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A network technician is configuring a dedicated point-to-point wireless link between two enterprise buildings using the IPv4 subnet $192.168.10.16/28$ . What is the maximum number of usable host IPv4 addresses available for assignment to physical network interfaces in this subnet?

Show answer & explanation

Answer: 14

Answer

The maximum number of usable host IPv4 addresses in a

/28

subnet is 14.

For a

/28

subnet, there are 4 host bits (

32 - 28 = 4

). Calculating total IP addresses yields

2^4 = 16

. Subtracting 2 reserved addresses (one network address and one broadcast address) leaves 14 usable host IPv4 addresses.

Step-by-Step Solution

Calculate the number of host bits available from the CIDR prefix

4 host bits (

32 - 28 = 4

)

An IPv4 address contains 32 bits in total, so subtracting the prefix length gives the remaining bits allocated for host addresses.

Calculate the total number of IP addresses in the subnet

16 total IP addresses (

2^4 = 16

)

The number of total IP combinations for

n

host bits is

2^n

Calculate the usable host address count by excluding reserved addresses

14 usable host IPv4 addresses (

16 - 2 = 14

)

The first IP address in the range is reserved as the network address, and the final IP address is reserved as the directed broadcast address.

Key Concept

Calculating Usable Host Addresses in an IPv4 Subnet

Question 702Question →

An enterprise router participating in an OSPF area receives a Link-State Update (LSU) packet containing a revised Link-State Advertisement (LSA) from an adjacent neighbor. Arrange the operational steps in the exact chronological sequence the router executes to process the LSA and update its routing table.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct operational sequence is: 1) Verify the LSU packet header checksum and validate area matching; 2) Compare the sequence number of the received LSA against the existing entry in the LSDB; 3) Store the newer LSA in the local LSDB and flood an LSU copy out all other active OSPF interfaces; 4) Execute Dijkstra's Shortest Path First (SPF) algorithm; 5) Install the newly calculated optimal routes into the router's RIB.

When a router receives an OSPF Link-State Update (LSU), it first validates packet headers and checksums to ensure packet integrity. Next, it compares the LSA sequence number to verify the update is newer than its existing LSDB entry. Once confirmed, it updates its local LSDB and floods the LSA out other OSPF interfaces to maintain area synchronization. After the LSDB is synchronized, the router executes Dijkstra's SPF algorithm on the updated topology map to calculate shortest path trees. Finally, the resulting shortest paths are installed into the Routing Information Base (RIB).

Step-by-Step Solution

Perform initial packet validation.

The router verifies that the LSU packet is uncorrupted and originated from a valid neighbor within the same area.

Invalid or corrupted control plane packets must be dropped prior to evaluating database changes.

Evaluate LSA freshness using sequence numbers.

The router confirms the received LSA has a higher sequence number than the matching entry in its LSDB.

Sequence numbers prevent stale topological updates from overwriting current network state.

Update local LSDB and flood the LSA.

The LSDB is updated with the new link state, and the update is forwarded to adjacent OSPF routers.

Immediate flooding maintains fast, network-wide link-state convergence.

Run Dijkstra's SPF algorithm.

The router computes a new shortest path tree rooted at itself.

Link-state updates require recalculation of the topological tree to determine optimal paths.

Update the Routing Information Base (RIB).

Best paths calculated by SPF are committed to the routing table.

The routing table uses the best-path output generated by the SPF execution for forward-plane lookup.

Key Concept

OSPF Link-State Update Processing and SPF Recalculation Sequence

Question 703Question →

A network engineer is auditing switchport trunk configurations and frame tagging operations across enterprise switches. Match each IEEE 802.1Q trunking configuration scenario or operational event on the left with its corresponding frame behavior or interface outcome on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Each 802.1Q trunking scenario correctly pairs with its respective protocol error behavior, frame tagging rule, or allowed list pruning action as outlined in the solution steps.

Matching each event to its technical description demonstrates core 802.1Q trunking principles: Native VLAN mismatches lead to protocol inconsistencies and improper VLAN leakage; untagged ingress frames map directly to the configured native VLAN without header addition; removing a VLAN from the trunk allowed list prunes traffic for that VLAN in both directions; and non-native egress frames are encapsulated with 4-byte 802.1Q headers containing TPID 0x8100 and the corresponding VLAN ID.

Step-by-Step Solution

Analyze Native VLAN Mismatch Behavior

Configuring conflicting native VLAN IDs (VLAN 99 vs VLAN 1) causes untagged traffic to cross broadcast domains, triggering CDP and PVST+ mismatch alerts and potential STP port inconsistency states.

Both endpoints of an 802.1Q trunk must share an identical native VLAN ID to prevent cross-VLAN frame leakage.

Determine Ingress Untagged Frame Association

Untagged frames arriving on an 802.1Q trunk configured with native VLAN 20 are internally classified under VLAN 20.

IEEE 802.1Q specifies that unencapsulated ingress frames are assigned to the port's configured native VLAN.

Evaluate CLI Allowed VLAN List Removal Command

Running 'switchport trunk allowed vlan remove 50' prunes VLAN 50 from the active trunk pass-through list.

Allowed VLAN lists restrict which VLAN broadcast domain traffic is permitted to traverse a trunk interface.

Examine Egress Tagging for Non-Native VLANs

Frames belonging to VLAN 10 sent over a trunk with native VLAN 20 must be tagged with a 4-byte 802.1Q header containing TPID 0x8100 and VLAN ID 10.

