Cisco CCNA 200-301 练习

The OSI model divides network communication into seven layers so vendors can design interoperable equipment. It is a conceptual framework, not an encryption or addressing system.

IP operates at Layer 3, the network layer, where logical addressing and routing happen. TCP and UDP operate at Layer 4, and Ethernet operates at Layer 2.

TCP and UDP are transport-layer protocols. They provide end-to-end communication between applications. IP is at the network layer below them.

A MAC address is a unique hardware address assigned to a network interface. IP addresses are logical and can change, while MAC addresses identify the local interface.

An IP address provides logical addressing that routers use to forward traffic across networks. MAC addresses identify local interfaces, and encryption is separate.

A subnet mask defines which bits of an IP address identify the network and which identify the host. It is essential for routing and subnetting.

IPv4 addresses are 32 bits long and are usually written as four octets. IPv6 uses 128 bits, and MAC addresses use 48 bits.

IPv6 addresses are 128 bits long, allowing many more addresses than IPv4. They are written in hexadecimal groups separated by colons.

Ethernet is the most common LAN technology. It uses frames, MAC addresses, and CSMA/CD or full-duplex operation on wired networks.

This statement is true. A switch forwards Ethernet frames based on MAC addresses, which is Layer 2 behavior. Routers operate at Layer 3.

A VLAN separates devices into logical broadcast domains even when they share the same switch. It improves security and reduces unnecessary broadcast traffic.

A trunk port carries traffic for multiple VLANs between switches using VLAN tagging. Access ports carry traffic for a single VLAN.

A broadcast domain includes devices that receive each others broadcast frames. VLANs create separate broadcast domains.

A collision domain is a segment where frames can collide during transmission. Switches break up collision domains by providing dedicated bandwidth to each port.

A duplex mismatch occurs when one device operates full duplex and the other half duplex. It causes collisions, errors, and poor performance on the link.

A rollover cable connects a computer to the console port of a Cisco device for initial configuration. Straight-through and crossover cables are used for network links.

Without auto-MDIX, a crossover cable is used to connect similar devices such as two switches. Straight-through cables connect different device types.

A router forwards packets between networks using IP addresses. Switches forward frames within a LAN, and hubs and repeaters work at the physical layer.

This statement is true. A MAC address is 48 bits and is normally written as six hexadecimal pairs. It is a hardware address on the network interface.

IPv4 uses 32-bit addresses divided into four octets. This limits the total IPv4 address space and is why IPv6 uses 128-bit addresses.

A default route, often 0.0.0.0/0, is used when no more specific route matches the destination. It is common on routers that send traffic toward the internet.

Static routing requires an administrator to manually configure routes. Dynamic routing protocols learn routes automatically through updates.

Dynamic routing uses protocols such as OSPF to exchange routing information and learn routes automatically. This reduces manual configuration.

OSPF is a link-state routing protocol. It builds a complete map of the network and calculates the best paths using cost.

A routing table stores known destination networks, next hops, and interfaces. Routers use it to forward packets toward their destination.

Inter-VLAN routing allows devices in different VLANs to communicate. It can be done with a router on a stick or a Layer 3 switch.

A next hop is the IP address of the next router toward a destination. Routing entries include a next hop and outgoing interface.

Administrative distance ranks the trustworthiness of routing information. Lower values are preferred, such as static routes over OSPF routes.

DHCP automatically provides IP addresses, subnet masks, gateways, and DNS servers to clients. DNS resolves names, and routing forwards packets.

A DHCP reservation always assigns the same IP address to a specific MAC address. It is useful for servers and printers that need a stable address.

DNS translates hostnames such as example.com into IP addresses. DHCP assigns addresses, and QoS prioritizes traffic.

NAT translates private addresses to public addresses so devices can reach the internet. PAT is a form of NAT that also uses ports.

PAT maps many private addresses to one public IP using different source ports. It is commonly called NAT overload.

NTP keeps device clocks synchronized with a time source. Accurate time is important for logging, authentication, and troubleshooting.

QoS classifies and prioritizes traffic so important applications receive better treatment. It does not encrypt or replace routing.

Syslog sends and stores log messages from devices. Administrators use logs to monitor events and troubleshoot problems.

SNMP lets management systems monitor device status and collect metrics. It is a network management protocol, not routing or addressing.

This statement is true. OSPF builds a link-state database and computes shortest paths using cost. It is a common interior gateway protocol.

A default route is used as a fallback when the routing table has no more specific match. It is often configured as 0.0.0.0/0.

A static route is manually entered by an administrator. It includes the destination network, prefix, and next hop or outgoing interface.

An access control list contains permit or deny rules that filter packets. ACLs are used for security and traffic control on routers and switches.

A standard ACL filters traffic based on source IP address. Extended ACLs can filter by source, destination, protocol, and ports.

Extended ACLs provide more granular filtering using source and destination addresses, protocols, and port numbers.

Port security restricts which MAC addresses can send traffic on a switch port. It helps prevent unauthorized devices from connecting.

DHCP snooping filters DHCP messages and blocks untrusted rogue DHCP servers. Trusted ports are usually uplinks to legitimate servers.

A VPN encrypts traffic between endpoints over a public network. It provides confidentiality and integrity for remote connections.

VLAN hopping is a security attack that tries to send traffic into a different VLAN. Disabling unused trunk ports and using native VLAN hardening reduce the risk.

AAA is a security framework that verifies identity, grants permissions, and records activity. It is commonly used with RADIUS or TACACS+.

SDN separates the control plane from the data plane and centralizes control in software. It enables programmatic network management.

An SDN controller makes control plane decisions and programs switches through southbound APIs. Switches focus on forwarding data.

A REST API uses HTTP methods such as GET, POST, PUT, and DELETE to interact with systems. It is common in network automation.

JSON is a text-based data format for exchanging structured information. It is widely used in REST APIs and network automation.

Ansible is an automation tool that uses YAML playbooks to configure devices. It is popular for network device automation.

Northbound APIs connect the SDN controller to applications and business logic. Southbound APIs connect the controller to network devices.

Ping sends ICMP echo requests and measures responses. It tests basic IP connectivity between hosts.

Traceroute displays each hop along the path to a destination. It helps identify where packets are delayed or dropped.

show interfaces displays interface status, errors, and counters. show ip route shows routing, and show vlan shows VLANs.

show ip route displays known routes in the routing table. Other show commands display interfaces, MAC tables, or configuration.

A duplex mismatch causes late collisions, runts, and poor throughput. Checking duplex settings on both ends is the correct troubleshooting step.

A loopback interface is a virtual interface that is always up. It is used for testing, management, and stable router IDs in protocols like OSPF.