Get Juniper JN0-650 Exam Practice Questions - Real and Updated

Answer : B

For maintenance scenarios where a router must remain operational but should not be used as a transit path for OSPF traffic, Junos OS uses the overload functionality.

OSPF Overload (Option B): When you enable overload under protocols ospf, the router advertises its own Link-State Advertisements (LSAs) with a maximum metric (65535) for all of its transit links.

Traffic Diversion: Because OSPF uses the Shortest Path First (SPF) algorithm to find the lowest-cost path, other routers in the network will see the overloaded router as an extremely high-cost path. They will calculate alternate routes, effectively moving transit traffic off the router while still allowing management traffic directed to the router's own interfaces.

Timeout Options: You can configure this to be permanent or set a timeout so that the router automatically resumes normal metric advertisements after a set period.

Answer : B, C

In Junos OS 24.4, the no-loss forwarding class is used for traffic that requires lossless delivery, such as iSCSI or FCoE, typically in a Data Center Bridging (DCB) environment.

Priority-Based Flow Control (Option C): To guarantee 'no-loss' behavior, the switch must support and use Priority-based Flow Control (PFC). PFC allows the switch to send 'pause' frames for a specific priority (forwarding class) to prevent buffer overflow and packet drops without affecting other traffic on the same link.

Forwarding Class Sets (Option B): In enhanced Layer 2 software (ELS) versions used by modern QFX and EX series switches, lossless traffic must be managed within forwarding class sets (also known as priority groups). This grouping is necessary to apply specific DCB properties, such as PFC and specific bandwidth guarantees, to the lossless traffic class.

Why A and D are incorrect: Default scheduler maps and default drop profiles do not provide the specialized buffer management or lossless signaling required for this class. Lossless traffic specifically requires the suppression of tail drops rather than standard drop profiles.

Answer : C

In a Juniper Q-in-Q (Layer 2 tunneling) environment, VLAN rewrites (specifically the swap operation) provide the most granular control over how customer traffic (C-VLANs) is mapped to service provider traffic (S-VLANs).

VLAN Rewrites (The Swap Operation): This method involves replacing the incoming customer VLAN tag with a service provider tag as the frame enters the tunnel. This is technically a 'swap' because the original C-VLAN tag is removed and the S-VLAN tag is written in its place. At the egress of the tunnel, the S-VLAN tag is swapped back for the original C-VLAN tag. This is often used when different customers use the same C-VLAN IDs and the provider needs to keep them unique within their core.

Many-to-Many: This is a mapping style where multiple customer VLANs are mapped to multiple service provider VLANs, but it typically relies on the 'push' (stacking) operation rather than a literal 'swap' of the tag itself.

All-in-One: This is the simplest form of Q-in-Q where all traffic entering an interface is 'pushed' into a single S-VLAN tag, regardless of any existing C-VLAN tags. No swapping occurs; the original tags are simply buried under the new provider tag.

L2PT (Layer 2 Protocol Tunneling): This is a feature used to tunnel Layer 2 control protocols (like STP, CDP, or LLDP) across a provider network by encapsulating them or changing their destination MAC addresses. It does not involve the swapping of VLAN tags.

Answer : B

In External BGP (EBGP), there is a default safety mechanism that requires the peer's next hop to be on a directly connected network.

TTL Constraint: By default, EBGP packets are sent with a Time-to-Live (TTL) value of 1. If the next hop is not directly connected (e.g., when peering via loopback interfaces or across a multi-hop path), the packet will expire before reaching the destination, causing the route to be discarded or the session to fail.

The Multihop Solution (Option B): To override this behavior, you must configure the multihop statement under the BGP neighbor or group hierarchy. This allows the BGP session to establish by increasing the TTL (typically to 64 or a user-defined value) and bypasses the 'directly connected' check.

Incorrect Options: Option A (accept-remote-nexthop) is used in internal BGP or specific routing-instance scenarios to resolve next hops that aren't in the local routing table, but it doesn't solve the EBGP TTL/direct-connection requirement. Option C (advertise-inactive) allows BGP to advertise routes that are not the best path in the routing table, which is irrelevant to next-hop reachability. Option D (multipath) is used for load-sharing across multiple paths.

Answer : A, C

In BGP path selection, the Local Preference attribute is one of the most common ways to influence outbound traffic from an Autonomous System (AS). It is a well-known discretionary attribute that is propagated throughout the AS to tell internal routers which path is preferred for a specific destination.

Priority Rule: In the BGP selection algorithm, a higher local preference value is always preferred over a lower one. The default value in Junos OS is 100.

Influencing Outbound Traffic (Option A): To ensure that Provider A is always preferred, you would apply an import policy on R1 (the router connected to Provider A) to set the local preference of all received routes to a value higher than the default (e.g., 200). Since 200 > 100, R3 and R4 will prefer the path via R1.

Alternative Method (Option C): Conversely, you can achieve the same result by applying an import policy on R2 (the router connected to Provider B) to set the local preference to a value lower than the default (e.g., 50). Since the routes from R1 remain at the default of 100, and 100 > 50, the path via R1 (Provider A) is preferred.

Why B and D are incorrect: Setting a higher local preference on R2 (Option B) would make Provider B the preferred exit point. Setting a lower local preference on R1 (Option D) would make Provider A the least preferred exit point.