The BIG-IP® system includes a feature called rate shaping. Rate shaping allows you to enforce a throughput policy on incoming traffic. Throughput policies are useful for prioritizing and restricting bandwidth on selected traffic patterns.
Rate shaping can be useful for an e-commerce site that has preferred clients. For example, the site might want to offer higher throughput for preferred customers, and lower throughput for other site traffic.
The rate shaping feature works by first queuing selected packets under a rate class, and then dequeuing the packets at the indicated rate and in the indicated order specified by the rate class. A rate class is a rate-shaping policy that defines throughput limitations and a packet scheduling method to be applied to all traffic handled by the rate class.
You configure rate shaping by creating one or more rate classes and then assigning the rate class to a packet filter or to a virtual server. You can also use the iRules® feature to instruct the BIG-IP system to apply a rate class to a particular connection.
You can apply a rate class specifically to traffic from a server to a client or from a client to a server. If you configure the rate class for traffic that is going to a client, the BIG-IP system does not apply the throughput policy to traffic destined for the server. Conversely, if you configure the rate class for traffic that is going to a server, the BIG-IP system does not apply the throughput policy to traffic destined for the client.
A rate class defines the throughput limitations and packet scheduling method that you want the BIG-IP® system to apply to all traffic that the rate class handles. You assign rate classes to virtual servers and packet filter rules, as well as through iRules®.
If the same traffic is subject to rate classes that you have assigned from more than one location, the BIG-IP system applies the last-assigned rate class only. The BIG-IP system applies rate classes in the following order:
You can create a rate class using the BIG-IP Configuration utility. After you have created a rate class, you must assign it to a virtual server or a packet filter rule, or you must specify the rate class from within an iRule.
The first setting you configure for a rate class is the rate class name. Rate class names are case-sensitive and might contain letters, numbers, and underscores (_) only. Reserved keywords are not allowed.
Each rate class that you define must have a unique name. This setting is required.
To specify a rate class name, locate the Name field on the New Rate Class screen and type a unique name for the rate class.
The Base Rate setting specifies the base throughput rate allowed for traffic that the rate class handles. The sum of the base rates of all child rate classes attached to a parent rate class, plus the base rate of the parent rate class, cannot exceed the ceiling of the parent rate class. For this reason, F5 Networks® recommends that you always set the base rate of a parent rate class to 0 (the default value).
You can specify the base rate in bits per second (bps), kilobits per second (Kbps), megabits per second (Mbps), or gigabits per second (Gbps). The default unit is bits per second. This setting is required.
The Ceiling Rate setting specifies the absolute limit at which traffic is allowed to flow when bursting or borrowing. You can specify the ceiling in bits per second (bps), kilobits per second (Kbps), megabits per second (Mbps), or gigabits per second (Gbps). The default unit is bits per second.
If the rate class is a parent rate class, the value of the ceiling defines the maximum rate allowed for the sum of the base rates of all child rate classes attached to the parent rate class, plus the base rate of the parent rate class.
You use the Burst Size setting when you want to allow the rate of traffic flow that a rate class controls to exceed the base rate. Exceeding the base rate is known as bursting. When you configure a rate class to allow bursting (by specifying a value other than 0), the BIG-IP® system saves any unused bandwidth and uses that bandwidth later to enable the rate of traffic flow to temporarily exceed the base rate. Specifying a burst size is useful for smoothing out traffic patterns that tend to fluctuate or exceed the base rate, such as HTTP traffic.
The value of the Burst Size setting defines the maximum number of bytes that you want to allow for bursting. Thus, if you set the burst size to 5,000 bytes, and the rate of traffic flow exceeds the base rate by 1,000 bytes per second, then the BIG-IP system allows the traffic to burst for a maximum of five seconds.
When you specify a burst size, the BIG-IP system creates a burst reservoir of that size. A burst reservoir stores bandwidth that the BIG-IP system uses for bursting later. The burst reservoir becomes depleted as the rate of traffic flow exceeds the base rate, and is replenished as the rate of traffic falls below the base rate. The Burst Size value that you configure in a rate class thus represents:
The burst size is measured in bytes. For example, a value of either 10000 or 10K equals 10,000 bytes. The default value is 0.
When the rate of traffic flow exceeds the base rate, the BIG-IP® system automatically depletes the burst reservoir, at a rate determined by the number of bytes per second that the traffic flow exceeds the base rate.
Continuing with our previous example in which traffic flow exceeds the base rate by 1,000 bytes per second, if the traffic-flow rate only exceeds the base rate for two seconds, then 2,000 bytes are depleted from the burst size and the maximum bytes available for bursting decreases to 3,000.
When the rate of traffic flow falls below the base rate, the BIG-IP® system stores the unused bandwidth (that is, the difference between the base rate and the actual traffic-flow rate) in the burst reservoir. Later, the BIG-IP system uses this bandwidth when traffic flow exceeds the base rate. Thus, the BIG-IP system replenishes the burst reservoir whenever it becomes depleted due to traffic flow exceeding the base rate.
The size of the burst reservoir cannot exceed the specified burst size. For this reason, the BIG-IP system replenishes the reservoir with unused bandwidth only until the reservoir reaches the amount specified by the Burst Size setting. Thus, if the burst size is set to 5,000, then the BIG-IP system can store only 5,000 bytes of unused bandwidth for later use when the rate of traffic flow exceeds the base rate.
This example illustrates the behavior of the BIG-IP® system when you set the Burst Size setting to a value other than 0.
This example shows throughput rates in units of bytes-per-second instead of the default bits-per-second. This is only to simplify the example. You can derive bytes-per-second from bits-per-second by dividing the bits-per-second amount by 8.
Suppose you configure the rate class settings with these values:
Consider the following scenario:
Using the Direction setting, you can apply a rate class to client or server traffic. Thus, you can apply a rate class to traffic going to a client, to a server, or to both client and server. Possible values are Any, Client, and Server. The default value is Any.
Specifying direction is useful in cases where the nature of the traffic is directionally-biased. For example, if you offer an FTP service to external clients, you might be more interested in limiting throughput for those clients uploading files to your site than you are for clients downloading files from your site. In this case, you would select Server as the direction for your FTP rate class, because the Server value only applies your throughput restriction to traffic going from the client to the server.
When you create a rate class, you can use the Parent Class setting to specify that the rate class has a parent class. This allows the child rate class to borrow unused bandwidth from the ceiling of the parent class. A child class can borrow unused bandwidth from the ceiling of its parent, but a parent class cannot borrow from a child class. Borrowing is also not possible between two child classes of the same parent class or between two unrelated rate classes.
A parent class can itself have a parent, provided that you do not create a circular dependency. A circular dependency is a relationship where a rate class is a child of itself, directly or indirectly.
If a rate class has a parent class, the child class can take unused bandwidth from the ceiling of the parent class. The process occurs in this way:
Borrowing only allows the child to extend its burst duration; the child class cannot exceed the ceiling under any circumstance.
This setting specifies a shaping policy that includes customized values for drop policy and queue method. The default value is None.
You can create additional shaping policies using the Traffic Management shell (tmsh).
The Queue Method setting determines the method and order in which the BIG-IP® system dequeues packets.
A rate class supports two queue methods:
The BIG-IP® system drops packets whenever the specified rate limit is exceeded. A drop policy specifies the way that you want the system to drop packets. The default value is fred.
Possible values are:
You can create additional drop policies using the Traffic Management shell (tmsh).