Free Practice Questions for the Nokia Network Routing Specialist II (NRS II) 4A0-112 Exam (2026 Updated)

The routing table manager (RTM) is responsible for selecting the best route when multiple routing protocols provide a route for the same destination prefix. It makes the decision on which route to add to the routing table based on the administrative distance, metric, and other criteria.

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).

In a single-area link-state routing protocol (such as OSPF), routers share specific information about the network topology, not their entire routing table. They exchange link-state advertisements (LSAs) that contain information about their directly connected interfaces and their state, allowing other routers to build a consistent view of the network.

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.

From the route tables of R3 and R4 , we can see that remote routes are present, with R3 and R4 both having routes referencing routers in different areas (Area 49.01 and 49.02). These remote routes are characteristic of route leaking , which is the process of sharing routes between different IS-IS areas.

R3 has routes for R1 , R2 , and R4 , which are in Area 49.01, suggesting that R1 and R2 have advertised their routes to R3 , possibly due to route leaking .

R4 has similar routes for R2 and R3 , indicating that R2 might have advertised its routes to R4 .

This sharing of routes between areas is indicative of route leaking being configured on both R1 and R2 , allowing these routes to be shared across the areas.

When a link-state update reaches its maximum age, it is removed from the router’s link-state database, not flooded to its neighbors. This prevents outdated information from continuing to affect the routing decisions. The router does not flood the aged update; instead, it will typically request a new link-state advertisement from the original source router if the information is still needed.

From the output, we can see that the usage column indicates whether a router is operating as an L1 or L2 router:

Routers R1 and R2 have a usage of L2 , meaning they are L2 routers.

Routers R3 and R4 have a usage of L1 , meaning they are L1 routers.

The L1/L2 designations refer to whether the routers participate in both Level 1 and Level 2 of IS-IS:

L1 routers only communicate within their own area.

L2 routers communicate between areas.

In this case, R1 and R2 are L2 routers, and R3 and R4 are L1 routers.

The head office has many connected subnetworks, so it will typically have a default route to forward traffic to the branch office (or external networks), since it may not need to define static routes for each branch network.

The branch office, which has only one subnetwork and a single connection to the head office, will have a specific static route to reach the head office subnet or other subnets at the head office, since it only needs to know the specific route to reach the head office's network.

The process of establishing an IS-IS adjacency on a broadcast link involves several steps, and the transition from the Initializing state to the UP state occurs when both routers exchange sufficient information to confirm they have a consistent view of the link-state database.

The CSNP (Complete Sequence Number PDU) packet is used to advertise the list of LSPs in the router's link-state database. When a router receives the first CSNP from the DIS (Designated Intermediate System) that lists the LSPs in the DIS's database, it indicates that the router has enough information to establish the adjacency and synchronize its database.