IP Connectivity

493 questions

All types493 Multiple choice250 Multiple select113 Matching25 Ordering60 Fill in the blank22 Short answer23

A router learns the destination network $10.20.30.0/24$ dynamically via RIPv2 with a default Administrative Distance of $120$ . A network engineer needs to configure a floating static backup route for this network via next-hop IP address $192.168.12.2$ . The backup route must only enter the routing table if the primary RIP route fails. Complete the Cisco IOS configuration command to assign an Administrative Distance of $130$ to the floating static route.

Fill in the blanks below

Router(config)# ip route 10.20.30.0 255.255.255.0 192.168.12.2

Show answer & explanation

Answer

130

A floating static route serves as a backup path and must be configured with an Administrative Distance (AD) strictly higher than that of the primary route. Since RIPv2 has a default AD of 120, specifying 130 as the trailing metric in the 'ip route' command ensures that the static route remains out of the routing table until the RIP route fails.

Step-by-Step Solution

Identify the Administrative Distance (AD) of the primary dynamic routing protocol.

RIPv2 has a default Administrative Distance of 120.

Routing decisions prioritize routes with lower Administrative Distance values.

Determine the required Administrative Distance for the backup floating static route.

The backup route must have an AD greater than 120 (specifically 130 as requested).

A higher AD keeps the static route inactive (floating) in the routing table as long as the primary route is active.

Complete the Cisco IOS command by appending the administrative distance integer at the end.

The trailing argument in 'ip route 10.20.30.0 255.255.255.0 192.168.12.2 130' sets the AD to 130.

In Cisco IOS syntax, an optional integer at the end of the 'ip route' command overrides the default static route AD of 1.

Key Concept

Floating Static Route Administrative Distance Configuration

Estimated Time:1m 0s

Question 82Question →

When establishing an OSPFv2 neighbor relationship between two Cisco routers on a broadcast multiaccess network, which parameter in the Hello packet must match on both routers?

OSPF Area ID

OSPF Process ID

OSPF Router ID

OSPF Interface Priority

Show answer & explanation

Answer: OSPF Area ID

Answer

OSPF Area ID

For two routers to form an OSPFv2 neighbor adjacency, several parameters in the Hello packet must match exactly, including the OSPF Area ID, Hello/Dead timers, IP subnet mask, authentication details, and stub area flag. If the Area ID differs, the routers discard the Hello packets and fail to form an adjacency.

Step-by-Step Solution

Identify mandatory parameters exchanged in OSPF Hello packets that must match for neighbor formation.

Hello packet fields that must match include Area ID, Subnet Mask, Hello and Dead intervals, Authentication parameters, and Stub area flag.

OSPF requires routers to reside in the same area to exchange Link State Advertisements (LSAs) for that area.

Evaluate non-matching or locally significant parameters.

Process ID is locally significant, Router IDs must be unique, and Router Priority determines DR/BDR election roles.

These parameters do not need to match across neighbors for the adjacency to form.

Key Concept

OSPFv2 Hello Packet Parameter Requirements for Adjacency

Estimated Time:45s

Question 83Question →

An enterprise router R1 learns a primary path to the remote network $172.16.50.0/24$ dynamically through OSPF with an Administrative Distance of 110. A network administrator needs to configure a floating static backup route to $172.16.50.0/24$ via the next-hop IPv4 address $10.0.12.2$ . Which TWO statements accurately describe the requirements and operational behavior of this IPv4 static route configuration? (Select two.)

Select all that apply

The floating static route command must specify an administrative distance value greater than 110 (such as 120) so that it is installed in the routing table only if the primary OSPF route fails.

When configured using only the next-hop IPv4 address

10.0.12.2

, the router must perform a recursive lookup in the routing table to resolve the outbound interface.

Configuring the floating static route with an administrative distance of 90 ensures it operates as a standby route while OSPF remains operational.

If a static default route (

0.0.0.0/0

) with an administrative distance of 120 is also present, router R1 will prefer that default route over the OSPF route for destination

172.16.50.10

Show answer & explanation

Answer: The floating static route command must specify an administrative distance value greater than 110 (such as 120) so that it is installed in the routing table only if the primary OSPF route fails.; When configured using only the next-hop IPv4 address $10.0.12.2$ , the router must perform a recursive lookup in the routing table to resolve the outbound interface.

Answer

The floating static route must be configured with an administrative distance greater than 110 (such as 120) to remain inactive while OSPF is up, and specifying only a next-hop IP address requires the router to perform a recursive routing lookup to resolve the exit interface.

For a static route to function as a floating backup, its Administrative Distance must be configured higher than the primary route's protocol AD (110 for OSPF). Additionally, static routes configured with only an IP next-hop rely on recursive lookup logic to identify the outgoing interface.

Step-by-Step Solution

Analyze the Administrative Distance (AD) requirement for floating static routes.

OSPF has an AD of 110. Standard static routes have an AD of 1. To make a static route act as a floating backup, its AD must be manually set higher than the active protocol (e.g., AD > 110).

The Cisco IOS routing table installs the route with the lowest Administrative Distance when multiple sources offer routes to the exact same prefix.

Evaluate router forwarding lookup behavior for next-hop static routes.

Specifying only the next-hop IPv4 address (

10.0.12.2

) obligates the router to recursively search the routing table to match

10.0.12.2

against directly connected egress interfaces.

Without an explicitly named local exit interface, the control plane must resolve how to reach the next-hop address.

Evaluate Longest Prefix Match rules against Administrative Distance.

A default route (

0.0.0.0/0

) is less specific than a /24 route. Longest prefix matching occurs prior to AD comparison, so a /24 route always beats a /0 default route.

Prefix length is the primary criterion in IPv4 forwarding decisions.

