IP Services

198 soru

Tüm türler198 Çoktan seçmeli102 Çoklu seçim45 Eşleştirme12 Sıralama27 Kısa cevap12

Place the following operational steps in the correct chronological order to show how a Cisco router configured as a DHCP relay agent processes an incoming client discovery message.

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Cevabı ve açıklamayı göster

Cevap

The correct sequence begins with the host client broadcasting a DHCP DISCOVER packet on its local subnet. Next, the local router interface receives the broadcast packet and evaluates the configured ip helper-address. The router then inserts its local receiving interface IP address into the Gateway IP Address (giaddr) field. Finally, the router converts the packet to a unicast IP packet and forwards it to the target DHCP server address.

When an unconfigured host requests an IP address, it broadcasts a DHCP DISCOVER frame. The local router interface intercepts this broadcast, modifies the DHCP header by adding its receiving interface IP to the giaddr field, and changes the destination from broadcast to unicast directed at the configured DHCP server IP.

Adım Adım Çözüm

Identify the client-side initiation of the DHCP process.

The host client generates a broadcast DHCP DISCOVER message.

Unconfigured hosts must use broadcast addressing to discover available DHCP servers on the local segment.

Determine the initial reception step by the relay agent.

The router interface captures the broadcast and checks for an active ip helper-address statement.

The ip helper-address command instructs the interface to process incoming UDP port 67 broadcast traffic.

Identify the mandatory payload modification performed by the relay agent.

The router writes its own interface IP into the packet's giaddr field.

Without the giaddr field populated, the central server cannot determine which pool and subnet address range to offer.

Determine the final packet forwarding operation.

The router forwards the modified DHCP request as a unicast packet to the central DHCP server.

Broadcasts are not routed by default; relaying requires converting the frame into a unicast transmission targeting the DHCP server.

Anahtar Kavram

DHCP Relay Agent Operation and Payload Modification (giaddr)

Tahmini Süre:45s

Soru 142Soru →

A network operations center engineer is reviewing syslog messages emitted by a Cisco IOS router. Arrange the following syslog events in order from HIGHEST severity (lowest numerical severity level) to LOWEST severity (highest numerical severity level).

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Cevap

The correct sequence from highest severity (lowest numeric value) to lowest severity (highest numeric value) is: 1) Hardware watchdog system failure (Level 0 - Emergency), 2) Duplex mismatch error (Level 3 - Error), 3) Configuration commit notice (Level 5 - Notice), 4) Syslog server initialization message (Level 6 - Informational), and 5) Debug packet trace output (Level 7 - Debugging).

The correct ordering aligns with the standard Cisco IOS Syslog numerical severity scale: 0 (Emergency), 1 (Alert), 2 (Critical), 3 (Error), 4 (Warning), 5 (Notice), 6 (Informational), and 7 (Debugging). The hardware failure message is Emergency (Level 0), followed by interface error (Level 3), configuration change (Level 5), syslog service initialization (Level 6), and debug packet trace output (Level 7).

Adım Adım Çözüm

Determine the numerical severity code assigned to each Cisco IOS event category in the Syslog standard.

System failure = Level 0 (Emergency); Duplex mismatch = Level 3 (Error); Configuration commit = Level 5 (Notice); Syslog host initialization = Level 6 (Informational); Debug packet trace = Level 7 (Debugging).

Cisco IOS categorizes log severity from Level 0 (most critical) through Level 7 (least critical).

Order the identified events in ascending numerical order of their severity levels.

The numerical order is 0 -> 3 -> 5 -> 6 -> 7.

A lower numerical severity level corresponds to a higher criticality event in Syslog architecture.

Anahtar Kavram

Cisco IOS Syslog severity level taxonomy (0-Emergency to 7-Debugging)

Soru 143Soru →

Clients connected to VLAN 10 successfully receive dynamic IP addresses from a remote server located at 192.168.100.50, but clients on VLAN 20 fail to obtain IP addresses and assign themselves 169.254.x.x addresses.

An engineer inspects the running configuration of router R1:

text
interface GigabitEthernet0/0.10
encapsulation dot1Q 10
ip address 10.10.10.1 255.255.255.0
ip helper-address 192.168.100.50
!
interface GigabitEthernet0/0.20
encapsulation dot1Q 20
ip address 10.10.20.1 255.255.255.0
!
interface GigabitEthernet0/1
description Connection to DHCP Server Subnet
ip address 192.168.100.1 255.255.255.0
ip helper-address 192.168.100.50

Which configuration change on router R1 will restore DHCP functionality for clients on VLAN 20?

Remove the helper address command from interface GigabitEthernet0/1 and add ip helper-address 192.168.100.50 under subinterface GigabitEthernet0/0.20.

Add ip helper-address 10.10.20.1 under interface GigabitEthernet0/1 to forward server response packets back to the subinterface.

Configure ip helper-address 10.10.20.255 under interface GigabitEthernet0/0 to flood DHCP broadcasts across all subinterfaces.

Add ip helper-address 192.168.100.255 under subinterface GigabitEthernet0/0.20 to broadcast requests across the destination subnet.

Cevabı ve açıklamayı göster

Cevap: Remove the helper address command from interface GigabitEthernet0/1 and add ip helper-address 192.168.100.50 under subinterface GigabitEthernet0/0.20.

Cevap

Remove the helper address configuration from interface GigabitEthernet0/1 and configure ip helper-address 192.168.100.50 under subinterface GigabitEthernet0/0.20.

To relay DHCP broadcast requests from clients to a server on a different subnet, the Cisco IOS `ip helper-address <server-ip>` command must be configured on the client-facing layer 3 interface (subinterface GigabitEthernet0/0.20). In the provided scenario, subinterface GigabitEthernet0/0.20 is missing the command, while interface GigabitEthernet0/1 mistakenly has it configured. Moving the command to GigabitEthernet0/0.20 allows R1 to intercept VLAN 20 broadcast DISCOVER messages, insert 10.10.20.1 as the gateway address (GIADDR), and unicast the request to 192.168.100.50.

