Glossary

Terms are grouped by topic rather than alphabetically, so related ideas sit together. Use your browser's find (Ctrl/Cmd + F) to jump to a specific term.

#Addresses and naming

MAC address — The 48-bit hardware address burned into every network interface, written as six pairs of hex digits (a4:c3:f0:12:ab:9e). Used by switches. Does not change when a device moves.

IP address — The logical address that identifies a device on a network. IPv4 addresses are 32 bits written as four decimal numbers (192.168.10.42); IPv6 addresses are 128 bits written in hex (2001:db8::42). Used by routers. Changes when a device moves to a different network.

Subnet — A range of IP addresses that share the same network portion and can reach each other without a router. Usually one subnet per VLAN.

Subnet mask / prefix length — Defines where the network portion of an address ends. 255.255.255.0 and /24 mean the same thing.

CIDR — Classless Inter-Domain Routing. In practice, the /24 slash notation for subnets.

Network address — The first address in a subnet, with all host bits zero. Identifies the subnet; can't be assigned to a device.

Broadcast address — The last address in a subnet, with all host bits one. Packets sent here reach every device in the subnet.

Default gateway — The router's address on the local subnet. Where a device sends everything not on its own subnet.

Private address — An address from 10.0.0.0/8, 172.16.0.0/12, or 192.168.0.0/16. Usable inside any network, never routed on the internet.

Link-local address — A 169.254.x.x address a device gives itself when DHCP fails. Seeing one means "no DHCP reached this device".

Loopback — 127.0.0.1 (or ::1): the device itself.

DNS — Domain Name System. Translates names (readylinks.io) into addresses. Record types include A (name → IPv4), AAAA (name → IPv6), CNAME (alias), MX (mail server), and PTR (reverse lookup).

TTL — Time To Live. In IP, a hop counter decremented by each router so a looping packet eventually dies. In DNS, how long a record may be cached.

#Protocols

Ethernet — The Layer 2 standard for wired local networks: frame format, MAC addressing, and the physical signalling over copper or fibre.

802.1Q — The standard for VLAN tagging. Adds four bytes to an Ethernet frame carrying the VLAN ID.

ARP — Address Resolution Protocol. Finds the MAC address that owns an IP address on the local subnet by broadcasting a question. IPv6 uses Neighbour Discovery instead.

IP — Internet Protocol. The Layer 3 protocol that carries packets between networks. IPv4 and IPv6 are the two versions.

ICMP — The control protocol alongside IP. ping and traceroute use it, as do "destination unreachable" errors.

TCP — Transmission Control Protocol. Connection-oriented, reliable, ordered delivery. Web, email, SSH, file transfer.

UDP — User Datagram Protocol. Connectionless, no delivery guarantee, low overhead. DNS, DHCP, NTP, voice, video.

Port (transport) — A 16-bit number in a TCP or UDP header identifying the program a packet is for. 443 is HTTPS, 53 is DNS, 67/68 are DHCP, 22 is SSH.

DHCP — Dynamic Host Configuration Protocol. Hands out IP addresses, masks, gateways, and DNS servers automatically via the four-step Discover/Offer/Request/Acknowledge exchange.

DHCP relay / IP helper — A function on a router that forwards DHCP broadcasts from one subnet to a DHCP server on another.

DHCP reservation — A DHCP server rule that always gives a particular MAC address the same IP.

DHCP scope / pool — The range of addresses a DHCP server may hand out on a subnet.

NAT — Network Address Translation. Lets many private addresses share one public address by rewriting source addresses and tracking the mappings.

Port forwarding — A manual NAT rule that sends inbound traffic on a public port to a specific internal device.

NTP — Network Time Protocol. Keeps device clocks correct. Required for certificate validation, so a device with the wrong time often can't reach cloud services.

STP / RSTP — (Rapid) Spanning Tree Protocol. Detects loops between switches and blocks redundant links until they are needed.

LACP — Link Aggregation Control Protocol. Negotiates bundling several links into one LAG.

LLDP — Link Layer Discovery Protocol. Lets neighbouring devices announce who they are, so a switch can show what is plugged into each port.

SNMP — Simple Network Management Protocol. An older standard for polling device statistics. ReadyView uses its own cloud connection instead.

TR-069 / CWMP — A remote-management protocol used by some service-provider equipment. ReadyLinks devices support it alongside ReadyView management.

G.hn — A standard for running Ethernet-like networking over existing coax, phone, or power wiring. Used by ReadyLinks hospitality and MDU products to deliver connectivity without re-cabling.

#Devices and roles

Endpoint / host / client — Any device that uses the network rather than forwards traffic for others: a PC, phone, camera, printer, server.

