Technical data

BLADE OS 5.1 Application Guide
112
 Chapter 7: Quality of Service BMD00136, November 2009
DSCP Re-Marking Configuration Example
1. Turn DSCP re-marking on globally, and define the DSCP-DSCP-802.1p mapping. You can use the
default mapping.
2. Enable DSCP re-marking on a port.
Using 802.1p Priorities to Provide QoS
802.1p Overview
BLADE OS provides Quality of Service functions based on the priority bits in a packet’s VLAN
header. (The priority bits are defined by the 802.1p standard within the IEEE 802.1q VLAN
header.) The 802.1p bits, if present in the packet, specify the priority that should be given to packets
during forwarding. Packets with a numerically higher (non-zero) priority are given forwarding
preference over packets with lower priority bit value.
The IEEE 802.1p standard uses eight levels of priority (0-7). Priority 7 is assigned to highest
priority network traffic, such as OSPF or RIP routing table updates, priorities 5-6 are assigned to
delay-sensitive applications such as voice and video, and lower priorities are assigned to standard
applications. A value of 0 (zero) indicates a “best effort” traffic prioritization, and this is the default
when traffic priority has not been configured on your network. The G8000 can filter packets based
on the 802.1p values, and it can assign or overwrite the 802.1p value in the packet.
Figure 15 Layer 2 802.1q/802.1p VLAN Tagged Packet
>> # qos dscp re-marking
>> # qos dscp dscp-mapping <dscp value (0-63)> <new value>
>> # qos dscp dot1p-mapping <dscp value (0-63)> <802.1p value>
>> # interface port 1
>> # qos dscp-remarking
7 6 5 4 3 2 1 0
Priority
7 6 5 4 3 2 1 0
VLAN Identifier (VID)
SFD
DMAC
SMAC Tag
E Type
Data
FCS
Preamble