Adım Adım Çözüm

Analyze client-to-relay path requirements

DHCP DISCOVER packets generated by clients are local Layer 2 broadcasts targeted to UDP port 67.

Routers drop Layer 2/Layer 3 broadcast packets by default and do not forward them between interfaces or subinterfaces.

Identify correct placement of the ip helper-address command

The `ip helper-address` command must be applied to the incoming (ingress) interface where client broadcasts originate (GigabitEthernet0/0.20).

When applied on the client interface, the router intercepts UDP broadcast traffic, populates the GIADDR field with the interface's IP address (10.10.20.1), and unicasts the packet to the specified DHCP server.

Evaluate the current flawed configuration on R1

Subinterface GigabitEthernet0/0.20 lacks `ip helper-address`, while the egress interface GigabitEthernet0/1 has an unnecessary `ip helper-address` configured.

Configuring `ip helper-address` on the egress interface towards the server does nothing for clients on VLAN 20 because client broadcasts enter on subinterface GigabitEthernet0/0.20 and are dropped before reaching interface GigabitEthernet0/1.

Anahtar Kavram

DHCP Relay Agent Configuration and Placement

Tahmini Süre:1m 30s

Soru 144Soru →

An administrator configures dynamic NAT on a Cisco IOS router using a pool containing a single public IP address ( $203.0.113.100$ ) to enable Internet connectivity for internal workstations. During testing, only the first internal user who initiates outbound traffic can access external sites. All subsequent attempts from other internal users to access the Internet fail. Which action on the router resolves this connectivity issue?

Append the `overload` keyword to the `ip nat inside source list <ACL> pool <POOL>` configuration command.

Expand the internal access list to match the public IP range

172.32.0.0/12

instead of RFC 1918 private space.

Reconfigure the translation using `ip nat inside source static` to dynamically allocate port numbers to the pool.

Swap the interface assignments so that the LAN interface is configured with `ip nat outside` and the WAN with `ip nat inside`.

Cevabı ve açıklamayı göster

Cevap: Append the `overload` keyword to the `ip nat inside source list <ACL> pool <POOL>` configuration command.

Cevap

Append the `overload` keyword to the global `ip nat inside source list <ACL> pool <POOL>` command to enable Port Address Translation (PAT).

When dynamic NAT is configured with an IP NAT pool containing a single public IP address, omitting the `overload` keyword restricts translations to a single 1-to-1 mapping. Once the first host initiates traffic, the single address in the pool is exhausted. Appending the `overload` keyword enables Port Address Translation (PAT), allowing multiple internal hosts to share the single IP address concurrently by tracking unique Layer 4 source port numbers.

Adım Adım Çözüm

Analyze the symptom of dynamic NAT failure.

Without port translation enabled, dynamic NAT allocates pool IP addresses on a strict 1-to-1 basis. With a single public IP address in the pool, only one internal host receives a translation entry.

Determines why subsequent internal hosts fail to obtain an outbound translation.

Identify the required feature for many-to-one translation using a single IP address.

Port Address Translation (PAT) allows thousands of internal hosts to multiplex outbound connections over a single IP address using unique TCP/UDP source ports.

PAT is activated on Cisco IOS dynamic NAT configurations by appending the `overload` keyword.

Select the correct command modification.

Modifying the translation statement to include `overload` (`ip nat inside source list <ACL> pool <POOL> overload`) resolves the single-host limitation.

Applies PAT, enabling all internal hosts to share the single public IP address concurrently.

Anahtar Kavram

Port Address Translation (PAT) Overload Configuration

Soru 145Soru →

A Cisco IOS router is configured as an authoritative DHCP server with IP address conflict detection enabled (using the default ping settings). Place the operational steps in the correct chronological order to show how the router handles an incoming broadcast DHCP DISCOVER packet from a new client.

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Cevap

The correct operational sequence is: 1) Select candidate IP address from pool based on client subnet -> 2) Send ICMP Echo Requests to verify address availability -> 3) Send DHCP OFFER to client after ICMP timeout -> 4) Receive client DHCP REQUEST accepting the offer -> 5) Create IP binding entry and send DHCP ACK.

When Cisco IOS conflict detection is active, the router evaluates an available IP address from the pool upon receiving a DHCP DISCOVER message. It probes the address using ICMP Echo Requests before transmitting a DHCP OFFER. If no reply is received, it sends the DHCP OFFER. The client responds with a DHCP REQUEST, and the server finishes the handshake by writing the binding and returning a DHCP ACK.

Adım Adım Çözüm

Address Selection

The router identifies an available IP address within the pool range matching the incoming interface subnet.

The server must choose a candidate address prior to testing its availability.

Conflict Detection (Ping Check)

The router emits ICMP Echo Request pings to the candidate IP address (2 pings by default in Cisco IOS).

Cisco IOS conflict detection prevents assigning duplicate IP addresses already active on the local segment.

DHCP OFFER Transmission

Having received no ICMP Echo Reply, the router builds and sends a DHCP OFFER containing the candidate IP address, subnet mask, default router, and DNS settings.

Absence of ping reply confirms the IP is free to offer.

DHCP REQUEST Receipt

The client processes the offer and broadcasts a DHCP REQUEST packet to notify all local DHCP servers of its choice.

The client must explicitly request the offered parameters.

Binding Creation and DHCP ACK

The server records the MAC-to-IP binding in `show ip dhcp binding` and sends a DHCP ACK back to the client.

The lease is finalized only when the server acknowledges the client request and stores the active binding.

Anahtar Kavram

Cisco IOS DHCP Server Address Conflict Detection Sequence during DORA Process

Soru 146Soru →

A network administrator is deploying SNMPv3 on a Cisco IOS router to allow a central Network Management System (NMS) located at $10.20.1.100$ to poll interface metrics. The administrator configures a custom MIB view and applies an inbound extended Access Control List (ACL) on the router's management interface ( $10.20.1.1$ ).

