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Question 161. Which Cisco IOS command displays the MAC address table of a switch?

1. show vlan brief
2. show arp
3. show mac address-table
4. show interfaces

Correct Answer: 3. show mac address-table

Explanation :-

The show mac address-table command displays MAC addresses that a Cisco switch has learned and the interfaces or VLANs associated with those addresses. Switches use this table to determine where Ethernet frames should be forwarded. The show vlan brief command displays VLAN information, while show arp displays IPv4-to-MAC mappings maintained by ARP. The show interfaces command provides detailed interface statistics and operational information. Exam questions commonly use the MAC address table to test understanding of Layer 2 forwarding and how switches learn source MAC addresses from incoming frames.

Question 162. Which IPv4 subnet mask corresponds to a /26 prefix length?

1. 255.255.255.192
2. 255.255.255.224
3. 255.255.255.128
4. 255.255.255.240

Correct Answer: 1. 255.255.255.192

Explanation :-

A /26 IPv4 prefix contains 26 network bits and 6 host bits. The corresponding subnet mask is 255.255.255.192. Each /26 subnet contains 64 total addresses, of which 62 are normally usable for hosts in traditional IPv4 subnetting because one address identifies the network and one is the broadcast address. A /27 uses 255.255.255.224, /25 uses 255.255.255.128, and /28 uses 255.255.255.240. Understanding prefix lengths and their corresponding subnet masks is essential for IPv4 addressing and subnet calculations.

Question 163. Which protocol is used to automatically assign IPv4 configuration information to network hosts?

1. DNS
2. SNMP
3. NTP
4. DHCP

Correct Answer: 4. DHCP

Explanation :-

Dynamic Host Configuration Protocol (DHCP) automatically provides hosts with network configuration information such as an IPv4 address, subnet mask, default gateway, and DNS server information. This eliminates the need to manually configure every host and helps reduce configuration errors. DHCP uses a client-server process to allocate addresses from a configured pool. DNS performs name resolution, SNMP provides network management and monitoring functions, and NTP synchronizes clocks. DHCP is therefore the protocol used when hosts need to receive their IPv4 network configuration automatically.

Question 164. What is the purpose of the Cisco Discovery Protocol (CDP)?

1. Encrypt management traffic
2. Discover information about directly connected Cisco devices
3. Assign IP addresses to hosts
4. Prevent Layer 2 loops

Correct Answer: 2. Discover information about directly connected Cisco devices

Explanation :-

Cisco Discovery Protocol (CDP) is a Cisco proprietary Layer 2 protocol that allows Cisco devices to discover information about directly connected Cisco neighbors. CDP can provide details such as the neighboring device’s hostname, platform, capabilities, and connected interface. It is useful during network discovery and troubleshooting. CDP does not assign IP addresses, encrypt management traffic, or prevent switching loops. Administrators can use commands such as show cdp neighbors to view discovered neighboring devices. CDP operates independently of Layer 3 addressing, which allows discovery even when IP connectivity is not configured.

Question 165. Which command places a switch interface into VLAN 20 as an access port?

1. switchport access vlan 20
2. switchport trunk allowed vlan 20
3. vlan database 20
4. encapsulation dot1q 20

Correct Answer: 1. switchport access vlan 20

Explanation :-

The switchport access vlan 20 command assigns an interface configured as an access port to VLAN 20. Access ports normally carry traffic for a single VLAN and are commonly connected to end-user devices. Before applying this command, the interface is typically configured with switchport mode access. The switchport trunk allowed vlan 20 command controls which VLANs are permitted on a trunk, while encapsulation dot1q 20 is associated with VLAN tagging on router subinterfaces. Therefore, switchport access vlan 20 is the appropriate command for assigning an access interface to VLAN 20.

Question 166. Which protocol is commonly used to provide authentication, authorization, and accounting for network access?

1. TFTP
2. ARP
3. RADIUS
4. ICMP

Correct Answer: 3. RADIUS

Explanation :-

Remote Authentication Dial-In User Service (RADIUS) provides centralized authentication, authorization, and accounting services for network access. It is commonly used with wireless networks, VPNs, and network access devices. A network device can forward user authentication requests to a RADIUS server instead of maintaining all credentials locally. TFTP is a file-transfer protocol, ARP resolves IPv4 addresses to MAC addresses, and ICMP provides network control and diagnostic messaging. Centralized AAA services such as RADIUS can simplify user management and provide consistent access-control policies across multiple network devices.

Question 167. What is the main function of a router in an IP network?

