IP Services

198 questions

Question 1Question

A network administrator is troubleshooting a DHCP relay issue on a Cisco IOS router. Host devices on VLAN 30 (172.16.30.0/24172.16.30.0/24) use subinterface GigabitEthernet0/0.30 (172.16.30.1172.16.30.1) as their default gateway. The centralized DHCP server is located at 10.10.10.5010.10.10.50, connected off router interface GigabitEthernet0/1 (10.10.10.110.10.10.1).

Packet captures at the DHCP server reveal that incoming relayed DHCP DISCOVER messages contain a Relay Agent IP Address (`giaddr`) of 10.10.10.110.10.10.1 instead of 172.16.30.1172.16.30.1. Consequently, the DHCP server fails to assign addresses from the intended 172.16.30.0/24172.16.30.0/24 pool.

Which router misconfiguration causes the `giaddr` field to be set to 10.10.10.110.10.10.1?

Show answer & explanation

Answer: The `ip helper-address 10.10.10.50` command was incorrectly applied to interface GigabitEthernet0/1 instead of subinterface GigabitEthernet0/0.30.

Answer

The `ip helper-address 10.10.10.50` command was incorrectly applied to interface GigabitEthernet0/1 instead of subinterface GigabitEthernet0/0.30.
When a Cisco router acts as a DHCP relay agent, it listens for broadcast UDP port 67 messages on interfaces configured with `ip helper-address <server_ip>`. When a DISCOVER packet is received on such an interface, the router converts the broadcast to a unicast packet sent to the helper IP and populates the `giaddr` (Gateway IP Address) field with the primary IP address of the INCOMING interface. Because `giaddr` was set to 10.10.10.110.10.10.1, the `ip helper-address` command was erroneously placed on interface GigabitEthernet0/1. Moving the command to GigabitEthernet0/0.30 ensures `giaddr` is populated as 172.16.30.1172.16.30.1, allowing the DHCP server to allocate from the correct 172.16.30.0/24172.16.30.0/24 pool.

Step-by-Step Solution

1
Analyze how a Cisco IOS DHCP Relay Agent populates the Relay Agent IP Address (`giaddr`) field.
When a router receives a client broadcast DHCP DISCOVER message on an interface enabled with `ip helper-address`, it sets the `giaddr` field to the primary IP address of the INGRESS interface where the request was received.
The DHCP server uses the `giaddr` field to determine which subnet scope/pool to select for IP address assignment.
2
Evaluate the captured `giaddr` IP address value (10.10.10.110.10.10.1).
10.10.10.110.10.10.1 corresponds to interface GigabitEthernet0/1, which is the egress interface connected to the DHCP server subnet, rather than ingress subinterface GigabitEthernet0/0.30 (172.16.30.1172.16.30.1).
This indicates that the `ip helper-address` command was mistakenly configured under interface GigabitEthernet0/1.
3
Identify the corrective configuration step.
Remove `ip helper-address 10.10.10.50` from interface GigabitEthernet0/1 and place it under subinterface GigabitEthernet0/0.30.
Placing the helper address on GigabitEthernet0/0.30 ensures the router intercepts VLAN 30 client broadcasts and sets `giaddr` to 172.16.30.1172.16.30.1.

Key Concept

DHCP Relay Agent Ingress Interface Binding and giaddr Population
Question 2Question

A security review on an enterprise switch named Core-SW1 reveals that virtual terminal sessions allow plain-text remote management and bypass local account verification. To harden management access on Core-SW1, which TWO commands must be configured specifically under line VTY configuration mode (config-line) to enforce local account credentials and restrict incoming traffic exclusively to SSH?

Select all that apply

Show answer & explanation

Answer: login local; transport input ssh

Answer

The correct commands to configure under line VTY configuration mode are 'login local' and 'transport input ssh'.
Securing virtual terminal (VTY) lines requires configuration within line subconfiguration mode (config-line). The command 'login local' ensures that any user connecting via VTY lines must authenticate against locally configured username accounts. The command 'transport input ssh' locks down line access so that only encrypted SSH sessions are permitted, disabling clear-text protocols like Telnet.

Step-by-Step Solution

1
Identify the CLI context required for line-specific remote access security controls.
Line configuration mode (config-line) is accessed via the command 'line vty 0 15'.
VTY lines handle inbound network connection sessions.
2
Select the line command that requires local database credentials.
The 'login local' command binds line authentication to local user accounts created in global configuration mode.
Without 'login local', VTY lines either request a simple line password or permit unauthenticated access.
3
Select the line command that filters inbound remote management traffic protocols.
The 'transport input ssh' command restricts incoming protocol traffic exclusively to SSH.
By default, Cisco IOS line VTY sessions allow incoming Telnet connections unless restricted.

