> For the complete documentation index, see [llms.txt](https://documentation.hak5.org/packet-squirrel-mark-ii/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://documentation.hak5.org/packet-squirrel-mark-ii/networking-tutorial/glossary.md). # Glossary

Term	Definition
Bridge	A network mode (or network device) which copies packets between two physical interfaces, without changing the content of the packets. Similar to a switch, a bridge copies packets from one physical network to another physical network, without modification.
Hub	A hub distributes packets from all connected devices to all other connected devices. A hub operates at the physical layer (layer 1) and has no insight into the contents of the data, and offers no protection against multiple devices transmitting at once.
Layer N	A reference to a layer in the OSI network model; typically used to describe the area of networking, such as layer 2 (raw packets), layer 4 (TCP and above), and so on.
MAC Address	A MAC address (Media Access Control), is the unique 6-byte addressed of a network card at the lowest layer. MAC addresses must be unique within a network. The first 3 bytes of the MAC address are known as the OUI (Organizational Unique Identifier); each manufacturer has a unique UI, which allows identifying (to some extent) what company has produced a network device. Since many network devices are re-branded or include network chipsets from other companies, this information is not always reliable.
NAT	Also known as Network Address Translation or Masquerading; a method where packets from multiple devices on a private network are rewritten to appear to be from a single device on the public network.
Packet	A packet represents a collection of data on the network transmitted as a single object. A stream of data (such as a web site or video stream) is broken up into many packets to traverse the network. Often used synonymously with the term "frame" to indicate a block of data on a physical network.
Router	A network mode (or network device) which directs packets from one logical network to another (such as from a private network to an Internet connection, often utilizing NAT in the process). Routers are responsible for passing packets from one network to another, such as a private local network passing packets to a larger corporate network or the Internet. Routers modify packets to direct them to the new network.
Switch	A network device which connects multiple Ethernet devices, while keeping traffic separate. A switch operates purely at the data layer (layer 2), and typically has no insight into the types of packets or the protocols contained in the packet.