Proper Use of Addressing Technologies

Subnetting – IP addresses can be class A, B or C. Class A addresses are for networks with a large number of hosts. The first octet is the netid and the 3 remaining octets are the hostid. Class B addresses are used in medium to large networks with the first 2 octets making up the netid and the remaining 2 are the hostid. Class C is for smaller networks with the first 3 octets making up the netid and the last octet comprising the hostid. The Network ID and the Host ID are determined by a subnet mask. The default subnet masks are as follows:

What if you wanted more than 1 subnet? Subnetting allows you to create multiple logical networks that exist within a single Class A, B, or C network. If you don’t subnet, you will only be able to use one network from your Class A, B, or C network. When subnetting is employed, the multiple networks are connected with a router which enables data to find its way between networks. On the client side, a default gateway is assigned in the TCP/IP properties. The default gateway tells the client the IP address of the router that will allow their computer to communicate with clients on other networks.

Classful versus Classless addressing – the original TCP/IP addressing method described above was called classful addressing which worked by dividing the IP address space into chunks of different sizes called classes. Classless addressing is referred to as Classless Inter-Domain Routing (CIDR) and is done by allocating address space to Internet service providers and end users on any address bit boundary, instead of on 8-bit segments. So 172.16.50.0 does not have to use the standard subnet mask of 255.255.0.0 which makes a Class B address space and which also puts it on the same network as 172.16.51.0 using the subnet mask of 255.255.0.0. (With classful addressing, our example has 172.16 as the network name and the 50.0 and 51.0 ranges are both part of the same host naming convention). Instead, by using classless addressing 172.16.50.0/24 puts these systems on a different network than 172.16.51.0/24 because the network names here are 172.16.50 and 172.16.51 which are different.

NAT – NAT stands for Network Address Translation and is a commonly used IP translation and mapping technology. Using a device (such as a router) or piece of software that implements NAT allows an entire home or office network to share a single internet connection over a single IP address. A single cable modem, DSL modem, or even 56k modem could connect all the computers to the internet simultaneously. Additionally, NAT keeps your home network fairly secure from hackers. NAT is built in to the most common Internet Connection Sharing technologies.

PAT – Port Address Translation is a feature of a network device that translates TCP or UDP communications made between hosts on a private network and hosts on a public network. It allows a single public IP address to be used by many hosts on a private network.

SNAT – Secure Network Address Translation an extension of the standard Network Address Translation (NAT) service. SNAT is done through one to one IP address translation of one internal IP address to one external IP address where NAT is effectively one external address to many internal IP addresses.

DHCP – Dynamic Host Configuration Protocol provides a solution that automatically assigns IP addresses to computers on a network. When a client is configured to receive an IP address automatically, It will send out a broadcast to the DHCP server requesting an address. The server will then issue a “lease” and assign it to that client. Some of the benefits of DHCP include the following:

• Prevents users from making up their own IP addresses.
• Prevents incorrect gateway or subnet masks from being entered.
• Decreases amount of time spent configuring computers especially in environments where computers get moved around all the time.

APIPA – Stands for Automatic Private Internet Protocol Addressing. Client systems that are configured for automatic IP address assignment / dynamic IP assignment will attempt to use DHCP to make a request for an IP address lease for a given network. When the DHCP server is unavailable the service on the client will automatically configure the system with an APIPA IP address in the 169.254.0.1 through 169.254.255.254 address range with a subnet mask of 255.255.0.0.

Unicast – the sending of information packets to a single network node. This type of network transmission is used where a private or unique resource such as media servers are being requested for two way connections that are needed to complete the network communication. So in the media server example, a client system may make the request for streaming content from the single source and the responding system may leverage unicast as part of the response to the session request to deliver the content.

Multicast – a single source address responding to multiple destination addresses with information to be sent. In a media server example, the single source address may need to send the data to multiple clients; it does this by sending the data with multiple destination IP addresses. All the clients that “see” this network traffic will check to see if it is meant for them with the supplied information. If it is not the client does not receive the data. If a network node does see that the data is intended for them the device will respond by receiving the packet.

Broadcast – traffic sent out from a network node that will reach every other node on the subnet / broadcast domain because the message is sent with the intent of reaching all nodes. The network node that is sending the traffic will use the broadcast address for that subnet and every device in that broadcast domain will receive the broadcast information. Generally the broadcast address is the last IP address of that segment. As an example, in the IP address range of 192.168.0.0 this broadcast address would be 192.168.255.255 and the traffic would reach all available nodes on the subnet. Additionally 255.255.255.255 could be used which is the broadcast address of the zero network (0.0.0.0). Internet Protocol standards outline that the zero network stands for the local network so only those node on the local network would hear the broadcast traffic across the 255.255.255.255 address.

**Source by wikipedia**

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