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Question 1181Question →

A network administrator needs to manually configure a floating static route on a Cisco IOS router to serve as a backup path. Arrange the required command components in the correct sequential order from left to right as typed in the CLI.

Drag items to arrange them in the correct order

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Answer

The correct sequence for configuring a floating IPv4 static route in Cisco IOS is: `ip route` keyword, destination network address, subnet mask, next-hop IPv4 address (or exit interface), and administrative distance.
The standard Cisco IOS syntax for configuring an IPv4 static route is `ip route <destination-prefix> <subnet-mask> {ip-address | exit-interface} [distance]`. Placing `ip route` first, followed by the destination network prefix, subnet mask, next-hop IP address, and finally the administrative distance creates a valid floating static route.

Step-by-Step Solution

1
Identify the global configuration command mode keyword
Start with `ip route`.
Cisco IOS requires the keyword `ip route` to initiate an IPv4 static route entry.
2
Specify target destination network parameters
Provide the destination network IP (`192.168.20.0`) followed by its subnet mask (`255.255.255.0`).
The router must know which destination address block this route applies to.
3
Define forwarding path
Specify the next-hop IP address (`10.1.1.2`) or local exit interface.
The router requires explicit instructions on where to send matching packets.
4
Configure administrative distance for backup behavior
Append an administrative distance value greater than the primary protocol's AD (e.g., `130`).
Setting an AD higher than the primary route (such as OSPF AD 110) ensures the static route remains floating until the primary fails.

Key Concept

Cisco IOS IPv4 Static Route Command Syntax and Floating Route Configuration
Question 1182Question →

A network engineer is deploying a centralized Cisco Wireless LAN Controller (WLC) connected to an upstream Cisco Catalyst switch port configured as an 802.1Q trunk. The WLC Management Interface is assigned the IP address 192.168.10.10/24192.168.10.10/24 with VLAN ID 10. The upstream switch trunk interface has a native VLAN configured as VLAN 10. Cisco Lightweight Access Points (APs) operating in Local mode are connected to remote access switchports in VLAN 20 (192.168.20.0/24192.168.20.0/24) and successfully acquire DHCP IP addresses. However, the APs fail to establish CAPWAP tunnels with the WLC management interface. Diagnostic captures confirm that the WLC sends tagged 802.1Q frames for VLAN 10, but the switch drops them because VLAN 10 is configured as the native VLAN on the trunk interface. Which configuration change will resolve this CAPWAP management connectivity issue?

Show answer & explanation

Answer: Change the native VLAN on the switch trunk port to an unused VLAN (e.g., VLAN 999) or set the WLC Management Interface VLAN ID to 0 (untagged).

Answer

Change the native VLAN on the switch trunk port to an unused VLAN (such as VLAN 999) or configure the WLC Management Interface VLAN ID to 0 (untagged).
When a Cisco Wireless LAN Controller management interface is explicitly configured with a VLAN identifier like VLAN 10, it appends an 802.1Q tag to all egress traffic. If the connected switch trunk port has native VLAN 10 configured, the switch expects untagged traffic for VLAN 10 and drops incoming tagged frames for that native VLAN. Changing the switch trunk native VLAN to an unused VLAN ID ensures VLAN 10 frames are tagged and accepted, or changing the WLC VLAN ID to 0 instructs the controller to transmit untagged frames, resolving the CAPWAP connectivity failure.

Step-by-Step Solution

1
Analyze the encapsulation behavior of Cisco WLC management interfaces on 802.1Q trunks.
When a WLC management interface is assigned a specific VLAN ID (e.g., VLAN 10), the WLC tags all outgoing frame headers with an 802.1Q VLAN 10 tag.
The WLC expects explicit 802.1Q tagging when a non-zero VLAN ID is configured.
2
Evaluate the upstream switch trunk port native VLAN configuration conflict.
The upstream switch trunk port has VLAN 10 configured as its native VLAN. Standard switch behavior expects untagged frames for the native VLAN and drops tagged frames arriving for the configured native VLAN ID.
Matching tagged frames to the native VLAN ID creates an 802.1Q native VLAN tagging mismatch.
3
Determine the corrective configuration change.
Changing the switch trunk native VLAN to an unused VLAN ID (e.g., VLAN 999) allows VLAN 10 traffic to remain tagged end-to-end, or setting WLC Management VLAN ID to 0 forces the WLC to transmit untagged frames that match native VLAN 10.
Aligning frame encapsulation between the WLC and switch restores bi-directional Layer 3 CAPWAP reachability.

Key Concept

802.1Q Native VLAN Matching for WLC Management Interfaces
Question 1183Question →

Refer to the following Cisco CLI routing table output:

text
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

Gateway of last resort is not set

S 172.31.50.0/24 [1/0] via 10.1.1.1, GigabitEthernet0/0/1
D 172.31.50.64/28 [90/307200] via 10.2.2.2, GigabitEthernet0/0/2
O 172.31.50.64/29 [110/20] via 10.3.3.3, GigabitEthernet0/0/3
R 172.31.50.68/30 [120/1] via 10.4.4.4, GigabitEthernet0/0/4

A router receives an IP packet addressed to 172.31.50.67172.31.50.67. Which next-hop IP address will the router select to forward this packet?