All traffic not belonging to the native VLAN requires explicit 802.1Q tagging to maintain VLAN identity across network switches.

Key Concept

802.1Q Trunk Tagging, Native VLAN Processing, and Allowed List Pruning

Question 704Question →

A network administrator is designing a wireless WAN connection to aggregate traffic from six distant regional utility substations back to a primary operations center. The design requires all substations to transmit telemetry directly to the operations center, but substations do not require direct interconnectivity between each other. Which network topology provides the most cost-effective architecture while meeting these connectivity requirements?

Hub-and-spoke (Point-to-Multipoint)

Full mesh

Physical bus

Storage Area Network (SAN)

Show answer & explanation

Answer: Hub-and-spoke (Point-to-Multipoint)

Answer

Hub-and-spoke (Point-to-Multipoint)

The hub-and-spoke topology (point-to-multipoint) routes all traffic through a central hub node. Because remote substations only need to transmit data back to headquarters and not to one another, hub-and-spoke delivers the exact connectivity required with minimal link overhead and centralized control.

Step-by-Step Solution

Analyze the traffic and connectivity requirements from the scenario.

The six remote substations must send data to the central operations center, but do not exchange traffic directly with each other.

Determining node communication paths identifies whether direct inter-site links are necessary.

Evaluate candidate network topologies based on cost efficiency and functional fit.

Connecting each remote site exclusively to the central hub satisfies all communication needs while eliminating extra circuit costs.

Hub-and-spoke maximizes cost efficiency by provisioning only

N

links for

N

remote sites, avoiding the

N(N-1)/2

requirement of mesh options.

Key Concept

Hub-and-Spoke (Point-to-Multipoint) Topology

Estimated Time:1m 0s

Question 705Question →

An enterprise network topology consists of four switches (Switch-1, Switch-2, Switch-3, and Switch-4) running 802.1D Spanning Tree Protocol (STP) using default revised 802.1D-1998 / 802.1w path cost values (10 Gbps = 2, 1 Gbps = 4, 100 Mbps = 19). The switches are configured with the following parameters:

* Switch-1: Priority 4096, MAC address 0011.2233.4455
* Switch-2: Priority 8192, MAC address 0011.2233.4422
* Switch-3: Priority 32768, MAC address 0011.2233.4411
* Switch-4: Priority 32768, MAC address 0011.2233.4433

The physical interconnections and link speeds between the switches are:
* Switch-1 to Switch-2: 10 Gbps
* Switch-1 to Switch-3: 1 Gbps
* Switch-2 to Switch-4: 10 Gbps
* Switch-3 to Switch-4: 1 Gbps
* Switch-2 to Switch-3: 100 Mbps

Which THREE of the following statements accurately describe the converged STP topology, root path costs, and port roles? (Select THREE)

Select all that apply

Switch-4 selects its connection to Switch-2 as its Root Port because it yields a lower Root Path Cost of 4 compared to a cost of 8 via Switch-3.

Switch-3 is elected as the Root Bridge because it possesses the lowest MAC address (0011.2233.4411) among all switches in the topology.

On the link segment connecting Switch-3 and Switch-4, Switch-3 hosts the Designated Port while Switch-4 blocks its port because Switch-3 has a lower MAC address.

Switch-4 selects its port connected to Switch-3 as its Root Port because Switch-3 has a lower Bridge ID than Switch-2.

Switch-3 places its port connected to Switch-2 into an Alternate/Blocking state because Switch-2 advertises a lower Root Path Cost (cost of 2) on that segment.

Show answer & explanation

Answer: Switch-4 selects its connection to Switch-2 as its Root Port because it yields a lower Root Path Cost of 4 compared to a cost of 8 via Switch-3.; On the link segment connecting Switch-3 and Switch-4, Switch-3 hosts the Designated Port while Switch-4 blocks its port because Switch-3 has a lower MAC address.; Switch-3 places its port connected to Switch-2 into an Alternate/Blocking state because Switch-2 advertises a lower Root Path Cost (cost of 2) on that segment.

Answer

The three correct statements are: Switch-4 selects its connection to Switch-2 as its Root Port due to a lower Root Path Cost of 4; Switch-3 hosts the Designated Port on the segment to Switch-4 based on a lower MAC address tie-breaker; and Switch-3 blocks its port connected to Switch-2 because Switch-2 has a lower Root Path Cost on that segment.

The Root Bridge is Switch-1 (lowest priority of 4096). Switch-4 reaches Switch-1 with a path cost of 4 via Switch-2 (10G + 10G) versus a path cost of 8 via Switch-3 (1G + 1G), making the port connected to Switch-2 its Root Port. On the segment between Switch-3 and Switch-4, both switches have an equal root path cost of 4; Switch-3 wins the Designated Port role because its MAC address is lower than Switch-4's MAC address. On the segment between Switch-2 and Switch-3, Switch-2 advertises a lower root path cost (2) than Switch-3 (4), making Switch-2's port Designated and causing Switch-3 to block its port on that link.

Step-by-Step Solution

Determine the Root Bridge

Switch-1 is elected Root Bridge

Bridge ID consists of Priority + MAC address. Switch-1 has the lowest numerical priority (4096).

