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A network engineer is evaluating internal dynamic routing protocols to replace legacy static routing across a multi-vendor enterprise infrastructure. The design requires a protocol that maintains complete topology visibility within an area and uses link bandwidth as its primary metric metric calculation. Which of the following statements correctly describe operational characteristics of Open Shortest Path First (OSPF)? (Select TWO.)

Select all that apply

OSPF uses Dijkstra's Shortest Path First algorithm to construct a loop-free topology tree based on link cost metrics.

OSPF encapsulates routing updates inside Layer 4 TCP segments using port 179 to guarantee transport delivery.

OSPF routers maintain full topology awareness of all routers and links within their designated local area via Link-State Advertisements.

OSPF requires Static NAT to translate internal IP routing prefixes before advertising routes to neighboring routers.

Show answer & explanation

Answer: OSPF uses Dijkstra's Shortest Path First algorithm to construct a loop-free topology tree based on link cost metrics.; OSPF routers maintain full topology awareness of all routers and links within their designated local area via Link-State Advertisements.

Answer

The correct statements are that OSPF uses Dijkstra's Shortest Path First algorithm to construct a loop-free topology tree based on link cost metrics, and that OSPF routers maintain full topology awareness of all routers and links within their designated local area via Link-State Advertisements.

OSPF relies on Link-State Advertisements (LSAs) to build a synchronized Link-State Database (LSDB) within an area, giving every router complete visibility into the area topology. Each router independently runs Dijkstra's Shortest Path First (SPF) algorithm on this database to determine the lowest cumulative cost path to every destination prefix.

Step-by-Step Solution

Analyze the operational classification of OSPF.

OSPF is categorized as an Interior Gateway Protocol (IGP) utilizing link-state mechanics.

Link-state protocols distribute neighbor and link condition information (LSAs) so each router builds a complete topological map (LSDB).

Evaluate path calculation and transport characteristics.

OSPF executes Dijkstra's SPF algorithm over link cost and runs directly on IP protocol 89 without using Layer 4 transport protocols like TCP.

Direct IP protocol encapsulation (protocol 89) eliminates Layer 4 overhead for intra-network routing exchanges.

Key Concept

Link-State Dynamic Routing Protocol Mechanics (OSPF)

Question 1662Question →

Following an office desk relocation project, a user reports that their workstation cannot connect to internal network resources. A technician inspects the computer and discovers it has self-assigned an IP address in the range of $169.254.0.0/16$ . The technician needs to physically trace the horizontal Ethernet cabling from the wall outlet in the user's office back through the patch panel to the designated access switch port inside the unlabelled IDF cabinet. Which documentation artifact should the technician consult to identify the precise physical mapping between the wall outlet jack and the patch panel port?

A cable run schedule documenting wall outlet jack identifiers, horizontal cabling pathways, and corresponding patch panel port assignments

A logical network topology diagram displaying IP subnet allocations, VLAN IDs, and default gateway addresses

A rack elevation diagram detailing vertical rack unit (U) positions, device dimensions, and power distribution unit placements

An 802.1Q trunking audit log listing native VLAN configurations and allowed VLAN trunks across switch interconnects

Show answer & explanation

Answer: A cable run schedule documenting wall outlet jack identifiers, horizontal cabling pathways, and corresponding patch panel port assignments

Answer

The technician should consult a cable run schedule, which documents wall outlet jack identifiers, horizontal cabling pathways, and corresponding patch panel port assignments.

The cable run schedule (also known as a wiring matrix or patch panel schedule) is the specific physical network documentation that records how horizontal cabling runs connect telecommunications outlets (wall jacks) to individual ports on a patch panel in an IDF or MDF. Consulting this document enables the technician to locate the exact patch panel port corresponding to the office wall outlet.

Step-by-Step Solution

Analyze the troubleshooting symptom and requirements

The workstation has an APIPA address (

169.254.x.x

), indicating a physical link or DHCP connectivity issue, and the technician must physically trace the unlabelled cable run from the workstation's wall jack to the patch panel in the IDF.

Resolving physical layer tracing issues requires physical layer documentation rather than logical or configuration logs.

Differentiate between physical and logical documentation types

Logical diagrams detail subnets and VLANs, rack elevations detail enclosure space allocation, and cable run schedules detail physical wiring endpoints and jack-to-patch-panel mappings.

Identifying physical cable terminations requires documentation specifically designed for structured cabling management.

Select the appropriate documentation artifact

The cable run schedule contains the exact pinouts, jack IDs, physical room locations, and patch panel port numbers required to locate the physical circuit.

Consulting the cable run schedule allows the technician to locate and test the correct patch panel port without manual tone-and-probe tracing.

Key Concept

Physical Network Documentation and Cable Management

Question 1663Question →

Match each routing decision concept on the left with its corresponding description in router path selection on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Longest Prefix Match pairs with the primary criteria evaluated first when choosing among multiple destination route entries with different subnet masks; Administrative Distance pairs with the rating of trustworthiness used to select the preferred routing source for identical prefixes; Metric pairs with the calculated cost value used by a single routing protocol to rank candidate paths; Next-Hop Address pairs with the IP address of the adjacent gateway device.

Each routing concept directly matches its fundamental role in packet forwarding decisions. Longest Prefix Match specifies that the entry with the longest subnet mask is chosen first. Administrative Distance compares trustworthiness across different routing protocols. Metric measures path desirability within a single protocol. Next-Hop Address identifies the immediate next gateway router on the path.

