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IP Connectivity

493 questions

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Question 381Question →

A network administrator is evaluating the IPv4 static routing configuration on router R1. Router R1 needs to reach the remote subnet 10.80.16.0/2010.80.16.0/20. The primary routing path to this destination is currently provided by OSPF, which has an administrative distance of 110. The administrator must configure two static routes:

1. A static route using next-hop IPv4 address 172.16.30.2172.16.30.2 that immediately takes precedence over the OSPF route.
2. A floating static route using next-hop IPv4 address 172.16.40.2172.16.40.2 that serves as a backup only if the OSPF route becomes unavailable.

Which TWO static route commands must be configured on router R1 to achieve this objective? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: ip route 10.80.16.0 255.255.240.0 172.16.30.2; ip route 10.80.16.0 255.255.240.0 172.16.40.2 120

Answer

The correct commands are 'ip route 10.80.16.0 255.255.240.0 172.16.30.2' for the primary route and 'ip route 10.80.16.0 255.255.240.0 172.16.40.2 120' for the floating static backup route.
To create a primary static route that overrides OSPF (AD 110), the standard command 'ip route 10.80.16.0 255.255.240.0 172.16.30.2' uses the default administrative distance of 1, which is lower than 110 and thus preferred. To configure a floating static backup route for the same subnet via next-hop 172.16.40.2, the command 'ip route 10.80.16.0 255.255.240.0 172.16.40.2 120' assigns an administrative distance of 120, which is higher than OSPF's 110, ensuring it only enters the routing table if the OSPF route drops.

Step-by-Step Solution

1
Convert prefix length /20 to dotted-decimal subnet mask format.
A /20 prefix corresponds to a subnet mask of 255.255.240.0.
Cisco IOS static route syntax requires the destination network mask in dotted-decimal format rather than CIDR notation.
2
Determine the required Administrative Distance (AD) for the primary static route.
Use the default static route AD of 1 (or any value lower than OSPF's AD of 110).
Lower administrative distance values are preferred in the Cisco routing table forwarding decision logic.
3
Determine the required Administrative Distance (AD) for the backup floating static route.
Configure an AD greater than 110 (such as 120) for the next-hop 172.16.40.2.
A floating static route must have a higher AD than the primary dynamic routing protocol (OSPF = 110) so it is installed in the routing table only when the primary path goes down.

Key Concept

Cisco IOS IPv4 static route syntax and floating static route administrative distance selection.
Question 382Question →

Match each OSPFv2 network type or election property on the left to its corresponding default operation or behavior on the right.

Click a left item, then click its matching right item

Items

Broadcast Multiaccess
Point-to-Point
Interface Priority 0
Equal Priority Tie-Breaker

Matches

Show answer & explanation

Answer

Broadcast Multiaccess matches electing a DR/BDR with 10s/40s timers; Point-to-Point matches forming adjacencies without DR/BDR election with 10s/40s timers; Interface Priority 0 matches excluding the router from DR elections; Equal Priority Tie-Breaker matches using the highest Router ID.
Each OSPF network type operates with specific election rules and default timers under standard Cisco OSPFv2 behavior: Broadcast multiaccess requires a DR/BDR with 10-second Hello timers; Point-to-Point bypasses DR selection with 10-second Hello timers; priority 0 excludes a device from election; and highest Router ID breaks priority ties.

Step-by-Step Solution

1
Determine which OSPFv2 network types perform DR/BDR election.
Broadcast multiaccess networks elect DR/BDR, whereas Point-to-Point networks bypass DR/BDR election.
DR/BDR selection is only required on multiaccess media to minimize full mesh neighbor adjacencies.
2
Evaluate the impact of configuring an interface priority of 0.
The router interface is disqualified from DR and BDR elections.
An interface priority value of 0 explicitly instructs OSPF to keep the interface in DROTHER status regardless of Router ID.
3
Identify the deterministic tie-breaker for DR elections when priorities match.
The router with the highest OSPF Router ID is elected.
OSPF DR election precedence evaluates interface priority first, followed by the highest Router ID.

Key Concept

OSPFv2 Network Types and DR/BDR Selection Rules
Question 383Question →

A network administrator is configuring a backup link on a Cisco router for destination network 10.50.0.0/2410.50.0.0/24. The primary path to this network is currently learned via OSPF, which has a default Administrative Distance (AD) of 110110. Which two statements correctly describe the requirements and operational behavior of the floating static route used for this backup path? (Select two.)

Select all that apply

Show answer & explanation

Answer: The administrative distance configured at the end of the static route command must be greater than 110110.; The floating static route will only be installed into the active routing table if the primary OSPF route is removed.

Answer

The floating static route must be configured with an administrative distance higher than the primary routing protocol's AD (greater than 110 for OSPF), and it will only populate the routing table when the primary OSPF route is removed.
A floating static route serves as a backup path by assigning an Administrative Distance (AD) higher than that of the primary routing protocol (OSPF AD = 110). Because Cisco IOS prefers routes with lower AD values, the floating static route is held in inactive standby and is only placed into the active routing table when the primary OSPF route disappears.

