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Question 101Question →

A network administrator is evaluating the operation of DNS protocol mechanisms and transport layer behavior within an enterprise network infrastructure. Which two statements accurately describe how DNS lookup processes and transport protocols function during name resolution? (Choose two.)

Select all that apply

Show answer & explanation

Answer: Standard DNS queries for IP address resolution (A or AAAA records) typically utilize UDP port 53 to reduce latency and connection overhead.; When a DNS response payload exceeds 512 bytes without EDNS0 support, the server sets the TrunCation (TC) bit, prompting the client to re-query using TCP port 53.

Answer

The two correct statements are that standard DNS queries for IP address resolution typically utilize UDP port 53 to reduce latency, and when a DNS response payload exceeds 512 bytes without EDNS0 support, the server sets the TrunCation (TC) bit to prompt the client to re-query using TCP port 53.
Standard DNS lookups operate over UDP port 53 because single-packet requests and responses do not warrant the overhead of a TCP connection. However, if a DNS response message is truncated due to exceeding 512 bytes (without extension mechanisms like EDNS0), the DNS server sets the TC (TrunCation) bit in the header. Upon receiving a truncated response, the client initiates a TCP connection on port 53 to reliably retrieve the complete set of resource records.

Step-by-Step Solution

1
Identify the primary transport protocol used for standard DNS queries.
DNS uses UDP port 53 for normal client-to-server and server-to-server queries to maintain low latency and minimize connection overhead.
Establishing a TCP connection for small request/response pairs adds unnecessary delay.
2
Determine the conditions under which DNS transitions from UDP to TCP transport.
DNS falls back to TCP port 53 when the response exceeds 512 bytes (indicated by the TC bit in the DNS header) or during DNS zone transfers (AXFR/IXFR).
TCP guarantees reliable delivery and reassembly for large payloads that cannot fit into standard UDP DNS packets.

Key Concept

DNS Transport Protocols and TrunCation (TC) Mechanism
Question 102Question →

A network administrator needs to configure a Cisco IOS router to synchronize its internal clock with an external centralized time source at IP address 192.168.10.50. Which Cisco IOS global configuration command must be used to accomplish this task?

Show answer & explanation

Answer: ntp server 192.168.10.50

Answer

The command 'ntp server 192.168.10.50' configures the router to act as an NTP client synchronizing from the specified NTP server.
The correct command is 'ntp server 192.168.10.50'. In Cisco IOS, entering 'ntp server' followed by an IP address configures the router to request time updates from that remote server.

Step-by-Step Solution

1
Identify the required NTP operational mode.
The router must act as an NTP client receiving time synchronization from a specified IP address.
The scenario specifies referencing a central time source at 192.168.10.50.
2
Select the appropriate Cisco IOS global configuration command syntax.
The command 'ntp server <ip-address>' establishes the client-server relationship.
'ntp server' is the dedicated Cisco IOS command for designated client NTP synchronization.

Key Concept

NTP Client Operations and Configuration
Estimated Time:45s
Question 103Question →

An enterprise router is configured for dynamic Network Address Translation (NAT) using an IP pool containing four public IP addresses (198.51.100.1198.51.100.1 to 198.51.100.4198.51.100.4). Internal users report that only four devices can access external resources at any given time, and subsequent connection attempts by other hosts fail until an existing session terminates. Which configuration change will allow all internal hosts to share the public IP address pool simultaneously?

Show answer & explanation

Answer: Append the overload keyword to the ip nat inside source list pool command.

Answer

Append the overload keyword to the ip nat inside source list pool command.
The correct response specifies appending the overload keyword to the dynamic NAT configuration statement (e.g., ip nat inside source list 1 pool NAT_POOL overload). This enables Port Address Translation (PAT), allowing multiple internal devices to share the public addresses by tracking unique source port numbers.

Step-by-Step Solution

1
Analyze the reported issue
Dynamic NAT without PAT provides strict 1-to-1 translations, restricting concurrent internet access to the exact number of public IP addresses in the pool (4 hosts).
Omitting port-level translation causes the router to exhaust available public addresses after 4 active sessions.
2
Identify the required Cisco IOS command enhancement
Appending the 'overload' keyword converts dynamic NAT to Port Address Translation (PAT).
PAT tracks source TCP/UDP port numbers, enabling thousands of inside private hosts to multiplex over the same pool of public IP addresses.

