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Question 161. What is the primary purpose of BFD

1. Create VLANs
2. Detect forwarding path failures quickly
3. Assign server identities
4. Build Fibre Channel zones

Correct Answer: 2. Detect forwarding path failures quickly

Explanation:

Bidirectional Forwarding Detection is designed to identify forwarding path failures very quickly between network devices. Cisco NX OS can use BFD with routing protocols such as BGP, OSPF, and EIGRP so those protocols do not need to wait for their normal hello and dead timers to detect a failed path. BFD can provide subsecond failure detection and more predictable convergence behavior. This is valuable in data centers where short interruptions can affect applications and storage traffic. BFD supplements the routing protocol rather than replacing the routing protocol itself.

Question 162. What is the default BFD detection multiplier on Nexus 9000

1. 1
2. 2
3. 5
4. 3

Correct Answer: 4. 3

Explanation:

Cisco NX OS uses a default BFD detection multiplier of three. The multiplier determines how many expected BFD packets can be missed before the peer is considered unavailable. It works together with the negotiated transmit and receive intervals to determine failure detection time. Cisco documents default transmit and receive intervals of 50 milliseconds in the referenced Nexus 9000 configuration guidance. Faster timers can improve convergence but also increase control processing requirements. Designers should select BFD settings that provide the required recovery time without creating unnecessary processing load across a large data center fabric.

Question 163. What must be done before configuring BFD on Nexus 9000

1. Enable the BFD feature
2. Enable OTV
3. Configure a VSAN
4. Create an ACI tenant

Correct Answer: 1. Enable the BFD feature

Explanation:

The BFD feature must be enabled before BFD can be configured on interfaces or routing protocols on Cisco Nexus 9000 switches. Cisco uses the feature based NX OS model in which many functions must first be activated globally. After BFD is enabled, administrators can configure global or interface specific timers and associate BFD with supported protocols such as OSPF or BGP. Cisco also recommends disabling ICMP redirects on interfaces where BFD operates. Correct prerequisites are important because routing protocol configuration alone does not automatically enable the underlying BFD function.

Question 164. Which BFD mode exchanges periodic control packets

1. Dense mode
2. Passive mode
3. Asynchronous mode
4. Flood mode

Correct Answer: 3. Asynchronous mode

Explanation:

BFD asynchronous mode exchanges periodic control packets between two devices to establish and maintain the BFD session. The peers negotiate timing parameters and monitor the arrival of expected control messages. If enough messages are missed according to the configured detection multiplier, BFD declares the forwarding path unavailable and notifies the associated routing protocol. Cisco NX OS uses asynchronous mode as the standard BFD operating mode. The mechanism provides a common failure detection process across different routing protocols and media types, making convergence behavior more consistent throughout the data center network.

Question 165. What is the default minimum BFD transmit interval shown in Cisco guidance

1. 500 milliseconds
2. 50 milliseconds
3. 5 seconds
4. 1 second

Correct Answer: 2. 50 milliseconds

Explanation:

Cisco documentation lists 50 milliseconds as the default desired minimum BFD transmit interval on the referenced Nexus 9000 platforms. The required minimum receive interval also defaults to 50 milliseconds. These timers combine with the detection multiplier to determine how quickly a forwarding path failure can be identified. Administrators can configure different intervals when application requirements or platform scale justify a change. Very aggressive timers can increase processing demands, particularly when a switch maintains many BFD sessions, so the design should balance rapid convergence against available system resources and operational requirements.

Question 166. What must be disabled on an interface using BFD according to Cisco guidance

1. ICMP redirects
2. IP routing
3. VLAN tagging
4. BGP

Correct Answer: 1. ICMP redirects

Explanation:

Cisco requires ICMP redirect messages to be disabled on interfaces where BFD is configured. This applies to the appropriate IPv4 or IPv6 redirect behavior depending on the interface design. BFD is intended to provide fast and deterministic forwarding path failure detection, so the interface configuration should follow Cisco prerequisites to ensure supported operation. The BFD feature must also be globally enabled before protocol specific BFD configuration is applied. Designers should include these interface requirements in standardized templates so fast convergence features are deployed consistently across leaf, spine, border, and external routing links.

Question 167. What does Micro BFD monitor

1. Individual port channel member links
2. Server BIOS settings
3. VXLAN tenant names
4. Fibre Channel zones

Correct Answer: 4. Individual port channel member links

Explanation:

Micro BFD creates separate BFD sessions on individual member links of a link aggregation group. This provides more detailed failure detection than monitoring only the logical port channel interface. If Micro BFD detects that one member link has failed, that member can be removed from forwarding while the remaining links continue to carry traffic. Cisco supports this capability for both LACP and non LACP based port channels on supported Nexus platforms. Micro BFD is useful in data center designs where rapid detection of individual link failures is important for maintaining predictable bandwidth and traffic distribution.

