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IP Connectivity

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Question 421Question →

An engineer reviews the operational status of router R1 connected to a shared multiaccess Ethernet segment:

text
R1# show ip ospf interface GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is up
Internet Address 10.10.10.1/24, Area 0
Process ID 10, Router ID 10.10.10.1, Network Type BROADCAST, Cost: 1
State DROTHER, Priority 0
Designated Router (ID) 10.10.10.3, Interface address 10.10.10.3
Backup Designated Router (ID) 10.10.10.2, Interface address 10.10.10.2

If both the Designated Router (DR) and Backup Designated Router (BDR) suffer a simultaneous hardware failure, which role will router R1 transition to on this broadcast segment?

Show answer & explanation

Answer: R1 will remain in the DROTHER state and will not participate in the election for DR or BDR.

Answer

R1 will remain in the DROTHER state and will not participate in the election for DR or BDR.
In OSPFv2 multiaccess networks, setting an interface priority to 0 disqualifies the router from participating in the DR/BDR election process. Even if both the active DR and BDR fail, a router with a priority of 0 will stay in the DROTHER state and will never assume the DR or BDR role.

Step-by-Step Solution

1
Inspect the interface priority value in the CLI snippet.
The interface priority on GigabitEthernet0/1 is set to 0 (`Priority 0`).
OSPF interface priority determines eligibility in DR/BDR elections.
2
Evaluate the OSPF DR/BDR election rules for priority 0.
A priority of 0 means the router is ineligible to become either DR or BDR.
Setting the priority to 0 is the administrative mechanism used to isolate a router from taking on DR or BDR election responsibilities.
3
Determine the operational state following DR and BDR failures.
R1 remains in the DROTHER state indefinitely until an eligible router (priority > 0) joins the segment.
Even if DR and BDR fail simultaneously, an ineligible router cannot be promoted.

Key Concept

OSPF Interface Priority 0 Election Exclusion
Estimated Time:1m 0s
Question 422Question →

An administrator is troubleshooting an OSPFv2 neighbor relationship between two directly connected routers, R1 and R2. Output from the command `show ip ospf neighbor` on R1 displays the neighbor state for R2 as `INIT/ -`. Which condition is the most likely cause of this neighbor state?

Show answer & explanation

Answer: R1 is receiving OSPF Hello packets from R2, but R2 is not receiving OSPF Hello packets from R1.

Answer

R1 is receiving OSPF Hello packets from R2, but R2 is not receiving OSPF Hello packets from R1.
The INIT state indicates that a router has received an OSPF Hello packet from a neighbor, but bidirectional communication has not yet been verified because the receiving router's own Router ID is not listed in the neighbor's Hello packet. This typically occurs due to unidirectional link failures or filtering (such as an ACL blocking traffic in one direction).

Step-by-Step Solution

1
Analyze OSPF neighbor state definitions
Identify what the INIT state signifies in the OSPF neighbor state machine.
The INIT state means a valid OSPF Hello packet has been received from the neighbor, but two-way communication has not yet been established because the receiving router's own Router ID is missing from the neighbor's Hello Active Neighbor field.
2
Evaluate the cause of unidirectional Hello reception
Determine that R1 receives Hellos from R2, but R2 does not receive Hellos from R1.
If an access control list (ACL) or physical fault blocks packets in only one direction (from R1 to R2), R2 never sees R1's Hello, so R2 never includes R1's Router ID in its own sent Hellos. R1 continues receiving R2's Hellos and stays in the INIT state.
3
Differentiate from other failure states
Rule out MTU mismatch (ExStart/Exchange state), OSPF process ID mismatch (no impact), and priority 0 (prevents DR/BDR election only).
Understanding distinct neighbor states ensures accurate diagnosis of OSPF adjacency issues.

Key Concept

OSPFv2 Neighbor States and Unidirectional Communication
Question 423Question →

Match each Cisco IPv4 routing table entry format on the left with its corresponding operational description on the right.

Click a left item, then click its matching right item

Items

D 192.168.10.0/24 [90/2170112]
O 10.1.1.0/24 [110/65]
C 172.16.1.0/24
S 0.0.0.0/0 [1/0] via 192.168.1.1

Matches

Show answer & explanation

Answer

D 192.168.10.0/24 [90/2170112] matches the EIGRP-learned route description; O 10.1.1.0/24 [110/65] matches the OSPF-learned route description; C 172.16.1.0/24 matches the directly connected route description; S 0.0.0.0/0 [1/0] via 192.168.1.1 matches the static default route description.
Each routing table notation correctly matches its protocol source code ('D' for EIGRP, 'O' for OSPF, 'C' for connected, 'S' for static) and accurately decodes the bracketed administrative distance and metric values.

