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203 questions

All types1,987 Multiple choice1,020 Multiple select452 Numeric18 Matching229 Ordering203 Fill in the blank22 Short answer43

Question 141Question →

A network administrator needs to provision a new VLAN for the Sales department (VLAN 50, named SALES) on a Cisco Catalyst switch and assign interface GigabitEthernet0/5 as a static access port belonging to this VLAN. Place the following Cisco IOS commands in the correct sequential order from privileged EXEC mode to complete this configuration.

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Answer

The correct sequence starts with entering global configuration mode (`configure terminal`), followed by creating VLAN 50 (`vlan 50`), naming it (`name SALES`), accessing interface configuration mode (`interface GigabitEthernet0/5`), setting static access mode (`switchport mode access`), and assigning the port to VLAN 50 (`switchport access vlan 50`).

Cisco IOS requires navigating through a strict prompt hierarchy. The administrator must first enter global configuration mode (`configure terminal`), instantiate and name the VLAN (`vlan 50` followed by `name SALES`), navigate to the specific interface (`interface GigabitEthernet0/5`), set the port operational mode to access (`switchport mode access`), and finally bind the access port to VLAN 50 (`switchport access vlan 50`).

Step-by-Step Solution

Execute `configure terminal` at the privileged EXEC prompt (`Switch#`).

Enters global configuration mode (`Switch(config)#`).

Global configuration mode is the entry point for defining system-level entities such as VLANs.

Execute `vlan 50`.

Creates VLAN 50 and moves to VLAN configuration mode (`Switch(config-vlan)#`).

VLAN ID 50 must be created before assigning a descriptive name or configuring interface membership.

Execute `name SALES`.

Names VLAN 50 as SALES.

VLAN names are assigned inside config-vlan subconfiguration mode.

Execute `interface GigabitEthernet0/5`.

Enters interface configuration mode (`Switch(config-if)#`).

Interface parameters must be modified from within the target interface's configuration prompt.

Execute `switchport mode access`.

Sets the administrative mode of GigabitEthernet0/5 to access.

Configuring explicit access mode prevents DTP trunk negotiation and secures the port.

Execute `switchport access vlan 50`.

Associates interface GigabitEthernet0/5 with VLAN 50.

Places untagged traffic entering GigabitEthernet0/5 into broadcast domain 50.

Key Concept

Cisco IOS hierarchical configuration sequence for VLAN creation and static access port assignment.

Estimated Time:1m 30s

Question 142Question →

During initial topology convergence for a VLAN running Rapid PVST+, switches exchange BPDUs to determine which switch assumes the Root Bridge role. Place the evaluation criteria steps in the correct order, from the first criterion evaluated to the final step establishing the Root Bridge.

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Answer

The correct sequence begins with comparing base priority values, adding the System ID Extension to calculate total priority, using the lowest MAC address as a tie-breaker if priorities match, and concluding with designating the switch with the lowest overall Bridge ID as the Root Bridge.

In Rapid PVST+, Root Bridge election follows a strict hierarchy based on the Bridge ID (BID). Switches first compare base bridge priority, add the System ID Extension (VLAN ID) to establish total priority, resolve any ties using the lowest MAC address, and finally designate the switch with the overall lowest BID as the Root Bridge.

Step-by-Step Solution

Evaluate Base Bridge Priority

Identifies the base priority component configured on each participating switch.

Base priority is the primary configurable metric evaluated in the Bridge ID.

Incorporate System ID Extension

Combines base priority and VLAN ID into the effective 16-bit priority value.

Rapid PVST+ requires unique per-VLAN bridge priorities by appending the VLAN number.

Evaluate MAC addresses for tie-breaking

Determines the winning switch when total priorities are identical.

The 48-bit switch MAC address serves as a unique secondary tie-breaker.

Confirm Root Bridge election outcome

The switch with the lowest resulting BID becomes the Root Bridge.

All switches in the spanning-tree domain recognize the switch with the lowest BID as Root.

Key Concept

Rapid PVST+ Root Bridge Election and Bridge ID Evaluation

Question 143Question →

An administrator needs to manually configure an IPv4 static route on a Cisco router to reach remote network $172.20.10.0/24$ using the next-hop IP address $10.0.0.2$ , and then permanently save the configuration. What is the correct sequence of steps to complete this configuration starting from Privileged EXEC mode?

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Answer

The correct order to enter global configuration mode, apply the static route command with the correct prefix, subnet mask, and next-hop IP, exit back to privileged EXEC mode, and save the active configuration to NVRAM is: Enter global configuration mode (`configure terminal`), Configure the static route (`ip route 172.20.10.0 255.255.255.0 10.0.0.2`), Return to privileged EXEC mode (`end`), and Save the configuration (`copy running-config startup-config`).

Configuring a persistent IPv4 static route on a Cisco router requires moving to global configuration mode via `configure terminal`, applying the static route with `ip route 172.20.10.0 255.255.255.0 10.0.0.2`, exiting back to privileged EXEC mode using `end`, and finally writing the running configuration to NVRAM using `copy running-config startup-config`.