Calculate Root Path Costs for each switch

Switch-2 cost = 2 (10G direct link); Switch-3 cost = 4 (1G direct link); Switch-4 cost via Switch-2 = 2 + 2 = 4, via Switch-3 = 4 + 4 = 8

Path cost accumulates cost of egress interfaces toward the Root Bridge.

Identify Root Ports for Switch-2, Switch-3, and Switch-4

Switch-2 Root Port -> Switch-1; Switch-3 Root Port -> Switch-1; Switch-4 Root Port -> Switch-2

Each non-root switch chooses the single interface with the lowest total path cost to the Root Bridge.

Determine Designated and Blocking Ports on remaining segments

Segment Switch-2 <-> Switch-3: Switch-2 is Designated (cost 2 < 4), Switch-3 blocks. Segment Switch-3 <-> Switch-4: Path costs tied (4 = 4), Switch-3 has lower MAC (0011.2233.4411 < 0011.2233.4433), so Switch-3 is Designated and Switch-4 blocks.

Segment with lowest advertising root path cost wins Designated status; tie-breakers use lower Bridge ID (Priority then MAC).

Key Concept

Spanning Tree Protocol Convergence Mechanics and Path Cost Calculation

Question 706Question →

A network engineer is configuring a newly provisioned server rack in a data center using the assigned IPv4 subnet block $10.50.16.0/27$ . What is the maximum number of usable host IPv4 addresses that can be assigned to active devices within this subnet block?

Show answer & explanation

Answer: 30

Answer

The maximum number of usable host IPv4 addresses in a /27 subnet is 30.

A CIDR prefix of /27 leaves 5 host bits (

32 - 27 = 5

). Raising 2 to the power of 5 gives 32 total addresses. Subtracting the network address and broadcast address (

32 - 2

) results in 30 usable host IP addresses.

Step-by-Step Solution

Determine the number of available host bits.

Host bits =

32 - 27 = 5

bits.

An IPv4 address has 32 bits total. Subtracting the prefix length yields the bits remaining for host addressing.

Calculate the total size of the address block.

Total IP addresses =

2^5 = 32

addresses.

Five host bits allow

2^5

distinct binary combinations.

Subtract reserved addresses to find the usable host count.

Usable host addresses =

32 - 2 = 30

addresses.

The network address (all host bits 0) and the directed broadcast address (all host bits 1) cannot be assigned to network hosts.

Key Concept

Usable Host Calculation in Subnetting

Question 707Question →

A network engineer is configuring a newly provisioned Layer 3 switch interface to relay DHCP traffic from a client subnet ( $10.100.20.0/24$ ) to a centralized DHCP server located at $10.200.10.5$ . Although the command `ip helper-address 10.200.10.5` has been applied to the client-facing VLAN interface, workstations on the subnet fail to obtain IP addresses. Packet captures on the centralized DHCP server indicate that relayed unicast packets arrive, but the server discards them because the Gateway IP Address ( $giaddr$ ) field in the DHCP header is set to $0.0.0.0$ . Which of the following configuration issues is the primary cause of this behavior?

The client-facing VLAN interface on the Layer 3 switch lacks an assigned IPv4 address, preventing the relay agent from identifying the client subnet scope.

The IP helper address was configured on the egress interface connecting toward the centralized DHCP server rather than the client gateway interface.

The switch modified the destination UDP port from port 67 to port 68 when converting the broadcast frame into a unicast packet.

The Layer 3 switch failed to flood the broadcast frame across all ports member to the management VLAN prior to encapsulation.

Show answer & explanation

Answer: The client-facing VLAN interface on the Layer 3 switch lacks an assigned IPv4 address, preventing the relay agent from identifying the client subnet scope.

Answer

The client-facing VLAN interface on the Layer 3 switch lacks an assigned IPv4 address, preventing the relay agent from identifying the client subnet scope.

DHCP Relay agents require a valid Layer 3 IPv4 address on the client-facing interface where the broadcast is received. This interface IP address is written into the

giaddr

field of the DHCP header before forwarding the packet via unicast to the DHCP server. If the interface lacks an IP address, the relay agent sets

giaddr

0.0.0.0

, causing the DHCP server to discard the request because it cannot determine which address pool/scope to allocate from.

Step-by-Step Solution

Analyze the role of the Gateway IP Address (

giaddr

) field in DHCP relay operation.

The

giaddr

field tells the DHCP server which subnet/pool the client belongs to when the request originates from a different broadcast domain.

Without a valid

giaddr

, the server cannot perform scope matching for cross-subnet clients.

Determine how the relay agent populates the

giaddr

field.

The relay agent inserts the IP address of its own interface receiving the client's original broadcast message.

This IP address represents the default gateway of the client subnet.

Evaluate the symptom (

giaddr = 0.0.0.0

If the receiving interface does not have an IP address configured, the relay agent cannot insert a valid gateway address into the header.

An unconfigured or unassigned interface IP address leaves

giaddr

initialized as

0.0.0.0

, causing the server to reject scope matching.

Key Concept

DHCP Relay Agent Subnet Selection via GIADDR Field

Estimated Time:2m 0s

Question 708Question →

An enterprise edge router participating in an OSPF dynamic routing domain learns three distinct paths to reach the remote subnet $10.10.0.0/16$ :

- Path 1: Learned as an Inter-area route (O IA) via Router West with a calculated total metric of $45$ .
- Path 2: Learned as an External Type 1 route (O E1) via Router East with a calculated total metric of $15$ .
- Path 3: Learned as an External Type 2 route (O E2) via Router North with a fixed external metric of $5$ .