Step-by-Step Solution

1
Identify routing protocol source codes
Map 'D' to EIGRP, 'O' to OSPF, 'C' to Directly Connected, and 'S' to Static.
Cisco IOS routing tables use standard single-letter source codes to indicate route origins.
2
Interpret bracket notation [AD/Metric]
Extract administrative distance as the first value and route metric as the second value inside the brackets.
The bracketed syntax standardizes administrative distance (route trustworthiness) and metric (path cost).
3
Pair routing lines to functional descriptions
Match each left routing entry string with its corresponding description on the right.
Ensures all routing table components are correctly identified and defined.

Key Concept

Cisco IPv4 Routing Table Component Interpretation
Estimated Time:1m 30s
Question 424Question →

An administrator examines the following routing table output on a Cisco router:

text
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 4 subnets, 3 masks
O 10.15.0.0/16 [110/20] via 192.168.1.1, 00:10:22, GigabitEthernet0/0
D 10.15.10.0/24 [90/307200] via 192.168.2.1, 00:05:14, GigabitEthernet0/1
S 10.15.10.128/25 [1/0] via 192.168.3.1, 01:12:05, GigabitEthernet0/2
C 10.15.10.0/28 is directly connected, GigabitEthernet0/3

Which two statements regarding route selection and routing table components in this output are correct?

Select all that apply

Show answer & explanation

Answer: Packets destined for host 10.15.10.130 are forwarded out interface GigabitEthernet0/2 because the subnet mask /25 provides the longest matching prefix for this destination.; The bracketed notation [90/307200] in the EIGRP entry indicates an administrative distance of 90 and a routing metric of 307200.

Answer

The two correct statements are that packets destined for host 10.15.10.130 are forwarded out interface GigabitEthernet0/2 due to longest prefix match (/25), and that the bracketed notation [90/307200] represents an administrative distance of 90 and a metric of 307200.
Longest prefix match is the primary rule for IP packet forwarding. Destination 10.15.10.130 matches 10.15.10.128/25 with a 25-bit mask, which is longer than /24 or /16, causing forwarding via GigabitEthernet0/2. Additionally, standard Cisco routing table format displays administrative distance first and metric second inside square brackets, making [90/307200] represent an AD of 90 and a metric of 307200.

Step-by-Step Solution

1
Evaluate destination host 10.15.10.130 against all matching routes in the routing table.
Matches 10.15.0.0/16, 10.15.10.0/24, and 10.15.10.128/25.
The router applies the longest prefix match rule, selecting /25 (10.15.10.128/25 via GigabitEthernet0/2).
2
Interpret routing table bracketed components [AD/Metric].
[90/307200] corresponds to AD 90 and Metric 307200.
The first number inside the brackets is always administrative distance and the second number is the routing metric.

Key Concept

Routing Table Lookup Logic & Component Interpretation
Question 425Question →

A network administrator needs to configure a floating static route on router R1 to serve as a backup path for the 192.168.100.0/24192.168.100.0/24 network. The primary path to this destination is currently learned dynamically via OSPF, which uses a default Administrative Distance of 110110. Which TWO statements correctly describe the requirements and operational behavior for this floating static route configuration?

Select all that apply

Show answer & explanation

Answer: The floating static route must be configured with an Administrative Distance value greater than 110.; The floating static route will only be installed into the routing table when the primary OSPF route disappears from the routing table.

Answer

The floating static route must be configured with an Administrative Distance greater than 110, and it will only be installed into the routing table after the primary OSPF route is removed.
A floating static route acts as an inactive backup line that only takes effect when the primary path goes down. Because Cisco IOS evaluates route preference using Administrative Distance (where lower is preferred), the backup static route must be configured with an AD higher than the primary protocol's AD (in this case, higher than OSPF's default AD of 110). Consequently, the backup route stays inactive in the background and is only installed into the IP routing table when the primary OSPF route is withdrawn.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
OSPF has a default AD of 110.
Administrative Distance defines route trustworthiness; lower values are preferred.
2
Determine the AD requirement for a backup (floating) static route.
The backup route AD must be strictly greater than 110 (e.g., 120).
If the AD were equal or lower, the router would prefer or load balance with the static route, preventing it from functioning strictly as a backup.
3
Analyze how Cisco IOS handles routing table selection with floating static routes.
The floating static route remains hidden from the routing table as long as the OSPF route (AD 110) exists.
When the primary OSPF route fails and is removed, the floating static route becomes the best available path for that destination prefix and is installed into the active routing table.

Key Concept

Floating Static Route AD Requirements and Routing Table Selection
Question 426Question →

A network administrator is troubleshooting an intermittent first-hop gateway issue on a dual-homed router pair (R1R1 and R2R2) providing redundancy for VLAN 50 (172.20.50.0/24172.20.50.0/24). R1R1 is intended to be the active HSRP router under normal operational conditions.

