IP Connectivity

493 questions

Question 201Question

A network administrator is configuring static routing on router R1 to forward traffic toward network 2001:db8:3c4d:10::/64. The administrator intends to use the link-local address fe80::211:22ff:fe33:4455 of the neighboring router connected to local interface GigabitEthernet0/1. Which Cisco IOS command correctly configures this static route?

Show answer & explanation

Answer: ipv6 route 2001:db8:3c4d:10::/64 GigabitEthernet0/1 fe80::211:22ff:fe33:4455

Answer

The command 'ipv6 route 2001:db8:3c4d:10::/64 GigabitEthernet0/1 fe80::211:22ff:fe33:4455' correctly configures the fully specified IPv6 static route.
The statement specifying the local exit interface GigabitEthernet0/1 followed by the next-hop link-local address fe80::211:22ff:fe33:4455 complies exactly with Cisco IOS requirements for fully specified IPv6 static routes.

Step-by-Step Solution

1
Identify the proper Cisco IOS command prefix for IPv6 routing
The command must start with 'ipv6 route' rather than 'ip route'.
Cisco IOS separates IPv4 and IPv6 static route configurations into distinct global commands.
2
Evaluate the next-hop address scope
The next-hop address 'fe80::211:22ff:fe33:4455' is a link-local IPv6 address (fe80::/10).
Link-local addresses exist on every IPv6-enabled interface, so an egress interface MUST be supplied to resolve ambiguity.
3
Verify Cisco IOS syntax parameter ordering
The syntax requires 'ipv6 route <prefix/length> <exit-interface> <link-local-address>'.
Specifying GigabitEthernet0/1 followed by fe80::211:22ff:fe33:4455 forms a valid fully specified static route.

Key Concept

Fully Specified IPv6 Static Routes with Link-Local Next-Hops
Question 202Question

An network administrator reviews routing table entries using the `show ip route` command on a Cisco IOS router. Which two statements correctly describe components of an IPv4 routing table entry?

Select all that apply

Show answer & explanation

Answer: Administrative distance indicates the trustworthiness of the route source, with lower values being preferred.; The metric is a value calculated by a routing protocol to select the best path among multiple routes to the same destination network.

Answer

The two correct statements are that administrative distance measures the trustworthiness of a routing source (with lower values preferred) and that metric is used by a routing protocol to select the best path to a destination network.
Administrative distance measures the trustworthiness of a routing source (where lower numbers represent greater trust), and metrics are used by individual routing protocols to identify the optimal path among available routes.

Step-by-Step Solution

1
Analyze the role of Administrative Distance (AD)
AD defines route trustworthiness from 0 (most trusted) to 255 (unbelievable/untrusted). Lower values are preferred.
AD helps the router choose which routing source to populate into the routing table when multiple sources offer the exact same destination network prefix.
2
Analyze the role of Metric
Metric measures path cost within a single routing protocol (e.g., OSPF cost, RIP hop count).
Routing protocols use metrics to evaluate competing paths to the same destination prefix and choose the best route.
3
Verify forwarding decision order and source codes
Longest prefix match is evaluated first during packet lookup, not AD. Source code 'S' stands for Static, while 'O' stands for OSPF.
This invalidates options suggesting AD precedes prefix length or misidentifying static routes as OSPF.

Key Concept

Routing Table Components and Metrics
Question 203Question

A network administrator is inspecting the IPv4 routing table on a Cisco IOS XE router using the `show ip route` command. Match each routing table entry line on the left to its corresponding architectural component description on the right.

Click a left item, then click its matching right item

Items

D EX 10.5.0.0/16 [170/2578560] via 192.168.1.2
O IA 10.2.0.0/24 [110/30] via 172.16.10.1
L 10.1.1.1/32 is directly connected, GigabitEthernet0/0/0
S* 0.0.0.0/0 [1/0] via 192.168.254.1

Matches

Show answer & explanation

Answer

Each routing entry line matches its unique protocol source code and administrative metric: 'D EX' matches external EIGRP (AD 170); 'O IA' matches OSPF inter-area; 'L 10.1.1.1/32' matches the interface local host route; and 'S* 0.0.0.0/0' matches the candidate default static route.
Each entry correctly aligns with its routing protocol source flag and structural component: 'D EX' designates external EIGRP with AD 170; 'O IA' identifies OSPF inter-area routes; 'L' with a /32 mask represents a local interface host route; and 'S*' indicates a static candidate default route.

Step-by-Step Solution

1
Examine the prefix source code flags at the beginning of each routing entry.
Identify 'D EX' as EIGRP external, 'O IA' as OSPF inter-area, 'L' as local host route, and 'S*' as static candidate default route.
Source codes in Cisco IOS show ip route output define how the route was learned or populated into the RIB.
2
Analyze the Administrative Distance (AD) and metric values inside the brackets [AD/metric].
Verify [170/2578560][170/2578560] for external EIGRP, [110/30][110/30] for OSPF, and [1/0][1/0] for static route.
Administrative Distance rates the trustworthiness of routing information sources.
3
Match each entry to its exact functional component definition.
All four entries correlate to their distinct protocol and structural roles.
Direct mapping of Cisco IOS routing table output identifiers to architectural standards.