Show answer & explanation

Answer: 10.3.3.3

Answer

The router forwards the packet to next-hop IP address 10.3.3.3 via interface GigabitEthernet0/0/3.
The correct choice identifies 10.3.3.3 as the next hop because the route 172.31.50.64/29 has the longest matching prefix (/29) among all valid candidate routes covering destination IP 172.31.50.67. A router always prefers the most specific route (longest prefix length) regardless of Administrative Distance or metric.

Step-by-Step Solution

1
Evaluate the target destination IP against all candidate routes in the routing table.
Destination IP 172.31.50.67172.31.50.67 is checked against each prefix mask.
The router must first find all matching subnets.
2
Determine subnet boundaries for candidate routes.
- 172.31.50.0/24 covers 172.31.50.0 to 172.31.50.255 (Match, length /24)
- 172.31.50.64/28 covers 172.31.50.64 to 172.31.50.79 (Match, length /28)
- 172.31.50.64/29 covers 172.31.50.64 to 172.31.50.71 (Match, length /29)
- 172.31.50.68/30 covers 172.31.50.68 to 172.31.50.71 (No match, 67 is outside range)
Routes must cover the target address to be valid candidates.
3
Apply the Longest Prefix Match (LPM) rule among all valid candidate routes.
The valid matching prefixes are /24, /28, and /29. The longest prefix match is /29 (172.31.50.64/29).
Longest Prefix Match is the absolute first criterion used by a router when forwarding packets, taking precedence over Administrative Distance and Metric.
4
Identify the next-hop IP address for the longest prefix match route.
The route 172.31.50.64/29 specifies next-hop IP 10.3.3.3.
Packets are forwarded to the next-hop specified by the winning route.

Key Concept

Longest Prefix Match (LPM) Logic
Question 1184Question →

In Cisco Rapid PVST+, a switch constructs an 8-byte (64-bit) Bridge ID (BID) for each VLAN instance to participate in Root Bridge election. Arrange the three components of the Rapid PVST+ Bridge ID in order from most significant bits (leftmost) to least significant bits (rightmost).

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Answer

The correct sequence from most significant bits to least significant bits is: 4-bit Bridge Priority, 12-bit System ID Extension (VLAN ID), and 48-bit MAC Address.
The 8-byte (64-bit) Rapid PVST+ Bridge ID is ordered from most significant to least significant bits as follows: 4-bit Bridge Priority (bits 63–60), 12-bit System ID Extension representing the VLAN ID (bits 59–48), and the 48-bit switch MAC Address (bits 47–0).

Step-by-Step Solution

1
Examine the 2-byte (16-bit) Priority field structure in the Rapid PVST+ Bridge ID.
The upper 4 bits represent the configurable Bridge Priority, making them the most significant bits of the entire 64-bit Bridge ID.
This layout ensures that user-defined priority configurations take precedence over VLAN IDs and MAC addresses.
2
Identify the remaining sub-field of the 2-byte Priority field.
The lower 12 bits of the Priority field carry the System ID Extension (VLAN ID).
Carrying the VLAN ID within these 12 bits allows Rapid PVST+ to maintain unique Bridge IDs per VLAN without requiring separate MAC addresses for each instance.
3
Identify the final 6 bytes (48 bits) of the Bridge ID.
The lowest 48 bits consist of the switch's burned-in MAC address.
The MAC address serves as the final tie-breaker during Root Bridge election when Bridge Priority and VLAN ID values are equal.

Key Concept

Rapid PVST+ Bridge ID (BID) Structure and System ID Extension
Question 1185Question →

An enterprise network deployment includes Lightweight Access Points (LAPs) managed by a centralized Wireless LAN Controller (WLC). During a scheduled link maintenance event, WAN connectivity between a branch office LAP and the centralized WLC is temporarily lost. The branch LAP is operating in FlexConnect mode with local switching and local authentication enabled for the employee SSID. Meanwhile, a campus LAP connected to the main network operates in default Local mode. Upon loss of the CAPWAP connection, clients connected to the FlexConnect AP continue transmitting data to local resources, whereas clients connected to the Local mode AP immediately lose network access. Which architectural requirement causes the Local mode AP to cease forwarding client data traffic when controller connectivity is lost?

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Answer: Local mode APs require an active CAPWAP data tunnel to encapsulate all client 802.11 payload into 802.3 frames at the WLC, preventing autonomous local Layer 2 frame switching at the AP level.

Answer

Local mode APs encapsulate all client traffic within CAPWAP data tunnels that terminate at the Wireless LAN Controller (WLC). When controller connectivity is lost, the CAPWAP data tunnel drops, making local switching impossible for Local mode APs.
In Cisco centralized wireless architectures, access points in default Local mode enforce central switching. All wireless client payload is encapsulated in CAPWAP data packets and forwarded over the network to terminate directly at the Wireless LAN Controller. If controller reachability is lost, the CAPWAP data tunnel drops, and because Local mode APs are not provisioned with local VLAN-to-SSID mappings, client traffic cannot be forwarded locally.

