JN0-364 Exam Dumps - Juniper JNCIS-SP Questions and Answers

In a Juniper Networks MPLS environment, the selection of a signaling protocol depends heavily on the requirement for traffic engineering and path control. To satisfy the requirement for anexplicit path—where the network architect defines specific hop-by-hop routers that the traffic must traverse—theResource Reservation Protocol (RSVP)is the necessary choice.

According to Juniper documentation, RSVP (specifically RSVP-TE) supports the use ofExplicit Route Objects (EROs). When you configure an LSP in Junos OS, you can define a path consisting of a series of IP addresses (strict or loose hops). RSVP then signals the LSP along that exact sequence of routers, reserving resources and establishing labels as it goes. This allows for precise control over the network's traffic patterns, enabling administrators to steer traffic away from congested links or toward specific high-bandwidth paths.

In contrast,LDP (Label Distribution Protocol)(Option D) is a "best-effort" signaling protocol. LDP strictly follows the Interior Gateway Protocol (IGP) shortest path. It does not support explicit paths or traffic engineering constraints; it simply builds a "mesh" of labels based on the existing routing table.IS-IS(Option C) is an IGP used to populate the routing table and TED but does not signal labels.BGP(Option A) is used for service delivery (like L3VPNs) but relies on an underlying transport LSP (built by RSVP or LDP) to reach its next hop. Therefore, only RSVP provides the mechanism for explicit path manipulation.

When implementingMultiprotocol BGP (MP-BGP)for IPv6, several architectural constants remain consistent with the original BGP design, while others have evolved to accommodate larger network scales.

Router ID (Option C):

A critical point in Juniper's Service Provider documentation is that theBGP Router IDremains a32-bit value, even when the protocol is carrying 128-bit IPv6 prefixes. The Router ID is typically represented in dotted-quad notation (e.g., 192.168.1.1). In an IPv6-only environment, a Juniper router cannot automatically derive this ID from an interface address, so it must be manually defined under [edit routing-options]. This 32-bit ID is essential for BGP tie-breaking and loop prevention within the AS.

Autonomous System Number (Option D):

TheAutonomous System Number (ASN)was originally a 16-bit value (0 to 65535). However, to address the exhaustion of available ASNs, the standard was extended to32-bit ASNs(documented in RFC 6793). In Junos OS, you can configure BGP using either the older 16-bit format or the newer 32-bit format (often represented in "asplain" or "asdot" notation). While the question mentions a 64-bit value, there is currently no standard for a 64-bit ASN in BGP; the transition from 16-bit to 32-bit satisfies current global scalability needs. Therefore, Option D is the most accurate within the context of current networking standards, as it acknowledges the coexistence of different ASN lengths.

One of the most significant architectural improvements in IPv6 is the move from a complex, variable-length header (as seen in IPv4) to a streamlined, fixed-length base header of 40 bytes. Additional functionality that was previously handled by "Options" in IPv4 is now moved toExtension Headers, which are inserted between the IPv6 base header and the upper-layer protocol (TCP/UDP).

According to Juniper Networks technical documentation and RFC 8200, the following are valid IPv6 Extension Headers:

Hop-by-Hop Options (Option B):This header carries optional information that must be examined by every node along the delivery path. It is used for features like the Router Alert and Jumbo Payload options.

Fragment (Option E):Unlike IPv4, where any router can fragment a packet, in IPv6, fragmentation is performed only by the source node. The Fragment header contains the information necessary for the destination to reassemble the packet (Offset, Identification, and More Fragments flag).

Destination Options (Option A):This header carries information intended only for the destination node. It can appear twice: once before a routing header and once after.

Why other options are incorrect:

Protocol (Option C):In IPv4, this was a field in the header. In IPv6, this is replaced by theNext Headerfield, which identifies the type of the following header (whether it's an extension header or the upper-layer protocol).

Header Checksum (Option D):This field was entirely removed in IPv6. IPv6 relies on the data link layer (Ethernet) and the transport layer (TCP/UDP) to perform error detection, significantly reducing the processing overhead for routers in the core of a service provider network.

Graceful Restart (GR)is a high-availability mechanism designed to minimize the impact of a routing protocol process (rpd) restart or a Routing Engine (RE) switchover. It allows a router to continue forwarding traffic while the control plane is recovering, provided that the data plane (Packet Forwarding Engine) remains intact.