Key Concept

Cisco IOS Routing Table Components and Protocol Source Codes
Question 204Question

A Cisco router has the following interface operational statuses and IPv4 configurations:

- GigabitEthernet0/0 (192.168.50.1/24192.168.50.1/24): line protocol up, operational state UP
- GigabitEthernet0/1 (192.168.100.1/24192.168.100.1/24): line protocol up, operational state UP
- Loopback 0 (10.254.1.1/3210.254.1.1/32): administratively down, line protocol down
- Loopback 1 (10.200.1.1/3210.200.1.1/32): line protocol down, operational state DOWN
- Loopback 2 (172.16.20.1/32172.16.20.1/32): line protocol up, operational state UP

The OSPFv2 routing process is initialized using `router ospf 1` without an explicitly configured static Router ID via the `router-id` command. What exact IPv4 address will OSPFv2 elect as the active Router ID for this process?

Show answer & explanation

Answer: 172.16.20.1

Answer

172.16.20.1
OSPFv2 uses a strict three-tier precedence logic to select the Router ID: 1) An explicitly configured 'router-id' command, 2) The highest IPv4 address among active (up/up) loopback interfaces, 3) The highest IPv4 address among active (up/up) physical non-loopback interfaces. Here, no explicit Router ID exists. Loopback 0 and Loopback 1 are both down, making Loopback 2 (172.16.20.1) the sole active loopback interface. Because active loopback interfaces take precedence over physical interfaces (such as GigabitEthernet0/1 with 192.168.100.1), 172.16.20.1 is selected as the Router ID.

Step-by-Step Solution

1
Check for an explicitly configured router ID using the 'router-id' command.
No explicit router ID is configured under 'router ospf 1'.
Explicit configuration takes highest priority in OSPF Router ID selection.
2
Evaluate all active (up/up) loopback interfaces to find the highest IPv4 address.
Loopback 0 and Loopback 1 are inactive (down). Loopback 2 (172.16.20.1) is active (up/up).
OSPF prefers active loopback interfaces over physical interfaces, but inactive loopbacks cannot participate in election.
3
Compare candidate addresses among active loopbacks.
172.16.20.1 is the only active loopback address.
Since Loopback 2 is the only active loopback interface, its IP address (172.16.20.1) is chosen over the physical interface IP addresses.

Key Concept

OSPFv2 Router ID Selection Priority Logic
Estimated Time:1m 30s
Question 205Question

A network administrator is configuring a backup route on a Cisco IOS router to reach a remote branch office network with the prefix 2001:db8:fedc:9900::/562001:\text{db8}:\text{fedc}:9900::/56. The primary path is currently provided by OSPFv3 with an administrative distance of 110110. The administrator must configure a floating static route using the next-hop router's link-local address fe80::cafe:1fe80::cafe:1 over the local exit interface GigabitEthernet0/0/1GigabitEthernet0/0/1. Which command correctly configures this backup floating static route on the router?

Show answer & explanation

Answer: ipv6 route 2001:db8:fedc:9900::/56 GigabitEthernet0/0/1 fe80::cafe:1 120

Answer

The command 'ipv6 route 2001:db8:fedc:9900::/56 GigabitEthernet0/0/1 fe80::cafe:1 120' correctly configures the backup floating static route.
The correct command syntax for an IPv6 static route using a link-local next-hop requires specifying both the local exit interface and the link-local address of the neighbor. Furthermore, setting the administrative distance to 120120 ensures it is higher than the primary OSPFv3 route's administrative distance of 110110, making it a true floating static route.

Step-by-Step Solution

1
Determine the required administrative distance for the backup route.
Since OSPFv3 has an administrative distance of 110110, the backup route must have an administrative distance greater than 110110 (such as 120120) to remain floating (inactive until the primary route fails).
Floating static routes rely on a higher administrative distance than the primary routing protocol.
2
Identify the next-hop address requirements for IPv6 static routing.
When using a link-local IPv6 address (fe80::/10fe80::/10) as the next-hop, Cisco IOS mandates a fully specified static route that includes the local exit interface (GigabitEthernet0/0/1GigabitEthernet0/0/1).
Link-local addresses are non-routable and only unique to the specific local link/interface.
3
Construct the exact Cisco IOS syntax.
'ipv6 route 2001:db8:fedc:9900::/56 GigabitEthernet0/0/1 fe80::cafe:1 120'
Syntax follows 'ipv6 route <prefix/mask> <exit-interface> <next-hop-address> [administrative-distance]'.

Key Concept

Fully Specified IPv6 Floating Static Route Configuration
Question 206Question

Refer to the following routing table output from a Cisco router:

text
Gateway of last resort is not set

10.0.0.0/8 is subnetted, 4 subnets
C 10.10.20.0/20 is directly connected, GigabitEthernet0/0
S 10.10.20.0/24 [1/0] via 172.16.1.1
O 10.10.20.128/25 [110/20] via 172.16.2.1
D 10.10.20.144/28 [90/307200] via 172.16.3.1

The router receives an IPv4 packet destined for host 10.10.20.150. Which two statements regarding the router forwarding decision are correct?