Key Concept

Floating Static Route Administrative Distance and Recursive Next-Hop Lookup

Question 84Question →

Refer to the following partial IPv4 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
O 172.16.0.0/16 [110/50] via 10.1.1.1, 01:14:22, GigabitEthernet0/0/1
D 172.16.35.0/24 [90/2172416] via 10.2.2.2, 00:42:10, GigabitEthernet0/0/2
S 172.16.35.32/27 [1/0] via 10.3.3.3
O 172.16.35.40/29 [110/30] via 10.4.4.4, 00:08:15, GigabitEthernet0/0/3

A packet with a destination IP address of $172.16.35.42$ arrives at the router. Which two statements correctly describe how the router makes its forwarding decision for this packet? (Select two.)

Select all that apply

The router forwards the packet to next-hop 10.4.4.4 because 172.16.35.40/29 provides the longest matching prefix for the destination address.

The router forwards the packet to next-hop 10.3.3.3 because static routes take precedence over OSPF routes regardless of subnet prefix length.

Administrative distance is evaluated only after the router identifies all candidate routes that share the longest matching prefix length.

The router drops the packet because 172.16.35.42 is the direct broadcast address for the 172.16.35.40/29 subnet.

Show answer & explanation

Answer: The router forwards the packet to next-hop 10.4.4.4 because 172.16.35.40/29 provides the longest matching prefix for the destination address.; Administrative distance is evaluated only after the router identifies all candidate routes that share the longest matching prefix length.

Answer

The router forwards the packet to next-hop 10.4.4.4 because 172.16.35.40/29 is the longest matching prefix, and administrative distance is evaluated only after determining candidate routes with the longest matching prefix length.

When a router receives a packet, it compares the destination IP against all entries in its routing table and selects the entry with the longest prefix match (most specific mask). Here, 172.16.35.40/29 matches 29 bits of the destination address 172.16.35.42, making it more specific than the /27 static route or /24 EIGRP route. Administrative distance is only evaluated when choosing among routes with identical prefix lengths.

Step-by-Step Solution

Evaluate all routes matching the destination IP address 172.16.35.42.

Matching routes: 0.0.0.0/0 (/0), 172.16.0.0/16 (/16), 172.16.35.0/24 (/24), 172.16.35.32/27 (/27), and 172.16.35.40/29 (/29).

The destination address 172.16.35.42 resides within the IP range 172.16.35.40 to 172.16.35.47 defined by the /29 subnet mask.

Apply the Longest Prefix Match (LPM) rule.

The route 172.16.35.40/29 has a 29-bit mask, which is longer than /27, /24, /16, or /0.

Routers always prefer the route with the most specific (longest) subnet mask first, before considering administrative distance or metric.

Verify if 172.16.35.42 is a valid unicast host IP in 172.16.35.40/29.

Subnet ID: 172.16.35.40, Usable hosts: 172.16.35.41 - 172.16.35.46, Broadcast: 172.16.35.47.

172.16.35.42 is a valid host address, so the packet is forwarded to next-hop 10.4.4.4 via GigabitEthernet0/0/3.

Key Concept

Longest Prefix Match (LPM) Rule in Cisco IPv4 Forwarding Logic

Estimated Time:1m 30s

Question 85Question →

A network administrator is troubleshooting an OSPFv2 neighbor relationship between two Cisco routers, Edge-R1 and Core-R1. Running the command 'show ip ospf neighbor' on Edge-R1 indicates that Core-R1 is persistently stuck in the INIT state. Verification confirms that both router interfaces are assigned to Area 0, have matching IP subnet masks, and share identical Hello and Dead timer intervals. Which underlying condition is the most likely cause of the neighbor relationship remaining stuck in the INIT state?

An Access Control List (ACL) on Core-R1 is filtering incoming OSPF Hello packets sent by Edge-R1.

The Maximum Transmission Unit (MTU) configured on Edge-R1's interface does not match the MTU configured on Core-R1's interface.

Edge-R1 and Core-R1 are configured with different OSPF process IDs in their global routing configuration.

The OSPF priority on Core-R1's interface is set to 0, preventing it from participating in Designated Router elections.

Show answer & explanation

Answer: An Access Control List (ACL) on Core-R1 is filtering incoming OSPF Hello packets sent by Edge-R1.

Answer

An Access Control List (ACL) on Core-R1 is filtering incoming OSPF Hello packets sent by Edge-R1.

The correct answer identifies that an inbound ACL on the remote router is filtering Hello packets in one direction. In OSPF, a router transitions a peer to the INIT state upon receiving a Hello packet. To progress to 2-WAY state, the router must see its own Router ID in the active neighbor list of the peer's incoming Hello packet. If an ACL blocks Hellos in one direction, the peer never receives the Hellos, never lists the local router's ID, and leaves the local router stuck in the INIT state.

Step-by-Step Solution

Analyze OSPF neighbor state progression mechanics.

Transition to the 2-WAY state requires bidirectional communication, meaning a router must see its own Router ID listed in the Received Hello packet's neighbor list from its peer.

When Edge-R1 sees Core-R1's Hello packet, it places Core-R1 into its neighbor table in the INIT state.

Evaluate the impact of unidirectionally dropped Hello packets.

Edge-R1 is receiving Hellos from Core-R1, but Core-R1 is NOT receiving Hellos from Edge-R1 due to an inbound ACL filter on Core-R1.

Because Core-R1 never receives Edge-R1's Hellos, Core-R1 cannot add Edge-R1's Router ID to its outgoing Hello packet neighbor list. Thus, Edge-R1 stays stuck in INIT.

Differentiate INIT state causes from EXSTART state and configuration parameters.

MTU mismatches cause EXSTART/EXCHANGE stuck states, whereas mismatched process IDs or priority 0 do not prevent FULL neighbor adjacency.

Only unidirectional traffic flow (or filtering of Hellos in one direction) accounts for a persistent INIT state when basic parameters like Area ID and timers match.

