IP Connectivity

493 questions

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

A network administrator is configuring a backup floating static route to reach an external corporate subnet 172.31.50.0/24. The primary path to this destination is learned dynamically via External BGP (eBGP). During testing while the primary eBGP connection is fully operational, the administrator observes that traffic toward 172.31.50.0/24 is being forwarded across the backup static path rather than the primary link. Which static route command entry in the router configuration caused this improper failover behavior?

ip route 172.31.50.0 255.255.255.0 192.168.12.2 15

ip route 172.31.50.0 255.255.255.0 192.168.12.2 25

ip route 172.31.50.0 255.255.255.0 192.168.12.2 90

ip route 172.31.50.0 255.255.255.0 192.168.12.2 110

Show answer & explanation

Answer: ip route 172.31.50.0 255.255.255.0 192.168.12.2 15

Answer

The command 'ip route 172.31.50.0 255.255.255.0 192.168.12.2 15' sets the administrative distance lower than eBGP, causing it to preempt the primary route.

Cisco IOS assigns default Administrative Distance values to evaluate route trustworthiness. External BGP (eBGP) routes carry a default AD of 20. To create a floating static backup route for an eBGP path, the trailing administrative distance argument in the 'ip route' command must be set higher than 20. Specifying an administrative distance of 15 makes the static route more preferred than the eBGP route (15 < 20), causing the router to immediately install the static path into the routing table even when the eBGP link is active.

Step-by-Step Solution

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

External BGP (eBGP) has a Cisco default Administrative Distance of 20.

Administrative Distance determines route trustworthiness when multiple sources advertise the exact same network prefix.

Evaluate the requirement for a floating static route.

A floating static route must have an AD strictly greater than the primary route's AD (greater than 20) so it stays inactive until the primary route drops out of the routing table.

The router installs the route with the lowest AD into the IP routing table.

Analyze the configured static route entries to identify why the backup route preempted the primary path.

Configuring an administrative distance of 15 gives the static route a lower AD than eBGP (15 < 20).

Because 15 is lower than 20, the router selects the static route over the operational eBGP path.

Key Concept

Floating Static Route Administrative Distance relative to eBGP

Estimated Time:1m 30s

Question 262Question →

A network engineer is configuring OSPFv2 between two directly connected routers over a GigabitEthernet link. Although physical link connectivity is established, OSPF neighbor discovery fails and no adjacency is formed. Which two interface-level parameters must match on both routers' interconnecting interfaces for an OSPFv2 neighbor relationship to establish? (Select two.)

Select all that apply

OSPF Area ID

OSPF Process ID

OSPF Hello and Dead timer intervals

OSPF Router Priority

Show answer & explanation

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

Answer

The OSPF Area ID and the OSPF Hello and Dead timer intervals must match on both interconnecting interfaces.

For two routers to establish an OSPFv2 neighbor adjacency, specific fields exchanged in Hello packets must match. These include the OSPF Area ID, Hello and Dead timer intervals, subnet mask, and authentication parameters. If either the Area ID or the Hello/Dead timers differ, Hello packets are discarded and the routers remain in a DOWN or INIT state.

Step-by-Step Solution

Analyze OSPF Hello packet fields required for neighbor establishment

Identify parameters carried in Hello packets that must agree between neighboring routers.

Routers drop incoming Hello packets if key fields in the Hello header do not match local interface configurations.

Verify matching requirements

Confirm that Area ID, Hello timer, Dead timer, Subnet Mask, and Authentication fields must match.

These mandatory matching fields ensure routers belong to the same logical area and communicate on compatible schedules.

Evaluate local vs global OSPF parameters

Process ID and Router Priority do not need to match.

Process ID is purely local to the router's IOS memory, and Router Priority determines DR/BDR election roles rather than neighbor eligibility.

Key Concept

OSPFv2 Mandatory Hello Packet Neighbor Matching Parameters

Estimated Time:1m 15s

Question 263Question →

A branch router receives an external EIGRP route (EIGRP EX, Administrative Distance of 170) for the corporate subnet $10.200.0.0/16$ over a primary MPLS link. A network administrator must configure a floating static backup route for $10.200.0.0/16$ using the secondary ISP next-hop address $192.168.1.2$ . The backup path must only be installed in the IPv4 routing table if the primary EIGRP EX path becomes unavailable. Which command must be configured on the router to achieve this requirement?

ip route 10.200.0.0 255.255.0.0 192.168.1.2 175

ip route 10.200.0.0 255.255.0.0 192.168.1.2 90

ip route 10.200.0.0 255.255.0.0 192.168.1.2 170

ip route 10.200.0.0 0.0.255.255 192.168.1.2 175

Show answer & explanation

Answer: ip route 10.200.0.0 255.255.0.0 192.168.1.2 175

Answer

The command 'ip route 10.200.0.0 255.255.0.0 192.168.1.2 175' correctly configures the floating static route.

A floating static route acts as a backup path and must have an Administrative Distance (AD) strictly higher than the primary route currently in use. Because External EIGRP routes have a default AD of 170, the backup static route must be configured with an AD greater than 170 (such as 175). Furthermore, Cisco IOS static route syntax requires the destination network mask to be specified as a standard subnet mask (255.255.0.0) rather than a wildcard mask.

Step-by-Step Solution

Identify the primary route's Administrative Distance (AD).