Step-by-Step Solution

1
Identify the primary routing protocol and its default Administrative Distance (AD).
The primary route is OSPF, which carries a default AD of 110110.
Administrative Distance determines the trustworthiness of routing sources in Cisco IOS.
2
Determine the required AD for the floating static route to function as a backup.
The static route AD must be set to a value higher than 110110 (such as 120120).
Lower AD values are preferred. Setting a higher AD ensures the static route is ignored as long as the OSPF route is present in the routing table.
3
Analyze how Cisco IOS installs the floating static route into the routing table.
The floating static route remains inactive in configuration until the OSPF route fails or is withdrawn, at which point the router installs the backup static route.
A router only installs the route with the lowest AD for a given prefix into the active routing table.

Key Concept

Floating Static Route Administrative Distance and Failover Mechanics
Estimated Time:1m 30s
Question 384Question →

An network engineer is analyzing how OSPFv2 resolves Designated Router (DR) selection on a multiaccess Ethernet segment when multiple candidate routers initialize simultaneously. Arrange the tie-breaking criteria in order of evaluation precedence, starting with the primary criterion evaluated first (highest precedence) at the top down to the final fallback tie-breaker at the bottom.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct evaluation sequence for OSPF DR selection precedence is: 1. Highest OSPF interface priority value (1–255), 2. Explicitly configured OSPF router ID (`router-id` command), 3. Highest IP address among active loopback interfaces, and 4. Highest IP address among active physical interfaces.
During an OSPF DR/BDR election on a broadcast multiaccess segment, routers first compare interface priority values (1 to 255). If priorities are tied, the election uses the OSPF Router ID as the tie-breaker. The Router ID selection hierarchy itself evaluates an explicitly configured router ID first, followed by the highest active loopback IP address, and finally the highest active physical interface IP address.

Step-by-Step Solution

1
Identify the primary parameter evaluated during OSPF DR/BDR elections on multiaccess networks.
OSPF interface priority is evaluated first. Priority values range from 0 to 255, where priority 0 disables election participation and higher values win.
Interface priority explicitly allows network administrators to control DR/BDR roles regardless of IP addressing.
2
Determine the highest precedence method for tie-breaking using the OSPF Router ID when interface priorities match.
An explicitly configured `router-id` under the OSPF router process is evaluated first.
Manual CLI configuration overrides all dynamic IP address collection logic.
3
Identify the dynamic fallback method for Router ID derivation when no manual Router ID is set.
The highest IPv4 address on any active (up/up) loopback interface is chosen.
Loopback interfaces are preferred over physical interfaces due to their logical stability.
4
Identify the final fallback method for Router ID derivation.
The highest IPv4 address on any active (up/up) physical interface is chosen.
Physical interface IP addresses serve as the last-resort tie-breaker when no explicit router ID or loopbacks are present.

Key Concept

OSPF DR/BDR election logic prioritizes interface priority first, using Router ID (derived via explicit CLI > highest loopback IP > highest physical IP) as a sequential tie-breaker.
Question 385Question →

A network engineer is troubleshooting an OSPFv2 neighbor relationship between router R1 and router R2 connected across a shared Ethernet segment. Command output from `show ip ospf neighbor` on R1 displays R2 in the `INIT/ -` state. Which condition is the primary cause of the neighbor relationship being stuck in the INIT state?

Show answer & explanation

Answer: An access control list is blocking OSPF Hello packets sent from R1 to R2, resulting in unidirectional communication

Answer

An access control list is blocking OSPF Hello packets sent from R1 to R2, resulting in unidirectional communication.
The INIT state indicates that R1 has successfully received OSPF Hello packets from R2, but R1 has not seen its own Router ID listed in R2's Hello packet. This scenario occurs when traffic flow is unidirectional—such as when an inbound or outbound Access Control List (ACL) blocks OSPF Hello packets transmitted from R1 to R2 while allowing Hellos from R2 to reach R1.

Step-by-Step Solution

1
Analyze OSPF neighbor state machine progression for the INIT state
The INIT state means a router has received an OSPF Hello packet from a neighbor, but its own Router ID is NOT present in the list of seen neighbors contained within that Hello packet.
Transitioning beyond INIT to 2-Way requires bi-directional communication, where both routers acknowledge receiving each other's Hello packets.
2
Evaluate the cause of unidirectional Hello reception
If R1 receives R2's Hellos, R1 transitions R2 to the INIT state. If R2 never receives R1's Hellos (e.g., due to an ACL filtering packets from R1 to R2), R2 will not include R1's Router ID in its outgoing Hellos.
Without R1's Router ID in R2's Hello packet, R1 cannot transition the neighbor relationship to 2-Way, leaving it permanently stuck in INIT.
3
Distinguish INIT state causes from DOWN and EXSTART state causes
Mismatches in Area ID, Hello/Dead timers, subnet mask, or authentication cause Hello packets to be dropped on arrival, keeping the neighbor in DOWN state. MTU mismatches cause neighbors to get stuck in EXSTART/EXCHANGE state.
Identifying which parameters are checked during Hello validation pinpoints why other mismatches fail earlier (DOWN) or later (EXSTART) in the adjacency process.