Step-by-Step Solution

Transition from Privileged EXEC mode (`Router#`) to Global Configuration mode (`Router(config)#`).

The router prompt changes to `Router(config)#`, allowing structural configuration commands.

Static routes cannot be defined directly in Privileged EXEC mode.

Issue the IPv4 static route command `ip route 172.20.10.0 255.255.255.0 10.0.0.2`.

The static route is added to the running configuration and installed into the IPv4 routing table.

Cisco IOS requires the syntax `ip route <prefix> <mask> <next-hop-ip|exit-interface>`.

Return to Privileged EXEC mode using `end` or `exit`.

The prompt reverts back to `Router#`.

File management and memory write commands must be issued from Privileged EXEC mode.

Write the active configuration from RAM to NVRAM using `copy running-config startup-config`.

The current running-config is saved to startup-config in NVRAM.

Without saving, configuration modifications will be lost if the device loses power or reboots.

Key Concept

Cisco IOS IPv4 Static Route CLI Configuration Workflow

Question 144Question →

Four candidate routers are connected to a shared multiaccess Ethernet segment to participate in an OSPFv2 Designated Router (DR) election. Arrange the evaluation criteria in order of precedence, starting with the primary criterion checked first at the top down to the final fallback tie-breaker at the bottom.

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Answer

The correct order of precedence for OSPF DR election tie-breaking is: 1) Highest OSPF interface priority setting, 2) Highest manually configured OSPF router ID, 3) Highest IPv4 address on an active loopback interface, and 4) Highest IPv4 address on an active physical interface.

The Designated Router election first evaluates the interface priority configured on the multiaccess segment. If priorities tie, OSPF resolves the election using the router's Router ID (RID). The RID is determined in order by: 1) explicit manual configuration via 'router-id', 2) highest IP address on an active loopback interface, and 3) highest IP address on an active physical interface.

Step-by-Step Solution

Evaluate segment interface priority

Highest interface priority wins the election (priority 0 disqualifies a router from becoming DR/BDR).

Interface priority (configured via 'ip ospf priority') is the top-level override mechanism for DR selection.

Check for explicit OSPF Router ID

If interface priorities tie, OSPF compares Router IDs, prioritizing a manually configured 'router-id'.

Manual Router ID configuration under the 'router ospf' process overrides dynamic interface IP selection.

Check active loopback interfaces

If no manual router ID is present, the highest IPv4 address on an active loopback interface is chosen as the Router ID.

Loopback interfaces offer stability over physical interfaces because they do not rely on physical link state.

Check active physical interfaces

If no loopback interfaces exist, the highest IPv4 address on an up/up physical interface becomes the Router ID.

This serves as the final dynamic tie-breaker for establishing the OSPF Router ID when no explicit or loopback settings exist.

Key Concept

OSPFv2 DR/BDR Election Precedence and Router ID Selection Criteria

Estimated Time:1m 0s

Question 145Question →

A network administrator is configuring a new Wireless LAN (WLAN) for guest client connectivity on a Cisco Wireless LAN Controller (WLC) using the GUI. Arrange the administrative steps in the correct chronological sequence from first to last to properly configure and enable the WLAN.

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Answer

The correct chronological sequence is: 1) Navigate to WLANs and select 'Create New', 2) Define Profile Name, SSID, and ID, 3) Map the dynamic interface under the General tab, 4) Configure Layer 2 security settings under the Security tab, and 5) Enable the WLAN Status checkbox under the General tab and Apply.

The proper administrative workflow in Cisco AireOS WLC GUI begins with creating the WLAN container ('Create New'). Next, the administrator assigns identity parameters (Profile Name and SSID). Once created, the administrator binds the WLAN to its dynamic interface under the General tab, configures Layer 2 security parameters under the Security tab, and finally checks the Status checkbox under the General tab to enable the network for client association.

Step-by-Step Solution

Navigate to the WLANs menu in the Cisco WLC GUI.

Access the WLAN configuration index page.

Choosing 'Create New' initiates the wizard to instantiate a new WLAN ID.

Input the Profile Name and SSID, then click Apply.

The WLC creates the WLAN profile instance.

Basic naming attributes are required before sub-tab parameters become editable.

Select the target dynamic interface/VLAN on the General tab.

Wireless client traffic on this WLAN is mapped to the selected network interface.

Interface binding ensures clients receive IP addresses from the correct subnet.

Select the Security tab and define Layer 2 security settings (e.g., WPA2/WPA3 PSK or 802.1X).

Encryption and authentication policies are bound to the WLAN.

Wireless clients must authenticate using matching security parameters to join.

Return to the General tab, check the Status box, and click Apply.

The WLAN state changes to Enabled.

WLANs are created in a disabled state by default to prevent client association during configuration.

Key Concept

Cisco WLC GUI WLAN Provisioning Lifecycle

Estimated Time:1m 30s

Question 146Question →

A Cisco router receives an IPv4 unicast packet on an ingress interface and prepares to forward it toward its final destination. Place the sequential steps of the router's packet forwarding decision process in the correct chronological order from first to last.

