Build an internet

In this in-class lab exercise you will work with a group. There will be 3 other groups. Each group will build a local network. Then the 4 networks will be combined into a single internet. See the "Lab exercise: build an internet" slides. They blueprint the plan. These step-by-step instructions accompany them.

For building its localnet, your group will be issued a kit consisting of:
 1 switch or hub, with power supply
 1 laptop
 2 USB NICs
 4 cables

Your localnet will also incorporate 2 of the classroom's existing desktops. Do as indicated below.

Construct 1 localnet for your group

add one of the USB NICs to your laptop
determine its name
cable it into your hub/switch

re-cable the 2 closest classroom desktops into your hub/switch

choose an internal network (netaddr & netmask)
choose 3 of its host addresses and apply them to your 3 hosts

make sure your 3 hosts can ping each other


Construct 2 localnets between groups

identify the other 2 localnets that are lateral, not diagonal, to you
(for example, if you are the Northwest localnet, Southeast is diagonal to you so your 2 lateral localnets are Southwest and Northeast)

add the other USB NIC to your laptop
determine its name
cable your laptop's 2 free NICs directly (no hub/switch) to the laptops of your 2 lateral localnets
do not cable any 2 USB NICs together: from a USB NIC always cable into the lateral localnet's laptop's built-in NIC only

confer separately with the students from those 2 localnets
with each:
 mutually choose an external network (netaddr & netmask)
 choose 2 of its host addresses
 apply them to your 2 laptops
 make sure your 2 laptops can ping one another


Make route table settings, for lateral integration

On your laptop
 add 2 network routes, one to each of the lateral localnets (gatewayed through the lateral routers)

On your desktops
 add default routes, on each, to your laptop

make sure your 2 desktops can ping both of your lateral networks' laptops
make sure your 2 desktops can ping all 4 desktops that belong to your lateral networks

Make route table settings, for diagonal integration

confer with students from your diagonal localnet
determine what their local network is (netaddr & netmask)

On your laptop
 add a network route to the diagonal localnet

On your desktops
 do nothing

make sure your laptop can ping both your diagonal network's desktops
make sure your 2 desktops can ping both your diagonal network's desktops

Sniff traffic on outside of laptop before and after adding IP masquerading (network address translation)

on your laptop run tcpdump on one external interface while executing a 1-time ping from one of your desktops through that interface (i.e., to either the laptop or a desktop in the other group)
note the source address of the ping request and destination address of the ping reply (one and the same address)
repeat, on your laptop's other external interface

apply masquerading on both interfaces, using the command for it shown in the slides

now again, on your laptop run tcpdump on one external interface while executing a 1-time ping from one of your desktops through that interface
note the source address of the ping request and destination address of the ping reply (one and the same address)
repeat, on your laptop's other external interface

Block (firewall) traffic, on outside of laptop, from leaving

apply firewalling on one of your laptop's external interfaces, using the command for it shown in the slides
run tcpdump on that firewalled interface while executing a 1-time ping from one of your desktops through that interface
run tcpdump on the laptop's other unfirewalled external interface while executing a 1-time ping from one of your desktops through that interface

undo the firewalling
run tcpdump on that formerly firewalled interface while executing a 1-time ping from one of your desktops through that interface

When finished 

shutdown laptops
disconnect equipment
recompose and return your kit
re-cable desktops to classroom network