Description
Internet Technology
Overview
In this project, you will set up a small IP network consisting of hosts and a router. Your network
will function with full end-to-end connectivity, and you will experiment with tools like ping and
traceroute.
Consider the following network topology:
Here, r1 is an IP router and h1 … h4 are endpoints. In a safe experimental setting running
inside a virtual machine, you will use the ip suite of commands to set up the right IP addresses
for all the interfaces, and the right routing table entries for all the routers and endpoints in this
network. Welcome to the AS352 network!
Step 1: Set up mininet
To create a safe virtualized environment, we will use a tool called mininet, which uses linux containers (see https://en.wikipedia.org/wiki/Linux_namespaces) to allow you to
create a small network of hosts and routers that can run inside your laptop. (If you’re interested
in learning more about mininet, you can read about it from the paper entitled “A network in a
laptop: Rapid prototyping for software-defined networks,” found at http://conferences.
sigcomm.org/hotnets/2010/papers/a19-lantz.pdf.)
First, download the standard mininet virtual machine (note, this is a 500+ MByte file).
https://github.com/mininet/mininet/releases/download/2.2.2/mininet-2.
2.2-170321-ubuntu-14.04.4-server-i386.zip
Set up the VM and play around according to the instructions at the link below. We recommend
that you use VirtualBox. By the end of this step, you must be able to log into the VM and run basic
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terminal commands like ls.
http://mininet.org/vm-setup-notes/
Step 2: Play with the topology Python file
Within the virtual machine, run the attached network topology file, AS352.py, which invokes
mininet’s Python API to create a network topology with 4 endpoints (hosts) and 1 router. Note
the use of sudo while running the program. Note that this program will be unsuccessful on any
machine without a viable mininet installation.
In particular, you cannot run AS352.py on ilab.
mininet@mininet-vm:˜/project5$ sudo python AS352.py
*** Creating network
*** Adding controller
*** Adding hosts:
h1 h2 h3 h4 r1
*** Adding switches:
*** Adding links:
(h1, r1) (h2, r1) (h3, r1) (h4, r1)
*** Configuring hosts
h1 h2 h3 h4 r1
*** Starting controller
c0
*** Starting 0 switches
*** Routing Table on Router:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
*** Starting CLI:
mininet>
Within the mininet shell, you can do various things to control the hosts and router we just
instantiated. One highly convenient aspect of mininet is that the hosts, the router, and the VM all
share the same filesystem, so the same files are visible from all hosts and the router. Also, you can
run commands, dump outputs into a file, and access it from any host or router or a regular terminal
inside the VM. Let’s walk through a few examples of playing around with the mininet topology.
Step 2.1. Run the ls command on host h1.
mininet> h1 ls
AS352.py
mininet>
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Note that the command is prefixed by h1 to indicate to mininet that the command must be run
on host h1. You can replace ls by any command which can run on h1, by just typing
h1
where is any command that would run on a regular Linux terminal. You can run
ls on any host or router by changing the prefix of the command:
ls
Step 2.2. Inspect the network topology from within mininet:
mininet> net
h1 h1-eth0:r1-eth1
h2 h2-eth0:r1-eth2
h3 h3-eth0:r1-eth3
h4 h4-eth0:r1-eth4
r1 r1-eth1:h1-eth0 r1-eth2:h2-eth0 r1-eth3:h3-eth0 r1-eth4:h4-eth0
c0
mininet>
Note that net is not prefixed by any host or router name. It is a native mininet command.
Step 2.3.
You can even run commands on the router! Mininet allows you to treat both endpoints
and the router as standard Linux machines, on which you get to run “regular” Linux commands.
Let’s dump the routing table on r1.
mininet> r1 ip route
mininet>
By default, there is nothing in the routing table on r1. As you may have guessed, that is one of
the things that you will add in this project.
Step 2.4. Mininet can also read a list of commands from a file. Suppose we added the text
h1 ls
net
r1 ip route
into the file commands.txt. Then, you can use the source mininet command to run all the
commands in sequence, one after another. For example:
mininet> source commands.txt
AS352.py commands.txt
h1 h1-eth0:r1-eth1
h2 h2-eth0:r1-eth2
h3 h3-eth0:r1-eth3
h4 h4-eth0:r1-eth4
r1 r1-eth1:h1-eth0 r1-eth2:h2-eth0 r1-eth3:h3-eth0 r1-eth4:h4-eth0
c0
mininet>
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You can find more examples of mininet commands and usage at http://mininet.org/
walkthrough/#interact-with-hosts-and-switches
Step 3: Set up your network
Now we get to the crux of the project. You need to set up the network interfaces on all hosts and
routers, as well as the routing tables, so that end to end IP communication is possible between all
hosts and the router interfaces. You will do this in three steps.