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Answer

The correct sequence starts with decapsulating the incoming Layer 2 frame, searching the routing table for candidate prefix matches, selecting the best match using Longest Prefix Match (LPM), determining the egress interface and next-hop IP, resolving the Layer 2 address of the next-hop device via ARP, and finally decrementing the TTL and encapsulating the packet into a new frame for transmission.

The router processes ingress packets sequentially: it first strips the Layer 2 frame to read the destination IP, searches the routing table, applies the Longest Prefix Match rule to pick the most specific network prefix, determines the next-hop IP and egress interface, resolves the next-hop Layer 2 MAC address, and finishes by decrementing TTL, updating the checksum, encapsulating the packet, and transmitting the frame.

Step-by-Step Solution

Frame Ingress & Decapsulation

The router strips the Layer 2 frame header/trailer to inspect the Layer 3 destination IPv4 address.

Routing decisions occur at Layer 3, requiring packet header extraction.

Routing Table Candidate Lookup

Identifies all routes in the IPv4 routing table that contain the destination IP address.

All matching network entries must be collected before evaluating prefix specificity.

Longest Prefix Match Selection

The route with the longest subnet mask (most matching network bits) is selected as the forwarding path.

Longest Prefix Match is the primary criterion for route lookup selection during packet forwarding.

Egress Interface & Next-Hop Identification

Extracted destination next-hop IPv4 address and outgoing physical/logical interface.

The selected route specifies where to send the packet next.

Layer 2 Next-Hop Address Resolution

ARP table lookup retrieves the MAC address associated with the next-hop IP.

Data-link layer framing requires a destination hardware address on Ethernet media.

Header Modification, Encapsulation, and Egress Transmission

TTL is decremented, checksum recalculated, new Layer 2 header attached, and frame sent out egress port.

Prevents routing loops via TTL expiration and prepares frame for transit across the next physical link segment.

Key Concept

Router IPv4 Forwarding Decision Pipeline

Question 147Question →

A switch running Rapid PVST+ receives BPDUs across multiple active interfaces and must determine which port will assume the Root Port role for a specific VLAN. Place the decision criteria evaluated by the switch in the correct sequential order, starting from the first criterion evaluated to the last.

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Answer

The correct sequence for selecting a Rapid PVST+ Root Port is: 1. Lowest cumulative Root Path Cost to the Root Bridge, 2. Lowest upstream neighbor Bridge ID (Sender BID), 3. Lowest upstream neighbor Port ID (Sender Port ID), 4. Lowest local Port ID on the receiving switch.

When selecting a Root Port, a Rapid PVST+ non-root switch evaluates received BPDU criteria in a strict hierarchical order: cumulative Root Path Cost first, followed by sender Bridge ID, sender Port ID, and finally local Port ID.

Step-by-Step Solution

Evaluate path efficiency

Identify the interface with the lowest cumulative cost to reach the Root Bridge.

STP prioritizes path efficiency before comparing device or port identifiers.

Evaluate upstream device identity

If path costs are equal, compare the Bridge IDs of the neighboring switches sending the BPDUs.

Connecting to a neighbor with a lower Bridge ID takes precedence when costs match.

Evaluate upstream port identity

If connected via multiple links to the same upstream switch, compare the Port IDs (port priority + port number) transmitted by the neighbor.

The upstream switch's lower sending port ID breaks ties for parallel links to the same neighbor.

Evaluate local port identity

If all received BPDU fields are identical, compare the local receiving switch's Port IDs.

The local switch uses its own lowest port ID as the final deterministic tie-breaker.

Key Concept

Rapid PVST+ Root Port Selection Algorithm

Estimated Time:1m 30s

Question 148Question →

A network administrator needs to create a new VLAN for isolated guest traffic (VLAN 80, named GUEST) on a Cisco Catalyst switch and configure interface GigabitEthernet0/12 as a static access port belonging to this VLAN. In what sequence should the administrator execute the CLI commands starting from Privileged EXEC mode?

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Answer

The correct sequence starts with 'configure terminal' to enter global configuration mode, followed by 'vlan 80' to create the VLAN, 'name GUEST' to name it, 'interface GigabitEthernet0/12' to enter interface mode, 'switchport mode access' to define the port mode, and 'switchport access vlan 80' to assign the port to the VLAN.

Configuring a VLAN and access port requires following Cisco IOS mode hierarchy: starting in Privileged EXEC mode, entering Global Configuration mode via 'configure terminal', instantiating VLAN 80 with 'vlan 80', assigning its label with 'name GUEST', navigating to the target port via 'interface GigabitEthernet0/12', locking its operational state with 'switchport mode access', and assigning it to the newly created VLAN with 'switchport access vlan 80'.

Step-by-Step Solution

Enter Global Configuration mode

Switch prompt changes to Switch(config)#

CLI commands for creating VLANs and accessing interfaces require global configuration context.

Create VLAN 80

Switch prompt changes to Switch(config-vlan)#

VLAN 80 must be created before naming or assigning interfaces to it.

Name the VLAN GUEST

VLAN 80 is assigned the name GUEST in the database

The name sub-command must be executed within config-vlan mode.

