You would expect to have a very simple and intuitive QoS troubleshooting toolkit on a native MQC platform. Well, the first thing that came into my mind after I’ve been told that Catalyst 3850 is a proper MQC platform was something like
Wow, finally I can use the very same range of ISR commands to troubleshoot QoS on a hardware switching platform!
Unfortunately, that ended up to be a hybrid implementation. Yes, we have to use MQC to configure QoS on Catalyst 3850, including queuing! No, you are unlikely to solely use MQC commands to troubleshoot QoS. Remember that show mls qos commands range on Catalyst 3750 platform? It’s still the same candy, in a different wrapping though. Read more …
This is a small post about one specific Cisco Catalyst 4500 Classification characteristic. The one I was lucky to find and read in advance before I deployed QoS configuration changes. Here it is.
If you run Cisco Catalyst 4500 on a Supervisor card older than V-10GE, software older than Cisco IOS Release 12.2(31)SG and you classify traffic with service-policy that refers to DSCP value (via ACL, or class-map match statements), you MUST HAVE qos trust dscp configured on a port!
Simple as that. If you don’t do that, your service-policy won’t see DSCP values, and won’t be able to classify traffic in a right manner. Here’s a screenshot from the Cisco Catalyst 4500 QoS configuration guide that proves my words.
It’s a pleasure to work with Cisco TAC. I would say this is the only way to instantly improve your troubleshooting skills in any area. I was involved in Cisco 6509 troubleshooting that turned to be an IOS software-to-hardware QoS configuration bug. With this post I will slightly cover the bug logic and will show you the way to confirm QoS configuration in Cisco 6509’s module hardware.
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