H3C S9500 Series Operating Manual page 4

Operation Manual – QoS
H3C S9500 Series Routing Switches
address, IP protocol, source address, destination address and port ID. Classification
rule often is limited to the information encapsulated at the packet header, rarely using
packet contents.
III. Packet filtering
Packet filtering refers to filtering operation applied to traffic flow. For example, the deny
operation drops the traffic flow which matches the classification rule and allows other
traffic to pass. Ethernet switches use complex classification rules, so that traffic flow
can be filtered purposefully to enhance network security.
There are two key steps in packet filtering:
Step 1: Classify the traffic at the port according to a specific rule.
Step 2: Run filtering operation (denying or permitting) to the identified traffic. By default,
permit operation is selected.
IV. Traffic policing
QoS can police traffic at the ingress port, to provide better services with the limited
network resources.
V. Redirection
You can re-specify forwarding direction for packets, based on QoS policy.
VI. Traffic priority
Ethernet switches can provide priority tags, including ToS, DSCP, 802.1p, and so on,
for specific packets. These priority tags are respectively applicable to different QoS
models.
The following describes IP priority, ToS priority, DSCP priority, EXP priority and 802.1p
priority.
1) IP priority, ToS priority, DSCP priority and EXP priority
Figure 1-1 DS field and ToS byte
As shown in
represent IP priority, in the range of 0 to 7; bits 3-6 stand for ToS priority, in the range of
0 to 15. RFC2474 redefines the ToS field in IP packets as DS (differentiated services)
Figure 1-1, the ToS field in the IP header contains 8 bits. The first three bits
1-2
Chapter 1 QoS Configuration