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Question 261. What does IGMP snooping control?

1. Unicast routing
2. PoE delivery
3. DHCP leases
4. Layer 2 multicast forwarding

Correct Answer: 4. Layer 2 multicast forwarding

Explanation:

IGMP snooping allows a Layer 2 switch to observe IGMP membership messages and learn which switch ports have hosts interested in specific IPv4 multicast groups. Instead of flooding multicast traffic to every port in the VLAN, the switch can forward it only toward relevant receivers and multicast-router ports. This reduces unnecessary bandwidth consumption and prevents endpoints from receiving unwanted multicast streams. Current AOS-CX 10.16 documentation provides VLAN-level IGMP snooping configuration and commands for displaying multicast group membership.

Question 262. What does IGMP track?

1. DNS names
2. Multicast group membership
3. VLAN priorities
4. LACP members

Correct Answer: 2. Multicast group membership

Explanation:

Internet Group Management Protocol allows IPv4 hosts to indicate that they want to receive traffic sent to a multicast group. Routers use IGMP to maintain receiver information, while Layer 2 switches can inspect those messages through IGMP snooping. When clients join or leave multicast groups, the network can adjust where multicast traffic is forwarded. This helps services such as IPTV or multicast application delivery avoid unnecessary flooding. AOS-CX supports IGMP on routed interfaces and provides separate IGMP snooping functions for Layer 2 VLANs.

Question 263. What does IGMP snooping learn?

1. Receiver-facing ports
2. OSPF costs
3. NTP servers
4. PoE classes

Correct Answer: 1. Receiver-facing ports

Explanation:

By observing IGMP messages, a switch learns which interfaces lead toward hosts that have joined particular multicast groups. It can then build Layer 2 multicast forwarding state and send multicast frames only to those ports and relevant router-facing ports. The show ip igmp snooping vlan group command can display participating multicast members and the ports associated with them. This helps administrators verify whether multicast receivers have been learned correctly when troubleshooting missing or excessive multicast traffic.

Question 264. What can unknown multicast filtering reduce?

1. OSPF adjacencies
2. DHCP discovery
3. Unwanted multicast flooding
4. NTP accuracy

Correct Answer: 3. Unwanted multicast flooding

Explanation:

When a switch receives multicast traffic for a group it has not yet learned, the default behavior may involve flooding that traffic throughout the VLAN. AOS-CX supports an IGMP snooping option to filter unknown multicast traffic, helping avoid this initial flooding. This can reduce unnecessary traffic on endpoint-facing ports and improve multicast efficiency. The feature should be deployed with an understanding of the multicast application because overly aggressive filtering can affect receivers if forwarding information has not yet been learned correctly.

Question 265. What does a DHCP relay do?

1. Forwards DHCP messages between subnets
2. Replaces the DHCP server
3. Creates VLAN trunks
4. Encrypts DHCP traffic

Correct Answer: 1. Forwards DHCP messages between subnets

Explanation:

DHCP clients initially send broadcast requests, but routers normally do not forward Layer 2 broadcasts between IP subnets. A DHCP relay receives the client request and forwards it toward a DHCP server on another network. The server’s response is then relayed back to the client. This allows one centralized DHCP server to serve many routed VLANs. HPE documents DHCP relay as enabled globally by default on supported AOS-CX platforms, with helper addresses configured on relevant routed interfaces or SVIs.

Question 266. What command identifies a remote DHCP server?

1. ip route
2. show arp
3. ip igmp
4. ip helper-address

Correct Answer: 4. ip helper-address

Explanation:

The ip helper-address configuration tells the AOS-CX relay which remote DHCP server should receive relayed client requests. HPE’s DHCP relay example configures an SVI for the client VLAN and then adds the DHCP server address as an IP helper. Once relay is enabled, DHCP broadcasts received on that subnet can be forwarded as routed traffic toward the server. This is particularly useful when many access VLANs share centralized DHCP infrastructure.

Question 267. What can DHCP Option 82 add?

