virtual wire.

For most situations, however, software L2 is adequate. In order to demonstrate software L2, either follow the guidance above to create the configuration, or one exists in the "SSLO 5.0 Software L2 Demo" UDF blueprint. The following instructions assume the UDF blueprint:

  • SSH or RDP to the outbound client. The client is at, and should be able to ping the gateway at through the VLAN group bridge. Assuming that works, a client browser should be able to navigate to external sites.
  • SSH or console to the Inline L2 device (simulated FireEye). Tcpdump on its eth1 interface (tcpdump -lnni eth1 -Xs0 not icmp and not icmp6). Generate HTTPS traffic on the client to see decrypted traffic in this capture. able to ping the webservers at Assuming that works, a client browser should be able to navigate to one of the internal test URLs:
  • SSH or console to the webserver and tcpdump on its eth1 interface (tcpdump -lnni eth1 not icmp and not arp). This traffic is re-encrypted so you won’t see clear text.