Step-by-Step Solution

1
Analyze the functional difference between Cisco LAP operational modes.
Local mode APs use Centralized Switching, sending all control and data traffic through CAPWAP tunnels to the WLC. FlexConnect APs support Local Switching, allowing traffic to bypass the CAPWAP tunnel at the branch switch interface.
Understanding data plane encapsulation is essential to evaluating behavior during controller connectivity outages.
2
Evaluate the impact of a lost CAPWAP tunnel on Local mode AP operations.
Without an reachable WLC to decapsulate CAPWAP packets and bridge client traffic onto local VLANs, a Local mode AP cannot locally switch 802.11 frames to 802.3 Ethernet frames.
Local mode APs lack the local VLAN mapping and switching configuration resident on FlexConnect APs.
3
Identify the option correctly describing CAPWAP data tunnel dependence.
The option specifying that Local mode APs require an active CAPWAP data tunnel for central frame processing and encapsulation is correct.
This directly explains why loss of WLC communication prevents Local mode APs from sustaining client data transmission.

Key Concept

Cisco Split-MAC Architecture and AP Modes (Local vs. FlexConnect)
Question 1186Question →

A network engineer is configuring a newly created WLAN on a Cisco Wireless LAN Controller (WLC) using the web GUI. The engineer needs to bind this WLAN to a specific dynamic interface so that connecting wireless clients are assigned to the correct IP subnet VLAN. On which tab within the WLANs > Edit menu is the Interface/Interface Group drop-down list located?

Show answer & explanation

Answer: General

Answer

The Interface/Interface Group drop-down list is located under the General tab of the WLAN edit menu.
On a Cisco Wireless LAN Controller (WLC) GUI, the General tab under WLANs > Edit is where core operational attributes are defined. This includes the Profile Name, SSID, Status enablement, Radio Policy, and the Interface/Interface Group mapping that links the WLAN to a specific dynamic interface/VLAN.

Step-by-Step Solution

1
Navigate to WLANs menu in the Cisco WLC web GUI
Displays the list of configured WLAN IDs and Profile Names.
Allows selection of the specific WLAN requiring modification.
2
Click the target WLAN ID to access the Edit menu
Opens the WLAN Edit window displaying multiple configuration tabs (General, Security, QoS, Policy-Mapping, Advanced).
Provides access to the settings of the selected WLAN.
3
Locate the Interface/Interface Group (GNS) drop-down menu on the General tab
Maps the wireless traffic of clients connecting to this SSID to the corresponding controller dynamic interface and backend VLAN.
The General tab houses essential WLAN parameters including Profile Name, SSID, Status checkbox, and Interface association.

Key Concept

WLAN Interface Association in Cisco WLC GUI
Estimated Time:45s
Question 1187Question →

A network engineer configures a Cisco router interface with the command `ipv6 address 2001:db8:cafe:40::/64 eui-64`. The physical MAC address of the interface is `7081.05e1.a2b3`. Which two statements accurately describe the resulting IPv6 addressing state on this interface? (Select two.)

Select all that apply

Show answer & explanation

Answer: The dynamically generated Global Unicast Address on the interface is 2001:db8:cafe:40:7281:5ff:fee1:a2b3.; The interface automatically derives a Link-Local address with the prefix fe80::/10 using the same modified EUI-64 interface identifier.

Answer

The dynamically generated Global Unicast Address is 2001:db8:cafe:40:7281:5ff:fee1:a2b3, and the interface automatically derives a Link-Local address with the prefix fe80::/10 using the same EUI-64 interface identifier.
The EUI-64 algorithm flips the 7th bit of the first MAC byte (0x70 to 0x72) and inserts FFFE into the middle, yielding the interface ID 7281:05ff:fee1:a2b3. Adding this to the prefix 2001:db8:cafe:40::/64 gives 2001:db8:cafe:40:7281:5ff:fee1:a2b3. Additionally, any IPv6-enabled interface automatically configures a Link-Local address under the fe80::/10 prefix using this same interface ID.

Step-by-Step Solution

1
Convert the MAC address to EUI-64 interface identifier form
MAC 7081.05e1.a2b3 splits into 70-81-05 and e1-a2-b3. Inverting the 7th bit of 0x70 (0011 0000 -> 0011 0010 = 0x72) yields 7281:05. Inserting FFFE between the halves yields 7281:05ff:fee1:a2b3.
EUI-64 requires flipping the U/L bit (7th bit) and placing FFFE in the middle of the 48-bit MAC address to form a 64-bit interface ID.
2
Combine the prefix with the EUI-64 interface identifier
Combining 2001:db8:cafe:40::/64 with 7281:05ff:fee1:a2b3 produces 2001:db8:cafe:40:7281:5ff:fee1:a2b3.
The prefix replaces the upper 64 bits and the EUI-64 identifier populates the lower 64 bits.
3
Evaluate link-local address generation
The router creates a link-local address within fe80::/10 using the interface ID 7281:5ff:fee1:a2b3.
IPv6 interfaces automatically assign a link-local address upon enabling IPv6 processing.

Key Concept

EUI-64 Interface Identifier Generation and IPv6 Address Scopes
Question 1188Question →

An engineer has globally defined an external RADIUS server under Controller > AAA > RADIUS > Authentication on a Cisco Wireless LAN Controller (WLC). The engineer then creates a new enterprise WLAN with Layer 2 Security set to WPA2 using 802.1X authentication. However, wireless clients attempting to connect are unable to authenticate, and debug logs indicate that no authentication requests are being transmitted to the RADIUS server. Which configuration action within the WLANs > Edit menu must be performed to resolve this client authentication failure?

