Monday, May 05, 2008

Practical (1st day 5/5/08)



Isnin 5/5/08
Tempat : IMATERA DIGITAL IMAGE SERVICES SDN BHD
Cawangan Utara (Perlis/Kedah/Penang)
Staf : 3 org
Practical Student : 2 ( PSP & KISMEC)
Tempoh Praktikal : 2 bulan [ 4 Mei 08- 3 July 08]
Waktu kerja : 8.30pg - 5.30ptg - Isnin-Jumaat (Sabtu & Ahad= Cuti.. yahoooo...heheheh)

Latar Belakang syarikat
http://portal.imateradigital.com/imatera/

Merupakan sebuah sykt yg telah di tubuhkan seawal tahun 1991 yg menawarkan perkhidmatan ICT khususnya kpd kerajaan dan swasta juga adalah syarikat milik bumiputera sepenuhnya.
Gabungan dari perkataan : (Faith and Harmony/ Tranquility ) Iman + Sejahtera = IMATERA.

Hmmm... hari ini buat apa ?
Alhamdulillah dapat peruntukan 1 pc utk diriku.
Hmmm.. byk virus lah pulak.. kena tukar Kaspersky baru best skit.. sok baru nk settle sebab tak bawa installer nyer ..
Bos suh copy struktur phpSQL lak dah...hmmm bab2 koding ni yg kureng..huh...
1 folder ada 68 perkara & lagi 1 ada 7 perkara di dalamnyer..
Alhamdulillah settle gak ptg tadi. So .. ini hari copy struktur dlm MS_Excel.

guna Winscap utk masuk root server
http://localhost/phpmyadmin

Tuesday, April 01, 2008

Linux_Shutdown_Commandline

RESTART/REBOOT LINUX
----------------------------------------------------------------------
Linux: Reboot: How to reboot from the command line??
Method: reboot from the command line:
 shutdown -fr now # restarts
or
 shutdown -r now # restarts
or
 reboot
---
---
Method: reboot using <DEL>
When in a text mode screen,
press <DEL>
---
SHUTDOWN LINUX
----------------------------------------------------------------------
Linux: shutdown: How to shutdown from the command line??
Method: shutdown from the command line:
 shutdown -fr now # shutdown

Web Development

RABU - 12/3/08

Web Development dibahagikan kpd 2 :
  • Static --- Pure HTML
  • Dynamic

Static
  • Content
  • nk ubah/edit perlu buka semula fail tersebut
  • pages yang tersedia

Dynamic
  • content can be anything (dynamicly loaded into web page)
  • Develop guna mySQL & PHP
  • Keperluan : web server (-> apache) + mySQL + PHP
  • Software : WAMP, XAMP, Easy PHP [ ada ketiga-tiga keperluan diatas -packages)
Web Authoring Tools -> Dreamweaver

Buat folder untuk...( step )
  1. /var/www/html
  2. mkdir shadia
  3. vim index.html

Web development is a broad term for any activities related to developing a web site for the World Wide Web or an intranet.
This can include e-commerce business development, web design, web content development, client-side/server-side coding, and web server configuration.
However, among web professionals, "web development" usually refers only to the non-design aspects of building web sites, e.g. writing markup and coding.
Web development can range from developing the simplest static single page of plain text to the most complex web-based internet applications, electronic businesses, or social network services.
For larger businesses and organizations, web development teams can consist of hundreds of people (web developers).
maller organizations may only require a single permanent or contracting webmaster, or secondary assignment to related job positions such as a graphic designer and/or Information systems technician.
Web development may be a collaborative effort between departments rather than the domain of a designated department.

Reference-http://en.wikipedia.org/wiki/Web_development



Thursday, February 28, 2008

Firewall

Merupakan suatu aplikasi @ perisian yang mengawal in & out bound (apa saja yg masuk dr network card) network traffic
  • menapis in / out dlm network
  • pengawal traffic (allow & block)
  • bukan antivirus
  • cth firewall (COMODO -> rules allow + block)
Keperluan pada pc :
  • utk kawal in & out bound yg berlaku dlm network card
  • control sebarang komunikasi atr pc dgn pc yg lain / host lain drpd network card.
  • hanya menggunakan rules
    • 1. allow + deny
    • 2. accept + firewall
    • 3. allow + block

