4A0-112 Nokia IS-IS Routing Protocol Question and Answers

In both broadcast and point-to-point interfaces, IS-IS routers identify neighbors using system IDs, not interface MAC addresses. The system ID is a unique identifier assigned to each router, and it is used to identify neighbors in both types of interfaces.

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.

Router R1 is configured as L1/L2, meaning it is part of both Level 1 and Level 2 IS-IS routing areas. This means R1 will generate two types of LSPs:

Level 1 LSP (for the local area 49.0001) to advertise its local topology to other Level 1 routers.

Level 2 LSP (for the backbone area 49.0002) to advertise the global network topology to Level 2 routers.

R1 also has two broadcast interfaces, and as the Designated Intermediate System (DIS) on these interfaces, it will generate an LSP for each interface (one per broadcast link).

This results in three total LSPs:

A Level 1 LSP for the local area (49.0001).

A Level 2 LSP for the backbone area (49.0002).

An LSP for each of the two broadcast interfaces, which may include interface-related topology information.

ARP for IPv4 and Neighbor Discovery Protocol (NDP) for IPv6 are both used to map a device's IP address to its MAC address. This is essential for communication within a local network.

ARP is used in IPv4 networks, and NDP performs a similar function in IPv6 networks, ensuring devices can communicate effectively on the same network segment.

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.

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.

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

TheCSNP (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 theDIS (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.