RFC 1918 sets aside three blocks of private IP addresses. They are one Class A address, 16 Class B addresses, and 256 Class C addresses. These addresses are for private, internal network use only. Packets containing these addresses are not routed over the Internet.
Public Internet addresses must be registered by a company with an Internet authority, for example, ARIN or RIPE. These public Internet addresses can also be leased from an ISP. Private IP addresses are reserved and can be used by anyone. That means two networks, or two million networks, can each use the same private address. A router should never route RFC 1918 addresses, because ISPs typically configure the border routers to prevent privately addressed traffic from being forwarded.
NAT provides great benefits to individual companies and the Internet. Before NAT, a host with a private address could not access the Internet. Using NAT, individual companies can address some or all of their hosts with private addresses and use
NAT to provide access the Internet.
NAT is designed to conserve IP addresses and enable networks to use private IP addresses on internal networks. These private, internal addresses are translated to routable, public addresses. This is accomplished by inter-network devices running specialized
NAT software and can increase network privacy by hiding internal IP addresses.
A
NAT enabled device typically operates at the border of a stub network. A stub network is a network that has a single connection to its neighbor network. When a host inside the stub network wants to transmit to a host on the outside, it forwards the packet to the border gateway router. The border gateway router performs the
NAT process, translating the internal private address of a host to a public, external routable address. In
NAT terminology, the internal network is the set of networks that are subject to translation. The external network refers to all other addresses.
Cisco defines the following
NAT terms:
Inside local address – The IP address assigned to a host on the inside network. The address is usually not an IP address assigned by the Network Information Center (NIC) or service provider. This address is likely to be an RFC 1918 private address.
Inside global address – A legitimate IP address assigned by the NIC or service provider that represents one or more inside local IP addresses to the outside world.
Outside local address – The IP address of an outside host as it is known to the hosts on the inside network.
Outside global address – The IP address assigned to a host on the outside network. The owner of the host assigns this address.
Yesterday morning when i woke up for school i felt chills. I knew then that sooner or later i'll get sick. But then the day get later i am feeling better. However, when the sun went down the fever came back and am suffering from until today. All day today i didnt let myself down just because i am not feeling well instead i clean and did laundry. Thankfully, i am feeling better and this time i hope this is for real;)
I hate being sick.
Also i have been having problem with my ex-boyfriend's wife. Early this year she asked me to be friend on myspace. Without any questions i accepted her request and didnt hold that against her. But it turned out she is a demented lady. She sent me a message saying that i look like i am on my 40's and that she looks very young on her age. Who in the world will compare theirselves to someone especially if that someone is your husband ex-girlfriend. I then figured out that i really dont need her friendship if she is there to criticize me. She believes that i am jealous of her because she has 3 kids and i dont. Holy mother of god, why would i be jealous if i dont have kids. I love my life, i dont need children to live my life to the fullest. For me career is my priority right now, period!!! God know how happy i am for my ex but for her to thinks i am still after him holy cow she has no idea. I havent spoken to him like 10 years. I dont even know he still exist until she came along and ruined my peaceful days. What a cuckoo. Unbelievable what can insecurities do to someone. I responded to her so many emails asking her if my ex still mention my name to her, because that would s_ck!! Thats the only reason i can think of why she hated me so much and cant get herself off my back. She is a great pretender and a scary stalker.Hahay life..;)
How Does Serial Communication Work?
You know that most PCs have both serial and parallel ports. You also know that electricity can only move at one speed. One way to get bits to move faster through a wire is to compress the data so that less bits are necessary and then require less time on the wire, or transmit the bits simultaneously. Computers make use of relatively short parallel connections between interior components, but use a serial bus to convert signals for most external communications.
Let's compare serial and parallel communications.
With a serial connection, information is sent across one wire, one data bit at a time. The 9-pin serial connector on most PCs uses two loops of wire, one in each direction, for data communication, plus additional wires to control the flow of information. In any given direction, data is still flowing over a single wire.
A parallel connection sends the bits over more wires simultaneously. In the case of the 25-pin parallel port on your PC, there are eight data-carrying wires to carry 8 bits simultaneously. Because there are eight wires to carry the data, the parallel link theoretically transfers data eight times faster than a serial connection. So based on this theory, a parallel connection sends a byte in the time a serial connection sends a bit.
