Assignment: Basic Networking - Ping

Networking

This assignment is a Xinu assignment allowing the student to more firmly understand how an operating system works. This assignment is part of the Student Built Xinu track for professors that are Teaching With Xinu. The entire working directory containing your Xinu operating system will be submission for this assignment.

Preparation

First, make a fresh copy of your work thus far.

  cp -R <old Xinu directory> <new Xinu directory>

Untar the new project files on top of this new directory:

  tar xvzf <tar-ball directory>

You should now see the new project files in with your old files. Be certain to make clean before compiling for the first time.

The Xinu Shell

With the addition of a full-featured TTY driver in the previous assignment, we can now add the command-line Xinu user interface, the Xinu Shell to the system. The new tarball includes a new subdirectory shell/ that provides the I/O processing necessary to parse user input and launch a small set of commands. Several useful commands are provided as examples. This assignment will be concerned primarily with the ping and pingserver commands.

Ethernet Driver

This project tarball equips your Xinu kernel with a block-oriented, asynchronous ethernet driver for the router's built-in BCM4713 network interface. You are not required to modify the ethernet driver (directory device/ether/), but it wouldn't be a bad idea to familiarize yourself with its workings. It follows the same standard device abstraction as we have seen in the TTY and disk device drivers.

Debugging Tools

For your convenience, we have also provided a snoop() function in network/snoop.c, which will attempt to provide human-readable interpretations of packets when called. This is provided strictly for debugging purposes. It takes a buffer that contains an ethernet packet and a designated length and prints out various values as well as a hexdump of the packet.

Student Implementation

Your task for this assignment is to implement a version ping that allows your main programs to send echo request packets to other machines and allows other machines to send echo requests packets to your allocated backend. This project can be split into two distinct parts, the client and the server. You should first implement a server that allows other machines to ping your backend while it is running. The second part of this project is to implement the client side which will allow you to write a main process that can ping other machines. In each of these parts you will deal with two types of ICMP packets, echo request and echo reply packets. The request packets are sent from a client to a target machine that is running a ping server. The reply packets are sent in response to a client's request back to the client.

Echo Reply (Ping) Server

The Ping Server is a process spawned by the pingserver shell command to listen to the Ethernet device for ping requests and construct correct replies. (See Echo Reply.) Due to the simplified nature of packet de-multiplexing in our current system, it will not be possible for your Xinu kernel to run both a ping server and a ping client simultaneously. (The two processes will "fight" over incoming packets.) Instead, use a second router to generate ping requests to test your server, or use the Linux command "ping" on a local server which has direct access to the private Xinu Network.

Echo Request (Ping) Client

The project tarball includes a starter stub for a ping command in the shell directory file shell/xsh_ping.c. Your ping command should take a single command-line argument consisting of a destination IP address in dotted decimal notation. It should

• generate a sequence of 20 (MAX_REQUESTS in include/network.h) ping packets at one second intervals;
• watch for ping replies from the target machine;
• print out replies received (see the icmp_reqreply function in network/icmp.c); and
• print out a summary of results.

The proper term for a "ping packet" is an ICMP Echo Request. An answering packet is an Echo Reply. For the sake of simplicity, this project will not implement a full ARP system to resolve IP addresses down to underlying Ethernet MAC Addresses. Instead, we will use a predefined static table, "arp_map" to match requested ping IP addresses for machines local to the private Xinu Network. Any address that is not known to the arp_map table will be assumed to be on another network, and the ping packet should instead be addressed to Zardoz, the Xinu Network Gateway. The gateway's MAC address is hard-coded in network.h with the constant PING_GATEWAY.

Resources

• Wikipedia: Ping
• RFC 792 - Internet Control Message Protocol (ICMP)
• Wikipedia: Internet Control Message Protocol (ICMP)