Cisco Small Business Managed Switches (Linksys Business Series)

The Quality of Service (QoS) feature allows you to specify priorities for different traffic. Lower priority traffic will be slowed down to allow greater throughput or less delay for high priority traffic.

The QoS tab includes links to the following screens.

CoS Settings
Queue Settings
CoS to Queue
IP Precedence/DSCP
IP Port
ACL Priority
Rate Limit

Class of Service Settings

Class of Service (CoS) allows you to specify which data packets have greater precedence when traffic is buffered in the switch due to congestion. This switch supports CoS with four priority queues for each port. Data packets in a port's high-priority queue will be transmitted before those in the lower-priority queues. You can set the default priority for each interface, and configure the mapping of frame priority tags to the switch's priority queues. The priority levels recommended in the IEEE 802.1p standard for various network applications are shown in the following table. However, you can map the priority levels to the switch's output queues in any way that benefits application traffic for your own network.

Priority Level
CoS value. (Range: 0-7, where 7 is the highest priority)

Traffic Type
Output queue buffer. (Range: 0-3, where 3 is the highest CoS priority queue)

Modify the default priority for any interface using the text field provided. CoS can be enabled or disabled by using the CoS Mode checkbox. Default settings can be restored using the Restore Defaults checkbox. Click Submit to save the changes.

After setting the COS for each port, you can ready to set the priority levels.

Queue Settings

This switch prioritizes each packet based on the required level of service, using four priority queues with strict or Weighted Round Robin Queuing. It uses IEEE 802.1p and 802.1Q tags to prioritize incoming traffic based on input from the end-station application. These functions can be used to provide independent priorities for delay sensitive data and best-effort data.

Queue Mode (Global). You can set the switch to service the queues based on a strict rule that requires all traffic in a higher priority queue to be processed before lower priority queues are serviced, or use Weighted Round-Robin (WRR) queuing that specifies a relative weight of each queue. WRR uses a predefined relative weight for each queue that determines the percentage of service time the switch services each queue before moving on to the next queue. This prevents the head-of-line blocking that can occur with strict priority queuing.

WRR
Weighted Round-Robin shares bandwidth at the egress ports by using scheduling weights 1, 2, 4, 6 for queues 0 through 3 respectively.

Strict
Services the egress queues in sequential order, transmitting all traffic in the higher priority queues before servicing lower priority queues. Set the Queue Mode to Strict or WRR using the Queue Mode drop-down menu then click submit. Enter a weight, select a traffic class (that is, output queue) then click submit to save the changes.

Weight Value.
Set a new weight for the selected traffic class. However, note that Queue 0 is fixed at a weight of 1, and cannot be configured. (Range: 1-31)

CoS to Queue

Class of Service. CoS value
(Range: 0-7, where 7 is the highest priority)

Queue
Output queue buffer. (Range: 0-3, where 3 is the highest CoS priority queue)
Assign priorities to the traffic classes (that is, output queues) for the selected interface.

Click Submit to save the changes.

IP Precedence/DSCP Settings

This switch supports several common methods of prioritizing layer 3/4 traffic to meet application requirements. Traffic priorities can be specified in the IP header of a frame, using the priority bits in the Type of Service (ToS) octet or the number of the TCP port. If priority bits are used, the ToS octet may contain three bits for IP Precedence or six bits for Differentiated Services Code Point (DSCP) service. When these services are enabled, the priorities are mapped to a Class of Service value by the switch, and the traffic then sent to the corresponding output queue. Because different priority information may be contained in the traffic, this switch maps priority values to the output queues in the following manner:

The precedence for priority mapping is IP Port Priority, IP Precedence or DSCP Priority, and then Default Port Priority. IP Precedence and DSCP Priority cannot both be enabled. Enabling one of these priority types will automatically disable the other. The switch allows you to choose between using IP Precedence or DSCP priority. Select one of the methods or disable this feature.