Key Concept

Port Address Translation (PAT) Overload Configuration
Estimated Time:1m 15s
Question 104Question →

An administrator notices that while the first host on the internal network (10.1.10.0/2410.1.10.0/24) can access the internet, subsequent hosts are unable to establish outbound connections simultaneously. Inspecting Router1 reveals the following running configuration:

text
access-list 105 permit ip 10.1.10.0 0.0.0.255 any
ip nat pool EDGE_POOL 203.0.113.5 203.0.113.5 prefix-length 32
ip nat inside source list 105 pool EDGE_POOL

Command output from `show ip nat statistics` confirms:
text
Total active translations: 1 (0 static, 1 dynamic, 0 extended)
Outside interfaces: GigabitEthernet0/1
Inside interfaces: GigabitEthernet0/0
Hits: 142 Misses: 18
Dynamic mappings:
-- Inside Source
access-list 105 pool EDGE_POOL ref count 1

Which configuration modification must be applied to Router1 to allow all internal hosts on the 10.1.10.0/2410.1.10.0/24 network to share the single IP address assigned to `EDGE_POOL` concurrently?

Show answer & explanation

Answer: Append the overload keyword to the statement: ip nat inside source list 105 pool EDGE_POOL overload

Answer

Appending the overload keyword to the inside source NAT configuration command (ip nat inside source list 105 pool EDGE_POOL overload) enables Port Address Translation (PAT).
The configuration present on Router1 establishes standard dynamic 1-to-1 NAT. Because the pool contains only one IP address (203.0.113.5), only the first internal host receives a translation. Appending the overload keyword modifies the translation engine to perform Port Address Translation (PAT), allowing multiple inside local hosts to share a single inside global address by using unique transport-layer port numbers.

Step-by-Step Solution

1
Analyze the configuration and verification output
The command 'ip nat inside source list 105 pool EDGE_POOL' without the overload keyword configures standard dynamic NAT. Because EDGE_POOL contains only a single IP address (203.0.113.5), only 1 dynamic translation entry (extended = 0) can exist at any given time.
Standard dynamic NAT allocates global IP addresses on a one-to-one basis. Once all pool addresses are exhausted, additional hosts attempting connection are dropped (misses increase).
2
Identify the missing component for port multiplexing
To allow multiple internal hosts to share one global IP address, Layer 4 port numbers must be tracked using Port Address Translation (PAT).
PAT requires the 'overload' keyword at the end of the 'ip nat inside source' command.
3
Formulate the correct configuration command
Execute 'ip nat inside source list 105 pool EDGE_POOL overload' on Router1.
This enables extended translations, allowing thousands of concurrent internal sockets to multiplex over port numbers assigned to 203.0.113.5.

Key Concept

Port Address Translation (PAT) Overload Keyword Requirement
Estimated Time:2m 0s
Question 105Question →

An administrator is verifying Network Time Protocol (NTP) operations on a Cisco IOS router. Which of the following statements regarding NTP functionality and status are correct? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The command `ntp master 4` configures the router to act as an NTP server serving time at stratum 4.; A stratum value of 16 indicates that the local device clock is unsynchronized and considered invalid.

Answer

The command `ntp master 4` configures the router as an NTP server at stratum 4, and a stratum level of 16 indicates an unsynchronized clock state.
Configuring `ntp master 4` causes the router to act as an authoritative NTP clock source at stratum 4. Furthermore, stratum 16 is the standard NTP representation for an unsynchronized device or an unreachable clock source.

Step-by-Step Solution

1
Analyze NTP stratum range and master configuration commands.
The `ntp master [number]` command allows an IOS router to advertise itself as an NTP master at the specified stratum. Valid synchronized strata are 1 through 15.
Stratum 1 is directly attached to a reference clock (like GPS/atomic), and each hop increments the stratum by 1. Stratum 16 defines an unsynchronized state.
2
Evaluate transport layer protocols used by NTP.
NTP uses UDP port 123.
UDP is chosen over TCP to minimize latency and synchronization overhead.

Key Concept

NTP Stratum Hierarchy and Master Configuration
Estimated Time:45s
Question 106Question →

A network engineer wants to configure managed switches to alert the SNMP management station upon link status changes. To prevent missed alerts due to unacknowledged packet delivery, the engineer requires a message type that mandates an explicit confirmation receipt back from the manager. Which SNMP message type should be configured on the switches?