Step-by-Step Solution

Identify the precedence rule for routing table lookup.

Longest Prefix Match is applied first before administrative distance or metric are considered.

Routers always prefer the most specific matching route entry for an incoming destination IP address.

Differentiate between inter-protocol and intra-protocol path selection criteria.

Administrative Distance breaks ties between different routing protocols for identical prefixes, whereas Metric breaks ties among multiple routes within the same protocol.

Routers need separate mechanisms to rate protocol source trustworthiness versus internal path performance.

Define the forwarding component of a routing table entry.

The Next-Hop Address provides the adjacent layer 3 egress point required to build the encapsulation frame.

Packets must be sent to an immediate downstream router interface to move closer to their final destination.

Key Concept

Routing Table Decision Process and Terminology

Estimated Time:1m 30s

Question 1664Question →

A network administrator is configuring a Layer 3 router to act as a DHCP relay agent for a newly established guest wireless subnet on VLAN 75 ( $192.168.75.0/24$ ). Client devices on VLAN 75 send broadcast DHCPDISCOVER requests, but none of them acquire an IP address from the centralized DHCP server located at $10.100.1.5$ . Upon reviewing the router's configuration, the administrator discovers that the `ip helper-address 10.100.1.5` command was mistakenly applied to the outbound WAN interface facing the core network rather than the subinterface corresponding to VLAN 75. Which of the following best describes the immediate operational failure caused by this misconfiguration?

The router drops or ignores the Layer 2 broadcast DHCPDISCOVER packets on the VLAN 75 subinterface because no active relay agent is listening on that ingress interface.

The router rewrites the DHCP payload using TCP port 67 instead of UDP port 67, causing the central DHCP server to discard incoming requests.

The router forwards the client's broadcast request as a unicast packet, but populates the source port with UDP 68 instead of UDP 67.

The central DHCP server receives the relayed request but attempts to issue an IP address lease from the WAN interface's IP scope instead of the VLAN 75 scope.

Show answer & explanation

Answer: The router drops or ignores the Layer 2 broadcast DHCPDISCOVER packets on the VLAN 75 subinterface because no active relay agent is listening on that ingress interface.

Answer

The router drops or ignores the Layer 2 broadcast DHCPDISCOVER packets on the VLAN 75 subinterface because no active relay agent is listening on that ingress interface.

DHCPDISCOVER packets are broadcast messages that stop at Layer 3 boundaries. For a router to convert these broadcasts into unicast messages directed to a central DHCP server, the relay agent (`ip helper-address`) must be enabled on the specific ingress interface (VLAN 75 subinterface) receiving the broadcasts. Placing the command on an outbound WAN interface means the router will never intercept the client broadcasts originating on VLAN 75.

Step-by-Step Solution

Identify the ingress boundary where DHCP broadcast messages originate.

Clients on VLAN 75 generate Layer 2 broadcast DHCPDISCOVER frames sent to

255.255.255.255

on their local subinterface.

Routers do not forward Layer 2 broadcast packets across subnets by default.

Evaluate the placement requirement of the DHCP Relay Agent (IP helper command).

The `ip helper-address` directive must be applied to the specific Layer 3 interface that receives the incoming client broadcasts.

The interface configuration enables the router to listen for UDP port 67 broadcasts on that specific segment and convert them to unicast traffic.

Determine the impact of placing the command on the outbound WAN interface.

Broadcasts arriving on the VLAN 75 interface are discarded without being intercepted or converted into unicast relay packets.

The outbound WAN interface receives routed traffic, not client broadcast requests originating from the local VLAN segment.

Key Concept

DHCP Relay Agent Interface Placement Requirements

Estimated Time:1m 30s

Question 1665Question →

A cloud network engineer is provisioning a subnetwork for a microservices cluster within a virtual private cloud (VPC). The subnetwork is assigned the IPv4 block $10.240.12.128/25$ . Which of the following IPv4 addresses represents the last usable host IP address that can be assigned to a container instance in this subnet?

10.240.12.254

10.240.12.255

10.240.12.128

10.240.12.253

Show answer & explanation

Answer: 10.240.12.254

Answer

10.240.12.254 is the last usable host IPv4 address in the 10.240.12.128/25 subnet.

With a /25 network mask, 7 host bits are available, creating a subnet size of 128 total IP addresses (

2^7 = 128

). The subnet range spans from 10.240.12.128 to 10.240.12.255. The network address is 10.240.12.128 and the broadcast address is 10.240.12.255. The usable host IP range is 10.240.12.129 through 10.240.12.254, making 10.240.12.254 the last usable host address.

Step-by-Step Solution

Determine the host bits and total addresses in the subnet

The prefix

/25

leaves

32 - 25 = 7

host bits. The total address block size is

2^7 = 128

addresses.

Calculating the block size identifies the IP boundary range.

Identify the network boundary range

Starting at

10.240.12.128

, adding

128

addresses yields the range

10.240.12.128

through

10.240.12.255

The network address is the first address (

10.240.12.128

) and the broadcast address is the last address (

10.240.12.255

Calculate the last usable host IP address

Subtract

1

from the broadcast address:

10.240.12.255 - 1 = 10.240.12.254

Usable host addresses reside between the network address and broadcast address.

Key Concept

IPv4 Subnet Boundaries and Usable Host Range Calculation

Estimated Time:1m 30s

Question 1666Question →

Match each wireless deployment term on the left with its corresponding definition on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

SSID matches the human-readable text name for a WLAN. BSSID matches the MAC address of an access point's radio interface. ESSID matches the identifier spanning multiple access points across a distribution network. WAP matches the layer 2 device connecting wireless clients to the wired network.