Key Concept

VTY Line Security Configuration for SSH Access
Question 3Question

A network administrator is configuring Quality of Service (QoS) classification using Differentiated Services (DiffServ) on an enterprise router. How many bits are allocated to the Differentiated Services Code Point (DSCP) field within the IPv4 Type of Service (ToS) byte?

Show answer & explanation

Answer: 6 bits

Answer

6 bits are allocated to the DSCP field within the IPv4 header.
The correct option stating 6 bits is right because Differentiated Services (DiffServ) redefines the 8-bit IPv4 Type of Service (ToS) byte such that the first 6 bits are used for the DSCP value, providing 64 different classification values (0630-63). The remaining 2 bits are used for Explicit Congestion Notification (ECN).

Step-by-Step Solution

1
Identify the IPv4 header field used for Differentiated Services QoS classification.
The IPv4 header contains an 8-bit Type of Service (ToS) byte (also referred to as the Differentiated Services field).
DiffServ redefines the ToS byte to provide backward-compatible QoS classification capabilities.
2
Determine the allocation of bits within the ToS byte for DSCP marking.
The 6 most significant bits (26=642^6 = 64 possible values) form the DSCP field, while the remaining 2 least significant bits are reserved for Explicit Congestion Notification (ECN).
This 6-bit field allows granular classification of traffic into Per-Hop Behaviors (PHBs) such as Expedited Forwarding (EF) and Assured Forwarding (AF).

Key Concept

DSCP Field Bit Length and Structure
Question 4Question

A network administrator executes the global configuration command `logging trap 4` on a Cisco IOS router that is configured to forward log messages to an external syslog server. Shortly after, an interface status change occurs, generating a syslog event message with severity level 5 (Notifications). How does the router handle this message regarding transmission to the remote syslog server?

Show answer & explanation

Answer: The router discards the message for remote syslog transmission because severity level 5 exceeds the configured threshold of level 4.

Answer

The router discards the message for remote syslog transmission because severity level 5 exceeds the configured threshold of level 4.
The command `logging trap 4` configures the router to send log messages with severity levels 0 through 4 (Emergency, Alert, Critical, Error, and Warning) to the remote syslog collector. Since severity level 5 (Notifications) is numerically greater than 4, it falls outside the forwarding threshold and will not be transmitted to the syslog server.

Step-by-Step Solution

1
Identify the Syslog severity scale in Cisco IOS.
Syslog severity ranges from 0 (Emergency, highest priority) to 7 (Debugging, lowest priority).
Understanding the inverse numerical scale is necessary to evaluate logging thresholds.
2
Analyze the scope of the configured `logging trap 4` command.
The `logging trap 4` command directs the router to send messages from severity level 0 up to severity level 4 (Warnings) to the remote syslog server.
Cisco IOS syslog traps capture all messages at or above the criticality of the configured level (numerically less than or equal to the configured level).
3
Compare the generated message severity level against the trap threshold.
The generated event has a severity level of 5 (Notifications). Because 5 is numerically greater than 4, it falls outside the range of messages forwarded to the syslog server.
Messages with a numerical value greater than the configured threshold are suppressed from being forwarded to the remote server.

Key Concept

Syslog severity level threshold behavior for remote log destination configuration
Estimated Time:1m 0s
Question 5Question

A network administrator configures a Cisco router WAN egress interface with a Modular QoS CLI (MQC) policy map. The policy assigns real-time Voice over IP (VoIP) traffic to a class using the `priority 512` command, while transactional data is assigned to a class using the `bandwidth 2048` command. During a period of interface congestion, incoming voice traffic spikes to 768 kbps768\text{ kbps}. Which statement accurately describes how the router handles the voice traffic that exceeds the 512 kbps512\text{ kbps} allocated threshold?

Show answer & explanation

Answer: The router drops the excess 256 kbps256\text{ kbps} of voice traffic using a built-in strict priority policer to prevent starving other bandwidth-guaranteed queues.

Answer

The router drops the excess voice traffic exceeding the 512 kbps512\text{ kbps} threshold using a built-in policing mechanism to protect other queues from bandwidth starvation during congestion.
Low Latency Queuing (LLQ) uses the `priority` command to create a strict priority queue for delay-sensitive traffic such as voice. To prevent a rogue stream or burst of voice traffic from starving other queues (configured via `bandwidth` statements) during link congestion, LLQ applies a built-in policer to the priority queue. Traffic offered to the priority queue up to the configured limit (512 kbps512\text{ kbps}) is serviced ahead of all other queues. Any excess traffic beyond 512 kbps512\text{ kbps} during congestion is dropped by the policer.