Show answer & explanation

Answer: SNMP InformRequest

Answer

SNMP InformRequest (or Inform) is the correct message type because it requires an explicit acknowledgement receipt from the receiving SNMP manager.
SNMP InformRequest messages are specifically designed to provide reliable notification handling. Unlike standard Traps, when an agent sends an Inform, the receiver must reply with an acknowledgement; if no confirmation is received, the agent can retransmit the alert.

Step-by-Step Solution

1
Identify the operational requirement in the scenario.
The requirement is an event alert notification originating from network switches that provides reliable delivery through mandatory receiver acknowledgement.
Event-driven notifications initiated by managed devices are either Traps or Informs.
2
Compare SNMP Trap and SNMP InformRequest operational mechanics.
Traps are unacknowledged (fire-and-forget), whereas Informs require the manager to send an SNMP response acknowledging receipt.
If an Inform message is not acknowledged by the NMS within a timeout period, the sending device can retransmit the notification.

Key Concept

SNMP Traps vs SNMP Informs Reliability Mechanics
Question 107Question →

A network engineer is configuring a new Cisco IOS router (R1) to synchronize its system time with a primary enterprise NTP server operating at Stratum 2. R1 is also expected to act as an NTP server for downstream switches once synchronized. Arrange the operational steps in the exact chronological sequence in which R1 processes NTP synchronization from initial CLI configuration to serving downstream clients.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence starts with entering the NTP server configuration command, followed by sending UDP port 123 query packets, receiving the Stratum 2 response, calculating the local Stratum 3 value, and finally transitioning to synchronized state while serving downstream clients.
The operational sequence moves logically from CLI command execution, outward network request over UDP 123, inbound response processing, mathematical stratum calculation (2+1=32 + 1 = 3), to local state synchronization and downstream service activation.

Step-by-Step Solution

1
Identify the initial configuration trigger
Execution of 'ntp server 10.10.10.1' initializes the local NTP daemon polling timer.
NTP operations cannot begin until a server association is defined in configuration.
2
Determine initial packet transmission details
R1 sends outgoing NTP client polling messages using UDP port 123.
NTP uses UDP port 123 for all client/server communications.
3
Process server response details
R1 receives packet payload containing Stratum 2 marker from 10.10.10.1.
The upstream server reports its own stratum distance from reference clock (Stratum 2).
4
Perform Stratum level mathematical calculation
Local stratum is evaluated as Server Stratum+1=2+1=3\text{Server Stratum} + 1 = 2 + 1 = 3.
Every network hop down the NTP hierarchy increments the Stratum level by exactly 1.
5
Establish synchronized state and downstream server role
System clock updates to synchronized state, enabling R1 to answer downstream queries at Stratum 3.
A Cisco router will not serve authoritative time to downstream clients until its own clock is synchronized to an upstream source.

Key Concept

NTP Client-Server Synchronization Workflow and Stratum Calculation
Estimated Time:2m 0s
Question 108Question →

A network administrator is implementing Port Address Translation (PAT) on a Cisco IOS router to allow hosts on the internal subnet 10.45.10.0/2410.45.10.0/24 to access the Internet. The WAN interface GigabitEthernet0/0/1 receives its dynamic IP address from the ISP, while interface GigabitEthernet0/0/0 connects to the internal LAN. Which two configuration steps or commands are required to successfully enable PAT using the WAN interface address? (Select TWO options.)

Select all that apply

Show answer & explanation

Answer: Specify the translation mapping using the command ip nat inside source list 1 interface GigabitEthernet0/0/1 overload; Identify NAT roles on the router interfaces by configuring ip nat inside on GigabitEthernet0/0/0 and ip nat outside on GigabitEthernet0/0/1

Answer

Port Address Translation (PAT) using a router interface requires defining the internal and external NAT interface designations (ip nat inside / ip nat outside) and creating the NAT statement referencing the matching ACL and interface with the overload keyword (ip nat inside source list 1 interface GigabitEthernet0/0/1 overload).
To successfully establish Port Address Translation (PAT) using an interface address, two mandatory requirements must be fulfilled: defining the NAT boundary interface roles (ip nat inside on the LAN side and ip nat outside on the WAN side) and writing the translation command linking the matching ACL to the WAN interface with the overload keyword present.

