Examkin

IP Connectivity

493 questions

All types493Multiple choice250Multiple select113Matching25Ordering60Fill in the blank22Short answer23
Question 281Question →

A Cisco IOS router receives an IPv4 packet destined for host 192.168.2.45192.168.2.45. The router's routing table contains a static route configured as `ip route 192.168.2.0 255.255.255.0 10.1.1.2`. Place the processing steps the router executes to resolve the exit interface and encapsulate the packet in the correct sequential order from first to last.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequential order for recursive static route lookup and forwarding is: 1) Match destination IP against the routing table to select the static route; 2) Identify next-hop IP address 10.1.1.2; 3) Perform a recursive lookup in the routing table for 10.1.1.2; 4) Match the connected route 10.1.1.0/24 to determine exit interface GigabitEthernet0/1; 5) Retrieve the ARP table entry for 10.1.1.2 to encapsulate and transmit the frame.
When a static route is configured using only a next-hop IP address (e.g., `ip route 192.168.2.0 255.255.255.0 10.1.1.2`), Cisco IOS must execute a recursive lookup process. The router first matches the packet destination IP (192.168.2.45192.168.2.45) against the static route in the routing table. Second, it identifies the configured next-hop IP (10.1.1.210.1.1.2). Third, it performs a secondary (recursive) lookup for 10.1.1.210.1.1.2 in the routing table. Fourth, it finds the directly connected route (10.1.1.0/2410.1.1.0/24), revealing the physical egress interface (GigabitEthernet0/1). Fifth, it queries the ARP table for the MAC address belonging to 10.1.1.210.1.1.2 to build the Ethernet frame and transmit it out GigabitEthernet0/1.

Step-by-Step Solution

1
Evaluate the incoming packet's destination IPv4 address.
The router matches host destination 192.168.2.45192.168.2.45 to static prefix 192.168.2.0/24192.168.2.0/24.
Routing decisions start by determining the longest matching prefix for the destination IP address.
2
Inspect forwarding parameters specified in the matched static route entry.
The router determines that the route specifies next-hop IP address 10.1.1.210.1.1.2.
Static routes configured strictly with a next-hop IP address do not directly name an exit interface.
3
Execute a recursive lookup for IP address 10.1.1.210.1.1.2.
The router searches the RIB for a route covering 10.1.1.210.1.1.2.
Recursive resolution is mandatory when a next-hop IP is used without an explicit exit interface specification.
4
Resolve the next-hop IP to a connected network route.
The router matches 10.1.1.210.1.1.2 to connected network 10.1.1.0/2410.1.1.0/24 on interface GigabitEthernet0/1.
The connected route provides the physical exit interface necessary to transmit the traffic.
5
Query the ARP table and perform Layer 2 frame encapsulation.
The destination MAC address associated with 10.1.1.210.1.1.2 is acquired and the frame is transmitted via GigabitEthernet0/1.
Multi-access Ethernet media require resolving the next-hop IPv4 address to its target MAC address before physical transmission.

Key Concept

Recursive Routing Lookup for IPv4 Static Routes
Question 282Question →

Refer to the following Cisco IOS command output executed on router R1:

text
R1# show ip ospf interface GigabitEthernet0/0
GigabitEthernet0/0 is up, line protocol is up
Internet Address 192.168.1.1/24, Area 0
Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1
Transmit Delay is 1 sec, State DROTHER, Priority 0
Designated Router (ID) 3.3.3.3, Interface address 192.168.1.3
Backup Designated router (ID) 2.2.2.2, Interface address 192.168.1.2

If the Designated Router (3.3.3.3) fails, which role will router R1 assume on this multiaccess network segment?

Show answer & explanation

Answer: It will remain in the DROTHER state and will not participate in the election.

Answer

Router R1 will remain in the DROTHER state and cannot become the DR or BDR because its interface priority is set to 0.
In OSPFv2 broadcast network types, setting an interface's OSPF priority to 0 disables DR/BDR election eligibility for that interface. Even if the current DR or BDR fails, the router remains in the DROTHER state.

Step-by-Step Solution

1
Examine the interface command output for R1's OSPF priority value.
The output displays 'Priority 0' and 'State DROTHER' for interface GigabitEthernet0/0.
An OSPF interface priority value of 0 explicitly designates the interface as ineligible for DR/BDR election.
2
Evaluate the effect of DR failure on a router with priority 0.
The existing Backup Designated Router (2.2.2.2) promotes to DR, but R1 remains DROTHER because its priority of 0 prevents election qualification.
Routers configured with priority 0 are permanently excluded from DR and BDR roles on broadcast networks.

Key Concept

OSPF Interface Priority 0 DR/BDR Exclusion
Question 283Question →

Router R1 learns the primary route to destination network 10.50.0.0/1610.50.0.0/16 via OSPF, which has a default Administrative Distance of 110. A network engineer must configure a static backup route to the same network that remains inactive in the routing table until the OSPF route fails. Which Administrative Distance value must be assigned to the static route?