This explanation brings up some questions. What is meant by theoretically faster? If parallel is faster than serial, is parallel more suitable for connecting to a WAN? In reality, it is often the case that serial links can be clocked considerably faster than parallel links, and they achieve a higher data rate, because of two factors that affect parallel communications: clock skew and crosstalk interference.
In a parallel connection, it is wrong to assume that the 8 bits leaving the sender at the same time arrive at the receiver at the same time. Rather, some of the bits get there later than others. This is known as clock skew. Overcoming clock skew is not trivial. The receiving end must synchronize itself with the transmitter and then wait until all the bits have arrived. The process of reading, waiting, latching, waiting for clock signal, and transmitting the 8 bits adds time to the transmission. In parallel communications, a latch is a data storage system used to store information in sequential logic systems. The more wires you use and the farther the connection reaches, compounds the problem and adds delay. The need for clocking slows parallel transmission well below theoretical expectations.
This is not a factor with serial links, because most serial links do not need clocking. Serial connections require fewer wires and cables. They occupy less space and can be better isolated from interference from other wires and cables.
Parallel wires are physically bundled in a parallel cable, and signals can imprint themselves on each other. The possibility of crosstalk across the wires requires more processing, especially at higher frequencies. The serial buses on computers, including routers, compensate for crosstalk before transmitting the bits. Since serial cables have fewer wires, there is less crosstalk, and network devices transmit serial communications at higher, more efficient frequencies.
In most cases, serial communications are considerably cheaper to implement. Serial communications use fewer wires, cheaper cables, and fewer connector pins.
VPN Technology
Security risks are incurred when a teleworker or remote office uses broadband services to access the corporate WAN over the Internet. To address security concerns, broadband services provide capabilities for using Virtual Private Network (VPN) connections to a VPN server, which is typically located at the corporate site.
A VPN is an encrypted connection between private networks over a public network such as the Internet. Instead of using a dedicated Layer 2 connection such as a leased line, a VPN uses virtual connections called VPN tunnels, which are routed through the Internet from the private network of the company to the remote site or employee host.
VPN Benefits
Benefits of VPN include the following:
Cost savings-VPNs enable organizations to use the global Internet to connect remote offices and remote users to the main corporate site, thus eliminating expensive dedicated WAN links and modem banks.
Security-VPNs provide the highest level of security by using advanced encryption and authentication protocols that protect data from unauthorized access.
Scalability-Because VPNs use the Internet infrastructure within ISPs and devices, it is easy to add new users. Corporations are able to add large amounts of capacity without adding significant infrastructure.
Compatibility with broadband technology-VPN technology is supported by broadband service providers such as DSL and cable, so mobile workers and telecommuters can take advantage of their home high-speed Internet service to access their corporate networks. Business-grade, high-speed broadband connections can also provide a cost-effective solution for connecting remote offices.
Types of VPN Access
There are two types of VPN access:
Site-to-site VPNs-Site-to-site VPNs connect entire networks to each other, for example, they can connect a branch office network to a company headquarters network, as shown in the figure. Each site is equipped with a VPN gateway, such as a router, firewall, VPN concentrator, or security appliance. In the figure, a remote branch office uses a site-to-site-VPN to connect with the corporate head office.
Remote-access VPNs-Remote-access VPNs enable individual hosts, such as telecommuters, mobile users, and extranet consumers, to access a company network securely over the Internet. Each host typically has VPN client software loaded or uses a web-based client.
Broadband Services
Broadband connection options are typically used to connect telecommuting employees to a corporate site over the Internet. These options include cable, DSL, and wireless.
Click the DSL button in the figure.
DSL
DSL technology is an always-on connection technology that uses existing twisted-pair telephone lines to transport high-bandwidth data, and provides IP services to subscribers. A DSL modem converts an Ethernet signal from the user device to a DSL signal, which is transmitted to the central office.
Multiple DSL subscriber lines are multiplexed into a single, high-capacity link using a DSL access multiplexer (DSLAM) at the provider location. DSLAMs incorporate TDM technology to aggregate many subscriber lines into a single medium, generally a T3 (DS3) connection. Current DSL technologies use sophisticated coding and modulation techniques to achieve data rates of up to 8.192 Mb/s.
There is a wide variety of DSL types, standards, and emerging standards. DSL is now a popular choice for enterprise IT departments to support home workers. Generally, a subscriber cannot choose to connect to an enterprise network directly, but must first connect to an ISP, and then an IP connection is made through the Internet to the enterprise. Security risks are incurred in this process, but can be mediated with security measures.
