Advanced Network Programming (ANP) Skeleton

ANP skeleton is the basic skeleton code used in the ANP course for developing your own networking stack.

Dependencies

sudo apt install cmake build-essential libcap-dev iputils-arping

Code

Corresponding to the figure 3 in the accompanying assignment, here is a brief overview of the various files in this project

• anp_netdev.[ch] : implements the application privide network interface with 10.0.0.4 IP address
• anpwrapper.[ch] : shared library wrapper code that provides hooks for socket, connect, send, recv, and close calls.
• arp.[ch] : ARP protocol implementation.
• config.h : various configurations and variables used in the project.
• debug.h : some basic debugging facility. Feel free to enhance it as you see fit.
• ethernet.h : Ethernet header definition
• icmp.[ch] : ICMP implementation (your milestone 2).
• init.[ch] : various initialization routines.
• ip.h : IP header definition
• ip rx and rx : IP tranmission and reception paths
• linklist.h : basic data structure implementation that you can use to keep track of various networking states (e.g., unacknowledged packets, open connections).
• route.[ch] : a basic route cache implementation that can be used to find MAC address for a given IP (linked with the ARP implementation).
• subuffer.[ch] : Linux kernel uses Socket Kernel Buffer (SKB) data strucutre to keep track of packets and data inside the kernel (http://vger.kernel.org/~davem/skb.html). This is our implementation of Socket Userspace Buffer (subuff). It is mostly used to build inplace packet headers.
• systems_headers.h : a common include file with many commonly used headers.
• tap_netdev.[ch] : implementation for sending/receiving packets on the TAP device. It is pretty standard code.
• timer.[ch] : A very basic timer facility implementation that can be used to register a callback to do asynchronous processing. Mostly useful in timeout conditions.
• utilities.[ch] : various helper routines, printing, debugging, and checksum calculation.

You are given quite a bit of skeleton code as a starting point. Feel free not to use or use any portion of it when developing your stack. You have complete freedom

How to build

cmake . 
make 
sudo make install  

This will build and install the shared library.

Scripts

• sh-make-tun-dev.sh : make a new TUN/TAP device
• sh-disable-ipv6.sh : disable IPv6 support
• sh-setup-fwd.sh : setup packet forwarding rules from the TAP device to the outgoing interface. This script takes the NIC name which has connectivity to the outside world.
• sh-run-arpserver.sh : compiles a dummy main program that can be used to run the shared library to run the ARP functionality
• sh-hack-anp.sh : a wrapper library to preload the libanpnetstack and take over networking calls.

Setup

After a clean reboot, run following scripts in the order

1. Make a TAP/TUN device
2. Disable IPv6
3. Setup packet forwarding rules

To run ARP setup

Make and install the libanpnetstack library. Then run ./sh-run-arpserver.sh and follow instructions from there. Example

atr@atr:~/anp-netskeleton/bin$ ./sh-run-arpserver.sh 
++ gcc ./arpdummy.c -o arpdummy
++ set +x
-------------------------------------------
The ANP netstack is ready, now try this:
 1. [terminal 1] ./sh-hack-anp.sh ./arpdummy
 2. [terminal 2] try running arping 10.0.0.4

atr@atr:~/anp-netskeleton/bin$ sudo ./sh-hack-anp.sh ./arpdummy
[sudo] password for atr: 
+ prog=./arpdummy
+ shift
+ LD_PRELOAD=/usr/local/lib/libanpnetstack.so ./arpdummy
Hello there, I am ANP networking stack!
tap device OK, tap0 
Executing : ip link set dev tap0 up 
OK: device should be up now, 10.0.0.0/24 
Executing : ip route add dev tap0 10.0.0.0/24 
OK: setting the device route, 10.0.0.0/24 
Executing : ip address add dev tap0 local 10.0.0.5 
OK: setting the device address 10.0.0.5 
GXXX  0.0.0.0
GXXX  0.0.0.0
GXXX  10.0.0.5
[ARP] A new entry for 10.0.0.5
ARP an entry updated 
ARP an entry updated 
^C
atr@atr:~/anp-netskeleton/bin$

From a second terminal

atr@atr:~/home/atr$ arping -I tap0 10.0.0.4 
ARPING 10.0.0.4 from 10.0.0.5 tap0
Unicast reply from 10.0.0.4 [??:??:??:??:??]  0.728ms
Unicast reply from 10.0.0.4 [??:??:??:??:??]  0.922ms
Unicast reply from 10.0.0.4 [??:??:??:??:??]  1.120ms
^CSent 3 probes (1 broadcast(s))
Received 3 response(s) 

In place of [??:??:??:??:??] you should see an actual mac address for the TAP device.

Getting started with hijacking socket call

• Step 1: run the TCP server in one terminal with a specific IP and port number
• Step 2: run the TCP client in another terminal, and first check if they connect, run, and pass the buffer matching test.

Then, you can run your client with the ./bin/sh-hack-anp.sh script as

sudo [path_to_anp]/bin/sh-hack-anp.sh [path]/bin/anp_client IP port 

In case you have some non-standard installation path, please update the path /usr/local/lib/libanpnetstack.so in the sh-hack-anp.sh script.

Author

Animesh Trivedi (for the ANP course)