Key terms used in this module, in alphabetical order.
| Term | Meaning |
|---|---|
| ACL | Access Control List: ordered permit/deny rules on a router or switch |
| AES | Advanced Encryption Standard; the common symmetric cipher |
| APIPA | Automatic Private IP Addressing: a 169.254.x.x address a client gives itself when DHCP fails |
| ARP | Address Resolution Protocol; maps IP to MAC on a LAN |
| Bandwidth | Maximum data capacity of a link |
| Broadcast domain | Part of a network reached by a broadcast frame; routers separate broadcast domains |
| CA | Certificate Authority; trusted body that signs certificates |
| CIDR | Classless Inter-Domain Routing; prefix notation such as /24 |
| Collision domain | Part of a network where frames can collide; each switch port is its own collision domain |
| CSMA/CA | Carrier Sense Multiple Access with Collision Avoidance, used by Wi-Fi |
| CSMA/CD | Carrier Sense Multiple Access with Collision Detection, used by early half-duplex Ethernet |
| Default gateway | The router interface a host sends traffic to for any destination outside its own subnet |
| DHCP | Protocol that automatically assigns IP settings |
| Digital certificate | An X.509 document, signed by a CA, that binds a public key to an identity |
| Digital signature | A value created with the sender's private key that proves origin and integrity |
| DMZ | Network zone for public-facing servers |
| DNS | System that translates names to IP addresses |
| DNSSEC | DNS Security Extensions: signs DNS records so answers can be verified |
| DORA | Discover, Offer, Request, Acknowledge: the four DHCP messages |
| Encapsulation | Adding a header (and trailer) at each layer as data moves down the stack |
| Firewall | Device or software filtering traffic by rules |
| FQDN | Fully Qualified Domain Name |
| Gateway | Router that links a network to others |
| Hash | Fixed-length one-way digest of data |
| Hypervisor | Software that runs virtual machines |
| IPsec | Network-layer VPN and security protocol suite |
| Latency | The time data takes to travel from source to destination |
| MAC address | 48-bit hardware address of a network interface |
| NAT | Translates private addresses to public ones |
| OSI model | Seven-layer reference model for communication |
| OUI | Organisationally Unique Identifier: the first 24 bits of a MAC address, identifying the manufacturer |
| Packet | Layer 3 data unit |
| PDU | Protocol Data Unit: the data unit at a layer (segment, packet, frame, bits) |
| PKI | Public Key Infrastructure; system managing certificates |
| Port | 16-bit number identifying a service on a host |
| RAID | Combining disks for speed and/or redundancy |
| Recursive resolver | DNS server that finds an answer for a client by querying other servers, then caches it |
| Registrar | Company that sells domain names |
| RSA | Widely used asymmetric algorithm |
| SLAAC | Stateless Address Autoconfiguration: IPv6 hosts build their own address from the router's prefix |
| Socket | An IP address plus a port number, for example 192.168.1.10:443 |
| SSH | Secure Shell; encrypted remote access |
| Subnet mask | Separates network and host parts of an IP address |
| TCP / UDP | Reliable / unreliable transport protocols |
| Throughput | The data rate actually achieved on a link, always at or below the bandwidth |
| TLS | Transport Layer Security; encrypts HTTPS and many other protocols |
| Topology | The physical or logical arrangement of devices and links in a network |
| Trunk | A switch link that carries several VLANs, with 802.1Q tags |
| TTL | Time To Live: how long a DNS answer may be cached |
| VLAN | Logical network on a switch |
| VLSM | Variable Length Subnet Masking |
| VPN | Virtual Private Network |
| VPS | Virtual Private Server |
| Zone | Part of the DNS namespace managed by one set of servers |