The interface configurations are shown below:

text
R1# show running-config interface GigabitEthernet0/1
interface GigabitEthernet0/1
ip address 172.20.50.2 255.255.255.0
standby 50 ip 172.20.50.1
standby 50 priority 115
standby 50 track GigabitEthernet0/0 20

R2# show running-config interface GigabitEthernet0/1
interface GigabitEthernet0/1
ip address 172.20.50.3 255.255.255.0
standby 50 ip 172.20.50.1
standby 50 priority 105
standby 50 preempt

When the uplink interface GigabitEthernet0/0 on R1R1 fails, R1R1's priority drops from 115 to 95 (115−20115 - 20), allowing R2R2 (priority 105, preemption enabled) to take over as the Active router. However, when GigabitEthernet0/0 on R1R1 recovers and its priority returns to 115, R2R2 remains the Active router and R1R1 stays in Standby state.

Which configuration change on R1R1 will resolve this issue so that R1R1 automatically reclaims the Active HSRP role upon link recovery?

Show answer & explanation

Answer: Configure standby 50 preempt under interface GigabitEthernet0/1 on R1.

Answer

Enabling preemption on R1 using the command 'standby 50 preempt' allows R1 to reclaim the Active gateway role after its tracked interface recovers.
By default, HSRP preemption is disabled. Even if a router has a higher priority than the current Active router, it will not attempt to take over the Active role unless preemption is explicitly configured using the 'standby <group> preempt' command. On R1, once its tracked interface recovered, its priority returned to 115 (higher than R2's 105), but because preemption was missing on R1, it remained in the Standby state. Adding 'standby 50 preempt' to R1 resolves the issue.

Step-by-Step Solution

1
Analyze initial HSRP priorities and roles
R1 has priority 115 and R2 has priority 105. R1 is Active.
Higher priority determines the Active HSRP router.
2
Evaluate failover behavior when R1's tracked interface fails
R1 priority drops to 95 (115 - 20). R2 has priority 105 and 'standby 50 preempt' enabled, so R2 takes over as Active.
R2 has preemption enabled and its priority (105) is now higher than R1's reduced priority (95).
3
Evaluate recovery behavior when R1's tracked interface comes back up
R1 priority returns to 115, but R1 remains Standby because it lacks the 'standby 50 preempt' command.
Without preemption explicitly configured, an HSRP router with a higher priority will not preempt an already operational Active router.
4
Determine the required configuration fix
Adding 'standby 50 preempt' to R1 allows it to preempt R2 (115 > 105) once priority is restored upon link recovery.
Preemption must be enabled on the router that needs to reclaim the Active state.

Key Concept

HSRP Preemption and Interface Tracking Mechanics
Question 427Question →

A Cisco router has three active interfaces with the following operational statuses and IPv4 addresses:
- Loopback 10: 10.200.1.1/24 (up/up)
- Loopback 20: 172.16.50.1/24 (up/up)
- GigabitEthernet 0/0: 192.168.100.1/24 (up/up)

The OSPFv2 process is initialized using the `router ospf 100` command without an explicitly configured router-id command.

What IPv4 address will be selected as the OSPFv2 Router ID for this router?

Show answer & explanation

Answer: 172.16.50.1

Answer

172.16.50.1
OSPFv2 determines its Router ID using a strict three-tier precedence logic: (1) an explicitly configured OSPF router-id command, (2) the highest IPv4 address among active loopback interfaces, and (3) the highest IPv4 address among active non-loopback (physical) interfaces. Because no manual router ID was configured, the router compares the loopback interfaces (10.200.1.1 and 172.16.50.1) and chooses the highest value, 172.16.50.1. Physical interfaces like GigabitEthernet 0/0 are not considered because active loopbacks exist.

Step-by-Step Solution

1
Check for manual OSPF Router ID configuration
No explicit `router-id` command was configured under the `router ospf 100` process.
Manual configuration always takes highest precedence in OSPF Router ID selection.
2
Evaluate active loopback interfaces
Two active loopback interfaces exist: Loopback 10 (10.200.1.1) and Loopback 20 (172.16.50.1).
In the absence of a manually configured Router ID, OSPF selects the highest IPv4 address among active loopback interfaces.
3
Compare loopback IPv4 addresses
172.16.50.1 is numerically higher than 10.200.1.1, so 172.16.50.1 is chosen.
Physical interface IPs (such as GigabitEthernet 0/0 with 192.168.100.1) are ignored when active loopback interfaces are present.

Key Concept

OSPFv2 Router ID Selection Precedence
Question 428Question →

An enterprise edge router receives its primary route to the 172.20.10.0/24172.20.10.0/24 destination network via OSPF, which uses a default Administrative Distance of 110110. A network administrator must configure a floating static backup route targeting next-hop IP address 192.168.12.2192.168.12.2 that will remain inactive in the routing table unless the primary OSPF route becomes unavailable. Which Cisco IOS command accomplishes this objective?

