Pass the Nokia Certified Data Center Fabric Professional 4A0-D01 Questions and answers with ExamsMirror

Comprehensive and Detailed Explanation with Exact Extracts:

Option B is FALSE:

The system-cpu-policer is a software-based policer running on the CPM CPU, not hardware-based.

Extract from Nokia SR Linux QoS Guide (Section: Control Plane Policing):

"The system-cpu-policer is enforced in software on the CPM. In contrast, distributed-policers are hardware-based and execute on line cards."

Other Options are TRUE:

A: Hierarchical policing (e.g., per-protocol child policers under an aggregate) is supported.

Extract: "Hierarchical policers allow aggregate rate-limiting plus per-protocol sub-policers (e.g., for BGP, OSPF)."

C: The system-cpu-policer polices the aggregate traffic reaching the CPM.

Extract: "system-cpu-policer applies to the sum of all traffic forwarded from line cards to the CPM."

D: CPM-filter entries can combine both policers:

distributed-policer (line card hardware) for early per-card rate-limiting.

system-cpu-policer (CPM software) for final aggregate policing.

Extract: "CPM-filter entries may reference both a distributed-policer (for per-line card enforcement) and a system-cpu-policer (for CPM-wide aggregation)."

Comprehensive and Detailed Explanation From Exact Extract:

Option A: FALSE – Checkpoint 0 is the latest (most recent), not the oldest.

"Checkpoints are numbered sequentially, with 0 representing the most recent checkpoint. Higher numbers indicate older checkpoints."

— SR Linux Configuration Management Guide, "Checkpoint Numbering"

Option B: TRUE – Checkpoints are stored as JSON files.

"Checkpoints capture the running configuration in JSON format for easy parsing and restoration."

— SR Linux CLI User Guide, "Checkpoint Operations"

Option C: TRUE – Reversion to any checkpoint is supported.

"Operators can revert to any saved checkpoint, restoring the system to that specific state."

— SR Linux Configuration Management Guide, "Checkpoint Revert"

Option D: TRUE – Checkpoints can be auto-generated on commit.

"The system can be configured to create a new checkpoint automatically upon successful commit."

— SR Linux CLI User Guide, "Commit Options"

Conclusion: Option A is false because checkpoint 0 is the newest.

Comprehensive and Detailed Explanation with Exact Extracts:

Option A is FALSE: Next-hop groups support indirect next-hops (non-local IPs requiring recursive lookup).

Extract from Nokia SR Linux Configuration Guide (Section: Next-Hop Groups):

"The next-hop can be a directly attached IP address or an indirect next-hop (e.g., a router IP not on a directly connected subnet)."

Option B is TRUE: Next-hop groups are reusable objects referenced by multiple static routes.

Extract from Nokia SR Linux Configuration Guide (Section: Next-Hop Groups):

"A single next-hop group can be referenced by multiple static routes, simplifying configuration for shared forwarding behavior."

Option C is FALSE: Blackhole next-hop groups silently drop traffic by default. ICMP unreachable messages require explicit configuration.

Extract from Nokia SR Linux Configuration Guide (Section: Blackhole Routes):

"When blackhole is configured, traffic is discarded without sending ICMP unreachable messages unless send-blackhole-icmp true is explicitly set."

Option D is FALSE: Next-hop groups support ECMP with multiple next-hops.

Extract from Nokia SR Linux Fundamentals Guide (Section: Next-Hop Groups):

"A next-hop group can define multiple next-hops for Equal-Cost Multi-Path (ECMP) load balancing."

Comprehensive and Detailed Explanation From Exact Extract:

Option A: TRUE – MAC-VRF is a Layer 2 instance.

"A MAC-VRF network instance operates as a Layer 2 bridging domain."

— SR Linux Network Instance Guide, "MAC-VRF Overview"

Option B: TRUE – Bridge tables map MACs to egress interfaces.

"The bridge table associates destination MAC addresses with exit interfaces."

— SR Linux Forwarding Guide, "MAC-VRF Forwarding"

Option C: FALSE – MAC-VRF uses MAC addresses (not IP) for forwarding.

"In a MAC-VRF, traffic is switched based solely on destination MAC addresses, not IP."

— SR Linux Network Instance Guide, "Bridging vs Routing"

Option D: TRUE – MAC-VRF groups devices in the same subnet.

"A MAC-VRF instance enables Layer 2 connectivity for devices sharing the same IP subnet."

— SR Linux EVPN Guide, "L2 Network Design"

Conclusion: Option C is false as MAC-VRF is L2-only.

