Network Implementation

424 questions

All types424 Multiple choice220 Multiple select80 Numeric11 Matching53 Ordering42 Short answer18

A network administrator is troubleshooting an issue where external email servers are unable to deliver messages to `example.com`. The administrator executes a DNS query tool to check the domain's mail configuration and receives the following output:

$ dig MX example.com +noall +answer
example.com. 3600 IN MX 10 mail.example.com.

When sending test emails, remote mail servers report a host resolution failure when attempting to reach `mail.example.com`.

Which of the following DNS resource records is missing from the authoritative zone file for `example.com`?

An A record mapping mail.example.com to its corresponding IPv4 address

A CNAME record mapping example.com directly to mail.example.com

A PTR record mapping mail.example.com to the mail server IPv4 address

An SRV record mapping port 25 on TCP to mail.example.com

Show answer & explanation

Answer: An A record mapping mail.example.com to its corresponding IPv4 address

Answer

An A record mapping mail.example.com to its corresponding IPv4 address

The MX (Mail Exchanger) record returns the hostname mail.example.com as the designated mail server for the domain. However, MX records do not contain IP addresses. For mail servers to establish a TCP connection, the DNS zone must contain a forward lookup host record (an A record for IPv4 or an AAAA record for IPv6) that maps mail.example.com to its IP address.

Step-by-Step Solution

Analyze the dig output

The MX record correctly points traffic for example.com to the host mail.example.com with priority 10.

An MX (Mail Exchanger) record maps a domain name to a fully qualified domain name (FQDN) of a mail server, not directly to an IP address.

Identify the cause of host resolution failure

Connecting servers cannot resolve the hostname mail.example.com into a Layer 3 IP address.

Without an authoritative host address record (A record for IPv4 or AAAA for IPv6) for mail.example.com, client queries for the mail server's IP address fail.

Determine the required record type to fix the issue

Add an A record mapping mail.example.com to its public IPv4 address in the zone file.

An A record provides the IPv4 address mapping required for clients to open a TCP connection to the mail server.

Key Concept

DNS MX Record and Host A Record Dependency

Question 342Question →

An enterprise administrator is finalizing the channel allocation plan for four wireless access points deployed in a linear arrangement along a long hallway to support 2.4 GHz legacy telemetry sensors. To minimize both co-channel interference (CCI) and adjacent-channel interference (ACI), which sequence of 2.4 GHz channels should be configured on the access points sequentially from one end of the hallway to the other?

Channels 1, 6, 11, and 1

Channels 1, 4, 7, and 10

Channels 1, 3, 6, and 9

Channels 2, 5, 8, and 11

Show answer & explanation

Answer: Channels 1, 6, 11, and 1

Answer

Channels 1, 6, 11, and 1

The correct answer specifies using channels 1, 6, 11, and 1. In standard 2.4 GHz Wi-Fi deployments, 20 MHz channel widths require 25 MHz separation between center frequencies to prevent spectral overlap. Channels 1, 6, and 11 are the only three non-overlapping channels available. When deploying four access points in sequence, recycling channel 1 on the fourth access point places identical channels as far apart as possible, minimizing co-channel interference.

Step-by-Step Solution

Identify the band and channel bandwidth constraints

The 2.4 GHz ISM band uses 20 MHz wide channels operating on center frequencies spaced only 5 MHz apart.

Because 20 MHz channels require 25 MHz of total spectral separation to avoid overlapping, only three channels can operate simultaneously without interfering with each other.

Determine the non-overlapping channel set

Channels 1, 6, and 11 form the industry-standard non-overlapping set.

Channel 1 spans 2.401-2.423 GHz, channel 6 spans 2.426-2.448 GHz, and channel 11 spans 2.451-2.473 GHz.

Apply frequency reuse across four sequential access points

Assign channels sequentially as 1 -> 6 -> 11 -> 1.

Placing the recycled channel 1 at the opposite end of the hallway maximizes physical distance from the first access point, keeping co-channel interference to a minimum.

Key Concept

2.4 GHz Non-Overlapping Channels and Frequency Reuse

Estimated Time:1m 15s

Question 343Question →

A network engineer is deploying IPv6 across an enterprise LAN using Stateless Address Autoconfiguration (SLAAC). A client workstation on the subnet has the physical MAC address $00:14:22:01:23:45$ . Which of the following represents the correct 64-bit interface identifier generated for this host using the modified EUI-64 format?

0214:22ff:fe01:2345

0014:22ff:fe01:2345

0214:22ff:ff01:2345

0114:22ff:fe01:2345

Show answer & explanation

Answer: 0214:22ff:fe01:2345

Answer

0214:22ff:fe01:2345

The interface identifier '0214:22ff:fe01:2345' correctly follows the modified EUI-64 conversion procedure. The MAC address 00:14:22:01:23:45 is divided into two 24-bit halves (00:14:22 and 01:23:45), the 16-bit hex string FFFE is inserted in the middle, and the 7th bit (Universal/Local bit) of the first byte is inverted from 0 to 1 (changing 0x00 to 0x02).

Step-by-Step Solution

Split the 48-bit MAC address into two 24-bit halves.

The left half is

00:14:22

and the right half is

01:23:45

Modified EUI-64 formatting requires inserting a 16-bit delimiter into the middle of the MAC address.

Insert the hex value

FFFE

between the two halves.

