VLANs on the BNT 10 Gigabit VFS may cause DCBX errors due to optional LLDP TLVs being enabled by default

Resolving The Problem

Source

RETAIN tip: H204829

Symptom

The creation of multiple Virtual Local Area Networks (VLANs) on the BNT Virtual Fabric 10 Gigabit Switch Module for IBM BladeCenter, Option part number 46C7191, may cause Data Center Bridging Protocol (DCBX) errors due to optional Link Layer Discovery Protocol (LLDP) Type Length Values (TLVs) being enabled by default.

For example, one might see the following log entries in the switch module event log:

Also, attempting to add more VLANs may not be possible and could result in the BNT Virtual Fabric 10 Gigabit switch module returning the following event log entries:

Affected configurations

The system is configured with one or more of the following IBM Options:

• BNT Virtual Fabric 10 Gigabit Switch Module for IBM BladeCenter, Option part number 46C7191, replacement part number 46C7194

This tip is not system specific.

This tip is not software specific.

The system has the symptom described above.

Solution

Update the BNT Virtual Fabric 10 Gb Switch Module for IBM BladeCenter to version 6.8.6 or higher.

The file is available by selecting the appropriate Product Group, type of System, Product name, Product machine type, and operating system on IBM Support's Fix Central web page, at the following URL:

• http://www.ibm.com/support/fixcentral/

Workaround

Disable optional LLDP TLVs that are not being used. Optional TLVs in use are environment specific, and need to be determined on a case by case basis.

To disable optional LLDP TLVs on a per port basis, perform the following:

1. Telnet to the switch.
   
2. Open the Configuration menu by typing cfg and pressing Enter.
   
3. Open the Layer 2 Menu by typing l2 and pressing Enter.
   
4. Open the LLDP Menu by typing lldp and pressing Enter.
   
5. Open the LLDP port menu by typing port and pressing Enter.
   
6. Enter a port number, for example, INT1 for blade Slot 1.
   
7. Enter the Optional TLVs Menu by typing tlv and pressing Enter.
   
8. Disable the Optional TLV. For example, to disable the vlanname TLV:
   
   1. Type vlanname and press Enter.
      
   2. Type disabled and press Enter.
      
   
   
9. Apply the configuration changes by typing apply and pressing Enter.
   
10. Save the configuration changes by typing save and pressing Enter.
    

The following shortcut can be used for steps 2-8 above:

Note: The optional TLVs vlanname and portprot add the most data in an Ethernet packet and are the recommended TLVs to disable first.

Additional information

By default, all LLDP optional TLVs are enabled in the BNT Virtual Fabric 10 Gigabit switch module. As more VLANs are associated with a given switch port, it increases the amount of administrative data that has to be included in each 1514 byte packet. If too much of this administrative data is in the packet, the switch ends up truncating the LLDP optional TLV data, which prevents the DCBX peer from responding to errors. By not including unnecessary LLDP optional TLVs such as vlanname and portprot, it frees up space inside each packet that is sent, thus allowing more VLANs to be created.

The switch firmware monitors how much administrative data it needs to include as VLANs begin to get created for a given port. Hence, it attempts to warn users and prevent them from creating too many VLANs in order to allow the DCBX peer to respond to messages.