Show answer & explanation

Answer: 120

Answer

120
A floating static route functions as a backup path by configuring its Administrative Distance (AD) to be higher than the AD of the primary routing protocol. Since OSPF has an AD of 110, setting the static route's AD to 120 ensures it is kept out of the routing table until the primary OSPF route becomes unavailable.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary dynamic routing protocol.
OSPF has a primary AD of 110.
Cisco IOS selects routes based on lower Administrative Distance values when multiple paths to the same destination exist.
2
Determine the required AD relationship for a floating static backup route.
The static route AD must be strictly greater than 110.
A floating static route must have a higher AD than the primary route so it remains hidden until the primary route disappears.
3
Select the option with an AD greater than 110.
120 is greater than 110.
Using an AD of 120 keeps the static route out of the routing table during normal operation.

Key Concept

Floating Static Route Administrative Distance Configuration
Estimated Time:45s
Question 284Question →

An enterprise router R1 learns an internal EIGRP route to the destination network 10.50.40.0/2410.50.40.0/24 with an Administrative Distance of 90. A network administrator attempts to configure a floating static backup route for this target subnet via next-hop address 192.168.12.2192.168.12.2 by issuing the command `ip route 10.50.40.0 255.255.255.0 192.168.12.2 85`. Which statement accurately describes the operational impact of this configuration on router R1?

Show answer & explanation

Answer: The static route immediately replaces the primary EIGRP route in the active routing table because its configured Administrative Distance of 85 is lower than EIGRP's Administrative Distance of 90.

Answer

The static route pre-empts the primary EIGRP route and becomes the primary active route in the routing table because its configured Administrative Distance of 85 is lower than internal EIGRP's Administrative Distance of 90.
In Cisco IOS routing, when multiple routing sources provide a path to the exact same prefix, the router installs the route with the lowest Administrative Distance (AD). Internal EIGRP has a default AD of 90. By setting the static route's AD to 85, the static route is considered more trustworthy than EIGRP and immediately pre-empts the EIGRP route in the routing table.

Step-by-Step Solution

1
Identify the Administrative Distance (AD) of the primary dynamic protocol.
Internal EIGRP has a default AD of 90.
Administrative Distance represents trustworthiness; lower values are preferred.
2
Analyze the configured static route parameter.
The command specifies an explicit AD metric of 85 (`ip route 10.50.40.0 255.255.255.0 192.168.12.2 85`).
The final optional integer argument in an `ip route` command sets the custom AD value.
3
Compare the AD values of both sources for the exact same destination prefix.
Static AD (85) < EIGRP AD (90).
To create a floating static route (backup), the configured AD MUST be higher than the primary route's AD (e.g., > 90). Setting it lower causes the static route to pre-empt the primary dynamic route.

Key Concept

Floating Static Route Administrative Distance Selection
Question 285Question →

An administrator configures OSPFv2 on a Cisco router with an active Loopback0 interface assigned IP address 10.254.1.1/32 and an active GigabitEthernet0/0 interface assigned IP address 172.20.10.1/24. Within OSPF router configuration mode, the administrator executes the command `router-id 1.1.1.1`. What IP address will the router process select as its OSPF Router ID upon initialization?

Show answer & explanation

Answer: 1.1.1.1

Answer

1.1.1.1
The explicit `router-id` command takes highest priority in OSPFv2 Router ID selection. Therefore, 1.1.1.1 is selected as the Router ID.

Step-by-Step Solution

1
Evaluate the OSPF Router ID election priority rules.
The selection order is: 1) Manually configured `router-id` command, 2) Highest IPv4 address on active loopback interfaces, 3) Highest IPv4 address on active physical interfaces.
An explicit manual configuration takes top priority and overrides dynamic interface election logic.
2
Apply the parameters given in the scenario to determine the winning Router ID.
Because `router-id 1.1.1.1` is explicitly configured under the OSPF process, the router selects 1.1.1.1 regardless of Loopback0 (10.254.1.1) or GigabitEthernet0/0 (172.20.10.1).
Interface IP addresses are only evaluated when an explicit `router-id` command is absent.

Key Concept

OSPFv2 Router ID Selection Precedence
Question 286Question →

A network engineer is configuring IPv6 static routes on a Cisco router to forward traffic to the destination network 2001:db8:acad:10::/642001:\text{db8}:\text{acad}:10::/64. The primary path must use the neighbor's link-local address fe80::2\text{fe80}::2 via the local exit interface GigabitEthernet0/0/1. A secondary floating static route must use the global unicast next-hop address 2001:db8:acad:3::22001:\text{db8}:\text{acad}:3::2 with an administrative distance of 130. Which two commands must be configured on the router?

