Practice Free JN0-281 Exam Online Questions
Question #11
Which statement is correct about an IRB interface?
- A . An IRB interface switches traffic within the same VLAN.
- B . An IRB interface trunks together VLANs on different switches.
- C . An IRB interface is a physical Layer 3 interface that connects VLANs together.
- D . An IRB interface is a Layer 3 interface that can be used to route between VLANs.
Correct Answer: D
D
Explanation:
An IRB (Integrated Routing and Bridging) interface provides routing functionality between VLANs at Layer 3, allowing devices in different VLANs to communicate with each other.
Step-by-Step Breakdown:
IRB Functionality:
The IRB interface enables routing between different VLANs by acting as a Layer 3 gateway. Traffic within the same VLAN is handled by Layer 2 switching, while traffic between VLANs is routed through the IRB interface.
Layer 3 Routing Between VLANs:
Each VLAN can be assigned an IP address on the IRB interface, which allows traffic to flow between VLANs based on Layer 3 IP routing.
Juniper
Reference: IRB Interface Configuration: Juniper supports IRB for inter-VLAN routing on devices like the EX and QFX series switches, facilitating Layer 3 communication in data centers.
D
Explanation:
An IRB (Integrated Routing and Bridging) interface provides routing functionality between VLANs at Layer 3, allowing devices in different VLANs to communicate with each other.
Step-by-Step Breakdown:
IRB Functionality:
The IRB interface enables routing between different VLANs by acting as a Layer 3 gateway. Traffic within the same VLAN is handled by Layer 2 switching, while traffic between VLANs is routed through the IRB interface.
Layer 3 Routing Between VLANs:
Each VLAN can be assigned an IP address on the IRB interface, which allows traffic to flow between VLANs based on Layer 3 IP routing.
Juniper
Reference: IRB Interface Configuration: Juniper supports IRB for inter-VLAN routing on devices like the EX and QFX series switches, facilitating Layer 3 communication in data centers.
Question #12
What are two device roles in a five-member Virtual Chassis? (Choose two.)
- A . PFE
- B . Control-board
- C . Line card
- D . Routing-engine
Correct Answer: C, D
C, D
Explanation:
In a Virtual Chassis (VC) configuration, multiple Juniper switches are interconnected to form a single logical device. Each member switch in the Virtual Chassis plays a specific role.
Step-by-Step Breakdown:
Line Card Role:
Member switches acting as line cards provide additional ports for traffic forwarding but do not perform control or routing functions. These switches depend on the routing engine to handle control-plane tasks.
Routing Engine Role:
A switch in the routing-engine role is responsible for control-plane operations such as routing protocol management and control of the Virtual Chassis.
Virtual Chassis Roles:
Master Routing Engine: Handles control-plane functions and manages the entire Virtual Chassis.
Backup Routing Engine: Takes over if the master fails.
Line Card: Provides additional ports and handles data-plane operations. Juniper
Reference: Virtual Chassis: In a five-member Virtual Chassis, multiple switches act as line cards, while one or more switches are designated as the routing engines (master and backup).
C, D
Explanation:
In a Virtual Chassis (VC) configuration, multiple Juniper switches are interconnected to form a single logical device. Each member switch in the Virtual Chassis plays a specific role.
Step-by-Step Breakdown:
Line Card Role:
Member switches acting as line cards provide additional ports for traffic forwarding but do not perform control or routing functions. These switches depend on the routing engine to handle control-plane tasks.
Routing Engine Role:
A switch in the routing-engine role is responsible for control-plane operations such as routing protocol management and control of the Virtual Chassis.
Virtual Chassis Roles:
Master Routing Engine: Handles control-plane functions and manages the entire Virtual Chassis.
Backup Routing Engine: Takes over if the master fails.
Line Card: Provides additional ports and handles data-plane operations. Juniper
Reference: Virtual Chassis: In a five-member Virtual Chassis, multiple switches act as line cards, while one or more switches are designated as the routing engines (master and backup).
Question #13
Which Junos OS routing table stores IPv6 addresses?
- A . inet.0
- B . inet0.6
- C . inet.6
- D . inet6.0
Correct Answer: D
D
Explanation:
In Junos OS, routing information is stored in different routing tables depending on the protocol and address family. For IPv6 addresses, the routing table used is inet6.0.