Each deployment term corresponds directly to its function: SSID is the text name of the WLAN, BSSID is the physical MAC address of an individual AP radio, ESSID refers to the multi-AP extended network name, and WAP is the physical hardware bridging wireless signals to the wired network.

Step-by-Step Solution

Identify the basic naming convention for individual wireless networks.

Recognize that SSID is the human-readable network name broadcasted or typed into client devices.

SSID is the standard user-facing identifier for wireless network access.

Differentiate logical network names from hardware addresses.

Map BSSID to the physical layer 2 MAC address of the Access Point radio.

BSSID uniquely identifies the physical radio cell at the Data Link layer.

Analyze multi-Access Point enterprise deployments.

Link ESSID to extended deployments covering larger areas with multiple Access Points.

ESSID allows clients to move between Access Points while maintaining connectivity to the same network identity.

Identify the physical hardware component bridging wireless to wired infrastructure.

Connect WAP to the infrastructure device that converts 802.11 wireless frames to 802.3 Ethernet frames.

The WAP serves as the core layer 2 bridge in wireless network deployment.

Key Concept

Wireless Network Identifiers and Infrastructure Terminology

Question 1667Question →

A network administrator needs to establish a dedicated outdoor point-to-point (PtP) wireless connection between two office buildings located 300 meters apart across an open campus. Which of the following implementation steps and equipment choices are appropriate for this specific wireless link? (Select TWO.)

Select all that apply

Mount directional antennas (such as parabolic dish or Yagi antennas) at both endpoints pointed directly at each other

Ensure an unobstructed physical line of sight and clear Fresnel zone between the two antenna positions

Use standard omnidirectional antennas at both endpoints to broadcast signal equally in all 360-degree directions

Configure the wireless bridge radios to operate on overlapping 2.4 GHz channels 2 and 3 simultaneously for bonded bandwidth

Place unshielded indoor access points directly on the building exterior walls to lower installation costs

Show answer & explanation

Answer: Mount directional antennas (such as parabolic dish or Yagi antennas) at both endpoints pointed directly at each other; Ensure an unobstructed physical line of sight and clear Fresnel zone between the two antenna positions

Answer

The two correct choices are to mount directional antennas aimed directly at each other and to ensure an unobstructed line of sight with a clear Fresnel zone between the two sites.

For a dedicated point-to-point outdoor connection between two fixed locations, directional antennas focus RF energy along a focused beam to maximize signal range and quality. Furthermore, keeping the Fresnel zone free of obstructions prevents signal diffraction and loss.

Step-by-Step Solution

Identify antenna requirements for a point-to-point wireless link.

Directional antennas (such as Yagi or parabolic dishes) are selected because they concentrate signal power in a single direction over distance.

Omnidirectional antennas waste power by radiating signal in 360 degrees, which is unsuitable for dedicated building-to-building bridging.

Determine RF path requirements between the two outdoor endpoints.

Establishing clear line of sight and preserving an unblocked Fresnel zone ensures signal waves travel cleanly without diffraction or blockage.

Physical obstacles inside the Fresnel zone cause signal reflections, phase cancellation, and overall link degradation.

Key Concept

Outdoor Point-to-Point Wireless Bridging & Antenna Selection

Question 1668Question →

A network administrator is assigning IPv4 addresses to host interfaces within a newly provisioned subnet allocated the address block $10.100.16.64/27$ . Which of the following IPv4 addresses are valid usable host IP addresses within this subnet? (Select TWO.)

Select all that apply

10.100.16.65

10.100.16.94

10.100.16.64

10.100.16.95

Show answer & explanation

Answer: $10.100.16.65$ ; $10.100.16.94$

Answer

The IP addresses

10.100.16.65

and

10.100.16.94

are valid usable host addresses within the

10.100.16.64/27

IPv4 subnet block.

For the IPv4 block

10.100.16.64/27

, a

/27

mask yields

32

total addresses per block. The subnet starts at network ID

10.100.16.64

and ends at broadcast address

10.100.16.95

. Subtracting these two reserved boundary addresses leaves the usable host address range of

10.100.16.65

through

10.100.16.94

. Therefore,

10.100.16.65

and

10.100.16.94

are both valid usable host IPs.

Step-by-Step Solution

Determine the subnet mask and total block size for a

/27

CIDR prefix.

/27

prefix corresponds to a subnet mask of

255.255.255.224

. The block size per subnet is

256 - 224 = 32

total addresses.

Establishing the block size defines the subnet boundaries for network and broadcast calculations.

Calculate the network address, broadcast address, and assignable host range for the subnet block.

Network ID:

10.100.16.64

. Broadcast address:

10.100.16.64 + 31 = 10.100.16.95

. Usable host range:

10.100.16.65

through

10.100.16.94

The network address (first IP) and broadcast address (last IP) are reserved and subtracted from the usable host address pool.

Evaluate the given choices against the usable host IP address range.

10.100.16.65

and

10.100.16.94

fall within the usable range (

10.100.16.65

–

10.100.16.94

), while

10.100.16.64

(Network ID) and

10.100.16.95

(Broadcast address) are reserved.

Only host addresses falling strictly between the network ID and broadcast address are assignable.