Show answer & explanation

Answer: ip route 172.20.10.0 255.255.255.0 192.168.12.2 120

Answer

The command 'ip route 172.20.10.0 255.255.255.0 192.168.12.2 120' correctly configures the backup floating static route.
The correct command specifies an Administrative Distance of 120 at the end of the syntax. Because 120 is higher than the default OSPF distance of 110, Cisco IOS keeps this static route out of the routing table as long as the OSPF route is active. If the OSPF route fails and is withdrawn, the floating static route with AD 120 becomes the best available path and is inserted into the routing table.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary dynamic routing protocol.
OSPF has a default Administrative Distance of 110.
Floating static routes rely on AD values to determine route preference.
2
Determine the required Administrative Distance for the floating static route.
The static route AD must be strictly greater than 110 (e.g., 120).
Routers select routes with the lowest AD. Setting a higher value keeps the static route inactive while OSPF is healthy.
3
Construct the Cisco IOS static route command syntax.
The syntax is 'ip route <prefix> <mask> <next-hop> <distance>'. Placing 120 at the end sets the floating distance.
Specifying 120 at the end of the command overrides the default static AD of 1.

Key Concept

Floating Static Routes and Administrative Distance
Question 429Question →

A network administrator is configuring IPv4 static routes on router R1. The administrator must implement a primary default static route pointing to next-hop IP address 203.0.113.1203.0.113.1, as well as a backup floating static route for destination subnet 172.16.10.0/24172.16.10.0/24 via next-hop IP 192.168.1.2192.168.1.2. The backup route must take effect only if the primary path learned via OSPF (Administrative Distance of 110) becomes unavailable. Which two commands must the administrator execute on router R1 to satisfy these requirements? (Select two.)

Select all that apply

Show answer & explanation

Answer: ip route 0.0.0.0 0.0.0.0 203.0.113.1; ip route 172.16.10.0 255.255.255.0 192.168.1.2 120

Answer

The administrator must configure the default route using `ip route 0.0.0.0 0.0.0.0 203.0.113.1` and the floating static backup route using `ip route 172.16.10.0 255.255.255.0 192.168.1.2 120`.
The default route requires the prefix and mask `0.0.0.0 0.0.0.0` pointing to next-hop 203.0.113.1203.0.113.1. To serve as a backup to an OSPF route with an Administrative Distance of 110, the floating static route must specify an Administrative Distance higher than 110, which the command specifying an AD of 120 accomplishes.

Step-by-Step Solution

1
Determine the standard command syntax for an IPv4 default static route.
A default route matches all destination networks using prefix 0.0.0.00.0.0.0 and mask 0.0.0.00.0.0.0, forming the command `ip route 0.0.0.0 0.0.0.0 203.0.113.1`.
Quad-zero notation (0.0.0.0 0.0.0.0) is required in Cisco IOS to represent any unlisted IPv4 destination.
2
Calculate the necessary Administrative Distance for a floating static route intended to back up OSPF.
OSPF has a default Administrative Distance of 110. The backup static route requires an Administrative Distance higher than 110 (such as 120).
Cisco routers select routes based on the lowest Administrative Distance. A higher AD keeps the static route inactive until the primary OSPF route is removed from the routing table.

Key Concept

IPv4 Default Static Route Syntax and Floating Static Route Administrative Distance Selection
Question 430Question →

Two Cisco routers, R10 and R20, are connected over an Ethernet segment and configured for OSPFv2 routing. Which two configuration parameters must match identically on the interconnecting interfaces of both routers for an OSPFv2 neighbor adjacency to form successfully? (Select two.)

Select all that apply

Show answer & explanation

Answer: OSPF Area ID; Hello and Dead timer intervals

Answer

The OSPF Area ID and the Hello and Dead timer intervals must match identically on both connected interfaces.
To form an OSPFv2 neighbor adjacency, connected interfaces must reside in the same OSPF Area ID and have identical Hello and Dead timer settings. If either parameter differs, the routers fail to proceed past the INIT state.

Step-by-Step Solution

1
Analyze OSPFv2 Hello packet contents required for adjacency validation
Identified fields that must match in Hello packets: Area ID, Subnet Mask, Hello/Dead timers, Authentication, and Stub area flags.
OSPF routers exchange Hello packets to negotiate neighbor relationships and verify matching network parameters.
2
Evaluate the requirement for Area ID and Timers
Area ID and Hello/Dead timer values are required to match across adjacent interfaces.
A mismatch in Area ID or Hello/Dead timers causes routers to ignore Hello packets or drop neighbor relationships.
3
Evaluate Router ID and Process ID requirements
Router IDs must be unique across routers, and Process IDs are locally significant.
Process ID is only used locally by Cisco IOS to identify the OSPF process instance, while Router ID identifies the node uniquely within the OSPF autonomous system.