Question 168. What is a main benefit of BFD with BGP

1. Larger VLAN scale
2. Faster BGP failure detection
3. Automatic storage zoning
4. Server profile creation

Correct Answer: 3. Faster BGP failure detection

Explanation:

BFD can significantly improve BGP convergence by detecting forwarding path failures faster than ordinary BGP timers. Once BFD determines that the path to a peer has failed, it can notify BGP so the affected neighbor and routes can be processed immediately. Cisco Nexus platforms support BFD with several BGP peering models, including supported single hop and multihop scenarios. This capability is particularly useful in leaf spine and border routing designs where applications depend on rapid traffic restoration. BFD enhances failure detection while BGP continues to provide the routing control plane and path selection logic.

Question 169. What is the role of a rendezvous point in PIM sparse mode

1. Meeting point for multicast sources and receivers
2. Ethernet loop prevention
3. Server identity allocation
4. Storage path selection

Correct Answer: 1. Meeting point for multicast sources and receivers

Explanation:

A rendezvous point acts as the meeting point for multicast sources and receivers in a PIM sparse mode network. Sources initially register their multicast traffic with the RP, while receivers build a shared tree toward the RP when they request a multicast group. Once source information becomes available, the receiver side can transition toward a source based shortest path tree when appropriate. Cisco uses PIM sparse mode in multicast capable VXLAN underlays and other data center multicast designs. RP placement and redundancy therefore influence multicast availability, convergence, and traffic efficiency.

Question 170. What does Anycast RP provide

1. Fibre Channel routing
2. GPU scheduling
3. DHCP relay
4. RP redundancy and load sharing

Correct Answer: 4. RP redundancy and load sharing

Explanation:

Anycast RP allows multiple multicast routers to share the same rendezvous point address. Sources and receivers can therefore reach a nearby RP while the RP devices exchange information about active multicast sources. Cisco describes Anycast RP as providing both redundancy and load sharing. If one RP becomes unavailable, another RP using the same shared address can continue providing rendezvous services. Cisco VXLAN underlay designs can place redundant Anycast RP functions on suitable spine switches so multicast based BUM replication does not depend on one physical rendezvous point device.

Question 171. What does MSDP exchange between PIM domains

1. Multicast source information
2. VLAN databases
3. UCS service profiles
4. GPU memory mappings

Correct Answer: 2. Multicast source information

Explanation:

Multicast Source Discovery Protocol exchanges information about active multicast sources between PIM sparse mode domains. MSDP peers send Source Active messages containing information such as the source address, multicast group, and originating RP information. This lets receivers in one multicast domain discover sources located in another domain. Cisco also supports using MSDP to build an Anycast RP design that provides RP redundancy and load sharing. Within one PIM domain, Cisco also supports the PIM Anycast mechanism as an alternative way to provide the Anycast RP function.

Question 172. Which MSDP message advertises an active multicast source

1. Hello message
2. Join message
3. Source Active message
4. Echo message

Correct Answer: 3. Source Active message

Explanation:

MSDP uses Source Active messages to advertise information about active multicast sources to its peers. Cisco documentation states that these messages include the multicast source address, the group address used by the source, and information identifying the RP or configured originator. When an RP learns about a new multicast source through a PIM register process, MSDP can create a Source Active message and distribute it to configured peers. Remote multicast domains can then build appropriate trees toward the source when receivers request the corresponding multicast group.

Question 173. What multicast protocol is used in the documented multicast VXLAN underlay

1. PIM sparse mode
2. PIM dense mode
3. IGMP only
4. MSDP only

Correct Answer: 4. PIM sparse mode

Explanation:

Cisco documents PIM sparse mode as the multicast routing protocol used in a multicast enabled VXLAN underlay. In this design, VTEP leaf switches connect through routed links to the spine layer, and selected spine devices can provide redundant Anycast RP functions. The multicast underlay supplies efficient replication for broadcast, unknown unicast, and multicast VXLAN traffic. This differs from ingress replication, where the source VTEP makes separate copies for remote VTEPs. Cisco NX OS does not support PIM dense mode on the referenced Nexus 9000 architecture.