Assuming all links are operational and default administrative distances apply, which route will the router install into its active routing table for traffic destined to $10.10.15.1$ ?

The Inter-area route (O IA) via Router West, because OSPF prioritizes Inter-area routes over External routes regardless of metric cost.

The External Type 2 route (O E2) via Router North, because it presents the absolute lowest metric value of 5.

The External Type 1 route (O E1) via Router East, because Type 1 routes include internal path cost to achieve a lower cumulative cost than Inter-area routes.

Equal-cost multi-path (ECMP) traffic splitting across all three routes because they originate from the same dynamic routing protocol instance.

Show answer & explanation

Answer: The Inter-area route (O IA) via Router West, because OSPF prioritizes Inter-area routes over External routes regardless of metric cost.

Answer

The Inter-area route (O IA) via Router West is selected and installed into the routing table because OSPF path-type precedence (Intra-area > Inter-area > External Type 1 > External Type 2) takes precedence over metric calculations.

In OSPF path selection, routes are evaluated according to a strict order of preference: Intra-area (O) > Inter-area (O IA) > External Type 1 (O E1) > External Type 2 (O E2). Because an Inter-area (O IA) route exists, OSPF selects it immediately over any External routes (E1 or E2), regardless of whether the external routes have lower metric costs.

Step-by-Step Solution

Analyze the prefix lengths of all candidate routes.

All three routes cover the identical prefix length of

10.10.0.0/16

, so Longest Prefix Match (LPM) does not eliminate any path.

Prefix length comparison always occurs first in IP routing selection.

Evaluate administrative distance across protocol sources.

All routes originate from the same OSPF process (Administrative Distance

110

Administrative Distance is only compared across different routing sources.

Apply OSPF route preference rules based on path type hierarchy.

OSPF path type order is: 1. Intra-area (O), 2. Inter-area (O IA), 3. External Type 1 (O E1), 4. External Type 2 (O E2).

OSPF path type precedence is evaluated before comparing metric costs.

Determine the winning path for installation into the Routing Information Base (RIB).

The Inter-area route (O IA) via Router West beats External Type 1 (O E1) and External Type 2 (O E2) paths, even though its metric cost (

45

) is higher.

Inter-area routes outrank any external route types in OSPF.

Key Concept

OSPF Route Selection Hierarchy (Path Type Precedence)

Question 709Question →

An enterprise network engineer configures a DHCP relay service on a Layer 3 router interface servicing a remote VoIP VLAN ( $172.16.30.0/24$ ). When an IP phone boots up and sends a broadcast DHCPDISCOVER frame, the router encapsulates this message into a unicast IPv4 packet targeted directly at the centralized DHCP server ( $10.10.5.50$ ). Which field in the DHCP message header does the relay agent populate with its own interface IP address ( $172.16.30.1$ ) so that the DHCP server selects the appropriate address pool?

giaddr (Gateway IP Address)

ciaddr (Client IP Address)

yiaddr (Your IP Address)

chaddr (Client Hardware Address)

Show answer & explanation

Answer: giaddr (Gateway IP Address)

Answer

The giaddr (Gateway IP Address) field is populated by the DHCP relay agent with its own interface IP address to tell the server which IP scope to allocate from.

When a DHCP relay agent intercepts a broadcast DHCPDISCOVER request, it modifies the packet by inserting the IP address of the local receiving interface into the giaddr (Gateway IP Address) field. It then forwards the packet via unicast to the remote DHCP server. Upon receipt, the DHCP server evaluates the giaddr value to match it against configured scopes, ensuring the client receives an IP address valid for its local IP subnet.

Step-by-Step Solution

Analyze the client DHCP request process across subnets

The client issues a layer 2/3 broadcast message (DHCPDISCOVER) because it does not yet possess an IP address or know the server location.

Routers drop layer 2 broadcast frames by default, requiring a relay agent (IP helper) to bridge communication across subnets.

Examine the role of the DHCP Relay Agent

The relay agent intercepts the local broadcast, sets the giaddr field to the router interface's IP address (

172.16.30.1

), and unicasts the packet to the DHCP server.

The centralized server uses the giaddr field to determine which address pool (

172.16.30.0/24

) matches the client's physical network segment.

Key Concept

DHCP Relay Agent and giaddr Header Field Processing

Question 710Question →

A network engineer is configuring an 802.1Q trunk link between `SW-CORE-01` and `SW-ACCESS-05`. Interface `GigabitEthernet 0/1` on `SW-CORE-01` is configured with `switchport trunk native vlan 50`. Interface `GigabitEthernet 0/1` on `SW-ACCESS-05` retains the default configuration of `switchport trunk native vlan 1`. Both switches have VLANs 10, 20, and 50 allowed on the trunk link.

When an untagged frame originating from an access port assigned to VLAN 50 on `SW-CORE-01` is forwarded across the trunk link, how will `SW-ACCESS-05` handle this frame upon arrival?

It will accept the untagged frame and forward it within VLAN 1 because VLAN 1 is configured as its local native VLAN.

It will drop the frame immediately because the frame's VLAN ID does not match the local native VLAN configuration.

It will inspect the 802.1Q header tag, strip it, and place the frame directly into VLAN 50.

It will automatically perform Layer 2 routing to forward the frame from VLAN 50 to VLAN 1 without requiring a router.