The router configuration is as follows:
text
snmp-server view IF_ONLY 1.3.6.1.2.1.2 included
snmp-server group MON_GROUP v3 priv read IF_ONLY
snmp-server user MON_USER MON_GROUP v3 auth sha Pass123 priv aes 128 Priv456
ip access-list extended MGMT_ACL
permit udp host 10.20.1.100 host 10.20.1.1 eq 162
deny ip any any
interface GigabitEthernet0/0
ip access-group MGMT_ACL in

When the NMS attempts to perform SNMP GetRequest operations to monitor interface statistics, all polling requests fail due to timeouts. Which modification will restore SNMP polling functionality?

Update MGMT_ACL to permit inbound UDP traffic targeted to destination port 161 on the router.

Remove the explicit deny ip any any statement from MGMT_ACL because Cisco IOS ACLs automatically permit stateless UDP response traffic.

Reconfigure the NMS client to initiate polling requests over TCP port 161 to establish connection state through the interface ACL.

Change the MIB object identifier in the IF_ONLY view from 1.3.6.1.2.1.2 to CDP TLV subtree 1.3.6.1.4.1.9 to allow interface polling.

Cevabı ve açıklamayı göster

Cevap: Update MGMT_ACL to permit inbound UDP traffic targeted to destination port 161 on the router.

Cevap

Update MGMT_ACL to permit inbound UDP traffic targeted to destination port 161 on the router.

SNMP uses two distinct UDP ports for operation: UDP port 161 is used by the SNMP agent (the router) to listen for requests (such as GetRequest, GetNextRequest, and SetRequest) sent by an NMS. UDP port 162 is used by an NMS or notification receiver to listen for asynchronous traps and informs sent by managed agents. Because the NMS is attempting to poll the router for interface stats, the incoming traffic targets UDP port 161. Updating the ACL to permit destination UDP port 161 allows these polling requests to reach the SNMP agent process.

Adım Adım Çözüm

Analyze the SNMP transport port requirements for polling vs notifications.

SNMP agents listen for incoming queries (Get, GetNext, Set) on UDP port 161. SNMP management stations listen for traps and informs on UDP port 162.

The NMS is initiating GetRequest operations toward the router, meaning incoming packets arriving at the router interface will have a destination port of UDP 161.

Inspect the inbound interface ACL MGMT_ACL applied to GigabitEthernet0/0.

The ACL permits UDP traffic from host 10.20.1.100 to host 10.20.1.1 eq 162 and drops all other traffic with deny ip any any.

Because destination port 161 is not permitted, the router drops incoming SNMP GetRequest packets from the NMS before they reach the SNMP engine, resulting in polling timeouts.

Determine the necessary ACL correction.

Modifying the ACL rule to match destination UDP port 161 allows the router to receive and process the SNMPv3 requests.

Permitting UDP port 161 aligns the firewall filter with standard SNMP agent listening behavior.

Anahtar Kavram

SNMP Transport Ports and Inbound Access Control

Soru 147Soru →

A network administrator is troubleshooting remote access on a branch gateway router (Branch-GW). SSH version 2 has been configured, but remote management attempts over SSH fail immediately with a transport layer connection error, whereas Telnet connections are unexpectedly accepted. The administrator collects the following configuration and status outputs from the router:

text
Branch-GW# show ip ssh
SSH Enabled - version 2.0
Authentication timeout: 60 secs; Authentication retries: 3
Device Mode: SSH Server
RSA Key size: 2048 bits

Branch-GW# show running-config | section line vty
line vty 0 4
access-class MGMT-ACCESS in
login local
transport input telnet
line vty 5 15
access-class MGMT-ACCESS in
login local
transport input telnet

Which configuration change must be applied to Branch-GW to resolve the connection issue and enforce secure SSH access on all VTY lines?

Execute transport input ssh under line vty 0 15 to allow inbound SSH sessions.

Add permit any to the MGMT-ACCESS access list because standard ACLs block SSH transport negotiation by default.

Re-execute crypto key generate rsa modulus 512 to reset the key length for SSH version 2 compatibility.

Change login local to login under line vty 0 15 to permit public-key authentication.

Cevabı ve açıklamayı göster

Cevap: Execute transport input ssh under line vty 0 15 to allow inbound SSH sessions.

Cevap

Execute transport input ssh under line vty 0 15 to allow inbound SSH sessions.

The output from 'show running-config' demonstrates that all virtual terminal lines (vty 0 15) are configured with 'transport input telnet'. This restricts incoming management traffic strictly to Telnet (TCP port 23) and causes the router to reject incoming SSH (TCP port 22) connection requests at the line level. Changing the setting to 'transport input ssh' permits SSH inbound sessions.

Adım Adım Çözüm

Analyze 'show ip ssh' verification output

SSH v2 is active and an RSA key of 2048 bits has been properly generated.

Verifies that global SSH preconditions (hostname, domain name, RSA key pair generation) are fully met.

Inspect VTY line configuration under 'show running-config'

'transport input telnet' is explicitly binding VTY lines 0 through 15 to accept only unencrypted Telnet traffic.

Even when SSH service is enabled globally, Cisco IOS VTY lines refuse incoming SSH transport connections if SSH is omitted from transport input.

Identify the required CLI configuration command

Navigate to 'line vty 0 15' and issue 'transport input ssh' (or 'transport input ssh telnet').

Re-enables inbound SSH connections across all virtual terminal lines.

Anahtar Kavram

VTY Line Transport Protocol Binding

Soru 148Soru →

An enterprise router is being configured to share a single public IPv4 address assigned to its WAN interface, Serial0/0/0, among private LAN devices matched by access list 105. What specific Cisco IOS keyword must be appended to the end of the global command `ip nat inside source list 105 interface Serial0/0/0` to enable Port Address Translation (PAT)?