Step-by-Step Explanation
Routing Tables in Junos:
inet.0: This is the primary routing table for IPv4 unicast routes.
inet6.0: This is the primary routing table for IPv6 unicast routes.
inet.3: This routing table is used for MPLS-related routing.
Other routing tables, like inet.1, inet.2, are used for multicast and other specific purposes.
inet6.0 Routing Table:
When IPv6 is enabled on a Juniper router, all the IPv6 routes are stored in the inet6.0 table. This includes both direct routes (connected networks) and learned routes (from dynamic routing protocols like OSPFv3, BGP, etc.).
Verification:
To view IPv6 routes, the command show route table inet6.0 is used. This will display the contents of the IPv6 routing table, showing the network prefixes, next-hop addresses, and protocol information for each route.
Juniper
Reference: Junos Command: Use show route table inet6.0 to check IPv6 routing entries.
IPv6 Routing: Ensure that the IPv6 protocol is enabled on interfaces and that routing protocols like OSPFv3 or BGP are properly configured for IPv6 traffic handling.
D
Explanation:
In Junos OS, routing information is stored in different routing tables depending on the protocol and address family. For IPv6 addresses, the routing table used is inet6.0.
Step-by-Step Explanation
Routing Tables in Junos:
inet.0: This is the primary routing table for IPv4 unicast routes.
inet6.0: This is the primary routing table for IPv6 unicast routes.
inet.3: This routing table is used for MPLS-related routing.
Other routing tables, like inet.1, inet.2, are used for multicast and other specific purposes.
inet6.0 Routing Table:
When IPv6 is enabled on a Juniper router, all the IPv6 routes are stored in the inet6.0 table. This includes both direct routes (connected networks) and learned routes (from dynamic routing protocols like OSPFv3, BGP, etc.).
Verification:
To view IPv6 routes, the command show route table inet6.0 is used. This will display the contents of the IPv6 routing table, showing the network prefixes, next-hop addresses, and protocol information for each route.
Juniper
Reference: Junos Command: Use show route table inet6.0 to check IPv6 routing entries.
IPv6 Routing: Ensure that the IPv6 protocol is enabled on interfaces and that routing protocols like OSPFv3 or BGP are properly configured for IPv6 traffic handling.
Question #14
Which two statements are correct about VLAN tags? (Choose two.)
- A . VLAN tags carry a VLAN ID and priority.
- B . VLAN tags are required on access ports.
- C . VLAN tags require multiple forwarding tables.
- D . VLAN tags can be inserted or removed by trunk interfaces.
Correct Answer: A, D
A, D
Explanation:
VLAN tags are used in Ethernet frames to identify and differentiate traffic between multiple VLANs.
They are especially important for devices like switches that handle multiple VLANs on the same physical link.
Step-by-Step Breakdown:
VLAN Tag Contents:
VLAN ID: The tag contains a 12-bit VLAN ID field that identifies the VLAN to which the frame belongs.
Priority: The tag also includes a 3-bit priority field (also known as 802.1p priority) used for QoS (Quality of Service) to prioritize traffic.
Trunk Ports and VLAN Tagging:
Trunk Ports are used to carry traffic for multiple VLANs across a single link. These interfaces insert (tag) VLAN identifiers into frames when they leave the switch and remove (untag) them when frames enter the switch.
Access Ports:
VLAN tags are typically not used on access ports (ports that connect to end devices) since those ports are configured to be part of a single VLAN, and the traffic doesn’t need VLAN tags. Juniper
Reference: VLAN Tagging: Juniper switches support VLAN tagging and ensure that frames are tagged or untagged as they traverse trunk or access ports, respectively.
A, D
Explanation:
VLAN tags are used in Ethernet frames to identify and differentiate traffic between multiple VLANs.
They are especially important for devices like switches that handle multiple VLANs on the same physical link.
Step-by-Step Breakdown:
VLAN Tag Contents:
VLAN ID: The tag contains a 12-bit VLAN ID field that identifies the VLAN to which the frame belongs.
Priority: The tag also includes a 3-bit priority field (also known as 802.1p priority) used for QoS (Quality of Service) to prioritize traffic.