External EIGRP (EIGRP EX) routes have a default Administrative Distance of 170.

Floating static routes must have an AD higher than the primary route's AD to remain inactive in the routing table until failure occurs.

Determine the required Administrative Distance for the floating static route.

The static route AD must be strictly greater than 170 (e.g., 175).

Cisco IOS selects routes with lower AD values first. A higher AD keeps the route out of the routing table while the primary path is active.

Verify Cisco IOS IPv4 static route syntax requirements.

The proper command structure is 'ip route <destination-prefix> <subnet-mask> <next-hop-ip> [distance]'.

Static IPv4 routing in Cisco IOS requires a standard dotted-decimal subnet mask (255.255.0.0 for /16), not an OSPF/ACL wildcard mask.

Key Concept

Floating static route configuration requiring higher Administrative Distance than dynamic primary routes

Question 264Question →

Two Cisco routers, R1 and R2, are connected via a dedicated serial link configured for OSPFv2 Area 0. A network engineer runs the command `show ip ospf neighbor` on R1 and notices that the neighbor relationship with R2 remains persistently stuck in the INIT state. Which condition is the most likely cause of this neighbor state?

R2 is receiving R1's OSPF Hello packets, but R2 is rejecting them due to a mismatched Hello/Dead interval and omitting R1's Router ID from its own Hello packets.

An Maximum Transmission Unit (MTU) mismatch exists between R1 and R2, preventing the exchange of Database Description (DBD) packets.

R1's interface OSPF priority is set to 0, which disables its ability to form neighbor adjacencies on point-to-point links.

An inbound Access Control List (ACL) on R1 is blocking incoming multicast traffic sent to destination address 224.0.0.5.

Show answer & explanation

Answer: R2 is receiving R1's OSPF Hello packets, but R2 is rejecting them due to a mismatched Hello/Dead interval and omitting R1's Router ID from its own Hello packets.

Answer

R2 is receiving R1's OSPF Hello packets, but R2 is rejecting them due to a mismatched Hello/Dead interval and omitting R1's Router ID from its own Hello packets.

The correct answer identifies that the INIT state occurs when a local router receives a Hello packet from a peer, but the peer does not list the local router's Router ID in its Hello neighbor field. This typically happens when the peer drops the local router's Hello packets due to mismatched Hello/Dead timers or Area IDs.

Step-by-Step Solution

Analyze what the OSPF INIT state signifies.

The INIT state means a router has received an OSPF Hello packet from a neighbor, but the receiving router's own Router ID is NOT listed in the neighbor field of that received Hello packet.

OSPF requires bidirectional communication. A router only moves past INIT to 2-WAY once it verifies that its peer acknowledges seeing it by listing its Router ID in outbound Hellos.

Determine why R2 would omit R1's Router ID from its Hello packets.

R2 is dropping R1's incoming Hello packets because of mismatched parameters (such as Hello/Dead intervals, Area ID, or authentication passwords).

Because R2 discards R1's incoming Hellos, R2 never processes R1 as a valid neighbor and does not include R1's Router ID in the neighbor list of its own transmitted Hello packets.

Evaluate the incorrect options against OSPF state mechanics.

MTU mismatches freeze adjacencies at ExStart/Exchange; priority 0 affects DR/BDR election eligibility; blocking inbound Hellos at R1 keeps the state DOWN.

Only an asymmetric drop of Hello packets by the peer router explains why R1 hears R2 (moving R1 to INIT) while R2 fails to acknowledge R1.

Key Concept

OSPFv2 Neighbor States and Hello Parameter Verification

Estimated Time:2m 0s

Question 265Question →

A network administrator is configuring a static backup route to take over if an existing primary route learned via OSPF (Administrative Distance 110) fails. Which TWO statements describe requirements for this floating static route to function correctly as a backup?

Select all that apply

The static route must be configured with an administrative distance value greater than 110.

The primary OSPF route must be removed from the routing table before the floating static route can be installed.

The static route must be configured with an administrative distance value lower than 110.

The static route must be configured with an administrative distance value equal to 110.

Show answer & explanation

Answer: The static route must be configured with an administrative distance value greater than 110.; The primary OSPF route must be removed from the routing table before the floating static route can be installed.

Answer

The static route must be configured with an administrative distance value greater than 110, and the primary OSPF route must be removed from the routing table before the floating static route can be installed.

A floating static route serves as a backup path by configuring an administrative distance higher than that of the primary route (greater than 110 for an OSPF primary route). Because routers prefer paths with lower administrative distance, the floating static route will only be installed into the routing table after the primary route fails and is removed.

Step-by-Step Solution

Evaluate the Administrative Distance requirement for backup routes.

Because OSPF has a default Administrative Distance (AD) of 110, a floating static route intended as a backup must be configured with an AD higher than 110 (such as 120).

Cisco IOS selects the route with the lowest AD value to place into the routing table.

Determine the condition under which the floating static route becomes active.

The floating static route remains inactive and out of the routing table until the primary OSPF route is lost or removed.

As long as the primary route with a lower AD exists in the routing table, higher-AD routes are kept in reserve.

Key Concept

Floating static routes use a higher Administrative Distance than the primary route protocol so they only enter the routing table when the primary route fails.