* Setiap komunikasi yang berlaku menggunakan IP + Port
Port
80 - http
8080 - proxy
21 - ftp
53 - DNS
110 - POPS
22 - ssh (hacker selalu guna)
20 - telnet

* Reason guna firewall Staff & student :
  • tidak benarkan mana-mana pihak boleh control server
  • Kalau student & staf boleh control server maka tiada fungsi Chief Network Server
* PC standalone tidak boleh control PC lain untuk block kerana ia bukan server (iaitu PC yg lain2 tidak connect pada PC tersebut)


A firewall is a dedicated appliance, or software running on another computer, which inspects network traffic passing through it, and denies or permits passage based on a set of rules.

Reference - http://en.wikipedia.org/wiki/Firewall

Monday, February 25, 2008

Latihan hacked di www.hackthissite.org

Di website ini disediakan cara2 utk hack website berdasarkan kepada Basic Level, Mission level dan seterusnya. Untuk Basic Level didalamnya terdapat 10 stage...
kusut kepala utk lepas setiap stage nih....aduhai... (kak murni kata utk menjadi hackers yg sebenaqnya kena fikior secara kritis / analitics thinking....)...
Tapi bagi diA,sebenarnya klu takde basic belajaq html coding, script (javascript & vbscript) tu tak leh gak... jadi blur2..gitu ;-p
Lama dah ngaji coding2 tuh....mcm siput jer nk buat ujian kt www.hackthissite.org ...hmmm
Sehingga tarikh hari ini 25/2/08 dari 22/2/08 baru lepas stage 7 @ nk masuk stage 8.

Hacked Website menggunakan SQL Injection (magic code)

SQL Injection - Magic Code

Berikut adalah antara website yg berjaya nadia masuki dan ketika ini mungkin website-website tersebut telah kemaskini (update) :
1. http://www.inneresteem.com
2. http://myeshop4u.com
3. pgcs.upm.edu.my/pli
4. www.diginex.com.my
5. http://www.alhidayah-tamesna.com
6. www.agriplaza.com.my
7. www.lamwood.net
8. http://www.iccweb.com
9. www.mcmweb.org
10. http://www.bima.net
11. www.melrosepyro.com
12. http://bcahosting.com
13. http://www.mathcounts.org
14. www.malangkab.go.id
15. www.nyscatholicconference.org

Wednesday, February 20, 2008

Remote File Inclusion (RFI)

Remote File Inclusion (RFI)

  • 1 teknik yang digunakan untuk ceroboh website internet drpd komputer kawalan jauh (remote computer)
  • is a technique used to attack Internet websites from a remote computer.
  • berlaku dlm programming yg tidak mempertimbangkan security khususnya dlm php
  • berlaku dalam url
  • include


Tuesday, February 19, 2008

Cross Site Scripting @ XSS

XSS
  • curi cookies
  • 1 teknik yg digunakan oleh attacker utk hantar sebrg script pd web user.
  • berlaku pd aplikasi web
  • script yg biasa digunakan oleh XSS Javascript@VBscript utk mdptkn cookies

  • cth :
  • masukkan script (vbscript) utk buatkan (dokumen.cookies) & dptkn cookies tsbt copy & paste pd website / pc.
  • website rujukan http://www.milw0rm.com

Definisi umum:

Mana2 attacker akan hantar script pd website user yg ada vulnerability, x kira mana2 script php,html script atau lain2 yg digunakan dihantar pd website user / aplikasi web utk bypass @ masuk website tsbt.
* cara utk hack komputer : (ada byk cara )
  1. SQL Injection
  2. Remote Injection
* masukkan
  • guestbook
  • upload file



"What is Cross Site Scripting?"

Cross site scripting (also known as XSS) occurs when a web application gathers malicious data from a user. The data is usually gathered in the form of a hyperlink which contains malicious content within it. The user will most likely click on this link from another website, instant message, or simply just reading a web board or email message. Usually the attacker will encode the malicious portion of the link to the site in HEX (or other encoding methods) so the request is less suspicious looking to the user when clicked on. After the data is collected by the web application, it creates an output page for the user containing the malicious data that was originally sent to it, but in a manner to make it appear as valid content from the website. Many popular guestbook and forum programs allow users to submit posts with html and javascript embedded in them. If for example I was logged in as "john" and read a message by "joe" that contained malicious javascript in it, then it may be possible for "joe" to hijack my session just by reading his bulletin board post. Further details on how attacks like this are accomplished via "cookie theft" are explained in detail below.