Step-by-Step Solution

1
Designate the internal and external NAT interfaces.
GigabitEthernet0/0/0 is configured with ip nat inside and GigabitEthernet0/0/1 is configured with ip nat outside.
Cisco IOS NAT needs to identify ingress and egress traffic boundaries to know when to apply translation rules.
2
Define an access list matching the internal subnet traffic.
Standard ACL permits 10.45.10.0 0.0.0.255.
The ACL acts as the interesting traffic filter to identify packets eligible for translation.
3
Configure the inside source PAT statement using the interface and overload keywords.
Command ip nat inside source list 1 interface GigabitEthernet0/0/1 overload is applied.
The overload keyword instructs Cisco IOS to track layer 4 TCP/UDP port numbers, enabling thousands of internal hosts to share one public IP address.

Key Concept

Inside Source PAT Configuration
Estimated Time:2m 0s
Question 109Question →

Match each SNMP component or operational term on the left with its correct defining characteristic on the right.

Click a left item, then click its matching right item

Items

SNMP Trap
SNMP Inform
Management Information Base (MIB)
SNMPv3 authPriv

Matches

Show answer & explanation

Answer

SNMP Trap matches the unacknowledged notification on UDP port 162; SNMP Inform matches the acknowledged notification requiring response; MIB matches the hierarchical database of OIDs; SNMPv3 authPriv matches the security level providing authentication and encryption.
Each SNMP term correctly maps to its defining operational characteristic. Traps provide unacknowledged alerts on UDP port 162, Informs provide acknowledged alerts, MIB represents the OID database structure, and SNMPv3 authPriv combines authentication with encryption.

Step-by-Step Solution

1
Identify the transmission mechanics of SNMP notifications
Traps are unacknowledged notifications sent on UDP 162, while Informs use acknowledgments for reliable delivery.
Traps rely on best-effort UDP transmission, whereas Informs guarantee receipt via NMS confirmation messages.
2
Identify data structure definitions in SNMP
The MIB defines all readable and writable objects on a managed device structured hierarchically using OIDs.
Network Management Systems query or modify specific OID paths defined within the MIB schema.
3
Evaluate SNMPv3 security levels
authPriv stands for authentication and privacy (encryption).
Unlike noAuthNoPriv (no security) or authNoPriv (authentication without encryption), authPriv enforces both cryptographic verification and payload encryption.

Key Concept

SNMP Notification Types, MIB Structures, and Security Levels
Question 110Question →

A network technician needs to configure a Cisco router to operate as an Network Time Protocol (NTP) client and synchronize its internal system clock with a central time server located at IP address 172.16.10.100. Which global configuration command must be executed on the router to accomplish this task?

Show answer & explanation

Answer: ntp server 172.16.10.100

Answer

The command 'ntp server 172.16.10.100' in global configuration mode configures the local Cisco device as an NTP client that synchronizes its system time from the specified IP address.
The command 'ntp server 172.16.10.100' instructs the Cisco IOS router to operate as an NTP client in client-server mode, sending unicast NTP requests to the specified IP address to synchronize its clock.

Step-by-Step Solution

1
Identify the role required for the router.
The router must act as an NTP client receiving time from an external server.
The requirement states that the router needs to synchronize its clock to an existing centralized server at IP address 172.16.10.100.
2
Evaluate Cisco IOS NTP configuration commands.
The command 'ntp server <ip-address>' establishes client-server NTP association.
Global configuration command 'ntp server 172.16.10.100' configures the router to query the NTP daemon at 172.16.10.100 for time updates.

Key Concept

NTP Client Configuration
Question 111Question →

An enterprise client host without a cached DNS entry needs to connect to an external server using its domain name. Place the steps of the full name resolution flow in the correct chronological order, starting from the client's initial lookup request to the final response delivery.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct chronological sequence begins with the client host issuing a recursive query to the internal DNS server after checking its local cache. Next, the internal DNS server executes iterative lookups starting at a root DNS server, followed by the TLD DNS server, and finally the domain's authoritative DNS server. Upon receiving the A/AAAA record from the authoritative server, the internal DNS server caches the result and delivers the IP address to the requesting client.
The correct order follows the standard hierarchy of enterprise DNS name resolution. First, the client checks its local cache and queries its local DNS server recursively. Second, if un-cached, the internal recursive DNS server initiates iterative lookups starting at the root servers. Third, the root server redirects the query to the TLD server. Fourth, the TLD server refers the query to the authoritative name server. Fifth, the authoritative name server provides the IP mapping, which the internal server caches before replying to the client host.

