AbbottLink™ - IP Address Overview 3/22/06

AbbottLink™ - IP Address Overview An IP address always consists of 4 numbers separated by periods, with the numbers having a possible range of 0 through 255. An example of how an IP address appears is: 192.168.1.10 Each computer on a network must have a different IP address to be able to communicate. If by accident the same IP address were assigned to two computers, then those computers would have what is called an "IP Conflict" and one of them will not be able to communicate. There are 2 ways that any network device will get its IP Address. One is manual entry by users / administrators which is a STATIC assignment. The other is automatically assigned by a process called DHCP (Dynamic Host Configuration Protocol). Using DHCP, a PC requests an IP address and the DHCP server on the network "leases" one address out of its available pool for a schedule period of time. An IP Address is comprised of 2 parts, a Network ID and a Host ID. Put simply, it’s like the Street Address and the Door Number, where Street Address is your Network ID and the Door number is the unique host ID. 3/22/06

AbbottLink™ - IP Address Overview Private IP Addresses There are blocks of IP addresses that are set aside for internal private use for computers not directly connected to the Internet. These IP addresses are not supposed to be routed through the Internet, and most service providers will block the attempt to do so. These IP addresses are used for internal use by company or home networks that do not want to be directly visible on the Internet. These IP ranges are: Private Start Address Private End Address Class A 10.0.0.0 10.255.255.255 Class B 172.16.0.0 172.31.255.255 Class C 192.168.0.0 192.168.255.255 3/22/06

AbbottLink™ - IP Address Overview Subnet Mask Subnet masks are a part of an IP address and the two values work together. Applying the subnet mask to an IP address splits the address into two parts, an "extended network address ID" and a host address or ID. A Subnet Mask is an address mask that allows systems to differentiate between the Network ID and the Host IDs in a IP Address. Through use of the subnet mask, each IP-enabled device is able to determine if another address is on its network, or should be forwarded to the default gateway Default Gateway A default gateway is a device on a computer network that serves as an access point to another network. If a system doesn't know where to send a set of packets, it will forward it to this device address which then routes the data to the appropriate destinations. The default gateway will specify the destination the information is to be sent to on another network. 3/22/06

AbbottLink™ - IP Address Overview DNS - Domain Name System Every device on the network or the internet is assigned an IP address. Navigating to them using their 12-digit IP address would be very cumbersome. DNS allows a user-friendly name to be used as a pseudonym for a specific IP address. (i.e. www.google.com). When you type www.google.com in your browser and press enter, the information is sent to a DNS server which looks up and translates (resolves) the name into a valid IP Address and tells the browser to where to go. The PC can then access the website. 3/22/06

AbbottLink™ - IP Address Overview Proxy Server A proxy server is a machine/program that acts as an intermediary between computers on a LAN and computers on the Internet. A Proxy allows users on a network to browse the Web and work with E-mail and other Internet services and permits machines on the network to use a shared internet connection. Some proxy servers also allow the filtering of web content or domains. Workstations request data (like web pages) from the proxy server to access the internet. The proxy server then retrieves the internet data, checks it’s filters, and returns it to the workstation that requested it Simply put, proxies are gateway applications used to route Internet and web access from within a firewall. Proxy servers work by opening a socket on the server and allowing the connection to pass through. 3/22/06

AbbottLink™ - IP Address Overview A proxy performs the following tasks: Receives a request from a client/PC inside the firewall Sends this request to the remote server outside of the firewall Reads the response Sends it back to the client 3/22/06

AbbottLink™ - IP Address Overview Firewalls Firewalls are software-based network security devices (either integrated into a network client, like a personal computer, network switch or router, or a single purpose hardware appliance) deployed to provide increased safety or security by controlling the data going into and out of a private network. A firewall’s primary role is to keep networks secure by preventing intruders, certain classes of viruses, and security threats from accessing a protected network. The level of security implemented will determine how these threats will be prevented access by the firewall. A firewall filters data from an unsecured network or an internet connection. A firewall can be customized to filter data based on conditions like source or destination network addresses, domain names or potentially hazardous protocols. A company can place a firewall at its internet connections and implement security rules. By using these rules, the company can control how employees connect to web sites and whether files are allowed to leave the company over the network . 3/22/06