Key Concept

OSPFv2 Mandatory Neighbor Adjacency Parameters
Question 431Question →

A network engineer is implementing First Hop Redundancy Protocols (FHRP) across an enterprise distribution layer, deploying HSRPv2 on VLAN 10 and VRRPv3 on VLAN 20. Which two statements correctly describe the operational mechanics, protocol addresses, and default behavior differences between HSRPv2 and VRRPv3? (Select two.)

Select all that apply

Show answer & explanation

Answer: HSRPv2 sends hello messages to the multicast destination IPv4 address 224.0.0.102, whereas VRRPv3 sends advertisement packets to the multicast address 224.0.0.18 for IPv4 deployments.; VRRP allows the virtual IP address to match a physical IP address assigned to the Master router's interface, whereas HSRP requires the virtual IP to be unique and different from all physical interface IP addresses in the group.

Answer

HSRPv2 sends hello packets to multicast address 224.0.0.102 while VRRPv3 uses 224.0.0.18, and VRRP permits configuring a virtual IP that matches a physical interface IP while HSRP requires a unique virtual IP address.
The correct statements correctly identify the protocol multicast addresses (HSRPv2 uses 224.0.0.102, whereas VRRPv3 uses 224.0.0.18) and the virtual IP assignment rules (VRRP allows the virtual IP to match a physical interface IP, whereas HSRP mandates a unique virtual IP address).

Step-by-Step Solution

1
Analyze multicast destination addressing for HSRPv2 and VRRPv3.
HSRPv1 uses 224.0.0.2, HSRPv2 uses 224.0.0.102 (UDP 1985). VRRPv2 and VRRPv3 (IPv4) use 224.0.0.18 (IP protocol 112).
Correct protocol understanding requires knowing transport and network layer multicast identifiers.
2
Evaluate virtual IP address assignment constraints.
HSRP requires the virtual IP to be unique within the subnet and not assigned as a physical IP on any participating gateway interface. VRRP permits the virtual IP to be identical to the IP address configured on the Master router's physical interface (IP address owner).
This is a fundamental architectural difference between Cisco proprietary HSRP and standard VRRP.
3
Evaluate preemption defaults for both protocols.
HSRP preemption is disabled by default. VRRP preemption is enabled by default.
Default preemption rules dictate failover and recovery behavior when a higher-priority device comes online.

Key Concept

FHRP Protocol Differences (HSRP vs. VRRP Addressing, Virtual IP Rules, and Preemption Defaults)
Question 432Question →

An engineer executes the following command on router R1 to inspect an OSPFv2 interface connected to a multiaccess Ethernet segment:

text
R1# show ip ospf interface GigabitEthernet0/1
GigabitEthernet0/1 is up, line protocol is up
Internet Address 192.168.1.1/24, Area 0, Attached via Network Statement
Process ID 1, Router ID 10.1.1.1, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DROTHER, Priority 0
Designated Router (ID) 10.3.3.3, Interface address 192.168.1.3
Backup Designated router (ID) 10.2.2.2, Interface address 192.168.1.2

If the current Designated Router with Router ID 10.3.3.3 unexpectedly reboots and goes offline, which router state transition will occur on this segment?

Show answer & explanation

Answer: The router with Router ID 10.2.2.2 will automatically transition from Backup Designated Router to Designated Router.

Answer

The router currently serving as the Backup Designated Router (Router ID 10.2.2.2) will automatically be promoted to the Designated Router role.
In OSPF broadcast multiaccess networks, when the active Designated Router (DR) fails or goes offline, the existing Backup Designated Router (BDR) is immediately promoted to become the new DR. In this output, the BDR is identified by Router ID 10.2.2.2, so it will assume the DR role.

Step-by-Step Solution

1
Analyze the current state of OSPF routers on the broadcast segment
Router ID 10.3.3.3 is the active Designated Router (DR), Router ID 10.2.2.2 is the Backup Designated Router (BDR), and Router R1 (10.1.1.1) has Priority 0 and is in State DROTHER.
Determines the current functional roles assigned across the multiaccess network.
2
Evaluate the effect of a DR failure
When the active DR fails, OSPF non-preemptive logic mandates that the existing BDR immediately becomes the new DR to minimize downtime.
Avoids holding a full re-election for the DR position when a designated backup already exists.
3
Determine eligibility for the new BDR role
Router R1 cannot become BDR because its configured OSPF interface priority is 0.
An OSPF interface priority of 0 explicitly disqualifies a router from participating in DR/BDR elections.

Key Concept

OSPFv2 DR/BDR State Transitions and Priority 0 Exclusion
Question 433Question →

A network administrator executes the command shown below to inspect the OSPFv2 configuration on interface GigabitEthernet0/0 of router R3 on a shared Ethernet segment:

text
R3# show ip ospf interface GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.10.3/24, Area 0
Process ID 1, Router ID 192.168.10.3, Network Type BROADCAST, Cost: 1
State DROTHER, Priority 0
Designated Router (ID) 10.1.1.1, Interface address 192.168.10.1
Backup Designated Router (ID) 10.2.2.2, Interface address 192.168.10.2

If the current Designated Router (10.1.1.1) reboots and permanently disconnects from the network, which state will router R3 transition to following the OSPF election process?