Key Concept

IPv4 Subnet Boundaries and Usable Host Range

Question 1669Question →

Match each enterprise wireless deployment scenario on the left with its corresponding optimal antenna selection and spatial configuration strategy on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Each scenario matches to its optimal spatial configuration based on RF radiation patterns, gain requirements, and channel width constraints: High-rack warehouse aisles pair with narrow horizontal beamwidth directional patch or Yagi antennas. High-density auditoriums pair with microcell deployments using low transmit power, small-cell directional patch antennas, and

20\text{ MHz}

channels. Long-range outdoor bridges pair with high-gain parabolic dish antennas in point-to-point topologies. Open single-floor offices pair with low-gain ceiling-mounted omnidirectional dipole antennas featuring wide azimuth and narrow elevation patterns.

Matching enterprise wireless requirements to antenna radiation patterns and channel configurations requires balancing coverage area, gain, and interference mitigation. Narrow warehouse aisles benefit from directional patch/Yagi antennas aligned with corridors. High-density venues require microcell designs with small directional coverage cells and narrow

20\text{ MHz}

channels to prevent co-channel interference. Long-distance building links require high-gain parabolic dishes for point-to-point focus. Single-floor offices require horizontal omnidirectional dipoles with narrow vertical elevation profiles.

Step-by-Step Solution

Analyze RF path geometry for warehouse aisle deployment.

Identified high signal attenuation and reflection caused by metal racks in narrow corridors.

Directional patch or Yagi antennas with narrow beamwidths concentrate RF energy down the aisle while preventing cross-aisle interference.

Evaluate high-density client requirements in open auditorium environments.

Determined that large cell coverage causes severe co-channel interference and spectrum congestion.

Microcells with low power, directional antennas (

60^\circ

beamwidth), and

20\text{ MHz}

channel widths isolate coverage zones and maximize channel reuse.

Calculate gain and directional requirements for long-distance point-to-point bridging.

Recognized extreme attenuation over

1.5\text{ km}

requiring high Effective Isotropically Radiated Power (EIRP) focus.

Parabolic dish antennas provide high directional gain with minimal side-lobes, ideal for dedicated PtP building-to-building links.

Select radiation pattern for single-floor open office space.

Required uniform horizontal coverage without inter-floor bleeding.

Omnidirectional dipole ceiling mounts emit a wide horizontal azimuth pattern and narrow vertical elevation beam.

Key Concept

Wireless Antenna Selection, Radiation Patterns, and High-Density Microcell Planning

Question 1670Question →

Company A acquires Company B, and a network engineer is tasked with establishing bidirectional host-to-host connectivity across a site-to-site IPsec VPN. During initial discovery, the engineer identifies that both organizations independently use the exact same private IPv4 addressing space ( $192.168.10.0/24$ ) for their core server subnets. Neither organization can re-address its servers due to legacy application dependencies. Which Network Address Translation (NAT) implementation strategy should the engineer deploy on the network gateways to resolve this IP address conflict?

Configure Twice NAT (overlapping NAT) on the gateway routers to perform simultaneous source and destination IP address translation for traffic crossing the VPN tunnel.

Deploy standard Port Address Translation (PAT / NAT Overload) using the WAN gateway IP to dynamically multiplex destination addresses across Layer 4 port numbers.

Implement Static NAT to map internal server IP addresses to external public IP addresses while keeping transport layer port numbers unmodified at Layer 2.

Reconfigure port forwarding rules on the edge firewalls to map standard service ports (such as port 80 and port 443) between the two overlapping subnets.

Show answer & explanation

Answer: Configure Twice NAT (overlapping NAT) on the gateway routers to perform simultaneous source and destination IP address translation for traffic crossing the VPN tunnel.

Answer

Twice NAT (overlapping NAT) should be configured on the gateway routers to translate both source and destination IP addresses across the VPN tunnel.

Twice NAT (also known as overlapping NAT) is specifically designed for scenarios where two connecting networks use overlapping IP address spaces. It rewrites both the source IP address and the destination IP address in the packet header as traffic traverses the router or firewall interface, mapping virtual dummy subnets to actual private addresses so traffic can be routed cleanly across an IPsec tunnel.

Step-by-Step Solution

Analyze the network conflict scenario

Identified that both networks use identical IPv4 subnets (

192.168.10.0/24

), causing routing ambiguity where local routers cannot distinguish local hosts from remote hosts.

When source and destination IP addresses belong to the same IP subnet, standard Layer 3 routing sends packets locally rather than forwarding them across a VPN tunnel.

Evaluate standard NAT and PAT limitations

Standard NAT/PAT translates only one address (typically the source IP for outbound traffic or destination IP for inbound port forwarding).

Translating only the source IP leaves the destination IP unchanged as

192.168.10.x

, which prevents proper routing over the site-to-site VPN.

Determine the required NAT technique for overlapping subnets

Select Twice NAT (Bidirectional/Overlapping NAT).

Twice NAT rewrites both the source address to a non-conflicting virtual pool address and the destination address from a dummy alias subnet to the actual destination address, enabling two-way routing between identical IP subnets.

Key Concept

Twice NAT / Overlapping NAT Implementation

Estimated Time:2m 0s

Question 1671Question →

In a switched network running standard IEEE 802.1D Spanning Tree Protocol (STP), Switch-C is connected to the Root Bridge (Switch-A) via a direct 100 Mbps link with a path cost of 19. Switch-C is also connected to Switch-B via a 1 Gbps link with a path cost of 4. Switch-B connects directly to Switch-A via a 1 Gbps link with a path cost of 4. Which port will Switch-C select as its Root Port, and what is the calculated Root Path Cost for that selection?