Question 174. Which interface used as an Anycast RP must have PIM sparse mode enabled

1. Management interface only
2. Loopback interface
3. Console interface
4. Server access port

Correct Answer: 1. Loopback interface

Explanation:

Cisco requires PIM sparse mode on the loopback interface used for a PIM Anycast RP. The loopback carries the shared or unique RP addressing required by the Anycast configuration and must be reachable through the unicast routing infrastructure. Multiple RP devices can share the common Anycast RP address while maintaining unique addresses used to exchange source information. Loopbacks are preferred because they remain logically available independently of individual physical interface failures. Proper routing and PIM configuration of the loopback are therefore essential to a resilient Anycast RP design.

Question 175. What is the primary purpose of OTV

1. Layer 2 extension between data centers
2. Fibre Channel zoning
3. GPU memory transport
4. Server BIOS management

Correct Answer: 3. Layer 2 extension between data centers

Explanation:

Overlay Transport Virtualization was designed to extend Layer 2 Ethernet connectivity between geographically separate data center sites across an IP transport network. OTV creates an overlay that carries MAC based traffic between separate Layer 2 domains while preserving the Layer 3 transport boundary between the sites. Cisco designed the technology to support workload mobility and data center interconnection without requiring the transport infrastructure itself to become one large Layer 2 network. This separation helps maintain fault isolation and allows existing routed transport infrastructure to carry the extended Ethernet segments.

Question 176. What does the OTV transport network fundamentally require

1. Fibre Channel connectivity
2. IP connectivity
3. One common VLAN
4. STP between sites

Correct Answer: 2. IP connectivity

Explanation:

OTV requires IP connectivity between participating data center sites. The underlying transport can use different technologies as long as it provides suitable IP reachability between OTV edge devices. Cisco specifically designed OTV so the transport does not need to become a shared Layer 2 extension itself. Ethernet frames from extended LAN segments are carried across the routed infrastructure through the OTV overlay. This approach allows existing Layer 3 interconnections to remain in place and helps preserve routing based fault isolation while selected Layer 2 networks are extended for application or workload mobility requirements.

Question 177. What data center property does OTV preserve between sites

1. Layer 3 failure boundaries
2. One shared STP domain
3. One shared server UUID
4. One Fibre Channel domain

Correct Answer: 4. Layer 3 failure boundaries

Explanation:

One of the important design goals of OTV is preserving Layer 3 failure boundaries between data center sites while still extending selected Layer 2 segments. Traditional Layer 2 extension techniques can enlarge the impact of loops, broadcast problems, and spanning tree events. OTV builds an overlay across the routed transport so each site can retain much of its local Layer 2 independence. Cisco identifies fault isolation, resiliency, multihoming, and loop prevention as important characteristics of OTV. Preserving failure boundaries reduces the chance that a Layer 2 issue in one location affects every interconnected data center.

Question 178. What type of traffic does OTV logically extend

1. Fibre Channel only
2. Layer 2 Ethernet traffic
3. GPU control traffic only
4. Console traffic only

Correct Answer: 2. Layer 2 Ethernet traffic

Explanation:

OTV extends Layer 2 Ethernet connectivity between separate sites by transporting Ethernet traffic across an IP based overlay. This allows workloads in different locations to appear as though they belong to the same logical Layer 2 network when the design requires that behavior. The routed transport infrastructure remains independent of the extended LAN segments. Cisco developed OTV for data center interconnection scenarios such as workload mobility, disaster recovery, consolidation, and migration. Designers should still limit Layer 2 extension to applications that actually require it because routed intersite boundaries generally provide stronger fault isolation.

Question 179. What is the default number of equal cost paths BGP installs before maximum paths is changed

1. One
2. Two
3. Four
4. Eight

Correct Answer: 1. One

Explanation:

Cisco NX OS documents a default BGP maximum paths value of one. Administrators can increase the maximum paths setting to allow several equal cost BGP routes to be installed for ECMP load sharing. This is particularly useful in data center designs that contain multiple equivalent uplinks or parallel routed paths. ECMP improves bandwidth utilization and resilience because traffic can use several next hops rather than depending on one preferred route. The exact supported path scale varies by platform and software release, so designers should confirm hardware capabilities before defining the desired ECMP fanout.

Question 180. What does weighted ECMP allow BGP to use

1. Only one path
2. Equal weights only
3. Different weights on multiple next hops
4. Fibre Channel paths only

Correct Answer: 3. Different weights on multiple next hops

Explanation:

Weighted ECMP allows traffic to be distributed across multiple BGP next hops using different weights. Cisco also refers to this capability as Unequal Cost Multipath. Traditional ECMP generally distributes traffic across paths considered equal, while weighted ECMP can intentionally send different proportions of traffic across available next hops. This is useful when links or paths have different capacities and a strictly equal traffic split would not be optimal. Designers can therefore align traffic distribution more closely with available bandwidth while retaining the resiliency benefits of multiple active routing paths.