Show answer & explanation

Answer: R3 will remain in the DROTHER state because an OSPF priority of 0 excludes the router from DR and BDR elections.

Answer

Router R3 will remain in the DROTHER state because an OSPF interface priority of 0 completely disables the router from participating in DR or BDR elections.
Configuring an OSPF priority of 0 on an interface ('ip ospf priority 0') explicitly prohibits the router from participating in Designated Router (DR) and Backup Designated Router (BDR) elections on multiaccess network segments. When the primary DR fails, the existing BDR becomes the new DR, but router R3 remains a DROTHER because its priority of 0 disqualifies it from election consideration regardless of its Router ID or interface IP.

Step-by-Step Solution

1
Analyze the CLI output for interface priority settings on router R3.
The CLI output displays 'State DROTHER, Priority 0' for interface GigabitEthernet0/0.
OSPF interface priority dictates election participation. Priority values range from 0 to 255.
2
Evaluate the effect of a priority 0 configuration during DR/BDR failover.
A priority of 0 (configured via 'ip ospf priority 0') strictly prevents the interface from becoming a DR or BDR.
Even when the existing DR fails and the current BDR moves up to DR, a router with priority 0 cannot participate in the election for the new BDR position.
3
Determine R3's resulting state after DR failover.
R3 stays in the DROTHER state while other eligible routers on the multiaccess segment contest the new BDR role.
Priority 0 overrides Router ID, Loopback IP addresses, and physical interface IP tie-breakers.

Key Concept

OSPFv2 DR/BDR Election Rules and Priority 0 Exclusion
Question 434Question →

A network engineer observes that traffic from a branch office router toward destination network 172.22.0.0/16172.22.0.0/16 is taking a low-speed backup WAN link instead of the primary OSPF path. Reviewing the running configuration reveals the following static route entry configured for the backup link:

`ip route 172.22.0.0 255.255.0.0 10.0.99.2 105`

Which statement correctly explains why the backup static route is overriding the primary OSPF path?

Show answer & explanation

Answer: The configured administrative distance of 105 is lower than the default administrative distance of OSPF (110), causing the router to prefer the static route.

Answer

The configured administrative distance of 105 is lower than the default administrative distance of OSPF (110), causing the router to prefer the static route.
Administrative distance measures route source believability on Cisco routers, where lower values are preferred. OSPF routes have a default administrative distance of 110. Because the static route was configured with an administrative distance of 105, which is lower than 110, the router installs the static route into the routing table instead of the OSPF route.

Step-by-Step Solution

1
Identify the destination prefix and protocol Administrative Distance (AD) values
The target prefix is 172.22.0.0/16. Standard OSPF routes have a default AD of 110.
Administrative Distance ranks the trustworthiness of routing information sources.
2
Analyze the configured static route command syntax
In `ip route 172.22.0.0 255.255.0.0 10.0.99.2 105`, the trailing value 105 sets the custom Administrative Distance for this static route.
By default, static routes have an AD of 1 unless a custom value is specified at the end of the command.
3
Compare the AD of the static route against the primary protocol
Since 105<110105 < 110, the router considers the static route more trustworthy than OSPF and places it into the routing table.
Lower administrative distance values win when comparing identical destination prefixes.

Key Concept

Floating Static Route Administrative Distance
Estimated Time:1m 0s
Question 435Question →

Place the Cisco Hot Standby Router Protocol (HSRP) router states in the correct sequential order from interface initialization to the state where the router assumes primary packet forwarding for the virtual gateway.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequential order of HSRP router states is: Initial State, Listen State, Speak State, Standby State, and Active State.
When HSRP is enabled on an interface, the router progresses systematically through five main states: Initial (interface up), Listen (receives Hello packets to learn virtual IP and detect peers), Speak (transmits periodic Hello packets to enter active/standby election), Standby (elected backup router), and finally Active (elected primary gateway responsible for handling virtual IP traffic).

Step-by-Step Solution

1
Identify the state representing initial interface bring-up
Initial State is the starting point before any HSRP communication begins.
HSRP process initiates when the underlying Layer 3 interface comes up.
2
Identify the state where the router observes existing HSRP peers without transmitting
Listen State follows Initial State.
The router must first hear if active or standby routers already exist on the segment.
3
Determine when the router starts transmitting Hello packets to join the election
Speak State follows Listen State.
The router sends Hello packets to announce its presence and participate in role selection.
4
Identify the interim role prior to becoming the primary forwarder
Standby State follows Speak State.
The router acts as the designated backup router before assuming the active role if election parameters permit.
5
Identify the final operational state responsible for forwarding virtual IP traffic
Active State is the final state.
The elected active router answers ARP requests for the virtual IP and forwards user traffic.