The port connected to Switch-B, with a calculated Root Path Cost of 8.

The port connected to Switch-A, with a calculated Root Path Cost of 19.

The port connected to Switch-B, with a calculated Root Path Cost of 4.

The port connected to Switch-A, because direct links bypass root path cost evaluations.

Show answer & explanation

Answer: The port connected to Switch-B, with a calculated Root Path Cost of 8.

Answer

The port connected to Switch-B, with a calculated Root Path Cost of 8.

Each non-root switch selects exactly one Root Port, which is the port providing the lowest cumulative path cost to the Root Bridge. The path via Switch-B totals a cost of 4 + 4 = 8, whereas the direct link to Switch-A has a cost of 19. Therefore, Switch-C designates the port connected to Switch-B as its Root Port with a Root Path Cost of 8.

Step-by-Step Solution

Determine the Root Path Cost for the direct connection from Switch-C to Switch-A.

Direct path cost = 19 (cost of the 100 Mbps link).

The cost advertised by the Root Bridge is 0, and Switch-C adds the port cost of 19.

Determine the Root Path Cost for the indirect connection from Switch-C through Switch-B to Switch-A.

Indirect path cost = 4 + 4 = 8.

Switch-B receives BPDU from Root Bridge with cost 0 and adds its link cost of 4 (advertising cost 4 to Switch-C). Switch-C then adds its local link cost of 4 to Switch-B.

Compare the path costs to select the Root Port.

8 < 19, so Switch-C selects the port leading to Switch-B as its Root Port.

STP selects the Root Port based on the lowest cumulative Root Path Cost.

Key Concept

STP Root Port Selection based on cumulative Root Path Cost

Question 1672Question →

A network monitoring engineer is configuring internal firewall rules to allow enterprise routers and switches to send unsolicited asynchronous event notifications (traps) to a centralized Network Management System (NMS). Which transport protocol and destination port must be permitted through the firewall for the NMS collector to receive these incoming trap messages?

UDP port 162

UDP port 161

TCP port 162

TCP port 161

Show answer & explanation

Answer: UDP port 162

Answer

UDP port 162 is the standard protocol and port used by Network Management System (NMS) collectors to receive SNMP Trap and Inform notifications from network agents.

Simple Network Management Protocol (SNMP) agents send unsolicited notification messages, known as Traps or Informs, to an NMS manager station over UDP port 162. UDP is chosen for its minimal protocol overhead during alert generation.

Step-by-Step Solution

Identify the specific SNMP operational communication flow described in the scenario.

The scenario specifies agent-initiated, unsolicited event notifications (traps) sent to an NMS collector.

Standard SNMP polling (GET/SET) and SNMP notifications (TRAP/INFORM) operate on different destination port numbers.

Determine the transport protocol used by SNMP messaging.

SNMP utilizes UDP due to its low overhead and connectionless nature.

Connectionless transport prevents management traffic from blocking device resources during network events.

Map the trap event direction to the standardized UDP port number.

SNMP Traps target UDP port 162 on the NMS receiver, whereas SNMP Manager queries target UDP port 161 on agents.

Distinguishing port 161 (polling listener on agents) from port 162 (trap listener on NMS) ensures correct firewall ACL directionality.

Key Concept

SNMP Port Differentiation (Polling UDP 161 vs. Traps UDP 162)

Question 1673Question →

An enterprise network needs to dynamically exchange routing information and path attributes between its own network infrastructure (Autonomous System 65100) and two distinct Internet Service Providers (AS 100 and AS 200). The solution must support path-vector routing and policy-based decisions across autonomous system boundaries. Which dynamic routing protocol should be implemented?

Border Gateway Protocol (BGP)

Open Shortest Path First (OSPF)

Routing Information Protocol (RIPv2)

Enhanced Interior Gateway Routing Protocol (EIGRP)

Show answer & explanation

Answer: Border Gateway Protocol (BGP)

Answer

Border Gateway Protocol (BGP) is the correct dynamic routing protocol for exchanging routes between different Autonomous Systems.

Border Gateway Protocol (BGP) is the standard Exterior Gateway Protocol (EGP) used across the internet to exchange routing and reachability information between independent Autonomous Systems (AS). It uses a path-vector routing algorithm and allows administrators to implement detailed routing policies.

Step-by-Step Solution

Identify the routing scope from the scenario requirements.

The requirement involves routing between distinct Autonomous Systems (AS 65100, AS 100, and AS 200).

Routing between autonomous systems requires an Exterior Gateway Protocol (EGP), whereas intra-AS routing uses Interior Gateway Protocols (IGPs).

Evaluate the path selection mechanism requested.

The protocol must use path-vector metrics and support policy-based path decisions.

Border Gateway Protocol (BGP) utilizes path vectors (such as AS-Path) to prevent routing loops and enforce policy routing across internet boundaries.

Key Concept

Exterior Gateway Protocol (EGP) vs. Interior Gateway Protocol (IGP)

Question 1674Question →

A network engineer is configuring a dual-homed router connecting a remote office to the corporate headquarters. The primary WAN connection dynamically receives routes via OSPF, while a secondary LTE backup link is configured using a static route to the same destination network ( $10.50.0.0/16$ ). The administrator wants the router to automatically prefer the OSPF route under normal operations and fall back to the static route only if the primary OSPF link fails. Given that default administrative distance (AD) values are used for OSPF, which administrative distance should the administrator manually assign to the backup static route?