Select interface GigabitEthernet0/12

Switch prompt changes to Switch(config-if)#

Interface configuration mode is required to apply port-specific switchport commands.

Configure operational mode as access

DTP negotiation is disabled for trunking and port is forced to access mode

Disabling dynamic trunking negotiation ensures the port functions strictly as an access port.

Assign the interface to VLAN 80

Interface GigabitEthernet0/12 is placed into VLAN 80 broadcast domain

Associates untagged ingress frames on GigabitEthernet0/12 with VLAN 80.

Key Concept

Cisco IOS CLI command hierarchy and sequence for creating a VLAN and configuring an access port.

Estimated Time:1m 30s

Question 149Question →

A network administrator needs to manually configure an IPv4 static route to the destination subnet $192.168.10.0/24$ using the next-hop IP address $10.1.1.2$ on a Cisco IOS router, starting from user EXEC mode. Place the CLI commands and actions in the correct sequential order from first to last.

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Answer

The correct sequence starts with entering privileged EXEC mode (`enable`), moving into global configuration mode (`configure terminal`), applying the static route command (`ip route 192.168.10.0 255.255.255.0 10.1.1.2`), and finally verifying the routing table entry (`show ip route static`) in privileged EXEC mode.

In Cisco IOS, configuration follows a strict hierarchy. User EXEC mode (`Router>`) must first be elevated to Privileged EXEC mode (`Router#`) using `enable`. Next, Global Configuration mode (`Router(config)#`) is accessed with `configure terminal`. The static route `ip route 192.168.10.0 255.255.255.0 10.1.1.2` is then entered. Finally, returning to Privileged EXEC mode permits running `show ip route static` to verify that the route is installed in the routing table.

Step-by-Step Solution

Elevate privileges from User EXEC mode to Privileged EXEC mode.

Prompt changes from `Router>` to `Router#` after running `enable`.

Configuration commands cannot be executed directly from User EXEC mode.

Navigate to Global Configuration mode.

Prompt changes to `Router(config)#` after running `configure terminal`.

Static route configuration via `ip route` is a global configuration parameter.

Configure the IPv4 static route.

The command `ip route 192.168.10.0 255.255.255.0 10.1.1.2` is committed to running-config.

Specifies destination network prefix, subnet mask, and next-hop IP address.

Exit configuration mode and verify the routing table.

The `show ip route static` command displays `S 192.168.10.0/24 [1/0] via 10.1.1.2`.

Confirms the static route is installed in the IPv4 routing table successfully.

Key Concept

Cisco IOS CLI hierarchy navigation and static route command syntax

Question 150Question →

A Cisco router receives an IPv4 packet destined for host $172.16.5.45$ . The routing table contains a static route configured with a next-hop IP address: `ip route 172.16.5.0 255.255.255.0 10.0.0.2`. In what chronological order does the router execute the forwarding decision and recursive lookup process to transmit this packet? Place the steps in order from first to last.

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Answer

The correct operational order begins with inspecting the packet header to extract the destination IPv4 address, followed by executing a longest prefix match in the routing table. Next, because the matching static route points to a next-hop IP rather than an exit interface, the router performs a recursive lookup to find the egress interface. Finally, the router resolves the next-hop MAC address via ARP, encapsulates the packet into a Layer 2 frame, and transmits it.

Packet processing follows a strict sequential pipeline in Cisco IOS: Layer 3 packet destination extraction → Longest Prefix Match routing table lookup → Recursive resolution of the next-hop IP address to an exit interface → ARP MAC address resolution and Layer 2 frame transmission.

Step-by-Step Solution

Packet Ingress & Header Inspection

Destination IP address

172.16.5.45

is extracted.

Routing decisions require identifying the target host IP in the IP packet header.

Primary Routing Table Lookup

The static route entry `172.16.5.0/24 via 10.0.0.2` is selected based on Longest Prefix Match.

Cisco IOS routes traffic using the most specific matching network mask in the routing table.

Recursive Next-Hop Lookup

The next-hop IP

10.0.0.2

is resolved to a directly connected network and outbound interface.

Static routes configured solely with a next-hop IP require an additional lookup step to identify which physical or logical interface sends the traffic.

Layer 2 Encapsulation & Transmission

ARP table yields the destination MAC address for

10.0.0.2

, frame is rewritten and transmitted.

Multi-access interfaces (like Ethernet) need a specific destination Layer 2 MAC address to transmit the packet.

Key Concept

IPv4 Static Route Recursive Lookup & Packet Forwarding Logic

Question 151Question →

An active OSPFv2 Designated Router (DR) on a multiaccess Ethernet segment suddenly fails. Place the operational recovery events and DR/BDR re-election steps in the correct chronological order from first to last.

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Answer

The correct order of events following an OSPF DR failure is: (1) Neighbor routers detect DR loss via Dead Timer expiration, (2) The current BDR immediately promotes to DR, (3) Eligible routers initiate an election for the open BDR post, (4) The candidate with the highest interface priority or Router ID is elected new BDR, and (5) DROTHER routers complete FULL adjacency with the DR and new BDR while remaining in 2-WAY state with peer DROTHERs.

