Command Line Interface Guide

884 Data Center Bridging Commands
The mapping between the ingress port’s 802.1p priority and TCG is not
direct. The mapping depends upon:
• The CoS map defining the CoS queue that a packet is egress forwarded for
the ingress 802.1p priority.
• Traffic Class Group map defining the CoS queue to TCG mapping.
The indirect mapping between the 802.1p priorities and the associated Traffic
Class Group mapping is advertised by DCBX as part of ETS TLVs. For this
indirect mapping to be valid, the following parameters need to be configured
in addition to the configuration of the TCGs.
1
Configure 8021.p priority to CoS mapping for the ingress ports.
2 Enable Trust mode on the ingress ports to trust the 802.1p priority present
in the frames.
ETS TLVs use DCBX Asymmetric attribute exchange mechanism to
exchange ETS information between the peers. In this exchange, each peer
device sends its ETS configuration via the “configuration” ETS TLV and
recommended ETS settings for the peer using the “recommend” ETS TLV.
Both the configuration and recommendation ETS TLVs are implemented for
PowerConnect switches in release 4.2.
The peer ETS TLVs are stored in the DCBX database and are accessible using
show commands.
The Application Priority TLV is accepted from auto-upstream devices and
propagated to auto-downstream devices. In addition, if iSCSI CoS is enabled,
an additional entry in the Application Priority TLV is added as discussed in
the iSCSI section.
Data Center Bridging Exchange Protocol Main Objective
The DCBX protocol implementation conforms to the IEEE 802.1Qaz
specification with some exceptions. To be interoperable with legacy industry
implementations of DCBX protocol, a hybrid model is used to support both
the IEEE version of DCBX and legacy DCBX versions. The hybrid version of
the DCBX conforms to all aspects of the legacy standards to the degree
necessary to support interoperability with a wide variety of FCoE capable
switches.
The main objective of DCBX is to perform the following operations:
• Discovery of DCB capability in a peer
2CSPC4.X8100-SWUM100.book Page 884 Wednesday, August 29, 2012 6:23 PM