Step 3.1. Set up the IP addresses of all interfaces.
Please assign the following IP addresses to the
corresponding network interface below.
10.0.0.1 h1-eth0
192.168.0.1 h2-eth0
10.0.0.3 h3-eth0
192.168.0.3 h4-eth0
10.0.0.2 r1-eth1
192.168.0.2 r1-eth2
10.0.0.4 r1-eth3
192.168.0.4 r1-eth4
Use the ip addr command to set up the correct IP address for each interface on each machine.
You need to set up 8 interface addresses in total. If you need help in using the command, try running
ip addr help.
Step 3.2. Set up the default routes for the hosts.
The hosts h1 … h4 are only connected to the
rest of the network through one interface. Any external communication must hence use a default
route, which moves the packets on the host towards the gateway router, r1. For example, all traffic
on host h1 must use the interface/device h1-eth0 to reach any destination (other than itself).
Use the command ip route command to set up all the routes. If you need help understanding
the command, try running ip route help. You will set up 4 default routes, one on each endpoint
h1 … h4.
Step 3.3. Set up the routes on the router.
We need to configure the router to interconnect the endpoints by matching incoming packets with the correct outgoing network interface. The forwarding
table entries on router r1 must look like:
Destination IP address -> Output port
————————————-
h1 -> r1-eth1
h2 -> r1-eth2
h3 -> r1-eth3
h4 -> r1-eth4
Once again, use the ip route command to set up these routes. You will need to set up 4
routes, one for each destination endpoint.
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Step 3.4. Test your network:
You’ve done all the hard work. Now check that your network works
as intended, using the ping and traceroute commands.
A correctly configured network must be able to execute a successful ping from any host or the
router to any valid IP address inside the network.
For example, you can ping h4 from h1, to check reachability:
mininet> h1 ping 192.168.0.3
PING 192.168.0.3 (192.168.0.3) 56(84) bytes of data.
64 bytes from 192.168.0.3: icmp_seq=1 ttl=63 time=168 ms
64 bytes from 192.168.0.3: icmp_seq=2 ttl=63 time=0.046 ms
64 bytes from 192.168.0.3: icmp_seq=3 ttl=63 time=0.044 ms
ˆC
— 192.168.0.3 ping statistics —
3 packets transmitted, 3 received, 0% packet loss, time 2004ms
rtt min/avg/max/mdev = 0.044/56.315/168.855/79.577 ms
mininet>
You can also run traceroute between any two points. For example, a traceroute from h1 to
h4 would show something like this:
mininet> h1 traceroute 192.168.0.3
traceroute to 192.168.0.3 (192.168.0.3), 30 hops max, 60 byte packets
1 10.0.0.2 (10.0.0.2) 0.018 ms 0.003 ms 0.003 ms
2 192.168.0.3 (192.168.0.3) 0.008 ms 0.003 ms 0.004 ms
mininet>
Note that there are 2 hops in the traceroute output: the router and the destination of the traceroute, with the IP address of the router interface connected to h1 showing up on the first row.
In case you received an error that the traceroute command isn’t found, install traceroute
by running
sudo apt-get update && sudo apt-get install traceroute
How we will test your commands
Once you have set up all the interfaces and routes, put all your commands into a file called
commands.txt. Please do not modify AS352.py; your commands must work with the unmodified Python script.
When all the commands in your commands file are run one after another (by typing source
commands.txt), subsequent commands should show (1) correct configuration of the interfaces
and routes (demonstrated through ip addr or ifconfig and ip route) and (2) full connectivity
between all the nodes in the network, such that a ping or traceroute from any endpoint or router
to any valid IP address in the network should succeed. We may test connectivity between any or
all pairs of endpoints and the router. We will only use ping and traceroute to test connectivity.
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You are free to use tools like iperf to do more sophisticated testing. An example of a test using
ping might look like:
*** Starting CLI:
mininet> source commands.txt
mininet> h1 ping 192.168.0.4
PING 192.168.0.4 (192.168.0.4) 56(84) bytes of data.
64 bytes from 192.168.0.4: icmp_seq=1 ttl=63 time=1070 ms
64 bytes from 192.168.0.4: icmp_seq=2 ttl=63 time=60.8 ms
64 bytes from 192.168.0.4: icmp_seq=3 ttl=63 time=0.030 ms
64 bytes from 192.168.0.4: icmp_seq=4 ttl=63 time=0.047 ms
ˆC
— 192.168.0.4 ping statistics —
4 packets transmitted, 4 received, 0% packet loss, time 3010ms
rtt min/avg/max/mdev = 0.030/282.820/1070.311/455.336 ms, pipe 2
mininet>
Please ensure that mininet does not crash when running your commands.txt.
