This is a basic demo application that uses the LWIP stack via PCAP to echo back anything sent to it.

It supports UDP, TCP, IPv4, and IPv6, on client and server side.

Install docker:

sudo dnf install docker

Docker daemon is running. If testing IPv4, run like this:

sudo dockerd

If testing IPv6, run dockerd like this:

  # ip6tables rules are only available if experimental features are enabled.
  # From this:
  #   https://docs.docker.com/config/daemon/ipv6/
  sudo dockerd --experimental --ip6tables --ipv6 \
    --fixed-cidr-v6 2001:db8::/104 \
    --default-gateway-v6 2001:db8::2

Clone or copy lwip src dir tree to this directory:

ls
CMakeLists.txt  Dockerfile  echo.c  echo.h  LICENSE  lwip  lwip-include  lwip.patch  main.c  README.md

Build the docker image:

sudo docker build -t lwip-test .

Run the newly created docker image:

docker run -it lwip-test

This will stay running until cancelled with Ctrl-C. In a new terminal, connect to the test service. The IP is hard coded to 2001:db8::1 when using IPv6, and 172.17.0.5 for IPv4, and the port to 11111:

nc -u6 2001:db8::5 11111

or

nc 172.17.0.5 11111

Anything you type into this console will echo on the other one. You can exit the app and nc with Ctrl-C.

Also, this example should appear as a new docker container and network:

$sudo docker container ls
CONTAINER ID   IMAGE       COMMAND                  CREATED              STATUS              PORTS     NAMES
7dc737cb4030   lwip-test   "/bin/sh -c /app/lwi…"   About a minute ago   Up About a minute             pedantic_morse

$sudo docker network ls
NETWORK ID     NAME      DRIVER    SCOPE
be4913c77e56   bridge    bridge    local
1b26983fe372   host      host      local
c4998617444d   none      null      local

You can get detailed info with docker network inspect bridge and docker container inspect <container id>.

The choice of UDP/TCP and client/server is hard-coded in echo.c here:

/* globals */
/* Toggle tcp/udp at build time. */
static int use_tcp = 0;
/* Toggle server/client mode. */
static int am_server = 0;

The choice of IPv4 vs IPv6 is set in lwip-include/lwipopts.h here

// Enable LWIP_IPV4 or LWIP_IPV6, but
// not both.
#define LWIP_IPV4                       0
#define LWIP_IPV6                       1

The lwip-include/arch directory is a copy of the lwIP directory from contrib/ports/unix/port/include/arch.