Trunk Ports and VLAN Tagging:
Trunk Ports are used to carry traffic for multiple VLANs across a single link. These interfaces insert (tag) VLAN identifiers into frames when they leave the switch and remove (untag) them when frames enter the switch.
Access Ports:
VLAN tags are typically not used on access ports (ports that connect to end devices) since those ports are configured to be part of a single VLAN, and the traffic doesn’t need VLAN tags. Juniper
Reference: VLAN Tagging: Juniper switches support VLAN tagging and ensure that frames are tagged or untagged as they traverse trunk or access ports, respectively.
Question #15
Which two statements are correct about rules for EBGP and IBGP? (Choose two.)
- A . EBGP peers have a TTL of 1, while IBGP peers have a TTL of 255.
- B . EBGP peers have a TTL of 255, while IBGP peers have a TTL of 1.
- C . EBGP routes are more preferred than IBGP routes.
- D . IBGP routes are more preferred than EBGP routes.
Correct Answer: A, C
A, C
Explanation:
EBGP (External BGP) and IBGP (Internal BGP) operate with different rules due to the nature of their
relationships.
Step-by-Step Breakdown:
TTL Differences:
EBGP: By default, EBGP peers have a TTL of 1, meaning they must be directly connected, or the TTL needs to be manually increased for multihop EBGP.
IBGP: IBGP peers within the same AS have a TTL of 255, as they are expected to communicate over multiple hops within the AS.
Preference for EBGP Routes:
Routes learned via EBGP are typically preferred over IBGP routes. This is because EBGP routes are considered more reliable since they originate outside the AS, while IBGP routes are internal. Juniper
Reference: BGP Configuration: The different handling of TTL and route preferences between EBGP and IBGP ensures proper route selection and security within Junos-based networks.
A, C
Explanation:
EBGP (External BGP) and IBGP (Internal BGP) operate with different rules due to the nature of their
relationships.
Step-by-Step Breakdown:
TTL Differences:
EBGP: By default, EBGP peers have a TTL of 1, meaning they must be directly connected, or the TTL needs to be manually increased for multihop EBGP.
IBGP: IBGP peers within the same AS have a TTL of 255, as they are expected to communicate over multiple hops within the AS.
Preference for EBGP Routes:
Routes learned via EBGP are typically preferred over IBGP routes. This is because EBGP routes are considered more reliable since they originate outside the AS, while IBGP routes are internal. Juniper
Reference: BGP Configuration: The different handling of TTL and route preferences between EBGP and IBGP ensures proper route selection and security within Junos-based networks.
Question #16
Which two statements are correct about EVPN-VXLAN overlay networking? (Choose two.)
- A . It is the only option to provide reachability between servers that reside in the same network segment in a data center.
- B . BGP provides the control plane within the overlay network.
- C . An encapsulation of the original packet is required to transport the packet across the network.
- D . OSPF provides the control plane within the overlay network.
Correct Answer: B, C
B, C
Explanation:
EVPN-VXLAN is an overlay technology used in data center networks to extend Layer 2 services over a
Layer 3 network.
Step-by-Step Breakdown:
BGP Control Plane:
BGP (Border Gateway Protocol) is used as the control plane for EVPN-VXLAN. BGP advertises MAC addresses and IP address reachability information across the VXLAN network, enabling efficient multi-tenant Layer 2 connectivity over a Layer 3 infrastructure.
Encapsulation:
VXLAN (Virtual Extensible LAN) encapsulates Layer 2 frames into Layer 3 packets. This encapsulation allows Layer 2 traffic to be transported across a Layer 3 network, effectively creating a tunnel for Ethernet frames.
Juniper
Reference: EVPN-VXLAN Configuration: Juniper supports EVPN-VXLAN with BGP as the control plane, allowing scalable Layer 2 connectivity over a routed infrastructure in modern data centers.
B, C
Explanation:
EVPN-VXLAN is an overlay technology used in data center networks to extend Layer 2 services over a
Layer 3 network.