Show answer & explanation

Answer: Select the active RADIUS server under the AAA Servers tab of the specific WLAN configuration.

Answer

Selecting the active RADIUS server under the AAA Servers tab of the specific WLAN configuration enables the WLC to route 802.1X client authentication requests to the RADIUS server.
Global RADIUS server configuration under the Controller menu merely registers the server with the WLC. To enable client authentication for a specific WLAN using 802.1X, an administrator must navigate to WLANs > Edit > AAA Servers tab and select the desired RADIUS server from the Authentication Servers drop-down menu.

Step-by-Step Solution

1
Analyze the prerequisite global configuration versus WLAN-specific mapping on Cisco WLC GUI.
Global configuration makes the RADIUS server available, but individual WLANs must be explicitly bound to the server.
Different WLANs may require different RADIUS servers or authentication server groups.
2
Identify the specific GUI tab in the WLANs > Edit menu responsible for authentication server assignment.
The AAA Servers tab contains drop-down menus for Authentication and Accounting servers.
This tab connects the WLAN's 802.1X security configuration to the desired RADIUS server index.
3
Select the primary RADIUS server from the Authentication Servers drop-down list.
The controller now forwards EAP-Request/Response packets between wireless clients and the designated RADIUS server.
Without this mapping, the WLC has no target server configured for client 802.1X requests on that WLAN.

Key Concept

WLAN AAA Server Mapping in Cisco WLC GUI
Estimated Time:1m 30s
Question 1189Question →

An engineer issues the `show etherchannel summary` command on Switch-A and observes that the logical interface `Port-channel 1` displays a status flag of `SD` (Layer 2, Down), with all member physical interfaces marked with the flag `I` (Stand-alone). Physical connectivity between the switches is up and running. Which configuration on the interconnected switches is the root cause of this operational state?

Show answer & explanation

Answer: Both switches are configured with `channel-group 1 mode passive` on their respective physical member interfaces.

Answer

Both switches are configured with LACP passive mode on their connected physical member interfaces.
Link Aggregation Control Protocol (LACP) requires at least one participating switch interface to actively initiate negotiation. When both endpoints are set to `passive` mode (`channel-group mode passive`), neither device sends LACP packets. Consequently, LACP negotiation never completes, leaving the port-channel interface down (`SD`) and placing the individual member interfaces in stand-alone (`I`) operational state.

Step-by-Step Solution

1
Analyze the reported flags in `show etherchannel summary`.
The `SD` flag indicates Layer 2 and Down status for the Port-channel, while `I` indicates that the physical member ports are operating independently (Stand-alone).
Physical interfaces fall back to stand-alone mode when LACP bundle negotiation fails to complete successfully.
2
Evaluate LACP mode interaction behavior.
LACP `passive` ports only respond to LACP packets and never initiate negotiation.
If both sides are set to `passive`, neither switch initiates LACP frame exchange, preventing EtherChannel establishment.

Key Concept

LACP Operational Modes and Negotiation Rules
Estimated Time:1m 15s
Question 1190Question →

Refer to the following routing table output from a Cisco router:

text
Gateway of last resort is 192.168.1.1 to network 0.0.0.0

S* 0.0.0.0/0 [1/0] via 192.168.1.1
D 172.31.0.0/16 [90/2172416] via 10.1.1.1, 01:24:12, GigabitEthernet0/0
O 172.31.45.0/24 [110/20] via 10.2.2.2, 00:45:10, GigabitEthernet0/1
S 172.31.45.128/26 [1/0] via 10.3.3.3
D 172.31.45.128/27 [90/307200] via 10.4.4.4, 02:11:05, GigabitEthernet0/2

The router receives an IP packet with a destination address of 172.31.45.138172.31.45.138. Which next-hop IP address will the router choose to forward this packet?

Show answer & explanation

Answer: 10.4.4.4

Answer

The router will forward the packet to next-hop IP address 10.4.4.4.
When forwarding a packet, a Cisco router compares the destination IP address against all network entries in the routing table and selects the route with the longest prefix match (the most specific subnet mask). The destination address 172.31.45.138 matches 172.31.45.128/27 (host range .128–.159), which has a 27-bit mask length. This is more specific than the /26, /24, /16, or default /0 routes. Therefore, the router forwards the packet to next-hop 10.4.4.4 via GigabitEthernet0/2.

Step-by-Step Solution

1
Determine which routing entries encompass the destination IP address 172.31.45.138.
The destination address 172.31.45.138 falls within the ranges for 0.0.0.0/0, 172.31.0.0/16, 172.31.45.0/24, 172.31.45.128/26 (range 172.31.45.128 to 172.31.45.191), and 172.31.45.128/27 (range 172.31.45.128 to 172.31.45.159).
A router evaluates all matching routes in its routing table before selecting the forwarding path.
2
Apply the Longest Prefix Match (LPM) rule among all valid matching routes.
Prefix lengths are /0, /16, /24, /26, and /27. The route with the longest prefix length is 172.31.45.128/27.
Routers always prioritize the most specific route (longest subnet mask / prefix length) regardless of administrative distance or metric.
3
Identify the next-hop IP associated with the winning route 172.31.45.128/27.
The route specifies 'via 10.4.4.4, GigabitEthernet0/2'.
The packet must be forwarded to the next-hop interface/IP designated by the longest matching routing table entry.