Reference : http://www.cgisecurity.com/articles/xss-faq.shtml#whatis

Tuesday, February 12, 2008

SQL Injection

Apa itu SQL Injection ?
  • Vulnerable system / internet website

  • Magic code

  • code string -> 'a or 'a' = a'

  • a' or 't'='t
    Pada username masukkan = admin
    Password “ = `1 or `1`=`1

    Atau

    Pada username masukkan = `1 or `1`=`1
    Password “ = `1 or `1`=`1

    Sistem tidak dapat detect ( ` `@ ` ` ) krn x ada username / password (user/pengguna) yg letak spt itu melainkan string shj spt 1 or 1 = 1, tidak `1 or `1`=`1.

SQL injection is a technique that exploits a security vulnerability occurring in the database layer of an application. The vulnerability is present when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and thereby unexpectedly executed. It is in fact an instance of a more general class of vulnerabilities that can occur whenever one programming or scripting language is embedded inside another.


Reference: Wikipedia, the free encyclopedia



Tujuan SQL injection :
  • DOS ( Denial of services)

  • Access / akses

  • Modify


HOW TO PROTECT FROM SQL INJECTION

  • protect di application level

  • server level

  1. if...else statement ( di bhg login )

  2. escape ' 1 ' single code

  3. parameter statement

4. Username -> email


password -> password

(Berikut adalah contoh coding SQL utk paparan interface di atas )


$ SQL = " SELECT nama_penyelia, tahap_penyelia, id_penyelia

FROM penyelia WHERE username = '$name' and

password = '$pass';



* Letakkan coding dibawah utk prevent SQL Injection : ataupun syarat dimana jika ada Hackers yg letakkan Magic Code x' or '1' = '1 maka website telah detect & akses tidak dibenarkan.

* variable name dihantar / dibaca dari belakang ke depan iaitu :

Tujuan if...else statement = utk - > (jika website sendiri)

  1. check $name contain
  2. reject- jika ada single code / reject jika true

* Server + mod security + Apache ( utk prevent injection di server jika melibatkan byk website)

* Setkn single code + SQL code (Magic string) di server utk reject sebarang cubaan hack.


Sniffer

Sniff = hidu @ menghidu data yang dihantar antara pc.

Sniffer = tools untuk hidu.

Network sniffer & Packet Sniffer.

Free useful sniffer software from internet :
  1. Cain

  2. Ethercap
Dimana kedua-duanya menggunakan konsep MITM.

Objektif :
  • untuk sniff apa yang pc orang lain buat (aktiviti)

  • alat / tools untuk hack password, poison network, email
Sniffer
  • plain -> hidu

  • MITM ( Men in the middle)


Skill set : (untuk mahir menggunakan sniffer)
  1. Ip Addressing

  2. Indentify - (target (tahu pc mana yg dikehendaki) & source

  3. Ptotokol - Tcp/Ip

  4. Filtering

htttps = guna port 443

http = port 80

Ms Outlook / email sistem = 25 & 110

Utk sniff ke google, tindakan yg perlu dilakukan :
  • Sniff ke pc D & sniff ke router shj krn laluan yang sama akan dilalui utk sniff & google menghantar semula penghantaran (jwpn)
  • Tetapi apabila aktiviti sniff dilakukan pc A @ lain2 pc tidak dapat sniff / lakukan aktiviti lain kerana kekacauan (sniff) menyebabkan network menjadi slow.

Monday, February 11, 2008

Tools yg telah dipraktikkan cara pengggunaannya.

UTP backbone cable


Serial Cable

Router back


Router back



Console Cable
Cisco router2600





Monday, February 04, 2008

Friday, February 01, 2008

4 UTP Cable


NETWORK CABLING

4 UTP CABLE :

  1. Unshielded Twisted Pair

  2. Shielded Twisted Pair

  3. Coaxial Cable

  4. Fiber Optic Cable

* kabel-kabel UTP boleh ditarik / digunakan sepjg max 100 meter.
1. Unshielded Twisted Pair

Telekomunikasi - ( Telefon, Internet, pc 2 pc, point 2 point, node 2 node)


DEFINITION: This definition closely duplicates the definition for twisted pair.