Notes that may be useful
Mininet has an FAQ/help page at https://github.com/mininet/mininet/wiki/FAQ.
There is also a mailing list where you can post (after checking the FAQ and the archives) if you
have questions.
To reduce the file size of the disk image, the mininet VM does not come with a pre-installed
graphical interface. Hence, using the VM may require you to get comfortable with the Linux
terminal/command line. You may find it convenient to use multiple terminals either from the VM
console or over SSH using terminal multiplexers like tmux and screen. Alternatively, you may
try following the instructions at
https://github.com/mininet/openflow-tutorial/wiki/Set-up-Virtual-Machine#
alternative-run-a-gui-in-the-vm-console-window
to install a graphical interface on the mininet VM. We have not tested those instructions ourselves, however.
You may be surprised to learn that even endpoints have routing tables. When endpoints are
connected through multiple network interfaces, a forwarding table on the endpoint determines
through which interface a given packet is transmitted.
You will often need to “debug” your network configuration by checking whether packets
reached the correct interface with the correct header values. Use a packet sniffer to do this.
You may be familiar with wireshark, but it requires a graphical user interface. Instead, we recommend using tcpdump which is a good command-line equivalent. For example, the following
command uses t¸cpdump to sniff the r1-eth2 interface on r1, and dumps the sniffed packets to a
file r1-dump.txt.
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mininet> r1 tcpdump -v -U -i r1-eth2 -x > r1-dump.txt &
mininet> h1 ping 192.168.0.2
PING 192.168.0.2 (192.168.0.2) 56(84) bytes of data.
64 bytes from 192.168.0.2: icmp_seq=1 ttl=63 time=0.021 ms
64 bytes from 192.168.0.2: icmp_seq=2 ttl=63 time=0.028 ms
64 bytes from 192.168.0.2: icmp_seq=3 ttl=63 time=0.037 ms
ˆC
— 192.168.0.2 ping statistics —
3 packets transmitted, 3 received, 0\% packet loss, time 1998ms
rtt min/avg/max/mdev = 0.021/0.028/0.037/0.009 ms
mininet>
In a separate window, you can check sample output of the tcpdump:
mininet@mininet-vm:˜/project5$ head r1-dump.txt
18:31:29.326269 ARP, Ethernet (len 6), IPv4 (len 4),
Request who-has 192.168.0.2 tell 192.168.0.1, length 28
0x0000: 0001 0800 0604 0001 feb5 2946 9994 c0a8
0x0010: 0001 0000 0000 0000 c0a8 0002
18:31:29.326278 ARP, Ethernet (len 6), IPv4 (len 4),
Reply 192.168.0.2 is-at 8e:17:54:31:99:e7 (oui Unknown), length 28
0x0000: 0001 0800 0604 0002 8e17 5431 99e7 c0a8
0x0010: 0002 feb5 2946 9994 c0a8 0001
18:31:29.326279 IP (tos 0x0, ttl 63, id 11901, offset 0, flags [DF],
proto ICMP (1), length 84)
10.0.0.2 > 192.168.0.2: ICMP echo request, id 10815, seq 1, length 64
0x0000: 4500 0054 2e7d 4000 3f01 4280 0a00 0002
0x0010: c0a8 0002 0800 d6cb 2a3f 0001 71cc 8f5e
mininet@mininet-vm:˜/project5$
Please start early to allow plenty of time for questions on Piazza should you run into difficulties.
What you must submit
For your project submission on Canvas, please turn in two files: commands.txt and your project
report report.pdf. Please do not change or upload AS352.py. The questions for the report are
listed below. Please compress the files into a single Zip archive before uploading to Canvas.
Only one team member must submit.
Project report. Please answer the following questions for your project report.
1. Team details: Clearly state the names and netids of your team members (there are 2 of you).
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2. Collaboration: Who did you collaborate with on this project? What resources and references did you consult? Please also specify on what aspect of the project you collaborated or
consulted.
3. Briefly discuss how you implemented each function: setting up interface configurations,
setting up default routes, and setting up the routes for each destination.
4. Is there any portion of your project that does not work as required in the description above?
Please explain.
5. Did you encounter any difficulties? If so, explain.
6. Describe one technical observation or facts you learned while working on this project. Please
answer in specific and precise terms. Your observations could relate to topics involving the
network layer in general, your implementation of network configuration in this project, the
specific commands you used, or other topics that are relevant to your implementation of this
project. Please ensure your responses are clear, specific, and technical.
Contact the course staff on Piazza if you have any questions.
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