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Configuring the priority trust mode
After you configure a priority trust mode for a port, the device maps the trusted priority in incoming
packets to the target priority types and values according to the priority maps.
The available priority trust modes include the following types:
•
Untrust
—Does not trust any priority included in packets.
•
Dot1p
—
Trusts the 802.1p priorities included in packets.
•
DSCP
—
Trusts the DSCP priorities included in IP packets.
Priority map
The device provides three priority maps: 802.1p-lp, DSCP-802.1p, and DSCP-DSCP. If a default
priority map cannot meet your requirements, you can modify the priority map as required.
Rate limit
Rate limit uses token buckets for traffic control. If there are tokens in the token bucket, bursty traffic is
allowed. Otherwise, packets are not forwarded until new tokens are generated. In this way, packets
are limited to the token generation rate while bursty traffic is allowed.
A token bucket has the following configurable parameters:
•
Mean rate at which tokens are put into the bucket, which is the permitted average rate of traffic.
It is typically set to the committed information rate (CIR).
•
Burst size or the capacity of the token bucket. It is the maximum traffic size permitted in each
burst. It is typically set to the committed burst size (CBS). The set burst size must be greater
than the maximum packet size.
Each arriving packet is evaluated. In each evaluation, if the number of tokens in the bucket is enough,
the traffic conforms to the specification and the tokens for forwarding the packet are taken away. If
the number of tokens in the bucket is not enough, the traffic is excessive.
When rate limit is configured on an interface, a token bucket handles all packets to be sent through
the interface for rate limiting. If enough tokens are in the token bucket, packets can be forwarded.
Otherwise, packets are put into QoS queues for congestion management. In this way, the traffic
passing the interface is controlled.