Select all that apply

Show answer & explanation

Answer: The router forwards the packet using next-hop IP 172.16.3.1 because the /28 route provides the longest prefix match for the destination address.; Longest prefix match logic is evaluated before comparing administrative distance values across routing protocols.

Answer

The router forwards the packet to next-hop 172.16.3.1 based on the longest prefix match rule, and prefix length evaluation strictly precedes administrative distance comparisons.
The router applies Longest Prefix Match (LPM) logic first when forwarding traffic. Among the matching entries in the routing table for 10.10.20.150, the subnet 10.10.20.144/28 has 28 matching bits, making it more specific than /25, /24, or /20. Therefore, the router forwards the packet to next-hop 172.16.3.1. Additionally, prefix length comparison occurs before comparing administrative distance or metric parameters.

Step-by-Step Solution

1
Determine which routes match the destination host IP 10.10.20.150.
The destination matches 10.10.20.0/20, 10.10.20.0/24, 10.10.20.128/25, and 10.10.20.144/28.
All four entries contain the IP address 10.10.20.150 within their subnet boundaries.
2
Compare prefix lengths among all matching routes to find the most specific match.
The /28 prefix (10.10.20.144/28) has 28 matching network bits, which is longer than /25, /24, or /20.
The longest prefix match rule requires routers to choose the route with the highest number of matching leading subnet bits.
3
Select the forwarding path according to the longest prefix match route.
The route via 172.16.3.1 is selected, regardless of the lower administrative distance of the static route.
Administrative Distance (AD) is only used to select between identical routes from different sources, not between routes of different prefix lengths.

Key Concept

Router Forwarding Decision Logic (Longest Prefix Match precedence)
Question 207Question

Two directly connected Cisco routers are configured to run OSPFv2 on their connecting GigabitEthernet interfaces. Interface GigabitEthernet0/0 on Router A is placed in OSPF Area 0, while interface GigabitEthernet0/0 on Router B is placed in OSPF Area 1. Which statement correctly describes the result of this configuration?

Show answer & explanation

Answer: The routers will fail to form an OSPF neighbor adjacency.

Answer

The routers will fail to form an OSPF neighbor adjacency.
For two OSPFv2 routers to establish a neighbor adjacency, key fields in their Hello packets must match. These mandatory matching parameters include the Area ID, Subnet Mask, Hello and Dead intervals, and Authentication fields. Because Router A is configured in Area 0 and Router B is configured in Area 1 on the connecting segment, the routers will discard each other's Hello packets and fail to form an adjacency.

Step-by-Step Solution

1
Identify the OSPF neighbor requirements for directly connected interfaces.
Neighbor adjacencies require identical Hello/Dead timers, Area ID, Subnet Mask, and MTU settings in Hello packets.
OSPF validation rules state that any mismatch in essential Hello packet fields will cause the router to drop incoming Hello packets.
2
Compare the configured OSPF Area IDs of Router A and Router B.
Router A is in Area 0 and Router B is in Area 1.
Because the Area IDs differ, Hello packet validation fails upon receipt.
3
Determine the resulting neighbor state.
No neighbor adjacency is formed and the routers remain in the Down state.
Without matching parameters, OSPF neighbor relationship negotiation cannot proceed.

Key Concept

OSPFv2 Neighbor Adjacency Requirements
Estimated Time:45s
Question 208Question

An enterprise router displays the following output from the `show ip route` command:

text
Gateway of last resort is not set

172.20.0.0/16 is subnetted, 4 subnets
S 172.20.0.0/16 [1/0] via 10.10.10.1
O 172.20.8.0/21 [110/65] via 10.10.20.1, 00:08:12, GigabitEthernet0/0/1
D 172.20.12.0/23 [90/2578560] via 10.10.30.1, 00:22:45, GigabitEthernet0/0/2
O 172.20.13.0/25 [110/110] via 10.10.40.1, 00:03:50, GigabitEthernet0/0/3

The router receives a packet with a destination IPv4 address of 172.20.13.45172.20.13.45. Based on the routing table components and forwarding logic, which next-hop IP address and outbound interface will the router select to forward this packet?

Show answer & explanation

Answer: 10.10.40.1 via GigabitEthernet0/0/3

Answer

Next-hop 10.10.40.1 via GigabitEthernet0/0/3
When a router receives an IP packet, it evaluates all matching prefix entries in its routing table and selects the entry with the longest prefix length (most specific mask). The destination address 172.20.13.45 falls within the range of 172.20.13.0/25 (172.20.13.0 to 172.20.13.127), which has a /25 prefix length. Because /25 is longer and more specific than /23, /21, or /16, the router forwards the packet to next-hop 10.10.40.1 out interface GigabitEthernet0/0/3 regardless of Administrative Distance.