Step-by-Step Solution

1
Evaluate host-level resolution steps
Client host checks local cache/hosts file, then sends a recursive lookup request to the configured internal DNS server.
Hosts must exhaust local name resolution mechanisms before querying network resolvers over port 53.
2
Trace top-of-hierarchy DNS server lookup
Internal recursive server queries a Root name server and receives a referral to the TLD name servers.
Iterative resolution moves top-down through the domain namespace starting at the root (".").
3
Trace mid-hierarchy DNS server lookup
Internal recursive server queries the TLD server (such as .com) and receives a referral to the authoritative name server.
TLD servers delegate authority for specific subdomains to organizational name servers.
4
Trace authoritative response acquisition
Internal recursive server queries the domain's authoritative name server and receives the final mapping.
Only the authoritative DNS server for a domain holds the definitive zone file records.
5
Complete recursive loop to client
Internal recursive server caches the mapping according to TTL and returns the resolved address to the client.
The client receives a single final response to satisfy its initial recursive query.

Key Concept

DNS Resolution Hierarchy and Iterative vs Recursive Query Roles
Question 112Question →

An enterprise network engineer configures an internal host to resolve domain names via a local Active Directory DNS server, which is configured to forward external queries to a public DNS resolver. During a packet capture analysis on the firewall boundary, the engineer observes that a specific DNS query originating from the internal AD DNS server towards an external authoritative DNS server for a large DNSSEC-signed domain initially uses UDP destination port 53, receives a response with the TrunCation (TC) bit set to 1, and immediately follows up with a new request to the same target server using TCP destination port 53. Which statement accurately explains the fundamental reason for this protocol switch during the name resolution process?

Show answer & explanation

Answer: The DNS server switches to TCP because the response payload exceeds the negotiated maximum transmission unit (or 512-byte traditional UDP DNS limit), requiring TCP stream reliability to reassemble and guarantee delivery of large resource record sets.

Answer

The DNS server switches to TCP port 53 because the DNS response payload exceeds the maximum supported UDP DNS buffer size, causing the responder to set the TrunCation (TC) bit and prompting the requester to re-query over TCP.
Standard DNS operations use UDP port 53 for fast, lightweight name resolution. However, when a DNS answer payload (such as large DNSSEC resource record sets) exceeds the supported UDP datagram size limit, the responding server truncates the response and sets the TrunCation (TC) flag bit in the DNS header. When the querying DNS entity detects TC=1, standard DNS behavior dictates establishing a TCP connection to port 53 and re-transmitting the query to receive the full, untruncated answer payload.

Step-by-Step Solution

1
Analyze the DNS packet capture details
Identified that the initial UDP query returned a DNS response with the TC (TrunCation) bit set to 1.
The TC bit indicates that the responding server truncated the answer because the payload exceeded the maximum allowable DNS UDP message size.
2
Evaluate transport layer behavior for DNS
DNS operates primarily over UDP port 53 for speed, but falls back to TCP port 53 when responses are truncated.
TCP provides stream-based transmission capable of handling payload sizes larger than the single-datagram UDP limit without losing data integrity.
3
Select the option that correctly describes TC bit functionality and TCP fallback
Confirmed that payload overflow leading to TC=1 triggers an immediate retry over TCP port 53.
This is a core DNS specification behavior defined in RFC 1035 and enhanced by EDNS0.

Key Concept

DNS Transport Layer Mechanics and TC Bit Truncation Fallback
Estimated Time:2m 0s
Question 113Question →

A network administrator is configuring Port Address Translation (PAT) on a Cisco IOS router to allow internal hosts in the 172.16.50.0/24172.16.50.0/24 subnet to access the Internet using the public IP address on interface GigabitEthernet0/0/0. Internal users report that they cannot establish any outbound internet connections. The running configuration reveals the following details:

interface GigabitEthernet0/0/0
ip address 203.0.113.1 255.255.255.248
ip nat outside
!
interface GigabitEthernet0/0/1
ip address 172.16.50.1 255.255.255.0
!
ip access-list standard NAT_ACL
permit 172.16.50.0 0.0.0.255
!
ip nat inside source list NAT_ACL interface GigabitEthernet0/0/0 overload

Which configuration change must be made on the router to resolve this issue?

Show answer & explanation

Answer: Configure the ip nat inside command under interface GigabitEthernet0/0/1.

Answer

Configure the ip nat inside command under interface GigabitEthernet0/0/1.
For Cisco IOS NAT to operate, at least one interface must be designated as 'ip nat inside' and at least one interface as 'ip nat outside'. In the provided configuration, interface GigabitEthernet0/0/1 lacks the 'ip nat inside' command, so packets arriving from internal hosts are not identified for translation.

