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Introduction

This folder contains the source code for the UDP portion of a go based echo server and the certificates for use against a secure TCP echo server. The UDP echo server is based upon the AWS FreeRTOS TCP/secure echo server implementation which can be found here:

https://github.com/aws/amazon-freertos/tree/master/tools/echo_server

A UDP echo server using this go code, plus a TCP echo server and a secure TCP echo server using the AWS FreeRTOS go code and the certificates, are running on a publicly accessible server ubxlib.com.

The running echo servers can be found at the following addresses:

  • UDP: ubxlib.com:5050
  • TCP: ubxlib.com:5055
  • Secure TCP: ubxlib.com:5065
  • Secure UDP: ubxlib.com:5070

Note: we used to use port 5060 for secure TCP but that port is commonly used by non-secure SIP and hence can be blocked by firewalls which want to exclude SIP, so port 5065 is now used instead.

Installation

The README.md at the above link was used to install TCP and secure TCP versions of the echo server. The certificates generated for the secure TCP echo server can be found in the certs directory. Then echo-server.go was copied and adapted to form echo-server-udp.go.

  • Make sure that golang is installed on your Linux server.
  • Copy this directory to a directory on your Linux server.
  • cd to that directory and run:
go mod tidy
go build echo_server.go
go build echo_server_udp.go
  • To just run all four echo servers manually, execute sh ./echo_server.sh (see note below if you get strange errors).
  • To start the echo servers as a service at boot, kill the processes that started running as a result of the above line (ps aux and kill xxx where xxx is the PID), modify the paths in the file echo_server.service appropriately, copy echo_server.service to /etc/systemd/system and then:
sudo chmod u+x echo_server.sh
sudo systemctl daemon-reload
sudo systemctl start echo_server
sudo systemctl enable echo_server
  • To test that it is working (or at least the TCP flavour is), open PuTTY or similar and connect a RAW socket to the server on port 5055 (for the TCP echo server): what you type in the PuTTY terminal should be echo'ed back to you (on a line-buffered basis).
  • You may use an application such as Packet Sender to check that UDP on port 5050 and SSL on port 5065 are working.
  • Haven't found a way to check that DTLS on port 5070 is working, but since it uses the same certificates as SSL on port 5065 there is less chance of failure.

Note: if you have FTP'ed echo_server.sh or echo_server.service across to your echo server from Windows they may well have the wrong line endings and strange things may happen; to give them the correct line endings, open the file in nano, press CTRL-O to write the file and then, before actually writing it, press ALT-D to switch to native Linux format and press <enter> to save the file.

Note: if you are debugging your setup by running tshark (the command-line version of Wireshark) on your server and you want to write the captured packets to file for later viewing in Wireshark, i.e. using a command-line something like sudo tshark -i eth0 -f "port 5070" -w wireshark.log then you may find that you get back a permission denied error; this can be fixed with something like touch wireshark.log followed by chmod o=rw wireshark.log.