Key Concept

OSPFv2 Neighbor States and Bidirectional Hello Communication Requirements

Estimated Time:2m 0s

Question 86Question →

An engineer is troubleshooting OSPFv2 neighbor establishment between Router-Edge1 and Router-Edge2 over their directly connected GigabitEthernet0/0/1 link. The running configurations for both routers are provided below:

text
[Router-Edge1]
interface Loopback0
ip address 10.255.255.1 255.255.255.255
shutdown
!
interface Loopback1
ip address 172.16.10.1 255.255.255.255
!
interface GigabitEthernet0/0/1
ip address 192.168.12.1 255.255.255.252
ip mtu 1500
ip ospf hello-interval 10
ip ospf dead-interval 40
ip ospf 1 area 0
!
router ospf 1
router-id 1.1.1.1

[Router-Edge2]
interface Loopback0
ip address 10.255.255.2 255.255.255.255
!
interface GigabitEthernet0/0/1
ip address 192.168.12.2 255.255.255.252
ip mtu 1400
ip ospf hello-interval 10
ip ospf dead-interval 30
ip ospf 1 area 0
!
router ospf 1

Based on these configurations, which TWO statements accurately describe the OSPFv2 neighbor behavior and Router ID operation between these routers? (Select TWO.)

Select all that apply

The routers will fail to establish an initial 2-WAY neighbor relationship because the configured OSPF Dead intervals on GigabitEthernet0/0/1 do not match.

If the Dead interval mismatch is corrected, the routers will become stuck in the EXSTART/EXCHANGE state due to the IP MTU mismatch on the GigabitEthernet0/0/1 interfaces.

Router-Edge1 dynamically elects 172.16.10.1 as its Router ID because Loopback0 is administrative shut down.

Router-Edge2 elects 192.168.12.2 as its Router ID because active physical interface IP addresses override loopback interface IP addresses during election.

Show answer & explanation

Answer: The routers will fail to establish an initial 2-WAY neighbor relationship because the configured OSPF Dead intervals on GigabitEthernet0/0/1 do not match.; If the Dead interval mismatch is corrected, the routers will become stuck in the EXSTART/EXCHANGE state due to the IP MTU mismatch on the GigabitEthernet0/0/1 interfaces.

Answer

The correct statements are that the routers will fail to establish a 2-WAY neighbor state due to mismatched Dead intervals, and if resolved, will remain stuck in EXSTART/EXCHANGE due to the IP MTU mismatch.

The option stating that mismatched Dead intervals prevent the 2-WAY neighbor relationship is correct because Hello and Dead intervals are mandatory parameters in OSPF Hello packets that must match between neighbors. The option noting that an IP MTU mismatch causes routers to become stuck in EXSTART/EXCHANGE is also correct because MTU validation occurs during DBD packet exchanges.

Step-by-Step Solution

Evaluate OSPF Hello packet parameter requirements for 2-WAY adjacency formation.

Router-Edge1 is configured with a Dead interval of 40 seconds, whereas Router-Edge2 is configured with 30 seconds. Hello/Dead intervals MUST match exactly between neighbors on a common link. Therefore, Hello packets are rejected, preventing 2-WAY state.

Matching Hello/Dead timers are a mandatory prerequisite for OSPF neighbor discovery and adjacency.

Analyze the impact of MTU settings during Database Description (DBD) packet negotiation.

Router-Edge1 has an IP MTU of 1500 bytes, while Router-Edge2 has an IP MTU of 1400 bytes. When MTUs mismatch, routers fail to process DBD packets during Master/Slave negotiation, remaining stuck in EXSTART/EXCHANGE state.

OSPF includes interface MTU in DBD packets to ensure MTU parity across adjacent neighbors.

Verify Router ID election logic for Router-Edge1 and Router-Edge2.

Router-Edge1 uses explicit 'router-id 1.1.1.1', which overrides all loopbacks and physical interfaces. Router-Edge2 has no explicit router-id command, so it selects its active Loopback0 IP (10.255.255.2), because loopbacks always take priority over physical interfaces.

Election order is strictly: 1. Manual 'router-id' command -> 2. Highest active loopback IP -> 3. Highest active non-loopback interface IP.

Key Concept

OSPFv2 Adjacency Requirements and Router ID Selection Order

Question 87Question →

A network administrator is configuring an IPv4 static route on router R1 to reach the remote network $10.10.40.0/24$ across an Ethernet multiaccess segment. After issuing the command `ip route 10.10.40.0 255.255.255.0 GigabitEthernet0/0`, the administrator observes high CPU utilization and a large ARP table on R1 because the router attempts to resolve ARP for every individual destination host address in the remote network. Which command modification correctly resolves this issue while maintaining reachability?

Specify the next-hop IPv4 address instead of specifying only the Ethernet exit interface.

Append an administrative distance value of 210 to the end of the existing static route command.

Replace the dotted-decimal subnet mask 255.255.255.0 with the wildcard mask 0.0.0.255.

Configure a default static route pointing to 0.0.0.0 0.0.0.0 using interface GigabitEthernet0/0.

Show answer & explanation

Answer: Specify the next-hop IPv4 address instead of specifying only the Ethernet exit interface.

Answer

Specify the next-hop IPv4 address instead of specifying only the Ethernet exit interface.

When a static route on a broadcast multiaccess link (like Ethernet) points solely to an exit interface without a next-hop IP address, the router considers all host addresses in the destination subnet directly connected. Consequently, for every destination packet, the router broadcasts an ARP request on the local segment. Specifying the next-hop IPv4 address ensures the router sends packets to the specific neighbor router's MAC address, preventing ARP flooding and excessive memory usage.

Step-by-Step Solution

Analyze the static route syntax and multiaccess interface behavior.

Configuring `ip route` on a multiaccess Ethernet link with only an exit interface causes the router to assume the destination prefix is directly attached to that Ethernet segment.

Because Ethernet is a multiaccess medium with multiple potential devices, the router must send an ARP request for every single destination IP address in the prefix if no next-hop IP is specified.