1. DNS encryption
2. Relay information
3. VLAN routing
4. OSPF authentication

Correct Answer: 2. Relay information

Explanation:

DHCP Option 82 is the Relay Agent Information Option. A relay device can insert information identifying the client’s network attachment point before forwarding the request to the DHCP server. This lets the server apply address-allocation or policy decisions based on where the request entered the network. AOS-CX supports several Option 82 behaviors, including replacing, keeping, or validating existing relay information. Option 82 therefore adds useful network context to DHCP exchanges without changing the fundamental client/server DHCP process.

Question 268. What does show dhcp-relay display?

1. VLAN clients only
2. DNS cache
3. Relay settings and statistics
4. WLAN channel use

Correct Answer: 3. Relay settings and statistics

Explanation:

The show dhcp-relay command displays the current DHCP relay configuration and operational counters. HPE output includes whether relay is enabled, Option 82 state, handling policies, and statistics for valid and dropped requests and responses. These counters are valuable when clients cannot obtain addresses from a remote DHCP server because they help determine whether the switch is receiving requests, forwarding them, and seeing responses. The command is therefore an important first-line DHCP relay troubleshooting tool.

Question 269. What does ARP resolve?

1. IPv4 address to MAC address
2. IPv6 address to hostname
3. VLAN to SSID
4. PoE class to watts

Correct Answer: 4. IPv4 address to MAC address

Explanation:

Address Resolution Protocol is used on IPv4 networks to discover the Layer 2 MAC address associated with a local IPv4 address. The resulting mapping is stored in the ARP table and helps the device build Ethernet frames for directly reachable IPv4 neighbors. AOS-CX show arp output includes the neighbor IPv4 address, MAC address, interface or VLAN, physical port, and state. IPv6 performs equivalent neighbor-resolution functions through Neighbor Discovery rather than ARP.

Question 270. What does show arp display?

1. IP-to-MAC mappings
2. SSID profiles
3. LACP settings
4. Firmware history

Correct Answer: 1. IP-to-MAC mappings

Explanation:

The show arp command displays entries in the AOS-CX ARP table. Typical output includes the IPv4 address, corresponding MAC address, VLAN or routed interface, physical port, and reachability state. This is helpful when troubleshooting IPv4 communication on a local subnet. If the expected neighbor is missing or remains incomplete, the administrator can investigate VLAN membership, Layer 2 connectivity, endpoint status, or ARP filtering. The command can also display entries within selected VRFs on supported platforms.

Question 271. What does an ARP reachable state mean?

1. Neighbor recently confirmed
2. Neighbor is deleted
3. Route is unreachable
4. Interface is disabled

Correct Answer: 3. Neighbor recently confirmed

Explanation:

A reachable ARP entry indicates that the neighbor has been successfully resolved and is considered reachable according to the device’s current neighbor-state information. AOS-CX show arp output can display states such as reachable, stale, incomplete, failed, or permanent depending on the situation and platform. The state helps administrators understand whether the switch has a usable neighbor mapping or whether further address resolution is needed. A stale entry can still exist but may need reconfirmation before continued use.

Question 272. What does a stale ARP entry mean?

1. It is manually configured
2. It exists but needs reachability confirmation
3. It is a multicast route
4. It is a DHCP lease

Correct Answer: 2. It exists but needs reachability confirmation

Explanation:

A stale ARP entry retains a previously learned IP-to-MAC mapping, but the switch has not recently confirmed that the neighbor is still reachable. The mapping can still be used initially, after which the neighbor-reachability process may refresh its state. AOS-CX reports stale entries separately from reachable, failed, incomplete, and permanent entries. Examining ARP state is useful when troubleshooting intermittent communication where the address mapping exists but neighbor connectivity is uncertain.

Question 273. What does show interface display?

1. Interface status and statistics
2. RADIUS passwords
3. SSID keys
4. DHCP pool contents only

Correct Answer: 1. Interface status and statistics

Explanation:

The AOS-CX show interface command displays active configuration and operational information for interfaces. Depending on the options used, it can show administrative and link state, speed, counters, errors, filtered packets, and other statistics. Administrators can request brief, physical, extended, human-readable, or monitoring views. This makes the command one of the most useful tools for diagnosing physical or data-link connectivity problems before moving to higher-layer troubleshooting.

Question 274. What can CRC/FCS errors indicate?

