4A0-112 Nokia IS-IS Routing Protocol Free Practice Exam Questions (2025 Updated)

Route redistributionis the process of sharing routing information between different routing protocols or routing domains. For example, a router might redistribute routes learned via OSPF into a BGP routing table or vice versa. This enables routers to exchange routing information even when they are using different routing protocols.

The static route configured on router R1 uses an indirect next-hop, which is10.10.10.3 (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 route10.4.100.0/24is reachable throughR3, but there is no reciprocal route inR3's routing table that allows the response to flow back towardsR1. This results in a failure to return the echo response to R1, causing the ping to fail.

When a router performs the SPF (Shortest Path First) calculation, it uses itself as the root of the shortest path tree (SPT). This router computes the shortest paths to all other routers in the network, treating itself as the origin and calculating the paths based on its view of the network.

In this scenario, the routers are configured with an Equal-Cost Multi-Path (ECMP) value of 4, meaning they can utilize up to 4 equal-cost paths to reach a destination. Since Router R5 is advertising the 192.168.3.0/24 prefix and all links have the same cost, router R3 will receive multiple routes to reach this destination.

Given that all the routers (R1, R2, R3, R4, and R5) are connected in a way that can support multiple equal-cost paths, and assuming ECMP is set to 4, the routing table on Router R3 will have up to 4 entries for the prefix 192.168.3.0/24.

Thus, Router R3's routing table will contain4 entriesfor the prefix 192.168.3.0/24.

During the IP forwarding process, routers use the routing table to determine the next hop based on the destination IP address. The source IP address is not directly involved in the lookup process for forwarding.

The ARP table is used to map IP addresses to MAC addresses, specifically for resolving the MAC address of the next hop (destination MAC address) for forwarding packets within the local network.

IS-IS routers use different types of Hello messages depending on whether the interface is configured as a broadcast (LAN) or point-to-point (P2P) link.

On a broadcast network (e.g., Ethernet), IS-IS routers use LAN Hello packets to establish adjacencies.

On a point-to-point link, IS-IS uses point-to-point Hello packets.

If one router is configured for a broadcast interface and the other for point-to-point, they will exchange incompatible Hello packets, and as a result, neither router will accept the other's Hello messages, preventing the adjacency from being established.

Theadjacency databasecontains information about the state of the router’s adjacencies (i.e., the routers that it is directly connected to and has established a neighbor relationship with). It does not store information about all links in the domain; that information is stored in thelink-state database.

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.

Router R1 is the one that performs the summarization of the two subnets (20.20.1.0/24 and 20.20.2.0/24) into the summarized route 20.20.0.0/16. However, R1 itself will not see any change in its routing table because it is directly connected to both subnets and already knows about them.

Router R2, which is in Area 49.0002, will benefit from this summarization because it previously had separate routes for both 20.20.1.0/24 and 20.20.2.0/24. After the summarization, R2 will only need to maintain a single route to 20.20.0.0/16, reducing the size of its routing table.

Router R4 does not directly benefit from the summarization because it is only connected to the Level 1 network and has no need for the summarized routes from R1. Thus, the summarization does not affect R4's routing table.

When a router receives a CSNP (Complete Sequence Number PDU) that references an older LSP (Link-State PDU) than the one in its local database, it indicates that the neighbor is missing newer information.

In response, the router sends back a PSNP (Partial Sequence Number PDU) to the neighbor, which includes a copy of the LSPs it has in its local database that the neighbor may not yet have. This helps to synchronize the link-state information between routers.