Show answer & explanation

Answer: It will accept the untagged frame and forward it within VLAN 1 because VLAN 1 is configured as its local native VLAN.

Answer

SW-ACCESS-05 will accept the untagged frame and process it as part of VLAN 1 because untagged frames arriving on an 802.1Q trunk are automatically assigned to the receiving interface's configured native VLAN.

The correct response highlights that untagged frames arriving on an 802.1Q trunk interface are mapped directly to the local interface's native VLAN. SW-CORE-01 transmits VLAN 50 frames untagged because VLAN 50 is its native VLAN. SW-ACCESS-05 receives the untagged frame and associates it with VLAN 1, which is its own native VLAN setting.

Step-by-Step Solution

Analyze frame egress behavior at SW-CORE-01

Since VLAN 50 is configured as the native VLAN on SW-CORE-01's trunk port, traffic originating from VLAN 50 is transmitted across the 802.1Q trunk link without an 802.1Q VLAN tag.

By standard 802.1Q behavior, frames belonging to the native VLAN are sent untagged across trunk links.

Analyze frame ingress behavior at SW-ACCESS-05

SW-ACCESS-05 receives an untagged frame on its trunk port where `native vlan 1` is configured.

When a switch receives an untagged frame on an 802.1Q trunk port, it maps that frame to its own configured native VLAN.

Determine the resulting network outcome

The frame sent from VLAN 50 on SW-CORE-01 leaks into VLAN 1 on SW-ACCESS-05.

A native VLAN mismatch across a trunk link causes traffic from one VLAN to bleed into a different VLAN on the remote switch.

Key Concept

802.1Q Native VLAN Tagging & Mismatch Behavior

Estimated Time:1m 30s

Question 711Question →

A network technician is deploying a new remote office client subnet (VLAN 40). Hosts connected to VLAN 40 are unable to reach the centralized DHCP server located across a Layer 3 WAN link at IP address 10.10.1.50, causing client machines to automatically receive 169.254.x.x addresses. Which of the following configuration actions on the router's VLAN 40 gateway interface will resolve this issue?

Configure an IP helper address specifying the destination IP 10.10.1.50.

Create an AAAA DNS resource record pointing the gateway hostname to 10.10.1.50.

Change the default gateway DHCP relay setting from UDP port 67 to TCP port 67.

Configure the IP helper address to point to the local interface APIPA network address.

Show answer & explanation

Answer: Configure an IP helper address specifying the destination IP 10.10.1.50.

Answer

Configure an IP helper address specifying the destination IP 10.10.1.50.

Because Layer 3 routers block broadcast messages by default, host DHCP DISCOVER broadcasts generated on VLAN 40 cannot reach a DHCP server residing on a different subnet. Setting an IP helper address on the router's local gateway interface acts as a DHCP Relay Agent, converting client broadcasts into directed unicast packets to IP 10.10.1.50.

Step-by-Step Solution

Identify the cause of client address allocation failure.

Clients on VLAN 40 generate APIPA addresses because local DHCP broadcast frames (DISCOVER) cannot traverse the Layer 3 router boundary to reach the central DHCP server.

Routers drop Layer 2/3 broadcast packets by default.

Determine the required service to enable cross-subnet DHCP functionality.

Deploying a DHCP Relay Agent (IP Helper) on the incoming default gateway interface intercepts broadcast traffic.

The relay agent wraps broadcast DISCOVER messages into unicast IP packets directed to the designated DHCP server address.

Select the correct interface configuration command.

Applying the IP helper address command pointing to 10.10.1.50 enables unicast forwarding of DHCP traffic across the WAN link.

This allows clients to successfully complete the DORA process and acquire valid IP leases from the central scope.

Key Concept

DHCP Relay / IP Helper Operation across Layer 3 Boundaries

Question 712Question →

A network router interface configured with an IP helper address receives an incoming DHCPDISCOVER broadcast packet from a local host. Which of the following actions does the router perform as part of its DHCP relay operation? (Select TWO.)

Select all that apply

Replaces the client broadcast destination IP address with a unicast IP address directed to the specified DHCP server.

Populates the gateway IP address (

giaddr

) field in the DHCP payload with its own receiving interface IP address.

Encapsulates the DHCP request into a TCP stream on port 67 to establish a reliable connection with the DHCP server.

Floods the broadcast packet out of all router interfaces to locate an available DHCP server across connected VLANs.

Show answer & explanation

Answer: Replaces the client broadcast destination IP address with a unicast IP address directed to the specified DHCP server.; Populates the gateway IP address ( $giaddr$ ) field in the DHCP payload with its own receiving interface IP address.

Answer

When a router acts as a DHCP relay agent, it converts the client's local broadcast packet into a unicast packet directed toward the centralized DHCP server and populates the gateway IP address (

giaddr

) field with the receiving interface's IP address.

A DHCP relay agent processes local client broadcast messages by converting the destination IP address to the unicast IP of the remote DHCP server and writing the receiving interface's IP address into the gateway IP address (

giaddr

) field of the DHCP payload so the server knows which subnet scope to select.

Step-by-Step Solution

Identify the primary role of a DHCP relay agent upon receiving a broadcast request.

The router intercepts the broadcast DHCPDISCOVER packet on the client subnet interface.

DHCP clients initially send broadcast requests because they do not know the network configuration or server address.

Determine how the router modifies the IP header for relaying.

The destination address changes from a broadcast address to the configured unicast address of the DHCP server.