Key Concept

OSPF Neighbor Adjacency States and Unidirectional Communication Troubleshooting
Question 386Question →

An administrator modifies the OSPFv2 network type on a GigabitEthernet interface shared by two routers from the default BROADCAST to POINT_TO_POINT using the command `ip ospf network point-to-point`. Which two statements correctly describe the operational changes resulting from this configuration? (Select two.)

Select all that apply

Show answer & explanation

Answer: Designated Router (DR) and Backup Designated Router (BDR) elections are bypassed on the interface.; OSPF packets continue to be sent to the AllSPFRouters multicast address (224.0.0.5), but the AllDRouters address (224.0.0.6) is no longer used.

Answer

On an OSPFv2 Point-to-Point network link, DR/BDR elections are entirely bypassed, and routers communicate using the AllSPFRouters multicast address (224.0.0.5) while discontinuing the use of 224.0.0.6.
Configuring `ip ospf network point-to-point` changes OSPF operating behavior such that DR and BDR elections are omitted because the link connects only two endpoints. In addition, all OSPF traffic (Hello, DBD, LSU, LSAck) on a point-to-point link uses the 224.0.0.5 multicast destination address, omitting 224.0.0.6.

Step-by-Step Solution

1
Analyze DR/BDR requirements for Point-to-Point network types.
Recognize that Point-to-Point links connect exactly two routers, making DR/BDR election unnecessary.
DR and BDR roles exist solely to reduce adjacency flood overhead on multiaccess networks.
2
Evaluate OSPF multicast address usage on Point-to-Point links.
Identify that 224.0.0.5 (AllSPFRouters) is used for all OSPF packet exchanges on Point-to-Point links, while 224.0.0.6 (AllDRouters) is unused.
Since there is no DR present on the segment, packets destined to DRs (224.0.0.6) are unnecessary.
3
Compare default timers and neighbor discovery behavior between Broadcast and Point-to-Point modes.
Confirm that both network types default to 10-second Hello and 40-second Dead timers and both dynamically discover neighbors via multicast.
Only NBMA and Point-to-Multipoint modes use 30/120 second default timers or require static neighbor statements.

Key Concept

OSPFv2 Point-to-Point vs Broadcast Network Type Characteristics
Question 387Question →

Two routers are connected across an Ethernet link and configured for OSPFv2 routing. Which TWO parameters exchanged in the OSPF Hello packet must match identically between the two routers for an OSPFv2 neighbor adjacency to form successfully?

Select all that apply

Show answer & explanation

Answer: Area ID configured on the connected interfaces; Hello and Dead timer intervals

Answer

The OSPF Area ID and the Hello and Dead timer intervals must match identically between neighboring routers.
For two OSPFv2 routers to establish a neighbor adjacency, specific parameters inside their Hello packets must be identical. These include the Area ID configured on the interface, the Hello and Dead timer intervals, the IP subnet mask (on broadcast/multiaccess links), and any stub/area option flags.

Step-by-Step Solution

1
Analyze OSPF Hello packet fields required for neighbor establishment
Identified mandatory match criteria: Area ID, Hello/Dead timers, Subnet Mask (on multiaccess networks), Stub area flag, and Authentication.
OSPF neighbor discovery requires agreement on basic link parameters before transitioning beyond the Init state.
2
Evaluate local vs global OSPF configuration settings
Process ID is purely local to the router process and is omitted from Hello packet negotiation.
Different routers in the same network can use different OSPF process IDs (e.g., Process 1 on R1 and Process 10 on R2).
3
Evaluate Router ID uniqueness requirements
Router IDs must be unique across the OSPF domain.
Duplicate Router IDs cause neighbor adjacencies to flap or fail to form.

Key Concept

OSPFv2 Hello Packet Mandatory Match Parameters
Question 388Question →

When a Cisco router receives an IPv4 unicast packet and must select the single best route for forwarding from multiple potential routing table candidates, in what sequence does the router apply its decision logic? Place the steps in the correct order from first to last.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order of router decision logic is: 1) Inspect the packet header to extract the destination IPv4 address, 2) Filter candidate routes using Longest Prefix Match (most specific subnet mask length), 3) Compare Administrative Distance (AD) to select the most believable routing source among identical prefix length matches, 4) Compare routing protocol metrics to choose the lowest cost path among identical prefix matches from the same protocol, and 5) Determine the next-hop IPv4 address and associated outbound interface from the selected best route entry.
Router forwarding decision logic follows a strict order of operations: First, the destination IPv4 address is read from the packet header. Second, the router searches its routing table for candidate routes and selects the longest prefix match (most specific mask). Third, if multiple routes have identical subnet mask lengths from different routing sources, Administrative Distance (AD) is evaluated to pick the lowest AD source. Fourth, if identical prefix routes come from the same routing source, the metric is evaluated to select the lowest cost path. Finally, the next-hop IP and egress interface are resolved for forwarding.