Step-by-Step Solution

1
Identify the QoS queuing feature configured by the `priority` command.
The `priority` command configures Low Latency Queuing (LLQ), creating a strict priority queue alongside Class-Based Weighted Fair Queuing (CBWFQ) classes.
LLQ provides strict priority servicing for delay-sensitive traffic like voice.
2
Analyze how LLQ behaves when traffic in the priority queue exceeds its allocated bandwidth during interface congestion.
To prevent strict priority traffic from monopolizing the interface and starving CBWFQ classes, LLQ implements an implicit policer built into the priority queue.
Without policing, priority traffic could burst endlessly and cause complete packet drop/starvation in other classes.
3
Determine the action taken on the 256 kbps256\text{ kbps} burst exceeding the 512 kbps512\text{ kbps} limit.
The internal policer drops all incoming voice traffic that exceeds 512 kbps512\text{ kbps} while congestion persists.
Policing drops out-of-profile packets immediately rather than buffering them.

Key Concept

Low Latency Queuing (LLQ) Priority Queue Policing
Estimated Time:2m 0s
Question 6Question

An enterprise network engineer is configuring a Cisco IOS router (R1) to forward DHCP requests from client hosts located on subnet 10.50.1.0/2410.50.1.0/24 to a centralized DHCP server with IPv4 address 172.16.10.25172.16.10.25. Client hosts connect directly to R1 via interface GigabitEthernet0/0/1 (10.50.1.1/2410.50.1.1/24), while interface GigabitEthernet0/0/0 (172.16.1.1/24172.16.1.1/24) routes traffic toward the DHCP server network. Which configuration command must be applied to ensure R1 properly relays client DHCP broadcast requests to the server?

Show answer & explanation

Answer: Apply the `ip helper-address 172.16.10.25` command under the incoming client gateway interface GigabitEthernet0/0/1 configuration mode.

Answer

Apply the command `ip helper-address 172.16.10.25` on interface GigabitEthernet0/0/1.
To function as a DHCP relay agent, a Cisco router interface receiving client broadcast requests must be configured with `ip helper-address <server-ip>`. Applying this command to the client-facing gateway interface (GigabitEthernet0/0/1) enables the router to listen for UDP port 67 broadcast traffic, encapsulate it as unicast, insert its gateway IP address (`giaddr`), and send it directly to the designated DHCP server (172.16.10.25172.16.10.25).

Step-by-Step Solution

1
Identify the ingress interface receiving client DHCP broadcasts
Interface GigabitEthernet0/0/1 receives the initial DHCPDISCOVER broadcast packets from client hosts on subnet 10.50.1.0/2410.50.1.0/24.
DHCP broadcast traffic (255.255.255.255255.255.255.255) is dropped by routers by default unless intercepted at the incoming gateway interface.
2
Determine the correct command syntax and placement for DHCP relay agent functionality
Executing `ip helper-address 172.16.10.25` within `config-if` mode on GigabitEthernet0/0/1 configures R1 to forward DHCP broadcasts as unicast packets to the target server IP address.
The router sets the `giaddr` (gateway IP address) field in the DHCP packet header to 10.50.1.110.50.1.1, allowing the remote server to select the correct IP pool.

Key Concept

DHCP Relay Agent Interface Placement and Operation
Estimated Time:1m 15s
Question 7Question

An enterprise network engineer is analyzing DNS name resolution behavior across internal workstations and external edge firewalls. The infrastructure uses an internal Active Directory DNS server that forwards unknown domain requests to an external resolver. Which two statements correctly describe DNS transport protocol operation and name resolution roles in this environment?

Select all that apply

Show answer & explanation

Answer: Standard DNS queries and responses primarily utilize UDP port 53, but DNS transitions to TCP port 53 when a response payload exceeds 512 bytes (without EDNS0 extensions).; The internal Active Directory DNS server acts as a recursive resolver for enterprise client hosts while functioning as an authoritative server for the local internal domain namespace.

Answer

The correct statements are that DNS queries primarily use UDP port 53 but switch to TCP port 53 when response payloads exceed 512 bytes without EDNS0, and that the internal Active Directory DNS server acts as a recursive resolver for internal clients while being authoritative for the local domain.
The correct options accurately identify that DNS relies primarily on UDP port 53 for standard client lookups, switching to TCP port 53 when responses exceed 512 bytes without EDNS0 extensions. Additionally, they correctly identify that an internal enterprise DNS server serves a dual role: authoritative for internal zone records and recursive resolver for endpoint clients requesting external or un-cached domain names.

