7/27/2019 network config

1/12

Ex No : 7 SETTING UP THE COMPLETE NETWORKINTERFACE

Aim :

To setup the completenetwork interfaceusingifconfig command like settinggateway,

DNS, IP tables,firewall.

Procedure :

Step 1 Setting up a static IP:

IFCONFIG is a toolprovided by Fedorasystem to configurenetwork interface(like

settingup a staticIP)

OPTION PURPOSE

-a Display all interfaceswhich are

available,even ifdown.

-s Display a short list.

-v Be more verbose for errorconditions.

Interface The name of the device interface,

usuallya drivername, followed by a unit

number. For eg. eth0

interface[up/do

wn]

upcauses the interfacetobe

deactivated.

For eg. ifconfig eth0 up

ifconfig eth0 down

interface

address

The ip address is assisnedto the

interface.

For eg. ifconfig eth0 192.168.0.10

Assignan IP address to the interfacecurrentlybeingconfigured.The address

configuredis static.

Usage:

Identifythe name of the network interfacesconfiguredwith the help of the a

option of ifconfig:

$ ifconfig a

7/27/2019 network config

2/12

To assignan IP address to aparticularinterface,say eth0 :

$ ifconfig eth0 192.168.0.10

To activatethe interface,afterthe IP address has been assigned:

$ ifconfig eth0 up

To deactivatethe interface:

$ ifconfig eth0 down

ifconfig with options a, -s :

7/27/2019 network config

3/12

A

7/27/2019 network config

4/12

Step 2 Set up a default gateway, using route:

Once a static IP address has been assignedto the interfaceunder

consideration, ROUTE system call is used to set up staticroutes to specifichosts or

networks via the interface.

OPTION PURPOSE

-v Selectverbose operation.

-n Show numerical address instead of trying to

determine.

-e Displays routingtablein netstat format.

Del Deletea route.

Add Add a new route.

target The destinationnetwork/host.

Gw Route packets via a GATEWAY (staticroute to

the gateway must be setbeforehand)

netmask When addinga network route, a network is to

be used.

7/27/2019 network config

5/12

Usage:

To add defaultgateway to the network interfacecurrentlyconfigured,use the

addoption of route:

$ route add default192.168.0.0

NOTE: The gateway is identifiedas defaultand must fall under the networkof

the interfaceconfigured,in order to be routed correctly.

To specifythe network address to route to a gateway (a more general usage)

$ route add net 292.168.0.0 netmask 255.255.0.0

route with options v, -n, -e, -net (adding a network), -host (adding a

host) :

7/27/2019 network config

6/12

7/27/2019 network config

7/12

7/27/2019 network config

8/12

Step 3 Setting up a nameserver(DNS):

When configuring the resolverlibrary to use the bindname service for lookups,

the name servers to be used are to be specified.

The details of such name servers are stored in a file resolv.conf in the etc

directory.

The most importantoptionis the name server, which givesthe IP address of

the server to be used.

For eg.

# /etc/resolv.conf

#domain

domainmydomian.com

#nameserver

nameserver 192.168.0.210

This settingcan be verified by usingthe PINGtool.

$ pingfacebook.com

Ifthe output command is:

unknown host facebook.com,

then the DNS server is eitherdown or not configuredproperly.

Manual And Dynamic Settings :

7/27/2019 network config

9/12

Step 4 Setting up network firewall using iptables:

Once nameservers have been successfullyconfigured,Firewall/NATpackages are

installedusingIPTABLES. Iptablesis an administrationtool forpacket filtering and

NAT.

Several tablesmay be defined.Each tableconsists of a numberofbuilt-in

chainsand user-definedchains.

A firewall rulespecifiesa criterion for a packet and a target. Ifpacket is

matched, the correspondingnext ruleis specifiedby value of the target, which

can be the name of the user-definedchains or one of the special values:

ACCEPT, DROP, QUEUE or RETURN.

ACCEPT:L

etpacket through.

DROP: Droppacket.

QUEUE: Pass packet to userspace.

RETURN: Stop traversingthe chainand return the next rulein calling

(previous)chain.

Chainscan be added to the following 4 tables:

OPTION PURPOSE

Filter Defaulttable

3 chains:

o INPUT: forpackets designedlocal sockets

o OUTPUT: for locally generated sockets

o FORWARD: forpacketsbeingrouted through the

box

nat Constructed,when a packet that creates a new

connectionis encountered.

7/27/2019 network config

10/12

3 built-in chains:

o PRE-ROUTING: alteringpackets as soon as they

come in

o OUTPUT: alteringlocally generatedpackets

before routing

o POST-ROUTING: alteringpackets as they are

about to go out

Manage Used for specializedpacket alteration.

Raw Configuring exceptionsfrom connectiontracking.

Usage:

To add a ruleto the inputchainto drop all the packets incomingthrough port

80:

$ iptablesA INPUT p tcp dport 80 j DROP

The above ruleonce added drops all packets coming intothe system through

port 80, usingtcp.

To add a ruleto the output chain:

$ iptablesA output p tcp --dport 80

This ruledrops all packets sent by the host through port 80, usingtcp.

To deletea rulefrom the inputchain,providethe chainname and no. of rulesto

delete:

$ iptablesD input2

The list of services, protocolsused and port numbers can be found in the file

etc/services.

7/27/2019 network config

11/12

Adding a rule to the INPUTchain

7/27/2019 network config

12/12

CONCLUSION : Thus the complete network interface using ifconfig commands like

setting gateway, DNS, IP tables,firewall have been performed successfully.