Step-by-Step Solution

1
Identify initial packet processing.
Destination IPv4 address is extracted from the IPv4 header.
The router needs the target IP address before searching the routing table.
2
Apply Longest Prefix Match (LPM).
Candidate routes are evaluated strictly by prefix length (number of matching subnet mask bits).
LPM is the primary criterion in IPv4 forwarding. AD and metric are ignored until LPM narrows candidates to identical prefix lengths.
3
Evaluate Administrative Distance (AD).
If a tie exists in prefix length between different routing sources, the route with the lowest AD is selected.
AD measures route believability/trustworthiness across different routing sources.
4
Evaluate protocol metric.
If candidate routes have identical prefix lengths and originate from the same routing protocol, the path with the lowest metric is chosen.
Metric measures the internal path cost for a specific routing protocol.
5
Extract forwarding parameters.
The router obtains the egress interface and next-hop IP address for packet encapsulation.
This information is needed to build the new Layer 2 frame and transmit the packet.

Key Concept

Router Forwarding Decision Hierarchy (LPM -> AD -> Metric -> Next-Hop Extraction)
Estimated Time:1m 30s
Question 389Question →

Router Edge-1 is connected to a primary service provider using external BGP (eBGP, Administrative Distance 20) and a secondary service provider using an IPv4 static route to reach destination network 192.168.100.0/24192.168.100.0/24. The network engineer intends for the static route to serve strictly as a floating backup path that only activates if the primary eBGP route fails. During a routing table audit, the engineer discovers that the static route is active in the routing table even while the primary eBGP link is fully operational.

The current static route configuration on Edge-1 is:
`ip route 192.168.100.0 255.255.255.0 10.0.12.2 15`

Which configuration change on router Edge-1 will ensure that the static route functions correctly as a backup path?

Show answer & explanation

Answer: Reconfigure the static route as `ip route 192.168.100.0 255.255.255.0 10.0.12.2 25` so its administrative distance exceeds that of eBGP.

Answer

Reconfigure the static route as `ip route 192.168.100.0 255.255.255.0 10.0.12.2 25` so its administrative distance exceeds that of eBGP.
A floating static route serves as a backup path and must have an Administrative Distance (AD) configured higher than that of the primary route source. Since eBGP routes have a default AD of 20, setting the static route's AD to 25 ensures it will only be installed into the routing table if the primary eBGP route fails.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
eBGP has a default Administrative Distance of 20.
Administrative Distance measures route trustworthiness; lower AD values are preferred by the routing table.
2
Analyze why the current static route is active in the routing table.
The current static route has an explicit AD of 15, which is lower than eBGP (20).
Because 15 < 20, the router selects the static route as the primary path instead of treating it as a backup.
3
Determine the AD requirement for a floating static route.
The static route's AD must be set to a value strictly greater than 20 (e.g., 25).
Setting the AD higher than the primary routing protocol ensures the static route remains inactive in the RIB until the primary eBGP route is withdrawn.

Key Concept

Floating Static Route Administrative Distance Calibration
Estimated Time:2m 0s
Question 390Question →

An administrator is configuring first-hop redundancy on router R1 for VLAN 50 using HSRPv2. Interface GigabitEthernet0/0/0 on R1 is assigned the IPv4 address 192.168.50.1/24192.168.50.1/24. The administrator enters interface configuration mode and issues the command `standby 50 ip 192.168.50.1` to establish the virtual IP address. Which outcome will result from this configuration attempt?

Show answer & explanation

Answer: The command line interface rejects the command because HSRP forbids assigning a router's physical interface IPv4 address as the virtual IP address.

Answer

The command line interface rejects the command because HSRP forbids assigning a router's physical interface IPv4 address as the virtual IP address.
In Cisco HSRP implementation, the virtual IPv4 address must be an unused IP address on the subnet segment. It cannot match the physical IP address assigned to any interface on any router participating in the HSRP group. Attempting to assign an existing physical IP address causes Cisco IOS to reject the `standby ip` command with a syntax validation error.

Step-by-Step Solution

1
Analyze the HSRP virtual IP assignment rule in Cisco IOS.
HSRP (both v1 and v2) mandates that the virtual IPv4 address must be an unassigned IP within the subnet segment, strictly distinct from any physical IP configured on participating routers.
Preventing IP overlaps ensures ARP resolution and virtual MAC binding operate without address conflicts.
2
Compare HSRP rules with VRRP rules regarding IP address ownership.
Unlike VRRP—where configuring the virtual IP to match a master router's physical IP address is allowed and automatically sets the VRRP priority to 255 (IP address owner)—HSRP does not support IP address ownership.
HSRP syntax validation rejects physical IP matches at CLI input time.
3
Determine the CLI outcome when `standby 50 ip 192.168.50.1` is entered on R1.
Cisco IOS generates an error message (such as `% Bad IP address` or `% Address on interface cannot be used as HSRP virtual IP`) and rejects the statement.
The input violates core HSRP validation rules.

Key Concept

HSRP Virtual IP Addressing vs VRRP IP Address Ownership
Estimated Time:1m 30s
Question 391Question →

A Cisco router displays the following output from the command `show ip route`:

text
Gateway of last resort is not set

10.45.12.0/24 is variably subnetted, 4 subnets, 4 masks
O 10.45.12.0/25 [110/20] via 192.168.1.2, 00:14:22, GigabitEthernet0/0
D 10.45.12.64/26 [90/307200] via 192.168.2.2, 00:08:15, GigabitEthernet0/1
S 10.45.12.80/28 [1/0] via 192.168.3.2
O E2 10.45.12.88/30 [110/20] via 192.168.4.2, 00:02:10, GigabitEthernet0/3

The router receives an IP packet with a destination address of 10.45.12.8910.45.12.89. Which next-hop address and exit interface will the router select to forward this packet?