Step-by-Step Solution

1
Analyze transport layer protocol usage for DNS queries and responses.
DNS uses UDP port 53 for standard low-overhead queries and responses under 512 bytes. If a response sets the Truncation (TC) bit because it exceeds 512 bytes, the client re-issues the query using TCP port 53.
UDP avoids connection establishment latency for small lookup packets, but TCP provides reliable stream delivery for oversized payloads.
2
Evaluate the distinction between authoritative DNS servers and recursive resolvers.
An internal Active Directory DNS server holds authoritative records for internal resources (such as domain controllers and local hostnames) and resolves non-local queries on behalf of client hosts recursively or via forwarders.
Clients do not query root and TLD servers directly; they rely on their configured recursive resolver to navigate the DNS hierarchy or forward requests.
3
Evaluate incorrect protocol and role assumptions.
Zone transfers require TCP port 53 due to database size and reliability requirements. Clients do not default to TCP port 53 for normal queries, nor do authoritative-only servers perform recursion for external clients.
Distinguishing between control plane operations (zone transfers), data plane lookups (client queries), and server roles (authoritative vs. recursive) clarifies correct DNS architecture.

Key Concept

DNS Transport Protocols and Server Roles in Enterprise Networks
Question 8Question

An enterprise WAN edge router frequently transmits micro-bursts of database traffic that temporarily exceed the contract rate limit set by the service provider. The network engineer must implement a Quality of Service (QoS) mechanism on the egress WAN interface that regulates outbound transmission rates to match the provider's limit by holding excess packets in memory queues for later transmission rather than immediately dropping them. Which QoS mechanism should be configured on the router interface?

Show answer & explanation

Answer: Traffic Shaping

Answer

Traffic Shaping is the correct mechanism because it uses software queues to buffer excess traffic and smooth out rate bursts before sending packets across the egress link.
Traffic Shaping is a traffic conditioning mechanism applied in the egress direction that buffers excess packets in memory queues when traffic exceeds the configured Committed Information Rate (CIR). It slowly releases packets over time, creating a smooth output rate that prevents service provider packet drops.

Step-by-Step Solution

1
Analyze the operational requirements stated in the scenario.
The requirement demands regulating outbound WAN traffic to a target rate while buffering bursty traffic instead of dropping it.
Understanding the difference between packet dropping and packet buffering key behavior is critical for QoS traffic conditioning selection.
2
Compare Traffic Shaping and Traffic Policing operational characteristics.
Traffic Shaping buffers out-of-profile packets in memory queues, whereas Traffic Policing drops or remarks out-of-profile packets.
Buffering enables smoothing of bursty traffic flows at the cost of slight delay, fulfilling the exact requirement.

Key Concept

Traffic Shaping vs. Traffic Policing Mechanisms
Question 9Question

To permit multiple internal private hosts to share the single public IPv4 address assigned to the GigabitEthernet0/0/0 WAN interface, which Cisco IOS command correctly implements Port Address Translation (PAT) for traffic permitted by Access Control List 15?

Show answer & explanation

Answer: ip nat inside source list 15 interface GigabitEthernet0/0/0 overload

Answer

The command 'ip nat inside source list 15 interface GigabitEthernet0/0/0 overload' correctly enables Port Address Translation (PAT).
The command specifying 'ip nat inside source list 15 interface GigabitEthernet0/0/0 overload' correctly binds the access list to the egress interface and appends the 'overload' keyword, which enables Port Address Translation (PAT) so multiple internal devices can share a single public IPv4 address.

Step-by-Step Solution

1
Identify the requirement for Port Address Translation (PAT)
Multiple internal hosts sharing a single public interface IP requires PAT (overload).
PAT uses unique source port numbers to track connections for multiple internal hosts behind a single IP address.
2
Formulate the Cisco IOS PAT interface command syntax
The correct command structure is 'ip nat inside source list <acl> interface <interface> overload'.
The 'inside source list' parameter references the internal traffic ACL, 'interface' specifies the egress IP source, and 'overload' enables port multiplexing.

Key Concept

Port Address Translation (PAT) Interface Overload Configuration
Question 10Question

A network administrator is setting up Port Address Translation (PAT) on a Cisco IOS router using a public address pool named `PAT_POOL` and Access Control List `5`. Which two commands are required to correctly establish PAT and configure the LAN interface to participate in address translation? (Select two.)

Select all that apply

Show answer & explanation

Answer: ip nat inside source list 5 pool PAT_POOL overload; ip nat inside

Answer

The two required commands are 'ip nat inside source list 5 pool PAT_POOL overload' entered in global configuration mode and 'ip nat inside' entered under the LAN interface configuration mode.
Configuring Port Address Translation (PAT) with an IP pool requires appending the 'overload' parameter to the global 'ip nat inside source list' command. Additionally, the internal interface connected to the local network must be identified with the interface-level command 'ip nat inside'.

Step-by-Step Solution

1
Identify the global configuration command for pool-based PAT
Determine that 'ip nat inside source list 5 pool PAT_POOL overload' is required to map inside local hosts matching ACL 5 to the PAT_POOL while enabling port overloading.
The 'overload' keyword allows multiple private internal IP addresses to share public IP addresses in the pool by tracking unique TCP/UDP port numbers.
2
Identify the interface configuration command for internal boundary identification
Select 'ip nat inside' on the LAN interface.
Cisco IOS routers require explicit designation of NAT boundaries to determine where packet translation takes place.