Disabled
Disables both priority services. (This is the default setting.)

IP Precedence
Maps layer 3/4 priorities using IP Precedence.

IP DSCP
Maps layer 3/4 priorities using Differentiated Services Code Point Mapping. Select Disabled, IP Precedence or IP DSCP from the drop-down menu.

Click Submit to save the changes.
To select the configuration type, select IP Precedence or IP DSCP from the drop-down menu.

Click Config to save the changes.

IP Port Settings

You can also map network applications to Class of Service values based on the IP port number (i.e., TCP/UDP port number) in the frame header. Some of the more common TCP service ports include: HTTP: 80, FTP: 21, Telnet: 23 and POP3: 110.

IP Port Priority Status
Enables or disables the IP port priority.

IP Port Priority Table
Shows the IP port to CoS map.

IP Port Number (TCP/UDP)
Set a new IP port number, such as HTTP: 80, FTP: 21, Telnet: 23 and POP3: 110.

Class of Service Value
Sets a CoS value for a new IP port. Note that "0" represents low priority and "7" represents high priority.

Set IP Port Priority Status to Enabled by checking the IP Port Priority Global Status checkbox.
Enter the port number for a network application in the IP Port Number box and the new CoS value in the Class of Service box.

Click Submit to save the changes.

To remove an IP Port Priority, select the priority to be removed from the table and click Remove IP Port.

ACL Priority Settings

Use ACL CoS Mapping to set the output queue for packets matching an ACL rule as shown in the following table. Note that the specified CoS value is only used to map the matching packet to an output queue; it is not written to the packet itself.

Port
Port identifier.

Name
Name of ACL.

Type
Type of ACL (IP or MAC).

CoS Priority
CoS value used for packets matching an IP ACL rule. (Range: 0-7)

ACL CoS Priority Mapping
Displays the configured information.

Select an ACL rule, specify a CoS priority, then click Add.

To remove an ACL CoS priority mapping click the Remove button in the row of the entry you wish to remove.

Rate Limit Settings

This function allows the network manager to control the maximum rate for traffic transmitted or received on an interface. Rate limiting is configured on interfaces at the edge of a network to limit traffic coming out of the switch. Traffic that falls within the rate limit is transmitted, while packets that exceed the acceptable amount of traffic are dropped.

Rate limiting can be applied to individual ports or lags. When an interface is configured with this feature, the traffic rate will be monitored by the hardware to verify conformity. Non-conforming traffic is dropped, conforming traffic is forwarded without any changes.

The rate limit screen displays both Fast Ethernet Granularity and Gigabit Granularity.

Rate limit granularity is an additional feature enabling the network manager greater control over traffic on the network. The "rate limit granularity" is multiplied by the "rate limit level" to set the actual rate limit for an interface. Granularity is a global setting that applies to Fast Ethernet or Gigabit Ethernet interfaces.

Use the drop-down menus to change the rate limit for fast ethernet and/or gigabit granularity, click Submit.

Set the Input Rate Limit Status or Output Rate Limit Status, then set the rate limit for the individual interfaces, and click Apply.

To configure input rate limit for each port or lag, click Port Conf or Trunk Conf in the Input row of the table respectively. To configure output rate limit for each port or lag, click Port Conf or Trunk Conf in the Output row of the table respectively.

Rate Limit Configuration

To configure Port Input Rate Limit, click the Enable checkbox and then set the rate limit level in the textfield provided. Port Rate Output Limit is configured the same way on the Port Output Rate Limit Configuration screen. If a port is assigned as a lag member then the rate limit of that port cannot be set in the port configuration screen.

Truck Rate Limit is configured the same way as port rate limit using the trunk Input and output screens.

Note: When the rate limit granularity is set to a low value (for 10/100 ports, less than 512 Kbps), the maximum bandwidth available on ports is restricted to a value that is "256 x granularity." This restriction also applies to ports with rate limiting disabled.