Key Concept

Longest Prefix Match (LPM) precedence in router forwarding logic
Question 1191Question →

A Cisco switch operating with Rapid PVST+ receives multiple BPDUs across several redundant trunk links connecting toward the Root Bridge. To elect its single Root Port for a given VLAN instance, the switch executes a standardized four-step tie-breaking sequence to select the best path.

In what chronological sequence does the switch evaluate these criteria, starting from the first criterion evaluated (highest precedence) to the final criterion evaluated (lowest precedence)?

Drag items to arrange them in the correct order

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Answer

The correct sequence for electing a Root Port in Rapid PVST+ evaluates: 1) Lowest cumulative Root Path Cost, 2) Lowest Sender Bridge ID, 3) Lowest Sender Port ID, and 4) Lowest Local Port ID.
In Rapid PVST+ (and standard 802.1D/802.1w STP), a non-root switch selects its single Root Port by comparing BPDU criteria in strict order: first, the lowest cumulative Root Path Cost; second, the lowest Sender (Designated) Bridge ID; third, the lowest Sender (Designated) Port ID; and fourth, the lowest Local (Receiver) Port ID.

Step-by-Step Solution

1
Evaluate candidate path metrics toward the elected Root Bridge.
The interface receiving the BPDU with the lowest cumulative Root Path Cost is preferred.
STP path selection prioritizes optimal forwarding efficiency to the Root Bridge.
2
Compare upstream neighbor identities if path costs match.
The interface connected to the neighbor switch possessing the lowest Bridge ID (Priority + MAC address) is chosen.
Sender BID serves as the primary tie-breaker when multiple paths yield identical path costs.
3
Compare upstream neighbor port identifiers if connecting to the same neighbor switch across parallel links.
The interface receiving BPDUs from the lower Sender Port ID (Port Priority + Port Index) is selected.
The upstream switch's Designated Port ID breaks ties when path cost and neighbor BID are identical.
4
Evaluate local receiving interface identifiers as the final tie-breaker.
The local port with the lowest internal Port ID (Port Priority + Port Number) becomes the Root Port.
When all external BPDU parameters match, the local switch uses its own port numerical priority as the final determinant.

Key Concept

Rapid PVST+ Root Port Decision Sequence
Question 1192Question →

An organization is upgrading its campus network architecture. The network engineering team needs to design an access-to-distribution layer interconnect that provides active-active path utilization across all uplinks, sub-second routing convergence, and complete elimination of Spanning Tree Protocol (STP) blocked ports. Which network topology design best satisfies these requirements?

Show answer & explanation

Answer: Extending Layer 3 routing to the access layer to establish a Routed Access architecture.

Answer

Extending Layer 3 routing to the access layer to establish a Routed Access architecture.
In a Routed Access architecture, Layer 3 routing functions are extended down to the access layer switches. By making the access-to-distribution uplinks Layer 3 routed interfaces, Spanning Tree Protocol is eliminated on those connections. Traffic can be load-balanced using Equal-Cost Multi-Path (ECMP), and routing protocols provide fast convergence without blocked links.

Step-by-Step Solution

1
Analyze the requirements for active-active uplinks, fast convergence, and STP elimination.
Traditional Layer 2 access-to-distribution designs require STP to block redundant links, preventing active-active forwarding and resulting in slower convergence.
Layer 2 topologies with redundant paths must block ports via STP to avoid loops.
2
Evaluate the impact of shifting the Layer 2/Layer 3 boundary to access layer switches.
Running Layer 3 routing on access switches converts uplinks to point-to-point IP links.
Routed links utilize routing protocols (such as OSPF or EIGRP) for path selection, permitting ECMP load balancing and eliminating Layer 2 loops and STP entirely.

Key Concept

Routed Access Layer Campus Architecture
Estimated Time:1m 30s
Question 1193Question →

An engineer is troubleshooting packet forwarding on router R1. A packet arrives at R1 with a destination IP address of 172.16.45.100.

Refer to the command output from R1:

text
R1# show ip route
Gateway of last resort is 10.0.0.5 to network 0.0.0.0

S* 0.0.0.0/0 [1/0] via 10.0.0.5
S 172.16.0.0/16 [1/0] via 10.0.0.1
O 172.16.45.0/24 [110/20] via 10.0.0.2
B 172.16.45.96/28 [20/0] via 10.0.0.4

Which next-hop IP address will router R1 use to forward this packet?

Show answer & explanation

Answer: 10.0.0.4

Answer

Router R1 will forward the packet to the next-hop IP address 10.0.0.4 based on the Longest Prefix Match rule.
When a router receives a packet, it compares the destination IP address against all routes in the routing table. If multiple routes match, the router strictly prefers the route with the most specific (longest) subnet mask (Longest Prefix Match). In this scenario, 172.16.45.100 matches 0.0.0.0/0, 172.16.0.0/16, 172.16.45.0/24, and 172.16.45.96/28. The /28 prefix is the longest match, so the packet is routed via next-hop 10.0.0.4.