Step-by-Step Solution

1
Identify all candidate routes that match the destination IP address 172.20.13.45
Candidate routes are 172.20.0.0/16, 172.20.8.0/21 (range 172.20.8.0 - 172.20.15.255), 172.20.12.0/23 (range 172.20.12.0 - 172.20.13.255), and 172.20.13.0/25 (range 172.20.13.0 - 172.20.13.127). All 4 entries encompass the destination address.
Before comparing route metrics or administrative distances, the router determines which routing table prefixes physically include the destination IP.
2
Apply the Longest Prefix Match (LPM) rule across all candidate matching entries
Prefix lengths are /16, /21, /23, and /25. The longest and most specific prefix mask is /25 (172.20.13.0/25).
The router forwarding decision logic always prioritizes the most specific prefix (highest prefix length value) over Administrative Distance or metric.
3
Determine the next-hop IP and exit interface associated with the winning route prefix
The route for 172.20.13.0/25 specifies next-hop 10.10.40.1 via interface GigabitEthernet0/0/3.
Packet forwarding parameters are derived directly from the winning prefix entry in the Routing Information Base.

Key Concept

Longest Prefix Match (LPM) resolution in Cisco routing tables
Question 209Question

A Cisco router receives an IPv4 packet on an ingress interface destined for a remote destination host. In what exact sequence does the router execute its internal forwarding decision and frame processing logic from packet arrival to egress transmission?

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequential order of the Cisco router forwarding decision logic is: First, de-encapsulate the frame, verify IP header integrity, and extract the destination IPv4 address. Second, search the IPv4 routing table for all matching prefix entries. Third, select the single best route entry strictly using Longest Prefix Match (LPM). Fourth, identify the egress exit interface and next-hop IPv4 address from the selected route. Fifth, resolve the next-hop Layer 2 MAC address, decrement TTL, rewrite the Layer 2 header, and transmit the frame.
The correct operational sequence begins when an IPv4 packet arrives at a router interface. The router first strips the ingress Layer 2 header, validates the IP checksum/TTL, and extracts the destination IP address. Next, it queries the IPv4 routing table for all matching subnets. It applies Longest Prefix Match (LPM) precedence to choose the candidate route with the longest subnet mask. After selecting the winning route, it extracts the next-hop IP address and outbound interface. Finally, it uses ARP to find the next-hop MAC address, decrements the TTL by 1, encapsulates the packet in a new Layer 2 header, and transmits it out the exit interface.

Step-by-Step Solution

1
Frame De-encapsulation and Header Validation
Layer 2 frame header is stripped, and the destination IPv4 address is extracted from the IPv4 header.
The router must inspect the Layer 3 destination header to determine where the packet needs to be routed.
2
Routing Table Candidate Search
A set of candidate subnet routes that cover the destination IPv4 address is identified.
All active routes in the Routing Information Base (RIB) or Forwarding Information Base (FIB) are scanned for binary subnet matching.
3
Longest Prefix Match (LPM) Evaluation
The route with the highest number of matching network bits (longest prefix mask) is selected.
Longest Prefix Match is the absolute primary criteria for route selection in IP routing, overriding Administrative Distance and routing metrics.
4
Forwarding Path Extraction
The destination next-hop IPv4 address and outgoing physical/logical exit interface are determined.
The router needs the exact forwarding instructions specified inside the winning routing table entry.
5
Layer 2 Encapsulation and Egress Transmission
The packet TTL is decremented, ARP cache provides the next-hop MAC address, a new Layer 2 frame is encapsulated, and the frame is transmitted.
The router must rewrite the Layer 2 header for the next-hop broadcast domain before transmitting the packet on the wire.

Key Concept

Router Forwarding Decision Logic and Longest Prefix Match
Question 210Question

A network engineer views the following line in a Cisco router's IPv4 routing table:

`O 10.50.4.0/24 [110/65] via 172.16.1.2, 00:18:32, GigabitEthernet0/1`

What component of the routing table entry is represented by the value `110` inside the brackets?

Show answer & explanation

Answer: Administrative distance

Answer

The value 110 represents the administrative distance of the routing protocol.
In Cisco routing table entries, bracketed notation follows the format `[Administrative Distance / Metric]`. The value `110` is the default Administrative Distance for OSPF routes, measuring the trustworthiness of the route source.

Step-by-Step Solution

1
Analyze the bracketed values in the routing table entry: `[110/65]`.
Identify that Cisco IOS routing entries format protocol trust and path cost as `[Administrative Distance / Metric]`.
Understanding standard Cisco CLI routing table component syntax.
2
Evaluate the first position inside the bracket.
The first number `110` corresponds to Administrative Distance, which is the default trustworthiness value for OSPF routes.
Distinguish Administrative Distance from the route metric.

Key Concept

Interpretation of Routing Table Bracketed Syntax [AD/Metric]
Question 211Question

A network administrator is configuring static routing on router HQ to forward traffic bound for remote subnet 2001:db8:feed:10::/642001:\text{db8}:\text{feed}:10::/64. The outbound connection uses a point-to-point serial-like Ethernet link where the remote router interface uses the link-local address fe80::21a:2bff:fe3c:4d5e\text{fe80}::21a:2bff:\text{fe3c}:4d5e on interface GigabitEthernet0/0/1. The primary path must use an administrative distance of 11, but if configured using a link-local next-hop address without an outbound interface specified, Cisco IOS will reject the command. Which command correctly establishes a fully-specified IPv6 static route for this destination using the link-local next hop?

