#readwise # Introduction to Networking - MAC Addresses ![rw-book-cover](https://readwise-assets.s3.amazonaws.com/static/images/article1.be68295a7e40.png) ## Metadata - Author: [[Hack The Box]] - Full Title: Introduction to Networking - MAC Addresses - URL: https://academy.hackthebox.com/module/34/section/307 ## Summary Every device on a network has a unique MAC address used for communication. MAC addresses are 48 bits long and can be represented in hexadecimal format. The Address Resolution Protocol (ARP) helps devices find each other's MAC addresses using their IP addresses. However, MAC addresses can be spoofed, making them unreliable for security. ## Highlights The MAC address consists of a total of `6 bytes`. The first half (`3 bytes` / `24 bit`) is the so-called `Organization Unique Identifier` (`OUI`) defined by the `Institute of Electrical and Electronics Engineers` (`IEEE`) for the respective manufacturers. ... The last half of the MAC address is called the `Individual Address Part` or `Network Interface Controller` (`NIC`), which the manufacturers assign. The manufacturer sets this bit sequence only once and thus ensures that the complete address is unique. ^pyalcx --- If a host with the IP target address is located in the same subnet, the delivery is made directly to the target computer's physical address. However, if this host belongs to a different subnet, the Ethernet frame is addressed to the `MAC address` of the responsible router (`default gateway`). ([View Highlight](https://read.readwise.io/read/01jnhdz04nq50zm0d7b3bgwv9k)) --- The last bit (of the first octet) identifies the MAC address as `Unicast` (`0`) or `Multicast` (`1`). With `unicast`, it means that the packet sent will reach only one specific host. ... With `multicast`, the packet is sent only once to all hosts on the local network, which then decides whether or not to accept the packet based on their configuration. --- The `multicast` address is a unique address, just like the `broadcast` address, which has fixed octet values. `Broadcast` in a network represents a broadcasted call, where data packets are transmitted simultaneously from one point to all members of a network. It is mainly used if the address of the receiver of the packet is not yet known. An example is the `ARP` (`for MAC addresses`) and DHCP (`for IPv4 addresses`) protocols. ([View Highlight](https://read.readwise.io/read/01jnhe6ghbkwdrhxnmvks9046v)) ---