The combined 64-bit value becomes

0014:22FF:FE01:2345

IEEE EUI-64 specifications define

FFFE

as the expansion sequence to turn a 48-bit MAC address into a 64-bit identifier.

Invert the Universal/Local (U/L) bit, which is the 7th bit of the first byte.

The first byte

00_{16}

(

00000000_2

) with its 7th bit inverted becomes

02_{16}

(

00000010_2

), giving

0214:22ff:fe01:2345

Inverting the U/L bit designates that the generated EUI-64 IPv6 interface identifier is derived from a globally unique IEEE MAC address.

Key Concept

Modified EUI-64 Interface Identifier Generation

Estimated Time:1m 30s

Question 344Question →

A network engineer is configuring DNS infrastructure to support an enterprise Voice over IP (VoIP) deployment. Automatic phone provisioning requires locating the Session Initiation Protocol (SIP) service and subsequently resolving the designated server hostname to its assigned IPv4 address. The engineer executes the following diagnostic query:

$ dig _sip._tcp.voip.net.corp SRV +short
10 60 5061 pbx-01.voip.net.corp.

Based on this output and deployment requirement, which TWO of the following DNS record types are required for successful service discovery and host reachability?

Select all that apply

SRV record to specify the service location, port 5061, and target hostname pbx-01.voip.net.corp

A record to resolve the target hostname pbx-01.voip.net.corp to its 32-bit IPv4 address

CNAME record to create an alias redirecting IP traffic directly to TCP port 5061

PTR record to handle forward service port mapping over UDP port 53

MX record to manage session negotiation protocols on TCP port 25

Show answer & explanation

Answer: SRV record to specify the service location, port 5061, and target hostname pbx-01.voip.net.corp; A record to resolve the target hostname pbx-01.voip.net.corp to its 32-bit IPv4 address

Answer

The SRV record and A record are both required to achieve full service discovery and hostname resolution.

VoIP clients rely on SRV records to discover the service port and target server hostname, and subsequently rely on an A record to resolve that target hostname to its corresponding IPv4 address.

Step-by-Step Solution

Analyze the service discovery query requirement

The query requires discovering the protocol, port, and hostname associated with the SIP VoIP service.

SRV records are designed specifically to publish service location parameters, including priority, weight, port (5061), and target hostname.

Identify the hostname resolution requirement

The SRV query returns the target domain name pbx-01.voip.net.corp.

Network clients require a standard A record to map this returned canonical hostname to a usable 32-bit IPv4 address for IP routing.

Key Concept

DNS SRV and A record pairing for network service auto-discovery

Question 345Question →

In an enterprise network running standard IEEE 802.1D Spanning Tree Protocol (STP), Switch-1 serves as the Root Bridge. Two non-root switches, Switch-2 and Switch-3, are directly connected to each other over a point-to-point Gigabit Ethernet link via port FastEthernet 0/1 on both switches. Both Switch-2 and Switch-3 have an identical Root Path Cost of 19. Switch-2 has a Bridge ID of 32768:00-11-22-AA-BB-CC, while Switch-3 has a Bridge ID of 32768:00-11-22-11-22-33. Which switch interface will be elected as the Designated Port for this inter-switch link segment and remain in the Forwarding state?

Switch-3 FastEthernet 0/1, because both switches have equal Root Path Costs and Switch-3 has the lower MAC address in its Bridge ID.

Switch-2 FastEthernet 0/1, because Switch-2 has a higher numerical MAC address value which takes precedence during STP tiebreaker evaluation.

Switch-2 FastEthernet 0/1, because it blocks untagged frames when a native VLAN mismatch occurs across the link segment.

Both interfaces enter the Blocking state automatically to isolate traffic and prevent a potential Layer 2 loop on the segment.

Show answer & explanation

Answer: Switch-3 FastEthernet 0/1, because both switches have equal Root Path Costs and Switch-3 has the lower MAC address in its Bridge ID.

Answer

Switch-3 FastEthernet 0/1 is elected as the Designated Port because both switches have equal Root Path Costs (

19

) and Switch-3 has the lower MAC address (

00\text{-}11\text{-}22\text{-}11\text{-}22\text{-}33 < 00\text{-}11\text{-}22\text{-}\text{AA}\text{-}\text{BB}\text{-}\text{CC}

For every network segment, STP must elect one Designated Port that forwards traffic. The election process follows a strict hierarchy: 1) Lowest Root Path Cost, 2) Lowest Sender Bridge ID (Priority + MAC), 3) Lowest Sender Port ID. Since both switches have a Root Path Cost of 19 and identical Bridge Priorities (32768), STP evaluates the MAC addresses. Switch-3's MAC address (00-11-22-11-22-33) is lower than Switch-2's MAC address (00-11-22-AA-BB-CC), making Switch-3's interface the Designated Port in the Forwarding state.

Step-by-Step Solution

Evaluate the Root Path Cost for both switches connected to the network segment.

Both Switch-2 and Switch-3 have an identical Root Path Cost of 19.

STP first compares Root Path Costs to elect the Designated Port on a network segment.

Compare the Sender Bridge IDs of Switch-2 and Switch-3 since the Root Path Costs are equal.

Bridge Priorities are identical (

32768

). Comparing MAC addresses shows

00\text{-}11\text{-}22\text{-}11\text{-}22\text{-}33

(Switch-3) is lower than

00\text{-}11\text{-}22\text{-}\text{AA}\text{-}\text{BB}\text{-}\text{CC}

(Switch-2).