Step-by-Step Solution

1
Analyze the existing router configuration for NAT/PAT components.
Interface GigabitEthernet0/0/0 is properly marked with 'ip nat outside', NAT_ACL permits 172.16.50.0/24172.16.50.0/24, and the global translation statement maps NAT_ACL to GigabitEthernet0/0/0 with 'overload'.
For Cisco IOS NAT/PAT to process packets, interfaces must be designated as inside or outside, and traffic must cross between them.
2
Inspect the internal interface configuration.
Interface GigabitEthernet0/0/1 is missing the 'ip nat inside' command.
Without 'ip nat inside' on the internal gateway interface, incoming packets from 172.16.50.0/24172.16.50.0/24 are routed normally without undergoing Network Address Translation.
3
Identify the required fix.
Add 'ip nat inside' under interface GigabitEthernet0/0/1 configuration.
This establishes the boundary between internal private addresses and the external public interface, enabling PAT processing.

Key Concept

Inside and Outside NAT Interface Designation
Estimated Time:1m 30s
Question 114Question →

An enterprise host needs to resolve the IP address of an internal web application server (app.corp.local) after the local cache has expired. Place the steps of the name resolution process in the correct chronological order from first to last.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence of DNS name resolution steps is: 1) The host checks its local OS DNS client resolver cache and local hosts file. 2) The host encapsulates a recursive DNS query in a UDP datagram with destination port 53 and sends it to its primary configured DNS server. 3) The enterprise DNS server receives the query and checks its authoritative DNS zones. 4) The DNS server formulates an authoritative response packet containing the requested A record. 5) The host receives the DNS response packet and stores the IP address mapping in its local DNS resolver cache.
The correct order follows the standard host-to-server DNS name resolution flow: first, local host resources (cache and hosts file) are inspected. If unresolved, the client sends a recursive UDP query (destination port 53) to its configured local DNS server. The DNS server processes the query against its zone database, generates an authoritative response containing the A record, and returns it to the host. Finally, the host receives the response and caches the IP address locally.

Step-by-Step Solution

1
Evaluate local host resolution mechanisms.
Local resolver cache and hosts file are queried first prior to generating outbound network requests.
Checking local host memory avoids unnecessary network traffic and reduces latency.
2
Transmit DNS request over the local network connection.
A UDP datagram targeted to destination port 53 is forwarded to the designated local DNS server.
Standard DNS queries use UDP port 53 for low-overhead client-to-server communications.
3
Process query at the targeted enterprise DNS server.
The server checks its local authoritative zone files for matching domain records.
Because the domain is internal (corp.local), the internal DNS server acts as the authoritative source.
4
Build DNS server response payload.
An authoritative DNS answer payload containing the IPv4 (A) record is created.
The server must supply the mapped IP address back to the requesting client.
5
Process response on the requesting client host.
The client receives the response and caches the entry according to the record's Time-to-Live (TTL).
Caching allows subsequent applications on the host to reuse the resolved IP address without repeating the DNS lookup.

Key Concept

Client DNS resolution sequence and DNS server roles
Question 115Question →

A network administrator needs to configure SNMPv3 on a Cisco IOS router to support both message integrity verification using SHA and payload encryption using AES. Which SNMPv3 security level must be configured to meet these security requirements?

Show answer & explanation

Answer: authPriv

Answer

The authPriv security level must be configured because it provides both authentication and privacy (encryption).
The authPriv security level is the highest security mode available in SNMPv3. It combines authentication algorithms (such as HMAC-SHA or HMAC-MD5) to ensure packet integrity and sender authentication with encryption algorithms (such as AES or DES) to provide privacy for management traffic.

Step-by-Step Solution

1
Identify the required security parameters from the scenario.
The requirements are SHA authentication and AES payload encryption.
The administrator explicitly specifies message integrity verification and data confidentiality.
2
Map the requirements to the standard SNMPv3 security models.
The authPriv security level meets both requirements.
SNMPv3 defines three security levels: noAuthNoPriv (no authentication, no encryption), authNoPriv (authentication without encryption), and authPriv (authentication with encryption).

