2016 NCTU P4 Workshop
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This document provides an overview of the NCTU P4 Workshop. It discusses: - The P4 programming language which allows specifying how switches process packets in a protocol-independent and target-independent way. - Key concepts in P4 including headers, parsers, tables, actions, and the control flow. - An example P4 architecture and how to define headers, parsers, tables, and the control flow. - How to get started with P4 including setting up the behavioral model compiler and runtime environment and using Mininet to test P4 programs. - A quick demo of a simple P4 program that uses a custom header to implement path routing and can be configured via the runtime
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Ingress control
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pkt[0:24] == 0xc0ffee
my_path_header
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2016 NCTU P4 Workshop
- 1. NCTU P4 Workshop Tseng Yi NCTU W2CNLab https://takeshi.tw/tag/p4/ 1
- 2. Outline • Introduction • Architecture • Header and Parser • Action and Table • Control flow • Register, Metadata, Counter and Meter • Getting start 2
- 3. Introduction • Programming Protocol-Independent Packet Processors. • Describe how to handle a packet for a target. • White box in white box. 3
- 4. Introduction • Protocol Independent • P4 programs specify how a switch processes packets. • Target Independent • P4 is suitable for describing everything from high- performance forwarding ASICs to software switches. • Field Reconfigurable • P4 allows network engineers to change the way their switches process packets after they are deployed.
- 5. P4 is not • SDN Software Switch • OpenFlow or Protocol • Network abstraction • Won’t compile to OpenFlow or any southbound message. 5
- 6. P4 can But OpenFlow Switch can’t • Parse or modify L5~ header (e.g. inner ethernet header from VXLAN, DNS query data, DHCP header…) • Define new protocol parser • Stateful switch (need newest version of OvS or modified OF switch) • Flexible match field and table size of any table. • Define new actions for tables. 6
- 7. Architecture Headers Parsers Control Program Table Config Packet Input Parser Tables Tables Queues and/or Buffers Ingress Egress 7 Deployment host P4 Target
- 8. How to write P4? 1. Define headers and parsers (parser graph) 2. Define actions, match fields for table. 3. Design a control flow for your target. 8
- 10. Header • Like “struct” from C/C++, but more flexible. header_type eth_t { fields { dst : 48; src : 48; ethType : 16; } } header eth_t eth; 10
- 11. Parser • Parse(extract) a packet step by step. • Eth ————> IPv4 ———>TCP parser parser_eth { extract(eth); return select(eth.type) { 0x800: parser_ipv4; default: ingress; } } parser parser_ipv4 { extract(ipv4); return select(latest.proto) { 6: parser_tcp; default: ingress; } } 11 type 0x0800 proto 6
- 12. Actions • Like a function(but no return value). • In one function, you can use one or more P4 API (e.g. modify_field, add_header…) • Can be executed in parallel (depends on implementation of target) 12
- 13. action set_dst_mac_and_output(new_mac, outport) { modify_field(eth.dst, new_mac); modify_field(standard_metadata.egress_spec, outport) } • For example, if we want to set destination mac address and output port. Actions 13
- 14. Table • Every table might contains different match field and actions. • Each table might have different features • Not just P4, Some vendors slice tables for different purpose, for example: OFDPA from Broadcom
- 15. Table definition table first_table { reads { ipv4.dst : lpm; // exact, lpm, ternary, range, valid } actions { drop; set_dst_mac_and_output; } size 1024; }
- 16. Add one Flow Entry • Currently, ways to control a P4 target (bmv2): • Use runtime command line interface • ONOS test app for bmv2 p4cli> table_add first_table set_dst_mac_and_output 10.0.0.0/24 => 00:00:00:00:00:01 1
- 17. Control flow • Also like a function, but no argument or return value • Main control flow: ingress and egress • In control flow, you can： • apply packet to specific tables • go to other control flows • When ingress ends, data will be sent to queue or buffer, then handle by egress control flow.
- 18. Control flow • Ingress: • Modify state (register) • Modify packet • Modify metadata • Modify egress_spec (e.g. queue, output port) • Egress: • Modify packet
- 19. Control Flow control ingress { apply(in_port); apply(vlan); apply(termination_mac): if(valid(ipv4)) { apply(l3_flow); } apply(unicast); apply(multicast); apply(bridging); apply(acl); }
- 20. Register & Metadata Counter & Meter
- 21. Register, Metadata • Register • Like global variable, store data • Can be use for stateful dataplane design • Metadata • Like local variable, reset after one control flow ended. • If we need to use register, we need to load register to metadata.
- 22. Counter • Counter • Count bytes or packets • Update when table match or action call • Fixed size, will stop counting or reset to zero (depends on program)
- 23. Meter • Like counter, but it monitoring packet rate, not packet/byte count.
- 24. Getting start
- 25. Getting start • Basic knowledge: • Linux shell (network & system commands) • Linux basic tools (git, tmux…) • GNU compiler toolchain (for bmv2) • Python & C/C++ • FSM, data structure, network
- 26. Getting start • Setup env： • bmv2 • https://github.com/p4lang/behavioral-model • p4c-bm • https://github.com/p4lang/p4c-bm • editor plugins (optional) • https://github.com/TakeshiTseng/atom-language-p4 • https://github.com/TakeshiTseng/vim-language-p4
- 27. Workflow（bmv2） • Write P4 program • Generate json file by using p4c-bmv2 • Use json to start a bmv2 target (e.g. simple_switch)
- 28. Use mininet • from p4_mininet import P4Switch, P4Host • Setup cls parameter for addSwitch and addHost.
- 29. Use mininet • net.addSwitch('s1', cls=P4Switch, sw_path=SW_PATH, json_path=JSON_PATH, thrift_port=9091) • sw_path: bmv2 target path • json_path: json file generated by p4c-bm • thrift_port: port number for runtime API
- 30. P4 thrift API • Connect bmv2 target and runtime CLI or Conroller (e.g. ONOS) • You can use runtime_CLI.py from bmv2 repository.
- 32. Quick Demo • Goal： • Use new protocol instead of ethernet. • Path routing. • Setup by runtime CLI.
- 33. Normal packet With path header src (16 bit) dst (16 bit) payload normal packet path (16 bit) preamble (24 bit)
- 34. start Ingress control pkt[0:24] != 0xc0ffee pkt[0:24] == 0xc0ffee my_path_header my_header
- 35. Parser apply “forward” apply “path_look_up” Egress path is not valid path header is valid
- 36. Demo topology P4 Switch 1 Host 3 Host 4 P4 Switch 2 P4 Switch 3 P4 Switch 4 Host 1 Host 2 Number of path : P(4, 2) = 12 00 02 02 00 02 02 1 1 1 1
- 37. Quick Demo
- 38. Software Defined Networking Developer Society • http://sdnds.tw • https://www.facebook.com/groups/sdnds.tw
Editor's Notes
- #37: Permutation