D-SNC-DY-00 Dell SONiC Deploy Practice Questions
Prepare for D-SNC-DY-00 with more than an answer.
- Exam fee
- $300 USD
- Level
- Specialist
Domains covered on the exam 6
- SONiC Bundles2%
- SONiC Installation11%
- SONiC Configuration40%
- Routing24%
- VXLAN16%
- QoS7%
- 1
An administrator needs to configure a QoS policy that maps incoming traffic with a DSCP value of 46 (EF - Expedited Forwarding) to a high-priority queue. Which SONiC configuration object is used to create this mapping between a DSCP value and an internal traffic class?
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Correct answer: C
In SONiC, QoS Maps are used to translate traffic markings into internal classifications. Specifically, a
DSCP_TO_TC_MAP(Differentiated Services Code Point to Traffic Class Map) is defined to map specific incoming DSCP values to internal Traffic Class (TC) numbers. This TC is then mapped to a specific hardware queue. - 2
A consultant is reviewing an MC-LAG configuration between two Dell SONiC switches. They notice that the
system-macaddress is configured identically on both peers. What is the primary purpose of this configuration?Show answer details
Correct answer: B
The LACP protocol uses a system ID, which is derived from the switch's system MAC address, to identify a unique LACP-speaking device. By configuring the same
system-macon both MC-LAG peers, they present an identical system ID to any downstream device (like a server). This makes the downstream device believe it is connected to a single logical switch, allowing it to form a standard LACP port-channel across the two physical switches. - 3
What are the key advantages of using the ONIE automatic installation method over the manual method for deploying Enterprise SONiC on a large number of switches? (Select THREE)
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Correct answer: A, C, E
The ONIE automatic method, driven by DHCP and a central image server, is designed for large-scale deployments. Its main advantages are speed/scalability (installing many switches simultaneously), consistency (all switches get the same image and initial setup), and a reduction in human error compared to manually accessing the console of each device.
- 4
An administrator configures a static route on a SONiC switch:
ip route 172.16.0.0/16 10.10.10.1 150. What does the value150represent in this command?Show answer details
Correct answer: B
In FRRouting commands, the final optional numeric value in a static route definition represents the administrative distance (AD). This value is used by the router to determine the trustworthiness of the routing source. A lower AD is preferred. By setting it to 150, the administrator is making this static route less preferred than, for example, an OSPF route (default AD 110).
- 5
True or False: When using BGP EVPN with Symmetric IRB, a separate L3 VNI must be configured and associated with each tenant VRF to handle inter-subnet routing.
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Correct answer: A
This statement is true. The core principle of Symmetric IRB is the use of a dedicated L3 VNI for routing traffic between different L2 VNIs (subnets) within the same tenant. Each tenant's routing domain, represented by a VRF, is mapped to a unique L3 VNI, which allows for scalable and efficient distributed routing across the fabric.
- 6
An administrator is troubleshooting a newly configured LACP port-channel between a SONiC switch and a server. The server administrator confirms their side is configured for LACP active mode. The port-channel on the SONiC switch is not coming up. Which LACP mode on the SONiC switch would prevent the port-channel from forming?
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Correct answer: C
If the server is configured for LACP (active mode), it will send LACPDU packets to negotiate the channel. If the SONiC switch is configured in 'On' mode (static LAG), it will not process or send LACPDU packets. This mismatch in protocols (LACP vs. static) will prevent the port-channel from ever establishing. To work with an LACP active peer, the switch must be configured as either active or passive.
- 7
Case Study
A regional ISP is expanding its services and needs to provide Layer 2 VPNs to its business customers. The ISP's core network is built on Dell PowerSwitch hardware running Enterprise SONiC and is fully routed with OSPF. Each customer requires the ability to use their own VLAN IDs, which may overlap with other customers' VLANs, and have this traffic transported transparently between two of their sites connected to the ISP's network.