Routers do not forward broadcast packets across network boundaries; unicast routing delivers the request across Layer 3 subnets.

Determine how the DHCP server identifies the correct scope.

The router inserts its own receiving interface IP address into the

giaddr

header field.

The DHCP server requires the

giaddr

information to select an IP address from the pool corresponding to the client's subnet.

Key Concept

DHCP Relay Unicast Forwarding and Gateway IP Address (

giaddr

) Insertion

Question 713Question →

An enterprise network has deployed a centralized DHCP server on VLAN 100 ( $10.100.0.10/24$ ). Client workstations on VLAN 15 ( $172.16.15.0/24$ ) and VLAN 25 ( $172.16.25.0/24$ ) connect to a Layer 3 switch serving as their default gateway but fail to receive dynamic IP leases, resulting in APIPA address assignments. Which of the following configuration steps and operational mechanics must be implemented on the Layer 3 switch to resolve this issue? (Select TWO.)

Select all that apply

Configure the `ip helper-address 10.100.0.10` command directly under the Switched Virtual Interfaces (SVIs) for VLAN 15 and VLAN 25.

The switch converts incoming client DHCP broadcasts into unicast UDP packets destined for port 67 of the central server address.

Configure the `ip helper-address 10.100.0.10` command once in global configuration mode to apply across all defined switch subnets.

Configure inter-VLAN Access Control Lists (ACLs) to permit TCP destination port 67 traffic from the client SVIs to the DHCP server.

Show answer & explanation

Answer: Configure the `ip helper-address 10.100.0.10` command directly under the Switched Virtual Interfaces (SVIs) for VLAN 15 and VLAN 25.; The switch converts incoming client DHCP broadcasts into unicast UDP packets destined for port 67 of the central server address.

Answer

The Layer 3 switch must be configured with `ip helper-address 10.100.0.10` on the SVIs for VLAN 15 and VLAN 25, and the switch operates by relaying broadcast DHCP client packets as unicast UDP destination port 67 traffic to the central server.

DHCP clients broadcast initial DHCPDISCOVER packets within their local VLAN. Because Layer 3 devices drop broadcasts, a DHCP Relay Agent (`ip helper-address`) must be configured on each client-facing Layer 3 interface (SVI). Upon receiving the broadcast, the relay agent converts the request into a unicast UDP packet (using UDP port 67 for both source and destination or forwarding to UDP 67) and sends it directly to the unicast IP address of the remote DHCP server.

Step-by-Step Solution

Identify the boundary requiring DHCP Relay Agent functionality.

Client broadcast packets for DHCP Discovery (UDP port 67) cannot cross Layer 3 VLAN boundaries natively.

Routers and Layer 3 switches drop broadcast traffic by default.

Determine interface-level configuration requirements.

Apply `ip helper-address` to the client-facing interface SVIs (VLAN 15 and VLAN 25).

The relay agent requires interface context to populate the `giaddr` header field with the interface's IP address, allowing the central server to select the correct IP address pool.

Verify protocol and transport-layer characteristics of relayed traffic.

Broadcast UDP packets received on port 67 are unicast to the target server on UDP port 67.

DHCP relay services convert local Layer 2/3 broadcasts into routable Layer 3 unicast UDP packets.

Key Concept

DHCP Relay Agent Architecture and UDP Forwarding Mechanics

Estimated Time:2m 0s

Question 714Question →

A network administrator is configuring static IP address assignments for high-availability database servers within an enterprise subnet designated as $172.20.48.0/28$ . Which of the following IP addresses are valid usable host IP addresses that can be assigned to these servers? (Select TWO)

Select all that apply

172.20.48.1

172.20.48.14

172.20.48.0

172.20.48.15

172.20.48.16

Show answer & explanation

Answer: 172.20.48.1; 172.20.48.14

Answer

The valid usable host IP addresses within the 172.20.48.0/28 subnet are 172.20.48.1 and 172.20.48.14.

For the network block 172.20.48.0/28, a prefix length of /28 provides 16 total IP addresses (

2^{32-28} = 16

). The reserved network address is 172.20.48.0 and the reserved broadcast address is 172.20.48.15. The range of assignable host addresses is 172.20.48.1 through 172.20.48.14 inclusive. Therefore, 172.20.48.1 and 172.20.48.14 are valid usable host addresses.

Step-by-Step Solution

Determine the block size for a /28 subnet prefix.

A /28 prefix leaves

32 - 28 = 4

host bits. The total number of IP addresses per subnet is

2^4 = 16

Calculating the total size of the subnet identifies the boundary conditions.

Identify the network ID and broadcast address for the subnet block.

The network address is 172.20.48.0. The broadcast address is

172.20.48.0 + 16 - 1 = 172.20.48.15

The network address is the first address in the block and the broadcast address is the last.

Determine the range of usable host IP addresses.

The usable host IP range spans from

172.20.48.1

(network ID + 1) to

172.20.48.14

(broadcast ID - 1).

Network and broadcast addresses are reserved and cannot be configured on individual host interfaces.

Evaluate the candidate options against the valid host range.

172.20.48.1 and 172.20.48.14 both fall within the usable range [172.20.48.1 - 172.20.48.14].

Only IP addresses strictly between the network ID and broadcast ID can be statically assigned to host devices.

