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HP Virtual Connect 4.01 Update: Priority Queue QoS

July 24th, 2013

HP has released a significant firmware update to its Virtual Connect line of HP Blade chassis switches.

This is part 4 of a 6 part post on HP Virtual Connect 4.01:

  1. HP Virtual Connect 4.01: What’s New
  2. HP Virtual Connect 4.01: Dual-hop FcOE support
  3. HP Virtual Connect 4.01: Min/Max Bandwidth Optimisation
  4. HP Virtual Connect 4.01: Priority Queue QoS
  5. HP Virtual Connect 4.01: SNMP and sFlow enhancements
  6. HP Virtual Connect 4.01: RBAC and Multicast + some more

Priority Queue QoS

QoS is the next major enhancement in VC 4.01.

Pre VC 4.01 there is very little QoS for any traffic. Traffic flows on a first in first out basis, if there’s any congestion, the traffic at the tail of the queue is dropped.


Basically you can control the Max that a FlexNic can transmit and receive but that’s it. VC performs no classification, marking, policing or traffic shaping. If there are any QoS traffic markings they are passed through VC in VLAN Tunnelled Mode but stripped out if using Mapped Mode with SUS.

VC 4.01 now adds 802.1Q L2 priority classification with up to 8 traffic classes. With QoS configured traffic flows according to priority values. Packets may enter the VC module in one order but exit in a different order based on the priority. During congestion, some packets may be dropped based on queue resource allocation.

image_thumb74For traffic coming into a VC module (ingress), VC supports up to 8 configurable traffic classes with or without FCoE using dot1p, DSCP or ToS classifiers with three pre-defined QoS configuration types.


Passthrough is the default behaviour which does not classify or alter incoming non-FCoE packets.

Custom (without FCoE Lossless) enabled QoS without FCoE and allows one system class (Best Effort) and up to 7 user defined classes.

Custom (with FCoE Lossless) enables QoS with a FCoE class and allows 2 system classes (Best Effort and FCoE Lossless) and up to 6 user defined classes.

One user defined class also can be designated as Real Time. Traffic from this class will have highest priority over all others including Lossless.


QoS markings can be handled in 3 ways, Preserve which passes through any markings without prioritising, Enforce which reuses external markings to prioritise and classify traffic and Map which remarks ingress layer 2/3 to Layer 2 on egress.

Mapping allows you to change the L2 802.1p tags as they pass through the VC module in effect changing the priority tags.


Mapping can also change the L3 DSCP (Differentiated Services Code Point) values to L2 802.1p as they pass through the VC module.


When traffic leaves the VC module (egress) and is using mapped mode, an egress 802.1p priority value associated with the traffic class is marked on the packet if the packet has a VLAN tag. For tunnelled traffic, the original 802.1p priority value is left alone and passes through.

Egress traffic is queued on the appropriate traffic class/queue of the egress port and the scheduler selects packets to egress based on bandwidth allocation for each class/queue.

The egress 802.1p priority associated with the traffic class is used on stacking links to achieve consistent QoS for traffic across the VC domain.


Next up: HP Virtual Connect 4.01: SNMP and sFlow enhancements

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