Click the Cable Modem button in the figure.
Cable Modem
Coaxial cable is widely used in urban areas to distribute television signals. Network access is available from some cable television networks. This allows for greater bandwidth than the conventional telephone local loop.
Cable modems provide an always-on connection and a simple installation. A subscriber connects a computer or LAN router to the cable modem, which translates the digital signals into the broadband frequencies used for transmitting on a cable television network. The local cable TV office, which is called the cable headend, contains the computer system and databases needed to provide Internet access. The most important component located at the headend is the cable modem termination system (CMTS), which sends and receives digital cable modem signals on a cable network and is necessary for providing Internet services to cable subscribers.
Cable modem subscribers must use the ISP associated with the service provider. All the local subscribers share the same cable bandwidth. As more users join the service, available bandwidth may be below the expected rate.
Click the Broadband Wireless button in the figure.
Broadband Wireless
Wireless technology uses the unlicensed radio spectrum to send and receive data. The unlicensed spectrum is accessible to anyone who has a wireless router and wireless technology in the device they are using.
Until recently, one limitation of wireless access has been the need to be within the local transmission range (typically less than 100 feet) of a wireless router or a wireless modem that has a wired connection to the Internet. The following new developments in broadband wireless technology are changing this situation:
Municipal WiFi-Many cities have begun setting up municipal wireless networks. Some of these networks provide high-speed Internet access for free or for substantially less than the price of other broadband services. Others are for city use only, allowing police and fire departments and other city employees to do certain aspects of their jobs remotely. To connect to a municipal WiFi, a subscriber typically needs a wireless modem, which provides a stronger radio and directional antenna than conventional wireless adapters. Most service providers provide the necessary equipment for free or for a fee, much like they do with DSL or cable modems.
WiMAX-Worldwide Interoperability for Microwave Access (WiMAX) is a new technology that is just beginning to come into use. It is described in the IEEE standard 802.16. WiMAX provides high-speed broadband service with wireless access and provides broad coverage like a cell phone network rather than through small WiFi hotspots. WiMAX operates in a similar way to WiFi, but at higher speeds, over greater distances, and for a greater number of users. It uses a network of WiMAX towers that are similar to cell phone towers. To access a WiMAX network, subscribers must subscribe to an ISP with a WiMAX tower within 10 miles of their location. They also need a WiMAX-enabled computer and a special encryption code to get access to the base station.
Satellite Internet-Typically used by rural users where cable and DSL are not available. A satellite dish provides two-way (upload and download) data communications. The upload speed is about one-tenth of the 500 kb/s download speed. Cable and DSL have higher download speeds, but satellite systems are about 10 times faster than an analog modem. To access satellite Internet services, subscribers need a satellite dish, two modems (uplink and downlink), and coaxial cables between the dish and the modem.
One of the most common types of WAN connection is the point-to-point connection. Point-to-point connections are used to connect LANs to service provider WANs, and to connect LAN segments within an Enterprise network. A LAN-to-WAN point-to-point connection is also referred to as a serial connection or leased-line connection, because the lines are leased from a carrier (usually a telephone company) and are dedicated for use by the company leasing the lines. Companies pay for a continuous connection between two remote sites, and the line is continuously active and available. Understanding how point-to-point communication links function to provide access to a WAN is important to an overall understanding of how WANs function. Point-to-Point Protocol (PPP) provides multiprotocol LAN-to-WAN connections handling TCP/IP, Internetwork Packet Exchange (IPX), and AppleTalk simultaneously. It can be used over twisted pair, fiber-optic lines, and satellite transmission. PPP provides transport over ATM, Frame Relay, ISDN and optical links. In modern networks, security is a key concern. PPP allows you to authenticate connections using either Password Authentication Protocol (PAP) or the more effective Challenge Handshake Authentication Protocol (CHAP).
I havent been on here much as i want to. Been busy with school and job hunting. I am hoping to get a job soon. If anyone knows a company or someone might be looking for a Network Engineer please let me know;)
With the situation we are in today I am still hopeful to get a job in my field.
I am so disgusted by other bloggers; no offend but isnt it blogging about making something of your own not taking someones else works? I dont know but i guess i am way beyond my head but i truly believe that you should work hard for something if you want them.