Show answer & explanation

Answer: ipv6 route 2001:db8:feed:10::/64 GigabitEthernet0/0/1 fe80::21a:2bff:fe3c:4d5e

Answer

The correct command is 'ipv6 route 2001:db8:feed:10::/64 GigabitEthernet0/0/1 fe80::21a:2bff:fe3c:4d5e', which specifies both the exit interface and the link-local address for a fully-specified IPv6 static route.
When configuring an IPv6 static route with a link-local address as the next hop, Cisco IOS requires a fully-specified static route syntax: 'ipv6 route <destination-prefix/prefix-length> <exit-interface> <link-local-next-hop>'. Since link-local addresses (FE80::/10) are only unique on the local link, specifying GigabitEthernet0/0/1 clarifies which link to transmit packets across.

Step-by-Step Solution

1
Identify the destination prefix and prefix length.
The target prefix is 2001:db8:feed:10::/642001:\text{db8}:\text{feed}:10::/64.
The prefix must be explicitly identified at the start of the Cisco IOS IPv6 static route command syntax.
2
Determine the next-hop mechanism requirements for link-local addresses.
When a link-local address (fe80::\text{fe80}::\dots) is used as a next hop, Cisco IOS requires specifying the local exit interface alongside the link-local address.
Link-local addresses are scope-limited to a single link, so the router needs the exit interface identifier to know which link to send the packet on.
3
Construct the exact syntax for a fully-specified route.
The syntax is 'ipv6 route <prefix/length> <exit-interface> <link-local-address>'.
This syntax creates a valid fully-specified IPv6 static route with the default administrative distance of 1.

Key Concept

IPv6 Fully-Specified Static Routing with Link-Local Next-Hop
Question 212Question

A Cisco router is configured to run OSPFv2 without an explicitly set `router-id` under the OSPF process. The current interface IP address configurations and states are as follows:

- Loopback0: 10.10.10.10/3210.10.10.10/32 (Administratively Down)
- Loopback1: 172.16.1.1/24172.16.1.1/24 (Up / Up)
- Loopback2: 192.168.100.1/24192.168.100.1/24 (Up / Up)
- GigabitEthernet0/0: 10.200.200.1/3010.200.200.1/30 (Up / Up)

What IP address will OSPF select as the router ID when the OSPF process initializes?

Show answer & explanation

Answer: 192.168.100.1

Answer

192.168.100.1
OSPFv2 uses a strict order of preference to establish its Router ID: 1) Explicitly configured `router-id` command, 2) Highest IP address among active (Up/Up) loopback interfaces, 3) Highest IP address among active physical interfaces. In this scenario, no manual router ID exists. Loopback0 is down so it is excluded. Loopback1 (172.16.1.1172.16.1.1) and Loopback2 (192.168.100.1192.168.100.1) are both active loopback interfaces. OSPF selects 192.168.100.1192.168.100.1 because it is the highest active loopback IP address.

Step-by-Step Solution

1
Check for an explicitly configured OSPF router ID
No manual OSPF router ID command is configured.
Explicit configuration takes precedence over all automatic election rules.
2
Evaluate all active (Up/Up) loopback interfaces
Loopback1 (172.16.1.1172.16.1.1) and Loopback2 (192.168.100.1192.168.100.1) are active. Loopback0 (10.10.10.1010.10.10.10) is administratively down and ignored.
OSPF election logic prioritizes active loopback interfaces over physical interfaces.
3
Compare IP addresses of active loopbacks to select the highest value
Between 172.16.1.1172.16.1.1 and 192.168.100.1192.168.100.1, 192.168.100.1192.168.100.1 is numerically higher.
OSPF selects the highest IP address among operational loopback interfaces.

Key Concept

OSPFv2 Router ID Selection Precedence
Estimated Time:1m 0s
Question 213Question

Refer to the following partial IPv4 routing table output from a Cisco router:

text
Gateway of last resort is not set

172.16.0.0/16 is variably subnetted, 4 subnets, 4 masks
O 172.16.10.0/24 [110/20] via 192.168.1.1, 00:05:12, GigabitEthernet0/0
D 172.16.10.0/25 [90/307200] via 192.168.1.2, 00:12:44, GigabitEthernet0/1
S 172.16.10.128/26 [1/0] via 192.168.1.3, 01:15:00, GigabitEthernet0/2
C 172.16.10.128/30 is directly connected, GigabitEthernet0/3

The router receives a packet destined for IP address 172.16.10.130. Which interface or next-hop IP address will the router select to forward this packet?