1. Learn MAC addresses only
2. Create Ethernet frames without forwarding packets
3. Assign VLAN membership to switch ports
4. Forward packets between different IP networks

Correct Answer: 4. Forward packets between different IP networks

Explanation :-

A router forwards packets between different IP networks using information in its routing table. When a packet arrives, the router examines the destination IP address and selects an appropriate next hop or outgoing interface. Routers separate broadcast domains and provide connectivity between different subnets. Switches primarily forward Ethernet frames using MAC addresses, while VLAN configuration determines Layer 2 segmentation on switches. Although routers can provide services such as DHCP, NAT, and security features, their fundamental role in an IP network is to make Layer 3 forwarding decisions between networks.

Question 168. Which IPv6 prefix identifies link-local unicast addresses?

1. 2000::/3
2. FE80::/10
3. FC00::/7
4. FF00::/8

Correct Answer: 2. FE80::/10

Explanation :-

The IPv6 prefix FE80::/10 identifies link-local unicast addresses. Link-local addresses are automatically associated with IPv6-enabled interfaces and are used for communication on the local link. They are not intended to be routed across different networks. The 2000::/3 range is used for global unicast addressing, FC00::/7 identifies unique local addresses, and FF00::/8 identifies multicast addresses. Link-local addressing is particularly important for IPv6 neighbor discovery and routing protocols because devices can communicate with local neighbors without requiring globally routable IPv6 addresses.

Question 169. Which command displays the IPv4 routing table on a Cisco router?

1. show ip route
2. show interfaces
3. show ip protocols
4. show arp

Correct Answer: 1. show ip route

Explanation :-

The show ip route command displays the IPv4 routing table on a Cisco router. The routing table contains routes learned through connected interfaces, static configuration, and dynamic routing protocols. Each route can include information such as its destination network, next-hop address, administrative distance, metric, and outgoing interface. show ip protocols provides information about configured routing protocols, while show arp displays IPv4-to-MAC address mappings. show interfaces provides interface details. The routing table is central to determining how a router forwards packets toward their destination networks.

Question 170. Which feature allows multiple VLANs to traverse a single physical switch-to-switch link?

1. Port security
2. EtherChannel
3. VLAN access mode
4. 802.1Q trunking

Correct Answer: 4. 802.1Q trunking

Explanation :-

IEEE 802.1Q trunking allows multiple VLANs to traverse a single physical Ethernet link by adding VLAN identification information to Ethernet frames. Trunk links are commonly used between switches and between switches and routers or multilayer switches. An access port normally carries traffic for one VLAN, while a trunk can transport traffic for multiple VLANs. EtherChannel combines multiple physical links into a logical bundle but does not itself provide VLAN tagging. Port security is a Layer 2 security feature used to control which MAC addresses can use an interface.

Question 171. Which command displays the software version and hardware information of a Cisco device?

1. show running-config
2. show version
3. show startup-config
4. show flash

Correct Answer: 2. show version

Explanation :-

The show version command provides important information about a Cisco device, including the IOS software version, device model, hardware information, uptime, memory information, and other system details. It is frequently used during troubleshooting and inventory checks. show running-config displays the active configuration, while show startup-config displays the saved configuration. show flash provides information about files stored in flash memory. When an administrator needs to determine which IOS version or hardware platform is running on a device, show version is one of the primary commands to use.

Question 172. Which routing protocol uses hop count as its primary metric?

1. OSPF
2. EIGRP
3. RIP
4. BGP

Correct Answer: 3. RIP

Explanation :-

Routing Information Protocol (RIP) uses hop count as its primary routing metric. Each router or Layer 3 hop between a source and destination network increases the hop count by one. RIP has a maximum usable hop count of 15, while a metric of 16 represents an unreachable destination. OSPF uses a cost metric, EIGRP uses a composite metric based on factors such as bandwidth and delay, and BGP uses path attributes for route selection. Although RIP is less commonly used in modern enterprise networks, its hop-count behavior remains an important networking concept.

Question 173. What is the purpose of Spanning Tree Protocol in a switched network?

1. Assign IP addresses
2. Encrypt VLAN traffic
3. Prevent Layer 2 switching loops
4. Translate private IP addresses

Correct Answer: 3. Prevent Layer 2 switching loops

Explanation :-

Spanning Tree Protocol (STP) prevents Layer 2 loops in networks containing redundant switch connections. Redundant links provide resilience, but without loop prevention they can cause broadcast storms, duplicate frames, and unstable MAC address tables. STP logically blocks selected redundant paths while keeping them available as potential alternatives if the active path fails. STP operates at Layer 2 and does not perform IP address assignment, encryption, or NAT. Understanding STP is important when designing networks with redundant switches and links because physical redundancy must be balanced with mechanisms that prevent forwarding loops.

Question 174. Which address represents the IPv4 loopback address commonly used to test the local TCP/IP stack?