Unshielded twisted pair is the most common kind of copper telephone wiring. Twisted pair is the ordinary copper wire that connects home and many business computers to the telephone company. To reduce crosstalk or electromagnetic induction between pairs of wires, two insulated copper wires are twisted.


Reference : http://www.bitpipe.com/tlist/Unshielded-Twisted-Pair-Cable.html




2. Shielded Twisted Pair
Pengalir - ( tahan gangguan elektrik / elektronik, distance )




3. Coaxial Cable

Tv, CCTV

Coaxial Cable - Orginally used for the cable television industry coaxial cable is now widely used for computer networks. Although it is more expensive than standard telephone wires it is less susceptible to interference and can transmit more data.


Reference - http://www.24by7.ca/glossary.htm



4. Fiber Optic Cable
Terdapat gentian kaca di dalamnya. – (Mahal, Rapuh, Tahan haba & kelembapan, cahaya, noise (bunyi bising), Server, Penghantaran data (laju)

Defination :
Optical fiber (or "fiber optic") refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber. Optical fiber carries much more information than conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company long-distance lines are now of optical fiber.
Transmission on optical fiber wire requires repeaters at distance intervals. The glass fiber requires more protection within an outer cable than copper. For these reasons and because the installation of any new wiring is labor-intensive, few communities yet have optical fiber wires or cables from the phone company's branch office to local customers (known as local loops).
A type of fiber known as single mode fiber is used for longer distances; multimode fiber fiber is used for shorter distances.

Saturday, January 26, 2008

Subnet Mask

Defination :
subnet mask is a screen of numbers used for routing traffic within a subnet. Once a packet has arrived at an organization's gateway or connection point with its unique network number, it can be routed to its destination within the organization's internal gateways using the subnet number.
The subnet mask consists of a screen of numbers indicating to the router which numbers it should look at underneath. In a binary mask, for example, a "1" over a number says "Look at the number underneath;" a "0" says "Don't look." Using a mask saves the router having to handle the entire 32 bit address; it can simply look at the bits selected by the mask.

Using the previous example (which is a very typical case), the combined network number and subnet number occupy 24 bits or three of the quads. The appropriate subnet mask carried along with the packet would be: 255.255.255.0

Or a string of all 1's for the first three quads (telling the router to look at these) and 0's for the host number (which the router doesn't need to look at). Subnet masking allows routers to move the packets on more quickly.

If you have the job of creating subnets for an organization (an activity called subnetting) and specifying subnet masks, your job may be simple or complicated depending on the size and complexity of your organization and other factors.

Ping

Defination :

Ping is a basic Internet program that allows a user to verify that a particular IP address exists and can accept requests. The verb ping means the act of using the ping utility or command. Ping is used diagnostically to ensure that a host computer you are trying to reach is actually operating. If, for example, a user can't ping a host, then the user will be unable to use the File Transfer Protocol (FTP) to send files to that host. Ping can also be used with a host that is operating to see how long it takes to get a response back. Using ping, you can learn the number form of the IP address from the symbolic domain name (see "Tip").

Loosely, ping means "to get the attention of" or "to check for the presence of" another party online. Ping operates by sending a packet to a designated address and waiting for a response. The computer acronym (for Packet Internet or Inter-Network Groper) was contrived to match the submariners' term for the sound of a returned sonar pulse.
Ping can also refer to the process of sending a message to all the members of a mailing list requesting an ACK (acknowledgement code). This is done before sending e-mail in order to confirm that all of the addresses are reachable.

Reference - http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci214297,00.html

ipconfig/all = utk melihat ip address, subnet mask, gateway, DNS1,DNS2.

IP : 10.1.0.55
SM : 255.255.0.0
Gateway Default : 10.1.0.4
DNS1 : 202.188.0.132
DNS2 : 202.188.0.133

CISCO Router - 22/1/08 (Selasa)

ROUTER
1 device utk mhubkn 2 network segment yg berbeza.

Cara berfungsi :
· Router akn extract paket yg diterima kpd destinasinya (destinasi ttentu kpd tuan punya paket).
· Akn memilih laluan terbaik bg paket & 4ward paket tsbt di spjng laluan yg dah dipilih.
· Terima, control, select de path & pilih de best router atr 2 network wlpun terdpt byk network.