1. RADIUS failure
2. DHCP exhaustion
3. NTP drift
4. Physical-link problems

Correct Answer: 4. Physical-link problems

Explanation:

CRC or FCS errors indicate that Ethernet frames were received with invalid frame-check information. Common causes include damaged cables, faulty transceivers, poor fiber connections, electrical interference, or other physical-layer problems. AOS-CX interface statistics can show error counters including CRC/FCS values. When such counters increase continuously, administrators should investigate the cabling and physical interfaces before spending time on higher-layer routing or application troubleshooting. Clean Layer 1 and Layer 2 connectivity is required before upper-layer protocols can operate reliably.

Question 275. What does show interface utilization show?

1. Port bandwidth usage
2. User roles
3. Certificate status
4. DHCP options

Correct Answer: 2. Port bandwidth usage

Explanation:

The show interface utilization command displays physical port throughput and utilization statistics. HPE output includes receive and transmit rates, packet rates, and utilization percentages measured over an interval. This is useful when troubleshooting congestion or investigating whether an interface is approaching its capacity. High utilization can explain application slowness even when the physical link remains up and free of errors. The command focuses on port traffic rates rather than AAA roles, certificates, or DHCP configuration.

Question 276. What does interface monitor mode provide?

1. Firmware rollback
2. Client authentication
3. Continuously refreshed interface statistics
4. VLAN creation

Correct Answer: 3. Continuously refreshed interface statistics

Explanation:

AOS-CX monitor mode displays interface statistics in real time and refreshes the values automatically until the administrator exits the view. This is useful when observing a transient traffic problem, verifying whether utilization changes during a test, or watching error counters while replacing cabling or moving traffic. HPE documentation notes that the refresh interval depends on platform and display conditions. Monitor mode provides live operational visibility and does not change the configuration of the monitored interfaces.

Question 277. What does a MAC move indicate?

1. One MAC was learned on different ports
2. The switch rebooted
3. The VLAN was deleted
4. NTP changed servers

Correct Answer: 2. One MAC was learned on different ports

Explanation:

A MAC move occurs when the same source MAC address is learned on a different switch port from where it was previously located. This can be legitimate, such as when a client physically moves, but repeated MAC moves can indicate a Layer 2 loop, misconfigured link aggregation, or another topology problem. AOS-CX provides a command that displays MAC addresses that have moved, including current port, previous port, move count, and last move time. These details are useful when investigating MAC flapping.

Question 278. What does show mac-address-table interface show?

1. DHCP leases
2. ARP entries
3. WLAN clients
4. MAC entries on one interface

Correct Answer: 4. MAC entries on one interface

Explanation:

The show mac-address-table interface command filters the Layer 2 forwarding table to entries associated with a selected interface. The output includes MAC address, VLAN, entry type, and interface information. This is helpful when identifying which endpoints the switch has learned behind a specific port. It can also help investigate unexpected devices or confirm that an endpoint’s frames are reaching the expected interface. HPE documents similar commands for filtering the MAC table by port, VLAN, or specific address.

Question 279. What does show mac-address-table vlan show?

1. MAC entries in a VLAN
2. OSPF neighbors
3. PoE clients
4. NTP peers

Correct Answer: 3. MAC entries in a VLAN

Explanation:

The show mac-address-table vlan command displays MAC addresses that have been learned or configured within a specific VLAN. HPE output includes the MAC address, entry type, and associated port. This is useful when troubleshooting Layer 2 reachability inside one broadcast domain or identifying which ports contain hosts belonging to a particular VLAN. It provides a more focused view than displaying the entire MAC address table on a large switch.

Question 280. Which tools BEST troubleshoot a LAN issue?

1. Interface counters, ARP, MAC table, and DHCP relay checks
2. Only firmware upgrade
3. Only WLAN spectrum analysis
4. Only NTP

Correct Answer: 1. Interface counters, ARP, MAC table, and DHCP relay checks

Explanation:

A structured LAN troubleshooting process starts with evidence from several layers. Interface counters confirm link state, utilization, drops, and physical errors. The MAC address table verifies Layer 2 learning and endpoint location. ARP confirms IPv4 neighbor resolution, while DHCP relay statistics help identify address-assignment problems when the server is remote. Combining these tools allows an administrator to narrow the fault domain before making configuration changes. This is more effective than immediately upgrading firmware or focusing on an unrelated subsystem such as WLAN spectrum analysis.