Key Concept

IPv4 Host Range Determination

Question 715Question →

A network administrator is deploying a multi-VLAN network on a Layer 3 switch. Workstations on VLAN 50 ( $10.50.0.0/24$ ) are failing to acquire IP addresses from a centralized DHCP server ( $192.168.10.10$ ). During troubleshooting, the administrator notices that the `ip helper-address 192.168.10.10` command was mistakenly configured on the physical trunk uplink interface connecting to the core router instead of the client subnet interface. Which configuration change must be implemented to allow VLAN 50 workstations to obtain DHCP leases?

Apply the `ip helper-address 192.168.10.10` command directly under the VLAN 50 Switch Virtual Interface (SVI).

Reconfigure the DHCP relay agent to forward client requests using TCP port 67 instead of UDP port 67.

Relocate the `ip helper-address` configuration statement to the network adapter properties of the central DHCP server.

Enable global broadcast routing on all physical access switchports assigned to VLAN 50.

Show answer & explanation

Answer: Apply the `ip helper-address 192.168.10.10` command directly under the VLAN 50 Switch Virtual Interface (SVI).

Answer

Configure the `ip helper-address 192.168.10.10` command directly under the VLAN 50 Switch Virtual Interface (SVI).

DHCP clients issue Layer 2 broadcast requests (`255.255.255.255`) that are constrained to their local VLAN. To relay these requests across subnets to a remote DHCP server, the DHCP relay service (`ip helper-address`) must be configured on the Layer 3 interface serving as the local default gateway for that VLAN—specifically the VLAN 50 Switch Virtual Interface (SVI). Once configured on the SVI, the switch intercepts the local broadcast, sets the Gateway IP Address (`giaddr`) field to the SVI IP address, and forwards the request as a unicast packet to

192.168.10.10

Step-by-Step Solution

Identify the ingress interface for client broadcast traffic

Workstations on VLAN 50 send initial DHCPDISCOVER messages as Layer 2 broadcasts targeting their local default gateway interface (the VLAN 50 SVI).

DHCP broadcast messages are contained within their local broadcast domain (VLAN) and will not reach physical trunk uplinks without local SVI relay processing.

Evaluate relay agent placement rules

The `ip helper-address` statement must reside on the interface listening for client broadcasts.

Placing the helper address on an outbound trunk interface bypasses the client broadcast domain, preventing the router/switch from intercepting client requests.

Apply the correct configuration location

Configuring `ip helper-address 192.168.10.10` under `interface Vlan50` enables the relay agent to capture broadcast requests, populate the `giaddr` field with

10.50.0.1

, and unicast the request to the central server.

This allows the remote DHCP server to select an available pool address matching the

10.50.0.0/24

subnet.

Key Concept

DHCP Relay Agent Placement on Switch Virtual Interfaces (SVIs)

Question 716Question →

A network administrator needs to publish an internal web server to the internet. The server is assigned a fixed private IPv4 address, and the organization requires a permanent, dedicated one-to-one mapping to a single public IPv4 address. Which NAT translation method should the network administrator implement?

Static NAT

Port Address Translation (PAT)

Frame Translation NAT

Dynamic NAT

Show answer & explanation

Answer: Static NAT

Answer

Static NAT is the correct solution because it provides a permanent, dedicated one-to-one mapping between a private IP address and a public IP address.

Static NAT configures a fixed, persistent 1-to-1 translation between an inside local private IP address and an inside global public IP address. This static mapping ensures that external users can consistently access the internal web server.

Step-by-Step Solution

Analyze the technical requirements of the scenario

The internal web server requires external internet access using a single dedicated public IP address that never changes.

Publicly accessible services such as web servers require consistent IP addressing so domain name records and external clients can reliably reach them.

Match the requirement to the appropriate Network Address Translation type

Static NAT provides a permanent 1:1 translation between an inside local private IP address and an inside global public IP address.

Unlike dynamic methods, Static NAT ensures that incoming traffic sent to the public IP is always routed to the designated internal web server.

Key Concept

Static NAT 1-to-1 Mapping

Question 717Question →

A system administrator is designing an isolated VLAN for a database cluster. The cluster requires $27$ usable IPv4 addresses for database nodes, $1$ address for the default gateway, and $2$ addresses for virtual IP load balancers. Which of the following represents the smallest CIDR prefix mask that provides sufficient usable IPv4 addresses for all required devices?

/28

/27

/26

/25

Show answer & explanation

Answer: $/27$

Answer

The smallest CIDR prefix mask that satisfies the requirement is

/27

The scenario requires

30

usable IP addresses (

27 + 1 + 2 = 30

). A

/27

subnet has

5

host bits (

32 - 27 = 5

), providing

2^5 = 32

total IP addresses. Subtracting

2

for the network address and broadcast address leaves exactly

30

usable host addresses (

32 - 2 = 30

), making

/27

the smallest prefix mask that satisfies the requirement.

Step-by-Step Solution

Calculate total usable IPv4 addresses required.

27 \text{ nodes} + 1 \text{ gateway} + 2 \text{ load balancers} = 30 \text{ usable host IP addresses}

All active host interfaces on the network segment require individual usable IP addresses.

Determine the required host bits (

h

) using the formula for usable hosts.

2^h - 2 \ge 30 \implies 2^h \ge 32 \implies h = 5

host bits.

Two IP addresses in every standard subnet are reserved for the network ID and broadcast address.

Calculate the CIDR prefix length.

32 - 5 = 27

, resulting in a

/27

subnet mask.

