Users Guide

640 iSCSI Optimization
How Does iSCSI Optimization Interact with DCBx?
The Data Center Bridging Exchange (DCBx) component supports the
reception, decoding, and transmission of the Application Priority TLV. In
general, if the Application Priority TLV has been received from the
configuration source, it will be transmitted to the other auto configuration
ports. The DCBx component contains a control to generate the Application
Priority TLV for iSCSI if it is not already present in the DCBX information.
DCBx generates an Application Priority TLV whenever the following
conditions are met:
• An EqualLogic array has been detected on the port
• iSCSI CoS is enabled using a VPT value
The generated Application Priority TLV will contain the following values (in
addition to any other information contained in the TLV):
• AE Selector=14
• AE Protocol=3260
• AE Priority=priority configured for iSCSI PFC by the iscsi cos vpt
command (default priority is 4)
The existing application priority entries being transmitted, if any, will not be
disturbed.
If DCBX is enabled (on Dell EMC Networking N4000 Series switches only),
the iSCSI application priority TLV is generated by the switch.
On Dell EMC Networking N4000 Series switches, when the iSCSI CoS mode
is disabled, the DCBX iSCSI Application Priority TLV is not generated by the
switch. In either case, if DCBX is enabled and ports are configured as auto-up
or auto-down, the Application Priority TLVs received from the configuration
source are proxied to the other ports and, on the Dell EMC Networking
N4000 Series switches, the CoS policy for iSCSI received via DCBX is applied
to iSCSI packets.
NOTE: The DCBx feature is available on the Dell EMC Networking N4000 Series
switches only.