WFQ provides traffic priority management that automatically sorts among individual traffic streams without requiring that you first define access lists. WFQ can also manage duplex data streams such as those between pairs of applications, and simplex data streams such as voice or video. There are two categories of WFQ sessions: high bandwidth and low bandwidth. Low-bandwidth traffic has effective priority over high-bandwidth traffic, and high-bandwidth traffic shares the transmission service proportionally according to assigned weights.
When WFQ is enabled for an interface, new messages for high-bandwidth traffic streams are discarded after the configured or default congestive messages threshold has been met. However, low-bandwidth conversations, which include control message conversations, continue to enqueue data. As a result, the fair queue may occasionally contain more messages than its configured threshold number specifies.
With standard WFQ, packets are classified by flow. Packets with the same source IP address, destination IP address, source TCP or User Datagram Protocol (UDP) port, or destination TCP or UDP port belong to the same flow. WFQ allocates an equal share of the bandwidth to each flow. Flow-based WFQ is also called fair queueing because all flows are equally weighted.
The Cisco IOS software provides two forms of flow-based WFQ:
Standard WFQ, which is enabled by default on all serial interfaces that run at 2 Mbps or below, and can run on all Cisco serial interfaces.
Distributed WFQ, which runs only on Cisco 7000 series routers with a Route Switch Processor (RSP)-based RSP7000 interface processor or Cisco 7500 series routers with a Versatile Interface Processor (VIP)-based VIP2-40 or greater interface processor. (A VIP2-50 interface processor is strongly recommended when the aggregate line rate of the port adapters on the VIP is greater than DS3. A VIP2-50 interface processor is required for OC-3 rates.) .
Flow-based WFQ uses a traffic data stream discrimination registry service to determine to which traffic stream a message belongs. Refer to the table accompanying the description of the
fair-queue (WFQ) command in the Cisco IOS Quality of Service Solutions Command Reference for the attributes of a message that are used to classify traffic into data streams.
Defaults are provided for the congestion threshold after which messages for high-bandwidth conversations are dropped, and for the number of dynamic and reservable queues; however, you can fine-tune your network operation by changing these defaults. Refer to the tables accompanying the description of the
fair-queue (WFQ) command in the Cisco IOS Quality of Service Solutions Command Reference for the default number of dynamic queues that WFQ and CBWFQ use when they are enabled on an interface or ATM VC. These values do not apply for DWFQ.
WFQ is the default queueing mode on interfaces that run at E1 speeds (2.048 Mbps) or below. It is enabled by default for physical interfaces that do not use Link Access Procedure, Balanced (LAPB), X.25, or Synchronous Data Link Control (SDLC) encapsulations. WFQ is not an option for these protocols. WFQ is also enabled by default on interfaces configured for Multilink PPP (MLP). However, if custom queueing (CQ) or priority queueing (PQ) is enabled for a qualifying link, it overrides fair queueing, effectively disabling it. Additionally, WFQ is automatically disabled if you enable autonomous or silicon switching.
If you enable flow-based DWFQ and then enable class-based DWFQ (either QoS-group based or ToS-based), class-based DWFQ will replace flow-based DWFQ.
If you enable class-based DWFQ and then want to switch to flow-based DWFQ, you must disable class-based DWFQ using the
class-based command before enabling flow-based DWFQ.
If you enable one type of class-based DWFQ and then enable the other type, the second type will replace the first.
DWFQ runs only on Cisco 7000 series routers with an RSP-based RSP7000 interface processor or Cisco 7500 series routers with a VIP-based VIP2-40 or greater interface processor. (A VIP2-50 interface processor is strongly recommended when the aggregate line rate of the port adapters on the VIP is greater than DS3. A VIP2-50 interface processor is required for OC-3 rates.)
DWFQ can be configured on interfaces but not subinterfaces. It is not supported on Fast EtherChannel, tunnel, or other logical or virtual interfaces such as MLP.
For flow-based DWFQ, packets are classified by flow. Packets with the same source IP address, destination IP address, source TCP or UDP port, destination TCP or UDP port, and protocol belong to the same flow.
To configure flow-based WFQ, perform the tasks described in the following sections.
Flow-based WFQ is supported on unavailable bit rate (UBR), variable bit rate (VBR), and available bit rate (ABR) ATM connections.