iSCSI Optimization | 279
Monitoring iSCSI Traffic Flows
The switch snoops iSCSI session-establishment and termination packets by installing classifier rules that
trap iSCSI protocol packets to the CPU for examination. Devices that initiate iSCSI sessions usually use
well-known TCP ports 3260 or 860 to contact targets. When you enable iSCSI optimization, by default the
switch identifies IP packets to or from these ports as iSCSI traffic.
You can configure the switch to monitor traffic for additional port numbers or a combination of port
number and target IP address, and you can remove the well-known port numbers from monitoring.
Application of Quality of Service to iSCSI Traffic Flows
The iSCSI CoS mode is user-configurable and controls whether CoS (dot1p priority) queue assignment
and/or packet marking is performed on iSCSI traffic. When you enable iSCSI CoS mode, the CoS policy is
applied to iSCSI traffic. When you disable iSCSI CoS mode, iSCSI sessions and connections are still
detected and displayed in the status tables, but no CoS policy is applied to iSCSI traffic.
You can configure whether the iSCSI optimization feature uses the VLAN priority or IP DSCP mapping to
determine the traffic class queue. By default, iSCSI flows are assigned to dot1p priority 4. Use the CoS
dot1p-priority command to map incoming iSCSI traffic on an interface to a dot1p priority-queue other than 4
(refer to QoS dot1p Traffic Classification and Queue Assignment).
You can configure whether iSCSI frames are re-marked to contain the configured VLAN priority tag or IP
DSCP when forwarded through the switch.
Information Monitored in iSCSI Traffic Flows
iSCSI optimization examines the following data in packets and uses the data to track the session and create
the classifier entries that enable QoS treatment:
• Initiator’s IP Address
• Target’s IP Address
• ISID (Initiator defined session identifier)
• Initiator’s IQN (iSCSI qualified name)
• Target’s IQN
• Initiator’s TCP Port
• Target’s TCP Port
If no iSCSI traffic is detected for a session during a user-configurable aging period, the session data is
cleared.
Note: On a switch in which a large proportion of traffic is iSCSI, CoS queue assignment may interfere with
other network control-plane traffic, such as ARP or LACP. Preferential treatment of iSCSI traffic needs to
be balanced against the needs of other critical data in the network.
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