When Root Path Costs tie, the switch with the lowest Bridge ID (Priority + MAC) wins the election.

Determine the port roles on the link segment.

Switch-3 FastEthernet 0/1 becomes the Designated Port (Forwarding state), and Switch-2 FastEthernet 0/1 becomes the Non-Designated/Alternate Port (Blocking state).

Each active segment must have exactly one Designated Port to forward frames while preventing Layer 2 loops.

Key Concept

STP Designated Port Election and Tiebreaking Rules

Question 346Question →

A network administrator is deploying a secondary authoritative DNS server to provide redundancy for the domain `corp.example.com`. While standard client queries resolve properly across the internal network, full zone transfers between the primary server (`10.0.1.50`) and the secondary server (`10.0.2.50`) consistently fail. Executing `dig @10.0.1.50 corp.example.com AXFR` from the secondary server results in the following output:

text
;; Connection to 10.0.1.50#53(10.0.1.50) for corp.example.com failed: connection refused.

Standard single-record DNS queries using UDP port 53 succeed without issue. Which firewall modification will resolve the zone transfer failure?

Permit traffic between the primary and secondary DNS servers on TCP port 53.

Permit traffic between the primary and secondary DNS servers on UDP port 53.

Permit traffic between the primary and secondary DNS servers on UDP port 5353.

Configure a CNAME record mapping the primary server IP address to the secondary server hostname.

Show answer & explanation

Answer: Permit traffic between the primary and secondary DNS servers on TCP port 53.

Answer

Permit traffic between the primary and secondary DNS servers on TCP port 53.

Allowing TCP port 53 enables the primary and secondary DNS servers to establish a reliable stream connection. DNS zone transfers (AXFR/IXFR) transport large volumes of resource records and require the reliability and packet ordering of TCP, whereas standard client resolution queries utilize UDP.

Step-by-Step Solution

Analyze the diagnostic command and failure output

The command `dig @10.0.1.50 corp.example.com AXFR` tests an Authoritative Zone Transfer (AXFR). The output indicates a connection failure on port 53, even though UDP queries succeed.

Standard lookups use UDP port 53, whereas AXFR zone transfers require TCP port 53 due to data size and reliability requirements.

Identify transport protocol requirements for DNS operations

DNS uses UDP/53 for small, fast queries/responses, but requires TCP/53 for zone transfers (AXFR/IXFR) and responses exceeding standard buffer sizes.

TCP guarantees reliable delivery and stream control when synchronizing entire DNS zone files between primary and secondary name servers.

Select the appropriate firewall rule update

Allowing TCP port 53 traffic between `10.0.1.50` and `10.0.2.50` will permit successful zone synchronization.

Opening TCP port 53 solves the underlying transport block preventing AXFR requests from completing.

Key Concept

DNS Transport Protocols (UDP vs TCP Port 53) and Zone Transfers

Question 347Question →

A network technician is deploying three wireless access points across a single-floor office space to provide coverage on the 2.4 GHz frequency band. To minimize co-channel interference and avoid adjacent-channel overlap while maintaining stable connectivity, which of the following deployment configurations should the technician implement? (Select TWO.)

Select all that apply

Assign the access points to channels 1, 6, and 11 respectively.

Set the channel width on all 2.4 GHz access points to 20 MHz.

Assign the access points to channels 1, 3, and 5 to keep frequencies closely grouped.

Enable 40 MHz channel bonding on all access points to double theoretical throughput.

Assign the access points to channels 2, 7, and 12 to avoid default factory settings.

Show answer & explanation

Answer: Assign the access points to channels 1, 6, and 11 respectively.; Set the channel width on all 2.4 GHz access points to 20 MHz.

Answer

The technician should assign the access points to channels 1, 6, and 11, and configure all 2.4 GHz access points to a 20 MHz channel width.

In 2.4 GHz Wi-Fi deployments, using channels 1, 6, and 11 ensures that adjacent access points operate without spectrum overlap. Restricting the channel bandwidth to 20 MHz preserves these non-overlapping boundaries, preventing co-channel and adjacent-channel interference across the multi-AP environment.

Step-by-Step Solution

Identify the non-overlapping channel scheme for the 2.4 GHz band

Channels 1, 6, and 11 are identified as the primary 20 MHz non-overlapping channels.

The 2.4 GHz band has 11 usable channels in standard regulatory regions, each 20 MHz wide with 5 MHz spacing, meaning only channels 1, 6, and 11 do not overlap.

Determine the appropriate channel width configuration

A 20 MHz channel width is selected for all access points.

Bonding to 40 MHz in 2.4 GHz leaves insufficient spectrum for three distinct APs without mutual interference.

Key Concept

2.4 GHz Non-Overlapping Channels and Channel Bandwidth Selection

Question 348Question →

A network administrator is configuring a 2.4 GHz wireless network deployment for a single-floor medical clinic featuring four access points arranged in a square grid formation. To minimize interference between adjacent wireless cells, which channel assignment strategy should the administrator implement?

Assign the access points to channels 1, 6, 11, and reuse channel 1 on the access point located diagonally farthest from the first channel 1 access point.

Assign the access points to channels 1, 3, 6, and 9 to evenly spread out the numerical channel values across the available frequency spectrum.