110

120

Show answer & explanation

Answer: 120

Answer

The administrator should assign an administrative distance higher than OSPF's default value of 110 (such as 120) to create a floating static route that only becomes active when the primary link fails.

To configure a floating static route that serves strictly as a backup path, the static route must be configured with an Administrative Distance (AD) higher than that of the primary dynamic routing protocol. Because OSPF has a default AD of 110, setting the static route's AD to a value such as 120 ensures that the router installs the OSPF route into the routing table during normal operation. The static route will only be installed into the routing table if the primary OSPF route becomes unavailable.

Step-by-Step Solution

Identify the Administrative Distance (AD) of the primary dynamic routing protocol.

OSPF has a standard default administrative distance of 110.

Administrative distance measures the trustworthiness of a routing information source, where lower values are preferred.

Determine the required behavior for a floating static backup route.

The static route must have a higher AD than the primary route so it remains inactive in the routing table while the primary route is available.

Routers select the route with the lowest AD when multiple routes to the same destination exist.

Select the AD value that satisfies the floating static route condition.

An AD of 120 is greater than 110, ensuring OSPF is preferred first and the static route acts as a secondary failover path.

Values equal to or less than 110 would cause the static route to be preferred or tied with the primary OSPF route.

Key Concept

Floating Static Routes and Administrative Distance Hierarchy

Estimated Time:1m 30s

Question 1675Question →

An enterprise firewall is configured with Port Address Translation (PAT / NAT Overload) using a single public IP address ( $203.0.113.50$ ) to provide outbound Internet connectivity for 350 internal hosts on the $10.100.0.0/22$ subnet. The enterprise also needs external clients to access an internal HTTPS web server at $10.100.0.25$ , and needs an internal IPsec VPN gateway at $10.100.0.10$ to establish native ESP (IP protocol 50) tunnels with external business partners. Which of the following statements regarding this address translation implementation are correct? (Select TWO)

Select all that apply

A 1:1 Static NAT mapping or dedicated public IP is required for the internal IPsec gateway because standard PAT relies on Layer 4 TCP/UDP port numbers, which are not present in raw ESP (IP protocol 50) traffic.

PAT automatically multiplexes raw IP protocol 50 (ESP) traffic across internal hosts by translating Layer 2 MAC addresses during the translation process.

Static Port Forwarding (Destination PAT) can be configured to map incoming TCP port 443 requests on

203.0.113.50

directly to the internal web server at

10.100.0.25:443

Static NAT must be implemented for all 350 internal workstations because PAT cannot support more than 254 concurrent outbound host sessions using a single public IP address.

Show answer & explanation

Answer: A 1:1 Static NAT mapping or dedicated public IP is required for the internal IPsec gateway because standard PAT relies on Layer 4 TCP/UDP port numbers, which are not present in raw ESP (IP protocol 50) traffic.; Static Port Forwarding (Destination PAT) can be configured to map incoming TCP port 443 requests on $203.0.113.50$ directly to the internal web server at $10.100.0.25:443$ .

Answer

A 1:1 Static NAT mapping or dedicated public IP is required for the internal IPsec gateway because standard PAT relies on Layer 4 TCP/UDP port numbers, which are missing in raw ESP (IP protocol 50) traffic; AND Static Port Forwarding can map incoming TCP port 443 traffic on the public IP to the internal web server.

The first correct statement accurately notes that standard Port Address Translation (PAT) requires Layer 4 TCP or UDP port headers to multiplex connections. Native IPsec ESP (IP protocol 50) lacks TCP/UDP port headers, requiring a 1:1 Static NAT mapping (or NAT Traversal). The second correct statement properly identifies Static Port Forwarding as the mechanism to route incoming public TCP port 443 traffic to the internal private web server.

Step-by-Step Solution

Analyze outbound PAT capabilities and limitations for non-TCP/UDP protocols

Standard PAT (NAT Overload) inspects Layer 4 TCP/UDP ports to differentiate connections sharing a single public IP address. Raw ESP (IP protocol 50) operates at Layer 3 without Layer 4 port headers, making standard PAT unable to multiplex it without 1:1 Static NAT or NAT-T (UDP 4500 encapsulation).

Identify protocol transport requirements for IPsec ESP.

Evaluate inbound reachability for the internal HTTPS web server

Inbound TCP port 443 traffic destined for the public IP address can be statically mapped using Destination PAT (Port Forwarding) to the internal private IP address

10.100.0.25:443

Determine how to expose an internal service to external clients while using a single public IP.

Evaluate and eliminate incorrect statements

Statements claiming PAT operates at Layer 2 MAC level or limiting PAT host capacity to 254 hosts are technically false.

PAT operates at Layer 3/4 and supports ~65,000 concurrent source sockets per public IP.

Key Concept

Port Address Translation (PAT) vs Static NAT and Port Forwarding limitations

Estimated Time:2m 0s

Question 1676Question →

A network administrator is auditing the IPv4 allocation for a newly provisioned department segment assigned the network block $192.168.50.0/26$ . Which of the following statements accurately describe the addressing characteristics and host capacities for this specific subnet? (Select TWO)

Select all that apply

The usable IP address range for host interfaces on this subnet spans from

192.168.50.1

through

192.168.50.62

The subnet accommodates a maximum of

62

usable host IP addresses.

The subnet accommodates a maximum of

64

usable host IP addresses.

The IPv4 address

192.168.50.63

can be assigned as a static IP to a host device's network card.

