Network Address Translation And Filter Tables example essay topic

Decision Support Systems Used in Network Hardware How does data pass through the internet? If you said decision support systems, you are correct. In an indecisive world, network hardware devices uses decision support systems (DSS) to efficiently and effectively route data, in a local area network, with the least amount of errors and inconsistencies. Decision support systems are the brains behind network hardware, and would be near impossible for them to work without the intelligent core of each distinct DSS. There are a variety of network hardware devices: switches, hubs, and routers; and they all use algorithms / procedures to transfer data towards the correct destination.

Although there are many more DSS related methods used to route traffic, this paper describes how these three devices use them and each of there functions. Other types of decision support systems that network hardware devices may use are firewall technology, network address translation, and filter tables, which are all described in this paper. Network hardware is used in the first three layers of the OSI reference model. The OSI reference model is the Open Systems Interconnections standard and consists of seven layers that build from the wire. At the first layer, "the physical layer", hubs maybe used for simple, inexpensive technology within a corporation.

Hubs, when receiving data sent to it, sends that data too all network interface cards, or NICS on each computer. If the data is at its correct destination, the NIC to read the data, but if it is not, the data is discarded. Of course, this setting is much slower, because the other NICS are waiting for there turn, which is after the first message is delivered or timed out. Raymond R. Panko writes this about the waiting state a hub goes in when transmitting data: "This creates latency (delay), which grows as the number of stations grows. Another way of saying this is that the speed of the hub is shared. (Panko 108) " As, you can tell, hubs are simple, and don't use more information than needed.

Switches, which are layer 2 devices, use decision based routing by storing NIC hardware addresses and port numbers on a table in the switch. By doing this, when data is received by the switch, it knows where the source was, and where the data needs to go. This allows for faster data transmission for all NICS that are connected, because it uses the switches full bandwidth and there is no broadcasting across ports. Panko writes this about switches: "This approach allows multiple conversations to take place at the same time...

There is no need to wait while another station is transmitting. (109) "Whereas switches and hubs are used within single networks, routers are used to connect two or more networks together into an internet. Roozbeh Razavi of HowStuffWorks. com writes: "Routers use routing algorithms to find the best route to a destination. When we say 'best route,' we consider parameters like the number of hops (the trip a packet takes from one router or intermediate point to another in the network), time delay and communication cost of packet transmission. (How Routing Algorithms Work 2nd pg. par 1) " More data is collected in a routing table on routers than there is on switches. For instance, a routing table on a router includes these attributes: Row #, Network / sub net, Mask (/prefix), Metric (cost), Interface, and Next-Hop Router.

Each row on the table accounts for a device connected to the router, and the last row on the table accounts for the broadcast channel for all devices. The network / sub net column of the table tells the router the address of another network connected to the router. The mask column is used by the router to calculate the network part of the network address, and the sub net part of the network address. The metric, or cost is the number or time it takes to reach a specific destination. The interface is the outgoing port on the router, and last but not least is the next-hop router, which tells the router the address of the next existing router that it is connected to. Michael J. Norton, a software engineer at Cisco Systems describes the next hop a little cleaner: Routers maintain information about other routers in the network.

A router that is on the same network segment as another router is said to be a routing neighbor. A distance metric is assigned to the neighbor router. This distance metric is called a hop. Neighboring routers are said to be one hop away from the local router (Norton par 11). To learn how a router knows where to send a packet of information, this detailed description describes these processes: The routing system selects an entry from the routing table and takes the net mask from that entry. The system then performs a logical AND of this value and the destination address.

The resulting value is compared to the network address in the table entry. If the two values are the same then the destination can be reached through the gateway in that entry. If the two values are different then the routing system moves to the next entry in the table. If the table is exhausted and no matching entry is found, then the usual result is for the routing system to discard the packet and generate a message notifying the sending application that the destination network is unreachable. (Whipple par 1) Routers, compared to the other two devices mentioned, hold more information about connections for the router to easily process requests.

Of course, this makes routers more expensive, increasing in price as the number of connections increases. The price of this technology is dropping rapidly, as more and more people are switching to wireless routers and NICS. Soon, switches and hubs will be replaced by more intelligent routers which do not even use physical lines, just radio frequencies, making local area network access easier to setup and to connect too. Maybe someday, more attributes or columns will be added to the table, hoping to increase speed and intelligence. For now, these routers with routing tables located on them are the way to go, because they work, and they work intelligently fast. Another form of decision support systems used by a router maybe a firewall, which protects a network from non allowed messages from the outside.