Show answer & explanation

Answer: 192.168.4.2 via GigabitEthernet0/3 because the /30 subnet mask provides the longest prefix match for the destination address.

Answer

The router forwards the packet to next-hop address 192.168.4.2 via interface GigabitEthernet0/3 because 10.45.12.88/30 provides the longest prefix match.
When a router receives a packet, it compares the destination IP address against all entries in the routing table and forwards the packet using the route with the most specific subnet mask (longest prefix match). For destination 10.45.12.89, all four table entries encompass the address, but 10.45.12.88/30 has the longest prefix length (/30), making next-hop 192.168.4.2 via GigabitEthernet0/3 the correct path.

Step-by-Step Solution

1
Evaluate candidate routes matching destination IP 10.45.12.89
Destination 10.45.12.89 falls into: 10.45.12.0/25 (.0-.127), 10.45.12.64/26 (.64-.127), 10.45.12.80/28 (.80-.95), and 10.45.12.88/30 (.88-.91). All 4 entries are valid candidate routes.
Before selecting a route, the router identifies all entries in the IPv4 routing table whose network boundaries encompass the destination address.
2
Apply Longest Prefix Match (LPM) rule
The prefix lengths are /25, /26, /28, and /30. The /30 route has the most specific mask (longest matching network prefix length of 30 bits).
Routers always prioritize prefix specificity (longest mask length) over Administrative Distance (AD) or metric when determining forwarding decisions.
3
Identify corresponding next-hop and interface
The entry 10.45.12.88/30 specifies next-hop 192.168.4.2 via interface GigabitEthernet0/3.
The forwarding table uses the next-hop IP and outgoing interface tied directly to the winning LPM route.

Key Concept

Longest Prefix Match (LPM) Rule
Estimated Time:1m 15s
Question 392Question →

A network engineer is managing a broadcast multiaccess Ethernet segment with four routers running OSPFv2 in Area 0. The output below is taken from router R2:

text
R2# show ip ospf interface GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.10.2/24, Area 0
Process ID 1, Router ID 2.2.2.2, Network Type BROADCAST, Cost: 1
State DROTHER, Priority 0
Designated Router (ID) 4.4.4.4, Interface address 192.168.10.4
Backup Designated Router (ID) 3.3.3.3, Interface address 192.168.10.3

The engineer executes the command `ip ospf priority 250` on R2's GigabitEthernet0/0 interface. Shortly after, the current Designated Router (R4) reboots. Assuming all other routers maintain their default priority of 1 and no OSPF processes are cleared manually, which role will router R2 assume on the segment after convergence?

Show answer & explanation

Answer: Backup Designated Router (BDR)

Answer

Backup Designated Router (BDR)
In OSPFv2 broadcast networks, elections are non-preemptive. When the active DR (R4) fails or reboots, the existing BDR (R3) is automatically promoted to DR. A new election is then held specifically to fill the now-vacant BDR role. Since R2's interface priority was increased from 0 to 250, R2 is eligible and wins the BDR election over any remaining routers with default priority 1. Therefore, R2 becomes the Backup Designated Router (BDR).

Step-by-Step Solution

1
Analyze initial OSPF roles and interface priority configuration
R4 is DR (Router ID 4.4.4.4), R3 is BDR (Router ID 3.3.3.3), and R2 is DROTHER because its priority was 0.
An OSPF priority of 0 excludes a router interface from participating in DR/BDR elections.
2
Evaluate the impact of changing interface priority to 250 on R2
R2 becomes eligible to participate in future DR/BDR elections with a priority of 250, but elections are non-preemptive while active DR/BDR roles are filled.
OSPF DR/BDR elections do not preempt active role holders upon configuration changes.
3
Determine role transitions following the failure/reboot of the DR (R4)
R3 (the active BDR) is immediately promoted to DR. A new election takes place to fill the vacant BDR position.
OSPF rules state that when a DR fails, the active BDR automatically becomes the new DR.
4
Select the winner of the new BDR election
R2 wins the election for BDR because its priority (250) is higher than the remaining candidate routers (priority 1).
The router with the highest non-zero priority wins the BDR election.

Key Concept

OSPF DR/BDR Election Non-Preemption and Promotion Rules
Estimated Time:1m 30s
Question 393Question →

A network administrator is configuring HSRP on a router's GigabitEthernet0/0 interface, which has been assigned the physical IPv4 address 192.168.10.1/24192.168.10.1/24. The administrator enters the command `standby 1 ip 192.168.10.1` under the interface configuration mode. What issue does this configuration introduce?

Show answer & explanation

Answer: It configures the HSRP virtual IP address to match a physical interface IP address, which is invalid in HSRP.