Select all that apply

Show answer & explanation

Answer: ipv6 route 2001:db8:acad:10::/64 gigabitethernet0/0/1 fe80::2; ipv6 route 2001:db8:acad:10::/64 2001:db8:acad:3::2 130

Answer

The two correct commands are the fully specified static route using interface GigabitEthernet0/0/1 with link-local next-hop fe80::2, and the static route specifying next-hop 2001:db8:acad:3::2 with administrative distance 130.
The command specifying GigabitEthernet0/0/1 alongside fe80::2 correctly formats a fully specified IPv6 static route using a link-local next-hop address. The command specifying 2001:db8:acad:3::2 followed by 130 correctly configures a floating static route with an administrative distance of 130.

Step-by-Step Solution

1
Identify the mandatory syntax requirement for IPv6 static routes using link-local next-hop addresses.
Link-local addresses (fe80::/10) are non-routable and ambiguous without a specific local interface identifier. Therefore, the command must include the local exit interface alongside the link-local next-hop address.
Cisco IOS requires a fully specified route format whenever a link-local address serves as the next hop.
2
Evaluate the administrative distance configuration for the backup floating static route.
The backup route uses global unicast next-hop 2001:db8:acad:3::2 and requires an administrative distance higher than the primary route (default AD = 1), so 130 must be appended to the command.
Floating static routes remain inactive in the routing table until the primary route fails, which occurs only if their administrative distance is higher than the primary route's AD.

Key Concept

IPv6 Static Route Command Syntax and Floating Static Route AD Configuration
Question 287Question →

A network administrator is troubleshooting an OSPFv2 connection between two directly connected routers, R1 and R2, over a point-to-point Ethernet link. Executing `show ip ospf neighbor` on R1 reveals that the neighbor state for R2 is perpetually stuck in the `EXSTART/ -` state.

Which misconfiguration is the most likely root cause of this neighbor adjacency state?

Show answer & explanation

Answer: The interface MTU setting on R1 does not match the interface MTU setting on R2.

Answer

The interface MTU setting on R1 does not match the interface MTU setting on R2.
In OSPFv2, routers exchange Database Description (DBD) packets during the EXSTART and EXCHANGE states to negotiate Master/Slave roles and initial sequence numbers. The DBD packet header explicitly contains the originating interface's MTU setting. If the MTU values on the interconnected interfaces do not match, the router with the smaller MTU will drop DBD packets that exceed its size or reject incoming DBDs carrying a higher MTU value. As a result, the neighbor negotiation stalls and remains stuck in the EXSTART (or EXCHANGE) state.

Step-by-Step Solution

1
Analyze OSPF Neighbor States and Hello exchange requirements
Parameters like Area ID, Hello/Dead timers, Subnet Mask, and Authentication must match in Hello packets to form 2-Way neighbor state.
If Hello packet parameters mismatch, the routers cannot form a bidirectional 2-Way relationship.
2
Analyze the EXSTART/EXCHANGE state behavior
In EXSTART, routers elect a Master/Slave relationship and exchange initial Database Description (DBD) packets containing the interface MTU value.
OSPF includes its interface MTU in the DBD packet header. If receiving router MTU is lower than sender MTU (or MTU mismatch enforcement is active), DBD packets are ignored or dropped.
3
Determine the root cause of neighbor stuck in EXSTART state
Mismatched interface MTU values cause DBD retransmissions and prevent the routers from completing ExStart/Exchange into Loading and Full states.
The correct solution identifies interface MTU mismatch as the primary cause of an OSPF neighbor relationship becoming stuck in EXSTART.

Key Concept

OSPFv2 Neighbor States and MTU Mismatch Behavior
Estimated Time:2m 0s
Question 288Question →

You are configuring a secondary gateway path on a corporate router for destination subnet 192.168.88.0/24 via next-hop IP address 10.5.5.2. The primary active route is learned dynamically via OSPF, which carries a default administrative distance of 110. What is the lowest administrative distance integer value that must be assigned at the end of the CLI command to ensure this static route functions as a floating backup route?

Fill in the blanks below

ip route 192.168.88.0 255.255.255.0 10.5.5.2
Show answer & explanation

Answer

111
A floating static route acts as a backup path and only enters the routing table when the primary routing path fails. Because Cisco routers prefer routes with lower administrative distance values, a floating static route must have an administrative distance higher than the primary route protocol. Since OSPF has a default administrative distance of 110, the lowest integer value that makes the static route floating is 111.

Step-by-Step Solution

1
Identify the administrative distance of the primary route.
The primary route is learned via OSPF, which has a default administrative distance of 110.
Cisco routers use administrative distance to rank route trustworthiness, preferring lower values.
2
Determine the minimum administrative distance required for a floating static backup route.
To ensure the static route remains inactive while OSPF is operational, its administrative distance must be strictly greater than 110.
The lowest integer greater than 110 is 111.