Question 266Question →

When establishing an OSPFv2 neighbor relationship between two directly connected router interfaces, certain interface parameters must be identical. Which two parameters must match for a neighbor adjacency to form successfully? (Select two.)

Select all that apply

OSPF Area ID

Hello and Dead timer intervals

OSPF Process ID

OSPF Router ID

Show answer & explanation

Answer: OSPF Area ID; Hello and Dead timer intervals

Answer

The OSPF Area ID and the Hello and Dead timer intervals must match between directly connected router interfaces to form an OSPFv2 neighbor adjacency.

For two Cisco routers to successfully form an OSPFv2 neighbor adjacency, specific fields exchanged in Hello packets must match. Both connected interfaces must be configured within the same OSPF Area ID and must share identical Hello and Dead timer intervals.

Step-by-Step Solution

Identify OSPFv2 Hello packet requirements for neighbor adjacency formation.

OSPF Hello packets verify essential parameters prior to forming a neighbor relationship.

Mismatched core parameters in Hello packets cause neighbor discovery to fail.

Analyze each candidate parameter against OSPFv2 neighbor requirements.

Area ID and Hello/Dead timers must match. Process ID is locally significant, and Router IDs must be unique rather than matching.

Process IDs do not traverse Hello packets, and duplicate Router IDs conflict within the LSDB.

Key Concept

OSPFv2 Neighbor Adjacency Requirements

Estimated Time:1m 0s

Question 267Question →

A network engineer configures an OSPFv2 routing process on router R1. At startup, the router has two operational interfaces: Loopback0 configured with IP address $10.1.1.1/32$ and GigabitEthernet0/0 configured with IP address $172.16.1.1/24$ . The OSPF process initializes and elects $10.1.1.1$ as its Router ID. Later, the engineer configures a new interface, Loopback1, with IP address $10.200.1.1/32$ . Upon issuing the `show ip ospf` command, the engineer observes that the active OSPF Router ID remains $10.1.1.1$ . Which action must be taken for R1 to begin using $10.200.1.1$ as its active OSPF Router ID?

Execute the clear ip ospf process command in privileged EXEC mode.

Configure the ip ospf priority 255 command under interface Loopback1.

Change the OSPF Area ID on interface Loopback1 to Area 0.

Shut down interface GigabitEthernet0/0 to force OSPF to re-evaluate active interfaces.

Show answer & explanation

Answer: Execute the clear ip ospf process command in privileged EXEC mode.

Answer

The network engineer must execute the 'clear ip ospf process' command in privileged EXEC mode to restart the OSPF routing process and trigger a re-election of the Router ID.

OSPF Router ID election is non-preemptive. Once the OSPF process selects a Router ID during initialization, it retains that ID even if a new interface with a higher IP address becomes active. To force the router to evaluate interfaces again and select the newly configured higher loopback address, the administrator must reset the routing process using the privileged EXEC command 'clear ip ospf process'.

Step-by-Step Solution

Understand OSPF Router ID selection priority.

OSPF Router ID is selected based on: 1) Manually configured 'router-id' command, 2) Highest IP address among active loopback interfaces, 3) Highest IP address among active non-loopback interfaces.

Loopback interfaces are preferred over physical interfaces due to their stability.

Analyze the non-preemptive nature of the OSPF Router ID.

Once an OSPF Router ID is elected and the OSPF process is running, adding a new interface with a higher IP address will NOT dynamically change the active Router ID.

Changing the Router ID dynamically would reset all neighbor adjacencies, so OSPF maintains stability by keeping the current Router ID.

Determine the required action to apply the new Router ID.

To force OSPF to adopt the new highest active loopback IP address (10.200.1.1), the OSPF process must be restarted using 'clear ip ospf process' or by reloading the device.

Restarting the OSPF process re-initializes election parameters and picks the new highest loopback address.

Key Concept

OSPFv2 Router ID Election and Non-Preemptive Behavior

Question 268Question →

A Cisco router receives an IP packet with a destination address of 10.45.12.85. Examine the following excerpt from the router's routing table:

text
Gateway of last resort is 192.168.1.1 to network 0.0.0.0

O 10.45.12.0/25 [110/20] via 192.168.12.2, GigabitEthernet0/0/1
D 10.45.12.64/26 [90/307200] via 192.168.14.2, GigabitEthernet0/0/2
S 10.45.12.80/28 [1/0] via 192.168.16.2, GigabitEthernet0/0/3
O 10.45.12.80/29 [110/50] via 192.168.18.2, GigabitEthernet0/0/4

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

192.168.18.2 via GigabitEthernet0/0/4 because 10.45.12.80/29 is the longest matching prefix for the destination IP address.

192.168.16.2 via GigabitEthernet0/0/3 because the static route has the lowest administrative distance among matching routes.

192.168.14.2 via GigabitEthernet0/0/2 because EIGRP has a lower administrative distance than the OSPF route matching 10.45.12.80/29.

192.168.12.2 via GigabitEthernet0/0/1 because 10.45.12.85 is an invalid host address in a /29 subnet, forcing a fallback to the /25 route.

Show answer & explanation

Answer: 192.168.18.2 via GigabitEthernet0/0/4 because 10.45.12.80/29 is the longest matching prefix for the destination IP address.

Answer

The router forwards the packet to next-hop IP 192.168.18.2 via exit interface GigabitEthernet0/0/4 based on the Longest Prefix Match rule.