Key Concept

HSRP State Machine Transitions
Question 436Question →

Match each OSPFv2 interface scenario or configuration on the left to its corresponding election behavior or operational characteristic on the right.

Click a left item, then click its matching right item

Items

Interface configured with `ip ospf network broadcast`
Interface configured with `ip ospf network point-to-point`
Interface configured with `ip ospf priority 0` on a multiaccess link
Router with priority 255 added to a link with an active, established DR

Matches

Show answer & explanation

Answer

Interface configured with `ip ospf network broadcast` matches 'Performs DR/BDR elections and uses default Hello/Dead timers of 10s and 40s.'
Interface configured with `ip ospf network point-to-point` matches 'Establishes neighbor adjacencies without electing a DR/BDR using 10s/40s timers.'
Interface configured with `ip ospf priority 0` on a multiaccess link matches 'Permanently remains a DROTHER and is excluded from DR/BDR election.'
Router with priority 255 added to a link with an active, established DR matches 'Fails to take over the DR role due to the non-preemptive nature of OSPF elections.'
Each OSPF interface setting dictates specific operational properties: Broadcast links use 10s/40s timers and elect DR/BDR; Point-to-Point links use 10s/40s timers without electing DR/BDR; Priority 0 prevents any DR/BDR candidacy resulting in DROTHER status; and DR/BDR elections are non-preemptive, preventing new higher-priority routers from taking over an active DR role.

Step-by-Step Solution

1
Analyze OSPF network type behaviors regarding DR/BDR election requirement.
Broadcast networks elect a DR and BDR to reduce adjacency overhead over multiaccess media. Point-to-point networks connect exactly two routers and omit the DR/BDR election process entirely.
DR/BDR selection depends on the underlying OSPF network type setting.
2
Evaluate the effect of interface priority configuration.
Setting `ip ospf priority 0` explicitly removes a router from participating in DR or BDR election, locking its state as DROTHER.
Priority values range from 0 to 255, where 0 represents absolute exclusion from election eligibility.
3
Determine election preemption behavior when topology changes occur.
OSPF elections are non-preemptive; an existing DR retains its role even if a router with a higher priority (such as 255) joins the network after election completion.
Non-preemption prevents network instability and continuous routing recalculations upon router reboots or link flaps.

Key Concept

OSPFv2 Network Types, Interface Priority, and Election Preemption Rules
Question 437Question →

A network administrator configures HSRP group 10 on two switches, R1 and R2, to provide gateway redundancy for VLAN 20. R1 is configured with a priority of 115, preemption enabled, and tracks interface GigabitEthernet0/1 with a priority decrement of 20. R2 is configured with a priority of 105, but preemption is disabled on R2. Initially, all interfaces are operational, and R1 is the Active router. If interface GigabitEthernet0/1 on R1 fails, which router will fulfill the Active role for HSRP group 10, and why?

Show answer & explanation

Answer: R1 remains the Active router because R2 does not have preemption enabled, even though R1's operational priority drops to 95.

Answer

R1 remains the Active router because preemption is not enabled on R2, preventing it from taking over despite having a higher operational priority.
In HSRP, when an active router's tracked interface fails, its priority is decremented (115 - 20 = 95). Even though the standby router has a higher priority (105 > 95), it cannot claim the Active role unless preemption ('standby preempt') is explicitly configured on the standby router itself. Therefore, the current Active router remains Active.

Step-by-Step Solution

1
Calculate R1's operational priority after the tracked interface failure.
Initial priority (115) minus decrement (20) equals operational priority 95.
Interface tracking reduces the active router's HSRP priority upon tracked link failure.
2
Compare the operational priorities of R1 and R2.
R1 operational priority is 95; R2 priority is 105.
R2 now possesses a higher numeric priority than R1.
3
Evaluate preemption settings on the standby router (R2).
R2 does not have preemption enabled.
In HSRP, a standby router with a higher priority will NOT seize the Active role from an existing Active router unless 'standby preempt' is explicitly configured on the standby router.

Key Concept

HSRP Preemption Mechanics and Interface Tracking
Question 438Question →

A router receives routes to the destination network 10.50.0.0/1610.50.0.0/16 via internal EIGRP (Administrative Distance 9090). An engineer intends to create a floating static route as a backup path and executes the command `ip route 10.50.0.0 255.255.0.0 192.168.12.2 80`. Which outcome occurs as a direct result of this configuration?

Show answer & explanation

Answer: The newly configured static route immediately replaces the EIGRP route in the routing table because its Administrative Distance of 8080 is lower than 9090.