Step-by-Step Solution

1
Identify all candidate routes matching the destination address 172.16.45.100.
The destination address matches 0.0.0.0/0, 172.16.0.0/16, 172.16.45.0/24, and 172.16.45.96/28.
172.16.45.96/28 spans usable IP range 172.16.45.97 to 172.16.45.110, which includes 172.16.45.100.
2
Compare prefix lengths of all matching candidate routes.
Prefix lengths are /0, /16, /24, and /28.
Router forwarding logic relies first on Longest Prefix Match (LPM) to choose the most specific route.
3
Select the route with the most specific (longest) prefix mask.
The route B 172.16.45.96/28 with next-hop 10.0.0.4 has the longest mask (/28).
LPM supersedes Administrative Distance and Metric during route selection.

Key Concept

Router Forwarding Decision Logic & Longest Prefix Match
Question 1194Question →

When implementing Link Aggregation (LAG) between a Cisco Wireless LAN Controller and an upstream switch, specific configuration rules apply to the physical interfaces and channel grouping. Which two statements describe valid operational characteristics or configuration requirements for this LAG deployment? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: Every physical distribution port on the wireless controller is combined into one single logical interface.; The switch ports attached to the controller must be statically bundled into an EtherChannel using mode 'on'.

Answer

Enabling LAG on a Wireless LAN Controller bundles all physical distribution system ports into a single logical interface, and the connected switch ports must be statically configured in EtherChannel mode 'on'.
Enabling Link Aggregation (LAG) on a Cisco Wireless LAN Controller aggregates all physical distribution system ports into a single logical EtherChannel. Because the controller does not participate in dynamic negotiation protocols like LACP or PAgP, the corresponding switch ports must be statically configured using EtherChannel mode 'on'.

Step-by-Step Solution

1
Identify the multi-port bundling behavior on a Cisco WLC when LAG is enabled.
Recognize that enabling LAG aggregates all physical distribution system ports into a single logical interface.
Cisco WLC architecture requires all distribution ports to form one unified EtherChannel pipe rather than multiple independent links.
2
Determine the supported EtherChannel negotiation mode on the connected switch interfaces.
Confirm that switch ports must be configured manually using 'channel-group mode on'.
The controller does not send or process LACP or PAgP negotiation frames when LAG is active.

Key Concept

WLAN Infrastructure Link Aggregation (LAG) Requirements
Question 1195Question →

A network engineer is configuring a routed (Layer 3) EtherChannel bundle on a Cisco switch using LACP active mode across physical interfaces GigabitEthernet 0/1 and 0/2. Place the CLI configuration commands in the correct sequential order from initial interface selection to final Layer 3 IP address assignment.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct configuration sequence is: enter physical interface range mode ('interface range GigabitEthernet 0/1 - 2'), convert physical member links to Layer 3 ('no switchport'), configure LACP mode ('channel-group 1 mode active'), enter port-channel interface mode ('interface Port-channel 1'), and assign the IP address ('ip address 10.1.1.1 255.255.255.252').
To deploy a routed (Layer 3) EtherChannel using LACP, the physical interfaces must first be selected ('interface range GigabitEthernet 0/1 - 2') and explicitly converted to routed ports ('no switchport'). Next, the LACP active negotiation mode is configured ('channel-group 1 mode active'), creating the logical bundle. Finally, the administrator navigates into the port-channel interface ('interface Port-channel 1') and assigns the IP address ('ip address 10.1.1.1 255.255.255.252').

Step-by-Step Solution

1
Select physical member interfaces
Enters interface range configuration mode for GigabitEthernet 0/1 and 0/2.
Configuration changes must be applied across both physical candidate interfaces simultaneously.
2
Disable Layer 2 functionality on member interfaces
Executes 'no switchport' on member interfaces.
Member interfaces must match the Layer 3 operation requirement before joining a routed EtherChannel.
3
Configure channel-group and LACP mode
Executes 'channel-group 1 mode active'.
Binds physical interfaces to channel-group 1 and actively initiates LACP negotiation.
4
Navigate to the logical port-channel interface
Enters 'interface Port-channel 1'.
Enables logical interface parameter configuration.
5
Assign Layer 3 IPv4 address
Executes 'ip address 10.1.1.1 255.255.255.252'.
Layer 3 IP addresses are configured directly on the port-channel interface, not on the individual physical member interfaces.

Key Concept

Layer 3 EtherChannel LACP Configuration Sequence
Estimated Time:1m 30s
Question 1196Question →

A Cisco Catalyst switch receives an Ethernet frame on interface GigabitEthernet0/3 configured in VLAN 15. The frame contains a source MAC address of 0050.56a1.1a01 and a destination MAC address of 0050.56a1.2b02. Upon reviewing its MAC address table, the switch finds that destination 0050.56a1.2b02 is already dynamic mapping to interface GigabitEthernet0/3 in VLAN 15, but there is no entry for source MAC address 0050.56a1.1a01. Which action will the switch perform upon receiving this frame?

Show answer & explanation

Answer: The switch records the source MAC address 0050.56a1.1a01 on interface GigabitEthernet0/3 in VLAN 15 and filters (drops) the frame.

