Lenovo ThinkSystem NE2552E, Application Manual

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NE2552E Application Guide for ENOS 8.4
Using 802.1p Priorities to Provide QoS
Lenovo ENOS 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 NE2552E can filter packets
based on the 802.1p values, and it can assign or overwrite the 802.1p value in the
packet.
Figure 24.
Layer 2 802.1q/802.1p VLAN Tagged Packet
Ingress packets receive a priority value, as follows:
 Tagged packets —NE2552E reads the 802.1p priority in the VLAN tag.
 Untagged packets —NE2552E tags the packet and assigns an 802.1p priority,
based on the port’s default priority.
Egress packets are placed in a COS queue based on the priority value, and
scheduled for transmission based on the scheduling weight of the COS queue.
To configure a port’s default 802.1p priority value, use the following commands.
See “Queuing and Scheduling” on page 229 for details on scheduling weights.
NE2552E(config)# interface port 1
NE2552E(config-if)# dot1p
<802.1p value (0 ‐ 7)>
NE2552E(config-if)# exit
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