Introduction to Networks

MAC address

48-bit addresses that are physically embedded on the Ethernet NIC. A MAC address is also known as the physical address or burned-in address (BIA) The Media Access Control address, or, MAC address, is a unique hardware identification number assigned to network interfaces. Common interfaces assigned MAC addresses include Ethernet cards, Wi-Fi cards, Bluetooth devices, and other wireless devices and accessories which require access to a data network.

daemon

A computer program that runs int he background and is usually initiated as a process. Daemons often support server processes

broadcast

A form of transmission where one device transmits to all devices within the network or on another network

ARP

Address Resolution Protocol Internet protocol used to map an IP address to a MAC address ARP itself is a protocol above ethernet, like IP or IPX. When a device wants to know the MAC address for a given IP address, it sends a packet to the broadcast MAC address asking "Who has IP address y.y.y.y?" All devices receive that packet, but only the one with the IP address y.y.y.y will respond with a packet "It's me." The asking device receives the answer and now knows that the source MAC address is the right MAC address to use. Of course the result will be cached, so the device does not need to resolve the MAC address every time.

DNS

Domain Name System DNS stands for "domain name system." Domain names are the human-readable website addresses we use every day. For example, Google's domain name is google.com. If you want to visit Google, you just need to enter google.com into your web browser's address bar. However, your computer doesn't understand where "google.com" is. Behind the scenes, the Internet and other networks use numerical IP addresses ("Internet protocol" addresses). Google.com is located at the IP address 173.194.39.78 on the Internet. If you typed this number into your web browser's address bar, you'd also end up at Google's website. We use google.com instead of 173.194.39.78 because addresses like google.com are more meaningful and easier for us to remember. DNS is often explained as being like a phone book - like a phone book, DNS matches human-readable names to numbers that machines can more easily understand.

DNS Servers

Domain name system servers match domain names like google.com to their associated IP addresses — 173.194.39.78 in the case of google.com. When you type google.com into your web browser's address bar, your computer contacts your current DNS server and asks what IP address is associated with google.com. Your computer then connects to the IP address and displays "google.com" in your web browser - the connection to 173.194.39.78 happens behind the scenes. The DNS servers you use are likely provided by your Internet service provider ("ISP"). If you're behind a router, your computer is likely using your router as your DNS server, but the router is likely forwarding requests to your Internet service provider's DNS servers.

DHCP

Dynamic Host configuration Protocol A protocol used to dynamically assign IP configurations to hosts. The services defined by the protocol are used to request and assign an IP address, default gateway, and DNS server address to a network host

How do IP addresses and MAC addresses work together?

IP is a protocol that is used on a layer above ethernet. Another protocol for example would be IPX. When your computer wants to send a packet to some IP address x.x.x.x, then the first check is if the destination address is in the same IP network as the computer itself. If x.x.x.x is in the same network, then the destination IP can be reached directly, otherwise the packet needs to be sent to the configured router. Up to now things seem to have gotten worse, because now we have two IP addresses: one is the original IP packet's target address, the other is the IP of the device to which we should send the packet (the next hop, either the final destination or the router). Since ethernet uses MAC addresses, the sender needs to get the MAC address of the next hop. There is a special protocol ARP (address resolution protocol) that is used for that. Once the sender has retrieved the MAC address of the next hop, he writes that target MAC address into the packet and sends the packet.

What are MAC addresses used for?

MAC addresses are the low level basics that make your ethernet based network work. Network cards each have a unique MAC address. Packets that are sent on the ethernet are always coming from a MAC address and sent to a MAC address. If a network adapter is receiving a packet, it is comparing the packet's destination MAC address to the adapter's own MAC address. If the addresses match, the packet is processed, otherwise it is discarded. There are special MAC addresses, one for example is ff:ff:ff:ff:ff:ff, which is the broadcast address and addresses every network adapter in the network.

broadcast address

Special address reserved for sending a message to all stations. Generally, a broadcast address is a MAC destination address of all ones.

three-way handshake

The process used by TCP to establish a session

BIA

burned-in-address The MAC address that is permanently assigned to a LAN interface or NIC. It is called burned-in because the address is burned into a chip on the card, and the address cannot be changed. Also called universally administered address (UAA)