Switch — Forwards frames between its ports based on MAC addresses. Defines a local network.

Layer 2 switch — A switch that only forwards on MAC addresses.

Layer 3 switch — A switch that can also route IP packets between the VLANs it hosts.

Router — Forwards packets between networks based on IP addresses. The boundary of a broadcast domain.

Firewall — A router that also enforces rules about which traffic may pass. Usually the device at the edge of a site that connects to the ISP.

Access point (AP) — A device that bridges Wi-Fi clients onto the wired network. Usually connected to a trunk port and PoE-powered.

Media converter — A small device that converts between copper and fibre Ethernet.

Transceiver / SFP — A pluggable module that adapts a switch port to a particular cable type, usually fibre. SFP (1G), SFP+ (10G), SFP28 (25G).

PSE / PD — Power Sourcing Equipment (the switch supplying PoE) and Powered Device (the thing receiving it).

Core / distribution / access — The tiers of a hierarchical network. Access switches connect endpoints; the core connects access switches together and to the router.

#Switching and VLANs

Frame — The unit of data at Layer 2: an Ethernet header plus payload. Lives for one hop.

Packet — The unit of data at Layer 3: an IP header plus payload. Travels end to end inside a succession of frames.

MAC address table — The switch's map of which MAC address was last seen on which port. Also called the CAM table or forwarding table.

Broadcast — A frame addressed to every device on the segment (ff:ff:ff:ff:ff:ff).

Broadcast domain — The set of devices that receive each other's broadcasts. One per VLAN; bounded by routers.

Flooding — What a switch does with a frame whose destination MAC it hasn't learned: send it out every port except the one it arrived on.

VLAN — Virtual LAN. A logically separate network on shared switch hardware, identified by a number 1–4094.

Access port — A port in exactly one VLAN, with no tags. For endpoints.

Trunk port — A port carrying several VLANs, each frame tagged with its VLAN ID. For links between switches, routers, and APs.

Tagged / untagged — Whether a VLAN's frames on a given port carry an 802.1Q tag. A port has at most one untagged VLAN and any number of tagged ones.

Native VLAN / PVID — The one untagged VLAN on a trunk port. Must match at both ends of the link.

Management VLAN — The VLAN that carries the switches' own IP addresses and administrative traffic.

SVI — Switch Virtual Interface. A Layer 3 switch's IP interface in a VLAN; the default gateway for that VLAN.

Inter-VLAN routing — Forwarding packets between VLANs, done by a router or a Layer 3 switch.

ACL — Access Control List. Rules on a switch or router that permit or deny traffic by address, protocol, or port.

Broadcast storm — Broadcasts multiplying around a loop until the network collapses. Prevented by STP.

BPDU guard — Shuts an access port down if a switch is detected on it, preventing accidental loops.

Storm control — Rate-limits broadcast or multicast traffic on a port.

LAG / port channel — Several physical links bundled into one logical link for bandwidth and redundancy.

Daisy chain — Switches cabled in a line, each one's uplink passing through the previous. Cheap but fragile.

Voice VLAN — A tagged VLAN carried on a desk port alongside the untagged data VLAN, so a phone and the PC behind it share one socket. The phone learns the VLAN via LLDP-MED.

Port isolation / protected ports — Ports in the same VLAN that can reach the uplink but not each other. Used for hotel rooms, kiosks, and IoT.

Private VLAN — The fuller form of port isolation, with promiscuous (uplink), isolated, and community port roles.

Dynamic VLAN assignment — Placing a port in a VLAN based on who authenticated (802.1X/RADIUS or MAC) rather than a static per-port setting.

QinQ / 802.1ad — Stacked VLAN tags: a provider's outer S-tag wrapped around a customer's inner C-tag, giving each customer a private VLAN space.

VLAN hopping — Attacks that reach a VLAN a device isn't in, by negotiating a trunk (switch spoofing) or by double tagging through the native VLAN.

VLAN pruning — Restricting a trunk to carry only the VLANs the far switch needs.

Root guard — Prevents a downstream switch from becoming the spanning-tree root.

Loop detection — A switch feature that sends probe frames out each port and reports a loop if a probe returns, catching loops that STP can't see. On ReadyLinks switches a port in detect mode only alerts; a port in control mode is also shut down. See Layer 2 security.

#Multicast

Multicast — Delivery to a group of interested receivers using a single transmission. IPv4 groups live in 224.0.0.0/4; IPv6 groups in ff00::/8.

Multicast group — A destination address that receivers join. 239.x.x.x is the organisation-local range used for IPTV and in-house video.

IGMP — Internet Group Management Protocol. How IPv4 receivers join and leave groups and answer queries. IPv6 uses MLD.