Assign all four access points to channel 6 while setting transmit power to maximum to enforce a unified channel architecture.

Assign the access points to channels 2, 5, 8, and 11 to maintain a consistent three-channel spacing interval between access point cells.

Show answer & explanation

Answer: Assign the access points to channels 1, 6, 11, and reuse channel 1 on the access point located diagonally farthest from the first channel 1 access point.

Answer

Assign the access points using non-overlapping channels 1, 6, and 11, while reusing channel 1 on the access point located diagonally farthest from the original channel 1 deployment.

In the 2.4 GHz spectrum, 20 MHz wide channels require a 5-channel separation to avoid overlapping. Channels 1, 6, and 11 are the primary non-overlapping channels. When deploying four access points, assigning channels 1, 6, and 11 to three APs and placing the reused channel 1 on the diagonally opposite AP maximizes physical distance, suppressing co-channel interference while eliminating adjacent-channel interference.

Step-by-Step Solution

Identify the frequency band and channel availability.

The 2.4 GHz Wi-Fi spectrum (802.11b/g/n) consists of 11 channels in North America, each spaced 5 MHz apart with a 20 MHz or 22 MHz channel width.

Because channels overlap if separated by less than 5 channel numbers, only channels 1, 6, and 11 provide zero spectral overlap.

Evaluate the grid topology for access point channel allocation.

With four access points in a 2x2 square grid, three non-overlapping channels (1, 6, 11) can be assigned to three adjacent APs.

The fourth AP must reuse one of the three non-overlapping channels.

Determine the optimal channel reuse placement.

Reusing channel 1 on the diagonally opposite access point maximizes the physical separation distance between identical channels.

Physical separation mitigates co-channel interference (CCI) while completely preventing adjacent-channel interference (ACI).

Key Concept

2.4 GHz Non-Overlapping Channel Selection and Co-Channel Interference Mitigation

Question 349Question →

Match each IPv6 address or prefix to its corresponding deployment scope and functional classification.

Click a left item, then click its matching right item

Show answer & explanation

Answer

2001:db8:3c4d:15::/64 matches Publicly routable address used for global internet connectivity; fe80::1a2b:3c4d:5e6f matches Non-routable link address required for local segment communication; fd12:3456:789a:1::1 matches Internally routable address designated for private site communication; ff02::1:ff00:1234 matches Multicast address utilized for IPv6 Neighbor Discovery address resolution.

Each specified IPv6 address or prefix corresponds to a distinct deployment classification: 2001:db8:: represents Global Unicast, fe80:: represents Link-Local, fd12:: represents Unique Local, and ff02::1:ff00:: represents Solicited-Node Multicast.

Step-by-Step Solution

Examine the prefix range of 2001:db8:3c4d:15::/64.

Identified as a Global Unicast Address (GUA).

The 2000::/3 prefix range is designated for publicly routable global unicast communication.

Examine the prefix range of fe80::1a2b:3c4d:5e6f.

Identified as a Link-Local address.

The fe80::/10 block specifies non-routable link-local traffic restricted to a single network segment.

Examine the prefix range of fd12:3456:789a:1::1.

Identified as a Unique Local Address (ULA).

The fc00::/7 (fd00::/8) range provides private enterprise routing capabilities similar to IPv4 RFC 1918 addresses.

Examine the prefix range of ff02::1:ff00:1234.

Identified as a Solicited-Node Multicast address.

The ff02::1:ff00:0/104 range is generated from the last 24 bits of a node's IPv6 address for NDP address resolution.

Key Concept

IPv6 Address Types, Prefixes, and Deployment Scopes

Question 350Question →

Match each IEEE 802.11 wireless standard on the left with its defining operational frequency and technological capability on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

IEEE 802.11ax matches the dual-band OFDMA/TWT description; IEEE 802.11ac Wave 2 matches the 5 GHz downlink MU-MIMO and 160 MHz bonding description; IEEE 802.11n matches the pioneer dual-band MIMO technology description; and IEEE 802.11g matches the 2.4 GHz 54 Mbps OFDM description.

Each IEEE 802.11 standard is accurately paired with its primary frequency spectrum and signature channel access/antenna technologies. 802.11ax utilizes dual-band OFDMA and TWT; 802.11ac Wave 2 utilizes 5 GHz MU-MIMO and 160 MHz channels; 802.11n introduced dual-band MIMO; and 802.11g provided 54 Mbps 2.4 GHz OFDM.

Step-by-Step Solution

Identify operating frequency support for each standard

IEEE 802.11ac is strictly 5 GHz; IEEE 802.11g is strictly 2.4 GHz; IEEE 802.11n and 802.11ax support dual-band operations.

Frequency bands separate single-band specifications (802.11g and 802.11ac) from dual-band specifications (802.11n and 802.11ax).

Distinguish single-band standards based on modulation and features

802.11g offers 54 Mbps via OFDM on 2.4 GHz. 802.11ac provides downlink MU-MIMO and 160 MHz channels on 5 GHz.

802.11g is legacy 2.4 GHz OFDM, whereas 802.11ac focuses on high-throughput 5 GHz capabilities.

Differentiate dual-band standards based on core PHY enhancements

802.11n introduced baseline MIMO, while 802.11ax introduced OFDMA and Target Wake Time.

OFDMA and TWT are key innovations of Wi-Fi 6 (802.11ax), whereas spatial multiplexing via basic MIMO originated in Wi-Fi 4 (802.11n).

