BACKGROUND

Today, forwarding elements commonly have control and data plane components. A forwarding element's control plane component often provides the interface for configuring the components of the data plane, while the data plane handles the forwarding of the data messages that the forwarding element receives. The data plane is often referred to as the forwarding plane. The data plane often is a custom-made application specific integrated circuit (ASIC) that includes multiple ingress pipelines, multiple egress pipelines, and a switching fabric between the ingress and egress pipelines. The control plane, on the other hand, is typically managed by one or more off-the-shelf processors, which supports the interface for locally or remotely receiving parameters for configuring the forwarding element.

Control plane processors can fail, and such failures can cause the forwarding elements to fail. Also, these processors add to the expense of the forwarding element. High-end processors not only cost more, but often require additional expensive components, such as high-end cooling systems, etc.

SUMMARY

Some embodiments of the invention provide a forwarding element that can be configured through in-band data-plane messages from a remote controller that is a physically separate machine from the forwarding element. The forwarding element of some embodiments has data plane circuits that include several configurable message-processing stages, several storage queues, and a data-plane configurator. A set of one or more message-processing stages of the data plane is configured (1) to process configuration messages received by the data plane from the remote controller and (2) to store the configuration messages in a set of one or more storage queues. The data-plane configurator receives the configuration messages stored in the set of storage queues and configures one or more of the configurable message-processing stages based on configuration data in the configuration messages.

In some embodiments, the configurable message-processing stages of the data plane include several ingress processing pipelines, several egress processing pipelines, and a traffic management stage between the ingress and egress processing pipelines. The traffic management stage in some embodiments includes the set of storage queues that store the configuration messages that the data-plane configurator receives. Also, in some embodiments, at least one ingress pipeline comprises a set of match-action units (MAUs) that processes configuration messages from the remote controller to convert the configuration messages from a packet-in first format to a second format for processing by the data-plane configurator. This set of MAUs in some embodiments also process other data messages as part of the data plane's forwarding operations that are needed for the forwarding element to forward data messages to their destinations or their next hop (e.g., the next forwarding element).

The data-plane configurator in some embodiments examines a configuration message to determine whether it has been corrupted, and if so, it drops the message. The configurator determines whether a data message is corrupted differently in different embodiments. For instance, in some embodiments, the data-plane configurator computes a checksum for the received message, and drops the message when the checksum indicates that the message has been corrupted. In other embodiments, the data-plane configurator performs a cyclic redundancy check (CRC) operation on the received message, and drops the message when the CRC operation indicates that the message has been corrupted. In still other embodiments, the configurator performs both checksum and CRC operations to determine whether the received message has been corrupted.

To perform a checksum operation, the data-plane configurator verifies a checksum value computed by a message-processing stage for a configuration message that the configurator receives. For instance, in some embodiments, an ingress pipeline includes a parser that extracts data from headers of the configuration messages and inserts the extracted data into message header vectors for processing by the set of MAUs. In some of these embodiments, at least one MAU in the set of MAUs computes an expected checksum value for a payload of a received message by computing a checksum of the message header and differentiating (e.g., differencing or subtracting) this computed checksum from a message checksum that was stored by the remote controller in the message header. This MAU then stores this expected checksum in the message's header vector. The data configurator then computes actual checksum value for the payload of the message and discards the message when its computed actual checksum value does not match the expected checksum value computed by the MAU.

The data-plane configurator checks the messages from the remote controller for data corruption in order to ensure reliable data plane communication between the remote controller and the configurator. To ensure reliable communication, the configurator also drops messages that do not include the appropriate transaction identifiers. Specifically, in some embodiments, the remote controller and the forwarding element insert session and transaction identifiers in the inner headers of the messages that they exchange, in order to ensure reliable data plane communication. In some embodiments, each session corresponds to a task that the forwarding element or the remote controller has to perform, and each session includes one or more transactions. A session identifier identifies each session, while a transaction identifier identifies each transaction. In some embodiments, the configurator drops any message when the message contains a transaction identifier that does not follow the transaction identifier of the previous message in the same session.

After processing a configuration message, the data-plane configurator in some embodiments generates a response message to the remote controller and supplies the response message to the message-processing stages to process and forward to the remote controller through intervening network fabric. In some embodiments, the data-plane circuit generates a first replicated message by replicating the response message for recirculating through the message-processing stages until the remote controller acknowledges receiving the response message, at which time the first replicated response message is discarded.

For instance, in the embodiments where the configurable message-processing stages includes the ingress and egress pipelines and the traffic management stage, the first replicated message is periodically stored in a rate-limited storage queue in the traffic management stage as the first replicated message recirculates through the ingress pipeline stage, the traffic management stage and the egress pipeline stage. In some of these embodiments, one of the message-processing stages (e.g., one of the MAUs) in the ingress pipeline designates a header vector associated with the data-plane configurator's response message (e.g., stores a particular value in this header vector) to direct the traffic management stage to replicate this message for recirculation.

When no acknowledgement is received from the remote controller within a duration of time, a message processing stage of the data-plane circuit modifies the first replicated message to generate a second replicated message addressed to the remote controller for retransmission of the configurator's response message to the remote controller. In some embodiments, the data-plane circuit first sends a notification to the data-plane configurator regarding the lack of response, and the data-plane configurator then directs the data-plane circuit to generate the second replicated message to send to the remote controller.

When the data-plane configurator has to provide a transport-layer acknowledgment message to the remote controller to acknowledge receiving a configuration message from the remote controller, the data-plane configurator in some embodiments provides the transport-layer acknowledgement by piggybacking this acknowledgement message in the response message that the data-plane configurator generates and provides to the message-processing stages for forwarding to the remote controller. In some of these embodiments, the response message has the same transaction and session identifiers as the remote-controller message to which it responds. In other embodiments, the configurator only embeds the session identifier in the response message, and not the transaction identifier.

The preceding Summary is intended to serve as a brief introduction to some embodiments of the invention. It is not meant to be an introduction or overview of all inventive subject matter disclosed in this document. The Detailed Description that follows and the Drawings that are referred to in the Detailed Description will further describe the embodiments described in the Summary as well as other embodiments. Accordingly, to understand all the embodiments described by this document, a full review of the Summary, Detailed Description and the Drawings is needed. Moreover, the claimed subject matters are not to be limited by the illustrative details in the Summary, Detailed Description and the Drawings, but rather are to be defined by the appended claims, because the claimed subject matters can be embodied in other specific forms without departing from the spirit of the subject matters.

