DOCA Documentation v2.10.0

GTP Parsing Example

This example demonstrates how to add a simple flex parser node to the existing hardware defined parse graph.

DPU_Flex_Parser_GTP-version-1-modificationdate-1739977489777-api-v2.png

The example starts with some basic definitions.

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#include <doca_model.p4> #include <doca_headers.p4> #include <doca_externs.p4> #include <doca_parser.p4>   const bit<32> WIRE_PORT = 32w00; const bit<32> GTP_VPORT = 32w01; const bit<32> DEFAULT_VPORT = 32w04;   struct metadata_t { } #define GTP_U_PORT 2152

Then we define the GTP-U version 1 header.

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header Gtp_v1_h { bit<3> version; /** For GTPv1, this has a value of 1. */ bit protocol_type; /** GTP (value 1) from GTP' (value 0) */ bit reserved; bit extension_header_flag; /** extension header optional field. */ bit seq_number_flag; /** Sequence Number optional field */ bit n_pdu_number_flag; /** N-PDU number optional field */ bit<8> message_type; /** types of messages are defined in 3GPP TS 29.060 section 7.1 */ bit<16> message_length; /** length of the payload in bytes */ bit<32> teid; /** Tunnel endpoint identifier */ bit<16> sequence_number; /** optional */ bit<8> n_pdu_number; /** optional */ bit<8> next_extension_hdr_type; /** optional if any of the E, S, or PN bits are on. The field must be interpreted only if the E bit is on */ }

Then we add NV_FIXED_HEADERS to the headers struct, along with the new GTP header.

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struct headers_t { NV_FIXED_HEADERS Gtp_v1_h gtpv1; }

Using the nv_transition_from annotation, the GTP parser state is connected as a select transition from the UDP state.

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parser packet_parser(packet_in packet, out headers_t headers) { NV_FIXED_PARSER(packet, headers)       @nv_transition_from("nv_parse_udp", GTP_U_PORT) state parse_gtp { packet.extract(headers.gtpv1); transition accept; } }

The control example uses a single flow table that matches on input port and GTP tunnel endpoint ID. The policy is then to forward the GTP packet to a port or drop the packet.

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/** * This control admits GTP packets only if the tunnel ID matches * */ control gtp_tunnel( inout headers_t headers, in nv_standard_metadata_t std_meta, inout metadata_t user_meta, inout nv_empty_metadata_t pkt_out_meta ) { NvDirectCounter(NvCounterType.PACKETS_AND_BYTES) gtp_counter;   action send_to_port(nv_logical_port_t port) {        gtp_counter.count();         nv_send_to_port(port); }   action drop() { gtp_counter.count();         nv_drop(); }   table gtp_table { key = { std_meta.ingress_port: exact; headers.gtpv1.teid: exact; } actions = { send_to_port; drop; } default_action = drop; direct_counter = gtp_counter;   const entries = { (WIRE_PORT, 0x000000001) : send_to_port(GTP_VPORT); (GTP_VPORT, 0x000000001) : send_to_port(WIRE_PORT); } }   apply { if (headers.gtpv1.isValid()) { if (gtp_table.apply().miss) { nv_send_to_port(DEFAULT_VPORT); } } drop(); } }   NvDocaPipeline( packet_parser(), gtp_tunnel() ) main;

See the full DPL example gtp_parsing.p4

© Copyright 2025, NVIDIA. Last updated on Mar 23, 2025.