Protocols govern how devices communicate on a network. They are the agreed rules that specify how data is formatted, transmitted, detected, and acknowledged, and how sessions start and end. With these rules, devices can exchange messages reliably, understand each other’s syntax, and handle issues like errors and ordering. For example, TCP handles reliable transport, IP handles addressing and routing, HTTP defines how web requests and responses are structured, and DNS maps domain names to IP addresses. The other descriptions don’t fit networking communication rules: electric signals for turning devices on refer to power, not data exchange; top-level domain names relate to naming rather than how communication happens; antivirus signatures pertain to security software patterns, not the protocols that govern data transfer.

Anycast addresses identify multiple destinations, with packets delivered to the nearest member. In IPv6, several devices can share the same anycast address, and when a packet is sent to that address, routers route it to the closest instance based on current routing metrics like cost or latency. This lets services be accessed from the nearest location without the sender needing to know which specific device will answer, which is ideal for things like regional DNS servers or nearby edge routers. This behavior is different from a multicast address, which delivers to all members of a group, and from a unicast address, which targets a single device. A global address is simply a routable unicast address type and does not imply multiple destinations.

The main idea is that ARP tables and MAC address tables serve different functions in how devices locate each other on a local network. An ARP table is about resolving addresses: it stores mappings from IP addresses to MAC addresses so a host can encapsulate an IPv4 packet in an Ethernet frame with the correct destination hardware address. These mappings are learned dynamically through ARP requests and replies and are used when a host needs to send data to another IPv4 device on the same subnet. A MAC address table, on the other hand, lives in switches and tells the switch which physical port to forward a frame to based on the destination MAC address. The switch learns these mappings by observing the source MAC of frames it sees, building a MAC-to-port map (often within the context of a VLAN). This speeds up forwarding and avoids broadcasting to all ports. So the statement that ARP tables map IP addresses to MAC addresses is the best description because it captures the purpose of ARP: translating an IP address to the hardware address needed to actually deliver the frame. The other ideas mix up the roles: a MAC address table maps MAC addresses to switch ports (not IPs), ARP tables are not limited to IPv6, and MAC tables aren’t defined by VLAN IDs themselves.

An inventory is a catalog of devices you have in the network, focusing on listing assets and how many of each exist. When you review it, the most reliable takeaway is the total count of routers deployed, because the primary purpose of an inventory is to track quantity for management, planning, and audits. While some records may include additional details like location or firmware, those fields aren’t guaranteed to be present or up to date in every inventory, and sensitive information such as admin passwords is not stored there for security reasons. So the number of routers you have is the detail you can definitively determine from reviewing the inventory.