Key Concept

Wireless Standards & Frequency Specifications

Question 351Question →

A workstation on an enterprise network needs to resolve the fully qualified domain name `app.partner-net.com` for the first time, starting with an empty local DNS cache. Place the steps of the standard DNS resolution process in the correct chronological order, from the initial client request to the final IP address response.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct chronological sequence for resolving an uncached domain name is: 1) Client stub resolver sends a recursive query to the local DNS server, 2) Local resolver sends an iterative query to a Root Name Server, 3) Root Name Server responds with a referral to the TLD Name Server, 4) Local resolver queries the TLD Name Server and receives a referral to the Authoritative Name Server, and 5) Local resolver queries the Authoritative Name Server to receive the final host A record mapping and sends it back to the client.

DNS resolution follows a top-down hierarchical tree structure when no cached records exist. The client sends a recursive query to its configured local recursive resolver. The local resolver then performs iterative queries by first asking a Root Name Server (`.`), receiving a referral to the `.com` TLD server, asking the TLD server, receiving a referral to the domain's authoritative server, and finally querying the authoritative server to obtain the final Host (A) record mapping.

Step-by-Step Solution

Client initiates request

Recursive query sent to local recursive resolver

The client application (e.g., web browser) invokes the stub resolver to resolve `app.partner-net.com`.

Local resolver queries Root hierarchy

Iterative query sent to Root server (`.`)

The local recursive server assumes responsibility for resolving the query step-by-step starting at the DNS root.

Root server refers to TLD

Referral to `.com` TLD name servers received

Root servers hold delegations for top-level domains and direct the query to the `.com` infrastructure.

Resolver queries TLD server

Referral to authoritative server for `partner-net.com` received

TLD servers maintain records for domain registrations within their top-level domain and delegate responsibility to the domain's specified name servers.

Resolver queries Authoritative server

Final A record received and delivered to client

The authoritative server contains the master zone record (A record) for `app.partner-net.com`, providing the definitive IP address mapping.

Key Concept

Recursive vs. Iterative DNS Resolution Hierarchy Flow

Question 352Question →

A network administrator is configuring DNS records for an enterprise web service. The administrator needs to map the alias hostname `portal.corp.example.com` to the primary canonical domain name `webserver01.corp.example.com`, which ultimately resolves to IPv4 address `10.50.10.15`.

Review the DNS lookup query output below:

text
$ dig portal.corp.example.com

;; QUESTION SECTION:
;portal.corp.example.com. IN A

;; ANSWER SECTION:
portal.corp.example.com. 300 IN ???? webserver01.corp.example.com.
webserver01.corp.example.com. 300 IN A 10.50.10.15

Which DNS record type is represented by `????` in the lookup response?

CNAME

PTR

SRV

Show answer & explanation

Answer: CNAME

Answer

The CNAME record type is used to map an alias domain name (portal.corp.example.com) to a canonical domain name (webserver01.corp.example.com).

A CNAME (Canonical Name) record is used in DNS to create an alias pointing one domain name to another true (canonical) domain name. In the provided dig output, portal.corp.example.com points to webserver01.corp.example.com, which subsequently resolves to IP address 10.50.10.15.

Step-by-Step Solution

Analyze the query output structure

The query requests an A record for portal.corp.example.com, but the first entry in the answer section maps portal.corp.example.com directly to another domain name (webserver01.corp.example.com).

Understanding how DNS chains resolutions requires examining the record relationship between the requested name and target name.

Identify the record type function

The record type that aliases one fully qualified domain name (FQDN) to another canonical FQDN is a Canonical Name (CNAME) record.

CNAME records allow multiple alias hostnames to point to a single canonical record without needing separate A/AAAA records for each host.

Key Concept

DNS Record Types and Functionality (CNAME vs. PTR/SRV/NS)

Estimated Time:1m 0s

Question 353Question →

A network engineer is designing a wireless deployment for a high-density corporate auditorium intended to support up to 500 active user devices simultaneously. Initial deployment testing reveals severe co-channel interference (CCI) and degraded throughput despite strong signal coverage throughout the room. Which TWO configuration changes should the engineer implement to mitigate CCI and optimize performance in this high-density environment?

Select all that apply

Reduce the radio transmit power (

Tx

power) on the access points to shrink individual cell sizes.

Disable legacy low data rates (such as

1\text{ Mbps}

and

2\text{ Mbps}

) to decrease management frame overhead and airtime utilization.

Increase the channel bonding width from

20\text{ MHz}

80\text{ MHz}

across all

2.4\text{ GHz}

and

5\text{ GHz}

access points.

Assign adjacent access points to overlapping

2.4\text{ GHz}

channels such as channels 2, 4, and 8 to spread out frequency usage.

Set omnidirectional antenna gain to maximum power on all access points to maximize coverage reach.

Show answer & explanation

Answer: Reduce the radio transmit power ( $Tx$ power) on the access points to shrink individual cell sizes.; Disable legacy low data rates (such as $1\text{ Mbps}$ and $2\text{ Mbps}$ ) to decrease management frame overhead and airtime utilization.

Answer

The two correct configuration changes are reducing radio transmit power on access points to shrink cell sizes and disabling low legacy data rates to minimize management frame overhead.