An IPv4 address consists of 32 bits; subtracting 5 host bits leaves 27 prefix bits for the network.

Key Concept

Calculating required subnet size and usable host counts using CIDR notation

Estimated Time:1m 30s

Question 718Question →

Match each Network Address Translation (NAT) implementation concept on the left with its corresponding operational description and traffic mapping behavior on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Static NAT matches the permanent one-to-one IP mapping for DMZ servers. Dynamic NAT matches the pool-based mapping without port alteration. Port Address Translation (PAT) matches many-to-one translation using Layer 4 source ports. Static PAT matches destination port redirection to an internal host and service port.

Each NAT type is accurately paired with its technical execution model: Static NAT provides permanent 1-to-1 IP mapping for unsolicited server access; Dynamic NAT allocates 1-to-1 public IPs dynamically from a pool without port alteration; PAT multiplexes many private IPs to one public IP using Layer 4 source ports; and Static PAT maps targeted public incoming transport ports directly to internal hosts.

Step-by-Step Solution

Analyze Static NAT requirements

Identified as a permanent 1:1 Layer 3 mapping between an Inside Local address and an Inside Global address.

Static NAT requires a dedicated public IP for each host and allows bidirectional, unsolicited inbound traffic (e.g., hosting public web servers).

Analyze Dynamic NAT operational characteristics

Identified as a dynamic 1:1 allocation from a pool of public IPv4 addresses on demand.

Dynamic NAT does not translate port numbers; sessions are allocated public addresses sequentially until the public pool is exhausted.

Analyze Port Address Translation (PAT / NAT Overload)

Identified as many-to-one mapping using transport-layer port tracking.

PAT modifies both IP addresses (Layer 3) and port numbers (Layer 4), storing socket pairs in the state table to allow thousands of internal hosts to share a single public IPv4 address.

Analyze Static PAT (Port Forwarding)

Identified as inbound port translation targeting specific internal host services.

Port Forwarding intercepts inbound traffic on a specific public port and forwards it to a private IP and service port destination.

Key Concept

Differentiation of Network Address Translation types (Static NAT, Dynamic NAT, PAT, and Static PAT/Port Forwarding) by Layer 3 vs Layer 4 translation behaviors, pool allocation, and directionality.

Question 719Question →

A workstation user initiates a file download request across a local network. Arrange the encapsulation processing steps executed by the host's networking stack in the correct chronological order, starting from the application request down to physical cable transmission.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order of encapsulation from host data creation to physical transmission is: 1) Application generates raw payload, 2) Transport layer appends port headers (segment), 3) Network layer prepends IP addresses (packet), 4) Data Link layer adds MAC header and FCS trailer (frame), and 5) Physical layer encodes bits into physical signals.

Outbound encapsulation follows a strict top-down progression through the OSI stack. The application layer creates the initial payload data. The transport layer prepends port headers to construct a transport segment. Next, the network layer adds IP addressing headers to construct a network packet. The data link layer then wraps the packet with MAC headers and a Frame Check Sequence (FCS) trailer to build a data link frame. Finally, the physical layer converts the frame's binary bits into physical signals for transmission over the network medium.

Step-by-Step Solution

Trace the movement of outbound data through the protocol stack

Outbound data traverses top-down from Layer 7 (Application) to Layer 1 (Physical).

Application data must be successively wrapped with control headers at each descending protocol layer before being placed on the wire.

Identify the Protocol Data Unit (PDU) generated at each layer

Data (Layer 7-5) → Segment (Layer 4) → Packet (Layer 3) → Frame (Layer 2) → Bits/Signals (Layer 1).

Each layer treats the upper layer's PDU as raw payload, appending its specific protocol headers and trailers.

Key Concept

Top-down Data Encapsulation Sequence

Estimated Time:1m 30s

Question 720Question →

A network administrator is auditing the core network architecture to ensure proper service deployment across enterprise subnets. Match each IP addressing service or feature on the left with its corresponding operational role on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Start of Authority (SOA) record matches the zone administrative metadata description; IP Address Management (IPAM) matches centralized IP tracking and planning; DHCP Option 82 matches appending switch port and VLAN relay metadata; Multicast DNS (mDNS) matches local-link zero-configuration name resolution.

Each feature correctly corresponds to its primary function: the SOA record holds domain zone parameters and contact metadata; IPAM offers central IP address visibility; DHCP Option 82 enriches DHCP discovery packets with relay attachment metadata; and mDNS performs zero-configuration local-link name resolution.

Step-by-Step Solution

Analyze the DNS Zone Administrative requirement.

Identify that the SOA record specifies authoritative zone data, serial numbers, and refresh timers.

SOA is the fundamental record defining zone parameters for DNS servers.

Identify the service for centralized network IP visibility.

Match IPAM to centralized IP address tracking and integration with DNS/DHCP servers.

IPAM consolidates subnet monitoring and address lifecycle management.

Evaluate the relay security and policy enforcement mechanism.

Match DHCP Option 82 to adding relay agent information (circuit ID/remote ID) to client requests.

Option 82 allows downstream DHCP servers to allocate leases or enforce security based on physical connection details.

Examine serverless name resolution for local links.

Match mDNS to resolving hostnames on local subnets without dedicated DNS infrastructure.

mDNS utilizes multicast packets on port 5353 for zero-configuration host discovery.

Key Concept

Core functions and operational roles of IP addressing, naming, and management services.

Estimated Time:1m 30s

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