Nokia Nokia IS-IS Routing Protocol 4A0-112 Exam Dumps: Updated Questions & Answers (September 2025)

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.

IS-IS routers must have matching authentication settings to establish an adjacency. If one router is configured with authentication and the other is not, the routers will not be able to establish an adjacency because their authentication parameters do not match.

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.

The output shows two levels of IS-IS databases: Level 1 (L1) and Level 2 (L2). This indicates that the domain is multi-area, as L1 routers are confined to a single area, while L2 routers can route between different areas. The presence of Level 1/Level 2 (L1/L2) routers also suggests that the domain spans multiple areas.

The LSP (Link-State PDU) entries show L1/L2 ATT attributes, which typically indicate that these routers are capable of routing both within their own area (Level 1) and across areas (Level 2), suggesting a multi-area design.

The IS-IS domain likely includes broadcast interfaces, as indicated by the "ATT" attribute (typically referring to the type of interface) and common IS-IS configuration practices on broadcast networks like Ethernet.

When a router receives a link-state advertisement (LSA), it doesnotupdate the age field before forwarding it. Theage fieldin an LSA is typically updated by the originating router or during the process of forwarding the LSA within the network. Routers do not modify the age field upon receiving and forwarding an LSA.

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.

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.

In IS-IS, routers are actually associated withinterfacesrather than the entire router being associated with a single area. A router can have interfaces in multiple areas, and it is the interface's configuration that determines which area it belongs to.

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.