Answer

The newly configured static route immediately replaces the EIGRP route in the routing table because its Administrative Distance of 80 is lower than 90.
Cisco routers use Administrative Distance (AD) to evaluate route trustworthiness when multiple sources learn paths to identical prefixes. Internal EIGRP has a default AD of 90. Configuring a static route with an AD of 80 makes it more preferred than EIGRP because a lower AD value indicates higher priority. As a result, the static route preempts the EIGRP route immediately in the routing table rather than functioning as a backup.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the existing primary route.
Internal EIGRP has a default AD of 9090.
Administrative Distance is used by Cisco IOS to select the best path when multiple routing sources supply routes to the same destination.
2
Analyze the configured AD of the static route command `ip route 10.50.0.0 255.255.0.0 192.168.12.2 80`.
The trailing value 8080 sets the static route's AD to 8080.
The default static route AD is 11, but appending a number at the end overrides the default AD value.
3
Compare the two AD values to determine routing table selection.
Since 80<9080 < 90, the static route is considered more trustworthy than EIGRP.
Lower AD values are preferred. To make a static route a floating backup, its AD must be higher than the primary protocol (e.g., AD of 95 or higher).

Key Concept

Floating Static Route Administrative Distance Requirements
Question 439Question →

A Cisco router receives an IPv4 packet with a destination IP address of 172.16.50.170. The router inspects its routing table and finds the following route entries:

S 172.16.50.0/24 [1/0] via 10.0.0.1, GigabitEthernet0/0
D 172.16.50.128/25 [90/2560] via 10.0.0.2, GigabitEthernet0/1
O 172.16.50.160/27 [110/50] via 10.0.0.3, GigabitEthernet0/2
S 172.16.50.176/28 [1/0] via 10.0.0.4, GigabitEthernet0/3

Which next-hop IP address and outgoing interface will the router select to forward this packet?

Show answer & explanation

Answer: 10.0.0.3 via GigabitEthernet0/2

Answer

10.0.0.3 via GigabitEthernet0/2
When a router performs a forwarding lookup for destination 172.16.50.170, it checks all installed routes to find matches. The prefix 172.16.50.160/27 includes addresses from 172.16.50.160 to 172.16.50.191. Because /27 is the longest (most specific) prefix length among all matching routes, the router selects this entry (next-hop 10.0.0.3 via GigabitEthernet0/2). Administrative distance is not evaluated during lookup across routes of different prefix lengths.

Step-by-Step Solution

1
Identify all candidate routing table entries that match the destination IP address 172.16.50.170.
Three routes match: 172.16.50.0/24 (range .0 - .255), 172.16.50.128/25 (range .128 - .255), and 172.16.50.160/27 (range .160 - .191). The route 172.16.50.176/28 (range .176 - .191) does not match.
Only matching routes are eligible for forwarding decisions.
2
Compare the prefix lengths of all matching candidate routes.
Prefix lengths are /24, /25, and /27. The longest prefix match is /27.
Routers use the Longest Prefix Match (LPM) rule first when making forwarding decisions.
3
Determine the next-hop and exit interface associated with the longest matching route.
The route 172.16.50.160/27 specifies next-hop 10.0.0.3 out interface GigabitEthernet0/2.
Administrative distance is only evaluated when comparing identical prefixes from different sources, not when comparing routes of different prefix lengths.

Key Concept

Longest Prefix Match (LPM) Routing Decision Logic
Question 440Question →

A network administrator needs to configure and verify a floating static route on a Cisco IOS router to back up a primary OSPF path (Administrative Distance 110) for destination network 10.50.0.0/2410.50.0.0/24 via next-hop IP 192.168.12.2192.168.12.2. Place the required configuration and verification steps in the correct chronological order.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct operational sequence begins with entering global configuration mode, configuring the static route with an administrative distance of 120 (higher than OSPF's 110), verifying that OSPF remains the active route in the routing table, simulating a primary path link failure, and finally confirming that the floating static route is inserted into the routing table.
The sequence follows standard configuration and verification workflow: enter global config mode -> apply the floating static route command with AD 120 -> verify primary path retention in RIB -> force failover by shutting down primary path -> verify backup static route installation in RIB.

Step-by-Step Solution

1
Access CLI configuration mode
Router transitions to global configuration prompt
CLI commands altering routing topology must be executed in global configuration mode.
2
Configure the IPv4 floating static route
Route `ip route 10.50.0.0 255.255.255.0 192.168.12.2 120` is added to router candidate table
An Administrative Distance of 120 ensures the static route is floating because it is higher than OSPF's AD of 110.
3
Verify initial RIB state
OSPF route is present in routing table; floating static route is absent
The router selects routes with lower Administrative Distance when multiple paths exist.
4
Simulate primary interface failure
OSPF path is removed from RIB due to dead neighbor / link down
The primary route withdrawal triggers route selection re-evaluation for destination network 10.50.0.0/2410.50.0.0/24.
5
Verify failover to backup floating static route
Static route via 192.168.12.2192.168.12.2 with AD 120 is installed in RIB
With the lower AD route gone, the floating static route becomes the best available path.

Key Concept

Floating Static Route Configuration and Failover Lifecycle
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