Key Concept

Floating Static Route Administrative Distance Selection
Estimated Time:45s
Question 289Question →

A network administrator initializes OSPFv2 on Router R1 when only interface GigabitEthernet0/0 (10.0.12.1/24) and Loopback 1 (172.31.1.1/24) are active. Later, the administrator performs two additional configuration changes on R1 without restarting the OSPF process:
1. Brings up Loopback 0 with IP address 10.254.254.1/32.
2. Configures `router-id 192.168.1.1` under the OSPF routing process.

Directly connected to R1's GigabitEthernet0/0 interface is Router R2 (10.0.12.2/24). R1's GigabitEthernet0/0 interface is assigned to OSPF Area 0, whereas R2's GigabitEthernet0/0 interface is configured for OSPF Area 1. Both routers share identical Hello/Dead timers and MTU settings.

Assuming no OSPF process resets have occurred, what is R1's active OSPF Router ID, and what neighbor relationship status will R1 report for R2?

Show answer & explanation

Answer: R1's active Router ID is 172.31.1.1, and no OSPF neighbor entry is established for R2.

Answer

R1's active Router ID remains 172.31.1.1, and no OSPF neighbor relationship is formed (no neighbor entry appears in R1's OSPF neighbor table).
OSPF Router ID election occurs when the OSPF process initializes. Once an active Router ID is chosen (in this case, 172.31.1.1 from the highest active loopback at process start), subsequent configuration changes—such as setting a manual 'router-id' or activating another loopback—do not alter the active Router ID until the OSPF process is explicitly reset via 'clear ip ospf process'. Furthermore, OSPF neighbor discovery requires matching Area IDs in Hello packets. Because R1 is in Area 0 and R2 is in Area 1, incoming Hello packets are dropped, resulting in no OSPF neighbor relationship being formed at all.

Step-by-Step Solution

1
Determine R1's active OSPF Router ID.
R1 selected 172.31.1.1 upon OSPF initialization because Loopback 1 was the highest IP among active loopback interfaces.
OSPF Router ID election logic follows: manual 'router-id' > highest active loopback IP > highest active physical interface IP. However, Router ID election is non-preemptive. Adding a manual 'router-id' or bringing up a higher loopback IP (Loopback 0) later does NOT update the active Router ID until the process is restarted using 'clear ip ospf process' or a system reboot.
2
Evaluate the OSPF Hello packet exchange and neighbor adjacency conditions.
R1 (Area 0) and R2 (Area 1) have an Area ID mismatch in their OSPF Hello packet headers.
For two OSPFv2 routers to establish a neighbor relationship, key parameters in the Hello packet must match identically: Area ID, Subnet Mask, Hello/Dead Timers, Authentication, and Stub Area flag. If the Area ID mismatches, received Hello packets are silently discarded.
3
Determine the resulting OSPF neighbor state.
No neighbor state (or neighbor entry) exists.
Because Hello packets are dropped on receipt due to the Area ID mismatch, neither router discovers the other, preventing even the INIT state from being reached.

Key Concept

OSPFv2 Router ID Stability & Mandatory Hello Packet Adjacency Parameters
Question 290Question →

A network engineer is configuring static routes on a Cisco IOS router to forward traffic to remote IPv6 networks. Which TWO statements accurately describe the requirements and behavior of IPv6 static route configurations? (Select TWO.)

Select all that apply

Show answer & explanation

Answer: When specifying an IPv6 link-local address as the next-hop address, the local exit interface MUST also be specified in the command.; To configure a floating static IPv6 backup route, the administrative distance value must be set higher than the administrative distance of the primary route.

Answer

The correct statements are: specifying the local exit interface is mandatory when using a link-local next-hop address, and configuring a floating static route requires an administrative distance higher than the primary route.
In Cisco IOS IPv6 static routing, link-local next-hop addresses require the specifying of the local exit interface because link-local addresses are ambient to the specific interface link. Furthermore, creating a backup (floating) static route requires setting an administrative distance value strictly higher than the primary route so it remains inactive until the primary path fails.

Step-by-Step Solution

1
Analyze link-local next-hop requirements
Link-local addresses are non-routable outside their local segment, making the exit interface mandatory for path identification.
Without specifying the exit interface, the router cannot determine which local link connects to the link-local neighbor.
2
Analyze floating static route administrative distance mechanics
Setting a higher administrative distance keeps the static route out of the routing table until the primary route drops.
Lower administrative distance routes are preferred by the Cisco IOS routing table logic.

Key Concept

IPv6 Static Route Next-Hop Types and Administrative Distance Configuration
Question 291Question →

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, 5d12h, GigabitEthernet0/0/0
S 10.200.0.0/16 [1/0] via 192.168.14.2, 3d02h, GigabitEthernet0/0/3
D 10.200.45.0/24 [90/307200] via 192.168.13.2, 00:15:30, GigabitEthernet0/0/2
O 10.200.45.64/29 [110/20] via 192.168.12.2, 00:04:12, GigabitEthernet0/0/1

The router receives a packet with a destination IP address of 10.200.45.6810.200.45.68. Which next-hop IP address and outbound interface will the router select to forward this packet?

