How to configure Layer 2 Discovery on Switching on 6.2 and above

03/20/2021 12 15509

DESCRIPTION:

This article provides information on how to configure Layer 2 Discovery on Switching on 6.2 and above.

SonicOS provides Layer 2 (data link layer) switching functionality with its unique PortShield architecture. Layer 2 switching features enhance the deployment and interoperability of SonicWall devices within existing Layer-2 networks with the following benefits:

Support for Layer 2 Discovery, also called L2 Discovery. Layer 2 Discovery uses theIEEE 802.1AB (LLDP) and Microsoft LLTD protocols and switch forwarding table to discover nodes visible from a port.

Layer 2 Discovery is supported in Receive only mode. LLDP in transmit mode is not supported for security reasons. SonicWall does not send any response to a received LLDPDU.

Layer 2 Discovery is only active for a short period of time when SonicWall boots up. Normally, Layer 2 Discovery is not active for security reasons. Layer 2 Discovery can be manually reactivated when needed.

Support for Layer 2 Discovery does not cross a broadcast domain.

The following diagram illustrates an example of Layer 2 Discovery. L2 discovery can discover many devices such as PC, Servers, switches, routers etc.

RESOLUTION:

Step 1. View the Layer 2 Discovery page

Login to the SonicWall UTM appliance and configure Layer 2 Discovery from the Switching | L2 Discovery page. To discover devices connected to an interface, they can only be discovered if they are running LLDP or LLTD protocols.

Step 2. Discover devices connected to an interface.

L2 Discovery does not proactively manage the discovery. Discovery is active when the system boots up and then does not restart unless you click the L2 Discovery refresh button in the SonicOS management interface.  To restart Layer 2 discovery on multiple interfaces, select the checkbox next to the desired interfaces and then click the Refresh Selected button at the bottom of the page or the round refresh button an each individual port.

NOTE: Do not Port Mirror any ports when they participate in Layer 2 Discovery.

Step 3. Demonstrate the L2 Discovery of devices

Show a Layer 2 Discovery example of a PC and a Switch connected to SonicWall. In this example two PCs are connected to port X1 and a HP Procurve switch to port X2.

In this example port X1 discovers two PCs and port X2 discovers a HP Procure switch.
 

Step 4. Show the configuration of the HP switch

Show the LLDP default configuration from the HP ProCurve switch (example HP ProCurve 2920, 2600-8-PWR etc). The LLDP transmit interval is set for every 30 seconds. On the 6.2 system the L2 Discovery is a manual restart procedure, you may need to click the L2 Discovery refresh button multiple times to discover a neighbor device in the SonicOS management interface.

Show the LLDPDUs sent by the switch to the SonicWall. The SonicWall does not send any replies and therefore the switchs  NumFramesRecvd  counter is zero.