Determine the solution for multiaccess static route next-hop resolution.

Including the next-hop IPv4 address (e.g., `ip route 10.10.40.0 255.255.255.0 192.168.1.2` or combining next-hop IP and exit interface) allows R1 to resolve ARP only for the next-hop router's IP address.

This avoids generating ARP requests for remote host IPs and prevents ARP table exhaustion and excessive CPU load.

Key Concept

Next-Hop IPv4 Address vs. Exit Interface in Multiaccess Static Routes

Estimated Time:1m 30s

Question 88Question →

A network engineer is configuring first-hop redundancy for VLAN 20 on two Cisco IOS routers, R1 and R2. Interface GigabitEthernet0/0 on R1 is assigned IPv4 address 10.20.0.2/24, and GigabitEthernet0/0 on R2 is assigned 10.20.0.3/24. The engineer attempts to configure HSRP group 20 on R1 using the command `standby 20 ip 10.20.0.2`. The Cisco IOS CLI rejects the command with an error message. However, when configuring VRRP using `vrrp 20 ip 10.20.0.2`, the command is accepted successfully. What fundamental operational difference between HSRP and VRRP causes this behavior?

VRRP permits the virtual IP address to match the physical IP address of a router interface, appointing that router as the IP address owner with a default priority of 255, whereas HSRP strictly prohibits assigning any router's physical IP address as the virtual IP.

HSRP requires the virtual IP address to be identical to the active router's physical interface IP address, whereas VRRP requires a separate IP address outside the interface subnet range.

HSRP requires preemption to be explicitly enabled before a virtual IP address can be specified under the interface configuration, whereas VRRP automatically enables preemption by default.

VRRP uses a dedicated multicast group address to resolve physical-to-virtual IP mapping conflicts, whereas HSRP relies on broadcast traffic that prevents physical IP reuse.

Show answer & explanation

Answer: VRRP permits the virtual IP address to match the physical IP address of a router interface, appointing that router as the IP address owner with a default priority of 255, whereas HSRP strictly prohibits assigning any router's physical IP address as the virtual IP.

Answer

In Cisco IOS, HSRP mandates that the virtual IP address must be a unique IP address on the subnet and cannot be identical to any physical IP address configured on a router's interface. In contrast, VRRP allows the virtual IP address to match the interface physical IP address; the router whose physical IP matches the VRRP group virtual IP assumes the role of Master with an unalterable priority of 255 (IP address owner).

Step-by-Step Solution

Analyze the HSRP virtual IP configuration restriction.

HSRP requires that the virtual IP address defined in `standby <group> ip <address>` must be a unique, unused IP address on the subnet, separate from all physical interface IP addresses of the participating routers.

Assigning an existing physical IP address as an HSRP virtual IP address causes an IP overlap/conflict on the interface and is rejected by the Cisco IOS CLI.

Analyze the VRRP virtual IP configuration capability.

VRRP allows the virtual IP address to be identical to the primary physical IP address of one of the VRRP routers. The router owning that physical IP becomes the IP Address Owner and automatically receives a VRRP priority of 255.

VRRP standard RFC 5798 explicitly defines the IP address owner role to allow interface IP address sharing.

Select the option that accurately contrasts this behavior between HSRP and VRRP.

The correct response highlights that VRRP allows IP address ownership with a priority of 255 while HSRP prohibits physical IP reuse as the virtual IP.

This directly explains why HSRP rejected the configuration while VRRP accepted it.

Key Concept

HSRP vs VRRP Virtual IP Address Assignment and IP Address Ownership

Question 89Question →

A network engineer is configuring an IPv4 static route on router R1 to reach destination network $172.20.40.0/24$ . The path connects through an Ethernet broadcast multi-access interface (GigabitEthernet0/1) to the next-hop router address $10.0.12.2$ . Which command configures a fully specified static route that prevents recursive lookup overhead while avoiding excessive Address Resolution Protocol (ARP) table expansion on the multi-access segment?

ip route 172.20.40.0 255.255.255.0 GigabitEthernet0/1 10.0.12.2

ip route 172.20.40.0 255.255.255.0 GigabitEthernet0/1

ip route 172.20.40.0 255.255.255.0 10.0.12.2 GigabitEthernet0/1

ip route 172.20.40.0 0.0.0.255 GigabitEthernet0/1 10.0.12.2

Show answer & explanation

Answer: ip route 172.20.40.0 255.255.255.0 GigabitEthernet0/1 10.0.12.2

Answer

The command 'ip route 172.20.40.0 255.255.255.0 GigabitEthernet0/1 10.0.12.2' correctly configures a fully specified static route.

The correct command uses the syntax 'ip route 172.20.40.0 255.255.255.0 GigabitEthernet0/1 10.0.12.2'. By providing both the local exit interface and the specific next-hop IPv4 address, the router creates a fully specified route. This prevents recursive table lookup overhead (associated with next-hop IP only) and avoids excessive ARP requests for individual destination IPs (associated with exit interface only on multi-access media).

Step-by-Step Solution

Identify the static route requirement for a broadcast multi-access network (Ethernet).

On Ethernet links, specifying only an exit interface causes the router to treat all destination IP addresses as directly connected, issuing ARP requests for every destination host.

Ethernet is a multi-access network requiring Layer 2 MAC address resolution.

Evaluate the difference between directly attached, next-hop, and fully specified static routes.

A fully specified static route includes both the local exit interface (GigabitEthernet0/1) and the next-hop IP address (10.0.12.2).

This eliminates the need for recursive routing lookups while pinpointing the exact Layer 2 next-hop neighbor.

Verify Cisco IOS syntax ordering and subnet mask formatting.

The correct syntax order is 'ip route <prefix> <mask> <exit-interface> <next-hop-ip>'.

Dotted-decimal subnet masks must be used instead of wildcard masks.

