Cisco Catalyst 3750-E Software Configuration Manual page 857

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Configuring QoS

Encapsulated Packet

Layer 2 ISL Frame

Layer 2 802.1Q and 802.1p Frame

Layer 3 IPv4 Packet

Layer 3 IPv6 Packet

All switches and routers that access the Internet rely on the class information to provide the same

forwarding treatment to packets with the same class information and different treatment to packets with

different class information. The class information in the packet can be assigned by end hosts or by

switches or routers along the way, based on a configured policy, detailed examination of the packet, or

both. Detailed examination of the packet is expected to happen closer to the edge of the network so that

the core switches and routers are not overloaded with this task.

Switches and routers along the path can use the class information to limit the amount of resources

allocated per traffic class. The behavior of an individual device when handling traffic in the DiffServ

architecture is called per-hop behavior. If all devices along a path provide a consistent per-hop behavior,

you can construct an end-to-end QoS solution.

Implementing QoS in your network can be a simple or complex task and depends on the QoS features

offered by your internetworking devices, the traffic types and patterns in your network, and the

granularity of control that you need over incoming and outgoing traffic.

QoS Classification Layers in Frames and Packets

Encapsulated frame 1...

3 bits used for CoS

IP precedence or DSCP

Traffic class

IP precedence or DSCP

Catalyst 3750-E and 3560-E Switch Software Configuration Guide

3 bits used for CoS (user priority)

Offset TTL Proto FCS IP-SA IP-DA Data

Understanding QoS

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Troubleshooting

Catalyst3560-e