When a router receives a packet, it compares the destination IP address (10.45.12.85) against all entries in the routing table. It selects the route with the most specific match (the longest subnet mask prefix length). In this scenario, 10.45.12.80/29 matches 10.45.12.85 (range 10.45.12.80–10.45.12.87) with a 29-bit prefix length, which is longer than /28, /26, /25, or /0. Consequently, the router routes traffic out GigabitEthernet0/0/4 to 192.168.18.2. Administrative distance is ignored because the matching routes do not have identical prefix lengths.

Step-by-Step Solution

Identify all candidate routes matching destination IP 10.45.12.85

Candidate routes: 10.45.12.0/25 (range .0-.127), 10.45.12.64/26 (range .64-.127), 10.45.12.80/28 (range .80-.95), 10.45.12.80/29 (range .80-.87), and default route 0.0.0.0/0.

The router compares the destination IP address against all routing table prefix entries.

Apply the Longest Prefix Match rule to determine the winning route

The route 10.45.12.80/29 has the longest prefix mask (/29 = 29 matching bits).

Prefix length (/29 > /28 > /26 > /25 > /0) takes precedence over administrative distance and metric during forwarding lookup.

Extract the next-hop IP and exit interface associated with the longest matching route

Next-hop: 192.168.18.2, Exit Interface: GigabitEthernet0/0/4.

The router uses the interface and gateway specified by the selected longest matching routing table entry.

Key Concept

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

Estimated Time:1m 30s

Question 269Question →

Fill in the blank with the exact Cisco IOS command needed to configure the specified static route.

Fill in the blanks below

To configure a fully specified IPv6 static route for the destination subnet 2001:db8:acad:1::/64 using the outbound interface GigabitEthernet0/1 and the next-hop link-local address fe80::1, enter the command:

Show answer & explanation

Answer

ipv6 route 2001:db8:acad:1::/64 GigabitEthernet0/1 fe80::1

When specifying an IPv6 link-local address as the next-hop, Cisco IOS requires a fully specified static route where both the local outbound interface and the neighbor's link-local IPv6 address are declared.

Step-by-Step Solution

Identify the target network prefix and length.

Destination network prefix is 2001:db8:acad:1::/64.

Static routing in IPv6 requires specifying the target prefix alongside its prefix length.

Determine the interface and next-hop address requirement for link-local routing.

Exit interface is GigabitEthernet0/1 and link-local next-hop address is fe80::1.

Because link-local addresses (fe80::/10) are only unique to a local link, Cisco IOS requires specifying the exit interface along with the link-local next-hop address to form a fully specified static route.

Assemble the complete global configuration mode command syntax.

ipv6 route 2001:db8:acad:1::/64 GigabitEthernet0/1 fe80::1

The correct command syntax in Cisco IOS is 'ipv6 route <prefix/length> <exit-interface> <next-hop-link-local-address>'.

Key Concept

IPv6 Fully Specified Static Route Syntax

Question 270Question →

A network engineer inspects a router configuration designed to provide a redundant secondary path to a branch subnet $10.240.12.0/24$ . The primary path to this destination is dynamically learned via OSPF (default Administrative Distance of $110$ ). The engineer finds the following static route entry in the running configuration:

`ip route 10.240.12.0 255.255.255.0 192.168.1.2 95`

During normal operation with the OSPF link operational, traffic continues to traverse the backup link. Which TWO statements accurately explain this behavior and the required configuration fix?

Select all that apply

The configured static route takes precedence over the OSPF route because its configured administrative distance of

95

is lower than the OSPF default administrative distance of

110

Reconfiguring the static route with an administrative distance greater than

110

allows OSPF to act as the primary route while maintaining the static route as a floating backup.

The router load-balances traffic between OSPF and the static route because static routes automatically inherit the metric of active dynamic protocols.

Changing the static route's administrative distance to

90

will deactivate the static route and restore the OSPF path into the routing table.

Show answer & explanation

Answer: The configured static route takes precedence over the OSPF route because its configured administrative distance of $95$ is lower than the OSPF default administrative distance of $110$ .; Reconfiguring the static route with an administrative distance greater than $110$ allows OSPF to act as the primary route while maintaining the static route as a floating backup.

Answer

The static route currently pre-empts OSPF because its administrative distance (

95

) is lower than OSPF's default (

110

). To function correctly as a floating backup, the static route's administrative distance must be set to a value greater than

110

Cisco IOS routing table selection relies strictly on Administrative Distance (AD) when comparing routes learned from different sources for the exact same network prefix. OSPF has a default AD of

110

. The configured static route has an AD explicitly set to

95

. Because

95

is lower than

110

, the router prefers the static route, placing it into the routing table and routing all traffic across the backup link. To convert this into a functional floating static route, the AD of the static route must be increased to a value higher than

110

(for example,

120

), allowing OSPF to be preferred while the primary link is healthy.

Step-by-Step Solution

Analyze the Administrative Distance (AD) of the primary path protocol.

OSPF has a standard Cisco IOS default AD of

110

Routing decisions prioritize paths with the lowest administrative distance when identical prefix lengths are compared.

Evaluate the configured static route's AD.

The command `ip route 10.240.12.0 255.255.255.0 192.168.1.2 95` assigns an explicit AD of

95

Since

95 < 110

, the router installs the static route into the routing table as the active route, suppressing the OSPF route.

