1154 Configuring Class-of-ServiceEach ingress port on the switch has a default priority value (set by configuringVLAN Port Priority in the Switching sub-menu) that determines the egressqueue its traffic gets forwarded to. Packets that arrive without a VLAN userpriority, or packets from ports you’ve identified as “untrusted,” get forwardedaccording to this default.What Are Trusted and Untrusted Port Modes?Ports can be configured in “trusted” mode or “untrusted” mode with respectto ingress traffic.Ports in Trusted ModeWhen a port is configured in trusted mode, the system accepts at face value apriority designation encoded within packets arriving on the port. You canconfigure ports to trust priority designations based on one of the followingfields in the packet header:• 802.1 Priority: values 0–7• IP DSCP: values 0–63A mapping table associates the designated field values in the incoming packetheaders with a traffic class priority (actually a CoS traffic queue).Ports in Untrusted ModeIf you configure an ingress port in untrusted mode, the system ignores anypriority designations encoded in incoming packets, and instead sends thepackets to a traffic queue based on the ingress port’s default priority.How Is Traffic Shaping Used on Egress Traffic?For unit/slot/port interfaces, you can specify a traffic shaping rate for the port(in Kbps) for egress traffic. The traffic shaping rate specifies an upper limit ofthe transmission bandwidth used. Once the traffic shaping rate has beenreached, frames that exceeded the limit remain queued for transmission untilthe next scheduling slot.