IGMP snooping — A switch listening to IGMP so it forwards each group only to the ports that joined it, instead of flooding it.

Querier — The device sending periodic IGMP queries that keep snooping tables alive. If no multicast router is present, the switch must do it.

Multicast router port — A switch port on which queries have been seen; every group is forwarded there.

Fast leave / immediate leave — Removing a port from a group as soon as a Leave arrives. For ports with a single receiver only.

mDNS — Multicast DNS on 224.0.0.251. How AirPlay, Chromecast, and printers discover each other. Link-local, so it never crosses VLANs without an mDNS gateway.

PIM — Protocol Independent Multicast. The routing protocol for carrying multicast between VLANs or sites.

SSM — Source-specific multicast: receivers join a group from a named source. Uses IGMPv3 and 232.0.0.0/8.

#Layer 2 security

DHCP snooping — Drops DHCP server replies arriving on untrusted ports and records legitimate leases in a binding table.

Trusted / untrusted port — For DHCP snooping and ARP inspection: trusted ports (uplinks, server ports) are exempt from checks; untrusted ports (user devices) are inspected.

Binding table — The DHCP snooping record of MAC, IP, VLAN, port, and lease for every client. The reference that DAI and IP source guard check against.

Rogue DHCP server — An unauthorised device answering DHCP requests, typically a home router plugged in backwards. Blocked by DHCP snooping.

ARP spoofing / poisoning — Sending false ARP replies so victims send traffic to the attacker. The standard in-VLAN man-in-the-middle attack.

Dynamic ARP inspection (DAI) — Dropping ARP packets on untrusted ports that don't match the binding table.

IP source guard — Dropping any packet from an untrusted port whose source IP and MAC don't match the binding table.

Option 82 — DHCP relay information inserted by the switch identifying the switch and port a request came from.

Port security / max MAC learn — Limiting how many MAC addresses a port may learn, defeating MAC flooding and unauthorised switches.

MAC flooding — Sending frames from many fake source MACs to fill the switch's table and force it to flood traffic.

Storm control — A per-port ceiling on broadcast, multicast, and unknown-unicast traffic.

BPDU guard — Shutting an access port down when a spanning-tree BPDU arrives on it, meaning a switch was plugged in.

802.1X — Port-based authentication. A port passes nothing until the device authenticates against a RADIUS server, which also returns the VLAN to use.

RADIUS — The authentication server protocol used by 802.1X, MAB, and often administrator logins.

MAB — MAC authentication bypass. Authenticating a device by its MAC address when it can't do 802.1X.

Supplicant / authenticator — In 802.1X, the device asking to join and the switch controlling the port.

TACACS+ — A protocol for centralised administrator authentication and command authorisation on network devices.

Protective down / recover — Shutting a port that exceeds a DHCP or ARP rate limit, then restoring it automatically after a timer.

#Physical

Cat 5e / 6 / 6A — Grades of twisted-pair copper cable rated for 1G, 1G (10G short), and 10G respectively over 100 m.

100 m rule — The maximum copper Ethernet run from switch port to device, patch leads included.

Duplex — Full duplex: both ends transmit simultaneously. Half duplex: they take turns. A duplex mismatch between ends causes a slow, error-prone link.

Auto-negotiation — The handshake by which two Ethernet ports agree on speed and duplex. Leave it on.

Multimode / single-mode — Fibre types for short (hundreds of metres) and long (kilometres) runs. Optics must match the fibre.

PoE / PoE+ / PoE++ — 802.3af (15 W), 802.3at (30 W), and 802.3bt (60–100 W) Power over Ethernet.

PoE budget — The total power a switch can deliver across all ports. Usually less than every port at maximum.

Uplink — The port or link that connects a switch toward the core or the internet.

Patch panel — The termination point for in-wall cabling in a rack, connected to switch ports with short patch leads.

#ReadyLinks terms

ReadyView — The ReadyLinks cloud dashboard that configures, monitors, and updates every device. See getting started.

Claiming — Adding a device to a ReadyView organisation by its MAC address so it can pull its configuration from the cloud. See the quickstart.

Network (ReadyView) — A grouping of devices in ReadyView that share settings such as VLANs and templates. Usually one per site.

Template — A reusable configuration that can be pushed to many switches at once. See templates.

ReadyLinks OS (RLOS) — The firmware on GL-series switches. Its command line is what the GL-24xT-P600D# prompts in these guides refer to; see the CLI quick reference.

VectorBoost — ReadyLinks' throughput engine for long copper and G.hn links. See VectorBoost.

Subscriber — In multi-tenant deployments, an individual customer or unit, typically mapped to its own VLAN and bandwidth plan. See subscriber management.