Cevabı ve açıklamayı göster

Cevap: overload

Cevap

overload

The keyword `overload` enables Port Address Translation (PAT) on Cisco IOS routers. Appending `overload` to `ip nat inside source list <acl> interface <interface>` enables transport-layer port multiplexing so multiple inside local IP addresses can be translated to a single inside global IP address simultaneously.

Adım Adım Çözüm

Analyze the global NAT configuration command syntax.

The statement `ip nat inside source list 105 interface Serial0/0/0` binds inside local traffic defined by ACL 105 to the WAN interface's public IP address.

Without port tracking enabled, dynamic NAT maps hosts on a strict 1-to-1 basis, exhausting the single IP address after one translation.

Identify the required keyword for enabling PAT (many-to-one translation).

Appending `overload` tells Cisco IOS to tracking source TCP/UDP port numbers, allowing multiple internal hosts to share the single IP address on interface Serial0/0/0.

The `overload` parameter explicitly instructs the router to perform Port Address Translation (PAT).

Anahtar Kavram

Port Address Translation (PAT) Interface-based Configuration Syntax

Soru 149Soru →

A network administrator is performing an initial configuration of SSH version 2 on a new branch router (Branch-R1). Place the required configuration steps in the correct sequential order from first to last.

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Cevap

The correct sequence for configuring SSH v2 on a Cisco IOS device is: first, set a non-default hostname; second, configure an IP domain name; third, generate the RSA key pair (minimum 768 bits for SSH v2); and fourth, configure line VTY settings to accept SSH input and require local login authentication.

SSH configuration in Cisco IOS follows a strict dependency sequence. First, a non-default hostname and an IP domain name must be defined so that the system has a valid Fully Qualified Domain Name (FQDN). Second, generating an RSA key pair using the FQDN automatically activates the SSH service. Finally, line VTY settings must be configured to bind incoming management traffic to SSH and enforce local login credentials.

Adım Adım Çözüm

Set a non-default hostname (e.g., hostname Branch-R1).

Establishes the host portion of the router's FQDN.

The default router hostname 'Router' is invalid for RSA key pair creation.

Define an IP domain name (e.g., ip domain-name cisco.com).

Completes the router's FQDN (Branch-R1.cisco.com).

Cisco IOS uses the FQDN as the name label when generating RSA keys.

Generate RSA keys with at least 768 bits (e.g., crypto key generate rsa modulus 1024).

Activates the SSH server subsystem on the device.

SSH v2 requires an RSA key pair; key sizes below 768 bits force the router to default to SSH v1.5.

Configure VTY lines (line vty 0 4) with transport input ssh and login local.

Disables unencrypted management (Telnet) and forces authentication against local device credentials.

Ensures remote sessions use secure SSH transport and authenticate via local database users.

Anahtar Kavram

Cisco IOS SSH Configuration Prerequisites and Sequence

Soru 150Soru →

A network engineer observes that periodic bandwidth statistics collected from a 10-GigabitEthernet interface on a Cisco router display inaccurate, negative, or wrapping byte counts during peak traffic hours. The Network Management System (NMS) currently uses SNMPv1 to poll standard 32-bit interface counters (`ifInOctets` and `ifOutOctets`). Which SNMP version capability and MIB object group should be deployed to resolve this counter rollover issue?

Migrate to SNMPv2c or SNMPv3 to poll 64-bit High Capacity (HC) counters (`ifHCInOctets` and `ifHCOutOctets`).

Retain SNMPv1 but increase the NMS polling frequency to poll 32-bit counters every 2 seconds.

Configure SNMP Traps on the router to automatically push 32-bit counter values whenever threshold limits are exceeded.

Enable SNMPv3 authPriv security level to automatically encrypt and expand 32-bit counter fields into 64-bit values.

Cevabı ve açıklamayı göster

Cevap: Migrate to SNMPv2c or SNMPv3 to poll 64-bit High Capacity (HC) counters (`ifHCInOctets` and `ifHCOutOctets`).

Cevap

Migrate to SNMPv2c or SNMPv3 to poll 64-bit High Capacity (HC) counters (`ifHCInOctets` and `ifHCOutOctets`).

High-speed interfaces (such as GigabitEthernet and 10-GigabitEthernet) rapidly roll over standard 32-bit MIB counters (`ifInOctets`/`ifOutOctets`) supported by SNMPv1. SNMPv2c and SNMPv3 introduce IF-MIB 64-bit High Capacity (HC) counters (`ifHCInOctets`/`ifHCOutOctets`), which allow accurate traffic monitoring without counter wrapping.

Adım Adım Çözüm

Analyze interface speed and counter limits

A 10 Gbps interface transmits up to

1.25 \times 10^9

bytes per second. A 32-bit counter caps at

2^{32} - 1 \approx 4.29 \times 10^9

bytes.

At maximum capacity, a 32-bit counter rolls over approximately every 3.4 seconds (

4.29 \times 10^9 / 1.25 \times 10^9

Evaluate SNMP version features regarding MIB counter capacity

SNMPv1 is restricted to 32-bit counter objects. SNMPv2c and SNMPv3 introduced 64-bit High Capacity (HC) MIB objects in IF-MIB.

64-bit counters (

2^{64} - 1 \approx 1.84 \times 10^{19}

) take hundreds of years to roll over even on 10 Gbps interfaces.

Select the correct SNMP configuration update

Upgrading to SNMPv2c or SNMPv3 and requesting `ifHCInOctets` / `ifHCOutOctets` provides accurate bandwidth metrics.

This directly resolves high-speed link counter rollover issues.

