In the last post, I began the process of creating a QoS strategy based on identification of traffic we care about (classification), determination of the DSCP or CoS tags to apply (marking), and desired bandwidth (queuing). This post will provide an overview of the configuration required to achieve the QoS goals defined by that strategy.
Since publishing the first post, I found this gem in the Nexus 9k QoS configuration guide:
“For VLAN-tagged packets, priority is assigned based on the 802.1p field in the VLAN tag and takes precedence over the assigned internal priority (qos-group). DSCP or IP access-list classification cannot be performed on VLAN-tagged frames.”
I have updated the original post with this documentation excerpt but need to make some changes to the policy maps to be used based. A quick glimpse of our 9k switches reflects that most of the ports are trunks and will thus be carrying VLAN-tagged packets. No problem, but I’m glad to have found this before moving forward on the configuration (and this post)! The silver lining here is that configuration should be greatly simplified, as we’ll rely on traffic classification and marking being performed on each connected host.
There are 8 possible CoS values, 3 of which will be mapped to specific QoS-groups on the switch (remember that codepoint 6 is for network control and is mapped to the Control QoS queue by the switch):