1. 192.168.1.1
2. 127.0.0.1
3. 169.254.1.1
4. 255.255.255.255

Correct Answer: 2. 127.0.0.1

Explanation :-

The IPv4 address 127.0.0.1 is the commonly used loopback address for testing the local host’s TCP/IP stack. Traffic sent to this address remains within the local device and does not require transmission through a physical network interface. The entire 127.0.0.0/8 range is reserved for loopback purposes. 169.254.0.0/16 is used for IPv4 link-local addressing, 255.255.255.255 is the limited broadcast address, and 192.168.1.1 is within a private address range. Loopback testing is useful for determining whether local IP functionality is operating correctly.

Question 175. Which Cisco feature can restrict the MAC addresses allowed on a switch port?

1. DHCP snooping
2. Port security
3. CDP
4. NTP

Correct Answer: 2. Port security

Explanation :-

Port security is a Cisco switch feature that can restrict which MAC addresses are permitted to use a switch interface. Administrators can configure secure MAC addresses manually or allow the switch to learn addresses dynamically depending on the configuration. Port security can help limit unauthorized devices from connecting to protected access ports. DHCP snooping provides protection against unauthorized DHCP servers, CDP discovers neighboring Cisco devices, and NTP synchronizes device clocks. Port security is therefore the feature most directly associated with controlling which source MAC addresses are permitted on a switch port.

Question 176. Which command displays the VLANs configured on a Cisco switch?

1. show vlan brief
2. show ip route
3. show cdp neighbors
4. show controllers

Correct Answer: 1. show vlan brief

Explanation :-

The show vlan brief command provides a concise listing of VLANs configured on a Cisco switch, including VLAN IDs, VLAN names, status, and associated access ports. It is commonly used to verify VLAN creation and port assignments. show ip route displays the IP routing table, show cdp neighbors displays information about directly connected Cisco devices, and show controllers provides hardware-related information. When troubleshooting VLAN membership or verifying that an access port has been assigned to the intended VLAN, show vlan brief is a useful command.

Question 177. Which protocol is used by IPv6 to discover neighboring devices and resolve link-layer addresses?

1. ARP
2. DHCPv4
3. NDP
4. FTP

Correct Answer: 3. NDP

Explanation :-

IPv6 uses Neighbor Discovery Protocol (NDP) to perform functions that include discovering neighboring devices and resolving IPv6 addresses to link-layer addresses. NDP operates through ICMPv6 messages and replaces the role that ARP performs in IPv4. NDP also supports functions such as router discovery and neighbor reachability detection. ARP is used with IPv4 rather than IPv6. DHCPv4 provides IPv4 configuration, and FTP is a file-transfer protocol. Understanding NDP is important for IPv6 troubleshooting because neighbor discovery is fundamental to local IPv6 communication and address resolution.

Question 178. Which command tests basic IP connectivity to a remote destination using ICMP Echo messages?

1. traceroute
2. ping
3. telnet
4. nslookup

Correct Answer: 2. ping

Explanation :-

The ping command tests basic IP connectivity by sending ICMP Echo Request messages to a destination and waiting for Echo Reply messages. It can help determine whether a destination is reachable and can provide information about round-trip time and packet loss. traceroute is used to identify the Layer 3 path toward a destination, while telnet can test TCP connectivity to a particular service port. nslookup is primarily used to query DNS information. Therefore, ping is the standard Cisco IOS command for a basic ICMP-based connectivity test.

Question 179. Which NAT function allows multiple private IPv4 hosts to share one public IPv4 address by using different TCP or UDP port numbers?

1. Static NAT
2. Dynamic routing
3. PAT
4. DHCP relay

Correct Answer: 3. PAT

Explanation :-

Port Address Translation (PAT), also called NAT overload, allows multiple private IPv4 hosts to share a single public IPv4 address by distinguishing individual connections through TCP or UDP port numbers. PAT is widely used in networks where many internal hosts need Internet access but there are limited public IPv4 addresses available. Static NAT typically provides a one-to-one mapping between private and public addresses, while dynamic NAT uses a pool of public addresses. DHCP relay forwards DHCP messages between clients and servers across Layer 3 boundaries and does not perform address translation.

Question 180. Which type of address is used to send an IPv4 packet to every host on the local subnet?

1. Unicast
2. Anycast
3. Multicast
4. Broadcast

Correct Answer: 4. Broadcast

Explanation :-

An IPv4 broadcast address is used to send traffic to all applicable hosts within a broadcast domain. The limited broadcast address 255.255.255.255 reaches hosts on the local network segment, while a directed broadcast can identify all hosts within a particular subnet. Unicast traffic is intended for a single destination, multicast traffic is sent to members of a multicast group, and anycast is primarily an IPv6 addressing concept used to reach one member of an address group based on routing. Broadcast behavior is therefore associated with one-to-all delivery within an IPv4 broadcast domain.