When an active DR fails, OSPF routers must first detect the loss when the Dead Router Timer expires. Upon detection, the active BDR is immediately promoted to DR without holding a new DR election. With the BDR position now vacant, remaining eligible routers (having priority > 0) participate in a BDR election, where the router with the highest interface priority (or highest Router ID if priorities are equal) wins. Finally, DROTHER routers form FULL adjacencies with both the DR and new BDR while maintaining 2-WAY state with non-DR/BDR peers.

Step-by-Step Solution

Detect DR failure

Neighbors observe Dead Router Timer expiration.

OSPF routers on multiaccess networks wait until the Dead Timer expires without receiving Hello packets from the DR before taking action.

Promote active BDR

The existing BDR assumes the DR role.

OSPF avoids holding a fresh DR election; the pre-elected BDR instantly fills the DR position to ensure fast network convergence.

Trigger new BDR election

Eligible routers (priority > 0) initiate an election for the vacant BDR role.

Because the previous BDR was promoted to DR, the BDR position is empty and must be filled by a new election.

Determine election winner

The candidate with the highest interface priority (or highest Router ID) becomes the new BDR.

OSPF tie-breaking rules evaluate highest interface priority first, followed by highest Router ID.

Establish neighbor adjacencies

DROTHER routers transition to FULL state with the DR and new BDR while maintaining 2-WAY state with each other.

Multiaccess network design requires routers to form full adjacencies only with the DR and BDR to restrict link-state advertisement overhead.

Key Concept

OSPFv2 DR/BDR Non-Preemption and Failure Recovery Sequence

Estimated Time:2m 0s

Question 152Question →

Four Cisco routers (R1, R2, R3, and R4) are booted simultaneously on a shared broadcast multiaccess Ethernet segment running OSPFv2 in Area 0. No explicit OSPF router ID is configured under the `router ospf` process on any router.

The interface and active IP configurations are as follows:
- R1: GigabitEthernet0/0 IP $192.168.1.1/24$ , Priority = $10$ ; Loopback0 IP = $10.1.1.1/32$
- R2: GigabitEthernet0/0 IP $192.168.1.2/24$ , Priority = $0$ ; Loopback0 IP = $172.16.1.1/32$
- R3: GigabitEthernet0/0 IP $192.168.1.3/24$ , Priority = $10$ ; Loopback0 IP = $10.2.2.2/32$
- R4: GigabitEthernet0/0 IP $192.168.1.4/24$ , Priority = $20$ ; Loopback0 IP = $10.0.0.1/32$

Order the routers in sequence from highest to lowest precedence during the initial Designated Router (DR) and Backup Designated Router (BDR) election, starting with the router selected as DR down to the completely ineligible router.

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Answer

The correct sequence from highest election precedence to lowest is: Router R4 (DR), Router R3 (BDR), Router R1 (DROTHER), and Router R2 (Ineligible).

The election evaluates interface priority first. Router R4 has the highest interface priority (20) and is elected DR. Router R2 has a priority of 0, making it strictly ineligible for DR/BDR election despite having the highest Loopback IP address. Between Router R1 and Router R3 (both having priority 10), Router R3 wins the BDR election because its loopback address (10.2.2.2) forms a higher Router ID than Router R1 (10.1.1.1). Router R1 becomes a DROTHER.

Step-by-Step Solution

Determine initial eligibility based on configured interface priority.

Router R2 has an OSPF interface priority of 0, which immediately disqualifies it from DR/BDR election eligibility, placing it at the bottom of the election ranking.

An OSPF interface priority of 0 specifies that the router cannot become a DR or BDR on the segment.

Evaluate eligible candidate routers by interface priority to select the DR.

Router R4 has a priority of 20, while Router R1 and Router R3 each have a priority of 10. Router R4 wins the DR election.

OSPF interface priority is the primary criteria for DR/BDR election; the router with the highest numeric priority value wins.

Break the priority tie between remaining eligible routers for BDR selection using Router ID.

Router R3 and Router R1 tie with an interface priority of 10. Router R3 has an active Loopback0 IP of 10.2.2.2, which becomes its Router ID. Router R1 has a Loopback0 IP of 10.1.1.1. Because 10.2.2.2 > 10.1.1.1, Router R3 is elected BDR and Router R1 becomes a DROTHER.

When interface priorities are equal, OSPF uses the highest Router ID (derived automatically from the highest active loopback IP address) as the secondary tie-breaker.

Key Concept

OSPFv2 DR/BDR Election Precedence (Interface Priority > Highest Router ID via Loopback > Priority 0 Ineligibility)

Estimated Time:2m 0s

Question 153Question →

Arrange the criteria used by OSPFv2 to determine Designated Router (DR) election precedence in order from highest precedence (evaluated first) to lowest precedence (evaluated last).

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Answer

The correct sequence from highest to lowest precedence is: Highest OSPF interface priority, followed by Highest explicitly configured OSPF router ID, then Highest IPv4 address on an active loopback interface, and finally Highest IPv4 address on an active physical interface.