Anahtar Kavram

64-bit MIB High Capacity (HC) counters introduced in SNMPv2c/SNMPv3 for high-speed interface monitoring

Soru 151Soru →

A network administrator is troubleshooting IP address allocation for clients on subnet $10.20.30.0/24$ . Clients connected to router interface GigabitEthernet0/0 ( $10.20.30.1/24$ ) fail to acquire dynamic IP addresses from a centralized DHCP server at $172.16.50.10$ . An audit of the router configuration shows that `ip helper-address 172.16.50.10` was configured on interface GigabitEthernet0/1 (the egress interface facing the DHCP server), while GigabitEthernet0/0 has no helper address configured. Which statement correctly explains why the clients on GigabitEthernet0/0 fail to receive IP leases?

The broadcast DHCP DISCOVER messages received on GigabitEthernet0/0 are dropped by default because the `ip helper-address` command must be applied on the client-facing ingress interface to convert local broadcasts into targeted unicast packets.

The router relays the DHCP DISCOVER message but populates the gateway IP address (giaddr) field with GigabitEthernet0/1's IP address, causing the DHCP server to select an incorrect address pool.

Routers automatically flood Layer 2 DHCP broadcasts across all operational interfaces by default, but the egress interface GigabitEthernet0/1 drops the frame because Option 82 metadata is missing.

The client DHCP DISCOVER broadcast reaches the server via default routing, but the server drops the request because the source IP address of the broadcast packet is unroutable.

Cevabı ve açıklamayı göster

Cevap: The broadcast DHCP DISCOVER messages received on GigabitEthernet0/0 are dropped by default because the `ip helper-address` command must be applied on the client-facing ingress interface to convert local broadcasts into targeted unicast packets.

Cevap

DHCP clients issue local broadcast messages to discover servers. Because routers do not forward broadcasts, the `ip helper-address` command must be applied directly to the client-facing interface (GigabitEthernet0/0). This instructs the router to intercept client broadcasts, set the gateway IP address (giaddr) field to GigabitEthernet0/0's IP address, and unicast the DHCP requests to the remote DHCP server.

Adım Adım Çözüm

Analyze client packet behavior at the gateway interface

Clients broadcast DHCP DISCOVER packets with source 0.0.0.0 and destination 255.255.255.255 on GigabitEthernet0/0.

DHCP clients do not yet have an IP address and must use local subnetwork broadcasts to find a server.

Evaluate router default broadcast handling

Router interface GigabitEthernet0/0 drops the 255.255.255.255 broadcast packet because no relay mechanism is active on that interface.

Cisco IOS routers break broadcast domains and drop limited broadcast frames by default.

Verify correct placement of the `ip helper-address` command

Applying `ip helper-address 172.16.50.10` under `interface GigabitEthernet0/0` enables the DHCP relay agent process on incoming client broadcasts.

The relay agent must intercept broadcasts on the ingress interface, insert its own interface IP into the giaddr field, and unicast the request to the DHCP server.

Anahtar Kavram

DHCP Relay Agent Interface Placement and Broadcast Handling

Soru 152Soru →

A network administrator must transfer multi-gigabyte Cisco IOS XE system software images across an enterprise WAN link to remote routers. The administrator is evaluating file transfer protocols for reliability, session management, and access control. Which two characteristics or operational behaviors distinguish FTP from TFTP, making FTP more appropriate for this large image transfer scenario? (Select TWO.)

Geçerli olan tümünü seçin

FTP utilizes TCP as its transport protocol, establishing connection-oriented sessions with sequence acknowledgment and windowing to ensure reliable delivery of large files.

FTP supports authentication using credentials and operates separate control (TCP port 21) and data (TCP port 20) channels for session management.

FTP operates using UDP port 69, which minimizes transport protocol overhead to achieve faster transmission speeds over lossy WAN links.

FTP leverages connectionless data streams to automatically recover from dropped packets without requiring TCP connection state tracking.

Cevabı ve açıklamayı göster

Cevap: FTP utilizes TCP as its transport protocol, establishing connection-oriented sessions with sequence acknowledgment and windowing to ensure reliable delivery of large files.; FTP supports authentication using credentials and operates separate control (TCP port 21) and data (TCP port 20) channels for session management.

Cevap

FTP is distinguished by its use of TCP for reliable, connection-oriented transfers with windowing and sequence tracking, as well as its support for user authentication and dual-channel operation over TCP ports 20 and 21.

FTP uses TCP as its underlying transport protocol, providing reliable end-to-end flow control, sequencing, and error recovery vital for large file transfers over WANs. Additionally, FTP supports user authentication and separates control management (TCP port 21) from data transmission (TCP port 20).

Adım Adım Çözüm

Analyze transport protocol characteristics for TFTP and FTP.

TFTP uses UDP (port 69) which is connectionless and unauthenticated, while FTP uses TCP (ports 20 and 21) which is connection-oriented, reliable, and authenticated.

Large Cisco IOS image transfers over WAN links require connection reliability, flow control, and access control.

Evaluate features that support multi-gigabyte WAN file transfers.

TCP windowing, sequencing, and error recovery in FTP prevent corruption or transfer aborts upon minor packet drops, unlike basic lock-step TFTP mechanisms.

FTP's separate control (port 21) and data (port 20) channels combined with credential checking enable controlled, robust file transfers.

Anahtar Kavram

FTP vs TFTP protocol mechanics, transport ports, and reliability features for system image transfers

Soru 153Soru →

A network administrator configures a Cisco IOS router with the following syslog parameters:

text
logging buffered 16000 informational
logging host 192.168.10.50
logging trap notifications
logging console errors

Which two statements correctly describe the behavior of syslog logging on this router? (Select two.)

Geçerli olan tümünü seçin

The remote syslog host at 192.168.10.50 receives log messages with severity levels 0 through 5, excluding informational and debugging messages.

The internal logging buffer stores a broader range of severity levels than what is displayed on the router's local console interface.

The remote syslog host receives level 6 (Informational) and level 7 (Debugging) logs because higher severity numbers take priority during trap transmission.

The console interface outputs warning messages (severity level 4) because console logging automatically inherits the severity threshold configured for syslog trap messages.

