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  • basic control plane communication between freeRouter and BMv2/simple_switch_grpc
  • and the simple packet_in/packet_out header used in this interface communication.

Requirement

  • Basic Linux/Unix knowledge
  • Service provider networking knowledge

image2020-6-29_13-54-48.png

Overview

P4 is a language for programming the data plane of network devices. From p4.org web site:

«P4 is a domain-specific programming language for specifying the behaviour of the dataplanes of network-forwarding elements. »

Article objective

This 1st article exposes:

...

Info
titleNote

This article is preliminary a pure introduction to P4lang P4. It does not correspond in any way to an extensive programming language description nor a P4 compilation guide

Diagram: P4 development workflow

[ #001 ] - Cookbook: P4 development workflow

Expand
titleP4 in a nutsgell

Based on what we mentioned, what "P4 Domain specific language" brings to you ? Concretely:

  1. you can write a program as you would in C or C++ but you'd have to follow P4 language specification. (The current is P4_16, there is also the a previous P4_14 specification)
  2. that program is compiled with a p4 compiler in P4_16 or P4_14. (similar to C++14/C++11) 
  3. Resulting compilation artefacts artifacts can be then loaded into an equipment implementing a P4 model commonly called a P4 target that is able to interpret/run p4 binaries. Here we will be using BMv2, a softwarized P4 target intended for learning.


Warning
titleTake away

The specificities are:

  • This P4 program is YOUR program
  • This P4 program allows you to define the YOUR OWN packet processing logic

In short, you can now program:

« how a packet that comes into your system, is processed and goes out your system»


Info
titleDiagram packet processing description

The diagram above depicts 2 perspectives: 

  • P4 program development workflow
    • It starts by writing your P4 program using your favorite editor
    • compile your program with the P4 compiler of your target
    • load your program into the P4 target
  • my_program.p4 packet progressing logic: "all packest packets arriving at port 4 is are switched/forwarded to port 8"
    • In this example, the switch has 8 ports
    • A ingress packet arrives at port 4
    • the ingress is port is then checked
    • If it is port 4, then the packet is switched to port 8
    • my_program.p4 does not implement a default condition, so all the packets not arriving on port 4 are then dropped
    • the ingress packets arrived with a header with charateristics set by the previous node
    • if needed my_program.p4 is able to set modify the egress packet header for further processing by the next network node (Example of Inband network Telemetry)


Router for Academia Research & Education (RARE) & P4

Expand
titleP4 rationale

RARE project objective is to provide a networking solution to Research & Education institution use cases. While we witnessed the birth of several control plane such as GNU Zebra, Bird, exaBGP, etc. The common point of these softwares is that they don't have the capability (yet) to be coupled easily with a hardware dataplane. Simply put, these software control plane cannot be used without specific/important development in order to run on an equipment able to forward nx100GE links at a high Mpps rate. 

There have been attempts with DPDK and other kernel bypass mechanism, that enabled higher throughput processing capability, but this is not comparable to commercial/vendor equipment's packet processing power. 

P4:

  • opens you the door to software AND hardware dataplane programmability
  • gives you the possibility to implement YOUR own packet processing algorithm 
Info
titleRARE contro plane: freeRouter

In RARE project we are using a software control plane called freeRouter:

  • It is an open source control plane
  • It has been developed and maintained by Csaba MATE, who is working for KIFU the Hungarian NREN
  • It has been deployed since 2014 and benefits from hours of production in various environment
  • Interworking has been extensively and continuously tested with major equipment vendors
  • Last but not least Csaba is included in RARE team which allowed Rapid Application development and prototyping in order to build control plane and P4 dataplane communication.


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Expand
titleP4 RARE use cases

This is the use cases enabled by the combination of P4 and RARE software:

  • Service Provider core router:

You can build a robust packet switching fabric at the scale of Telecom Service Provider able to switch packet at nx100GE

  • Service Provider edge router: 

You can build an edge router an Interconnect the core router above. These router will terminate your backbone network service like L2/L3 plain IP or VPN services (IPv4 - IPv6)  

  • Datacenter ToR switch 

With the WEDBE100BF32X you can have 2x100GE uplinks toward 2 distinct "leave leaf switches", it leaves you 30x100GE servers connections.

  • Datacenter Spine/Leave switch 

The WEDGE100BF32X is also a good candidate router in DC as a core/leave switch. You can create a fabric able to switch 6.4 Tbps trafic rates

  • Internet Exchange

In this case, the WEDGE100BF32X is 100GE peer aggregator or simply integrated into the IXP distributed core fabric.

  • MAN/CPE router

The STORDIS BF2556X-1T presents flexible connectivities is a good candidate for regional network implementation. It has 8x100GE ports, 2 of them can be used as uplinks toward their main transit provider, 2 other can be used to provide EAST/WEST connection via 2 different fire routes, this leave 4x100 ports in case you need to increase capacity. The STORDIS also has 16x[1/10/25] GbE ports, 32x[10/25] GbE ports which gives the possibility to interconnects users via various access port bandwidth.

Conclusion

In this article you:

  • had a brief introduction of P4Lang P4 language
  • had been presented a 10 thousand feet view of P4 development workflow
  • had been exposed a list of P4 targets and the use cases enabled by these targets

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