problem 1) In this section, you will learn a couple of practical tools: route, and ifconfig, and netstat. Below is a very brief explanation of what they do.

route The route command can be used to view and manipulate IP routing table.

netstat is a tool which can be used to exhibit network connections, routing tables, interface statistics and many other things.

ifconfig The ifconfig command is used to configure a network interface and to display the status of the currently active interfaces.

(a) Run the route command. prepare down the use of the entry with netmask 0.0.0.0?

(b) Assume a malicious attacker runs \route del" to delete routing entry corresponding to 128.2.13.128/26 on one of the unix.andrew.cmu.edu machines. Now you try to run \ping www.cnn.com". Do you expect the ping to get through? Harry Bovik, the local networking guru argues that \Well, there is still a default route, so the ping should go through!" Harry's pessimistic alter ego suggests otherwise, but does not have a reason. Should Harry believe his alter ego or dismiss it as a case of unjustified pessimism? Give a brief 1-2 line answer why.

(c) Name the command to view the routing table of your machine using netstat? What is the command to only show IP addresses and not host names in the routing table?

(d) How can you use netstat to determine what the network interfaces of your machine are? What is the MTU of your Ethernet interface?

(e) Run ifconfig. What information does the field \Mask" give you?

(f) What happens if you run ifconfig and configure an interface to be in promiscuous mode?

problem 2) A forwarding table for a router in a network using CIDR is given below.

Address prex         Next hop
200.0.0.0/5                 A
192.0.0.0/2                 B
128.0.0.0/2                C
0.0.0.0/0                     D

(a) If the router receives a packet with destination 199.42.13.37, what will the next hop be?

(b) If the router recieves a packet with destination 255.255.255.255, what will the next hop be?

(c) Assume I add the entry 128.25.0.0/16 to the routing table. Will lookups still yield a single forwarding entry? describe.

(d) What actually happens to packet which only matches 0.0.0.0/0?