Authentic Juniper Certification Exam JN0-650 Questions Answers

To interoperate with Cisco switches running Per-VLAN Spanning Tree Plus (PVST+), Juniper devices must use VLAN Spanning Tree Protocol (VSTP).

PVST+ Compatibility: VSTP is specifically designed to handle the per-VLAN BPDU requirements of Cisco's PVST+. It generates a separate spanning tree instance for each VLAN and uses the same multicast destination MAC address as Cisco devices.

Other Protocols: MSTP (B) is used for grouping VLANs into regions; RSTP (D) is a single-instance protocol (IEEE 802.1w) and is generally incompatible with per-VLAN BPDU requirements without additional configuration.

OSPF stub areas are used to reduce the size of the Link-State Database (LSDB) in routers with limited resources by restricting the flooding of external routes.

Virtual Links (Option C): According to OSPF standards (both v2 and v3), virtual links cannot pass through stub areas. A virtual link must transit a "transit area," which must be a standard (non-stub) area with a full routing table.

Totally Stubby Areas (Option D): A stub area (which blocks Type 5 External LSAs) can be further restricted into a totally stubby area. In Junos OS, this is done by adding the no-summaries statement to the stub configuration. This blocks both Type 5 and Type 3 (Inter-area) LSAs, replacing them with a single default route.

Incorrect Statements: Option A is incorrect because standard stub areas cannot contain an ASBR; only Not-So-Stubby Areas (NSSA) allow for an ASBR. Option B is incorrect because an area is either a Stub or an NSSA; they are mutually exclusive configurations for the same area.

When 802.1X server fail fallback is enabled with the vlan-name feature, the switch provides a specific survival mechanism for both existing and new sessions when the RADIUS server becomes unreachable.

Existing Clients (Statement B): Clients that have already successfully authenticated are unaffected by the server's unavailability in the short term. They maintain their current network access until their specific re-authentication timer expires. Only then will the switch attempt to contact the server again and trigger the fallback action if the server remains down.

New Clients (Statement D): For any new device attempting to connect while the RADIUS server is down, the switch cannot perform a standard authentication. Under the vlan-name fallback configuration, these new clients are automatically placed into the specified fallback VLAN and granted access based on the local policy defined for that VLAN.

Why others are incorrect: Statement A is incorrect because disconnecting active users would cause unnecessary service disruption. Statement C is incorrect because new clients cannot "request" a VLAN during the 802.1X handshake; the switch assigns it based on the fallback configuration.