In high-density wireless deployments, optimizing performance requires mitigating co-channel interference (CCI) and maximizing airtime efficiency. Reducing access point transmit power shrinks coverage cell radii so adjacent access points operating on the same channel do not overlap or interfere. Additionally, disabling slow legacy data rates (such as

1\text{ Mbps}

2\text{ Mbps}

) reduces management frame overhead transmitted at low data rates and forces client devices to disconnect and roam to closer access points when signal quality degrades.

Step-by-Step Solution

Analyze the high-density deployment problem

Identified co-channel interference (CCI) and high airtime utilization as primary root causes of performance degradation.

When many APs operate in close proximity, large cell footprints cause APs on the same channel to hear each other and contend for airtime.

Evaluate cell sizing strategies

Lowering

Tx

power shrinks RF cell boundaries.

Smaller cell footprints allow frequency reuse without RF overlap between access points on identical channels.

Evaluate airtime efficiency measures

Disabling legacy data rates (

1\text{ Mbps}

2\text{ Mbps}

5.5\text{ Mbps}

) forces higher data rate modulations.

Management frames (beacons, probe responses) transmitted at basic rates consume significant medium time; disabling slow rates frees up channel capacity.

Key Concept

High-density wireless network optimization requires reducing AP cell size via transmit power tuning and disabling legacy basic data rates to control co-channel interference and airtime contention.

Question 354Question →

A network administrator is documenting the primary gateway interface for a newly provisioned IPv6 network segment. The central management portal requires all IPv6 host addresses to be recorded strictly following the RFC 5952 canonical representation standard. The interface has been assigned the uncompressed address $2001:0db8:0000:0000:00ab:0000:0000:0001/64$ . Which of the following options represents the correct RFC 5952 compressed format for this address?

2001:db8::ab:0:0:1/64

2001:db8:0:0:ab::1/64

2001:db8::ab::1/64

2001:0db8::ab:0:0:1/64

Show answer & explanation

Answer: 2001:db8::ab:0:0:1/64

Answer

The correct RFC 5952 representation of the IPv6 address is 2001:db8::ab:0:0:1/64.

According to RFC 5952, canonical compression requires removing leading zeros from every 16-bit hextet (reducing '0db8' to 'db8', '00ab' to 'ab', and '0001' to '1'). When an address contains two separate sequences of zero fields of equal length (in this case, two runs of two zero hextets), the double-colon (::) must compress the first sequence on the left. This yields the canonical format 2001:db8::ab:0:0:1/64.

Step-by-Step Solution

Suppress leading zeros in all 16-bit hex fields (hextets).

2001:0db8:0000:0000:00ab:0000:0000:0001 becomes 2001:db8:0:0:ab:0:0:1.

RFC 5952 mandates that leading zeros within each 16-bit field must be removed (e.g., 0db8 becomes db8, 00ab becomes ab, 0000 becomes 0, and 0001 becomes 1).

Identify candidate consecutive zero sequences for double-colon (::) compression.

Two separate zero runs of equal length exist: fields 3-4 (0:0) and fields 6-7 (0:0).

The double-colon symbol can only be used once in an IPv6 address to represent consecutive zero fields.

Apply RFC 5952 tie-breaking rules for equal-length zero sequences.

Compress the first zero sequence (fields 3-4), producing 2001:db8::ab:0:0:1/64.

RFC 5952 Section 4.2.3 explicitly specifies that when multiple zero sequences of equal maximum length exist, the first sequence must be compressed.

Key Concept

RFC 5952 IPv6 Address Canonical Representation and Compression Rules

Question 355Question →

Match each DNS resource record type to its primary administrative function within an enterprise network infrastructure.

Click a left item, then click its matching right item

Show answer & explanation

Answer

SRV matches service location with host and port information; PTR matches reverse DNS IP-to-hostname mapping; TXT matches text data storage for email security mechanisms like SPF and DKIM; MX matches designation of recipient mail servers.

Each record type handles distinct DNS functionalities: SRV specifies service endpoints with port numbers; PTR maps IP addresses to hostnames in reverse lookups; TXT contains arbitrary text payloads used primarily for domain authentication like SPF and DKIM; MX designates the authoritative mail processing servers for a domain.

Step-by-Step Solution

Analyze the function of SRV records

SRV records include both target hostnames and destination port numbers.

Applications like VoIP (SIP) and Active Directory rely on SRV records to discover service endpoints on custom ports.

Analyze the function of PTR records

PTR records perform reverse DNS resolution in pointer zones.

PTR maps an IP address to a fully qualified domain name (FQDN).

Analyze the function of TXT records

TXT records carry text payload for domain validation and mail security.

Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) records are published within TXT record fields.

Analyze the function of MX records

MX records specify designated mail servers for a domain.

SMTP servers query MX records to route incoming messages to the correct destination host.

Key Concept

DNS Resource Record Types and Functions

Question 356Question →

A network technician is performing an audit on core router configuration files and identifies an uncompressed Unique Local IPv6 Address (ULA) recorded in full hexadecimal format as `fd12:0000:0000:a1b2:0000:0000:0000:0099`. To ensure compliance with enterprise documentation guidelines, the technician must format this address according to standard RFC 5952 rules. What is the correctly compressed RFC 5952 representation of this IPv6 address?