Key Concept

Inside Source Port Address Translation (PAT) configuration requiring the overload keyword and inside interface designation.
Question 11Question

A network administrator configures a Cisco IOS router to synchronize its internal clock with an enterprise NTP server operating at Stratum 2. Arrange the operational steps in chronological order from initial packet transmission to the point where the router can act as a valid time source for downstream clients.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence of operations is: 1) The router sends an NTP client mode query (UDP port 123) to the server. 2) The router receives an NTP server mode response with Stratum 2 metadata. 3) The router computes round-trip delay, dispersion, and clock offset algorithms. 4) The router synchronizes its system clock and increments its operational stratum to Stratum 3. 5) The router begins answering incoming NTP queries from downstream clients.
NTP synchronization follows a strict sequential process: outbound UDP 123 request initiation, receipt of server time payload and stratum attributes, statistical filtering of offset and round-trip delay, local clock adjustment accompanied by stratum incrementing (N+1N+1), and finally responding to downstream client requests as a synchronized master time source.

Step-by-Step Solution

1
Initiate communication
Router sends an outbound NTP client packet over UDP port 123 to the NTP server address.
Synchronization starts when the client polls the server for time information.
2
Receive server response
Server replies with timestamp, stratum level (Stratum 2), and reference clock identification.
The server must supply its current time and stratum attributes back to the client.
3
Process NTP statistical filtering
Router calculates offset and network delay while filtering out jitter and invalid timestamps.
Packet delay and clock drift must be calculated before modifying the local system time.
4
Update local system time and stratum
Local clock synchronizes, and local stratum becomes Stratum 3 (2+12 + 1).
A synchronized NTP device always assumes a stratum number one unit higher than its synchronization source.
5
Serve downstream clients
Router processes and responds to NTP requests from local hosts.
Downstream devices can only receive valid, synchronized time after the router completes synchronization and establishes a valid stratum (< 16).

Key Concept

NTP Client-Server Initialization Sequence and Stratum Calculation
Question 12Question

A network engineer is configuring Port Address Translation (PAT) on a Cisco IOS router using an IP NAT pool named `INTERNET_POOL` for internal endpoints matched by access list `10`. Which global configuration command correctly enables PAT using this address pool?

Show answer & explanation

Answer: ip nat inside source list 10 pool INTERNET_POOL overload

Answer

The command 'ip nat inside source list 10 pool INTERNET_POOL overload' correctly enables Port Address Translation using the specified pool.
The correct command uses 'ip nat inside source list 10 pool INTERNET_POOL overload'. The 'inside source' parameter specifies translation for outbound traffic originating inside the network, 'list 10' identifies hosts permitted by ACL 10, 'pool INTERNET_POOL' designates the global address pool, and 'overload' enables port-level multiplexing (PAT) so multiple internal endpoints can share pool addresses simultaneously.

Step-by-Step Solution

1
Identify the direction of translation.
Internal hosts initiating outbound connections require 'inside source' translation.
Inside source NAT translates private local IP addresses to public global addresses.
2
Identify the method of matching source addresses and defining the public addresses.
Access list 10 filters inside local hosts, and the named pool 'INTERNET_POOL' defines the public IPv4 addresses.
The 'list 10 pool INTERNET_POOL' syntax binds the ACL host match condition to the pool range.
3
Determine the keyword required for Port Address Translation (PAT).
Adding the 'overload' keyword enables multiplexing multiple internal hosts onto pool addresses using unique TCP/UDP port numbers.
Without 'overload', Cisco IOS restricts dynamic NAT to a strict 1-to-1 IP address mapping.

Key Concept

Port Address Translation (PAT) configuration using dynamic address pools in Cisco IOS
Estimated Time:1m 0s
Question 13Question

An administrator needs to configure Port Address Translation (PAT) on a Cisco IOS router so that all internal hosts on the subnet 172.16.50.0/24172.16.50.0/24 can access the Internet using the IPv4 address assigned to the WAN interface GigabitEthernet0/1. Interface GigabitEthernet0/0 connects to the internal LAN. Which configuration set correctly accomplishes this requirement?

Show answer & explanation

Answer: interface GigabitEthernet0/0
ip nat inside
!
interface GigabitEthernet0/1
ip nat outside
!
access-list 15 permit 172.16.50.0 0.0.0.255
ip nat inside source list 15 interface GigabitEthernet0/1 overload

Answer

The command sequence configuring GigabitEthernet0/0 as ip nat inside, GigabitEthernet0/1 as ip nat outside, ACL 15 matching 172.16.50.0 0.0.0.255, and 'ip nat inside source list 15 interface GigabitEthernet0/1 overload' correctly enables PAT.
The correct command set properly sets GigabitEthernet0/0 as the inside interface and GigabitEthernet0/1 as the outside interface, specifies standard ACL 15 to match the 172.16.50.0/24 subnet, and uses the 'overload' keyword with the egress interface to enable Port Address Translation (PAT).

