Packet forwarding modes 编辑

The Citrix ADC appliance can either route or bridge packets that are not destined for an IP address owned by the appliance (that is, the IP address is not the NSIP, a MIP, a SNIP, a configured service, or a configured virtual server). By default, L3 mode (routing) is enabled and L2 mode (bridging) is disabled, but you can change the configuration. The following flow chart shows how the appliance evaluates packets and either processes, routes, bridges, or drops them.

Figure 1. Interaction between Layer 2 and Layer 3 Modes

An appliance can use the following modes to forward the packets it receives:

• Layer 2 (L2) Mode
• Layer 3 (L3) Mode
• MAC-Based Forwarding Mode

Enable and disable layer 2 mode

Layer 2 mode controls the Layer 2 forwarding (bridging) function. You can use this mode to configure a Citrix ADC appliance to behave as a Layer 2 device and bridge the packets that are not destined for it. When this mode is enabled, packets are not forwarded to any of the MAC addresses, because the packets can arrive on any interface of the appliance and each interface has its own MAC address.

With Layer 2 mode disabled (which is the default), the appliance drops packets that are not destined for one of its MAC address. If another Layer 2 device is installed in parallel with the appliance, Layer 2 mode must be disabled to prevent bridging (Layer 2) loops. You can use the configuration utility or the command line to enable Layer 2 mode.

Note: The appliance does not support the Spanning Tree Protocol. To avoid loops, if you enable L2 mode, do not connect two interfaces on the appliance to the same broadcast domain.

To enable or disable Layer 2 mode by using the CLI

At the command prompt, type the following commands to enable/disable Layer 2 mode and verify that it has been enabled/disabled:

• enable ns mode <Mode>

• disable ns mode <Mode>

• show ns mode

  Examples

    > enable ns mode l2
    Done
    > show ns mode

    Mode Acronym Status
    ------- ------- ------
    1) Fast Ramp FR ON
    2) Layer 2 mode L2 ON
    .
    .
    .
    Done
    >

    > disable ns mode l2
    Done
    > show ns mode

    Mode Acronym Status
    ------- ------- ------
    1) Fast Ramp FR ON
    2) Layer 2 mode L2 OFF
    .
    .
    .
    Done
    >
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