OSPFv2 DR/BDR election process evaluates interface priority first. If priorities are equal, it breaks ties using the Router ID, which is selected in the following order of precedence: (1) explicitly configured router ID command, (2) highest IP address on an active loopback interface, and (3) highest IP address on an active physical interface.

Step-by-Step Solution

Evaluate the primary election criteria: OSPF Interface Priority

The router with the highest configured OSPF interface priority (1-255) is elected DR. Priority 0 disqualifies a router entirely.

Interface priority provides explicit administrative control over DR/BDR election.

Evaluate explicit Router ID configuration

If interface priorities are equal (the default is 1), OSPF uses the Router ID as a tie-breaker, checking for a manually configured 'router-id' first.

Explicit configuration takes precedence over dynamically selected interface IP addresses.

Evaluate active loopback interfaces

If no explicit router ID is configured, OSPF selects the highest IPv4 address among all active logical (loopback) interfaces.

Loopback interfaces are preferred over physical interfaces because they are stable and do not go down due to physical line failures.

Evaluate active physical interfaces

If no loopback interfaces are configured, OSPF defaults to selecting the highest IPv4 address configured on any up/up physical interface.

Physical interface IP addresses serve as the final tie-breaking mechanism.

Key Concept

OSPFv2 DR/BDR Election Precedence Rules

Question 154Question →

A Cisco router receives an IPv4 unicast packet and must select the best path from its routing table to forward the traffic. Arrange the steps in the correct sequential order that the router follows to evaluate candidate routes and make a forwarding decision.

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Answer

The correct order of steps in router forwarding decision logic is: 1) Identify candidate routes that match the destination IP, 2) Select the route with the longest prefix match, 3) Compare Administrative Distance if equal-length prefix ties exist between different routing sources, and 4) Compare route metrics if equal-length prefix ties exist within the same routing protocol.

The forwarding engine follows a strict evaluation hierarchy: first, matching candidate routes are identified; second, Longest Prefix Match (LPM) filters for the most specific subnet mask; third, Administrative Distance breaks ties between routes of equal prefix length from different protocols; fourth, metric breaks ties between routes of equal prefix length from the same protocol.

Step-by-Step Solution

Identify matching candidate routes

A set of candidate routing table entries whose subnet masks encompass the packet's destination IPv4 address is compiled.

The router must locate all possible valid routes for the target destination before applying selection logic.

Apply Longest Prefix Match (LPM)

The candidate route with the longest prefix length (most specific mask) is selected.

LPM is the fundamental decision rule in IPv4/IPv6 packet forwarding. Prefix specificity overrides Administrative Distance and metric entirely.

Evaluate Administrative Distance (AD)

If multiple routes have identical prefix lengths from different sources, the route with the lower AD value (e.g., static AD 1 vs OSPF AD 110) is chosen.

AD acts as a tie-breaker between different route origins when prefix lengths are equal.

Evaluate Route Metric

If multiple routes have identical prefix lengths from the same protocol, the path with the lowest metric is selected (or load-balanced if equal).

Metrics are protocol-specific cost values used to determine the best path among routes learned via the same routing protocol.

Key Concept

Router Forwarding Decision Hierarchy (LPM > AD > Metric)

Estimated Time:1m 30s

Question 155Question →

A Cisco router receives an IPv4 packet destined for a remote subnet. Place the operational steps performed by the router to evaluate IPv4 static routes and forward the packet into the correct sequential order from first to last.

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Answer

The correct sequence of operations is: (1) Extract and inspect the destination IPv4 address from the incoming packet header, (2) Search the routing table for matching static routes and identify the candidate entry with the longest prefix match, (3) Evaluate Administrative Distance if multiple static routes exist for the identical network prefix, and (4) Encapsulate the packet into a Layer 2 frame and transmit it out the resolved exit interface toward the next hop.

When an IPv4 packet arrives on a Cisco router interface, the router inspects the destination IP address in the packet header. It then searches the routing table to find all matching network prefixes, selecting the entry with the longest prefix match (most specific mask). If there are multiple static routes configured for the exact same prefix length, the router breaks the tie by choosing the route with the lowest Administrative Distance. Finally, the router determines the exit interface/next-hop IP, rewrites the Layer 2 frame, and transmits the packet.

Step-by-Step Solution

Packet Ingress & Header Inspection

The destination IPv4 address is read from the packet.

The router requires the target destination address to perform a routing table lookup.

Longest Prefix Match Selection

The routing table entry with the longest subnet mask matching the destination IP is selected.

Cisco IOS router forwarding logic prioritizes the most specific prefix match over less specific routes.

Administrative Distance Tie-Breaking

If multiple static routes exist for the exact same prefix, the route with the lowest Administrative Distance is used.

Administrative Distance ranks route believability when multiple routes exist for identical destination prefixes.

Layer 2 Encapsulation and Forwarding

The packet is encapsulated into the outbound Layer 2 frame format and sent out the exit interface.

Final forwarding requires rewriting Layer 2 headers for the outbound physical or logical link.