Key Concept

SNMPv3 Security Levels (noAuthNoPriv, authNoPriv, authPriv)
Question 116Question →

An network administrator is troubleshooting an issue where client workstations attached to VLAN 20 (subnet 192.168.20.0/24) fail to receive IPv4 dynamic configuration settings from a centralized DHCP server located at 10.1.100.50 in VLAN 100. The administrator inspects the configuration on the Cisco IOS router acting as the default gateway for both subnets:

interface GigabitEthernet0/0/1.20
encapsulation dot1Q 20
ip address 192.168.20.1 255.255.255.0
!
interface GigabitEthernet0/0/1.100
encapsulation dot1Q 100
ip address 10.1.100.1 255.255.255.0
ip helper-address 10.1.100.50

Based on the router configuration output, why are the clients in VLAN 20 failing to obtain IP addresses from the DHCP server?

Show answer & explanation

Answer: The ip helper-address command is configured on the router interface facing the DHCP server rather than on the incoming client gateway interface.

Answer

The ip helper-address command is configured on the router interface facing the DHCP server rather than on the incoming client gateway interface.
DHCP clients broadcast their DHCP Discover messages to 255.255.255.255. To relay these broadcasts to a unicast DHCP server in a different subnet, the 'ip helper-address' command must be configured on the router interface receiving those broadcasts (the client default gateway, GigabitEthernet0/0/1.20). In the provided configuration, the command was incorrectly placed on the subinterface facing the server (GigabitEthernet0/0/1.100), preventing the router from intercepting client requests.

Step-by-Step Solution

1
Analyze client traffic flow and DHCP request behavior.
Clients in VLAN 20 send DHCP Discover packets as Layer 3 broadcasts (255.255.255.255) arriving on interface GigabitEthernet0/0/1.20.
DHCP clients do not initially have an IP address and broadcast their requests to locate a server.
2
Evaluate placement of the ip helper-address statement.
The ip helper-address 10.1.100.50 command is currently under GigabitEthernet0/0/1.100 instead of GigabitEthernet0/0/1.20.
The router listens for incoming broadcasts on the interface where the command is applied. Because it is absent on GigabitEthernet0/0/1.20, incoming broadcasts from VLAN 20 clients are discarded.
3
Formulate the correct configuration change.
Move ip helper-address 10.1.100.50 from subinterface .100 to subinterface .20.
Applying the helper address on GigabitEthernet0/0/1.20 allows the router to intercept client broadcasts, convert them to unicast packets directed to 10.1.100.50, and populate the giaddr field with 192.168.20.1 so the server selects the correct address pool.

Key Concept

DHCP Relay Agent Interface Placement and Operation
Question 117Question →

A network administrator configures the IP address of an external DNS server on a Cisco IOS router using the command `ip name-server 10.1.1.1`. However, when attempting to ping a remote server by its hostname (`ping server1.example.com`), the router immediately fails to resolve the name and no DNS query packets are transmitted. Which command must be entered in global configuration mode to enable the router to perform DNS queries for hostname resolution?

Show answer & explanation

Answer: ip domain lookup

Answer

The command `ip domain lookup` must be configured in global configuration mode to enable Cisco IOS DNS hostname resolution.
The `ip domain lookup` command globally enables the DNS host name resolution feature on a Cisco IOS router. Without this command enabled, the router will not generate DNS request packets to configured DNS servers specified by `ip name-server`.

Step-by-Step Solution

1
Identify the role of the Cisco IOS device in name resolution
The router is acting as a DNS client trying to resolve hostnames to IP addresses for local CLI operations.
Configuring `ip name-server` defines the destination DNS server IP address, but the DNS lookup process must be globally enabled on the device.
2
Determine the global command required to enable client DNS lookups
Executing `ip domain lookup` enables the IP DNS client feature in Cisco IOS.
If DNS lookup is disabled (via `no ip domain lookup`), Cisco IOS will not initiate DNS queries over UDP port 53 even if valid name servers are defined.

Key Concept

Cisco IOS DNS Client Configuration and Hostname Resolution Mechanics
Question 118Question →

An enterprise client workstation attempts to access an external web application at `app.partner.example.net` for the first time. Arrange the steps of the complete DNS resolution process in the correct chronological order, starting from the client's initial lookup request to the final IP address retrieval.

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Answer

The correct sequence begins with the client host checking its local resolver cache and hosts file, followed by sending a recursive query to the local internal DNS resolver. The internal resolver then performs iterative queries starting at the root server, proceeding to the .net TLD server, and finally querying the authoritative server for partner.example.net before caching the record and returning the resolved IP address to the client.
The proper sequence follows standard operating system and DNS protocol operational order: local client cache and hosts file check -> client recursive query to the local internal DNS resolver -> internal resolver iterative query to the root name server -> root referral to the TLD server -> TLD referral to the domain authoritative server -> authoritative answer returned, cached by the internal resolver, and forwarded to the client.