Key Concept

Fully Specified IPv4 Static Route Syntax on Multi-access Networks

Estimated Time:1m 15s

Question 90Question →

A network administrator configures OSPFv2 across four Cisco routers connected to a single Ethernet switch on a broadcast multiaccess segment. After allowing time for network convergence, the administrator issues the `show ip ospf neighbor` command on Router R3, which is neither the Designated Router (DR) nor the Backup Designated Router (BDR). The output shows that the neighbor relationship with Router R4 (also a DROther) is in the `2WAY/DROTHER` state. Which statement correctly describes this scenario?

This is normal expected behavior because non-DR/BDR routers on a broadcast network form bi-directional communication but do not proceed to full database synchronization with each other.

The routers are stuck due to an Interface Maximum Transmission Unit (MTU) size mismatch preventing the exchange of Database Description (DBD) packets.

Router R4 is failing to process incoming OSPF Hello packets from R3 due to a mismatched OSPF process ID configured on the local interface.

The neighbor relationship failed to reach the FULL state because the OSPF Hello and Dead interval timers are improperly configured on R4.

Show answer & explanation

Answer: This is normal expected behavior because non-DR/BDR routers on a broadcast network form bi-directional communication but do not proceed to full database synchronization with each other.

Answer

This is normal expected behavior because non-DR/BDR routers on a broadcast network form bi-directional communication but do not proceed to full database synchronization with each other.

On broadcast multiaccess networks (such as Ethernet), OSPF elects a Designated Router (DR) and Backup Designated Router (BDR). All other routers on the segment are designated as DROthers. To minimize routing overhead and redundant LSA exchanges, DROthers only establish FULL adjacencies with the DR and BDR. Between two DROther routers, bi-directional communication is established and maintained at the 2-WAY state, which is normal and expected behavior.

Step-by-Step Solution

Analyze the network topology and router roles

The network is a broadcast multiaccess Ethernet segment with four OSPFv2 routers. R3 and R4 are identified as DROther routers (neither DR nor BDR).

OSPF behaves differently on broadcast networks depending on whether the routers involved are DR/BDR or DROthers.

Evaluate the OSPF neighbor state machine logic for DROther to DROther communications

DROther routers achieve 2-WAY state with one another once bi-directional Hello exchange succeeds.

To prevent redundant LSA exchanges and conserve network resources on multiaccess media, full database synchronization (FULL state) only occurs between DROthers and the DR/BDR.

Determine if troubleshooting is required for the 2WAY/DROTHER status

No troubleshooting is needed; the neighbor state is operating normally as designed by OSPF standards.

Reaching 2-WAY state confirms correct matching of Area ID, subnet mask, authentication, MTU handling, and Hello/Dead timers.

Key Concept

OSPF DR/BDR neighbor adjacency states on broadcast networks

Question 91Question →

A network administrator configures a static route using only a next-hop IP address. Place the operational steps in the correct order that a Cisco IOS router performs to process and forward a packet using this recursive static route.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence of packet forwarding steps for a recursive static route is: 1) Evaluate destination against routing table for longest prefix match, 2) Identify matching static route and extract next-hop IP, 3) Perform recursive lookup to resolve next-hop IP to an exit interface, 4) Query ARP table for next-hop MAC address on that interface, 5) Encapsulate frame and forward out the exit interface.

When an IPv4 static route is configured using only a next-hop IP address, Cisco IOS must resolve the outgoing interface by performing a second (recursive) lookup in the routing table. First, the router matches the packet destination address to the static route entry. Second, it extracts the next-hop IP. Third, it recursively resolves that next-hop IP to a connected interface. Fourth, it uses ARP on that interface to determine the next-hop MAC address. Finally, it encapsulates the packet and forwards it out the interface.

Step-by-Step Solution

Examine incoming packet destination

Longest match matching the static route prefix is found

Cisco IOS routing logic always evaluates the destination IPv4 address against all known routes using longest prefix matching first.

Extract next-hop IP address

Next-hop IPv4 address identified

Static routes configured in the format 'ip route prefix mask next-hop-ip' do not explicitly define the outgoing interface.

Perform recursive routing lookup

Exit interface and directly connected network identified

The router must locate a connected or dynamic route entry that covers the next-hop IP address to find the exit interface.

Resolve Layer 2 address

Next-hop MAC address obtained from ARP cache

For multi-access Ethernet interfaces, the router requires the destination MAC address of the next-hop gateway.

Frame encapsulation and transmission

Packet successfully transmitted

The packet is encapsulated with the local exit interface source MAC and next-hop destination MAC address.

Key Concept

Recursive Static Route Lookup and Packet Forwarding Process

Question 92Question →

A Cisco router initializes OSPFv2 process 100 with no explicitly configured router ID and no active loopback interfaces. The router has three physical interfaces configured with the following IPv4 addresses and operational states:

- GigabitEthernet0/0: 10.200.15.1/24 (Status: up, Line Protocol: up)
- GigabitEthernet0/1: 172.25.1.254/16 (Status: up, Line Protocol: up)
- GigabitEthernet0/2: 192.168.50.5/30 (Status: up, Line Protocol: down)

Which IPv4 address will OSPFv2 select as the Router ID when the routing process starts?

Show answer & explanation

Answer: 172.25.1.254; 172.25.1.254/16

Answer

172.25.1.254

When OSPF process initializes without an explicit 'router-id' command or any active loopback interfaces, it chooses the highest IPv4 address among operationally active (up/up) physical interfaces. Since GigabitEthernet0/2 is inactive (up/down), only GigabitEthernet0/0 (10.200.15.1) and GigabitEthernet0/1 (172.25.1.254) are eligible. 172.25.1.254 is the highest active address.

Step-by-Step Solution

Evaluate the OSPF Router ID election precedence rules

OSPF selects the router ID using the following priority: 1) Manually configured 'router-id' command, 2) Highest IPv4 address of any active loopback interface, 3) Highest IPv4 address of any active non-loopback physical interface.

