SDN Programming with Go

SDN Programming
with Golang
28 Feb 2019
Donaldson Tan
donaldson.tan@shukra-networks.com
Founder / Software Engineer

Shukra Networks
● Telecommunications startup
● Developing our own proprietary SDN stack
● Our focus is on
○ Wide Area Networking
○ inter-AS routing

Table of Content
● Network Programmability
● OSI Reference Model
● SDN Architecture
● Decoupling
● Using NFF-Go
● Packet Processing Graph
● User Defined Functions
● Packet Modification

Network Programmability
● Network Programmability is the capacity to
initialise, control, change and manage network
behavior dynamically via open interfaces.
● Software Defined Networking (SDN) is a specific
type of network programmability that supports the
separation of the control and forwarding planes via
standardised interfaces.
RFC 7426

Terminology
➔ Forwarding Plane
Collection of all network devices
responsible for forwarding packets.
Also known as Data Plane.
➔ Control Plane
Collection of functions that instructs
network devices how to process and
forward packets.
➔ Management Plane
Collection of functions that is
responsible for monitoring, configuring,
and managing network devices.
RFC 7426

OSI Reference Model
● The OSI paradigm describes computer networking
between 2 hosts from an application developer’s
perspective.
● The application developer emphasises on
transmitting/receiving data across the network.
● Network topology, network services, network
management are an awkward fit in the OSI model.

SDN Architecture
Network Services
Control Plane Management Plane
Forwarding Plane
● The SDN paradigm describes
computer networking from a
network operator’s perspective.
● The network operator emphasises
on managing and optimising the
network for cost and reliability.
● Note: The Management Plane
talks to the Forwarding Plane
because it uses the Forwarding
Plane to collect network statistics.
Applications

Decoupling Forwarding and Control Planes
● There are many ways to access the Forwarding Plane but we will be
focusing how to do it via Golang.
● Data Plane Development Kit (DPDK)
○ Hardware support by Intel, Marvell, Mellanox, Cavium
○ QEMU-Virtio also supports DPDK
○ NFF-Go provides Go binding to the DPDK
○ Install DPDK and NFF-Go separately.
○ Important: Register the NIC(s) with the DPDK driver and setup 1GB
Huge Pages. Don’t register the Management NIC.

Using NFF-Go
● import “github.com/intel-go/nff-go/flow”
● import “github.com/intel-go/nff-go/packet”
● A skeletal NFF-Go program consists of
○ A packet processing graph
■ A DAG consists of Entry, Transient and Exit Nodes
○ User Defined Functions (UDF)
■ UDFs may be attached to each flow
■ UDFs are responsible for processing individual packets, such as
● Modify packet content
● Update flow counters, program state
○ An optional interface for communicating with an external controller
■ E.g. API, RPC, RMI, XMPP
■ Important: Run the interface on the Management NIC.

Packet Processing Graph
Entry
Transient
Exit

● Directed Acyclic Graph (DAG), which means NO LOOPS.
● Initialise with flow.SystemInit(flow.Config{CPUList:”0-7”})
○ This tells NFF-Go to reserve logical cores 0-7 exclusively.
○ Do not use up all the logical cores, so they may be assigned to the Go
scheduler, hypervisor.
○ Use Go’s default scheduler to run the Management Interface.
● Launch the Packet Processing Graph with flow.SystemStart()

● Entry Nodes are specified by
○ flow1, err := flow.SetReceiver( uint port)
○ flow1, err := flow.SetGenerator(UDF, speed, context)
○ flow1, err := flow.SetReader(pcap_file, n)
● Exit Nodes are specified by
○ flow.SetStopper(flow1)
○ flow.SetSender(flow1, port_number)
○ flow.SetWriter(flow1, pcap_filename)

● Transient Nodes are specified by
○ rejectedFlow, err := flow.SetSeparator(flow1, UDF, context)
○ outputFlows, err := flow.SetSplitter(flow1, UDF, num_outflows, context)
○ mFlow, err := flow.SetPartitioner(flow, N, M)
○ mergedFlow, err := flow.SetMerger(flowArrays)

User Defined Functions
● Attach UDF to a flow using
○ err := flow.SetHandler(UDF, flow1)
● Take note of the several UDF types
○ HandleFunction(Packet, Context)
○ VectorHandleFunction(PacketVector[], Context)
○ SeparateFunction(Packet, Context) Bool
● Packet modification takes place inside the UDF
○ The first parameter is the packet itself.

Packet Modification
● Packet headers can be read and modified with the packet data type.
● Built-in methods for generating
○ default packets for Ethernet, IPv4, IPv6
○ ICMP/ARP requests / replies
● The more important methods are
○ pkt.GetIPv4NoCheck() /pkt.GetIPv6NoCheck()
○ pkt.GetTCPNoCheck()
○ pkt.GetUDPNoCheck()
● These methods return the packet’s relevant header which you may
rewrite directly.
● Next slides show the header format for IPv4, IPv6, TCP and UDP.

Packet Modification
● IPv4 Header ● IPv6 Header

Packet Modification
● TCP Header ● UDP Header

But how do I separate the
forwarding and control
planes in the OSI model?
You don’t!

Open vSwitch
VM1 VM2
Open vSwitch
VM3 VM4
Host 1 Host 2
Physical Network
VXLAN Tunnel
What is SDN used for?
● Network Virtualisation. E.g. Amazon’s VPC is actually a
L2VPN distributed across multiple hypervisors.
VPC

● High Performance
Cloud Network
Appliances
● Security
○ DDoS Filtering
○ Deep Packet
Inspection

● Custom Traffic Engineering
○ Network telemetry
○ Load Balancing
○ Intelligent Routing
○ Congestion Control
○ Traffic Shaping
○ QoS

SDN Programming with Go

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