Key Concept

IPv4 Static Route Lookup and Forwarding Decision Logic

Question 156Question →

A non-root Cisco Catalyst switch running Rapid PVST+ receives BPDUs on multiple interfaces connected to neighboring switches for VLAN 20. The switch must determine which of its interfaces will become the single Root Port for VLAN 20. Place the tie-breaking steps evaluated by Rapid PVST+ in the exact sequential order from first step evaluated to last step evaluated.

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Answer

The correct order of tie-breaking evaluation for Rapid PVST+ Root Port selection is: 1. Lowest cumulative Root Path Cost, 2. Lowest Sender Bridge ID (BID), 3. Lowest Sender Port ID, 4. Lowest local Receiver Port ID.

Rapid PVST+ evaluates Root Port selection using a strict four-step tie-breaker hierarchy: 1. Lowest cumulative Root Path Cost, 2. Lowest Sender Bridge ID (BID), 3. Lowest Sender Port ID (neighbor's port priority and index), 4. Lowest Receiver Port ID (local port priority and index).

Step-by-Step Solution

Identify the primary STP metric for Root Port selection.

The switch calculates total path cost by adding link costs to reach the Root Bridge. Lowest cumulative path cost is evaluated first.

STP prioritizes reaching the Root Bridge via the least costly path.

Apply the first tie-breaker if path costs are equal.

The switch evaluates the Sender Bridge ID (Bridge Priority + Extended System ID + MAC address) of the upstream neighbor switches.

Preferring the neighbor with the lowest Bridge ID ensures a deterministic loop-free structure.

Apply the second tie-breaker if path costs and neighbor BIDs are equal.

The switch checks the Sender Port ID (Port Priority + Port Number) advertised in the BPDU by the neighbor switch.

This differentiates multiple parallel links connecting to the exact same neighbor switch.

Apply the final tie-breaker if all upstream BPDU fields are identical.

The switch selects its own local interface with the lowest Port ID.

Local port ID is the final fallback when upstream BPDU data offers no difference.

Key Concept

Rapid PVST+ Root Port Tie-Breaking Sequence

Question 157Question →

A Cisco router receives an IPv4 packet destined for host $192.168.50.45$ . The router's routing table contains a static route `ip route 192.168.50.0 255.255.255.0 10.1.1.2` and a directly connected network $10.1.1.0/30$ out interface `GigabitEthernet0/1`. Arrange the sequential processing steps executed by the router to forward this packet from initial ingress lookup to egress transmission.

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Answer

The correct sequence is: Extract the destination IP address -> Perform primary routing lookup -> Perform recursive lookup for the next-hop IP -> Query ARP table for next-hop MAC -> Encapsulate packet and transmit out egress interface.

When a Cisco router receives an IP packet, it first extracts the destination IP address. Using longest prefix match, it matches the static route entry pointing to next-hop IP 10.1.1.2. Because this route specifies an IP next-hop rather than an outbound interface directly, the router performs a recursive lookup to find which connected interface reaches 10.1.1.2 (GigabitEthernet0/1). Knowing the egress Ethernet interface, it resolves the next-hop MAC address using ARP, encapsulates the IPv4 packet in an Ethernet frame, and transmits it out GigabitEthernet0/1.

Step-by-Step Solution

Inspect destination header

Destination IPv4 address

192.168.50.45

is extracted from the incoming frame.

Routing decisions are based on the packet's destination IPv4 address.

Execute primary route table lookup

Matches route `192.168.50.0 255.255.255.0` with next-hop IP

10.1.1.2

The router uses longest prefix matching to select the route entry.

Execute recursive lookup

Resolves

10.1.1.2

to directly connected route

10.1.1.0/30

on interface `GigabitEthernet0/1`.

Static routes configured solely with a next-hop IP address require a recursive lookup to identify the exit interface.

Resolve Layer 2 next-hop address

Obtains the target MAC address for

10.1.1.2

from the ARP table.

Ethernet encapsulation requires a destination Layer 2 MAC address for the next hop.

Encapsulate and egress

Frame is sent out `GigabitEthernet0/1`.

Final physical delivery step out the egress interface.

Key Concept

IPv4 Static Route Recursive Lookup & Packet Forwarding Pipeline

Estimated Time:2m 0s

Question 158Question →

A network administrator needs to deploy Link Aggregation (LAG) on a Cisco AireOS Wireless LAN Controller (WLC) connected to an upstream Cisco Catalyst switch. Place the operational steps required to enable and establish the LAG connection in the correct sequential order from first to last.

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Answer

The correct sequential order to deploy LAG on an AireOS WLC is: 1) Enable LAG in WLC settings, 2) Save configuration and reboot the WLC, 3) Configure connected upstream switch ports into an EtherChannel using mode 'on', and 4) Verify operational status of the aggregated bundle.

To successfully deploy LAG on an AireOS Wireless LAN Controller, the feature must first be enabled in WLC global controller settings. Because enabling LAG reorganizes physical ports into a single logical interface, the configuration must be saved and the controller rebooted to take effect. Following the reboot, the upstream Catalyst switch physical ports must be configured into a single EtherChannel using mode 'on' (static aggregation, since AireOS does not negotiate via LACP or PAgP). Finally, the network engineer verifies that the Port-Channel is operational and passing traffic across mapped WLAN VLANs.