Theres nothing really going on today but a birthday party of one of my closest friend here in Colorado. I was awaken by a friend this morning that i am little disappointed of because i really want to stay in bed as much as i can before i head to the party; but no i got interrupted by my phone ;(
Everyone have a fabulous Saturday.
As I ponder the love that I saw in his eyes,
A Godly love, given without compromise....
I recall many times that he stood by my side,
And prodded me on with great vigor and pride.
His voice ever confident, firm and yet fair,
Always speaking with patience, tenderness and care.
The power and might of his hands was so sure,
I knew there was nothing we couldn't endure.
It's true, a few others provided insight,
Yet, he laid the foundation that kept me upright.
He's the grandest of men to have lived on this earth,
Although he's not royal by stature or birth.
He's a man of great dignity, honor and strength.
His merits are noble, and of admirable length.
He's far greater than all other men that I know,
He's my Dad, he's my mentor, my friend and hero.
Teleworkers typically use diverse applications (for example, e-mail, web-based applications, mission-critical applications, real-time collaboration, voice, video, and videoconferencing) that require a high-bandwidth connection. The choice of access network technology and the need to ensure suitable bandwidth are the first considerations to address when connecting teleworkers.
Residential cable, DSL and broadband wireless are three options that provide high bandwidth to teleworkers. The low bandwidth provided by a dialup modem connection is usually not sufficient, although it is useful for mobile access while traveling. A modem dialup connection should only be considered when other options are unavailable.
Teleworkers require a connection to an ISP to access the Internet. ISPs offer various connection options. The main connection methods used by home and small business users are:
Dialup access - An inexpensive option that uses any phone line and a modem. To connect to the ISP, a user calls the ISP access phone number. Dialup is the slowest connection option, and is typically used by mobile workers in areas where higher speed connection options are not available.
DSL - Typically more expensive than dialup, but provides a faster connection. DSL also uses telephone lines, but unlike dialup access, DSL provides a continuous connection to the Internet. DSL uses a special high-speed modem that separates the DSL signal from the telephone signal and provides an Ethernet connection to a host computer or LAN.
Cable modem - Offered by cable television service providers. The Internet signal is carried on the same coaxial cable that delivers cable television. A special cable modem separates the Internet signal from the other signals carried on the cable and provides an Ethernet connection to a host computer or LAN.
Satellite - Offered by satellite service providers. The computer connects through Ethernet to a satellite modem that transmits radio signals to the nearest point of presence (POP) within the satellite network.
Movement to change from IPv4 to IPv6 has already begun, particularly in Europe, Japan, and the Asia-Pacific region. These areas are exhausting their allotted IPv4 addresses, which makes IPv6 all the more attractive and necessary. Japan officially started the move in 2000 when the Japanese government mandated the incorporation of IPv6 and set a deadline of 2005 to upgrade existing systems in every business and public sector. Korea, China, and Malaysia have launched similar initiatives.
In 2002, the European Community IPv6 Task Force forged a strategic alliance to foster IPv6 adoption worldwide. The North American IPv6 Task Force has set out to engage the North American markets to adopt IPv6. The first significant North American advances are coming from the U.S. Department of Defense (DoD). Looking into the future and knowing the advantages of IP-enabled devices, DoD mandated, as early as 2003, that all new equipment purchased not only be IP-enabled, but also be IPv6-capable. In fact, all U.S. government agencies must start using IPv6 across their core networks by 2008, and the agencies are working to meet that deadline.
The ability to scale networks for future demands requires a limitless supply of IP addresses and improved mobility that DHCP and
NAT alone cannot meet. IPv6 satisfies the increasingly complex requirements of hierarchical addressing that IPv4 does not provide.
Given the huge installed base of IPv4 in the world, it is not difficult to appreciate that transitioning to IPv6 from IPv4 deployments is a challenge. There are, however, a variety of techniques, including an auto-configuration option, to make the transition easier. The transition mechanism you use depends on the needs of your network.
The figure compares the binary and alphanumeric representations of IPv4 and IPv6 addresses. An IPv6 address is a 128-bit binary value, which can be displayed as 32 hexadecimal digits. IPv6 should provide sufficient addresses for future Internet growth needs for many years to come. There are enough IPv6 addresses to allocate more than the entire IPv4 Internet address space to everyone on the planet.
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