Comprehensive and Detailed Explanation with Exact Extracts:

Exhibit Analysis:

The configuration defines a log file named bgp-log (not a buffer) under system logging.

It includes messages from subsystems bgp and netinst (network-instance).

SR Linux Logging Command Syntax:

show system logging file  is the operational command to display contents of a log file.

show system logging buffer  is used for memory buffers, not files.

info commands display configuration, not log contents.

Verification from Documentation:Extract from Nokia SR Linux CLI Guide (Section: Logging Commands):

"Use show system logging file  to display the current contents of a configured log file. For example:

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A:dc-leaf-1# show system logging file bgp-log

This outputs the log entries stored in the specified file."

Extract from Nokia SR Linux Configuration Guide (Section: Log Files):

"Log files are persistent entities stored in /var/log/srlinux/. Their contents are viewed exclusively via show system logging file, not info or buffer commands."

Why Other Options Are Incorrect:

A: buffer references in-memory logs, not persistent files.

C/D: info displays configuration (e.g., info system logging shows the snippet in the exhibit), not log contents.

Comprehensive and Detailed Explanation with Exact Extracts:

Option A is FALSE: SR Linux does not use a simple modulo operation for ECMP hashing. Modulo can lead to uneven distribution and poor resilience. Instead, it uses a more advanced hash algorithm (like CRC32 or murmur) applied to packet header fields (e.g., 5-tuple).

Extract from Nokia SR Linux Configuration Guide (Section: ECMP Configuration):

"The system uses a hash algorithm (e.g., crc32, murmur) over selected fields in the packet header (such as source/destination IP, protocol, source/destination port) to determine the next-hop path. A modulo operation on the hash result relative to the number of paths is not the primary method; the hash space is designed for better spread and minimal disruption."

Option B is FALSE: Resilient ECMP aims for the opposite behavior. Using the same hash seed across routers ensures that a flow taking a specific path on one router will likely take the same corresponding path on downstream routers ("flow stickiness"), preventing localized congestion. Hash buckets map flows to paths consistently network-wide.

Extract from Nokia SR Linux Fundamentals Guide (Section: Resilient Hashing):

"Consistent hash seeds across all routers in the network are critical for resilient ECMP. This ensures that flows hashing to a particular path on an upstream router will hash to the same logical path on downstream routers, maintaining overall traffic distribution and preventing hot-spots."

Option C is FALSE: Using different hash seeds on downstream routers would cause flows following the same path upstream to be randomly distributed downstream, creating potential congestion points ("polarization"). Resilient ECMP requires the same hash seed to be configured consistently across the network for predictable, stable, and congestion-free flow paths.

Extract from Nokia SR Linux Configuration Guide (Section: ECMP Resilient Hashing):

"The hash-seed parameter must be configured identically on all routers within a domain utilizing resilient ECMP. Different seeds cause flow polarization on downstream nodes, defeating the purpose of resilient load balancing and potentially causing link congestion."

Option D is TRUE: This is the core principle of resilient hashing (also called consistent hashing). When a next-hop fails, the hash mapping is recalculated. Only flows that were previously mapped to the failed next-hop need to be remapped to the remaining healthy next-hops. Flows originally mapped to healthy next-hops remain entirely unaffected.

Extract from Nokia SR Linux Fundamentals Guide (Section: Resilient Hashing Benefits):

"A key advantage of resilient hashing is minimal disruption during next-hop failures. When a single next-hop becomes unavailable, only the flows that were hashed to that specific next-hop are affected and need to be rehashed among the remaining next-hops. Flows assigned to other next-hops continue to use their original paths without interruption."

Extract from Nokia SR Linux Configuration Guide (Section: ECMP Resilient Hashing):

"Resilient hashing minimizes the number of flows that need to change paths when the set of next-hops changes (due to failure or addition). This provides greater stability compared to traditional modulo-based hashing, where a topology change can impact a large portion of flows."

Comprehensive and Detailed Explanation with Exact Extracts:

Option A & B are FALSE: While recursive lookups are required for both next-hops (10.1.1.0 and 10.2.1.0), there is no dependency between them. Each next-hop must be resolved independently via a separate recursive lookup in the routing table. Neither next-hop is resolved "using" the other.

Extract from Nokia SR Linux Configuration Guide (Section: Static Routes):

"An indirect next-hop is not directly connected. The system must perform a recursive lookup in the routing table to find a route that matches the indirect next-hop IP address and resolve it to a directly attached next-hop and egress interface. Each indirect next-hop in a route is resolved independently."

Extract from Nokia SR Linux Fundamentals Guide (Section: Route Resolution):

"Routes with indirect next-hops require recursive route lookup. The router searches its routing table for a path to the indirect next-hop IP address itself. Multiple indirect next-hops in a single route entry are resolved in parallel, not sequentially."