Determine the required administrative distance for a floating static route.

The static route's AD must be set higher than the primary path (

> 110

), such as

120

130

A floating static route remains out of the routing table until the primary lower-AD route is removed due to network topology changes or link failure.

Key Concept

Floating static routes rely on configuring an Administrative Distance higher than the primary dynamic routing protocol.

Estimated Time:2m 0s

Question 271Question →

An enterprise router displays the following output in its routing table:

text
Gateway of last resort is not set

10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
O 10.45.0.0/16 [110/20] via 192.168.1.1, 00:04:12, GigabitEthernet0/0

A network administrator needs to configure a backup floating static route to destination prefix $10.45.0.0/16$ via next-hop IP $192.168.2.1$ . The backup route must remain inactive in the routing table until the primary OSPF route becomes unavailable. Which command must be configured on the router to fulfill this requirement?

ip route 10.45.0.0 255.255.0.0 192.168.2.1 120

ip route 10.45.0.0 255.255.0.0 192.168.2.1 100

ip route 10.45.0.0 255.255.0.0 192.168.2.1

ip route 10.45.0.0 255.255.0.0 192.168.2.1 110

Show answer & explanation

Answer: ip route 10.45.0.0 255.255.0.0 192.168.2.1 120

Answer

The command 'ip route 10.45.0.0 255.255.0.0 192.168.2.1 120' correctly configures the floating static route.

The active route to network

10.45.0.0/16

is learned via OSPF, which has an Administrative Distance of 110. To create a floating static route that serves strictly as a backup, the static route must be configured with an Administrative Distance strictly greater than 110. Specifying a distance of 120 keeps the route out of the routing table while OSPF is functional, and allows Cisco IOS to automatically insert the static route if OSPF fails.

Step-by-Step Solution

Identify the Administrative Distance (AD) of the active primary route.

The routing table shows OSPF route [110/20], indicating a default Administrative Distance of

110

for OSPF.

Floating static routes rely on Administrative Distance comparison to determine installation eligibility in the routing table.

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

The backup static route must have an AD strictly greater than

110

(such as

120

Cisco IOS installs the route with the lowest Administrative Distance. Setting a higher AD keeps the static route floating in configuration without entering the active routing table until the primary route fails.

Formulate the correct Cisco IOS static route command syntax.

ip route 10.45.0.0 255.255.0.0 192.168.2.1 120

The trailing argument in the 'ip route' command defines the custom Administrative Distance.

Key Concept

Floating Static Route Administrative Distance Selection

Estimated Time:1m 30s

Question 272Question →

An administrator must create a static route on a Cisco router for destination prefix $2001:\text{db8}:\text{fed}::/64$ . The next-hop router's link-local address is $\text{fe80}::2$ , reached via local interface GigabitEthernet0/1, and the route must be configured with an administrative distance of 110. Which Cisco IOS command correctly completes this configuration?

ipv6 route 2001:db8:fed::/64 GigabitEthernet0/1 fe80::2 110

ipv6 route 2001:db8:fed::/64 fe80::2 110

ip route 2001:db8:fed::/64 GigabitEthernet0/1 fe80::2 110

ipv6 route 2001:db8:fed::/64 GigabitEthernet0/1 fe80::2

Show answer & explanation

Answer: ipv6 route 2001:db8:fed::/64 GigabitEthernet0/1 fe80::2 110

Answer

ipv6 route 2001:db8:fed::/64 GigabitEthernet0/1 fe80::2 110

The correct command follows the exact Cisco IOS syntax for a fully specified IPv6 static route: 'ipv6 route <destination-prefix/mask> <exit-interface> <next-hop-link-local-address> [administrative-distance]'.

Step-by-Step Solution

Identify the proper global configuration command prefix for IPv6 static routing.

Use 'ipv6 route' rather than IPv4's 'ip route'.

Cisco IOS separates IPv4 and IPv6 routing table management commands.

Evaluate link-local next-hop address rules in Cisco IOS IPv6 static routes.

When a link-local address (fe80::/10) is used as the next hop, the local exit interface (GigabitEthernet0/1) MUST also be specified (fully specified static route).

Link-local addresses are valid only on the local link and are shared across multiple interfaces, creating ambiguity if an exit interface is not designated.

Append the optional Administrative Distance (AD) value to the end of the command.

Place '110' at the end of the command string.

Setting an explicit AD overrides the default static route administrative distance of 1.

Key Concept

Fully specified IPv6 static route command syntax requiring an exit interface when using a link-local next-hop address.

Estimated Time:1m 15s

Question 273Question →

During network troubleshooting, an administrator discovers that Router A is receiving OSPFv2 Hello packets from directly connected Router B. However, Router B is dropping all incoming Hello packets from Router A because of an inbound interface access list. In which OSPF neighbor state will Router A remain with respect to Router B?

Init

2-Way

ExStart

Attempt

Show answer & explanation

Answer: Init

Answer

Router A will remain in the Init neighbor state.

When a router receives an OSPF Hello packet from a neighbor, it places that neighbor into the Init state. To transition to the 2-Way state, bidirectional communication must be verified—meaning the receiving router must see its own Router ID listed inside the neighbor's Hello packet. Because the access list blocks Router A's Hellos from reaching Router B, Router B never learns of Router A and never includes Router A's Router ID in its Hellos. Consequently, Router A remains stuck in the Init state.