Definition router

A device that routes data between networks using IP addressing. Routers provide firewall security.

A device or setup that finds the best route between any two networks, even if there are several networks to traverse. Like bridges, remote sites can be connected using routers over dedicated or switched lines to create WANs.

The hardware or software that handles connection between networks online. In other words, it tells your computer where to go.

A router is a computer networking device that buffers and forwards data packets across an internetwork toward their destinations, through a process known as routing. Routing occurs at layer 3 (the Network layer e.g. IP) of the OSI seven-layer protocol stack.

A network device that transmits message packets, routing them over the best route available at the time. Routers are used to connect multiple network segments, including those based on differing architectures and protocols.







Thursday, January 24, 2008

Ip Address-latihan 16/1/08 (Rabu)

Router

Definition: Routers are physical devices that join multiple wired or wireless networks together. Technically, a wired or wireless router is a Layer 3 gateway, meaning that the wired/wireless router connects networks (as gateways do), and that the router operates at the network layer of the OSI model.
Home networkers often use an Internet Protocol (IP) wired or wireless router, IP being the most common OSI network layer protocol. An IP router such as a DSL or cable modem broadband router joins the home's local area network (LAN) to the wide-area network (WAN) of the Internet.
By maintaining configuration information in a piece of storage called the "routing table," wired or wireless routers also have the ability to filter traffic, either incoming or outgoing, based on the IP addresses of senders and receivers.
Some routers allow the home networker to update the routing table from a Web browser interface. Broadband routers combine the functions of a router with those of a network switch and a firewall in a single unit.
Reference - http://compnetworking.about.com/cs/routers/g/bldef_router.htm



Wednesday, January 23, 2008

DHCP

Definition: DHCP allows a computer to join an IP-based network without having a pre-configured IP address. DHCP is a protocol that assigns unique IP addresses to devices, then releases and renews these addresses as devices leave and re-join the network.
Internet Service Providers (ISPs) usually use DHCP to allow customers to join the Internet with minimum effort. Likewise, home network equipment like broadband routers offers DHCP support for added convenience in joining home computers to the LAN.
DHCP environments require a DHCP server set up with the appropriate configuration parameters for the given network. Key DHCP parameters include the range or "pool" of available IP addresses, the correct subnet masks, plus gateway and name server addresses.
Devices running DHCP client software can then automatically retrieve these settings from DHCP servers as needed. Using DHCP on a network means system administrators do not need to configure these parameters individually for each client device.
Reference -http://compnetworking.about.com/cs/protocolsdhcp/

DHCP is a key technology that broadband routers, Internet connection sharing software like Microsoft ICS, and corporate proxy servers all rely on.
Reference - http://compnetworking.about.com/b/2004/01/18/what-is-dhcp.htm

The Dynamic Host Configuration Protocol (DHCP) supports automatic address assignment and improved configuration management of IP networks.
Reference -http://compnetworking.about.com/cs/protocolsdhcp/

Subnet

Defination :
A subnet (short for "subnetwork") is an identifiably separate part of an organization's network. Typically, a subnet may represent all the machines at one geographic location, in one building, or on the same local area network (LAN). Having an organization's network divided into subnets allows it to be connected to the Internet with a single shared network address.

Without subnets, an organization could get multiple connections to the Internet, one for each of its physically separate subnetworks, but this would require an unnecessary use of the limited number of network numbers the Internet has to assign. It would also require that Internet routing tables on gateways outside the organization would need to know about and have to manage routing that could and should be handled within an organization.
The Internet is a collection of networks whose users communicate with each other.

Each communication carries the address of the source and destination networks and the particular machine within the network associated with the user or host computer at each end. This address is called the IP address (Internet Protocol address). This 32-bit IP address has two parts: one part identifies the network (with the network number) and the other part identifies the specific machine or host within the network (with the host number). An organization can use some of the bits in the machine or host part of the address to identify a specific subnet. Effectively, the IP address then contains three parts: the network number, the subnet number, and the machine number.
The standard procedure for creating and identifying subnets is provided in Internet Request for Comments 950.

