Open-source domain-specific language (DSL) for programmable ... E.g. PISA architecture, ingress/egress pipeline architec
Introduction to P4 ONOS-P4 Brigade Work Days, Seoul (Korea) September 18-29, 2017
What is P4? • Open-source domain-specific language (DSL) for programmable dataplanes • Protocol independent • Support for a variety of targets: ASICs, FPGAs, NICs, software • Field reconfigurable: add/remove capabilities to switches after they are deployed
• Based on the well known Match+Action forwarding model • 2 versions of the language: P4_14, P4_16 • We focus on P4_16
Outline • Programmable switch architecture • Workflow • P4 tools • p4c (compiler) • BMv2 (reference software switch) • P4Runtime (control plane framework)
Not covering the language, we will reverse engineer the example program during the hands-on
P4 Paradigm
OpenFlow or legacy
PISA: Protocol-Independent Switch Architecture Programmer declares the headers that should be recognized and their order in the packet
Slide courtesy: Vladimir Gurevich, P4_16 Tutorial. P4 Workshop 2017
Programmer defines the tables and the exact processing algorithm
Programmer declares how the output packet will look on the wire
Mapping a simple logical pipeline on PISA
Ethernet address table
Slide courtesy: Vladimir Gurevich, P4_16 Tutorial. P4 Workshop 2017
IPv4 address table
IPv6 address table
ACL filter table
P4 programs
my_program.p4 Defines the processing of each block
switch_arch.p4
Defines which blocks are available and the interface of each block
P416 terminology • P4 Target
• An embodiment of a specific hardware or software implementation • E.g. Barefoot’s Tofino chip, Netronome’s SmartNICs, BMv2 software switch, etc.
• P4 Architecture
• Set of P4-programmable components, externs, fixed components and their interfaces available to the P4 programmer • E.g. PISA architecture, ingress/egress pipeline architecture, etc. • Expressed as a P4 program Community-developed P416 Language
P416 Core Library
Vendor-supplied Architecture definition
Extern libraries
Portable Switch Architecture (PSA) • Community-developed architecture
• https://github.com/p4lang/p4-spec/tree/master/p4-16/psa
• Describes common capabilities of a network switch
• Which process and forward packets across multiple interface ports
• 6 programmable P4 blocks + 2 fixed-function blocks • P414 constructs removed from P416 now defined as PSA-specific externs • Counters, meters, stateful registers, hash functions, etc.
Workflow overview Control plane
p4c my_program.p4
P4 Compiler
arch.p4
Target-specific configuration/binary
Manufacturer supplied
P4Runtime
LOAD
Tables
Extern objects
BMv2
Data plane
p4c • https://github.com/p4lang/p4c • Open-source front-end compiler Compiler$data$flow • Support multiple back-ends (vendor-supplied)
• Generate code for ASICs, NICs, FPGAs, software switches and other targets • Some of them are open-source (BMv2, eBPF)
P414
P414 parser
v1 IR
ebpf back*end
C$code
mid* end
BMv2 back*end
JSON
mid* end
your own backend
target* specific code
convert IR
P416
mid* end
P416 parser
Slide courtesy: M. Budiu, C. Doss. The architecture of the P4_16 compiler. P4 Workshop 2017
frontend
IR
BMv2 • https://github.com/p4lang/behavioral-model • BMv2 = Behavioral-Model version 2 • User-space software switch to emulate a P4 data plane • Aimed at being 100% conformant to the P4 specification • Performance is non-goal, i.e. low throughput • Architecture-independent • Mostly generic code which can be used to implement any P4 target • Some targets provided as part of the repo, e.g. simple_router, simple_switch
BMv2’s simple_switch target
Parser
Packets Ingress pipeline
Multicast groups management
Packet Replication Engine (PRE)
configure
p4c-bm-ss my_program.p4
p4c compiler with simple_switch back-end
my_program.json
Table management Thrift-based RPC API
Egress pipeline
Deparser
Table management
P4Runtime • https://github.com/p4lang/PI • Framework for runtime control of P4-enabled devices • Developed by the p4.org API WG • Specification is still work-in-progress by API WG
Remote controller (e.g. ONOS) p4runtime.proto (interface)
• Specifically targeted for remote controllers • Protobuf + gRPC implementation
• P4 program-independent
• API doesn’t change with the P4 program
• Enables field-reconfigurability
• Ability to push a new P4 program to the device
Program-independent control server (gRPC) HW/SW target (e.g. BMv2 simple_switch, tofino chip, etc.)
Switch
p4runtime.proto • Allow interacting with entities defined in a P4 program • Tables, counters, meters, externs, etc.
• Bidirectional stream channel
• For packet-ins/outs, mastership updates, etc.
• P4 architecture-independent
• Easily extensible to support vendor-specific externs • Hardcoded support for PSA
Refers to P4 entities by integer IDs. How to get such IDs?
P4Runtime workflow P4Runtime PI Interface Workflow
switch.p4
• P4Info proto
• captures target-independent P4 program attributes • defines numeric IDs for P4 tables, actions, params, ● P4Info proto ○ captures target-independent P4 program attributes etc. ○
defines IDs for P4 tables, actions, params, etc.
• Target config ●
p4c front-end
IR
P4Info
IR = P4 compiler intermediate representation
• P4Info + device-specific configuration (e.g. BMv2’s ● Target Config JSON, Tofino binary, etc.) ○
●
p4c back-end
P4Info + P4-program mapping to silicon
target config
P4Runtime defines the PI interface ○
Refers to P4 entities by integer IDs coming from P4Info
rpc Controller Front-end p4runtime protos
Slide courtesy: S. Abdi, W. Mohsin, Y. Yetim, A. Ghaffarkhah. P4 Program-Dependent Controller Interface for SDN Applications. P4 Workshop 2017
PI
P4Runtime Interface
Switch 3
P4Info example P4Info Example action set_vrf(bit id) { meta.vrf_id = id; } table vrf_classifier_table { key = { hdr.ethernet.etherType : exact; hdr.ethernet.srcAddr : ternary; smeta.ingress_port: exact; } actions = { set_vrf; } default_action = set_vrf(0); }
action id: 16777233 param id: 50336000
p4c front-end
table id: 33554433 match_field id: 67108875 match_type: EXACT match_field id: 67108864 match_type: TERNARY match_field id: 67108870 match_type: EXACT action_ref id: 16777233
vrf.p4 vrf.p4 Slide courtesy: S. Abdi, W. Mohsin, Y. Yetim, A. Ghaffarkhah. P4 Program-Dependent Controller Interface for SDN Applications. P4 Workshop 2017
P4Info for vrf.p4 P4Info for vrf.p4
4
PIP4Runtime example Proto Example action set_vrf(bit id) { meta.vrf_id = id; } table vrf_classifier_table { key = { hdr.ethernet.etherType : exact; hdr.ethernet.srcAddr : ternary; smeta.ingress_port: exact; } actions = { set_vrf; } default_action = set_vrf(0); }
vrf.p4
table_entry { table_id: 33554433 match { field_id: 67108875 exact { value: \x08\x00 } } match { field_id: 67108870 exact { value: \x00\x00\x00\x00\x11\x01 } } ...
... table_action { action { action_id: 16777233 params { param_id: 50336000 value: \x00\x00\x00\x70 } } } }
PI message instance
Slide courtesy: S. Abdi, W. Mohsin, Y. Yetim, A. Ghaffarkhah. P4 Program-Dependent Controller Interface for SDN Applications. P4 Workshop 2017
5
Questions?