Since no manual router ID or loopback interface exists, the selection defaults to active physical interfaces.

Filter interfaces by operational status

GigabitEthernet0/0 (10.200.15.1) and GigabitEthernet0/1 (172.25.1.254) are both up/up (active). GigabitEthernet0/2 (192.168.50.5) is up/down (inactive) and is disqualified from router ID selection.

OSPF only considers interfaces whose line protocol is operationally active (up/up).

Determine the highest active IPv4 address

Compare active addresses 10.200.15.1 and 172.25.1.254. 172.25.1.254 is numerically higher.

Numeric comparison of active physical interface IPv4 addresses yields 172.25.1.254 as the highest value.

Key Concept

OSPFv2 Router ID election logic prioritizes active loopback interfaces over physical interfaces, selecting the highest IPv4 address among operationally active (up/up) interfaces when no manual router ID is specified.

Question 93Question →

An engineer inspects the OSPFv2 operational status of interface GigabitEthernet0/0 on router R1 using the `show ip ospf interface` command:

text
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.1.10/24, Area 0
Process ID 1, Router ID 192.168.1.10, Network Type BROADCAST, Cost: 1
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 active Designated Router (10.3.3.3) reboots and leaves the network, which role will router R1 assume?

R1 will become the new Backup Designated Router because its interface IP address is higher than that of the current BDR.

R1 will remain in the DROTHER state and will not participate in the election for Designated Router or Backup Designated Router.

R1 will preempt the Backup Designated Router and immediately become the new Designated Router.

R1 will become the new Designated Router while the current Backup Designated Router retains its BDR role.

Show answer & explanation

Answer: R1 will remain in the DROTHER state and will not participate in the election for Designated Router or Backup Designated Router.

Answer

Router R1 will remain in the DROTHER state and will not participate in the election for Designated Router or Backup Designated Router.

In OSPFv2 broadcast multiaccess networks, setting an interface priority to 0 completely disables DR/BDR election eligibility for that interface. Even if the current DR fails and a new election occurs, any router with a priority of 0 remains strictly in the DROTHER state.

Step-by-Step Solution

Analyze the output of the 'show ip ospf interface' command for router R1.

Interface GigabitEthernet0/0 has an OSPF priority set to 0 ('Priority 0').

OSPF interface priority determines eligibility for DR and BDR roles during elections on multiaccess networks.

Apply OSPF DR/BDR election rules regarding priority values.

A router interface configured with an OSPF priority of 0 (ip ospf priority 0) is ineligible to become a DR or BDR.

Setting priority to 0 forces the router interface to remain in the DROTHER state indefinitely regardless of router ID, IP address, or failures of existing DR/BDR routers.

Determine the outcome when the active DR fails.

The current BDR (10.2.2.2) promotes to DR, and R1 remains a DROTHER, taking no part in any subsequent BDR election.

R1 is excluded from all DR/BDR election calculations due to its priority of 0.

Key Concept

OSPF Priority 0 Exclusion from DR/BDR Selection

Question 94Question →

A Cisco router relies on OSPF (administrative distance 110) to reach destination network $192.168.10.0/24$ . A backup path is connected via next-hop IPv4 address $10.0.0.2$ . The network engineer must configure a floating static route so that traffic uses this secondary link only when the primary OSPF path becomes unavailable. Which command correctly configures this backup static route?

ip route 192.168.10.0 255.255.255.0 10.0.0.2 120

ip route 192.168.10.0 255.255.255.0 10.0.0.2 90

ip route 192.168.10.0 255.255.255.0 10.0.0.2

ip route 192.168.10.0 0.0.0.255 10.0.0.2 120

Show answer & explanation

Answer: ip route 192.168.10.0 255.255.255.0 10.0.0.2 120

Answer

The command 'ip route 192.168.10.0 255.255.255.0 10.0.0.2 120' correctly configures the floating static route.

The command specifying 'ip route 192.168.10.0 255.255.255.0 10.0.0.2 120' uses proper Cisco IOS syntax with a subnet mask and assigns an administrative distance of 120. Because 120 is higher than OSPF's administrative distance of 110, the route will stay out of the routing table until the OSPF route is lost.

Step-by-Step Solution

Identify the primary routing protocol's Administrative Distance (AD)

OSPF has an AD of 110.

Floating static routes must have an AD strictly higher than the primary routing protocol to remain inactive while the primary route is present in the routing table.

Verify Cisco IOS static route command syntax

Syntax: 'ip route <destination-network> <subnet-mask> <next-hop-ip> [distance]'.

Cisco static routes require a dotted-decimal subnet mask (e.g., 255.255.255.0) rather than a wildcard mask.

Select the correct Administrative Distance value

An AD of 120 is greater than 110.

Setting the AD to 120 ensures the static route remains floating in backup state until the primary OSPF route (AD 110) fails.

Key Concept

Floating Static Route Administrative Distance

Estimated Time:1m 15s

Question 95Question →

Match each OSPFv2 interface configuration command or operational trait on the left with its corresponding network type property or election behavior on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The interface priority 0 command forces DROTHER state and excludes the router from elections; point-to-point network type on Ethernet suppresses DR/BDR election while using 10s/40s timers; broadcast network type enables DR/BDR election with 10s/40s timers; and equal priority elections break ties using the highest Router ID.

Each item matches its corresponding operational trait: priority 0 forces DROTHER status and excludes the interface from elections; configuring point-to-point on Ethernet suppresses DR/BDR election while using default 10s/40s timers; broadcast networks elect DR/BDR with 10s/40s timers; and equal priority ties are broken by the highest Router ID.

Step-by-Step Solution

Analyze OSPF priority 0 behavior

Interface priority 0 prevents a router from ever becoming a Designated Router or Backup Designated Router.

An interface priority of 0 explicitly removes the router from DR/BDR candidate status on multi-access networks.