Answer

Assigning the physical interface IPv4 address as the HSRP virtual IP address is an invalid configuration because HSRP requires the virtual IP to be a separate, distinct IP address within the subnet.
In Cisco Hot Standby Router Protocol (HSRP), the virtual IP address shared by the group must be a unique IP address on the local subnet that is not assigned to any router's physical interface. Attempting to assign a router's physical IP address as the HSRP virtual IP address is invalid and prevents proper operation.

Step-by-Step Solution

1
Identify the IP address assigned to the physical interface and the IP address specified in the `standby` command.
The physical interface IP address is 192.168.10.1192.168.10.1, and the command sets the virtual IP to 192.168.10.1192.168.10.1.
Comparing these addresses verifies whether the virtual IP collides with a physical IP.
2
Recall HSRP rules regarding virtual IP address assignment.
Unlike VRRP (which allows owning the IP address), HSRP requires the virtual IP address to be an unused IP address on the subnet, distinct from all router physical interface IPs in the group.
Enforces proper HSRP protocol behavior and prevents address duplicate conflicts.

Key Concept

HSRP Virtual IP Address Assignment Rules
Question 394Question →

An edge router receives the primary route to remote destination network 10.10.0.0/1610.10.0.0/16 via external BGP (eBGP) from ISP-1 using default settings. The network administrator attempts to configure a floating static backup route toward ISP-2 using the command `ip route 10.10.0.0 255.255.0.0 192.168.1.2 15`. Which behavior will be observed on the router regarding this destination?

Show answer & explanation

Answer: The static route immediately replaces the eBGP route as the primary active route in the routing table because its Administrative Distance of 15 is lower than the default eBGP Administrative Distance of 20.

Answer

The static route immediately replaces the eBGP route as the primary active route in the routing table because its Administrative Distance of 15 is lower than the default eBGP Administrative Distance of 20.
In Cisco IOS, lower Administrative Distance values take precedence. The default Administrative Distance for external BGP (eBGP) is 20. Because the static route was configured with an explicit Administrative Distance of 15, the router considers it more reliable than the eBGP route. As a result, the static route becomes the primary active path in the routing table rather than remaining an inactive backup.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary routing protocol.
The primary route is learned via external BGP (eBGP), which has a default Cisco IOS Administrative Distance of 2020.
Administrative Distance indicates the trustworthiness of a routing source.
2
Analyze the configured Administrative Distance of the static route.
The trailing argument in `ip route 10.10.0.0 255.255.0.0 192.168.1.2 15` specifies an Administrative Distance of 1515.
The optional metric value at the end of the `ip route` syntax overrides the default static route AD of 1.
3
Compare the AD values to determine routing table selection.
Since 15<2015 < 20, the static route is considered more believable than the eBGP route.
Routers select the route with the lowest Administrative Distance when multiple sources advertise the exact same prefix length.

Key Concept

Floating Static Route Administrative Distance Precedence
Question 395Question →

Router R3 is configured with the following interfaces and IP address states:

- Loopback0: 10.255.255.1/32 (Status: up, Line Protocol: up)
- Loopback1: 172.16.100.1/32 (Status: administratively down, Line Protocol: down)
- GigabitEthernet0/0: 192.168.1.1/24 (Status: up, Line Protocol: up)

OSPFv2 process 1 is initialized on R3 without a manually configured router ID. Later, a network engineer enters the following commands:

R3(config)# router ospf 1
R3(config-router)# router-id 1.1.1.1

No additional commands are executed and the OSPF process is not reset. What IPv4 address is currently active as the OSPF router ID for process 1?

Show answer & explanation

Answer: 10.255.255.1

Answer

10.255.255.1
Upon initial process startup, OSPF selects 10.255.255.1 because active loopback interfaces take priority over physical interfaces, and Loopback0 is the only active loopback (Loopback1 is administratively down). When the 'router-id 1.1.1.1' command is subsequently entered under the OSPF process, Cisco IOS requires the process to be reset (e.g., via 'clear ip ospf process') before the change becomes active. Since no reset occurred, 10.255.255.1 remains the active OSPF router ID.

Step-by-Step Solution

1
Determine initial OSPF Router ID election upon process initialization
10.255.255.1 is chosen as the active router ID
When OSPF process 1 starts without a manual router-id command, it selects the highest IPv4 address among active (up/up) loopback interfaces. Loopback0 (10.255.255.1) is active, while Loopback1 is administratively down and ignored. Physical interfaces like GigabitEthernet0/0 are ignored because an active loopback interface exists.
2
Evaluate the impact of configuring 'router-id 1.1.1.1' on a running OSPF process
The new router ID 1.1.1.1 is queued but does not take immediate effect
OSPF Router ID selection in Cisco IOS is non-preemptive. Changing the router ID under the OSPF process does not dynamically update the active router ID for an already running process.
3
Check if any process reload or reset command was executed
No reset occurred; the original router ID remains active
A process restart (such as executing 'clear ip ospf process') or device reload is required to apply the newly configured router ID. Because no reset was performed, 10.255.255.1 remains the active router ID.

