HP Network Direr Software Products manual Key Concepts

Key Concepts 625

Classification is configured on a device as a set of rules. Each rule defines a particular way of identifying the type of traffic. For example, a rule may state that SNMP traffic can be identified as UDP packets that have either the source or the destination UDP port set to the value 161.

Marking Due to the numerous possibilities for classifying packets, not every device can classify the same packets in the same manner. Some devices are capable of extremely complex classification (complex classification devices), while other devices may only be able to match traffic based on the content of one or two fields (simple classification devices). For example, this can mean that while one device in your network is able to identify traffic to and from your database server using the destination or source IP address in the packets, another device may not be able to.

There are two standards that specify how a complex classification device can modify packets in a straightforward manner so that a simple classification device can still identify how important those packets are.

This modification of packets is known as marking and the two standards are:

IEEE 8 02.1D — defines an extended MAC header (known as a tagged header) which contains a user priority field (known as the 802.1p tag), which takes one of eight values (0 - 7) to represent the priority of the packet.

IETF RFC 2474 — defines the use of the Differentiated Services (DiffServ) field in the IP header. This field can take one of sixty-four values (0 - 63) which are known as DiffServ codepoints (or DSCPs) to represent the quality of service requirements of the packet. There are no restrictions on what a particular codepoint value may mean, however one use could be to simply represent the priority of the packet.

More information on these standards is available in “User Priority Field” on page 652 and “DiffServ Codepoint Field” on page 653.