Step-by-Step Solution

Analyze the flow of OSPF Hello packets between Router A and Router B.

Router A receives Hello packets sent by Router B, but Router B does not receive Hello packets from Router A due to the inbound access list.

Unidirectional communication is occurring.

Evaluate the requirement for transitioning out of the Init state.

To move from Init to 2-Way state, Router A must see its own Router ID listed in the Neighbor field of Router B's Hello packet.

This verifies bidirectional communication between the two neighbors.

Determine Router A's resulting neighbor state.

Because Router B never receives Router A's Hellos, Router B never includes Router A's Router ID in its Hello packets. Router A remains stuck in the Init state.

Receiving a Hello packet without seeing one's own Router ID keeps the neighbor in the Init state.

Key Concept

OSPF Neighbor State Machine (Init State & Bidirectional Communication)

Question 274Question →

A Cisco router receives an IPv4 packet on an ingress interface. Place the sequential steps of the router's forwarding decision and packet processing logic in the correct order from initial receipt to egress transmission.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence for router forwarding decision logic is: 1) Inspect the destination IPv4 address and search the routing table for matching prefixes, 2) Select the route with the longest prefix match, 3) Extract the next-hop IPv4 address and exit interface, 4) Query the ARP cache for the next-hop Layer 2 MAC address, and 5) Decrement packet TTL, encapsulate into a new Layer 2 frame, and transmit out the exit interface.

When a router receives an IPv4 packet, the forwarding process follows a strict sequence: First, the destination IPv4 address is compared against candidate routes in the routing table. Next, the router selects the route entry with the longest prefix match (most specific subnet mask). Once the best route is selected, the router identifies the next-hop IPv4 address and exit interface. It then queries the local ARP cache to find the corresponding destination MAC address for the next hop. Finally, it modifies the packet by decrementing the Time to Live (TTL) by 1, recalculating the IPv4 checksum, encapsulating the packet into a new Layer 2 frame with updated source/destination MAC addresses, and forwarding it out the exit interface.

Step-by-Step Solution

Receive packet and parse IPv4 header.

Destination IPv4 address extracted for routing table comparison.

The router must compare the destination address against candidate prefix entries in the routing table.

Apply Longest Prefix Match (LPM) evaluation.

The route entry with the highest mask length (e.g., /28 over /24) is selected.

LPM is the primary rule for forwarding lookup in Cisco routers.

Identify forwarding path details.

Next-hop IPv4 address and egress interface determined.

The matching route entry specifies the destination gateway and physical/logical outbound interface.

Perform Layer 2 resolution.

Target MAC address obtained from the ARP table.

Layer 2 framing requires the destination MAC address of the next-hop router or end-host.

Process packet header modifications and frame encapsulation.

Frame transmitted out the egress interface.

The router updates TTL/checksum fields and constructs new source/destination MAC addresses for outbound transmission.

Key Concept

Router Forwarding Decision Logic and Layer 2 Frame Rewrite

Estimated Time:1m 30s

Question 275Question →

Arrange the evaluation steps in the correct order of precedence used by OSPFv2 routers to determine Designated Router (DR) selection on a multiaccess network segment, from the initial eligibility filter to the final tie-breaker.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct order of precedence for OSPFv2 DR selection is: 1) Disqualify priority 0 interfaces, 2) Select the candidate with the highest OSPF interface priority, 3) Break priority ties using the highest explicit Router ID or loopback IPv4 address, and 4) Break remaining ties using the highest active physical interface IPv4 address.

During an OSPFv2 DR election on a multiaccess network segment, candidate routers first exclude any interfaces configured with an OSPF priority of 0. Next, routers compare interface priorities to select the highest value. If interface priorities tie, OSPF compares Router IDs by selecting the candidate with the highest explicitly configured Router ID or highest loopback IPv4 address. Finally, if no loopback interface is present, the highest active physical interface IPv4 address is used as the tie-breaker.

Step-by-Step Solution

Filter out non-eligible candidate interfaces.

Interfaces configured with `ip ospf priority 0` are excluded from DR/BDR candidacy.

A priority of 0 explicitly revokes a router's ability to serve as DR or BDR.

Compare candidate interface priority values.

The router with the highest numeric priority value (1 to 255) is preferred.

Interface priority is the primary metric for OSPF DR election.

Evaluate Router ID using explicit setting or loopback addresses.

If interface priorities tie, the router with the highest explicit Router ID or highest active loopback IP address is selected.

Router ID serves as the secondary selection criteria when priorities are tied.

Evaluate physical interface IP addresses.

If no explicit Router ID or loopback interfaces exist, the highest active physical interface IPv4 address breaks the tie.

Physical interface IPv4 addresses are the final tie-breaker for Router ID assignment and election decisions.

Key Concept

OSPFv2 DR/BDR Election Precedence

Question 276Question →

A Cisco router initializes OSPFv2 Process 1 with the following operational interfaces:
- Loopback0: 10.1.1.1/32 (status up, line protocol up)
- GigabitEthernet0/0: 172.16.10.1/24 (status up, line protocol up)

After OSPF Process 1 is fully active, a network engineer performs the following configuration actions in exact chronological sequence:
1. Configures Loopback1 with IP address 10.254.254.254/32 (status up, line protocol up).
2. Enters OSPF router configuration mode and executes the command `router-id 192.168.99.1`.
3. Configures GigabitEthernet0/1 with IP address 192.168.200.1/24 (status up, line protocol up).