Step-by-Step Solution

1
Identify and designate the NAT interfaces
GigabitEthernet0/0 is configured with 'ip nat inside' (internal LAN) and GigabitEthernet0/1 is configured with 'ip nat outside' (WAN interface).
Cisco IOS NAT requires specifying directionality on interfaces to know where translation occurs.
2
Define an Access Control List (ACL) matching internal private IPs
Access-list 15 matches subnet 172.16.50.0 with wildcard mask 0.0.0.255.
The ACL identifies which internal source IP addresses are eligible for address translation.
3
Configure PAT using interface overloading
Execute 'ip nat inside source list 15 interface GigabitEthernet0/1 overload'.
The 'overload' keyword enables Port Address Translation (PAT), allowing multiple internal hosts to share the single IP address assigned to the egress interface by tracking layer 4 port numbers.

Key Concept

Port Address Translation (PAT) Configuration using Interface Overload
Estimated Time:1m 15s
Question 14Question

A network administrator is reviewing telemetry and alerting mechanisms across enterprise Cisco routers. Which TWO statements accurately describe the operational differences between SNMP traps and SNMP informs? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: SNMP traps are unacknowledged notification messages sent asynchronously by managed devices to an SNMP management station over UDP port 162.; SNMP informs require the receiving SNMP manager to acknowledge receipt of the notification, providing reliable delivery confirmation to the sending device.

Answer

SNMP traps are unacknowledged notifications sent over UDP port 162, while SNMP informs require an explicit acknowledgement from the receiving SNMP management station to confirm delivery.
SNMP traps are unacknowledged notifications sent to UDP port 162 on the management station. In contrast, SNMP informs provide reliable delivery by requiring the manager to respond with an acknowledgement PDU.

Step-by-Step Solution

1
Identify the transport port and delivery mechanism for SNMP traps.
SNMP traps are unacknowledged UDP messages directed to UDP port 162 on the NMS.
Traps provide best-effort, fire-and-forget event reporting.
2
Identify the acknowledgment behavior of SNMP informs.
SNMP informs require an explicit application-layer response from the receiving NMS.
If no acknowledgement is received, the agent holds the inform in memory and retransmits it until confirmed or timed out.

Key Concept

SNMP Trap vs Inform Operations and UDP Port Assignments
Question 15Question

A network engineer is troubleshooting internet connectivity issues on a Cisco IOS router configured for Network Address Translation. Internal hosts on the 10.10.10.0/2410.10.10.0/24 network report that only one host can access external resources at any given time. Subsequent host traffic is dropped. The engineer inspects the router configuration and operational state using verification commands:

text
Router# show ip nat statistics
Total active translations: 1 (0 static, 1 dynamic, 1 extended)
Outside interfaces:
GigabitEthernet0/1
Inside interfaces:
GigabitEthernet0/0
Hits: 48 Misses: 12
CEF Translated packets: 48, Fast Switched packets: 0
Expired translations: 15
Dynamic mappings:
-- Inside Source
[id 1] access-list 101 pool INTERNET-POOL refcount 1
pool INTERNET-POOL: netmask 255.255.255.252
start 203.0.113.1 end 203.0.113.1
type generic, total addresses 1, allocated 1 (100%), misses 12

Router# show running-config | include ip nat
ip nat pool INTERNET-POOL 203.0.113.1 203.0.113.1 netmask 255.255.255.252
ip nat inside source list 101 pool INTERNET-POOL
access-list 101 permit ip 10.10.10.0 0.0.0.255 any

Which configuration change is required to allow all internal hosts on the 10.10.10.0/2410.10.10.0/24 network to share the single public IPv4 address simultaneously?

Show answer & explanation

Answer: Append the overload keyword to the command ip nat inside source list 101 pool INTERNET-POOL.

Answer

Appending the overload keyword to the statement ip nat inside source list 101 pool INTERNET-POOL converts dynamic 1-to-1 NAT into Port Address Translation (PAT), enabling multiple internal hosts to share a single public IP address using unique source port numbers.
The command output indicates that the NAT pool contains only one IP address (203.0.113.1) and is 100% allocated without overload enabled. Because the overload keyword was omitted from the inside source translation statement, Cisco IOS performs dynamic 1-to-1 translation. Appending the overload keyword enables Port Address Translation (PAT), allowing multiple inside hosts to share the single IP address by using unique Layer 4 port numbers.

