JN0-364 Exam Dumps - Service Provider Routing and Switching - Specialist (JNCIS-SP)

In a Juniper Networks environment running Junos OS, understanding the interaction between different versions of OSPF is essential for multi-protocol environments.OSPFv2(defined in RFC 2328) is the standard protocol used for routing IPv4 unicast traffic.OSPFv3(defined in RFC 5340) was originally developed to support IPv6 routing. However, OSPFv3 was later extended via RFC 5838 to support multiple address families (AF), allowing it to carry IPv4 unicast, IPv4 multicast, and other address types within a single OSPF instance.

According to Juniper technical documentation, Junos OS implements this multi-AF support in OSPFv3 through the use ofrealms. When the realm ipv4-unicast statement is configured under the [edit protocols ospf3] hierarchy, the OSPFv3 process becomes capable of calculating and advertising IPv4 routes.

In the provided exhibit, routerR2has a dual-protocol configuration. First, it is running standard OSPFv2, with the ge-0/0/1.0 interface (which is directly connected to the 172.16.2.0/24 network) participating in Area 0. This ensures that the prefix is advertised as a standard IPv4 LSA to its neighbor,R1. Second, R2 is running OSPFv3 with the realm ipv4-unicast specifically enabled on that same ge-0/0/1.0 interface. Because of this realm, OSPFv3 also treats the 172.16.2.0/24 prefix as a reachable IPv4 destination and advertises it to R1 as an OSPFv3 IPv4-unicast LSA.

As a result, whenR1(which is also running both protocols) receives these routing updates, it will see the same destination prefix advertised by two different protocols. Its routing table (inet.0) will contain one entry learned from the OSPFv2 process and a second, separate entry learned from the OSPFv3 process. While the Junos Routing Engine will ultimately select one as the "active" route based on route preference (both protocols have a default preference of 10), both entries will technically exist within the Routing Information Base (RIB). This confirms that statementBis the correct description of the operational state of the network.

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In the IS-IS protocol,TLVs (Type, Length, Value)are the fundamental building blocks used to carry information withinLink-State PDUs (LSPs). Unlike some other protocols that have a fixed, rigid packet format, IS-IS was designed from the ground up to be modular and extensible. This extensibility is achieved through the use of TLVs, which allow the protocol to carry different types of data without requiring changes to the core protocol state machine.

According to Juniper Networks technical documentation,TLVs allow flexible encoding of routing information (Option C). Each TLV specifies the "Type" of information it carries (such as neighbor information or IP reachability), the "Length" of that information, and the "Value" (the actual data). This architecture is what allowed IS-IS to easily support IPv6 by simply adding new TLVs (like TLV 236 for IPv6 reachability) without redesigning the protocol. It also supports Traffic Engineering (TE) extensions used in MPLS environments by adding TLVs that describe link bandwidth and administrative groups.

Furthermore, a singleLSP can contain multiple TLVs (Option D). When a Juniper router generates an LSP, it packs all the necessary information—such as the router's area addresses, its neighbors, and its local interface prefixes—into various TLVs and places them into a single PDU. If the amount of information exceeds the Maximum Transmission Unit (MTU) of the interface, the router will generate additional LSPs (fragmented LSPs) to carry the remaining TLVs.

Options A and B are incorrect because restricting an LSP to a single TLV would make the protocol incredibly inefficient, and the very nature of IS-IS is its ability to support multiple network layer protocols (not just IPv4) through its agnostic TLV-based transport.

In theIS-IS (Intermediate System to Intermediate System)protocol, communication between routers is performed usingProtocol Data Units (PDUs). To discover neighbors and maintain adjacencies, IS-IS relies on theHello PDU (IIH - IS-IS Hello).

According to Juniper Networks technical documentation, when IS-IS is enabled on an interface, the router begins transmitting Hello PDUs to a multi-destination address (multicast). These PDUs contain essential information such as the router'sSystem ID, its configuredArea Addresses, and itsLevel capability(Level 1, Level 2, or both). For two routers to become neighbors, they must exchange these Hello PDUs and agree on specific parameters, such as the MTU of the link and the hello/hold timers.

Once an adjacency is established, the Hello PDU serves as a "keepalive" mechanism. If a router stops receiving Hello PDUs from a neighbor for a duration exceeding theHolding Time, it assumes the neighbor is down and flushes the associated Link-State PDUs (LSPs) from its database.

To clarify the other options:

Link-State PDU (Option A):These are used to distribute actual topology and reachability information, not to form adjacencies.

Partial Sequence Number PDU (Option C):PSNPs are used on point-to-point links to acknowledge the receipt of LSPs or to request missing LSPs.

Update PDU (Option D):This is not a standard IS-IS term; in IS-IS, updates are handled via the flooding of LSPs.