Step-by-Step Breakdown:
BGP Control Plane:
BGP (Border Gateway Protocol) is used as the control plane for EVPN-VXLAN. BGP advertises MAC addresses and IP address reachability information across the VXLAN network, enabling efficient multi-tenant Layer 2 connectivity over a Layer 3 infrastructure.
Encapsulation:
VXLAN (Virtual Extensible LAN) encapsulates Layer 2 frames into Layer 3 packets. This encapsulation allows Layer 2 traffic to be transported across a Layer 3 network, effectively creating a tunnel for Ethernet frames.
Juniper
Reference: EVPN-VXLAN Configuration: Juniper supports EVPN-VXLAN with BGP as the control plane, allowing scalable Layer 2 connectivity over a routed infrastructure in modern data centers.
Question #17
What are two requirements for an IP fabric? (Choose two.)
- A . a Layer 3 routing protocol
- B . a single connection between each spine and leaf
- C . a single connection between each leaf
- D . a Layer 2 switching protocol
Correct Answer: A, B
A, B
Explanation:
An IP fabric is a network architecture commonly used in data centers to provide scalable, high-throughput connectivity using a spine-leaf topology.
Step-by-Step Breakdown:
Layer 3 Routing Protocol:
An IP fabric relies on a Layer 3 routing protocol, typically BGP or OSPF, to provide routing between the leaf and spine switches. This ensures efficient traffic forwarding across the network. Single Connection Between Spine and Leaf:
In an IP fabric, each leaf switch connects to every spine switch with a single connection. This ensures that traffic between any two leaf switches can travel through the spine layer in just two hops.
Juniper
Reference: Spine-Leaf Design: Juniper’s IP fabric implementations are designed for scalability and low-latency
routing, often using protocols like BGP for Layer 3 control.
A, B
Explanation:
An IP fabric is a network architecture commonly used in data centers to provide scalable, high-throughput connectivity using a spine-leaf topology.
Step-by-Step Breakdown:
Layer 3 Routing Protocol:
An IP fabric relies on a Layer 3 routing protocol, typically BGP or OSPF, to provide routing between the leaf and spine switches. This ensures efficient traffic forwarding across the network. Single Connection Between Spine and Leaf:
In an IP fabric, each leaf switch connects to every spine switch with a single connection. This ensures that traffic between any two leaf switches can travel through the spine layer in just two hops.
Juniper
Reference: Spine-Leaf Design: Juniper’s IP fabric implementations are designed for scalability and low-latency
routing, often using protocols like BGP for Layer 3 control.
Question #18
What information in the Ethernet header is used to populate the bridging table?
- A . destination address
- B . source address
- C . type
- D . protocol
Correct Answer: B
B
Explanation:
The source MAC address in the Ethernet header is used to populate the bridging table (also called the MAC address table) on a switch. When a frame arrives at a switch, the switch examines the source MAC address and records it along with the ingress port in its MAC address table.
Step-by-Step Breakdown:
Learning Process:
When an Ethernet frame arrives on a switch port, the switch looks at the source MAC address and adds this MAC address to the MAC table along with the port it was received on. This process is called MAC learning.
Purpose:
The switch uses this information to determine the correct port to send frames destined for that MAC address in future transmissions, thus ensuring efficient Layer 2 forwarding. Juniper
Reference: Ethernet Switching: Juniper switches use source MAC addresses to build and maintain the MAC address table, which is essential for Layer 2 switching.
B
Explanation:
The source MAC address in the Ethernet header is used to populate the bridging table (also called the MAC address table) on a switch. When a frame arrives at a switch, the switch examines the source MAC address and records it along with the ingress port in its MAC address table.
Step-by-Step Breakdown:
Learning Process:
When an Ethernet frame arrives on a switch port, the switch looks at the source MAC address and adds this MAC address to the MAC table along with the port it was received on. This process is called MAC learning.
Purpose:
The switch uses this information to determine the correct port to send frames destined for that MAC address in future transmissions, thus ensuring efficient Layer 2 forwarding. Juniper
Reference: Ethernet Switching: Juniper switches use source MAC addresses to build and maintain the MAC address table, which is essential for Layer 2 switching.
Question #19
What are two reasons why you would deploy an IP fabric instead of a traditional Layer 2 network in a
data center? (Choose two.)
- A . Layer 2 networks only support a single broadcast domain.