Answer

The switch records the source MAC address 0050.56a1.1a01 on interface GigabitEthernet0/3 in VLAN 15 and filters (drops) the frame.
When an Ethernet frame reaches a switch port, the switch always performs MAC address learning first by inspecting the frame's source MAC address and updating its MAC address table with the ingress port and VLAN. Next, the switch looks up the destination MAC address to make a forwarding decision. If the destination MAC address is located on the exact same port where the frame entered, the switch determines that the destination host is already on the local collision domain/segment and filters (drops) the frame to avoid sending redundant traffic.

Step-by-Step Solution

1
Examine ingress frame header and process source MAC address learning
The switch inspects the source MAC address (0050.56a1.1a01) and adds an entry mapping 0050.56a1.1a01 to interface GigabitEthernet0/3 in VLAN 15 in its MAC address table.
Layer 2 switches learn source MAC addresses from all incoming Ethernet frames on the port they arrive on.
2
Lookup destination MAC address in the MAC address table
The destination MAC address (0050.56a1.2b02) is found in the MAC address table and is mapped to interface GigabitEthernet0/3 in VLAN 15.
Switch lookup determines which egress port should be used to reach the target destination.
3
Compare ingress port with target egress port and apply forwarding/filtering logic
Since the target egress port (GigabitEthernet0/3) matches the ingress port (GigabitEthernet0/3), the frame is filtered (dropped).
Devices connected through a hub or shared segment on GigabitEthernet0/3 receive local traffic directly; retransmitting the frame out the same port would create unnecessary collision and traffic overhead.

Key Concept

Layer 2 Frame Filtering and MAC Address Table Operation
Question 1197Question →

An administrator enables Cisco STP PortFast on edge access ports connected to end-user workstations. Which two operational benefits or behaviors result from enabling PortFast on these interfaces? (Select two.)

Select all that apply

Show answer & explanation

Answer: The interface transitions immediately to the Forwarding state upon linkup, bypassing the 802.1D Listening and Learning states.; Link state changes on the interface do not trigger Spanning Tree Protocol Topology Change Notifications (TCNs).

Answer

Enabling PortFast on edge access ports allows the interface to bypass the Listening and Learning states to reach Forwarding immediately, and prevents link state changes on that port from triggering Topology Change Notifications (TCNs).
Enabling PortFast on an edge access port allows it to immediately enter the Forwarding state upon link activation without waiting through the Listening and Learning states. Additionally, link status transitions on PortFast ports do not generate Topology Change Notifications (TCNs), keeping MAC address tables stable across the switched network.

Step-by-Step Solution

1
Analyze standard 802.1D convergence states.
Standard STP ports spend 15 seconds in Listening and 15 seconds in Learning before Forwarding, totaling a 30-second delay.
PortFast bypasses Listening and Learning for edge devices so DHCP and other initial network communications do not time out.
2
Analyze topology change notification impact.
Edge port state changes do not indicate a core topology failure.
Suppressing TCNs on PortFast ports stops switches across the LAN from reducing MAC table aging timers unnecessarily.

Key Concept

STP PortFast operational mechanics and TCN suppression
Question 1198Question →

Refer to the following partial output from a Cisco router's routing table:

text
Codes: C - connected, S - static, O - OSPF, D - EIGRP

O 172.16.10.0/24 [110/20] via 10.1.1.1, GigabitEthernet0/0
D 172.16.10.64/26 [90/307200] via 10.1.1.2, GigabitEthernet0/1
S 172.16.10.64/27 [1/0] via 10.1.1.3, GigabitEthernet0/2

The router receives an IP packet with a destination IP address of 172.16.10.68. Which statements correctly describe how the router handles this forwarding decision? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: The router selects the static route to 172.16.10.64/27 because it has the longest prefix match for the destination address.; The packet is forwarded out interface GigabitEthernet0/2 toward next-hop IP address 10.1.1.3.

Answer

The router selects the static route to 172.16.10.64/27 because it has the longest prefix match, and forwards the packet out GigabitEthernet0/2 toward next-hop 10.1.1.3.
When forwarding a packet, a router compares the destination IP address against all known routes and chooses the entry with the longest prefix match (most specific netmask). The subnet 172.16.10.64/27 has a 27-bit mask, making it the longest match among the candidates. Consequently, the router routes the packet out GigabitEthernet0/2 to next-hop 10.1.1.3.

Step-by-Step Solution

1
Evaluate destination host IP against candidate subnet ranges in the routing table.
Destination 172.16.10.68 matches 172.16.10.0/24, 172.16.10.64/26, and 172.16.10.64/27.
All three routes encompass the target address within their subnet ranges.
2
Apply the Longest Prefix Match (LPM) rule.
172.16.10.64/27 has a 27-bit mask, which is longer than /26 and /24.
Routers always prefer the route with the most specific (longest) subnet mask first, regardless of administrative distance or metric.
3
Determine the forwarding action based on the selected route entry.
The route specifies exit interface GigabitEthernet0/2 and next-hop 10.1.1.3.
The router forwards the packet using the egress interface and next-hop associated with the winning LPM route.

Key Concept

Router Forwarding Decision Logic & Longest Prefix Match
Question 1199Question →

A network engineer is analyzing a Layer 2 topology operating with Cisco Rapid PVST+ for VLAN 10. Switch-1 is the Root Bridge. Switch-2 connects to Switch-1 via interface Gi0/1 and to Switch-3 via interface Gi0/2. Both links are full-duplex point-to-point connections. Currently, interface Gi0/1 on Switch-2 is the Root Port, and interface Gi0/2 on Switch-2 is selected as an Alternate port. Which two statements accurately describe the operational behavior and roles of interface Gi0/2 on Switch-2? (Select two.)