Show answer & explanation

Answer: 192.168.12.2 via GigabitEthernet0/0/1

Answer

The router forwards the packet to next-hop IP 192.168.12.2 via GigabitEthernet0/0/1.
When a router receives a packet, it compares the destination IP against all entries in its IP routing table and selects the match with the longest subnet mask (Longest Prefix Match). The subnet 10.200.45.64/29 covers IP addresses 10.200.45.64 through 10.200.45.71, which includes host 10.200.45.68. Because /29 is more specific than /24, /16, or /0, the router chooses next-hop 192.168.12.2 via GigabitEthernet0/0/1.

Step-by-Step Solution

1
Identify all candidate routes that match destination IP 10.200.45.68
Matching routes: 0.0.0.0/0 (matches all), 10.200.0.0/16 (range 10.200.0.0-10.200.255.255), 10.200.45.0/24 (range 10.200.45.0-10.200.45.255), and 10.200.45.64/29 (range 10.200.45.64-10.200.45.71).
Before comparing administrative distance, the router identifies all routes whose network/prefix bounds contain the target IP.
2
Apply the Longest Prefix Match (LPM) rule across candidate routes
Prefix lengths are /0, /16, /24, and /29. The longest prefix match is /29.
The router always prioritizes the route with the most specific prefix (highest number of network bits).
3
Select the forwarding decision based on the winning route entry
The route for 10.200.45.64/29 points to next-hop 192.168.12.2 via interface GigabitEthernet0/0/1.
Administrative Distance is not evaluated across different prefix lengths, so the OSPF route /29 wins outright.

Key Concept

Longest Prefix Match Rule in Cisco IPv4 Forwarding Logic
Question 292Question →

Two Cisco routers, R1 and R2, are directly connected over their GigabitEthernet0/0 interfaces in OSPFv2 Area 0. Interface GigabitEthernet0/0 on R1 has an IP address of 172.16.12.1/24172.16.12.1/24 with a default IP MTU of 15001500 bytes. Interface GigabitEthernet0/0 on R2 has an IP address of 172.16.12.2/24172.16.12.2/24 and its IP MTU has been modified to 14001400 bytes. Both routers successfully exchange Hello packets and recognize each other as neighbors, but the output of `show ip ospf neighbor` on R1 shows R2 perpetually stuck in the `EXSTART` state.

If the network administrator cannot alter the IP MTU size on either router interface, which configuration command must be configured under interface GigabitEthernet0/0 to allow the OSPF neighbor relationship to reach the `FULL` state?

Show answer & explanation

Answer: Apply the `ip ospf mtu-ignore` command under the interface configuration mode on either or both routers.

Answer

The neighbor relationship can reach the FULL state by configuring the `ip ospf mtu-ignore` command on the interface with the MTU mismatch.
The correct option applies `ip ospf mtu-ignore` under interface configuration mode. When OSPF routers transition from 2-WAY to EXSTART, they negotiate Master/Slave roles and exchange Database Description (DBD) packets. Each router includes its interface MTU in the DBD packet. If there is an MTU mismatch, the router receiving the larger MTU value drops or ignores the DBD packet, keeping the adjacency stuck in EXSTART (or EXCHANGE). Executing `ip ospf mtu-ignore` forces OSPF to ignore the MTU value in incoming DBD packets, allowing the exchange to proceed to the FULL state.

Step-by-Step Solution

1
Analyze the OSPF neighbor state
Neighbors reached the EXSTART state, confirming that Hello packet parameters (Area ID, Subnet Mask, Hello/Dead timers, Authentication) match.
Mismatched Hello parameters prevent neighbors from reaching 2-WAY or EXSTART entirely.
2
Identify the cause of the EXSTART state lockup
R1 has an IP MTU of 15001500 bytes while R2 has an IP MTU of 14001400 bytes.
During the EXSTART/EXCHANGE state, routers exchange Database Description (DBD) packets containing the interface MTU field. If a router receives a DBD packet specifying an MTU higher than its local interface MTU, it will reject the packet and remain stuck in EXSTART/EXCHANGE.
3
Select the appropriate mitigation command
Applying `ip ospf mtu-ignore` on the interface disables the MTU mismatch check during DBD negotiation.
This allows DBD packet processing to continue without modifying the physical or logical interface MTU values.

Key Concept

OSPF Neighbor Adjacencies and MTU Negotiation in ExStart State
Question 293Question →

An administrator is troubleshooting an OSPFv2 adjacency issue between two directly connected Cisco routers, R1 and R2. Executing `show ip ospf neighbor` on R1 displays the neighbor state for R2 as stuck in `INIT/ -`. Which network condition or configuration error is the primary cause of this specific neighbor state?