Assuming no router reboot or `clear ip ospf process` command has been executed, what IP address is currently used as the operational OSPFv2 Router ID for Process 1?

Show answer & explanation

Answer: 10.1.1.1

Answer

10.1.1.1

When OSPF Process 1 initially started, 10.1.1.1 was elected as the Router ID because Loopback0 was the sole operational loopback interface. OSPF Router ID selection is non-preemptive once an active process has selected its ID. Adding a loopback with a higher IP address (10.254.254.254), configuring an explicit `router-id 192.168.99.1` command, or activating new physical interfaces will not modify the operational Router ID until `clear ip ospf process` is executed or the router reboots. Thus, the active Router ID remains 10.1.1.1.

Step-by-Step Solution

Determine the initial OSPFv2 Router ID selected when Process 1 started.

Loopback0 (10.1.1.1) was selected because operational loopback interface IP addresses take priority over physical interface IP addresses during initial Router ID election.

In Cisco IOS OSPFv2, if no manual router ID is configured at startup, the router chooses the highest IP address among operational loopback interfaces.

Evaluate the impact of configuring Loopback1 (10.254.254.254/32).

The active Router ID remains 10.1.1.1.

OSPF Router ID election is non-preemptive. Dynamically elected Router IDs do not change automatically when new interfaces with higher IP addresses come online.

Evaluate the impact of executing `router-id 192.168.99.1`.

The active Router ID remains 10.1.1.1.

Configuring a manual OSPF router ID on an already running OSPF process does not take effect until the process is reset or the router is rebooted.

Evaluate the impact of adding GigabitEthernet0/1 and determine the final operational Router ID.

The active Router ID stays 10.1.1.1.

Without a process reset via `clear ip ospf process` or a device reload, none of the subsequent configuration changes displace the active Router ID.

Key Concept

OSPFv2 Router ID Non-Preemption and Reset Requirement

Question 277Question →

A network router currently receives its primary path to network 10.0.0.0/24 via RIP, which has a default administrative distance of 120. A network engineer needs to configure a static route to network 10.0.0.0/24 via the next-hop address 192.168.1.2 to act as a floating backup, activating only if the primary RIP route fails. Which command correctly configures this floating static route?

ip route 10.0.0.0 255.255.255.0 192.168.1.2 130

ip route 10.0.0.0 255.255.255.0 192.168.1.2

ip route 10.0.0.0 255.255.255.0 192.168.1.2 110

ip route 10.0.0.0 255.255.255.0 192.168.1.2 120

Show answer & explanation

Answer: ip route 10.0.0.0 255.255.255.0 192.168.1.2 130

Answer

ip route 10.0.0.0 255.255.255.0 192.168.1.2 130

The command 'ip route 10.0.0.0 255.255.255.0 192.168.1.2 130' assigns an administrative distance of 130 to the static route. Because 130 is greater than RIP's administrative distance of 120, Cisco IOS keeps the static route out of the routing table as long as the RIP route remains active. If the RIP route fails, the floating static route is inserted into the routing table as the backup path.

Step-by-Step Solution

Identify the primary routing protocol and its administrative distance.

The primary route is learned via RIP, which has a default administrative distance of 120.

Floating static routes rely on administrative distance values to determine route priority.

Determine the required administrative distance for a floating static route.

The administrative distance of the floating static route must be configured strictly greater than 120 (e.g., 130).

Cisco IOS prefers routes with lower administrative distances. To remain inactive in the routing table as a backup until the primary path disappears, the backup static route's administrative distance must be higher than that of the primary route.

Select the Cisco IOS command line syntax matching the required administrative distance.

The command 'ip route 10.0.0.0 255.255.255.0 192.168.1.2 130' correctly specifies a distance of 130.

Specifying 130 trailing the next-hop address correctly sets the administrative distance higher than RIP (120).

Key Concept

A floating static route requires an administrative distance configured higher than that of the active primary dynamic routing protocol.

Question 278Question →

An enterprise edge router dynamically learns the network prefix 10.50.40.0/24 from an internal switch via Internal EIGRP (Administrative Distance 90). A network administrator needs to configure a floating static backup route for this prefix using the next-hop IPv4 address 192.168.254.2 across a secondary connection. Which Cisco IOS command correctly configures the floating static route so that it remains inactive in the routing table until the primary EIGRP path fails?

ip route 10.50.40.0 255.255.255.0 192.168.254.2 95

ip route 10.50.40.0 255.255.255.0 192.168.254.2 90

ip route 10.50.40.0 255.255.255.0 192.168.254.2

ip route 10.50.40.0 0.0.0.255 192.168.254.2 95

Show answer & explanation

Answer: ip route 10.50.40.0 255.255.255.0 192.168.254.2 95

Answer

ip route 10.50.40.0 255.255.255.0 192.168.254.2 95

The correct option uses standard subnet mask notation (255.255.255.0) and specifies an administrative distance of 95. Because 95 is higher than Internal EIGRP's administrative distance of 90, the router retains this static route as an inactive backup and installs it into the IPv4 routing table only if the EIGRP path becomes unavailable.