Step-by-Step Solution

1
Analyze the output of show ip nat statistics and show running-config.
The pool INTERNET-POOL contains 1 total public IPv4 address (203.0.113.1). Allocation shows 1 allocated (100%) with 12 misses, indicating address pool exhaustion.
Without port multiplexing, dynamic NAT performs strict 1-to-1 mapping. Once all pool addresses are allocated, subsequent translation requests fail.
2
Identify the missing keyword in the NAT translation command.
The configuration entry ip nat inside source list 101 pool INTERNET-POOL lacks the overload keyword.
The overload keyword instructs Cisco IOS to track Layer 4 source port numbers (PAT), enabling thousands of concurrent internal connections over a single IP address.
3
Formulate the correct configuration fix.
Reconfigure the router statement to ip nat inside source list 101 pool INTERNET-POOL overload.
This modification resolves translation misses and allows all hosts on the 10.10.10.0/24 network to share 203.0.113.1 simultaneously.

Key Concept

Port Address Translation (PAT) Overload Configuration
Question 16Question

An enterprise network administrator is updating the SNMP monitoring configuration on a Cisco IOS XE core router to meet strict security and monitoring compliance standards. The updated policy mandates two specific requirements for outbound system event notifications sent to the central Network Management System (NMS):
1. All notifications must be encrypted using AES privacy and cryptographically authenticated using SHA.
2. Outbound notifications must require explicit application-layer acknowledgments from the NMS, causing the router to resend notification packets if no acknowledgment is received.

Which combination of SNMP protocol settings and message types must be configured on the router to fulfill both requirements?

Show answer & explanation

Answer: SNMPv3 operating at the authPriv security level utilizing SNMP Informs

Answer

The router must be configured for SNMPv3 operating at the authPriv security level using SNMP Informs.
SNMPv3 with the authPriv security level supports both authentication (SHA/MD5) and encryption/privacy (AES/DES). SNMP Informs provide reliable notification delivery because the managed device holds the notification in memory and retries transmission until an explicit acknowledgment PDU is received from the NMS.

Step-by-Step Solution

1
Evaluate the security requirement (authentication and encryption).
Identify that SNMPv3 defines three security models: noAuthNoPriv (no security), authNoPriv (authentication without encryption), and authPriv (authentication with encryption).
To satisfy the mandate for SHA authentication combined with AES encryption, the authPriv security level must be selected.
2
Evaluate the notification delivery requirement (acknowledgments and retries).
Differentiate between SNMP Traps and SNMP Informs.
SNMP Traps are unacknowledged notifications (fire-and-forget). SNMP Informs require the receiving NMS to return an acknowledgment PDU; if the agent does not receive an ACK within the timeout period, it retransmits the Inform.
3
Synthesize the security and operational mechanics requirements.
Selecting SNMPv3 authPriv with SNMP Informs satisfies both cryptographic security and reliable delivery criteria.
Combining authPriv (for SHA/AES) and Informs (for acknowledged delivery) satisfies all security policy constraints.

Key Concept

SNMPv3 Security Levels (authPriv) and Notification Reliability Mechanics (Informs vs Traps)
Question 17Question

A network engineer is troubleshooting event notifications on a Cisco IOS XE router. During periods of heavy WAN link congestion, critical interface state notifications sent to the Network Management System (NMS) are occasionally dropped and lost. The organization mandates that all management notifications must require an explicit application-layer acknowledgment from the NMS to trigger retransmissions if unacknowledged, while ensuring message integrity, authentication, and payload encryption. Which SNMP configuration change satisfies both the operational delivery guarantee and security requirements?

Show answer & explanation

Answer: Configure the router to send SNMP Informs rather than Traps, and define the SNMPv3 host with the authPriv security level.

Answer

Configure the router to send SNMP Informs rather than Traps, and define the SNMPv3 host with the authPriv security level.
SNMP Traps are unidirectional, unacknowledged UDP messages sent to port 162. Under congested network conditions, lost Traps are never retransmitted. In contrast, SNMP Informs require the receiving Network Management System (NMS) to return an SNMP response back to the agent; if an acknowledgment is not received within a timeout period, the router retransmits the notification. Additionally, SNMPv3 authPriv provides both HMAC authentication and payload encryption (privacy), satisfying the strict security policy.

Step-by-Step Solution

1
Analyze notification delivery requirements.
Identified that SNMP Traps are unacknowledged UDP messages (fire-and-forget), whereas SNMP Informs require an application-layer SNMP response (acknowledgment) from the NMS and will retransmit if no response is received.
To survive packet drops during WAN congestion, application-layer acknowledgments provided by SNMP Informs are required.
2
Analyze security model requirements.
Identified that authentication (integrity/hashing) plus payload encryption (privacy) corresponds strictly to the SNMPv3 authPriv security level.
authNoPriv provides authentication without encryption, and noAuthNoPriv provides neither authentication nor encryption.
3
Combine operational mechanics and security configuration.
Selected SNMP Informs combined with SNMPv3 authPriv as the correct solution.
This combination satisfies both reliable delivery via retransmissions and strict data confidentiality/integrity.

