The process of direct linking to websites files such as images, videos etc is called as Hot Linking. It is like using an image (tag/image link) which you have found on someone else web page, and would be using on your blog. Every time the blog is browsed image will be shown because it is Hot linked from it’s original source.

This becomes a point of concern when your website is Hot linked by someone else.

Let me explain
Every website has a fixed bandwidth (bandwidth - Amount of data transferred from website to a users computer). When any internet user browses a website and if that website is hot linked to your site then your website’s
bandwidth is used in transferring the requested data.
??? => This means you are paying for the bandwidth which is not used by you.

To overcome Hot linking(Bandwidth Theft) Hotlink Protection is used. It prevents other websites from directly linking to files (as specified above) to your website.
Hotlink Protection can be set from Plesk Control Panel as well.

lets assume server which has SNMP and RRDTool means monitor server has ip address 10.10.10.1
and server which you want to monitor has IP address 99.99.99.99

SNMP Installation
SNMP packages require for querring .

- type command at the prompt
#yum search snmp
It will show you different snmp packages.
You neet to install 2 packages
net-snmp
net-snmp-devel
type command
#yum install net-snmp
#yum install net-snmp-devel

RRDTool Installation

RRD store and display time-series data (i.e. network bandwidth, server load average). It stores the data in a very compact way that will not expand over time, and it presents useful graphs by processing the data to enforce a certain data density.

RRDTool 1.2.x has dependancies ,hence you need to install following packages.

* libart_lgpl-2.3.11-2.i386.rpm
* libart_lgpl-devel-2.3.11-2.i386.rpm

* freetype-2.1.3-6.i386.rpm
* freetype-devel-2.1.3-6.i386.rpm
* zlib-1.1.4-8.i386.rpm
* zlib-devel-1.1.4-8.i386.rpm
* libpng-1.2.2-16.i386.rpm
* libpng-devel-1.2.2-16.i386.rpm

Download RRDTool from http://ftp.idilis.ro/mirrors/rrdtool/

lets assume you have rrdtool-1.2.12.tar.gz

To extract RRDTool run this command:

#tar -xzvf rrdtool-1.2.12.tar.gz

then change directory:
#cd rrdtool-1.2.12

to compile ans install RRDTool type:
#./configure –disable-tcl
#make
#make install

Apply following step on server which you want to monitor means 99.99.99.99
Install net-snmp
Type following commands
#yum search snmp
#yum install net-snmp

then edit snmpd.conf file and create readonly community
#vi /etc/snmp/snmpd.conf

add following line in snmpd.conf file
rocommunity  community_name ip_address_of_monitor_server

start snmpd service
/etc/init.d/snmpd start

Apply following step on monitor server means 10.10.10.1
To monitor bandwidth you need to create RRD file,which will store bandwidth data.

step 1
Create RRD file.
rrdtool create bandwidth.rrd -s 60 \
DS:in:COUNTER:300:U:U \
DS:out:COUNTER:300:U:U \
RRA:AVERAGE:0.5:1:10080

step 2
Update RRD file.

/usr/bin/rrdupdate bandwidth.rrd \
N:`/usr/bin/snmpget -v 1 -c community_name -Oqv 9.99.99.99 IF-MIB::ifInOctets.2`: \
`/usr/bin/snmpget -v 1 -c community_name -Oqv 99.99.99.99 IF-MIB::ifOutOctets.2`

Above command should be run with 1 or 5 minute interval as per your need,hence add above command in cronjob.

step 3
Generate graph from bandwidth.rrd file

rrdtool graph bandwidth.png \
–end now –start end-30h –width 400 \
–x-grid HOUR:1:HOUR:6:HOUR:2:0:%H \
–imgformat=PNG \
–title=”your title” \
–rigid \
–base=1000 \
–height=120 \
–width=500 \
–alt-autoscale-max \
–lower-limit=0 \
–vertical-label=”bits per second” \
DEF:a=bandwidth.rrd:in:AVERAGE \
DEF:b=bandwidth.rrd:out:AVERAGE \
VDEF:totin=a,TOTAL \
VDEF:totout=b,TOTAL \
CDEF:cdefa=a,8,* \
CDEF:cdeff=b,8,* \
AREA:cdefa#00CF00:”Incoming”  \
GPRINT:cdefa:LAST:”Cur\:%6.2lf %sb/s”  \
GPRINT:cdefa:AVERAGE:”Avg\:%6.2lf %sb/s”  \
GPRINT:cdefa:MAX:”Max\:%6.2lf %sb/s”  \
GPRINT:cdefa:MIN:”MIN\:%6.2lf %sb/s\l”  \
LINE1.3:cdeff#0000FF:”Outgoing”  \
GPRINT:cdeff:LAST:”Cur\:%6.2lf %sb/s”  \
GPRINT:cdeff:AVERAGE:”Avg\:%6.2lf %sb/s”  \
GPRINT:cdeff:MAX:”Max\:%6.2lf %sb/s”  \
GPRINT:cdeff:MIN:”MIN\:%6.2lf %sb/s\l”  \
GPRINT:totin:”Total IN\:%6.2lf %sb/s”  \
GPRINT:totout:”Total OUT\:%6.2lf %sb/s”  \
VRULE:1084777200#FF0000:”"

After firing  above command, a file bandwidth.png will be in current direcoty which is bandwidth graph for server 99.99.99.99