Show answer & explanation

Answer: GigabitEthernet0/3

Answer

The router will forward the packet out interface GigabitEthernet0/3 because the directly connected route 172.16.10.128/30 provides the longest prefix match for destination 172.16.10.130.
The destination host 172.16.10.130 matches three entries in the routing table: 172.16.10.0/24, 172.16.10.128/26, and 172.16.10.128/30. According to Cisco router forwarding logic, the router evaluates Longest Prefix Match (LPM) first. Because /30 has 30 matching network bits, it is the most specific route and will be used to forward the packet out GigabitEthernet0/3.

Step-by-Step Solution

1
Evaluate all routes in the routing table against the destination IP address 172.16.10.130 to identify matching subnets.
Matching subnets are 172.16.10.0/24, 172.16.10.128/26, and 172.16.10.128/30. The subnet 172.16.10.0/25 covers addresses .0 through .127 and is not a match.
Routing lookup requires identifying all candidate routes that encompass the target destination host address.
2
Compare the prefix lengths of all matching candidate routes.
Prefix lengths are /24, /26, and /30. The longest prefix length is /30.
Cisco routers use the Longest Prefix Match (LPM) rule as the primary criteria for forwarding decisions before considering Administrative Distance.
3
Select the route corresponding to the longest prefix match.
The route 172.16.10.128/30 is selected, which directs traffic to the directly connected interface GigabitEthernet0/3.
The most specific route (/30) always wins the forwarding decision regardless of administrative distance or metric.

Key Concept

Longest Prefix Match (LPM) is the fundamental rule routers use to select a route from the routing table when forwarding a packet. The router selects the route with the highest number of matching network bits (longest prefix length), regardless of administrative distance.
Estimated Time:1m 30s
Question 214Question

Two Cisco routers, R1 and R2, are directly connected via their GigabitEthernet 0/0 interfaces in OSPFv2 Area 0. An administrator configures `ip ospf hello-interval 5` on R1's GigabitEthernet 0/0 interface, while R2's interface retains the default OSPF Hello interval of 10 seconds. What is the impact of this configuration on the OSPF neighbor relationship between R1 and R2?

Show answer & explanation

Answer: The routers fail to establish an OSPF neighbor adjacency and the neighbor state remains down.

Answer

The routers fail to establish an OSPF neighbor adjacency and the neighbor state remains down.
For two routers to establish an OSPFv2 neighbor relationship, essential parameters in their OSPF Hello packets must match exactly. These parameters include the Area ID, Hello interval, Dead interval, Subnet mask (on broadcast networks), and Authentication settings. Because the Hello interval on R1 is set to 5 seconds while R2 is using 10 seconds, both routers reject incoming Hello packets from one another, keeping the neighbor state in the Down state.

Step-by-Step Solution

1
Analyze OSPF Hello packet field validation requirements for neighbor adjacency formation.
Identified that specific fields in received Hello packets must match local interface configurations, including Area ID, Subnet Mask, Hello/Dead intervals, Authentication, and Stub flags.
OSPF routers verify these parameters before accepting a neighbor and placing it into the OSPF neighbor table.
2
Compare the configured Hello interval on R1 (5 seconds) with the default Hello interval on R2 (10 seconds).
A mismatch in Hello intervals exists across the link.
R1 expects Hello packets with a 5-second interval, while R2 sends Hello packets with a 10-second interval (and vice versa for Dead intervals).
3
Determine the resulting OSPF neighbor state.
Both routers drop incoming Hello packets from each other due to parameter mismatch, preventing neighbor discovery and adjacency formation.
Without matching Hello/Dead intervals, OSPF neighbor relationship setup cannot proceed past the Down state.

Key Concept

OSPFv2 Hello Packet Parameter Verification and Neighbor Adjacency Requirements
Question 215Question

A network administrator is configuring IPv6 static routing on router R1 to reach the destination network 2001:db8:acad:10::/642001:\text{db8}:\text{acad}:10::/64. Router R1 connects to neighboring router R2 via interface GigabitEthernet0/0/1. Router R2's connected interface has a global unicast address of 2001:db8:acad:12::2/642001:\text{db8}:\text{acad}:12::2/64 and a link-local address of fe80::2\text{fe80}::2.

Which two Cisco IOS commands represent valid IPv6 static route configurations on R1? (Select two.)

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:12::2

Answer

The valid IPv6 static route configurations are 'ipv6 route 2001:db8:acad:10::/64 GigabitEthernet0/0/1 fe80::2' and 'ipv6 route 2001:db8:acad:10::/64 2001:db8:acad:12::2'.
In Cisco IOS, IPv6 static routes using a link-local address as the next hop require a fully specified syntax that includes the local exit interface. Alternatively, static routes using a global unicast address as the next hop require only the destination prefix and the next-hop IPv6 address.

Step-by-Step Solution

1
Evaluate link-local next-hop static route requirements in Cisco IOS.
Link-local addresses (fe80::/10\text{fe80}::/10) are scoped only to a single link. Therefore, Cisco IOS requires specifying the local exit interface alongside the link-local next-hop address.
Without specifying the exit interface, the router cannot determine which physical link to forward the packet out of.
2
Evaluate global unicast next-hop static route requirements in Cisco IOS.
Global unicast addresses are globally unique, allowing the router to perform a recursive routing table lookup to find the egress interface.
Specifying only the global unicast next-hop address creates a valid recursive static route.

