Juniper JN0-280 Practice Test - Questions Answers, Page 4

In Layer 2 switching, switches learn MAC addresses based on the source MAC address of incoming frames and forward frames based on the destination MAC address.

Step-by-Step Breakdown:

MAC Learning:

When a switch receives a frame, it records the source MAC address and the port on which it arrived. This allows the switch to know where to send traffic destined for that MAC address.

Forwarding Based on Destination:

The switch then looks at the destination MAC address and forwards the frame out of the port associated with that MAC address. If the MAC is unknown, the switch floods the frame to all ports.

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Reference:

Layer 2 Switching: Juniper switches use source MAC addresses to build MAC tables and forward traffic based on the destination MAC address.

A collision domain is a network segment where data packets can 'collide' with one another when being sent on the same network medium.

Step-by-Step Breakdown:

Increased Collision Probability: If all devices are in a single collision domain, the likelihood of packet collisions increases as more devices attempt to send packets simultaneously, leading to network inefficiencies.

Increased Resource Consumption: More collisions result in increased network resource consumption as devices need to retransmit packets, causing higher utilization of bandwidth and slowing down network performance.

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Reference:

Collision Domains: Proper network segmentation using switches reduces collision domains, thereby improving network performance and reducing packet collisions.

In IBGP (Internal Border Gateway Protocol), all routers within the same AS (Autonomous System) must have a logical full-mesh topology. This means that every IBGP router must be able to communicate with every other IBGP router directly or indirectly to ensure proper route propagation.

Step-by-Step Breakdown:

Logical Full Mesh:

In an IBGP setup, routers do not re-advertise routes learned from one IBGP peer to another IBGP peer. This rule is in place to prevent routing loops within the AS.

To ensure full route propagation, a logical full mesh is required, meaning every IBGP router must peer with every other IBGP router in the AS. This can be done either directly or via route reflection or confederation.

Physical Full Mesh Not Required:

The physical topology does not need to be a full mesh, but the BGP peering relationships must form a logical full mesh. Techniques like route reflectors or BGP confederations can reduce the need for manual full-mesh peering.

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Reference:

IBGP Configuration: IBGP logical full mesh requirements can be simplified using route reflectors to avoid the complexity of manually configuring many IBGP peers.

High availability and fast convergence are critical in data center networks to minimize downtime and maintain optimal performance. The following technologies contribute to achieving these goals:

Graceful Restart (GR):

GR allows routers to maintain forwarding state during control plane restarts, ensuring continuous packet forwarding while minimizing network disruptions.

Bidirectional Forwarding Detection (BFD):

BFD provides fast detection of path failures, allowing routing protocols to converge quickly by detecting link failures much faster than traditional timers.

Link Aggregation Group (LAG):

LAG increases both redundancy and bandwidth by combining multiple physical links into one logical link, providing load balancing and fault tolerance.

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Reference:

High Availability Techniques: These technologies are fundamental in ensuring rapid recovery and failover within Juniper-based data center environments.

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.

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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.

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.

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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.

To configure aggregated Ethernet (AE) interfaces on a Junos device, the configuration is done under the [edit chassis] hierarchy.

Step-by-Step Breakdown:

Chassis Configuration:

The chassis configuration is responsible for enabling the hardware to support Link Aggregation Groups (LAGs), allowing multiple physical interfaces to be bundled into a single logical interface for load balancing and redundancy.

Command Example:

set chassis aggregated-devices ethernet device-count <number>

This command enables a specific number of aggregated Ethernet interfaces on the device.

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Reference:

LAG Configuration in Junos: The chassis hierarchy is used to allocate and manage hardware resources for aggregated Ethernet interfaces in Juniper devices.

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.

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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.

In the exhibit, the ae0 and ae1 interfaces are in a link down state. This occurs when no physical interfaces (member interfaces) have been added to the LAG (Link Aggregation Group) interfaces, or the member interfaces are not operational.

Step-by-Step Breakdown:

LAG Configuration:

A LAG interface (aggregated Ethernet interface) is a logical interface that combines multiple physical interfaces for redundancy and increased bandwidth. The LAG will only be operational if at least one member interface is active and configured correctly.

No Operational Member Interfaces:

If no member interfaces are added or if the member interfaces are down, the LAG will remain in a down state, as shown in the exhibit for ae0 and ae1.

Resolution:

Verify that physical interfaces have been added to the LAG using commands like:

LAG Interface Status: In Juniper, the link status of the LAG depends on its member interfaces, which must be operational for the LAG to function.