Cevabı ve açıklamayı göster

Cevap: The remote syslog host at 192.168.10.50 receives log messages with severity levels 0 through 5, excluding informational and debugging messages.; The internal logging buffer stores a broader range of severity levels than what is displayed on the router's local console interface.

Cevap

The remote syslog host receives messages from severity level 0 up through severity level 5 (Notifications), and the internal buffer records a wider variety of severity levels (levels 0-6) than the local console interface (levels 0-3).

The command 'logging trap notifications' sets the syslog server threshold to severity level 5. Cisco IOS syslog destinations process messages at or below the configured numeric level, so levels 0 through 5 are sent to the syslog server. Additionally, 'logging buffered informational' sets the buffer threshold to level 6 (levels 0-6), while 'logging console errors' limits console output to level 3 (levels 0-3), making the buffer capture a wider range of logs than the console.

Adım Adım Çözüm

Map the configured keywords to their corresponding Cisco IOS Syslog numeric severity levels.

Console = level 3 (Errors), Trap = level 5 (Notifications), Buffered = level 6 (Informational).

Cisco IOS syslog severity levels range from 0 (Emergency, most severe) to 7 (Debugging, least severe).

Evaluate the destination threshold for remote syslog trap forwarding.

Messages with severity levels 0, 1, 2, 3, 4, and 5 are sent to 192.168.10.50.

Configuring 'logging trap notifications' forwards messages at the specified severity level (5) and all lower numeric values.

Compare the destination thresholds between the logging buffer and console output.

Buffered logging captures levels 0-6, whereas console logging captures levels 0-3.

Level 6 includes more message types than level 3, making the buffer's scope broader than the console's.

Anahtar Kavram

Cisco IOS Syslog Severity Thresholds and Log Destination Operation

Soru 154Soru →

A network engineer is troubleshooting an issue where only the first internal user from subnet $192.168.10.0/24$ can access external destinations at any given time. The Cisco IOS router configuration and verification command output are shown below:

text
ip nat pool OUTSIDE_POOL 203.0.113.50 203.0.113.50 netmask 255.255.255.248
ip nat inside source list 10 pool OUTSIDE_POOL
!
access-list 10 permit 192.168.10.0 0.0.0.255

text
Router# show ip nat statistics
Total active translations: 1 (0 static, 1 dynamic, 0 extended)
Hits: 412 Misses: 15
Expired translations: 12
Dynamic mappings:
-- Inside Source
access-list 10 pool OUTSIDE_POOL refCount 1

Which configuration change is required to allow multiple internal hosts to share the single pool IP address simultaneously?

Append the overload keyword to the statement ip nat inside source list 10 pool OUTSIDE_POOL.

Change access-list 10 to permit traffic from the public range 172.32.10.0 0.0.0.255 instead of the current subnet.

Configure ip helper-address 203.0.113.50 on the internal gateway interface to forward NAT translation requests.

Set an administrative distance of 210 on the dynamic NAT pool to ensure translated packets take priority.

Cevabı ve açıklamayı göster

Cevap: Append the overload keyword to the statement ip nat inside source list 10 pool OUTSIDE_POOL.

Cevap

Append the overload keyword to the statement ip nat inside source list 10 pool OUTSIDE_POOL.

Without the 'overload' keyword, Cisco IOS implements basic dynamic NAT, mapping inside local IP addresses to inside global IP addresses on a strict one-to-one basis. Because the defined NAT pool has only one IP address (203.0.113.50), only one internal device can translate its IP address at any given time, as confirmed by 'Total active translations: 1 (0 static, 1 dynamic, 0 extended)' in the output. Appending 'overload' converts dynamic NAT into Port Address Translation (PAT), allowing multiple inside hosts to share the single public IP address concurrently using unique source L4 port numbers.

Adım Adım Çözüm

Analyze the existing router configuration and command output

The current command 'ip nat inside source list 10 pool OUTSIDE_POOL' without the 'overload' keyword performs standard 1-to-1 dynamic NAT mapping.

Because the pool OUTSIDE_POOL contains only a single IP address (203.0.113.50), standard dynamic NAT exhausts all available addresses after assigning it to the first host.

Identify the missing Port Address Translation (PAT) parameter

Adding 'overload' enables port-level multiplexing (PAT), creating extended translation entries that track source port numbers.

PAT allows thousands of concurrent internal hosts to share a single public IPv4 address simultaneously.

Anahtar Kavram

Port Address Translation (PAT) Overload Keyword Configuration

Soru 155Soru →

A network administrator is transferring a Cisco IOS software image from a router to a central backup server using Trivial File Transfer Protocol (TFTP). Which transport-layer protocol and default destination port are used by TFTP for this operation?

UDP port 69

TCP port 69

TCP port 21

UDP port 21

Cevabı ve açıklamayı göster

Cevap: UDP port 69

Cevap

TFTP uses UDP as its transport-layer protocol and listens on default destination port 69.

Trivial File Transfer Protocol (TFTP) is designed to operate over UDP using destination port 69 for basic, low-overhead file management operations.

Adım Adım Çözüm

Identify the file transfer protocol specified in the question.

The scenario specifies Trivial File Transfer Protocol (TFTP).

Distinguishing between TFTP and standard FTP determines the underlying transport protocol and port number.

Determine the transport-layer protocol used by TFTP.

TFTP operates over UDP (User Datagram Protocol).

TFTP uses UDP to avoid the connection establishment overhead of TCP, implementing simple error recovery at the application layer.

Identify the standard well-known port number for TFTP.

TFTP uses port 69 as its standard UDP server port.

Port 69 is assigned by IANA for TFTP daemon communication.

Anahtar Kavram

TFTP Transport Layer Mechanics and Port Numbers

Soru 156Soru →

Match each Simple Network Management Protocol (SNMP) mechanism or operational requirement on the left with its corresponding protocol characteristic or SNMP message type on the right.