Key Concept

IPv6 Static Route Next-Hop Syntax Rules
Question 216Question

An engineer is configuring a backup fully-specified IPv6 static route on router R1 toward the remote destination network 2001:db8:500:10::/642001:\text{db8}:500:10::/64. The primary path is learned via OSPFv3. The backup route must forward traffic to the next-hop router's link-local address fe80::2\text{fe80::2} via local interface GigabitEthernet0/1 with an administrative distance of 130. Complete the required Cisco IOS configuration command.

Fill in the blanks below

ipv6 route 2001:db8:500:10::/64 130
Show answer & explanation

Answer

The complete command is 'ipv6 route 2001:db8:500:10::/64 GigabitEthernet0/1 fe80::2 130'.
When configuring an IPv6 static route using a link-local next-hop address, Cisco IOS requires a fully specified static route format: `ipv6 route <prefix/length> <exit-interface> <link-local-address> [administrative-distance]`. Thus, GigabitEthernet0/1 must be specified as the exit interface in the first blank, and fe80::2 as the next hop in the second blank.

Step-by-Step Solution

1
Identify the target IPv6 network prefix and length.
The destination prefix is 2001:db8:500:10::/64.
IPv6 static routes require the destination network prefix with prefix length.
2
Determine the required syntax for using a link-local address as a next hop.
When a link-local address (fe80::2) is specified as the next hop, Cisco IOS requires the local exit interface (GigabitEthernet0/1) to precede the link-local address in the command.
Link-local addresses are only unique to the local link, so the router must know which egress interface to send the traffic out of.
3
Append the administrative distance parameter.
An administrative distance of 130 is placed at the end of the command.
The primary OSPFv3 route has an administrative distance of 110; setting the static route to 130 creates a floating static route.

Key Concept

IPv6 Fully Specified Static Route and Floating Static Route Syntax
Question 217Question

A Cisco router running OSPFv2 has no manually configured router ID (`router-id` command). The router has the following active and operational interfaces configured with IP addresses:

- Loopback 0: 10.10.10.1/32
- Loopback 1: 172.16.50.1/32
- GigabitEthernet0/0: 192.168.1.1/24
- GigabitEthernet0/1: 192.168.2.1/24

What IP address will OSPF automatically select as the OSPF Router ID?

Show answer & explanation

Answer: 172.16.50.1

Answer

172.16.50.1
In OSPFv2, the router ID election order is: 1) Manually configured router ID (`router-id` command), 2) Highest IP address among active loopback interfaces, and 3) Highest IP address among active non-loopback (physical) interfaces. Because active loopbacks exist and no manual router ID is specified, OSPF chooses the highest loopback IP address, which is 172.16.50.1.

Step-by-Step Solution

1
Check for a manually configured OSPF router ID
No manually configured OSPF router ID exists
Manual configuration using the `router-id` command takes highest priority.
2
Evaluate active loopback interfaces
Two active loopback interfaces exist: 10.10.10.1 and 172.16.50.1
If no explicit router ID is set, OSPF evaluates the IP addresses assigned to up/up loopback interfaces.
3
Select the highest IP address among active loopback interfaces
172.16.50.1 is selected as the Router ID
Comparing numerically, 172.16.50.1 is greater than 10.10.10.1.

Key Concept

OSPFv2 Router ID Election Order
Question 218Question

An enterprise edge router receives internal routing updates for the prefix 192.168.50.0/24192.168.50.0/24 via OSPFv2 (Administrative Distance 110) and iBGP (Administrative Distance 200). A network administrator intends to provision a floating static route via next-hop 10.0.12.210.0.12.2 that remains inactive during normal operation, activates as a backup if the OSPF path fails, and takes precedence over the iBGP path. The administrator executes the following Cisco IOS command:

`ip route 192.168.50.0 255.255.255.0 10.0.12.2 105`

What is the operational result of this configuration, and what modification is required to achieve the desired routing behavior?

Show answer & explanation

Answer: The static route immediately replaces the OSPF route in the routing table because its Administrative Distance of 105 is lower than 110; the Administrative Distance must be reconfigured to a value between 111 and 199.

Answer

The static route immediately overrides the OSPF path because an Administrative Distance of 105 is lower than OSPF's default distance of 110. To function as a floating static backup for OSPF while remaining preferred over iBGP, the Administrative Distance must be configured to a value strictly between 111 and 199.
Cisco IOS selects routes for installation in the routing table based on Administrative Distance (AD), where lower values represent higher trustworthiness. OSPFv2 has a default AD of 110 and iBGP has a default AD of 200. Configuring the static route with AD 105 makes it more trustworthy than OSPF (105<110105 < 110), causing it to immediately active in the routing table rather than functioning as a backup. To properly float behind OSPF but remain ahead of iBGP, its AD must be set within the range of 111 to 199 (such as 120).