The IPv4 address

192.168.50.64

acts as the directed broadcast address for this subnet.

Show answer & explanation

Answer: The usable IP address range for host interfaces on this subnet spans from $192.168.50.1$ through $192.168.50.62$ .; The subnet accommodates a maximum of $62$ usable host IP addresses.

Answer

The two correct statements are that the usable host address range spans from

192.168.50.1

192.168.50.62

, and the subnet accommodates a maximum of

62

usable host IP addresses.

For a /26 prefix length, there are

32 - 26 = 6

bits allocated for hosts, giving

2^6 = 64

total IP addresses per subnet block. Subtracting the network identifier (

192.168.50.0

) and the broadcast address (

192.168.50.63

) leaves exactly

62

usable host addresses spanning from

192.168.50.1

192.168.50.62

Step-by-Step Solution

Calculate host bits and total IP address count

Host bits

h = 32 - 26 = 6

. Total addresses =

2^6 = 64

CIDR /26 leaves 6 bits available for host addressing.

Calculate usable host count

Usable hosts =

2^6 - 2 = 64 - 2 = 62

The network identifier address and the directed broadcast address must be reserved.

Determine subnet boundaries and usable host IP range

Network ID:

192.168.50.0

. First usable:

192.168.50.1

. Last usable:

192.168.50.62

. Broadcast ID:

192.168.50.63

The block size is 64, ranging from .0 to .63.

Key Concept

IPv4 Subnetting and Usable Host Range Calculation

Question 1677Question →

Four switches—Switch-A, Switch-B, Switch-C, and Switch-D—are interconnected in a square physical ring topology using 1 Gbps Ethernet links (default STP path cost of 4). The switches are configured with standard IEEE 802.1D Spanning Tree Protocol using the following Bridge IDs:

- Switch-A: Priority 32768, MAC Address 00:11:22:33:44:AA
- Switch-B: Priority 32768, MAC Address 00:11:22:33:44:BB
- Switch-C: Priority 4096, MAC Address 00:11:22:33:44:CC
- Switch-D: Priority 32768, MAC Address 00:11:22:33:44:DD

Which TWO of the following statements regarding the resulting Spanning Tree Protocol (STP) topology and port roles are correct?

Select all that apply

Switch-C is elected as the Root Bridge because it has the lowest numerical Bridge Priority value.

Switch-B transitions its interface connected to Switch-D into the Blocking state to eliminate the Layer 2 loop.

Switch-A is elected as the Root Bridge because its MAC address is numerically lower than Switch-B, Switch-C, and Switch-D.

Switch-B selects its interface connected to Switch-D as its Root Port because Switch-D presents a higher MAC address.

A native VLAN mismatch across the trunk link between Switch-B and Switch-C will force all switches to immediately reset their STP port states to Forwarding.

Show answer & explanation

Answer: Switch-C is elected as the Root Bridge because it has the lowest numerical Bridge Priority value.; Switch-B transitions its interface connected to Switch-D into the Blocking state to eliminate the Layer 2 loop.

Answer

The correct statements indicate that Switch-C becomes the Root Bridge due to having the lowest bridge priority (4096), and Switch-B places its interface connected to Switch-D into the Blocking state due to higher root path cost on that segment compared to Switch-D.

The election of the Root Bridge prioritizes the lowest Bridge Priority (4096 on Switch-C vs 32768 on others). On the segment between Switch-B and Switch-D, Switch-D advertises a lower Root Path Cost (4) to the Root Bridge than Switch-B (8), making Switch-D's port Designated and causing Switch-B to block its port to prevent loops.

Step-by-Step Solution

Determine the Root Bridge election outcome.

Compare Bridge IDs (Priority + MAC). Switch-C has priority 4096; all others have priority 32768. Switch-C is elected as Root Bridge.

STP selects the switch with the lowest numerical Bridge ID, evaluating priority first.

Calculate Root Path Costs for non-root switches.

Switch-A (cost 4 direct to Switch-C), Switch-D (cost 4 direct to Switch-C), Switch-B (cost 8 via Switch-A or Switch-D).

Each 1 Gbps link adds a path cost of 4 to the cumulative distance to the Root Bridge.

Determine Root Ports for non-root switches.

Switch-A and Switch-D set their direct links to Switch-C as Root Ports. Switch-B compares upstream neighbors Switch-A (MAC 44:AA) and Switch-D (MAC 44:DD). Switch-B selects the port facing Switch-A as its Root Port.

When path costs are equal, the lower designated bridge ID is preferred.

Determine Designated and Alternate/Blocking Ports on the segment between Switch-B and Switch-D.

Switch-D has a lower root path cost (4) than Switch-B (8). Switch-D's port becomes Designated, while Switch-B's port becomes Alternate/Blocking.

On shared links, the switch advertising the lower root path cost owns the Designated Port; the other side blocks.

Key Concept

STP Root Bridge Election and Port Role Determination

Question 1678Question →

A network engineer is deploying a new dual-stack email gateway ( $mail.corp.example.com$ ) for the domain $corp.example.com$ . External mail servers are failing to deliver messages to the organization, and secondary DNS servers fail to synchronize large zone files from the primary authoritative DNS server. The engineer runs diagnostic queries and receives the following output:

text
$ dig +noall +answer mail.corp.example.com AAAA
mail.corp.example.com. 3600 IN AAAA 2001:db8:85a3::8a2e:370:7334

$ dig +noall +answer corp.example.com MX
(no output returned)

Which TWO of the following DNS infrastructure and record configuration actions must be taken to resolve mail delivery and DNS synchronization issues?