Key Concept

OSPFv2 Router ID Election Precedence and Non-Preemptive Re-election
Estimated Time:2m 0s
Question 396Question →

An engineer inspects the operational status of an active OSPFv2 broadcast network using the following Cisco IOS CLI output from router HQ-R1:

text
HQ-R1# show ip ospf interface GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 10.10.10.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DR, Priority 1
Designated Router (ID) 1.1.1.1, Interface address 10.10.10.1
Backup Designated router (ID) 2.2.2.2, Interface address 10.10.2.2
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:03
Neighbor Count is 1, Adjacent neighbor count is 1
Adjacent with neighbor 2.2.2.2 (Backup Designated Router)

A third router, HQ-R3 (Router ID 3.3.3.3), is subsequently connected to the same Ethernet switch segment with its OSPF interface priority configured as 255. If all existing routers remain powered on with active OSPF processes, which statement correctly describes the OSPF role assignment for HQ-R3 once neighbor adjacencies settle?

Show answer & explanation

Answer: HQ-R3 operates as a DROTHER because active DR and BDR roles in OSPFv2 are non-preemptive.

Answer

HQ-R3 becomes a DROTHER because OSPFv2 DR and BDR elections are non-preemptive once operational roles are established on a multiaccess network segment.
In OSPFv2 broadcast multiaccess networks, DR and BDR elections are non-preemptive. Once a DR and BDR are elected and active, adding a new router with a higher interface priority (such as 255) will not trigger a role change. The new router assumes the DROTHER role until the DR or BDR router fails, disconnects, or has its OSPF process reset.

Step-by-Step Solution

1
Analyze the existing OSPFv2 segment state from the CLI output.
HQ-R1 (1.1.1.1) is actively serving as the Designated Router (DR) and HQ-R2 (2.2.2.2) is serving as the Backup Designated Router (BDR).
The election process has already taken place and active DR/BDR roles are currently filled.
2
Evaluate the impact of introducing HQ-R3 with interface priority 255 onto the broadcast network.
HQ-R3 establishes adjacency but does not trigger a re-election for DR or BDR.
OSPFv2 DR/BDR elections are strictly non-preemptive. A newly attached router will not displace an active DR or BDR regardless of priority or Router ID.
3
Determine the final OSPF state of HQ-R3.
HQ-R3 transitions to the DROTHER state on the multiaccess link.
Because both DR and BDR roles are already filled, HQ-R3 functions as a 2-WAY / FULL neighbor (DROTHER) with non-DR/BDR routers.

Key Concept

OSPFv2 Non-Preemptive DR/BDR Election Rule
Question 397Question →

Match each Cisco IOS IPv4 routing table entry component to its correct functional definition or metric descriptor.

Click a left item, then click its matching right item

Items

Administrative Distance (AD)
Routing Metric
Next-Hop Address
Prefix Length

Matches

Show answer & explanation

Answer

Administrative Distance matches the measure of route source trustworthiness; Routing Metric matches the path cost calculated by a specific protocol; Next-Hop Address matches the IPv4 address of the adjacent router interface; Prefix Length matches the subnet mask specifier in CIDR notation used for longest prefix match.
Each entry component in a Cisco IOS routing table plays a distinct role: Administrative Distance measures source believability (0-255), Routing Metric determines the best path within a specific routing protocol, the Next-Hop Address defines the adjacent router's interface IP for forwarding, and the Prefix Length dictates how many bits match the destination address during lookup.

Step-by-Step Solution

1
Analyze Administrative Distance (AD)
AD evaluates protocol trustworthiness (e.g., lower AD is preferred when different protocols report the same prefix).
It allows Cisco IOS to prioritize route sources.
2
Analyze Routing Metric
Metric measures path desirability within a single routing protocol.
It acts as a tie-breaker when multiple paths exist within the same protocol.
3
Analyze Next-Hop Address
Next-hop represents the forwarding neighbor's IP interface.
It tells the router where to transmit layer 3 packets.
4
Analyze Prefix Length
Prefix length defines the network mask.
It is used by the forwarding engine during longest prefix matching.

Key Concept

Interpretation of Routing Table Components and Attributes
Question 398Question →

Which of the following statements correctly compare the default operational characteristics and parameters of HSRP (v1) and VRRP (v2)? (Select two.)

Select all that apply

Show answer & explanation

Answer: HSRPv1 uses virtual MAC addresses in the format 0000.0c07.acXX, whereas VRRPv2 uses the format 0000.5e00.01XX.; HSRP names the primary forwarding gateway the Active router, whereas VRRP names it the Master router.

Answer

The correct statements are that HSRPv1 uses virtual MAC addresses formatted as 0000.0c07.acXX while VRRPv2 uses 0000.5e00.01XX, and HSRP designates the forwarding router as Active while VRRP designates it as Master.
HSRPv1 and VRRPv2 differ in virtual MAC schemes (0000.0c07.acXX vs 0000.5e00.01XX) and role naming conventions (Active/Standby in HSRP vs Master/Backup in VRRP).

Step-by-Step Solution

1
Analyze virtual MAC address structure for both protocols
HSRPv1 uses standard MAC prefix 0000.0c07.ac followed by the group ID. VRRPv2 uses 0000.5e00.01 followed by the group ID.
Each protocol reserves a specific IEEE OID/MAC range for virtual gateway identification.
2
Compare role terminology between Cisco proprietary HSRP and open standard VRRP
HSRP uses Active/Standby roles, whereas VRRP uses Master/Backup roles.
Standardization differences lead to distinct terminology for equivalent primary/secondary forwarding roles.
3
Evaluate IP address assignment and preemption rules
VRRP supports using an interface's physical IP as the virtual IP address and enables preemption by default. HSRP requires a separate virtual IP address and disables preemption by default.
Differentiates implementation behavior between the two First Hop Redundancy Protocols.