Step-by-Step Solution

1
Analyze the Administrative Distance (AD) hierarchy of the active protocols and proposed static route.
Primary path: OSPFv2 (AD 110). Secondary requirement: Floating static backup. Tertiary path: iBGP (AD 200). Configured static route AD: 105.
Administrative Distance determines route trustworthiness in the Cisco IOS Routing Table. Lower AD values are preferred.
2
Evaluate the effect of configuring AD 105 on the router.
Since 105<110105 < 110, the static route overrides OSPF immediately and enters the routing table as the active route, breaking its intended role as a backup route.
A floating static route must have an AD higher than the primary route protocol so that it remains inactive until the primary route drops.
3
Determine the valid AD range for the floating static route.
The AD value XX must satisfy 110<X<200110 < X < 200 (e.g., X=120X = 120).
This guarantees that OSPF (110) is preferred when available, the static route (XX) activates when OSPF fails, and iBGP (200) is used only as a last resort.

Key Concept

Floating Static Route Administrative Distance Calibration
Estimated Time:2m 0s
Question 219Question

A network administrator is configuring a backup floating static IPv6 route on router R1 to reach the remote prefix 2001:db8:acad:44::/642001:\text{db8}:\text{acad}:44::/64. The primary route to this subnet is learned via OSPFv3 with an administrative distance of 110. The administrator wants to route backup traffic through the link-local address fe80::211:23ff:fe45:6789fe80::211:23ff:fe45:6789 of the neighboring router connected to interface GigabitEthernet0/0/1GigabitEthernet0/0/1, assigning an administrative distance of 130. Which Cisco IOS command correctly configures this floating static route?

Show answer & explanation

Answer: ipv6 route 2001:db8:acad:44::/64 GigabitEthernet0/0/1 fe80::211:23ff:fe45:6789 130

Answer

The command 'ipv6 route 2001:db8:acad:44::/64 GigabitEthernet0/0/1 fe80::211:23ff:fe45:6789 130' correctly configures the fully specified floating static IPv6 route.
The correct command uses the syntax 'ipv6 route <prefix/mask> <exit-interface> <next-hop-address> [administrative-distance]'. When a link-local address is used as the next hop, the local exit interface is mandatory because link-local addresses are scoped to the local link. Specifying an administrative distance of 130 ensures the route functions as a floating static route, acting as a backup to the OSPFv3 route which has an administrative distance of 110.

Step-by-Step Solution

1
Identify the requirements for using a link-local address as an IPv6 static route next hop.
Because IPv6 link-local addresses (FE80::/10) are non-routable and exist only on a single local link, Cisco IOS requires specifying the local exit interface alongside the link-local next-hop address (a fully specified static route).
Without the exit interface, the router cannot resolve which interface to forward packets out of toward the non-unique link-local address.
2
Determine the administrative distance required for a floating static backup route.
The primary route has an OSPFv3 administrative distance of 110. To create a backup route that remains dormant in the routing table until the primary route fails, the static route AD must be set higher than 110 (specifically 130 as requested).
Lower administrative distances are preferred by the Cisco IOS routing table logic.
3
Verify syntax and address accuracy.
The syntax 'ipv6 route <prefix/mask> <exit-interface> <link-local-next-hop> <administrative-distance>' yields 'ipv6 route 2001:db8:acad:44::/64 GigabitEthernet0/0/1 fe80::211:23ff:fe45:6789 130'.
This matches all parameters, including proper EUI-64 link-local address formatting and correct AD placement.

Key Concept

Fully specified IPv6 static routes using link-local next-hop addresses and floating static administrative distance configuration.
Question 220Question

A router receives routes for the destination network 10.20.0.0/16 dynamically from OSPF, which uses a default administrative distance of 110. A network administrator needs to create a backup static route for this network using the next-hop address 192.168.1.2 so that it only becomes active if the primary OSPF path fails. Which Cisco IOS command correctly configures this floating static route?

Show answer & explanation

Answer: ip route 10.20.0.0 255.255.0.0 192.168.1.2 120

Answer

The command 'ip route 10.20.0.0 255.255.0.0 192.168.1.2 120' correctly configures the floating static route.
The correct command uses standard Cisco IOS syntax with destination network 10.20.0.0, subnet mask 255.255.0.0 for /16, next-hop address 192.168.1.2, and an administrative distance of 120. Because 120 is greater than OSPF's default AD of 110, the static route remains inactive in the routing table until the primary OSPF route fails.

Step-by-Step Solution

1
Identify the required static route components in Cisco IOS syntax
Syntax format: ip route <destination-network> <subnet-mask> <next-hop-ip> [administrative-distance]
Cisco IOS requires exact keyword ordering and standard dotted-decimal subnet masks.
2
Convert the /16 prefix length to a dotted-decimal subnet mask
/16 equals 255.255.0.0
IPv4 static routing commands require a subnet mask, not a wildcard mask.
3
Determine the required Administrative Distance (AD) for a floating static route
The AD must be higher than the primary routing protocol's AD (OSPF = 110), so an AD of 120 is chosen
Floating static routes are kept out of the routing table until the primary route with a lower AD becomes unavailable.

Key Concept

Floating static route configuration requires an administrative distance higher than the primary dynamic routing protocol.
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