Net prog1-net-7

Technical Foundation of Computer Science 5Network Programming I

Maria Sawaby

Department of Communication and Operating System

May 26, 2015

Lecture-7 (Network-Department) Net-Prog I May 26, 2015 1 / 12

Contents

1 Basic networking primer

2 Name server and DNS (Domain Name Service)DNS lookupSetting default gateway, showing routing table information

3 Summary

Lecture-7 (Network-Department) Net-Prog I May 26, 2015 2 / 12

Basic networking primer

shell scripts can be used to con�gure nodes in a network, test theavailability of machines, automate execution of commands at remotehost and so on

ifcon�g is used to display details about network interfaces, subnetmask and so on

The ifcon�g command displays details of every network interfaceavailable on the system

we can restrict it to a speci�c interface by using

$ifcon�g iface_name

$ifcon�g wlan0

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ifcon�g

In order to set the IP address for a network interface

$sudo ifcon�g iface-name IP-address

$sudo ifcon�g wlan0 192.168.1.10

$sudo ifcon�g wlan0 192.168.1.10 netmask 255.255.255.0

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Spoo�ng Hardware Address (MAC Address)

In certain circumstances where authentication or �ltering of computerson a network is provided by using the hardware address, we can usehardware address spoo�ng

# ifcon�g eth0 hw ether 00:1c:bf:87:25:d5

this command will assign "00:1c:bf:87:25:d5" as the new MAC address

Lecture-7 (Network-Department) Net-Prog I May 26, 2015 5 / 12

Name server and DNS (Domain Name Service)

DNS servers con�gured with our network resolve the domain nameinto the corresponding IP address

Name servers assigned to the current system can be viewed by reading/etc/resolv.conf

$cat /etc/resolv.conf

We can add name servers manually

$sudo echo nameserver IP_ADDRESS � /etc/resolv.conf

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DNS lookup

host and nslookup are two DNS lookup utilities which will request aDNS server for an IP address resolution

Lecture-7 (Network-Department) Net-Prog I May 26, 2015 7 / 12

DNS lookup

Without using the DNS server, it is possible to add a symbolic nameto IP address resolution just by adding entries into �le /etc/hosts

In order to add an entry

# echo IP_ADDRESS symbolic_name � /etc/hosts

# echo 192.168.0.9 backupserver.com � /etc/hosts

After adding this entry, whenever a resolution to backupserver.comoccurs, it will resolve to 192.168.0.9

Lecture-7 (Network-Department) Net-Prog I May 26, 2015 8 / 12

Setting default gateway, showing routing table informationroute

The operating system maintains a table called the routing table, whichcontains information on how packets are to be forwarded and through

which machine node in the network $ route

Lecture-7 (Network-Department) Net-Prog I May 26, 2015 9 / 12

Setting default gateway, showing routing table informationroute

A default gateway is set as follows:

# route add default gw IP_ADDRESS INTERFACE_NAME

For example:# route add default gw 192.168.0.1 wlan0

Lecture-7 (Network-Department) Net-Prog I May 26, 2015 10 / 12

Summary

ifcon�g, used to display details about network interfaces

host and nslookup are used to resolve a name to an IP address byasking a DNS server

route, to set default gateway and showing routing table information

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