Step-by-Step Solution

1
Check local OS resolution mechanisms.
The host OS scans the local `hosts` file and client DNS cache for `app.partner.example.net`.
Local lookup prevents unnecessary network overhead if the IP address is already known locally.
2
Transmit recursive query from client host to configured DNS server.
A UDP port 53 recursive query is sent to the internal enterprise DNS resolver.
The client delegates name resolution responsibility entirely to its configured local DNS server.
3
Initiate iterative resolution from the DNS root hierarchy.
The internal DNS server queries a DNS root hint server (`.`).
When resolving an un-cached external FQDN, the recursive resolver starts lookups at the root zone.
4
Process root referral response.
The root server responds with NS and glue A records for the `.net` TLD servers.
Root servers maintain delegation points for top-level domains.
5
Query TLD name server for domain authority.
The `.net` TLD server provides NS records pointing to authoritative servers for `partner.example.net`.
TLD servers maintain delegations for secondary registered domains under their top-level domain.
6
Fetch definitive record from authoritative server and respond to client.
The authoritative server responds with the `A` record, which the internal server caches and forwards to the requesting client.
Only authoritative name servers hold the master resource records for the targeted domain.

Key Concept

DNS Lookup and Name Resolution Roles in Enterprise Networks
Estimated Time:2m 0s
Question 119Question →

A network engineer is tasking a Cisco IOS router with Port Address Translation (PAT) to enable Internet access for internal endpoints on the 192.168.20.0/24192.168.20.0/24 network using the public IPv4 address assigned to interface GigabitEthernet0/0/1. Which two configuration steps are required on the router to accomplish this requirement? (Select two.)

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Answer: Define an IPv4 Access Control List (ACL) that permits traffic originating from the internal 192.168.20.0/24192.168.20.0/24 subnet.; Execute the global configuration command `ip nat inside source list <ACL> interface GigabitEthernet0/0/1 overload`.

Answer

To configure interface-based PAT (overload) on Cisco IOS, an administrator must define an ACL identifying the inside local host network and bind that ACL to the outside WAN interface using `ip nat inside source list <ACL> interface <interface-id> overload`.
Configuring interface-based Port Address Translation (PAT) requires creating an ACL that permits internal host addresses (192.168.20.0/24192.168.20.0/24) and linking that ACL to the egress interface with `ip nat inside source list <ACL> interface GigabitEthernet0/0/1 overload`. The `overload` keyword is mandatory to enable layer 4 port tracking so multiple hosts can share one IP.

Step-by-Step Solution

1
Identify the internal host network requiring translation.
Internal subnet is identified as 192.168.20.0/24192.168.20.0/24.
An Access Control List (ACL) must be configured to match traffic coming from 192.168.20.0/24192.168.20.0/24.
2
Bind the matching ACL to the external interface using PAT.
The command `ip nat inside source list <ACL> interface GigabitEthernet0/0/1 overload` is configured.
The `overload` keyword allows multiple internal hosts to share the single interface IP address by tracking unique L4 port numbers.

Key Concept

Port Address Translation (PAT) interface overload configuration
Question 120Question →

A client workstation is configured to obtain IPv4 addressing dynamically. Arrange the four messages exchanged during the standard DHCP lease process (DORA) in chronological order from first to last.

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Answer

The chronological sequence of the IPv4 DHCP operation is DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, and DHCPACK.
The standard IPv4 DHCP lease negotiation process follows the four-step DORA sequence: Discover (client broadcast), Offer (server response), Request (client selection broadcast), and Acknowledge (server confirmation).

Step-by-Step Solution

1
Identify the initial client discovery broadcast.
DHCPDISCOVER is sent first by the client.
The client has no assigned IP address and must broadcast to discover active DHCP servers.
2
Identify the server offer response.
DHCPOFFER is sent second by the server.
A server receiving the discovery broadcast offers an available IP address and subnet parameters.
3
Identify the client acceptance broadcast.
DHCPREQUEST is sent third by the client.
The client broadcasts its intent to accept the specific offer, allowing unselected servers to release their reserved offers.
4
Identify the server final acknowledgment.
DHCPACK is sent fourth by the server.
The server acknowledges the request and locks in the IP lease parameters for the client.

Key Concept

DHCP DORA Process (Discover, Offer, Request, Acknowledge)
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