Homework Assignments: 22C:178 & 055:134
Computer Communications Spring 1998
A number of commands are quite useful for monitoring network
performance and learning about the Internet. This assignment
starts to experiment with four basic commands.
- is a tool for monitoring current conditions
on your host and statistics for the network interfaces on
your host. Different Unix systems have different implementations
of netstat, so you will have to see man netstat
output for a description of the command syntax. A copy of the
Linux man pages for netstat is located
- is a tool to test network connectivity. Use the
ping command to see if a specified Internet host is
reachable from your machine. A copy of the
Linux man pages for ping is located
Warning: the ping command can get into a loop
if you do not specify a count with the -n option, or
it can wait for a long period if the specified host is not
connected to the Internet. Use control-c to force ping to
exit in these cases.
Note: the syntax and man pages for ping
unfortunately differ depending on the Unix implementation. For
instance on HP machines, the -n option specifies how many
times the specified host will be tested; under Linux this is
specified with the -c option.
- is a powerful utility for resolving names,
looking for IP addresses and names wherever they can be
resolved, whether by /etc/hosts, DNS, or even NIS.
But the primary terminology for nslookup is the
DNS database of records. The nslookup utility can
be executed either as a command or as an interactive program.
If you use it as an interactive program, you will need to
type exit to quit, just as you would for a Unix shell.
To see a copy of the
Linux man pages for nslookup, click
- is an interesting tool, since you learn
about current routing tables and conditions in the Internet.
to see a copy of the Linux manpage for traceroute.
Your task for this assignment is to try a number of different
commands, examine the output, and attempt to explain the output.
To start, try these commands:
Now that you've tried a few basic versions of the commands and
examined the man pages, try answering these questions.
- ping localhost -n 3
- nslookup localhost
- traceroute localhost
- nslookup www.yahoo.com
- nslookup www.yahoo.com (again after an hour;
did you get the same result?)
- nslookup 22.214.171.124
- ping www.yahoo.com -n 3
- traceroute www.yahoo.com
- How many gateways and interfaces are on your host and subnetwork?
(Perhaps the netstat command can be used to answer this.)
- What happens if you ping non-existent addresses?
- What happens if you ping just the hostname of some
host on your subnetwork?
- Two numbers are reserved in the final octet of the dotted
decimal notation, that is, there are two numbers
never used for host IP addresses in the final digit z of an IP
address of the form w.x.y.z. What are these numbers?
What happens if you ping one of these numbers on your local subnet?
- The man page for nslookup mentions something
about listing all the hosts in a particular domain. Use
nslookup interactively to determine the names of all
the hosts on your subnetwork.