Soldaki öğeye tıklayın, sonra eşleşen sağdaki öğeye tıklayın

Cevabı ve açıklamayı göster

Cevap

Unacknowledged notifications correspond to SNMP Trap; reliable notifications requiring acknowledgment correspond to SNMP Inform; authentication with encryption corresponds to SNMPv3 authPriv; sequential MIB traversal corresponds to SNMP GetNext.

Each SNMP concept is paired to its defining technical attribute: Traps are unacknowledged notifications (UDP 162), Informs provide explicit acknowledgment and retransmission, authPriv adds cryptographic encryption alongside authentication, and GetNext handles sequential MIB walking (UDP 161).

Adım Adım Çözüm

Analyze notification reliability types.

Unacknowledged messages sent to UDP port 162 are Traps, whereas acknowledged notifications are Informs.

Traps use best-effort UDP transport without application-layer confirmations, while Informs retransmit until an acknowledgment PDU is returned.

Evaluate SNMPv3 security levels.

The combination of authentication (auth) and privacy/encryption (priv) defines the authPriv security model.

noAuthNoPriv uses plain community-like checks, authNoPriv adds hashing without encryption, and authPriv adds payload encryption.

Identify MIB querying operational PDU types.

Retrieving the next lexicographical object instance in a MIB tree corresponds to the GetNext operation.

Get requests retrieve a specific OID instance, whereas GetNext accesses the subsequent entry, enabling MIB walk capabilities.

Anahtar Kavram

SNMP Operational Mechanics, Traps vs. Informs, and SNMPv3 Security Levels

Soru 157Soru →

A network administrator is configuring Port Address Translation (PAT) on a Cisco IOS router to allow hosts on the private subnet $172.16.20.0/24$ to access the Internet using an IP NAT pool named `PAT_POOL` with the public address $198.51.100.10$ . Which TWO commands are required to successfully complete this dynamic PAT pool configuration?

Geçerli olan tümünü seçin

ip nat inside source list 15 pool PAT_POOL overload

ip nat pool PAT_POOL 198.51.100.10 198.51.100.10 netmask 255.255.255.252

ip nat inside source list 15 pool PAT_POOL

access-list 15 permit 172.32.20.0 0.0.0.255

Cevabı ve açıklamayı göster

Cevap: ip nat inside source list 15 pool PAT_POOL overload; ip nat pool PAT_POOL 198.51.100.10 198.51.100.10 netmask 255.255.255.252

Cevap

The configuration requires defining the dynamic IP NAT pool using `ip nat pool PAT_POOL 198.51.100.10 198.51.100.10 netmask 255.255.255.252` and referencing that pool in the NAT source translation statement with the `overload` keyword appended: `ip nat inside source list 15 pool PAT_POOL overload`.

Configuring PAT using a dynamic NAT pool requires defining the pool parameters via `ip nat pool <name> <start-ip> <end-ip> netmask <mask>` and linking an access list that identifies private traffic to that pool using `ip nat inside source list <acl> pool <name> overload`. The `overload` keyword enables multiplexing multiple internal sockets onto a single public address using port numbers.

Adım Adım Çözüm

Define the public NAT address pool

Configured `ip nat pool PAT_POOL 198.51.100.10 198.51.100.10 netmask 255.255.255.252` to specify the public IPv4 address available for outbound translation.

A pool must exist before dynamic NAT/PAT mapping rules can reference it by name.

Bind the access list to the pool with port overload enabled

Executed `ip nat inside source list 15 pool PAT_POOL overload`.

The `overload` keyword instructs Cisco IOS to perform Port Address Translation (PAT), allowing multiple inside private hosts to share the single pool address by tracking unique TCP/UDP port numbers.

Anahtar Kavram

Port Address Translation (PAT) Pool Configuration Syntax

Soru 158Soru →

A network engineer is configuring a Cisco IOS router to relay DHCP requests from clients residing in VLAN 10 ( $192.168.10.0/24$ ) and VLAN 20 ( $192.168.20.0/24$ ) to a centralized DHCP server at $10.10.10.10$ located off uplink interface GigabitEthernet 0/1. Which two statements correctly describe the required interface configuration and relay agent behavior on the router?

Geçerli olan tümünü seçin

The ip helper-address 10.10.10.10 command must be applied directly under subinterfaces GigabitEthernet 0/0.10 and GigabitEthernet 0/0.20.

The router replaces the incoming DHCP Discover broadcast with a unicast packet to 10.10.10.10 and inserts the subinterface IP address into the Gateway IP Address (giaddr) field.

The ip helper-address 10.10.10.10 command must be applied on the egress interface GigabitEthernet 0/1 facing the centralized server.

The router floods the original Layer 2 broadcast DHCP Discover frame unchanged across all active router interfaces to reach the server.

Cevabı ve açıklamayı göster

Cevap: The ip helper-address 10.10.10.10 command must be applied directly under subinterfaces GigabitEthernet 0/0.10 and GigabitEthernet 0/0.20.; The router replaces the incoming DHCP Discover broadcast with a unicast packet to 10.10.10.10 and inserts the subinterface IP address into the Gateway IP Address (giaddr) field.

Cevap

The ip helper-address command must be configured on the incoming client-facing interfaces (GigabitEthernet 0/0.10 and GigabitEthernet 0/0.20), and the router converts the incoming DHCP broadcast into a unicast frame while inserting its local interface IP into the gateway IP address (giaddr) field.

DHCP relay agents must be configured on the interface receiving the client DHCP broadcast requests (the incoming subinterfaces for VLAN 10 and VLAN 20). When the router intercepts the broadcast DHCP Discover packet, it encapsulates the payload into a unicast IP packet destined for the configured helper address (10.10.10.10) and places the receiving interface IP address into the Relay Agent IP Address (giaddr) field so the DHCP server can identify the correct subnet pool.

