go-gtp: GTP in Golang

Package gtp provides simple and painless handling of GTP(GPRS Tunneling Protocol), implemented in the Go Programming Language.

Features

• Flexible enough to control everything in GTP protocol.;
  • For developing mobile core network nodes (see examples).
  • For developing testing tools like traffic simulators or fuzzers.
• Many helpers kind to developers provided, like session, bearer, and TEID associations.
• Easy handling of multiple connections with fixed IP and Port with UDP (or other net.PacketConn).
• No platform-specific codes inside, so it works almost everywhere Golang works. Currently, it works only on Linux and macOS since netlink support is introduced. I'll make them separated from the base to let it work even on Windows in the future.

Getting Started

Prerequisites

go-gtp supports Go Modules. Just run go mod tidy in your project's directory to collect the required packages automatically.

go mod tidy

This project follows the Release Policy of Go.

Running examples

End-to-end

We have a set of tools called GW Tester at examples/gw-tester. See the document for how it works and how to run it. It is also used for the integration test of this project. Workflow setting may help as well.

Individual node

Examples work as it is by go build and executing commands in the following way.

Note for MacOs users: before running any go service, make sure to execute ./mac_local_host_enabler.sh you will find at examples/utils

1. Open four terminals on a machine and start capturing on the loopback interface.

2. Start P-GW on terminal #1 and #2

// on terminal #1
./pgw

// on terminal #2
./pgw -s5c 127.0.0.53 -s5u 127.0.0.5

3. Start S-GW on terminal #3

// on terminal #3
./sgw

4. Start MME on terminal #4

// on terminal #4
./mme

5. You will see the nodes exchanging Create Session and Modify Bearer on C-Plane, and ICMP Echo on U-Plane afterwards.

If you want to see fewer subscribers, please comment-out the v2.Subscriber definitions in example/mme/main.go.

Developing by your own

Each version has net.PacketConn-like APIs and GTP-specific ones, which are often version-specific. The basic idea behind the current implementation is;

• Dial or ListenAndServe to create a connection(Conn) between nodes.
• Register handlers to the Conn for specific messages with AddHandler, allowing users to handle the messages coming from the remote endpoint as flexible as possible, with less pain.
• CreateXXX to create session or PDP context with arbitrary IEs given. Session/PDP context is structured, and they also have some helpers like AddTEID to handle known TEID properly.

For the detailed usage of a specific version, see README.md under each version's directory.

And don't forget testing once you are done with your changes

go test ./...

Note for MacOs users: the first time you run any test, make sure to execute ./mac_local_host_enabler.sh you will find at examples/utils. You will have to run the script again after each reboot.

Supported Features

Note that "supported" means that the package provides helpers that make it easier to handle. In other words, even if a message/IE is not marked as "Yes", you can make it work with some additional effort.

Your contribution is welcome to implement helpers for all the types, of course!

Disclaimer

This is still an experimental project. Any part of implementations(including exported APIs) may be changed before released as v1.0.0.

Author(s)

Yoshiyuki Kurauchi (Website / Twitter)

I'm always open to welcome co-authors! Please feel free to talk to me.

LICENSE

MIT