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By default, the switch uses the priority from the 802.1p tag field, if present, to classify a frame.
If you do not change any of the QoS default settings and the frame does not have an 802.1 tag or Cisco ISL tag, the switch assigns the priority of the physical port to the packet. Each physical port has a default priority of 3. For information on how to change the priority for a physical port, see "Setting the Priority of a Physical Port" later in this chapter.
However, the priority of the 802.1 tag and Cisco ISL tag take precedence over the priority of the physical port, so the switch uses the priority of the physical port only if:
For information on how to set a port to ignore priorities in tags, see "Setting a Physical Port to Ignore Tag Priority" later in this chapter.
Note: 802.1p packets that are received with a tag priority of 0 on a 50-series layer 2 (non-routing) module, and that must be routed via the FORE path on an 80-series supervisor, are queued and transmitted with a priority of 4. This priority change is due to the conversion from the high-low priority system that 50-series modules use to the 8-level priority system that 80-series modules use.
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