Adım Adım Çözüm

Identify client ingress interfaces

DHCP clients broadcast on their local subinterfaces (GigabitEthernet 0/0.10 and GigabitEthernet 0/0.20).

The router must listen for UDP port 67 broadcast messages on the interfaces connected to the clients.

Apply helper address configuration

Configure 'ip helper-address 10.10.10.10' under GigabitEthernet 0/0.10 and GigabitEthernet 0/0.20.

This instructs Cisco IOS to intercept incoming DHCP broadcasts on those specific client segments.

Analyze Relay Agent packet transformation

Broadcast Discover packets are unicast to 10.10.10.10, and the giaddr field is populated with the subinterface's IP address.

The giaddr field tells the remote DHCP server which IP address pool scope to select from for lease assignment.

Anahtar Kavram

DHCP Relay Agent Operation and Configuration

Soru 159Soru →

An enterprise router connects a branch office to the head office over a sub-rate Metro Ethernet circuit with a Committed Information Rate (CIR) of 20 Mbps on a 100 Mbps physical Ethernet handoff. Users report that during peak hours, TCP file transfers experience severe throughput degradation due to packet drops and retransmissions, while real-time UDP streams undergo frequent drops during bursts. An audit of the egress WAN interface reveals a QoS policy enforcing the 20 Mbps bandwidth limit using traffic policing. Which explanation correctly identifies why traffic shaping should be implemented instead of traffic policing on this egress interface?

Traffic shaping buffers excess out-of-profile packets in queues and transmits them smoothly over time up to the CIR rate, whereas traffic policing immediately drops or remarks packets exceeding the rate limit without buffering.

Traffic policing buffers non-conforming burst traffic until interface queue capacity opens, whereas traffic shaping immediately drops out-of-profile packets to prevent TCP window size expansion.

Traffic policing dynamically adjusts physical Layer 1 interface signaling speeds to match CIR limits, whereas traffic shaping alters Layer 2 framing headers to drop non-conforming packets.

Traffic shaping operates exclusively at Layer 2 using CoS bits to prioritize bursty data frames, whereas traffic policing operates at Layer 3 by rewriting IP TOS precedence values to drop packets.

Cevabı ve açıklamayı göster

Cevap: Traffic shaping buffers excess out-of-profile packets in queues and transmits them smoothly over time up to the CIR rate, whereas traffic policing immediately drops or remarks packets exceeding the rate limit without buffering.

Cevap

Traffic shaping mitigates bursty traffic drops on sub-rate interfaces by storing out-of-profile packets in software queues and pacing their transmission at the CIR rate over time. Traffic policing does not buffer packets; non-conforming traffic exceeding the CIR is immediately dropped or remarked, leading to high TCP retransmissions and stream degradation during bursts.

Adım Adım Çözüm

Analyze the operational behavior of Traffic Policing.

Traffic policing measures the traffic rate against a configured limit (such as CIR). Traffic that exceeds the profile is either immediately dropped or remarked to a lower priority (e.g., lower DSCP value). Policers do not buffer traffic, causing TCP window collapses and packet loss during traffic bursts.

Policing is designed for hard rate enforcement, usually applied inbound or at service provider handoffs.

Analyze the operational behavior of Traffic Shaping.

Traffic shaping measures the traffic rate against a configured CIR profile, but excess traffic above the rate limit is retained in software queues and scheduled for delayed transmission. This smoothes out bursty traffic profiles.

Shaping prevents packet loss caused by transient traffic bursts by using memory buffering, making it ideal for sub-rate Ethernet access links.

Compare policing versus shaping for the sub-rate WAN scenario.

Because the physical port operates at 100 Mbps while the ISP contract limits throughput to 20 Mbps CIR, bursty transmissions from the router fill the link at 100 Mbps burst rates. Traffic policing drops these bursts immediately. Traffic shaping holds excess packets in queues and meters them out at 20 Mbps, preventing TCP retransmissions and stream drops.

Shaping is recommended egress on sub-rate WAN interfaces to avoid provider policer drops and smooth bursty traffic.

Anahtar Kavram

Difference between QoS Traffic Policing and Traffic Shaping

Soru 160Soru →

A network administrator notices that critical link failure notifications sent from an edge router to the central Network Management System (NMS) are periodically dropped during high WAN congestion without any alert being logged by the NMS. The enterprise security policy requires all network telemetry notifications to support delivery receipts and enforce both cryptographic authentication and data encryption. Which configuration approach on the Cisco IOS router meets these operational and security requirements?

Configure SNMPv3 Informs using the authPriv security level.

Configure SNMPv3 Traps using the authPriv security level.

Configure SNMPv2c Informs with a read-write community string using TCP port 162.

Configure SNMPv3 Informs using the authNoPriv security level.

Cevabı ve açıklamayı göster

Cevap: Configure SNMPv3 Informs using the authPriv security level.

Cevap

Configure SNMPv3 Informs using the authPriv security level.

SNMP Informs fulfill the reliability requirement by requiring the receiving Network Management System (NMS) to acknowledge receipt, retransmitting the message if no acknowledgment is received. Pairing Informs with the SNMPv3 authPriv security level ensures both authentication of the manager/agent and encryption of transmitted notification data, meeting all listed requirements.

Adım Adım Çözüm

Analyze notification reliability requirements

Identified the need for acknowledged notifications (Informs rather than Traps).

Traps are unacknowledged UDP messages that offer no delivery confirmation. Informs require the NMS to reply with an SNMP response PDU, retrying transmission if no confirmation is received within a timeout period.

Analyze security model requirements

Identified the need for the authPriv security model in SNMPv3.

authPriv provides both cryptographic authentication (MD5/SHA) and encryption (DES/AES). noAuthNoPriv provides no security, authNoPriv provides authentication without encryption, and SNMPv2c uses cleartext community strings.

Anahtar Kavram

SNMP Inform operational mechanics vs Traps and SNMPv3 security levels (authPriv)

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