The 32-bit IP address is often depicted as a dot address (also called dotted quad notation) - that is, four groups (or quads) of decimal numbers separated by periods. Here's an example: 130.5.5.25

Each of the decimal numbers represents a string of eight binary digits. Thus, the above IP address really is this string of 0s and 1s:
10000010.00000101.00000101.00011001

As you can see, we inserted periods between each eight-digit sequence just as we did for the decimal version of the IP address. Obviously, the decimal version of the IP address is easier to read and that's the form most commonly used.

Some portion of the IP address represents the network number or address and some portion represents the local machine address (also known as the host number or address). IP addresses can be one of several classes, each determining how many bits represent the network number and how many represent the host number. The most common class used by large organizations (Class B) allows 16 bits for the network number and 16 for the host number. Using the above example, here's how the IP address is divided:
<--Network address--><--Host address-->
130.5 . 5.25

If you wanted to add subnetting to this address, then some portion (in this example, eight bits) of the host address could be used for a subnet address. Thus: <--Network address--><--Subnet address--><--Host address-->
130.5 . 5 . 25

To simplify this explanation, we've divided the subnet into a neat eight bits but an organization could choose some other scheme using only part of the third quad or even part of the fourth quad.
Once a packet has arrived at an organization's gateway or connection point with its unique network number, it can be routed within the organization's internal gateways using the subnet number. The router knows which bits to look at (and which not to look at) by looking at a subnet mask, which is a screen of numbers that tells you which numbers to look at underneath. In a binary mask, a "1" over a number says "Look at the number underneath"; a "0" says "Don't look." Using a mask saves the router having to handle the entire 32 bit address; it can simply look at the bits selected by the mask.

Reference - http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci213065,00.html

Tuesday, January 22, 2008

Ip Address

Sebagai pengenalan bagi sesebuah komputer/host.
Ip address adalah berpandukan kepada Class A,B atau C.
Class A : 11111111 00000000 00000000 00000000
255 0 0 0
Class B : 11111111 111111111 00000000 00000000
255 255 0 0
Class C : 11111111 111111111 11111111 11111111
255 255 255 0

Class B & C selalu digunakan dan Class A jarang digunakan.

10.1.0.x-----------> ip address bg anggaran pc/host mencecah ribu
192.168.1.x-------> " ratusan & kebawah.
202.188.0.133---->segment 202 adalah kepunyaan TMnet.
Bagi mengurangkan kadar traffic line(talian sibuk) maka perlu block ip address fail-fail exe.,download,movie,audio @ lain2 yg selalu dilawati. [Bagi mana2 student IPT/KISMEC :) ]

An IP address (Internet Protocol address) is a unique address that certain electronic devices currently use in order to identify and communicate with each other on a computer network utilizing the Internet Protocol standard (IP)—in simpler terms, a computer address.

Any participating network device—including routers, switches, computers, infrastructure servers (e.g., NTP, DNS, DHCP, SNMP, etc.), printers, Internet fax machines, and some telephones—can have its own address that is unique within the scope of the specific network.

Some IP addresses are intended to be unique within the scope of the global Internet, while others need to be unique only within the scope of an enterprise.

The IP address acts as a locator for one IP device to find another and interact with it. It is not intended, however, to act as an identifier that always uniquely identifies a particular device. In current practice, an IP address is not always a unique identifier, due to technologies such as dynamic assignment and network address translation.

Reference - http://en.wikipedia.org/wiki/Ip_address



Definition of: static IP address (Ip yang disetkan oleh administrator)

A permanent numeric identification assigned by the network administrator to a node in a TCP/IP network. Static IP addresses are used for shared resources such as Web servers and Webcams.

ISPs assign static IP addresses to the Internet connections of their large business customers, which command a premium over dynamic IP addresses. Contrast with dynamic IP address. See IP address.


Definition of: dynamic IP address (Ip yang diberi @ disetkan oleh modem.)
A temporary numeric identification assigned to a node in a TCP/IP network. When computers and devices in the network are turned on, they are assigned an IP address by a DHCP server.

ISPs typically assign dynamic addresses to the Internet connections of their residential and small business customers, which are less expensive than static addresses. That means the IP address to the outside world in a cable or DSL modem may change every month, every day or even every hour (see DDNS). Contrast with static IP address. See IP address and DHCP.