Show answer & explanation

Answer: An Access Control List (ACL) on R2 is filtering incoming OSPF Hello packets sent by R1, creating unidirectional communication.

Answer

An Access Control List (ACL) on R2 is filtering incoming OSPF Hello packets sent by R1, creating unidirectional communication.
The OSPF INIT state means a router has received a Hello packet from a neighbor, but the receiving router's own Router ID was not included in the neighbor's list of seen routers. This condition indicates one-way (unidirectional) communication. If an Access Control List on the remote router blocks incoming OSPF multicast or unicast traffic from the local router, the remote router will never record the local router's ID, causing the local router to remain stuck in the INIT state.

Step-by-Step Solution

1
Analyze the reported OSPF neighbor state
The neighbor state is `INIT/ -`.
The INIT state signifies that R1 has successfully received OSPF Hello packets from R2, but R1's own Router ID was not listed in R2's Hello packet active neighbor list.
2
Evaluate the cause of unidirectional Hello reception
R2 is sending Hellos to R1 (which R1 receives), but R2 is not receiving Hellos from R1.
If an ACL on R2 drops R1's incoming Hellos, R2 never processes R1's Hello, so R2 does not add R1's Router ID to its outgoing Hello packets.
3
Distinguish INIT state causes from DOWN and EXSTART state causes
Parameter mismatches (Area ID, Hello/Dead timers, Authentication) cause packets to be dropped before reaching INIT (remaining DOWN). MTU mismatches cause neighbors to freeze in EXSTART/EXCHANGE.
Only unidirectional traffic flow (such as an ACL blocking traffic in one direction) allows Hello reception without mutual Router ID acknowledgment.

Key Concept

OSPFv2 Neighbor States and Unidirectional Communication Troubleshooting
Estimated Time:1m 30s
Question 294Question →

An administrator needs to manually configure an IPv4 static route on a Cisco router to reach remote network 172.20.10.0/24172.20.10.0/24 using the next-hop IP address 10.0.0.210.0.0.2, and then permanently save the configuration. What is the correct sequence of steps to complete this configuration starting from Privileged EXEC mode?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order to enter global configuration mode, apply the static route command with the correct prefix, subnet mask, and next-hop IP, exit back to privileged EXEC mode, and save the active configuration to NVRAM is: Enter global configuration mode (`configure terminal`), Configure the static route (`ip route 172.20.10.0 255.255.255.0 10.0.0.2`), Return to privileged EXEC mode (`end`), and Save the configuration (`copy running-config startup-config`).
Configuring a persistent IPv4 static route on a Cisco router requires moving to global configuration mode via `configure terminal`, applying the static route with `ip route 172.20.10.0 255.255.255.0 10.0.0.2`, exiting back to privileged EXEC mode using `end`, and finally writing the running configuration to NVRAM using `copy running-config startup-config`.

Step-by-Step Solution

1
Transition from Privileged EXEC mode (`Router#`) to Global Configuration mode (`Router(config)#`).
The router prompt changes to `Router(config)#`, allowing structural configuration commands.
Static routes cannot be defined directly in Privileged EXEC mode.
2
Issue the IPv4 static route command `ip route 172.20.10.0 255.255.255.0 10.0.0.2`.
The static route is added to the running configuration and installed into the IPv4 routing table.
Cisco IOS requires the syntax `ip route <prefix> <mask> <next-hop-ip|exit-interface>`.
3
Return to Privileged EXEC mode using `end` or `exit`.
The prompt reverts back to `Router#`.
File management and memory write commands must be issued from Privileged EXEC mode.
4
Write the active configuration from RAM to NVRAM using `copy running-config startup-config`.
The current running-config is saved to startup-config in NVRAM.
Without saving, configuration modifications will be lost if the device loses power or reboots.

Key Concept

Cisco IOS IPv4 Static Route CLI Configuration Workflow
Question 295Question →

Match each OSPFv2 network type or interface configuration setting to its corresponding DR/BDR election behavior.

Click a left item, then click its matching right item

Items

Broadcast network type
Point-to-Point network type
OSPF interface priority set to 0

Matches

Show answer & explanation

Answer

Broadcast network type matches with electing a DR and BDR. Point-to-Point network type matches with not electing a DR or BDR. An OSPF interface priority set to 0 matches with ineligibility for DR/BDR election.
Broadcast network types require a Designated Router (DR) and Backup Designated Router (BDR) to minimize adjacency traffic across shared multiaccess segments. Point-to-Point network types connect only two routers, so DR and BDR elections are omitted completely. Configuring an OSPF interface priority of 0 excludes that router from participating in elections, forcing its role to DROTHER.

