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

In IPv6, consecutive sections of zeros can be abbreviated with a double colon (::) once in an address. Also, leading zeros in each hextet (group of four hexadecimal digits) can be removed.

The original address is2001:0da8:0000:0000:0024:0000:4ab9:0300.

Removing leading zeros and applying the abbreviation:

0da8becomesda8.

0000becomes0(and multiple consecutive 0000 sections can be represented by ::).

The final result becomes2001:da8::24:0:4ab9:300, which matches option A when properly formatted.

In IPv6, the Neighbor Discovery Protocol (NDP) replaces the Address Resolution Protocol (ARP) used in IPv4. NDP is responsible for several functions, including resolving IP addresses to MAC addresses (similar to ARP), detecting duplicate IP addresses, and discovering other devices on the network.

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.

Based on theIPv6 route tableoutput forR3andR4, 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 ofroute leaking, where routes from one area are being shared across areas.

TheroutesfromR3(level-1 router) are being advertised toR4(level-1 router), and vice versa, withISISas the protocol. This implies that there is route leaking configured to allow information to pass between areas.

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 exchangelink-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.

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.

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

RoutersR1andR2have a usage ofL2, meaning they are L2 routers.

RoutersR3andR4have a usage ofL1, meaning they are L1 routers.

TheL1/L2designations refer to whether the routers participate in both Level 1 and Level 2 of IS-IS:

L1 routersonly communicate within their own area.

L2 routerscommunicate between areas.

In this case,R1andR2are L2 routers, andR3andR4are L1 routers.

From R1 to R7: The path will be R1 → R2 → R4 → R6 → R7 because this path has the least cumulative metric of 10 + 10 + 10 + 10 = 40.

From R7 to R1: The reverse path will follow R7 → R6 → R4 → R2 → R1 because it is the shortest return path with the same metrics.

Router R4 is in Area 49.0001 and R6 is in Area 49.0002. Both routers are Level 2 (L2), meaning that they can communicate across areas using Level 2 IS-IS routing.

Since R2 is the L1/L2 router that connects both Area 49.0001 and Area 49.0002, it will be the next-hop for router R4 to reach R6’s system IP address.

The IS-IS protocol will ensure that R4 will have a route to R6’s system IP address via R2 as the next-hop.