In this bonus lab, we will implement application layer routing that is used to build infrastructure services such as overlay networks. Problem 1 of this lab is a bonus problem that contributes up to 10 points toward the midterm component of the course. It is completely optional. For students who have gotten 91 or higher in the midterm and whose total exceeds 100 after adding points from lab6, points in excess of 100 will be added to the final exam. Note the earlier due date as new university rules do not allow assignments to be due during quiet week.
The application layer router has two components: approutes which is the router that runs on a number of lab machines (in general, machines configured with IP interfaces), and approutec which instructs approutes how to route packets. As in lab4, the data plane will use UDP, and we will use our UDP ping app to test application layer routing. The control plane uses TCP to configure approutes.
The set-up procedure for application layer routing is as follows: first run
approutec on a lab machine, say, amber01
% approutec
where approutec will print a prompt "? " on stdout and await user input
from stdin.
Second, open terminal
windows to several lab machines, say, amber02, amber03, amber04, and execute
approutes at each machine
% approutes router-address port-num
where router-address is the IP address of a lab machine (amber02, amber03, amber04)
and port-num is a starting port number used to configure 3 different sockets.
approutes will create a TCP socket, bind to an unused port number starting at
port-num (use the incrementing method), then output the port number to stdout.
approutes will create two UDP sockets, bind them to two unused port numbers
starting at port-num, then output the two port numbers to stdout. The first
UDP port number we will refer to as port-in, the second as port-out.
Third, at the machine where the approutec runs (amber01) enter on stdin data
plane forwarding instructions for each of the application layer routers (amber02,
amber03, amber04) one by one:
? router-ip tcp-port next-hop-IP next-hop-port
where router-ip is the IP address of an application layer router
(e.g., 128.10.112.132 for amber02) and tcp-port is its port number (output
earlier to stdout by approutec on amber02). next-hop-IP specifies the
IPv4 address of the next hop router and its UDP port (port-in) to forward
a UDP packet to. For example, if the next hop is amber03 then
router-ip is 128.10.112.133 and port-in is the port number output to
stdout by approutec running at amber03 in the first step.
approutec opens a TCP connection to router-ip tcp-port and calls write()
to transmit 6 bytes containing next-hop-IP and next-hop-port which instructs
router-ip how to forward UDP data plane packets.
This is repeated for the all the application layer routers (amber03 and amber04). For the last application layer router (amber04), next-hop-IP specifies the IP address of host (e.g., amber07) where an app process acting as receiver runs, in our case, the UDP ping server, pings. next-hop-port specifies the UDP port number that pings awaits UDP ping packets.
After printing one TCP and two UDP port numbers for the three sockets approutes has created, it listens on the TCP socket for an instruction from the configuration manager approutec. When accept() returns, approutes calls read() to read 6 bytes where the first 4 bytes represent the IP address of the next hop to forward UDP packets to and the next hop's port number. The payload that approutes forwards on the UDP data plane are UDP packets arriving on its port-in UDP port configured in the second step. We will call UDP packets arriving on port-in the forward path which are sent out using the socket bound to port-out.
When the first UDP packet arrives at port-in, approutes remembers the senders IP address and port number which will be used to forward UDP packets arriving on port-out which constitutes the reverse path. Thus the next hop IP address and port number of the reverse path are learned through the first packet arriving on the forward path. Each time a UDP packet arrives on the forward or reverse path, approutes outputs to stdout the sender's IP address (in dotted decimal form) and port number for monitoring purpose.
After all the application layer routers have been configured, run the UDP ping
app on two lab machines (e.g., amber09, amber10). For example, on amber10 run
the ping server
pings 128.10.112.140 port-out
where port-out is the next-hop-port of last application layer
router instructed by approutec in the third step. On amber09 run the ping client
pingc first-hop-ip port-in 128.10.112.139
where first-hop-ip is the IPv4 address of the first application layer router
and port-in is the UDP port number output by the first hop router approutes for
accepting data plane packets in the forward path. 128.10.112.139 is the address
of amber09.
Place your code along with Makefile and README in subdirectory v1/. Test and verify that your application layer router works with 1, 3, 5 intermediate routers. Note the RTT values returned by pingc. Discuss your results in lab6.pdf.
Electronic turn-in instructions:
We will use turnin to manage lab assignment submissions. Go to the parent directory of the directory lab6/ where you deposited the submissions and type the command
turnin -v -c cs536 -p lab6 lab6
This lab is an individual effort. Please note the assignment submission policy specified on the course home page.