The FlowAdapter: Enable Flexible Multi-Table Processing On Legacy Hardware

Heng Pan , Hongtao Guan, Junjie Liu (ICT, CAS)

Wanfu Ding, Chengyong Lin (Huawei Technologies Co. Ltd.)Gaogang Xie (ICT, CAS)

Heterogeneous OpenFlow Switches Different number of flow tables. Various match field types

Diversity of controller-issued rules Elimination to the heterogeneity of OpenFlow switch Abstraction of hardware capabilities for rules Flexibility and programmability in the heterogeneous OpenFlow

network.

Motivation

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Motivation (cont.)

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Hardware Capability

Hardware Capability

Motivation (cont.)

Hardware Capability

Hardware Capability

Legacy Switch

Rules

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How to issue rules to switch hardware correctly? How to express packet processing functionality in a way

that is independent of the specific capabilities of the switch hardware?

How to capitalize on legacy data-plane hardware?

Questions

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Our goals To address the mismatch between the controller-issued rules

and the capabilities of the hardware switches Challenges

The unpredictability of controller-issued rules The types of match fields The flow tables involved The hardware capabilities of diverse switches ……

The equivalent conversion of multi-stage flow tables The match result The actions

Challenges

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Convert M-stage flow tables into N-stage flow tables equivalently Packet match result Packet match fields’ modification Packet execution actions

Design and implement a adapter layer Allow programmers to write rules more flexibly Capitalize on more legacy switches

Contributions

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Architecture Software data plane

To support flexible multi-stage

rule tables

Hardware data plane To achieves high-speed packets

forwarding

The FlowAdapter A mid layer let controller-rules

fit hardware capabilities

Overview

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Enable controller-issued rules fit into hardware MTO

Convert M-stage flow tables into One-stage flow table– M-stage flow tables are from software data plane– Flexibility and Scalability

OTN Convert One-stage flow table into N-stage flow tables

– N-stage flow tables are based on hardware capabilities– Limited by hardware

Based on OpenFlow1.2

The FlowAdapter

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The pipeline processing of multi-stage flow tables is complex A flow entry may belong to many rules. Not all rules begin from flow table 0.

What are Complete rules? Rules consist of many flow entries. The flow entries of the last table of the pipeline don’t contain

the Goto-table instruction.

Observation

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Representing the pipeline Node type

Default: – This type nodes don’t contain match fields.– It is a table miss when the packet does not match a flow entry in a flow

table.– The behavior storing in this type node will be executed when it occurs a

table miss. Normal:

– This type nodes contain match fields.– The Instruction set of the node will be executed if packets are matched

against the node.

Data structure

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Representing the pipeline N-tree

Type one– Root node is from flow table 0.– The root node and child nodes are normal type.

Type two– Root node is the default type.– Child nodes are default type or normal type. Those normal type nodes

are the root of type three N-tree. Type three

– Root node is not from flow table 0.– The root node and Child nodes are normal type.

Data structure (cont.)

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Data structure (cont.)

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MTO Construct three types N-trees

Using metadata to achieve the pipeline of M-stage flow tables

Obtain leaf nodes Only need to get the leaf nodes of type 1 and type 3 N-trees A leaf node can represent a completed rule

Generate One-stage flow table To construct a one-stage flow entry Eliminate redundant match fields and instructions

– E.g. Goto-Table and Write-Metadata instructions

Design and Implementation

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MTO (cont.)

Design and Implementation

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OTN Initializing N-stage flow tables

Being configured flexibly by programmers Including numbers and each table match fields

Splitting One-stage flow table rules Constructing a flow entry for each N-stage flow table Padding match fields and instructions into those flow entries

– Based on the configuration of N-stage flow table Deleting those flow entries which don’t contain any match field

Inserting the flow entries into N-stage flow tables

Design and Implementation

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OTN (cont.)

Design and Implementation

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Flow table Initialization

One-stage flow table rules split

The FlowAdapter is a efficient Adaptation layer to enable controller-issued rules fit into hardware

The conversion between M-stage flow tables and N-stage flow tables

Improve the existing model Incremental update of the N-tree Improve the scalability of the FlowAdapter

Conclusions and Future work

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Thank you!

More information: http://fi.ict.ac.cn