Current Infrastructure:
The ISP has two Point of Presence (PoP) locations, PoP-A and PoP-B. The network between these PoPs is a robust Layer 3 core. A new customer needs to connect a server at Site-A (connected to PoP-A) to a server at Site-B (connected to PoP-B). The customer uses VLAN 20 for this traffic and expects it to be delivered as tagged VLAN 20 traffic at the destination site.Technical Requirements:
- Transport customer's 802.1Q tagged frames, including their original VLAN tag (C-VLAN), across the ISP's L3 core.
- Maintain traffic isolation between different customers.
- The solution must not require complex tunneling protocols like MPLS or VXLAN for this specific service.
- The configuration should be straightforward and applied at the provider edge (PE) switches in each PoP.
Diagram:
graph LR subgraph Site-A ServerA[Server in VLAN 20] end subgraph PoP-A PE1[SONiC PE Switch] end subgraph ISP Core (OSPF) CoreRouter1[...] CoreRouter2[...] end subgraph PoP-B PE2[SONiC PE Switch] end subgraph Site-B ServerB[Server in VLAN 20] end ServerA -- C-VLAN 20 --> PE1 PE1 -- S-VLAN --> CoreRouter1 CoreRouter1 --- CoreRouter2 CoreRouter2 -- S-VLAN --> PE2 PE2 -- C-VLAN 20 --> ServerBWhich Enterprise SONiC feature should the ISP engineer configure on the customer-facing ports of switches PE1 and PE2 to meet these requirements?
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Correct answer: C
Q-in-Q, or IEEE 802.1ad, is the ideal solution for this use case. It allows the service provider to encapsulate the customer's entire 802.1Q frame (including their C-VLAN tag) within a second provider tag (S-VLAN). This doubly-tagged frame can then be switched across the provider's core network based on the S-VLAN, keeping the customer's traffic isolated and their original VLAN information intact. The S-VLAN tag is stripped off at the egress PE switch before being delivered to the destination site.
- 8
A network architect is designing a VXLAN BGP EVPN fabric for a multi-tenant data center. The primary requirement is to optimize inter-subnet (East-West) traffic routing by performing routing lookups on both the ingress and egress VTEPs, thereby minimizing traffic hair-pinning and distributing the routing workload. Which VXLAN IRB model and BGP EVPN route type are specifically designed to meet this requirement?
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Correct answer: B
Symmetric IRB is designed for optimal East-West routing by performing routing at both ingress and egress VTEPs. This is achieved by using a dedicated L3 VNI for inter-subnet traffic and advertising IP prefixes using BGP EVPN Type-5 (IP Prefix) routes. This model avoids forcing all routed traffic through a centralized gateway or specific border leafs.
- 9
A storage administrator reports high latency and packet drops for a critical RoCEv2 application running on Dell PowerSwitch nodes with Enterprise SONiC. To ensure lossless transport for this traffic, which two QoS features must be configured and enabled? (Select TWO)
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Correct answer: A, B
RoCEv2 (RDMA over Converged Ethernet) requires a lossless network fabric. This is achieved in SONiC by implementing Priority-based Flow Control (PFC) to prevent packet loss due to buffer exhaustion by sending pause frames on specific traffic classes, and Explicit Congestion Notification (ECN) to mark packets to signal congestion before it leads to drops, allowing endpoints to adjust their sending rates.
- 10
During the deployment of a new Dell PowerSwitch, a junior engineer attempts to configure a 100G port to break out into 2x50G interfaces. After applying the configuration and restarting the swss service, the interfaces do not come up. The senior engineer points out that not all platforms support all breakout modes dynamically. What is the most reliable way to determine the supported port breakout modes for a specific Dell PowerSwitch platform model running Enterprise SONiC?
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Correct answer: B
Port breakout capabilities are hardware-dependent and vary between different switch models and even ASICs. The definitive source for supported breakout modes, speeds, and configuration specifics is the official Dell Technologies documentation, specifically the Enterprise SONiC User Guide for that particular PowerSwitch model.