Analyze point-to-point network type behavior on Ethernet media

Modifying network type to point-to-point bypasses DR/BDR election while maintaining standard 10s/40s timers.

Point-to-point connections assume only two routers exist, making DR/BDR election redundant.

Analyze default broadcast interface behavior

Broadcast networks elect DR/BDR neighbors and use Hello/Dead timers of 10 seconds and 40 seconds.

Broadcast multi-access links require a DR/BDR to limit adjacency formation across shared media.

Identify the election tie-breaker rule

The highest Router ID breaks priority ties among DR candidates.

OSPF DR election precedence evaluates priority first; if priorities match, the highest Router ID wins.

Key Concept

OSPFv2 Network Types and DR/BDR Election Mechanics

Question 96Question →

Router R1 and Router R2 are directly connected via their GigabitEthernet0/0 interfaces. An administrator configures OSPFv2 on both interfaces in Area 0. On R1, GigabitEthernet0/0 uses default OSPF timers (Hello 10 seconds, Dead 40 seconds). On R2, the Hello timer is manually set to 15 seconds and the Dead timer to 60 seconds. What will be the outcome of this OSPFv2 configuration between R1 and R2?

The routers will fail to establish an OSPF neighbor relationship because Hello and Dead timers must match exactly.

The routers will form an adjacency and reach the FULL state, but routing updates will fail to synchronize.

The routers will dynamically negotiate timers during the EXSTART state and become stuck in EXSTART.

The routers will achieve a 2-WAY neighbor state but will fail to elect a Designated Router (DR).

Show answer & explanation

Answer: The routers will fail to establish an OSPF neighbor relationship because Hello and Dead timers must match exactly.

Answer

The routers will fail to establish an OSPF neighbor relationship because Hello and Dead timers must match exactly.

For two OSPFv2 routers to form a neighbor relationship, key parameters in their Hello packets must match exactly. These include Area ID, Subnet Mask, Hello Interval, Dead Interval, Authentication settings, and Option flags. Because R1 has timers set to 10s/40s and R2 has timers set to 15s/60s, neither router will process the other's Hello packets as valid, preventing any neighbor relationship from forming.

Step-by-Step Solution

Identify the OSPF Hello packet parameters required for neighbor discovery.

Mandatory matching fields include Area ID, Subnet Mask, Hello/Dead intervals, Authentication, and Stub flag.

When a router receives an OSPF Hello packet, it compares these fields against its local interface parameters.

Compare the configured timer values on R1 and R2.

R1 uses Hello 10s / Dead 40s, while R2 uses Hello 15s / Dead 60s.

Because the values do not match, both routers silently drop the incoming Hello packets from each other.

Determine the final neighbor state.

No neighbor relationship is established.

Without matching parameters in Hello packets, routers cannot progress to the INIT or 2-WAY neighbor state.

Key Concept

OSPFv2 Mandatory Hello Packet Matching Parameters

Question 97Question →

A network engineer is configuring router R1 to maintain redundant connectivity to an upstream ISP. R1 currently learns a default route ( $0.0.0.0/0$ ) via OSPF, which has a default Administrative Distance of 110. The engineer needs to configure a floating static default route using the next-hop IP address $192.168.12.2$ over a secondary link so that it serves strictly as a backup if the OSPF path fails. Which TWO of the following statements accurately describe the configuration or operational behavior of this floating static route?

Select all that apply

The command `ip route 0.0.0.0 0.0.0.0 192.168.12.2 120` correctly configures the floating static route with an administrative distance higher than OSPF.

The configured floating static route remains in the running configuration but is excluded from the IPv4 routing table while the OSPF default route is active.

The command `ip route 0.0.0.0 0.0.0.0 192.168.12.2 90` creates a valid floating backup static route for the primary OSPF path.

When the primary OSPF link fails, Cisco IOS dynamically alters the administrative distance of the static route from 1 to 120 to activate it.

Show answer & explanation

Answer: The command `ip route 0.0.0.0 0.0.0.0 192.168.12.2 120` correctly configures the floating static route with an administrative distance higher than OSPF.; The configured floating static route remains in the running configuration but is excluded from the IPv4 routing table while the OSPF default route is active.

Answer

The correct statements are that `ip route 0.0.0.0 0.0.0.0 192.168.12.2 120` correctly configures the floating static route, and that the floating static route remains in the running configuration but is excluded from the active IPv4 routing table as long as the primary OSPF default route is active.

A floating static route acts as a backup path and must be configured with an Administrative Distance higher than the primary route protocol (OSPF AD 110). Using `ip route 0.0.0.0 0.0.0.0 192.168.12.2 120` properly assigns an AD of 120. Because Cisco IOS installs only the path with the lowest AD into the routing table, the static route is held in the running configuration and only populated into the IPv4 routing table if the OSPF default route is removed.

Step-by-Step Solution

Identify the Administrative Distance (AD) of the primary dynamic routing protocol

OSPF has a default AD of 110.

Floating static routes rely on having a higher AD than the primary routing method so they are not chosen while the primary route is functional.

Evaluate the required static route syntax and AD parameter

The command `ip route 0.0.0.0 0.0.0.0 192.168.12.2 120` specifies an AD of 120, which is higher than 110.

Setting the AD to 120 satisfies the floating static route requirement.

Determine Cisco IOS routing table insertion rules for floating routes

The static route with AD 120 is stored in configuration but withheld from the routing table while the lower AD OSPF route (AD 110) exists.

The Cisco IOS RIB only installs the route with the lowest AD for a given destination prefix.

Key Concept

Floating Static Routes and Administrative Distance

Question 98Question →

A network engineer is configuring OSPFv2 on a broadcast multiaccess Ethernet network segment connecting two Cisco routers. Which two parameters must match between the connected router interfaces for an OSPFv2 neighbor adjacency to form successfully? (Select two.)

