1-10
Port Rate Limiting
Port rate limiting refers to limiting the total rate of inbound or outbound packets on a port.
Port rate limiting can be implemented through token buckets. That is, if you perform port rate limiting
configuration for a port, the token bucket determines the way to process the packets to be sent by this
port or packets reaching the port. Packets can be sent or received if there are enough tokens in the
token bucket; otherwise, they will be dropped.
Compared to traffic policing, port rate limiting applies to all the packets passing a port. It is a simpler
solution if you want to limit the rate of all the packets passing a port.
Traffic Redirecting
Traffic redirecting identifies traffic using ACLs and redirects the matched packets to specific ports. By
traffic redirecting, you can change the way in which a packet is forwarded to achieve specific purposes.
Queue Scheduling
When the network is congested, the problem that many packets compete for resources must be solved,
usually through queue scheduling.
In the following section, strict priority (SP) queues, weighted round robin (WRR), and HQ-WRR (High
Queue-WRR) queues are introduced.
1) SP
queuing
Figure 1-6
Diagram for SP queuing
SP queue-scheduling algorithm is specially designed for critical service applications. An important
feature of critical services is that they demand preferential service in congestion in order to reduce the
response delay. Assume that there are four output queues on the port and the preferential queue
classifies the four output queues on the port into four classes, which are queue 3, queue 2, queue 1,
and queue 0. Their priorities decrease in order.
In queue scheduling, SP sends packets in the queue with higher priority strictly following the priority
order from high to low. When the queue with higher priority is empty, packets in the queue with lower
priority are sent. You can put critical service packets into the queues with higher priority and put
non-critical service (such as e-mail) packets into the queues with lower priority. In this case, critical