Show answer & explanation

Answer: fd12:0:0:a1b2::99

Answer

fd12:0:0:a1b2::99

Under RFC 5952 rules, leading zeros in every 16-bit hexadecimal field are suppressed, reducing `0000` to `0` and `0099` to `99`. When multiple zero runs exist, the double colon `::` must replace the single longest contiguous run of zero fields. In `fd12:0000:0000:a1b2:0000:0000:0000:0099`, the first zero run spans 2 fields (`0:0`) and the second zero run spans 3 fields (`0:0:0`). Compressing the longer 3-field sequence yields `fd12:0:0:a1b2::99`.

Step-by-Step Solution

Suppress leading zeros in each 16-bit hexadecimal field.

fd12:0:0:a1b2:0:0:0:99

RFC 5952 Section 4.1 mandates that leading zeros in a 16-bit field must be removed (e.g., '0000' becomes '0' and '0099' becomes '99').

Identify all contiguous sequences of all-zero 16-bit fields.

Sequence 1 has 2 zero fields ('0:0'); Sequence 2 has 3 zero fields ('0:0:0').

To apply double-colon ('::') compression properly, the lengths of all consecutive zero runs must be evaluated.

Apply double-colon ('::') compression strictly to the longest sequence of zero fields.

fd12:0:0:a1b2::99

RFC 5952 Section 4.2.2 requires that '::' must replace the single longest run of consecutive zero fields. Sequence 2 (3 fields) is longer than Sequence 1 (2 fields).

Key Concept

RFC 5952 IPv6 Address Text Representation and Zero Compression Rules

Estimated Time:1m 0s

Question 357Question →

A network administrator is troubleshooting a reverse DNS resolution failure for an internal database server with IP address $192.168.10.45$ . The administrator executes a diagnostic command on a client workstation and receives the following output:

text
$ dig -x 192.168.10.45

;; QUESTION SECTION:
;45.10.168.192.in-addr.arpa. IN PTR

;; ANSWER SECTION:

;; AUTHORITY SECTION:
10.168.192.in-addr.arpa. 3600 IN SOA ns1.corp.internal. admin.corp.internal. 2026072701 7200 3600 1209600 3600

;; SERVER: 192.168.10.2#53(192.168.10.2)

Based on the diagnostic output, which of the following DNS configuration changes is required on the authoritative server to resolve the query successfully?

Add a PTR record mapping

45.10.168.192.in-addr.arpa.

to the database server's fully qualified domain name (FQDN).

Add an A record mapping the database server's hostname directly to the IP address

192.168.10.45

in the forward lookup zone.

Configure a dynamic CNAME record to map port 53 DNS query requests directly to port 80 HTTP services.

Reconfigure the client resolver to force TCP transport instead of UDP for standard reverse query lookups on port 53.

Show answer & explanation

Answer: Add a PTR record mapping $45.10.168.192.in-addr.arpa.$ to the database server's fully qualified domain name (FQDN).

Answer

Add a PTR record mapping

45.10.168.192.in-addr.arpa.

to the database server's fully qualified domain name (FQDN).

The `dig -x` diagnostic tool requests a reverse DNS lookup for an IP address. The command output shows a query for `

45.10.168.192.in-addr.arpa.

`. Because the server returns an AUTHORITY section with an SOA record but no ANSWER section, the reverse lookup zone is present on the server, but the specific PTR record for host address

192.168.10.45

has not been configured.

Step-by-Step Solution

Analyze the command and query type

The `dig -x 192.168.10.45` command initiates a reverse DNS lookup, requesting a Pointer (PTR) record for the domain `

45.10.168.192.in-addr.arpa.

Reverse DNS resolution queries the `.in-addr.arpa` domain hierarchy using octets reversed.

Inspect the query output sections

The ANSWER section is empty, while the AUTHORITY section provides the SOA record for the zone `10.168.192.in-addr.arpa.`.

An empty ANSWER section with an authoritative SOA response indicates the server is authoritative for the zone, but no resource record matching `

45.10.168.192.in-addr.arpa.

` exists.

Identify the required record creation

Create a PTR record for host

45

within the

10.168.192.in-addr.arpa.

reverse zone pointing to the canonical FQDN.

PTR records perform IP address-to-hostname resolution.

Key Concept

Reverse DNS Resolution and PTR Records

Question 358Question →

A network administrator is deploying a wireless network across a multi-story office building. Due to high access point density, multiple access points on different floors must share the same $5\text{ GHz}$ channel, resulting in co-channel interference (CCI) and contention delays. Which feature introduced in the IEEE 802.11ax standard enables access points to identify overlapping basic service sets and transmit simultaneously over shared channels when preamble energy levels are below a color-aware threshold?

BSS Coloring

Dynamic Frequency Selection (DFS)

Orthogonal Frequency-Division Multiple Access (OFDMA)

Explicit Transmit Beamforming

Show answer & explanation

Answer: BSS Coloring

Answer

BSS Coloring is the Wi-Fi 6 (802.11ax) spatial reuse mechanism designed to differentiate traffic from overlapping basic service sets on the same channel.

The correct option is BSS Coloring. In IEEE 802.11ax (Wi-Fi 6), BSS Coloring adds a 6-bit identifier (color code) to the preamble of wireless frames. This mechanism enables wireless devices to distinguish between frame transmissions from their own network and neighboring overlapping networks on the same channel. When a frame from an overlapping network is detected with a different 'color', the receiver can adjust its adaptive signal detection threshold, enabling simultaneous transmissions (spatial reuse) and significantly mitigating co-channel interference.