Key Concept

HSRP and VRRP Operational Differences
Question 399Question →

An enterprise router R1 is configured as the active HSRPv1 router for Group 10 with an initial priority of 110 and preemption enabled. R1 tracks its WAN uplink interface GigabitEthernet0/1 with a priority decrement value of 20. Router R2 is configured as the standby router for Group 10 with a priority of 100 and preemption enabled. Place the operational events in the exact chronological sequence following a line-protocol failure on R1's GigabitEthernet0/1 interface until failover convergence completes.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct chronological sequence is: (1) R1 detects tracked interface failure -> (2) R1 decrements priority to 90 -> (3) R1 sends Hello with priority 90 -> (4) R2 compares priorities (100 vs 90) -> (5) R2 transmits an HSRP Coup message -> (6) R2 enters Active state and issues a Gratuitous ARP while R1 becomes Standby.
HSRP convergence follows a strict sequence when interface tracking degrades priority: detection of interface failure occurs first, leading to immediate priority calculation on the active router. The reduced priority is then advertised to the standby router via standard Hello messages. The standby router evaluates the lower priority, triggers preemption by sending a Coup message, assumes the Active state, and finally sends a Gratuitous ARP to re-align Layer 2 switch forwarding tables.

Step-by-Step Solution

1
Detect Link Failure
R1 detects line-protocol failure on GigabitEthernet0/1.
Interface tracking monitors the operational state of the configured interface.
2
Calculate Priority Decrement
R1's priority changes from 110 to 90.
The configured track action automatically subtracts 20 from R1's active priority (110−20=90110 - 20 = 90).
3
Advertise New Priority
R1 sends an HSRP Hello packet containing priority 90.
HSRP routers communicate state changes via periodic Hello messages sent to 224.0.0.2.
4
Evaluate Preemption Criteria
R2 identifies that its priority (100) exceeds R1's reported priority (90).
With preemption configured, a standby router constantly compares received active priority against its own.
5
Signal Takeover
R2 sends an HSRP Coup message.
The Coup message informs the current active router that a higher-priority router is asserting control.
6
Final Convergence & Traffic Steering
R2 transitions to Active, issues a Gratuitous ARP for the virtual IP/MAC, and R1 steps down to Standby.
The Gratuitous ARP updates Layer 2 switch forwarding tables so host traffic is immediately steered to R2.

Key Concept

HSRP Interface Tracking and Preemption Mechanism
Question 400Question →

A Cisco router receives an IP packet destined for host 172.20.16.68. The network engineer checks the routing table and observes the following entries:

text
C 172.20.16.0/23 is directly connected, GigabitEthernet0/0/0
S 172.20.16.0/25 [1/0] via 192.168.1.1, GigabitEthernet0/0/1
D 172.20.16.64/27 [90/2570240] via 192.168.1.5, GigabitEthernet0/0/2
O 172.20.16.64/28 [110/30] via 192.168.1.9, GigabitEthernet0/0/3

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

Show answer & explanation

Answer: Next-hop 192.168.1.9 via GigabitEthernet0/0/3

Answer

The router will select next-hop 192.168.1.9 via interface GigabitEthernet0/0/3 because the /28 route provides the longest prefix match for destination 172.20.16.68.
When a router performs a destination lookup in the routing table, it evaluates all matching entries and selects the route with the most specific prefix length (Longest Prefix Match). The host address 172.20.16.68 falls within all four candidate subnet ranges, but 172.20.16.64/28 has the highest mask length (/28 > /27 > /25 > /23). Therefore, the router forwards the packet using next-hop 192.168.1.9 via GigabitEthernet0/0/3 regardless of the higher administrative distance of OSPF.

Step-by-Step Solution

1
Determine which routing table entries match the destination IP address 172.20.16.68.
All four routes cover 172.20.16.68:
- 172.20.16.0/23 covers 172.20.16.0 - 172.20.17.255
- 172.20.16.0/25 covers 172.20.16.0 - 172.20.16.127
- 172.20.16.64/27 covers 172.20.16.64 - 172.20.16.95
- 172.20.16.64/28 covers 172.20.16.64 - 172.20.16.79
Before comparing metrics or administrative distance, the router must evaluate match candidates against the destination address.
2
Apply the Longest Prefix Match (LPM) rule to select the best route.
The subnet masks are /23, /25, /27, and /28. The /28 route is the most specific prefix (longest prefix match).
Cisco IP forwarding logic always prioritizes prefix length over administrative distance or metric when multiple matching routes exist.
3
Identify the next-hop and interface associated with the longest matching prefix.
The OSPF route 172.20.16.64/28 specifies next-hop 192.168.1.9 via GigabitEthernet0/0/3.
This entry dictates the forwarding decision.

Key Concept

Longest Prefix Match (LPM) in IP Routing
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