DELL N3000 User Manual

Configuring iSCSI Optimization

In networks containing iSCSI initiators and targets, iSCSI Optimization 

helps to monitor iSCSI sessions or give iSCSI traffic preferential QoS 

treatment. Dynamically-generated classifier rules generated by snooping 

iSCSI traffic are used to direct iSCSI data traffic to queues that can be given 

the desired preference characteristics over other data traveling through the 

switch. This may help to avoid session interruptions during times of 

congestion that would otherwise cause iSCSI packets to be dropped. 

However, in systems where a large proportion of traffic is iSCSI, it may also 

interfere with other network control-plane traffic, such as ARP or LACP.
The preferential treatment of iSCSI traffic needs to be balanced against the 

needs of other critical data in the network.

The switch snoops iSCSI session establishment (target login) and 

termination (target logout) packets by installing classifier rules that trap 

iSCSI protocol packets to the CPU for examination. Devices that initiate 

iSCSI sessions generally use well-known TCP ports 3260 or 860 to contact 

targets. When iSCSI optimization is enabled, by default the switch identifies 

IP packets to or from these ports as iSCSI session traffic. In addition, the 

switch separately tracks connections associated with a login session (ISID) 

(dynamically allocated source/destination TCP port numbers). You can 

configure the switch to monitor traffic for additional port numbers or port 

number-target IP address combinations, and you can remove the well-known 

port numbers from monitoring. You can also associate a target name with a 

configured target TCP port entry.

The iSCSI CoS mode is configurable and controls whether CoS queue 

assignment and/or packet marking is performed on iSCSI traffic. When the 

iSCSI CoS mode is enabled, the CoS policy is applied to packets in detected 

iSCSI sessions. In addition, if DCBX is enabled (on N4000 switches only), the 

iSCSI application priority TLV is generated by the switch. When the iSCSI 

CoS mode is disabled, iSCSI sessions and connections are detected and 

shown in the status tables, but no CoS policy is applied to packets.