Step-by-Step Solution

1
Identify the election requirement for multiaccess media.
Broadcast networks elect a DR and BDR to manage adjacencies.
Ethernet broadcast networks are multiaccess, requiring centralized LSA flooding via DR/BDR.
2
Identify the election requirement for point-to-point media.
Point-to-Point networks form full adjacencies directly between the two endpoints without electing a DR or BDR.
There are only two devices on a point-to-point link, so a DR/BDR role provides no architectural benefit.
3
Determine the effect of configuring priority 0.
Setting ip ospf priority 0 makes the interface ineligible to become a DR or BDR.
Priority 0 is specifically reserved in OSPF to ensure a router stays in the DROTHER state regardless of Router ID.

Key Concept

OSPF DR/BDR Election Mechanics and Interface Types
Estimated Time:45s
Question 296Question →

Complete the Cisco IOS command below to configure a floating static route for destination network 10.40.15.0/2410.40.15.0/24 using next-hop IP address 192.168.254.2192.168.254.2 to serve as a backup for a primary route learned via Internal EIGRP (Administrative Distance 90), specifying an administrative distance of 130130.

Fill in the blanks below

Router(config)# ip route 10.40.15.0 255.255.255.0
Show answer & explanation

Answer

The completed Cisco IOS configuration command is `ip route 10.40.15.0 255.255.255.0 192.168.254.2 130`.
In Cisco IOS, the syntax for a static route is `ip route <prefix> <mask> <next-hop-ip> [administrative_distance]`. Specifying `192.168.254.2` as the next-hop IP address and appending `130` configures a floating static route. Because 130 is higher than Internal EIGRP's administrative distance of 90, the router keeps this static route inactive in the routing table until the primary EIGRP route is removed.

Step-by-Step Solution

1
Identify the target network prefix and network mask.
The target prefix is 10.40.15.010.40.15.0 and the subnet mask for /24/24 is 255.255.255.0255.255.255.0.
Cisco IOS static route syntax requires the destination network prefix followed by its subnet mask.
2
Identify the next-hop IP address.
The next-hop IP address for the first blank is 192.168.254.2192.168.254.2.
Traffic destined for 10.40.15.0/2410.40.15.0/24 over the backup link will be forwarded to this next-hop IP.
3
Determine the administrative distance value to make the static route floating.
The administrative distance for the second blank is 130130.
An administrative distance value greater than the primary routing protocol's AD (Internal EIGRP AD = 90) ensures the static route remains floating (inactive in the routing table) until the primary route fails.

Key Concept

Floating Static Route Configuration & Administrative Distance
Question 297Question →

Two Cisco routers, R1 and R2, are connected via a direct GigabitEthernet link. R1 has been configured with an explicit OSPF router ID of 1.1.1.1. Router R2 has no explicit router ID configured under its OSPF process, but has the following active interfaces:
- Loopback0: 10.10.10.1/32 (up/up)
- Loopback1: 10.20.20.1/32 (up/up)
- GigabitEthernet0/0: 172.16.1.1/24 (up/up)

Which two conditions or behaviors accurately reflect the OSPFv2 Router ID selection and neighbor adjacency formation process between R1 and R2? (Select two.)

Select all that apply

Show answer & explanation

Answer: Router R2 automatically selects 10.20.20.1 as its OSPF router ID because it is the highest IP address among active loopback interfaces.; Hello intervals, Dead intervals, Area IDs, and subnet masks must match between R1 and R2 for a neighbor relationship to form across the link.

Answer

The correct statements are that R2 automatically selects 10.20.20.1 as its router ID (highest IP address among active loopbacks), and that Hello intervals, Dead intervals, Area IDs, and subnet masks must match between the neighbors to establish adjacency.
Router ID selection follows a strict order: explicit 'router-id' command > highest active loopback IP > highest active physical interface IP. Since R2 has active loopback interfaces, 10.20.20.1 is selected as the highest loopback IP. Additionally, OSPF neighbor formation strictly requires matching Hello/Dead timers, Area ID, Subnet Mask, and Authentication flags in exchanged Hello packets.

Step-by-Step Solution

1
Evaluate the OSPF Router ID election logic for R2
Since no explicit 'router-id' command exists, OSPF evaluates active loopbacks. Loopback1 (10.20.20.1) is higher than Loopback0 (10.10.10.1).
Loopback interfaces take precedence over physical interfaces, and the highest IPv4 address among loopbacks is chosen.
2
Evaluate mandatory OSPF Hello packet fields for neighbor adjacency
Hello timer, Dead timer, Area ID, Subnet Mask (on multiaccess/point-to-point), and authentication credentials must match in incoming Hello packets.
Mismatches in any of these primary Hello fields prevent routers from transitioning past the INIT state.
3
Analyze the impact of MTU mismatches
MTU is negotiated in DBD packets during ExStart state, not in initial Hello exchanges.
Hello packets are exchanged successfully despite MTU mismatches, but adjacency fails during database description synchronization.

Key Concept

OSPFv2 Router ID Precedence and Hello Packet Neighbor Adjacency Requirements
Estimated Time:2m 0s
Question 298Question →

A network administrator is configuring a static route on a Cisco router using a link-local address (fe80::2) as the next hop to reach the remote network 2001:db8:10:20::/64. The local egress interface is GigabitEthernet0/0/1. Which Cisco IOS command correctly configures this route?