Step-by-Step Solution

Enable LAG feature on the WLC

The controller prepares the internal distribution system interfaces for multi-port bundling.

Global LAG setting must be changed prior to restarting the appliance.

Save configuration and restart WLC

The WLC reboots and binds all physical distribution ports into a single logical LAG interface.

AireOS hardware architecture requires a system reboot to apply LAG implementation across distribution ports.

Configure switch ports with static EtherChannel

The upstream Catalyst switch binds its corresponding interfaces into a single port-channel using mode 'on'.

AireOS WLCs do not support dynamic EtherChannel negotiation protocols like LACP or PAgP.

Verify port-channel operation and data flow

Operational status is confirmed and WLAN VLAN traffic flows across the unified bundle.

Ensures that all bundled interfaces forward traffic properly without port mismatches or STP blocking.

Key Concept

AireOS WLC Link Aggregation deployment workflow and static switch EtherChannel requirements.

Question 159Question →

Four Cisco routers (Alpha, Beta, Gamma, and Delta) are connected to the same Ethernet broadcast domain and simultaneously boot and establish OSPFv2 adjacencies. The routers are configured with the following OSPF interface priorities and Router IDs:

- Router Alpha: Priority = 2, Router ID = 1.1.1.1
- Router Beta: Priority = 2, Router ID = 2.2.2.2
- Router Gamma: Priority = 1, Router ID = 10.10.10.10
- Router Delta: Priority = 0, Router ID = 192.168.1.1

Arrange the routers in order of their resulting OSPF roles on the shared segment, starting from the Designated Router (DR) at the top, followed by the Backup Designated Router (BDR), the eligible DROTHER router, and ending with the router completely excluded from election eligibility.

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Answer

The correct order of routers from DR to election-ineligible is: Router Beta (DR), Router Alpha (BDR), Router Gamma (DROTHER), and Router Delta (Ineligible).

In OSPFv2 multiaccess networks, DR and BDR election precedence is determined first by highest interface priority. Router Alpha and Router Beta tie with the highest priority (2), so their Router IDs break the tie: Router Beta (2.2.2.2) becomes DR and Router Alpha (1.1.1.1) becomes BDR. Router Gamma has a lower priority (1) and becomes an eligible DROTHER. Router Delta has a priority of 0, which makes it ineligible to participate in DR/BDR selection regardless of its high Router ID.

Step-by-Step Solution

Evaluate interface priority values for all routers.

Routers Alpha and Beta have priority 2, Router Gamma has priority 1, and Router Delta has priority 0.

OSPFv2 uses interface priority as the primary criterion for DR/BDR election.

Identify election eligibility.

Router Delta (priority 0) is marked ineligible for DR/BDR roles and placed at the bottom of election hierarchy.

An interface priority of 0 explicitly prevents a router from becoming a DR or BDR.

Determine DR and BDR roles among highest priority routers using Router ID as a tie-breaker.

Router Beta (

2.2.2.2 > 1.1.1.1

) is elected DR, and Router Alpha becomes BDR.

When priority values are equal, the router with the highest Router ID wins the DR election, and the next highest becomes BDR.

Place remaining eligible routers into DROTHER status.

Router Gamma (priority 1) assumes the DROTHER role.

Eligible routers with non-zero priority that do not win DR or BDR election remain DROTHERs.

Key Concept

OSPFv2 DR/BDR election precedence prioritizes non-zero interface priority first (highest wins; 0 is ineligible), followed by highest Router ID as a tie-breaker.

Question 160Question →

An enterprise workstation needs to access a web server using its Fully Qualified Domain Name (FQDN). Arrange the steps of the DNS name resolution process in the correct chronological order from first to last.

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Answer

The correct sequence of DNS name resolution begins with the client checking its local resolver cache and hosts file, followed by sending a recursive query to the configured DNS server on UDP port 53. The DNS server performs iterative lookups against authoritative root, TLD, and domain servers, and finally returns the resolved IP address back to the requesting workstation.

The name resolution process follows a strict hierarchy. First, local system resources (cache and hosts file) are inspected. If unresolved, the client generates a recursive DNS query to its configured DNS server via UDP port 53. The DNS server resolves the query via external hierarchy (Root, TLD, Authoritative servers) as needed, and lastly sends the reply back to the workstation while saving the mapping in its local cache.

Step-by-Step Solution

Check local client sources

Host determines whether the mapping is already known in local memory or local configuration files.

Checking local host cache avoids unnecessary network overhead.

Initiate DNS request

Host transmits a UDP packet to port 53 of the primary DNS server.

The client delegates full resolution responsibility to its recursive resolver.

Perform recursive server lookup

The internal DNS server communicates with authoritative DNS infrastructure.

The recursive server traverses the DNS hierarchy to find the authoritative answer.

Deliver and cache response

The workstation receives the IP address and completes establishing connection to the destination.

Caching speeds up future resolution queries within the TTL period.

Key Concept

DNS Lookup Process and Name Resolution Roles

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