Step-by-Step Solution

Identify the primary network performance issue

Co-channel interference (CCI) caused by overlapping access points operating on identical frequency channels.

When access points share a channel, legacy Wi-Fi contention (CSMA/CA) forces devices to defer transmission whenever any preamble on that channel is detected above the clear channel assessment (CCA) threshold.

Analyze the features introduced in IEEE 802.11ax for spatial reuse

802.11ax introduces BSS Coloring, which attaches a 6-bit color field to the PHY header of frames.

This allows a client or AP to distinguish between its own basic service set (my BSS) and a neighboring BSS (overlapping BSS). If the frame is from an overlapping BSS and below a secondary energy threshold, the device can transmit concurrently.

Key Concept

BSS Coloring and Spatial Reuse in IEEE 802.11ax

Question 359Question →

An enterprise systems engineer is resolving name lookup and mail transport issues for the internal domain `hr.enterprise.internal`. The engineer executes the following diagnostic command to inspect the domain's resource records:

$ dig +noall +answer hr.enterprise.internal MX
hr.enterprise.internal. 3600 IN MX 10 smtp1.enterprise.internal.

A subsequent lookup query directed to `smtp1.enterprise.internal` returns no address records, preventing mail transfer agents from connecting to the server.

Based on standard DNS infrastructure requirements and protocol operations, which TWO of the following configurations or administrative actions are required to restore proper functionality?

Select all that apply

Add an A or AAAA record for host `smtp1.enterprise.internal` mapping the hostname to the mail server's IP address.

Ensure that network firewall rules permit client and server traffic on UDP port 53 for standard DNS name resolution queries.

Replace the MX record entry with a CNAME record pointing directly to the target IP address of the mail host.

Configure DNS client resolvers to send name resolution queries to the DNS server using TCP port 25.

Require all client DNS host resolution queries to use TCP port 53 exclusively because UDP is reserved strictly for zone transfers.

Show answer & explanation

Answer: Add an A or AAAA record for host `smtp1.enterprise.internal` mapping the hostname to the mail server's IP address.; Ensure that network firewall rules permit client and server traffic on UDP port 53 for standard DNS name resolution queries.

Answer

The resolution requires adding an A or AAAA record mapping `smtp1.enterprise.internal` to its IP address, and ensuring firewalls permit UDP port 53 traffic for standard DNS name queries.

Mail Exchanger (MX) records point to host domain names rather than IP addresses directly. Consequently, an A record (for IPv4) or an AAAA record (for IPv6) must exist for the specified target hostname so that clients can resolve the mail server's IP address. Additionally, DNS name resolution relies on UDP port 53 for standard client query and response traffic.

Step-by-Step Solution

Analyze the MX record output from the diagnostic lookup.

The MX record points to the hostname `smtp1.enterprise.internal` as the designated mail server.

An MX record only specifies the domain name of the mail gateway, requiring an underlying address record to determine the target IP.

Identify the missing host address record required to complete host resolution.

An A record (IPv4) or AAAA record (IPv6) must be configured for `smtp1.enterprise.internal`.

Without an A/AAAA record, mail transfer agents cannot translate the host domain name returned by the MX query into a network layer IP address.

Identify the proper protocol and port configuration for DNS service traffic.

Ensure UDP port 53 is open and accessible.

Standard iterative and recursive DNS queries rely on UDP port 53 for lightweight, low-overhead communication.

Key Concept

DNS MX Record Host Resolution Dependency and Core DNS Port/Protocol Operation

Question 360Question →

A network technician is preparing antenna hardware for various deployment zones across a new corporate campus facility. Match each antenna type on the left with its corresponding radiation pattern and primary deployment scenario on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Omnidirectional Antenna pairs with 360-degree central ceiling coverage; Patch Antenna pairs with semi-directional wall coverage for hallways; Parabolic Dish Antenna pairs with narrow high-gain beam for long-distance point-to-point outdoor links; Yagi Antenna pairs with directional moderate-gain coverage for point-to-multipoint links.

Each antenna type is uniquely matched to its radiation geometry: omnidirectional antennas broadcast 360 degrees indoors; patch antennas provide semi-directional coverage along flat walls/hallways; parabolic dish antennas generate focused high-gain beams for long-range point-to-point bridges; and Yagi antennas provide directional moderate-gain coverage for outdoor links.

Step-by-Step Solution

Analyze the radiation pattern requirement for general indoor open office spaces.

Central indoor coverage requires equal signal distribution in all horizontal directions (360 degrees), matching the omnidirectional antenna pattern.

Ceiling-mounted access points in the middle of a floor plan rely on omnidirectional radiation to reach clients surrounding the access point.

Analyze corridor and wall-mounted indoor directional needs.

A wall-mounted deployment directing signal along a hallway requires semi-directional coverage, matching the patch antenna.

Patch antennas prevent RF energy from radiating into wall spaces behind the antenna and focus energy forward.

Differentiate between outdoor directional antennas based on distance and beamwidth focal properties.

Extremely narrow beamwidth over long distances requires a high-gain parabolic dish, while moderate directional links utilize a Yagi antenna.

Parabolic reflector dishes maximize gain and minimize beam dispersion across multi-kilometer point-to-point links.

Key Concept

Wireless Antenna Types, Radiation Patterns, and Deployment Scenarios

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