Jeff Tyson of HowStuffWorks. com writes this about firewalls: "Basically, a firewall is a barrier to keep destructive forces away from your property. In fact, that's why its called a firewall. Its job is similar to a physical firewall that keeps a fire from spreading from one area to the next" (How Firewalls Work par 3). Firewalls work wonders for companies that only want certain incoming data to be processed.

The router itself either rejects or accepts an incoming message based on a pass-or-deny decision, sort of like a security guard at the gate of a secure building. The Business Data Networks and Telecommunications textbook lists some important examples of things a certain type of firewall, a packet filter firewall, considers: If the source IP address in a packet arriving from outside the network is that of a host known to be inside the firewall (on the corporate network side), the packet must be from an attacker spoofing (counterfeiting) the source IP address. ICMP ping (echo) messages usually are stopped because they can be used in scanning attacks to identify potential victim hosts. In TCP, acknowledgment (ACK) messages are stopped if there is no current connection between hosts because hosts would respond by returning reset (RST) messages that contain the host's IP address. This gives the same type of information a ping does. In both TCP and UDP, port number fields are examined.

Usually, only a few port numbers are allowed, most notably Port 80, which is used by HTTP for web services. (Panko 282-283) A firewall may also use a thing called network address translation, or NAT, to hide a company's internal IP (internet protocol) address given to them by an internet service provider. Jeff Tyson of HowStuffWorks. com writes "Network Address Translation allows a single device, such as a router, to act as an agent between the Internet (or 'public network') and a local (or 'private') network. (How NAT Works par 6) " How does NAT hide a company's internal IP address? Well it just replaces the real IP address being sent out, to sort of like a made up IP address, created by the router. The router stores the real internal IP address and port number, and the external IP address and port number together on a table called the translation table.

By utilizing NAT on a router, a company disguises its address from outside sources that may be trying to "sniff" the company. When the message is returned to the router, the router reads the destination address on the message, looks on the translation table for a match, and then delivers the message. If there is not a match on the table, the message is neglected, and never seen beyond the firewall. Yet another technology hosted by some firewall systems today is filter tables. These are just tables, with addresses that a company knows not to receive information from (there are many out there). Gorry Fairhurst of the University of Aberdeen in England gives this description of how a filter table works: The filter table is usually manually configured, and contains a list of addresses and other packet header details which, if they match a received packet, will cause the packet to be examined in detail and possibly rejected.

This may be used to prevent unauthorized packets being forwarded (e.g. to act as a firewall). When a packet is detected by a network interface card (i.e. it matches an entry in the forwarding table), it may be either discarded by the network interface immediately, or forwarded directly to the general purpose processor for further processing. This table is often called an Access Control List (ACL), and may become very complex in some applications. (Fairhurst par 35) In conclusion, network hardware uses many decision support systems to intelligently and securely transmit data over a wide area of networks. From the cheapest hub, to the most expensive router, these devices create the web known today as the internet. Firewalls, filter tables and network address translation, both with decisive methods, will both aid in the security of a network from potential hackers.

Now, data mining tools are being used to uncover the congestion that slows network traffic down. With all these DSS type applications working together in harmony, the internet can be faster and safer to surf, than ever before. SourcesFairhurst, Gorry. "Operation of a Router". 10 Jan, 2001. "How Firewalls Work".

HowStuffWorks (web), by Jeff Tyson. HowStuffWorks Inc., 2002". How LAN Switches Work". HowStuffWorks (web), bye Jeff Tyson. How Network Address Translation Works". How Routing Algorithms Work.

' HowStuffWorks (web), by Roozbeh Razavi. Norton, Michael J. "Layer 3 Switching -- Introducing the Router". The O'Reilly Network. 13 Apr. 2001. web Raymond R. "Business Data Networks and Telecommunication". New Jersey: Pearson Education, 2003. Whipple, William L. "TCP / IP For Internet Administrators".

A Searchable Technical Reference Document. Western Logic Works: 1997 (web).