Common network diagnostic and configuration utilities

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Common network diagnostic and configuration
utilities

• A toolkit for network users and managers when
  troubleshooting is needed on your network

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Kudlick Classroom
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lectern
Each student workstation has two Intel PRO1000
Gigabit Ethernet Controllers one is named
eth0 and it is connected to a LAN switch that
has a gateway to the campus network and the
Internet the other is named eth1 and it is
connected to a different switch which does not
offer an Internet gateway
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hostname

• This command will quickly show you the network
  name for your host machine (or will allow you to
  change that name if you possess the necessary
  authorization)
• Example hostname
• This command works by calling a standard library
  function (e.g., gethostname() ) that well
  often be using in our own programs

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ping

• A standard UNIX tool for testing whether a
  particular host is reachable across an IP network
  and if so, then how quickly?
• Example ping 138.202.171.14
• It also confirms that a Network Interface
  Controller is operating properly, and that a
  hostname can be resolved to its address
• Example ping stargate.cs.usfca.edu

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traceroute

• A tool for determining what route is being taken
  by packets sent over an IP network
• Example traceroute cs.stanford.edu
• This tool will report on each of the hops
  between network routers along a path to the
  specified destination, and the elapsed times for
  each hop (in milliseconds)
• (A similar tool for Linux is tracepath)

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route

• It lets users display current information in a
  hosts routing table database -- and it lets a
  privileged user manipulate that info
• Example /sbin/route -n
• The routing tables entries tell the kernels
  networking subsystem how to deliver, or forward,
  or else discard, any IP-network packets that are
  being received by a NIC

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tcpdump

• This is a packet decoding tool it shows where
  a packet is coming from, where it is going to, as
  well as its size and its purpose
• But its only available to a privileged user
• Example sudo /usr/sbin/tcpdump i eth0
• For an active interface on the internet, the
  volume of output normally produced is so intense
  as to overwhelm a humans view!

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netstat

• It can show a lot of information about the
  current state of your hosts networking subsystem
  such as routing-table entries, active
  connections, ports and protocols, or statistics
  for the active Network Interfaces
• Example netstat -i
• Its not a privileged command any user can
  execute Linuxs netstat utility ?

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whois

• Its queries an official Internet database to
  determine the current owner of a network domain
  name or host name
• Example whois 138.202.0.0
• It allows users to find out who they can contact
  in order to report any abuses or malfunctions
  that have been identified as originating from a
  particular IP-address

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ifconfig

• This program allows a user to view status
  information and statistics for any network
  interfaces which exist in your machine, or to
  modify the state of a network interface if you
  possess the necessary authorizations
• Example /sbin/ifconfig -a
• With sudo privileges, we will be able to make
  changes to our interfaces states

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ftp

• This offers a convenient command-line interface
  to the File-Transfer Protocol which is
  implemented on the Internet
• Example ftp hopper.usfca.edu
• You will usually need to enter a password and a
  sequence of ftp-specific commands in order to
  download (or upload) a file using this
  standard UNIX ftp application

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telnet

• This program lets users communicate with remote
  servers using the telnet protocol
• Example telnet rainmaker.wunderground.com
  3000
• Of course, the remote host must allow the
  connection for specified port-number and for the
  user who is attempting to connect
• System administrators often configure a networks
  firewall to reject telnet-requests

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Thanks, Alex!

• Our System Administrator, Alex Fedosov, has
  kindly provided a list of several other
  networking utilities that he finds are very
  useful in managing the CS Departments various
  local networks and its gateways
• Most of those tools are not mentioned by our
  textbook because they are mainly of use for
  specialized management tasks

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nmap

• This is a networking security port-scanner with
  lots of options and capabilities that a Network
  Administrator would find helpful for doing
  security-related troubleshooting
• Example nmap localhost

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lsof

• This utility lists a hosts open files and its
  network connections (i.e., sockets), and shows
  which processes are using them
• Example /usr/sbin/lsof
• There are lots of command-line options (see the
  online manual man lsof ) that can make the
  displayed information be more helpful for your
  specific purpose

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host

• This is a Domain Name Service resolver allowing
  a user to find out the hostname for a particular
  Internet Protocol address
• Example host 138.202.1.15
• Notice that the order in which the numeric
  components of the hosts IP-address are shown in
  this programs output has been reversed (bringing
  up the endian topic)

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arp

• This utility displays information in a hosts ARP
  cache (Address Resolution Protocol) and allows a
  user to manipulate that info
• Example /sbin/arp

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Demo nicwatch.cpp

• This is packet sniffer that your Instructor has
  created for your use in studying how the network
  interfaces in our classroom machines are working,
  and for assistance in debugging your own
  network programs
• Example nicwatch eth0
• You can redirect its screen-output to a file if
  you want to examine it more leisurely!

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In-class exercise 1

• Find out what IP-address is being used by your
  classroom workstation ping hrn235xx
• Now look at your workstations routing table to
  see which interfaces are currently being used
• /sbin/route -n
• Then use the ifconfig utility to assign an
  IP-address to your machines secondary NIC (i.e.,
  to the eth1 network interface)
• sudo /sbin/ifconfig eth1 192.168.1.xxx up
• Did this cause any routing-table changes?

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In-class exercise 2

• Now that your secondary NIC is up and is using
  an IP-address on the 192.168.1.0 local area
  network, you can use ping to see if other host
  are reachable on the LAN
• ping 192.168.1.yyy
• In a separate window you can execute our
  nicwatch utility while ping is running
• nicwatch eth1