- B . IP fabrics are better suited to smaller networks where scale is less important.
- C . Layer 3 networks support load balancing.
- D . Layer 2 networks are susceptible to loops.
Correct Answer: C, D
C, D
Explanation:
IP fabrics are Layer 3-centric network designs often used in data centers due to their scalability,
efficient routing, and loop-free architecture.
Step-by-Step Breakdown:
Layer 3 Load Balancing:
IP fabrics use Equal-Cost Multipath (ECMP) to distribute traffic across multiple paths, providing effective load balancing and improving bandwidth utilization. This capability is absent in traditional Layer 2 networks, which do not support ECMP for routing decisions.
Layer 2 Loops:
Layer 2 networks are prone to loops because of the lack of TTL (Time-to-Live) mechanisms. Spanning Tree Protocol (STP) is required to prevent loops, but it can introduce inefficiencies by blocking links. In contrast, IP fabrics based on Layer 3 protocols are loop-free and do not need STP. Juniper
Reference: IP Fabric: Juniper’s IP fabric solutions offer efficient Layer 3 routing with built-in load balancing and loop prevention, making them ideal for modern data center architectures.
C, D
Explanation:
IP fabrics are Layer 3-centric network designs often used in data centers due to their scalability,
efficient routing, and loop-free architecture.
Step-by-Step Breakdown:
Layer 3 Load Balancing:
IP fabrics use Equal-Cost Multipath (ECMP) to distribute traffic across multiple paths, providing effective load balancing and improving bandwidth utilization. This capability is absent in traditional Layer 2 networks, which do not support ECMP for routing decisions.
Layer 2 Loops:
Layer 2 networks are prone to loops because of the lack of TTL (Time-to-Live) mechanisms. Spanning Tree Protocol (STP) is required to prevent loops, but it can introduce inefficiencies by blocking links. In contrast, IP fabrics based on Layer 3 protocols are loop-free and do not need STP. Juniper
Reference: IP Fabric: Juniper’s IP fabric solutions offer efficient Layer 3 routing with built-in load balancing and loop prevention, making them ideal for modern data center architectures.
Question #20
A switch receives a frame with a MAC address of FF-FF-FF-FF-FF-FF.
Which action will the switch take on this frame?
- A . It will flood it out of all interfaces, except for the ingress interface.
- B . It will flood it out of all interfaces, except for the directly connected VLAN.
- C . It will flood it out of all interfaces, except for the next-hop interface.
- D . It will flood it out of all interfaces.
Correct Answer: A
A
Explanation:
A MAC address of FF-FF-FF-FF-FF-FF is the Ethernet broadcast address. When a switch receives a frame with this destination MAC address, it is required to forward the frame to all interfaces except the one it was received on.
Step-by-Step Breakdown: Broadcast Frame Handling:
When a frame with the broadcast MAC address is received, the switch will flood it out of all active ports that belong to the same VLAN as the incoming frame. The broadcast frame is not sent back out of the ingress interface (the interface where the frame was originally received).
Purpose of Flooding:
Broadcasting is used to ensure that the frame reaches all devices within the broadcast domain (all devices within the same VLAN), which may not have a specific entry for the MAC address in their MAC address table.
Juniper
Reference: Layer 2 Frame Forwarding: Juniper switches flood broadcast frames to all ports in the same VLAN, except the port the frame was received on.
A
Explanation:
A MAC address of FF-FF-FF-FF-FF-FF is the Ethernet broadcast address. When a switch receives a frame with this destination MAC address, it is required to forward the frame to all interfaces except the one it was received on.
Step-by-Step Breakdown: Broadcast Frame Handling:
When a frame with the broadcast MAC address is received, the switch will flood it out of all active ports that belong to the same VLAN as the incoming frame. The broadcast frame is not sent back out of the ingress interface (the interface where the frame was originally received).
Purpose of Flooding:
Broadcasting is used to ensure that the frame reaches all devices within the broadcast domain (all devices within the same VLAN), which may not have a specific entry for the MAC address in their MAC address table.
Juniper
Reference: Layer 2 Frame Forwarding: Juniper switches flood broadcast frames to all ports in the same VLAN, except the port the frame was received on.
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