Question 1

Refer to the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Nokia_4A0-112_IS-IS_Routing_Protocol/page_4_img_1.jpg All routers in the diagram are running an interior gateway protocol (IGP) and have been configured with an ECMP value of 4. Router R5 advertises the prefix 192.168.3.0/24 using the IGP. Assuming all links have the same cost, how many entries for prefix 192.168.3.0/24 will be in router R3’s routing table?

Accepted Answer

D

Explanation: When IS-IS runs SPF, every lowest-cost path to a destination is eligible for installation. Because all links in the diagram carry the same metric, the SPF calculation seen from R3 produces four next-hops toward R5 that have an identical total cost. The ECMP parameter on every router has been set to 4, so SR OS will keep up to four equal-cost routes. Consequently, R3’s routing table will list four entries (one per next-hop) for prefix 192.168.3.0/24.

Question 2

When multiple routing protocols offer a route for the same prefix, what part of the router is in charge of deciding which route to make active?

Accepted Answer

B

Explanation: The Routing Table Manager (RTM) is the control plane process responsible for maintaining the routing information base (RIB). When multiple routing protocols, such as IS-IS, OSPF, or BGP, provide a route to the same destination prefix, the RTM selects the single best route. This selection is primarily based on the configured preference (administrative distance) for each protocol. The route from the protocol with the lowest preference value is chosen as the active route and is then installed into the forwarding information base (FIB) for use in packet forwarding.

Question 3

When using IS-IS in native mode for routing in a dual-stack IPv4/IPv6 environment, which of the following statements is FALSE?

Accepted Answer

C

Explanation: In a dual-stack IPv4/IPv6 IS-IS environment, the SPF (Shortest Path First) algorithm is only run once per router for each protocol (IPv4 or IPv6). The topology is shared, but the SPF calculations for IPv4 and IPv6 are separate. This means that the SPF algorithm will run twice (once for IPv4 and once for IPv6) for each L1/L2 router, not four times.

Question 4

Refer to the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Nokia_4A0-112_IS-IS_Routing_Protocol/page_18_img_1.jpg In the diagram, all routers are using IS-IS as their routing protocol. The number next to each link is its metric value. What path will traffic follow from router R6 to router R3, and from router R3 to router R6?

Accepted Answer

A

Explanation: The metric values between the routers dictate the routing paths, and IS-IS will calculate the shortest path based on these values. R6 to R3: The path from R6 to R3 will go through R5 and R2, as this route has the least cumulative metric (10 + 10 + 15 = 35). R3 to R6: The reverse path from R3 to R6 will follow R3 → R2 → R5 → R6 because this route is also the shortest with a total metric of 10 + 10 + 10 = 30.

Question 5

Refer to the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Nokia_4A0-112_IS-IS_Routing_Protocol/page_8_img_1.jpg A static route has been configured on router R1 to reach the PC at 139.120.121.2. What might be causing the ping to fail?

Accepted Answer

C

Explanation: In the configuration on router R1, the static route is defined with the next-hop IP address of 139.120.121.1. However, the next-hop IP address 139.120.121.1 does not belong to the same subnet as the directly connected interface on R1, which is 172.31.1.1/30. For the static route to work properly, the next- hop IP address must be reachable via a directly connected interface, meaning it must be within the same subnet. Therefore, this mismatch in subnet adjacency is likely causing the failure to reach the destination (139.120.121.2).

Question 6

On a broadcast interface, an IS-IS router receives an LSP that is newer than the one on its database. Which of the following statements best describes the actions taken by the router as a consequence?

Accepted Answer

C

Explanation: When an IS-IS router receives a newer LSP (Link-State PDU) than the one already in its database, it takes the following actions: Updates its link-state database with the new LSP. Acknowledges the LSP with a PSNP (Partial Sequence Number PDU), which is sent to the router that originated the LSP, confirming the receipt of the newer LSP. Floods a copy of the updated LSP to its neighbors on other interfaces to ensure all routers in the network have the updated topology information.

Question 7

Which of the following statements about the IP forwarding process on a router is TRUE?

Accepted Answer

B

Explanation: The fundamental purpose of the IP forwarding process on a router is to determine the next hop for a packet on its path to the final destination. When a router receives an IP packet, it examines the destination IP address in the packet header. It then performs a lookup in its routing table to find the most specific, or longest prefix, match. This matching routing table entry provides the necessary information, such as the outgoing interface and the IP address of the next-hop router, to forward the packet correctly. This destination-based lookup is the core of the IP forwarding decision.

Question 8

Refer to the exhibit. https://kxbjsyuhceggsyvxdkof.supabase.co/storage/v1/object/public/file-images/Nokia_4A0-112_IS-IS_Routing_Protocol/page_12_img_1.jpg Routers R1 through R4 are running an IGP in such a way that they have each other’s system IP addresses in their routing tables. A static route is configured on router R1 so that it can reach subnetwork 10.4.100.0/24. The network administrator decides to use an indirect static route, as shown in the diagram. However, pinging the server from router R1 fails. What may be the problem in this case?

Accepted Answer

D

Explanation: The static route configured on router R1 uses an indirect next-hop, which is 10.10.10.3 (R3). While the echo request from R1 reaches the server through the IGP, the problem lies in the return path for the echo response. The route 10.4.100.0/24 is reachable through R3, but there is no reciprocal route in R3's routing table that allows the response to flow back towards R1. This results in a failure to return the echo response to R1, causing the ping to fail.

Question 9

Which component of the Nokia 7750 SR is in charge of performing the longest prefix match lookup on packets that arrive on the physical interfaces?

Accepted Answer

D

Explanation: The Input/Output Module (IOM) is the line card in the Nokia 7750 SR responsible for data plane processing. Each IOM contains a forwarding engine and maintains a local copy of the Forwarding Information Base (FIB). When a packet arrives on a physical interface of a Media Dependent Adapter (MDA), it is passed to the parent IOM. The IOM's forwarding engine then performs the longest prefix match lookup against its local FIB to determine the packet's next hop and egress interface. This distributed architecture allows for high-performance, line-rate forwarding.

Question 10

Consider the exhibit. All routers are running IS-IS with IPv6 support enabled. Based on the topology shown, and the route tables of routers R3 and R4, which of the following statements is TRUE?

Accepted Answer

D

Explanation: Based on the IPv6 route table output for R3 and R4, we can see that the routers have remote routes listed as "Remote ISIS", indicating that the route is being advertised from a different area (area 49.01 or 49.02). This is a sign of route leaking, where routes from one area are being shared across areas. The routes from R3 (level-1 router) are being advertised to R4 (level-1 router), and vice versa, with ISIS as the protocol. This implies that there is route leaking configured to allow information to pass between areas.

Free Nokia 4A0-112 IS-IS Routing Protocol Actual Exam Questions