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Virtual Connect and the Class-of-Service (CoS) value in a VLAN Tag

Trusted Contributor

Virtual Connect and the Class-of-Service (CoS) value in a VLAN Tag

Wim had a VLAN tagging question:




Does anybody know if the layer 2 Class of Service value in a VLAN tag (802.1p), if the VLAN tag is send by a blade server, is preserved if it is send over a VC tunnel or in VLAN mapping mode?




Ramu replied:




If the priority bit is set by the Blade servers, VC will preserve it. Because all, VC checks is the Vlan Tag.




Comments or questions?

Trusted Contributor

Re: Virtual Connect and the Class-of-Service (CoS) value in a VLAN Tag

A comment pointed out by Diane is that the VLAN tagging and passing of the tags unaltered is only valid in "tunnel" mode:


From the Virtual Connect for Cisco Network Administrators white paper:


Quality of Service

In the current version of firmware, Virtual Connect does not support any user-configurable settings

for traffic classification, marking, or prioritization. In addition, VC does not utilize layer 2 quality of

service markings (802.1p Class of Service) nor layer 3 quality of service markings (TOS, DSCP) for

frame prioritization. However, just like with any server-to-Cisco-switch deployment, QoS settings can

be applied to the Cisco switch port connected to VC uplinks.

If an Administrator needs the blade server NIC ports to receive layer 2 QoS markings (Class of

Service), then the server NIC ports will need to be assigned to a vNet operating in 802.1Q\p

tunneling mode. See the section above entitled “VC Uplinks and VLAN Trunking” for more



Any other comments?