Option C is TRUE: The exhibit shows a single static route (192.168.20.0/30) with two indirect next-hops (10.1.1.0 and 10.2.1.0). This configuration defines a next-hop group with two members for this route, enabling Equal-Cost Multi-Path (ECMP) load balancing or redundancy.

Extract from Nokia SR Linux Configuration Guide (Section: Static Routes):

"Multiple next-hop addresses can be specified for a static route. This creates a next-hop group. Traffic matching the route prefix is load-balanced across all active next-hops in the group using ECMP."

Extract from Nokia SR Linux Fundamentals Guide (Section: Static Routing):

"A static route entry listing multiple next-hops implies a next-hop group. The number of next-hops listed in the show route-table output for a single route ID directly indicates the number of next-hops configured in the group."

Option D is FALSE: The preference value (Pref) is configured per route, not per next-hop within the route. Both next-hops (10.1.1.0 and 10.2.1.0) share the same preference value (5), as they belong to the same route entry (ID 0). Next-hop selection within the group is based on the ECMP hashing algorithm, not preference. Preference is used to choose between different routes (from different protocols) to the same prefix.

Extract from Nokia SR Linux Configuration Guide (Section: Static Routes):

"The preference value is a property of the static route itself, not individual next-hops within it. All next-hops in a static route's next-hop group inherit the same preference value."

Extract from Nokia SR Linux Fundamentals Guide (Section: Route Selection):

"When multiple next-hops exist for a route (ECMP), the active next-hop for a specific flow is determined by a hash of packet header fields (e.g., 5-tuple). Preference values are only compared when selecting between different routes (e.g., static vs. BGP) to the same prefix."

Comprehensive and Detailed Explanation with Exact Extracts:

Options A, B, and C are Day 2+ operations:

A: Telemetry enables real-time monitoring.

B: Health analysis supports proactive maintenance.

C: Sandbox validates changes pre-deployment.

Extract from Nokia FSS Day 2 Operations Guide:

"Day 2+ includes telemetry-based monitoring, health analytics, and sandbox testing for upgrades/changes."

Option D is a Day 0 activity:

Fabric intents define initial design templates (Day 0), not ongoing operations.

Extract from Nokia FSS Lifecycle Management Guide:

"Fabric intents are used during Day 0 design to build templates. Day 2+ focuses on operational tasks like monitoring (A), health checks (B), and sandbox validation (C)."

Comprehensive and Detailed Explanation with Exact Extracts:

Option A (Valid): Log sources can be defined using Linux syslog facilities (e.g., local6) and priorities.

Extract from Nokia SR Linux Configuration Guide:

"Log sources are identified using Linux facilities (e.g., kernel, local6) and priorities (e.g., info, error)."

Option B (Valid): The console is a valid source for log messages (e.g., kernel boot logs).

Extract from Nokia SR Linux Fundamentals Guide:

"Console output is treated as a log source, particularly for kernel and early-boot messages captured before system services initialize."

Option C (Valid): SR Linux subsystems (e.g., bgp, system) generate logs with specific priorities.

Extract from Nokia SR Linux Configuration Guide (Section: Log Filters):

"Logs generated by SR Linux subsystems (e.g., network-instance, interface) can be filtered by subsystem name and priority."

Option D (Invalid): "Syslog filter" is not a source—it is a configuration mechanism.

Extract from Nokia SR Linux System Management Guide:

"Filters (/system logging filter) are applied to log sources (facilities/subsystems) to select messages for destinations. Filters themselves do not generate logs."

Comprehensive and Detailed Explanation From Exact Extract:

Option A is TRUE: SR Linux is fully model-driven.

"Every configuration and state element in SR Linux is defined by a YANG model."

— SR Linux YANG Data Modeling Guide, "Introduction"

Option B is FALSE: Containers are branches (grouping nodes), and leafs are data components (terminal values). The description is reversed.

"YANG structures data hierarchically: containers organize child nodes (branches), while leafs hold actual data values (e.g., integers, strings)."

— SR Linux YANG Data Modeling Guide, "Tree Structure"

Option C is TRUE: YANG supports JSON/XML encoding.

"YANG models serialize natively to XML or JSON for machine-to-machine communication."

— SR Linux gNMI and JSON-RPC Guide, "Data Encoding"

Option D is TRUE: YANG enables standardized access via gNMI/NETCONF.

"YANG provides a consistent schema for applications to retrieve/configurate data via protocols like gNMI."

— SR Linux Automation Guide, "Model-Driven Interfaces"