Step-by-Step Solution

Determine the administrative distance of the primary route.

Internal EIGRP has a default administrative distance of 90.

Floating static routes must have an administrative distance strictly greater than the active primary routing protocol to stay hidden from the routing table during normal operation.

Evaluate Cisco IOS IPv4 static route syntax requirements.

The command syntax requires 'ip route <prefix> <mask> <next-hop-ip> [administrative-distance]'.

Subnet masks must be written in standard dotted-decimal notation (e.g., 255.255.255.0) rather than inverse wildcard notation.

Select the option with valid CLI syntax and an administrative distance higher than 90.

The command setting an administrative distance of 95 satisfies all criteria.

An administrative distance of 95 ensures the static route remains floating until the primary EIGRP route with AD 90 is withdrawn.

Key Concept

Floating Static Route Administrative Distance Selection

Question 279Question →

Router R1 learns paths to remote subnet $192.168.100.0/24$ from two dynamic routing protocols: an Internal EIGRP path with an administrative distance of 90 and an OSPF path with an administrative distance of 110. An engineer must configure a floating static route pointing to next-hop $10.1.1.2$ that remains dormant in the routing table and only activates if both dynamic paths fail. Which command must be configured on R1?

ip route 192.168.100.0 255.255.255.0 10.1.1.2 115

ip route 192.168.100.0 255.255.255.0 10.1.1.2 95

ip route 192.168.100.0 255.255.255.0 10.1.1.2 1

ip route 192.168.100.0 255.255.255.0 10.1.1.2 90

Show answer & explanation

Answer: ip route 192.168.100.0 255.255.255.0 10.1.1.2 115

Answer

The command 'ip route 192.168.100.0 255.255.255.0 10.1.1.2 115' correctly configures the floating static route.

The correct command specifies an administrative distance of 115. Cisco IOS routers select routes for insertion into the routing table based on the lowest administrative distance. Because EIGRP has an AD of 90 and OSPF has an AD of 110, an AD value higher than 110 (such as 115) ensures the static route is ignored as long as either EIGRP or OSPF delivers a valid path. It will only be installed into the routing table as a floating backup when both dynamic routes are removed.

Step-by-Step Solution

Identify administrative distances of all active routing sources for destination 192.168.100.0/24

Internal EIGRP has AD = 90; OSPF has AD = 110.

Floating static routes rely on administrative distance values to dictate route installation hierarchy.

Determine the required administrative distance for the backup floating static route

The static route AD must be strictly greater than 110 (e.g., 115).

To ensure the static route activates only when BOTH dynamic paths (AD 90 and AD 110) are lost, its AD must exceed the highest AD of the active primary dynamic routes.

Select the command matching the syntax 'ip route <prefix> <mask> <next-hop> <distance>'

'ip route 192.168.100.0 255.255.255.0 10.1.1.2 115'

This command specifies destination 192.168.100.0/24 via next-hop 10.1.1.2 with an administrative distance of 115.

Key Concept

Floating Static Route Administrative Distance Selection

Question 280Question →

A Cisco router, R4, has the following interface states and IPv4 configurations:

- Loopback0: 192.168.250.1/24 (line protocol is down)
- Loopback1: 172.20.100.1/24 (line protocol is up)
- Loopback2: 10.100.1.1/24 (line protocol is up)
- GigabitEthernet0/0: 192.168.1.1/30 (line protocol is up)
- GigabitEthernet0/1: 10.254.254.1/30 (line protocol is up)

An engineer initially configures the router with the following commands:

text
router ospf 100
router-id 1.1.1.1

Later, the engineer enters subconfiguration mode and executes `no router-id 1.1.1.1`. To force the OSPF process to recalculate its router ID, the engineer executes `clear ip ospf process` and confirms the action.

What IPv4 address will R4 select as its operational OSPFv2 router ID?

Show answer & explanation

Answer: 172.20.100.1

Answer

172.20.100.1

When the explicit `router-id` command is removed and the OSPF process is cleared using `clear ip ospf process`, OSPF fallback election logic applies. OSPF selects the highest IPv4 address among operational (up/up) loopback interfaces. Although Loopback0 has the highest loopback IP (192.168.250.1), its line protocol is down, excluding it from election. Between active loopbacks Loopback1 (172.20.100.1) and Loopback2 (10.100.1.1), Loopback1 has the higher numerical IPv4 address (172.20.100.1).

Step-by-Step Solution

Evaluate explicit router-id configuration

The explicit `router-id 1.1.1.1` command was negated via `no router-id 1.1.1.1`.

When the explicit router ID command is removed and the OSPF process is cleared, OSPF reverts to automatic selection logic.

Identify operational loopback interfaces

Loopback1 (172.20.100.1) and Loopback2 (10.100.1.1) are operational (up/up). Loopback0 (192.168.250.1) is down.

OSPF router ID selection prioritizes active (up/up) loopback interfaces over physical interfaces, but inactive/down interfaces cannot be selected regardless of IP value.

Compare active loopback IPv4 addresses to select highest IP

Comparing 172.20.100.1 and 10.100.1.1 yields 172.20.100.1 as the highest IPv4 address.

Among all operational loopback interfaces, the highest numerical IPv4 address is selected as the router ID upon process restart.

Key Concept

OSPFv2 Router ID Selection Priority Logic

Estimated Time:1m 30s

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