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MAC and IP Routing

A simple demonstration with clients and routers to illustrate how IP and MAC addresses work together to route packets.

This demonstration is a part of my talk on MAC and IP Routing.

Network Topology

Setup

Some of the instructions are pertaining to a Windows base OS, but it should be easy to find similar instructions for other OSs online.

  • Install Docker to simulate clients, routers and subnets.
  • Install an X Server for GUI support.
  • Navigate to the project root directory (mac-ip-routing).
  • Build the custom Docker image with the name nhttpd (Networked HTTPd) from the Dockerfile.
    • Ensure that no existing image has the name nhttpd using the docker image ls command.
      • If an image with that name already exists, then either delete that image (docker image rm <image_id>) or change the image name in the command below and then in the the compose.yaml file as well.
    • Build Docker image: docker build . -t nhttpd
  • Create and/or start containers and subnets
    • Ensure that no existing containers have the same names as the container_name field in all the services listed in the compose.yaml file using the command docker container ls.
      • If any containers have their names matching any of the names in the compose.yaml file, either delete the existing container (docker container rm <container_id>) or change the corresponding container_name field in the compose.yaml file.
    • Ensure that no existing networks have the same names as the name field in all the networks listed in the compose.yaml file using the command docker network ls.
      • If any networks have their names matching any of the names in the compose.yaml file, either delete the existing network (docker network rm <container_id>) or change the corresponding name field in the compose.yaml file.
    • Use Docker Compose (bundled with the default Docker installation) to create and/or start the clients and routers, and if required, to create the networks as well: docker compose up
    • If faced with Docker bugs and errors, please clear all containers (docker container rm node-a node-b node-c router-1 router-2 router-3) and networks (docker network rm net-1 net-2 net-3 net-4) before running docker compose up again.

Commands

On the Base Host Machine

Please run these commands in the project's root directory.

  • All setup commands are listed above in the 'Setup' section.

  • Docker commands

  • List all running Docker containers

    $ docker container ls

  • Go into Docker container and run Bash

    $ docker exec -it container_name bash

  • Remove all containers and networks created for this demonstration

    $ sh clean-up.sh

In the Containers

  • Packet capture

    NOTE:

    $ tcpdump -envA -i any -w htdocs/file_name.pcap

  • Packet analysis

    NOTE:

    $ wireshark htdocs/file_name.pcap

  • List ARP cache

    $ arp -n

  • Clear ARP cache

    $ ip -s -s neigh flush all

    source

  • List IP table

    $ ip route show table all

Working without an X Server

  • Packet capture is done using tcpdump and its results are stored in file_name.pcap packet capture files in the /usr/local/apache2/htdocs directory if the commands in the 'In the Containers' section are followed.
  • Wireshark is used to open those packet capture (.pcap) files to analyse them.
  • The X Server is installed so that Docker can have GUI support to open Wireshark's GUI.
  • Now if the X Server is not installed on the base host machine or is not working, then
    • Install Wireshark on the base host machine.
    • Open the packet capture files from each of the node or router directories in this project (Eg: ./node-a, etc.) in Wireshark
      • This is possible as these directories are mapped to the /usr/local/apache2/htdocs directory of each container.