Select all that apply

OSPF Area ID

OSPF Hello and Dead timer intervals

OSPF Process ID

OSPF Router ID

Show answer & explanation

Answer: OSPF Area ID; OSPF Hello and Dead timer intervals

Answer

The parameters that must match between neighboring routers for an OSPFv2 adjacency to form are the OSPF Area ID and the OSPF Hello and Dead timer intervals.

For two routers to establish an OSPFv2 neighbor adjacency on a broadcast segment, several parameters in the OSPF Hello packets must match, including the Area ID, IPv4 subnet mask, Hello/Dead timer intervals, and authentication type/key.

Step-by-Step Solution

Identify mandatory matching parameters contained in OSPF Hello packets

OSPF neighbor adjacencies require matching Area ID, Subnet Mask, Hello and Dead Timers, and Authentication fields.

A mismatch in any of these Hello packet fields prevents routers from progressing past the Init neighbor state.

Evaluate non-matching and unique OSPF configuration parameters

OSPF Process ID is locally significant, while OSPF Router ID must be globally unique across the autonomous system.

Process IDs are not communicated across neighbor links, and duplicate Router IDs cause database synchronization failures.

Key Concept

OSPFv2 Neighbor Adjacency Requirements

Question 99Question →

An engineer inspects the OSPFv2 neighbor status on router R1, which is connected to a shared Ethernet segment alongside routers R2, R3, and R4. The command output on R1 displays the following neighbor table:

text
Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 1 FULL/DR 00:00:33 192.168.1.2 GigabitEthernet0/0
3.3.3.3 1 FULL/BDR 00:00:36 192.168.1.3 GigabitEthernet0/0
4.4.4.4 255 FULL/DROTHER 00:00:31 192.168.1.4 GigabitEthernet0/0

The administrator wants R4 (Router ID 4.4.4.4) to become the Designated Router (DR) on this network segment without changing any interface priorities. Which action will force a new DR election across the segment?

Execute the clear ip ospf process command on all routers on the multiaccess segment.

Reload router R4 so that its interface priority of 255 forces an immediate preemption of the active DR.

Configure ip ospf priority 0 on router R1's GigabitEthernet0/0 interface.

Change the OSPF network type on interface GigabitEthernet0/0 on R4 to point-to-point.

Show answer & explanation

Answer: Execute the clear ip ospf process command on all routers on the multiaccess segment.

Answer

Execute the clear ip ospf process command on all routers on the multiaccess segment.

The correct answer identifies that OSPFv2 DR/BDR elections are non-preemptive. Once a DR and BDR are elected on a multiaccess broadcast network, a newly added router with a higher interface priority (such as R4 with priority 255) will remain in the DROTHER state. To force a new election where R4 can claim the DR role based on its priority, the OSPF adjacencies across the segment must be restarted using the `clear ip ospf process` command.

Step-by-Step Solution

Analyze the current DR/BDR operational roles and OSPF priorities from the output snippet.

R2 (priority 1) is currently the active DR, R3 (priority 1) is the BDR, and R4 (priority 255) is in the DROTHER state.

R4 likely joined the segment after R2 and R3 had already established DR and BDR roles.

Evaluate OSPFv2 preemption behavior.

OSPF DR/BDR elections are non-preemptive. Even though R4 has a higher interface priority (

255 > 1

), it will not displace an active DR or BDR while their OSPF processes remain operational.

Non-preemption prevents network instability and frequent routing table recalculations.

Determine the necessary operational command to trigger a fresh election.

Executing `clear ip ospf process` forces all routers on the broadcast domain to reset their OSPF adjacencies and conduct a new DR/BDR election.

During a new election with all routers participating simultaneously, R4 will win the DR role because it has the highest configured interface priority.

Key Concept

OSPFv2 DR/BDR elections on broadcast multiaccess networks are non-preemptive; active DR/BDR roles persist until adjacencies are reset or the active DR/BDR interfaces go down.

Question 100Question →

A border router receives a primary IPv4 route for destination network $198.51.100.0/24$ via external BGP (eBGP), which has an administrative distance of $20$ . The network engineer must configure a backup floating static route via next-hop IPv4 address $203.0.113.5$ that remains inactive in the routing table unless the primary eBGP path becomes unavailable. Which command must be configured on the border router to achieve this requirement?

ip route 198.51.100.0 255.255.255.0 203.0.113.5 25

ip route 198.51.100.0 255.255.255.0 203.0.113.5 15

ip route 198.51.100.0 255.255.255.0 203.0.113.5 20

ip route 198.51.100.0 0.0.0.255 203.0.113.5 25

Show answer & explanation

Answer: ip route 198.51.100.0 255.255.255.0 203.0.113.5 25

Answer

The command `ip route 198.51.100.0 255.255.255.0 203.0.113.5 25` correctly configures the backup floating static route.

To configure a floating static route as a backup to an eBGP-learned route (which has a default administrative distance of

20

), the static route must be assigned an administrative distance strictly greater than

20

. Setting the distance to

25

ensures that Cisco IOS places the static route into the routing table only when the eBGP route is withdrawn. Additionally, Cisco IOS static route configuration requires a dotted-decimal subnet mask rather than a wildcard mask.

Step-by-Step Solution

Identify the administrative distance of the primary route protocol.

The primary route is learned via eBGP, which has a default administrative distance of

20

Cisco IOS selects routes with the lowest administrative distance for placement in the routing table.

Determine the required administrative distance for the backup route.

The administrative distance must be set to a value strictly greater than

20

(such as

25

A higher administrative distance keeps the static route floating (inactive) in the background until the primary eBGP path drops.

Verify Cisco IOS IPv4 static route syntax requirements.

The syntax is `ip route <network-prefix> <subnet-mask> <next-hop-ip> [administrative-distance]`.

The command requires a standard subnet mask rather than an OSPF/ACL wildcard mask.

Key Concept

Floating Static Route Administrative Distance Configuration

Estimated Time:1m 30s

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