According to Juniper Networks documentation, Graceful Restart operates in two distinct roles:

Restarting Mode:This is the role of the router that is actually undergoing the restart. In Junos OS, this mode isnot enabled by default (Option A). An administrator must explicitly configure graceful-restart under the [edit routing-options] hierarchy to allow the router to signal its neighbors that it is attempting a graceful recovery.

Helper Mode:This is the role of the neighboring routers. When a neighbor sees a router restart, if it is in "helper mode," it will continue to forward traffic toward the restarting router and will not flush the associated routes from its forwarding table for a specified period. In Junos,helper mode is enabled by default (Option B)for most protocols (OSPF, BGP, IS-IS). This means that even if you haven't configured GR on your own router, it will automatically assist its neighbors if they perform a graceful restart.

Why other options are incorrect:

Option C:WhileGRES (Graceful Routing Engine Switchover)is often usedwithGraceful Restart to handle hardware-level RE failures, they are independent features. GR can function during a simple software process restart without dual REs or GRES.

Option D:Nonstop Bridging (NSB)is a separate high-availability feature for Layer 2 protocols (like STP). While it shares a similar goal, Graceful Restart is specifically a Layer 3 protocol mechanism (Layer 2 does not use "helper" routers in the same way).

In Juniper Networks Junos OS,Generic Routing Encapsulation (GRE)andIP-in-IP (IP-IP)are common tunneling mechanisms used to transport packets across a network by encapsulating them within another protocol. Understanding the header structure and the limitations of these protocols is essential for proper MTU (Maximum Transmission Unit) management and security design.

Overhead (Option A):

Both GRE and IP-IP tunnels operate by adding an additional IP header to the original packet. An IP-IP tunnel (Protocol 4) adds a20-byteIPv4 header. A GRE tunnel (Protocol 47) adds the same20-bytedelivery IP header plus a minimum4-byteGRE header (totaling 24 bytes, which can increase if keys or sequencing are used). Because these headers are added to the payload, the total size of the packet increases. This "overhead" means that if the original packet was already at the MTU limit (e.g., 1500 bytes), the encapsulated packet will exceed it, potentially leading to fragmentation or the need to adjust theTCP MSS (Maximum Segment Size).

Encryption (Option D):

Crucially, according to Juniper Service Provider documentation, neither GRE nor IP-IP provides nativeencryptionor data confidentiality. They are encapsulation protocols, not security protocols. The payload remains in cleartext and is visible to any device along the path. If security and encryption are required for data traversing these tunnels, they must be combined withIPsec (IP Security). While GRE is often used as the "carrier" for IPsec (to allow multicast or dynamic routing protocols which IPsec alone does not support), the GRE protocol itself remains an unencrypted delivery mechanism. Therefore, statements A and D accurately describe the architectural behavior of these tunnel types.

For Juniper platforms equipped with dualRouting Engines (REs), the fundamental technology required to provide high availability during a hardware or software failure of the primary RE isGraceful Routing Engine Switchover (GRES).

According to Juniper Networks technical documentation, GRES allows the backup RE to stay in a "hot" standby state. When GRES is enabled, the primary RE synchronizes critical state information with the backup RE, specifically thechassis stateand theinterface state. This synchronization includes the Packet Forwarding Engine (PFE) configuration.

When the primary RE fails, the backup RE takes over immediately. Because the PFE (which resides on the line cards) was already synchronized and is not restarted during the switchover, the routercontinues to forward packetsthat are already in flight or part of established flows. This prevents a complete network outage during an RE failover.

Comparison with other options:

NSB (Non-Stop Bridging - Option A):Focuses specifically on maintaining Layer 2 protocol states (like STP) during a switchover.

LAG (Link Aggregation - Option B):Provides redundancy for physical links, not the control plane or the RE.

BFD (Bidirectional Forwarding Detection - Option C):Is a protocol used for rapid detection of link or neighbor failures; it does not protect the RE or maintain forwarding during an internal switchover.

It is important to note that while GRES maintains theforwardingstate, it does not by itself maintain therouting protocolstate (adjacencies). To keep OSPF or BGP sessions from dropping during the switchover, GRES must be paired withNon-Stop Active Routing (NSR). However, as the question focuses on the core requirement of continuing to forward packets,GRESis the foundational technology.