Select all that apply

Add an MX record for corp.example.com pointing to mail.corp.example.com with an appropriate preference value.

Ensure firewall rules permit TCP traffic on port 53 between primary and secondary DNS servers for zone transfers.

Create a CNAME record at the zone apex (corp.example.com) pointing directly to 2001:db8:85a3::8a2e:370:7334.

Replace the AAAA record with a PTR record in the primary forward lookup zone file.

Reconfigure DNS zone transfer traffic to use UDP port 25 to match mail delivery protocols.

Show answer & explanation

Answer: Add an MX record for corp.example.com pointing to mail.corp.example.com with an appropriate preference value.; Ensure firewall rules permit TCP traffic on port 53 between primary and secondary DNS servers for zone transfers.

Answer

To resolve mail routing and DNS zone synchronization failures, an MX record must be added pointing to mail.corp.example.com, and firewall security rules must allow TCP traffic on port 53 for zone transfers.

Mail delivery requires an explicit MX (Mail Exchanger) resource record mapping the domain to the mail gateway hostname (mail.corp.example.com). Furthermore, DNS zone transfers between primary and secondary DNS servers rely on reliable TCP transport over port 53 because zone data transfers involve multi-packet payloads.

Step-by-Step Solution

Analyze the MX lookup diagnostic output.

The dig query for MX records returned no answer, indicating external sending servers cannot identify the designated mail exchanger for corp.example.com.

Creating an MX record pointing to the mail gateway hostname with a preference integer enables external MTA routing.

Analyze the zone transfer failure requirement.

Standard DNS queries use UDP port 53, but zone transfers (AXFR/IXFR) and oversized DNS payloads require connection-oriented TCP port 53 transport.

Firewalls blocking TCP port 53 prevent secondary name servers from synchronizing zone updates from primary authoritative servers.

Key Concept

DNS Record Types and Transport Protocols

Question 1679Question →

A network technician is deploying three wireless access points (APs) to cover adjacent office areas using the 2.4 GHz frequency band. To minimize co-channel interference and maintain optimal throughput, which combination of non-overlapping channels should the technician assign to the access points?

Channels 1, 6, and 11

Channels 1, 2, and 3

Channels 2, 4, and 6

Channels 5, 10, and 15

Show answer & explanation

Answer: Channels 1, 6, and 11

Answer

Channels 1, 6, and 11

In 2.4 GHz Wi-Fi deployments, each standard 20 MHz channel occupies a frequency envelope that extends across adjacent channel numbers. To deploy multiple access points within wireless range of one another without causing adjacent-channel interference, administrators must select non-overlapping channels. In North America and standard international guidelines, channels 1, 6, and 11 are the primary three channels that do not overlap.

Step-by-Step Solution

Identify the operating frequency band and channel bandwidth requirement.

The scenario specifies the 2.4 GHz frequency band using standard 20 MHz channel widths.

Understanding the channel spacing in 2.4 GHz is necessary to determine non-overlapping frequency ranges.

Calculate the required channel separation to prevent spectral overlap.

Each 2.4 GHz channel is spaced 5 MHz apart, requiring a separation of at least 5 channel numbers (25 MHz total band width including guard bands) to avoid overlap.

Selecting non-overlapping channels ensures access points operating in close proximity do not interfere with each other.

Select the standard set of three non-overlapping 2.4 GHz channels.

Channels 1, 6, and 11 represent the three primary non-overlapping channels in standard 2.4 GHz deployments.

This configuration maximizes spatial frequency reuse without introducing adjacent-channel noise.

Key Concept

2.4 GHz Non-Overlapping Wireless Channels

Question 1680Question →

A network technician is provisioning an isolated management subnet for a server rack containing $5$ hardware management controllers. The subnet must be carved from the $192.168.45.0/24$ network block using the smallest possible prefix length that satisfies the requirement while minimizing unassigned addresses. What is the broadcast address of this newly provisioned subnet?

192.168.45.5

192.168.45.7

192.168.45.8

192.168.45.15

Show answer & explanation

Answer: $192.168.45.7$

Answer

The broadcast address of the subnet is

192.168.45.7

To host 5 devices, the formula

2^h - 2 \ge 5

yields

h = 3

host bits (

6

usable addresses), resulting in a

/29

prefix (

255.255.255.248

). The block size is

2^3 = 8

. Starting from

192.168.45.0

, the subnet encompasses addresses

192.168.45.0

through

192.168.45.7

. The highest address in the block,

192.168.45.7

, is the broadcast address.

Step-by-Step Solution

Determine the required number of host bits.

3 host bits are required.

Using the usable host formula

2^h - 2 \ge \text{hosts}

2^3 - 2 = 6

usable host addresses, which satisfies the

5

host interface requirement.

Calculate the CIDR prefix length and block size.

Prefix length is

/29

and block size is

8

32 - 3 = 29

. A

/29

subnet mask (

255.255.255.248

) allocates

2^{32-29} = 8

total IP addresses per subnet.

Find the broadcast address for the subnet starting at

192.168.45.0/29

Broadcast address is

192.168.45.7

The IP range for

192.168.45.0/29

spans from

192.168.45.0

(network ID) to

192.168.45.7

(broadcast address).

Key Concept

IPv4 Subnetting and Broadcast Address Calculation

Estimated Time:1m 30s

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