Select all that apply

Show answer & explanation

Answer: Interface Gi0/2 operates in the Discarding port state while actively receiving BPDUs and maintaining a backup path to the Root Bridge.; If interface Gi0/1 loses connectivity, interface Gi0/2 can immediately transition to the Root Port role and move directly into the Forwarding state.

Answer

Interface Gi0/2 operates in the Discarding port state while actively receiving BPDUs, and if interface Gi0/1 fails, interface Gi0/2 can immediately transition to the Root Port role and enter the Forwarding state.
In Rapid PVST+ (802.1w), an Alternate port provides a redundant path to the Root Bridge and remains in the Discarding state during normal operations. If the current Root Port fails, Rapid PVST+ allows the Alternate port to immediately assume the Root Port role and transition directly into the Forwarding state without undergoing timer-driven Listening and Learning delays.

Step-by-Step Solution

1
Identify the Rapid PVST+ role and state for interface Gi0/2 under normal conditions.
Interface Gi0/2 is an Alternate port, which in Rapid PVST+ maps to the Discarding port state while processing incoming BPDUs from Switch-3.
802.1w consolidates Disabled, Blocking, and Listening states into the single Discarding state.
2
Determine the failover behavior of an Alternate port upon loss of the active Root Port (Gi0/1).
Interface Gi0/2 immediately transitions to the Root Port role and enters the Forwarding state.
Rapid PVST+ enables instant convergence for Alternate ports without waiting for traditional 802.1D Forward Delay (Listening/Learning) timers.

Key Concept

Rapid PVST+ Port Roles (Alternate vs Backup) and Fast Transition Convergence Mechanics
Question 1200Question →

A network administrator is designing a VLSM addressing scheme for a branch office using the parent IPv4 block 172.31.96.0/21172.31.96.0/21. The subnets must be allocated contiguously starting from the lowest available address in the block, ordered by host requirements from largest to smallest:

- VLAN 10 requires at least 130 usable host IP addresses
- VLAN 20 requires at least 60 usable host IP addresses
- VLAN 30 requires at least 28 usable host IP addresses

What is the last usable IPv4 host address allocated to VLAN 30?

Show answer & explanation

Answer: 172.31.97.94172.31.97.94

Answer

The last usable IPv4 host address allocated to VLAN 30 is 172.31.97.94172.31.97.94.
Allocating subnets using VLSM in descending order gives VLAN 10 the block 172.31.96.0/24172.31.96.0/24 (range 172.31.96.0172.31.96.0–172.31.96.255172.31.96.255) and VLAN 20 the block 172.31.97.0/26172.31.97.0/26 (range 172.31.97.0172.31.97.0–172.31.97.63172.31.97.63). VLAN 30 receives the next available block 172.31.97.64/27172.31.97.64/27. The broadcast address of this block is 172.31.97.95172.31.97.95, making the last usable host address 172.31.97.94172.31.97.94.

Step-by-Step Solution

1
Calculate the prefix size and subnet range for VLAN 10 (130 hosts).
To support 130 hosts, 28−2=2542^8 - 2 = 254 usable hosts are required, requiring 8 host bits (/24 mask). Starting at 172.31.96.0172.31.96.0, the subnet is 172.31.96.0/24172.31.96.0/24, covering 172.31.96.0172.31.96.0 through 172.31.96.255172.31.96.255.
VLSM allocations must satisfy 2h−2≥required hosts2^h - 2 \ge \text{required hosts} and align on bit boundaries.
2
Calculate the prefix size and subnet range for VLAN 20 (60 hosts).
To support 60 hosts, 26−2=622^6 - 2 = 62 usable hosts are required, requiring 6 host bits (/26 mask). The next available address is 172.31.97.0172.31.97.0. The subnet is 172.31.97.0/26172.31.97.0/26, covering 172.31.97.0172.31.97.0 through 172.31.97.63172.31.97.63.
Subnets must be assigned sequentially starting immediately after the preceding subnet's broadcast address.
3
Calculate the prefix size and subnet range for VLAN 30 (28 hosts).
To support 28 hosts, 25−2=302^5 - 2 = 30 usable hosts are required, requiring 5 host bits (/27 mask). The next available address is 172.31.97.64172.31.97.64. The subnet is 172.31.97.64/27172.31.97.64/27, covering network ID 172.31.97.64172.31.97.64 to broadcast 172.31.97.95172.31.97.95.
A /27 block provides 32 total addresses (252^5), yielding a broadcast address of 172.31.97.64+31=172.31.97.95172.31.97.64 + 31 = 172.31.97.95.
4
Determine the last usable host IP address for VLAN 30.
The broadcast address is 172.31.97.95172.31.97.95, so the last usable host address is 172.31.97.95−1=172.31.97.94172.31.97.95 - 1 = 172.31.97.94.
The usable host range excludes the network ID and the broadcast address.

Key Concept

Variable Length Subnet Masking (VLSM) and Usable Host Range Derivation
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