TheBorder Gateway Protocol (BGP)operates based on a strict set of advertisement rules designed to prevent routing loops while ensuring global reachability. These rules differ significantly depending on whether the relationship isExternal BGP (EBGP)orInternal BGP (IBGP).

1. EBGP Advertisement (Option A):In a standard EBGP scenario, a router acts as an exit/entry point for an Autonomous System. When an EBGP speaker receives a valid route from any peer (Internal or External), it will, by default, advertise that route to all of its other EBGP peers. This is the primary mechanism that allows prefixes to propagate across the global internet from one AS to another.

2. IBGP Split Horizon (Option D):

The most critical rule within an AS is theIBGP Split Horizonrule. To prevent loops within an AS, BGP dictates that a route learned from an IBGP peermust notbe advertised to any other IBGP peer. This is why BGP requires a "full mesh" of IBGP sessions or the use ofRoute Reflectorsto ensure all internal routers learn all routes. Without this rule, a route could circulate infinitely within the AS because IBGP does not update the AS_PATH attribute.

3. EBGP to IBGP Propagation (Option B):

When a router learns a route from an EBGP peer, it is permitted to advertise that route to all of its IBGP peers. This ensures that everyone inside the network knows how to reach external destinations. However, it is important to remember that in Junos OS, theBGP Next Hopis not modified by default when sending routes to IBGP peers, often requiring a "next-hop-self" policy to ensure internal reachability.

Options C and E are incorrect because they directly contradict these fundamental BGP loop-prevention and propagation mechanisms.

In a Multiprotocol Label Switching (MPLS) environment, label operations are categorized into three primary actions:Push(adding a label),Swap(replacing a label), andPop(removing a label). The specific behavior described in the question refers to a mechanism calledPenultimate Hop Popping (PHP).

According to Juniper Networks technical documentation, the goal of PHP is to improve forwarding efficiency at the egress point of a Label-Switched Path (LSP). TheEgress Label Edge Router (LER), which is the final destination for the LSP, would normally have to perform two lookups if it received a labeled packet: first, it would look up the label in its MPLS table to see it is the destination, and second, it would look up the underlying IP payload in its IP routing table (inet.0) to forward the packet.

To alleviate this burden, the Egress LER signals a special label value calledImplicit Null (Label 3)to its upstream neighbor (the penultimate router) during the signaling process (RSVP or LDP). When thepenultimate routerreceives a packet destined for that egress LER, it sees the instruction to pop the transport label. Consequently, the penultimate router performs aPopoperation, stripping away the outer MPLS label and sending the raw IP packet (or the remaining inner service label) to the Egress LER.

This allows the Egress LER to perform only a single lookup. If the transport label was the only label, the Egress LER simply performs a standard IP lookup. If there is a VPN label remaining, it performs a single MPLS lookup for the VRF. This "default" behavior in Junos OS optimizes the performance of the egress router by offloading the final label removal to the penultimate hop. Note that ifUltimate Hop Popping (UHP)were configured (via the explicit-null command), the penultimate router would perform aSwapto Label 0 instead of a Pop.

BGP attributes are categorized into four distinct types based on how they are handled by a BGP speaker:Well-known mandatory,Well-known discretionary,Optional transitive, andOptional non-transitive. Understanding these categories is essential for traffic engineering and ensuring consistent policy across an Autonomous System.

According to Juniper Networks technical documentation, theCommunityattribute is classified as anoptional transitiveattribute. The term "optional" implies that a BGP implementation is not required to support or recognize the attribute. However, because it is "transitive," if a Juniper router receives an update containing a community tag that it does not recognize or has no specific policy for, it must accept the attribute and pass it along to other BGP peers unchanged. This ensures that community-based policies can be signaled across intermediate ASes that may not be configured to act upon those specific tags.

In contrast:

Origin (Option A)andAS Path (Option B)arewell-known mandatoryattributes. Every BGP update must include these, and every BGP-compliant router must recognize them.

MED (Option D)(Multi-Exit Discriminator) is anoptional non-transitiveattribute. If a router receives a MED and advertises that route to an EBGP peer, the MED is typically stripped away (unless specific configurations like path-selection cisco-non-deterministic are used), as it is intended only to influence the immediate neighboring AS.

The Community attribute (defined in RFC 1997) is a powerful tool in Junos OS, often used for tagging routes to trigger specific routing policies, such as setting local preference or identifying the geographic origin of a prefix. By being transitive, it allows for sophisticated administrative control across complex multi-provider environments.