Key Concept

SNMP Informs vs Traps operational mechanics and SNMPv3 Security Levels (authPriv)
Question 18Question

A network administrator is configuring a Cisco IOS router to function as a DHCP server for a local subnet. To avoid IP address conflicts with statically configured devices such as default gateways and printers, the administrator must prevent the DHCP server from allocating addresses in the range 192.168.10.1 through 192.168.10.10. Which command should be executed in global configuration mode to accomplish this requirement?

Show answer & explanation

Answer: ip dhcp excluded-address 192.168.10.1 192.168.10.10

Answer

The command 'ip dhcp excluded-address 192.168.10.1 192.168.10.10' entered in global configuration mode correctly reserves the designated range of IP addresses so the local Cisco IOS DHCP server will not allocate them to dynamic clients.
Executing 'ip dhcp excluded-address 192.168.10.1 192.168.10.10' in global configuration mode instructs the Cisco IOS DHCP server to reserve all IP addresses from 192.168.10.1 through 192.168.10.10 inclusive, ensuring they are never offered to dynamic DHCP clients.

Step-by-Step Solution

1
Identify the configuration requirement for reserving static IP addresses on a Cisco IOS DHCP server.
Recognize that static IP addresses must be excluded before the DHCP server assigns them to pool clients to prevent duplicate IP address conflicts.
Cisco IOS DHCP servers issue any available address in a configured pool unless explicitly told not to assign specific addresses.
2
Select the appropriate Cisco IOS command mode and syntax.
Determine that global configuration mode command 'ip dhcp excluded-address <low-ip> <high-ip>' is used.
Exclusions are defined globally outside of the specific DHCP pool configuration mode context.

Key Concept

DHCP Address Exclusion Configuration
Question 19Question

A network technician needs to verify the configured SSH version, authentication timeout, and maximum retry limits on a Cisco IOS switch named SW-Access-01. Which privileged EXEC mode command provides this specific operational summary?

Show answer & explanation

Answer: show ip ssh

Answer

The command 'show ip ssh' displays global SSH status, protocol version, authentication timeout, and retry settings on a Cisco IOS device.
The command 'show ip ssh' displays global SSH server operational parameters on Cisco IOS, including whether SSH is enabled, the active version (v1 or v2), authentication timeout, and maximum authentication retries.

Step-by-Step Solution

1
Identify the CLI verification requirement
The requirement asks for global SSH server settings including version, timeout, and retry limits.
Different verification commands display distinct aspects of remote access operations.
2
Distinguish between 'show ip ssh' and 'show ssh'
'show ip ssh' displays protocol configuration and status, while 'show ssh' displays active user connection sessions.
Understanding command output specificity is essential for Cisco IOS verification.

Key Concept

Cisco IOS SSH Verification Commands
Estimated Time:45s
Question 20Question

A network administrator is configuring Port Address Translation (PAT) on an enterprise Cisco IOS router. The internal subnets matched by Access Control List 15 require multiple internal IP addresses to share a dynamic pool of public IPv4 addresses named GUESTNATPOOLGUEST_NAT_POOL. Which Cisco IOS global configuration command correctly enables PAT using this dynamic address pool?

Show answer & explanation

Answer: ip nat inside source list 15 pool GUEST_NAT_POOL overload

Answer

The correct command to configure dynamic PAT using an IP address pool is 'ip nat inside source list 15 pool GUEST_NAT_POOL overload'.
The correct command syntax for dynamic NAT with PAT using an IP address pool is 'ip nat inside source list <acl-number> pool <pool-name> overload'. The 'overload' keyword enables Layer 4 source port tracking so multiple internal IP addresses can share the IP addresses in the pool simultaneously.

Step-by-Step Solution

1
Identify the source direction and dynamic NAT type
Inside source traffic matching an ACL requires 'ip nat inside source list <ACL>'.
Internal private hosts initiating outbound connections must undergo inside source NAT.
2
Specify the target public address pool
Append 'pool GUEST_NAT_POOL' to map matching ACL traffic to the designated pool.
The scenario requires using a pre-defined named pool of public IP addresses instead of a single interface.
3
Enable port multiplexing (PAT)
Append the 'overload' keyword at the end of the command.
Without 'overload', Cisco IOS configures standard dynamic NAT (1-to-1 translation), whereas PAT (many-to-one/many-to-few using layer 4 ports) explicitly requires 'overload'.

Key Concept

Port Address Translation (PAT) pool configuration using the overload keyword
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