Hello World in P4

Published on 28 April 2022 (Updated: 25 September 2022)

Hello World in P4

Welcome to the Hello World in P4 page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

>/* -*- P4_16 -*- */



/*************************************************************************

    This is a P4 "Hello World" code:

    When a packet arrives to the switch with some payload
    data of 88 bites, the switch will forward the packet 
    changing the payload to "Hello World".

    The program is not intended to calculate a new checksum,
    many errors can occur avoiding that process.

    @ecwolf

*************************************************************************/


#include <core.p4>
#include <v1model.p4>

const bit<16> TYPE_IPV4 = 0x800;
const bit<8> UDP_TYPE = 0x11;
const bit<8> TCP_TYPE = 0x06;

/*************************************************************************
*********************** H E A D E R S  ***********************************
*************************************************************************/

typedef bit<9>  egressSpec_t;
typedef bit<48> macAddr_t;
typedef bit<32> ip4Addr_t;

header ethernet_t {
    macAddr_t dstAddr;
    macAddr_t srcAddr;
    bit<16>   etherType;
}

header ipv4_t {
    bit<4>    version;
    bit<4>    ihl;
    bit<8>    diffserv;
    bit<16>   totalLen;
    bit<16>   identification;
    bit<3>    flags;
    bit<13>   fragOffset;
    bit<8>    ttl;
    bit<8>    protocol;
    bit<16>   hdrChecksum;
    ip4Addr_t srcAddr;
    ip4Addr_t dstAddr;
}

header udp_t
{
    bit<16> srcPort;
    bit<16> dstPort;
    bit<16> len;
    bit<16> checksum;
    bit<88> payload;
}

struct metadata {
    /* empty */
}

struct headers {
    ethernet_t          ethernet;
    ipv4_t              ipv4;
    udp_t               udp;
}

/*************************************************************************
*********************** P A R S E R  ***********************************
*************************************************************************/

parser MyParser(packet_in packet,
                out headers hdr,
                inout metadata meta,
                inout standard_metadata_t standard_metadata) {

    state start {
        transition parse_ethernet;
    }

    state parse_ethernet {
        packet.extract(hdr.ethernet);
        transition select(hdr.ethernet.etherType) {
            TYPE_IPV4: parse_ipv4;
            default: accept;
        }
    }

    state parse_ipv4 {
        packet.extract(hdr.ipv4);
        transition select(hdr.ipv4.protocol) {
            UDP_TYPE : parse_udp;
            default : accept;
        }
    }

    state parse_udp {
        packet.extract(hdr.udp);
        transition accept;

    }


}

/*************************************************************************
************   C H E C K S U M    V E R I F I C A T I O N   *************
*************************************************************************/

control MyVerifyChecksum(inout headers hdr, inout metadata meta) {   
    apply {  }
}

/*************************************************************************
**************  I N G R E S S   P R O C E S S I N G   *******************
*************************************************************************/

control MyIngress(inout headers hdr,
                  inout metadata meta,
                  inout standard_metadata_t standard_metadata) {
    
    action drop() {
        mark_to_drop(standard_metadata);
    }
    
    action ipv4_forward(macAddr_t dstAddr, egressSpec_t port) {
        standard_metadata.egress_spec = port;
        hdr.ethernet.srcAddr = hdr.ethernet.dstAddr;
        hdr.ethernet.dstAddr = dstAddr;
        hdr.ipv4.ttl = hdr.ipv4.ttl - 1;
        hdr.udp.payload = 0x48656C6C6F20576F726C64; // payload='Hello World'
    }
    
    table ipv4_lpm {
        key = {
            hdr.ipv4.dstAddr: lpm;
        }
        actions = {
            ipv4_forward;
            drop;
            NoAction;
        }
        size = 1024;
        default_action = drop();
    }

    apply {
        ipv4_lpm.apply();
    }
}

/*************************************************************************
****************  E G R E S S   P R O C E S S I N G   *******************
*************************************************************************/

control MyEgress(inout headers hdr,
                 inout metadata meta,
                 inout standard_metadata_t standard_metadata) {
    apply {}
}

/*************************************************************************
*************   C H E C K S U M    C O M P U T A T I O N   **************
*************************************************************************/

control MyComputeChecksum(inout headers  hdr, inout metadata meta) {
     apply {}
}

/*************************************************************************
***********************  D E P A R S E R  *******************************
*************************************************************************/

control MyDeparser(packet_out packet, in headers hdr) {
    apply {
        packet.emit(hdr.ethernet);
        packet.emit(hdr.ipv4);
        packet.emit(hdr.udp);
    }
}

/*************************************************************************
***********************  S W I T C H  *******************************
*************************************************************************/

V1Switch(
MyParser(),
MyVerifyChecksum(),
MyIngress(),
MyEgress(),
MyComputeChecksum(),
MyDeparser()
) main;

Hello World in P4 was written by:

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

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