Show answer & explanation

Answer: ipv6 route 2001:db8:10:20::/64 GigabitEthernet0/0/1 fe80::2

Answer

The correct command is 'ipv6 route 2001:db8:10:20::/64 GigabitEthernet0/0/1 fe80::2'.
When configuring an IPv6 static route using a link-local next-hop address, Cisco IOS requires a fully specified static route where the local exit interface (GigabitEthernet0/0/1) is provided prior to the next-hop IPv6 address (fe80::2).

Step-by-Step Solution

1
Identify the global configuration command syntax for IPv6 static routing.
The command structure must start with 'ipv6 route' followed by destination-prefix/prefix-length.
IPv6 static routes in Cisco IOS require the 'ipv6 route' keyword.
2
Determine the formatting requirements for link-local next-hop addresses.
Because link-local addresses (FE80::/10) are reused across multiple links, the router requires a fully specified route that includes the local exit interface before the link-local next-hop address.
Without specifying the exit interface, Cisco IOS rejects the link-local next hop as ambiguous.

Key Concept

Fully Specified IPv6 Static Routes using Link-Local Next-Hop Addresses
Question 299Question →

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

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order of precedence for OSPF DR election tie-breaking is: 1) Highest OSPF interface priority setting, 2) Highest manually configured OSPF router ID, 3) Highest IPv4 address on an active loopback interface, and 4) Highest IPv4 address on an active physical interface.
The Designated Router election first evaluates the interface priority configured on the multiaccess segment. If priorities tie, OSPF resolves the election using the router's Router ID (RID). The RID is determined in order by: 1) explicit manual configuration via 'router-id', 2) highest IP address on an active loopback interface, and 3) highest IP address on an active physical interface.

Step-by-Step Solution

1
Evaluate segment interface priority
Highest interface priority wins the election (priority 0 disqualifies a router from becoming DR/BDR).
Interface priority (configured via 'ip ospf priority') is the top-level override mechanism for DR selection.
2
Check for explicit OSPF Router ID
If interface priorities tie, OSPF compares Router IDs, prioritizing a manually configured 'router-id'.
Manual Router ID configuration under the 'router ospf' process overrides dynamic interface IP selection.
3
Check active loopback interfaces
If no manual router ID is present, the highest IPv4 address on an active loopback interface is chosen as the Router ID.
Loopback interfaces offer stability over physical interfaces because they do not rely on physical link state.
4
Check active physical interfaces
If no loopback interfaces exist, the highest IPv4 address on an up/up physical interface becomes the Router ID.
This serves as the final dynamic tie-breaker for establishing the OSPF Router ID when no explicit or loopback settings exist.

Key Concept

OSPFv2 DR/BDR Election Precedence and Router ID Selection Criteria
Estimated Time:1m 0s
Question 300Question →

Two directly connected Cisco routers, R1 and R2, are configured for OSPFv2 on their GigabitEthernet0/0 interfaces. Router R1 has its interface configured in OSPF Area 0, while Router R2 has its connecting interface configured in OSPF Area 1. All physical interfaces and IP subnet parameters are operating correctly.

What is the expected OSPF neighbor outcome between R1 and R2?

Show answer & explanation

Answer: The routers will fail to establish an OSPF neighbor relationship because Area IDs in Hello packets must match.

Answer

The routers will fail to establish an OSPF neighbor relationship because Area IDs in Hello packets must match.
For two routers to form an OSPFv2 neighbor relationship, specific fields in their Hello packets must match exactly on the interconnecting link. These required matching parameters include the Area ID, Subnet Mask, Hello and Dead intervals, Primary IP Subnet, Authentication credentials, and Stub Area flag. Because R1 is configured in Area 0 and R2 is configured in Area 1, their Hello packets will be dropped by the receiving interfaces, and no neighbor relationship will be established.

Step-by-Step Solution

1
Analyze OSPF Hello packet matching requirements for neighbor adjacency.
Identify that the Area ID field is a mandatory matching parameter in OSPFv2 Hello packets.
For two routers to establish any OSPF neighbor state (starting from Init), primary parameters in the Hello packet must match exactly.
2
Compare the interface configuration settings of R1 and R2.
R1 is in Area 0 and R2 is in Area 1.
The Area IDs on the interconnecting link are mismatched.
3
Determine the impact of the Area ID mismatch on neighbor discovery.
R1 drops Hello packets received from R2 (and vice versa), preventing neighbor formation completely.
When a router receives an OSPF Hello packet with a mismatched Area ID, it drops the packet without adding the sending router to its neighbor table.

Key Concept

OSPFv2 Neighbor Adjacency Requirements
PreviousPage 15 / 25Next
IP Connectivity Practice Questions — Cisco CCNA — Page 15 | Examkin