JNCIP-ENT EVPN — 20 Questions

Question 1

An administrator is deploying EVPN multi-homing with all-active mode on an MX Series router. Which configuration element uniquely identifies the provider edge (PE) router's attachment circuit to an Ethernet segment?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Ethernet Segment Identifier (ESI). The Ethernet Segment Identifier (ESI) is a 10-octet unique identifier configured under the interface or access link to identify an Ethernet segment for multi-homing.

Answer

Route Distinguisher (RD)

Answer

Ethernet Tag ID

Answer

ESI Label Extended Community

Question 2

You are troubleshooting a suboptimal traffic forwarding issue in an EVPN-VXLAN fabric with multi-homed devices. Traffic destined for a multi-homed server is being sent to only one of the PEs despite all-active mode being configured. Which EVPN route type and mechanism are responsible for enabling load balancing across all available PEs attached to the same Ethernet segment?

Accepted Answer

Route Type 1 (Ethernet Auto-Discovery per EVI). Type 1 Ethernet A-D routes per EVI are used for multi-homing aliasing, allowing PEs that do not learn a specific MAC address locally to still load-balance traffic to that MAC across all PEs advertising the ESI via Type 1 routes.

Answer

Route Type 2 with MAC mobility extended community

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Route Type 4 (Ethernet Segment Route)

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Route Type 3 (Inclusive Multicast)

Question 3

You are configuring a Junos EVPN-VXLAN environment where Type-3 (Inclusive Multicast Ethernet Tag) routes are being exchanged. A remote MX router is failing to establish ingress replication tunnels because it does not import the Type-3 route. Which configuration statement under the routing-instance is missing or misconfigured?

Accepted Answer

route-target import. EVPN Type-3 routes carry the Inclusive Multicast Ethernet Tag and rely on route targets for import and export. If the import route-target does not match the advertising router's export route-target, the tunnel endpoints are not dynamically bound.

Answer

no-normalization

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multicast-snooping

Answer

vtep-source-interface lo0.0

Question 4

An administrator notices that broadcast, unknown unicast, and multicast (BUM) traffic sent from a local host is looping back to the originating multi-homed PE when using an all-active Ethernet segment. Which mechanism prevents this loop in EVPN?

Accepted Answer

EVPN Split Horizon filtering using ESI labels. EVPN uses Split Horizon filtering via the ESI Label Extended Community or local split-horizon checks to ensure that BUM traffic received from a remote PE on a shared Ethernet segment is not sent back out to the same segment.

Answer

BGP Best Path Selection algorithm

Answer

Designated Forwarder (DF) election

Answer

Spanning Tree Protocol (STP) root guard

Question 5

During a maintenance window, an administrator needs to manually force a Designated Forwarder (DF) role change on a multi-homed Ethernet segment for an EVPN instance. Which parameter must be adjusted to influence the DF election algorithm in Junos OS?

Accepted Answer

Ethernet segment preference value. Junos OS allows influencing the DF election by adjusting the interface preference or local preference values associated with the Ethernet Segment, altering how the DF election algorithm selects the forwarder.

Answer

BGP AS path prepending

Answer

Route Distinguisher value

Answer

Router ID of the BGP speaker

Question 6

When configuring VXLAN data plane encapsulation inside an EVPN routing instance on Junos OS, which logical interface type must be bound to the bridge domain to provide VXLAN VNI mapping?

Accepted Answer

VLAN interface (vlan statement with vni). In Junos OS, VXLAN encapsulation is configured using logical tunnel interfaces or integrated routing and bridging (IRB) interfaces mapped via a vni statement under the bridge-domains hierarchy.

Answer

lo0.0

Answer

gre0

Answer

fxp0

Question 7

Which specific EVPN route type is responsible for carrying IP prefix routes, often used for inter-subnet forwarding in an IP-VRF-to-EVPN integration scenario?

Accepted Answer

Route Type 5. EVPN Route Type 5 is the IP Prefix Route, which allows the advertisement of IP prefixes (host or subnet routes) independently of MAC addresses, facilitating integrated routing and bridging (IRB) and inter-subnet forwarding.

Answer

Route Type 3

Answer

Route Type 2

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Route Type 1

Question 8

An engineer is troubleshooting EVPN type 2 routes between two MX Series routers and notices that MAC addresses learned locally are not being advertised to the remote VTEP. Which command should the engineer use to verify that the EVPN instance is actively generating and exporting MAC-VRF routes?

Accepted Answer

show route advertising-protocol bgp <neighbor-ip>. The 'show route advertising-protocol bgp' command allows an engineer to verify which routes (including EVPN type 2 MAC/IP routes) are being advertised to a specific BGP peer or peer group for an EVPN routing instance.

Answer

show bridge mac-table

Answer

show bgp summary

Answer

show evpn database

Question 9

When configuring centralized gateway or distributed gateway routing models in an EVPN-VXLAN environment, how does a distributed gateway using Integrated Routing and Bridging (IRB) interfaces operate regarding default gateway functionality?

Accepted Answer

All leaf nodes act as default gateways using the same virtual MAC and IP address, terminating traffic locally.. In a distributed gateway model, every leaf/VTEP acts as the default gateway for its directly attached subnets, using anycast MAC and IP addresses so hosts can send traffic to their local VTEP regardless of which leaf they connect to.

Answer

Routing is disabled on leaf nodes, requiring all packets to be tunneled to spine nodes for L3 lookup.

Answer

A single designated MX core router handles all inter-subnet routing via centralized IRB interfaces.

Answer

Hosts must run VRRP between leaf nodes to dynamically elect a single active gateway.

Question 10

An enterprise network architect is designing an EVPN-VXLAN fabric and wants to ensure that MAC address churn (frequent moving of a MAC between ports) does not destabilize the control plane. Which feature should be enabled in the EVPN instance?

Accepted Answer

MAC limit and MAC mobility sequence numbering. MAC mobility features, including MAC move detection and sticky MAC or suppression mechanisms, protect the EVPN control plane from frequent MAC moves by incrementing sequence numbers and applying penalties if movement thresholds are exceeded.

Answer

Spanning Tree BPDU protection

Answer

Fast-reroute backup paths

Answer

BGP route flap damping

Question 11

An engineer is verifying MAC learning behavior in an EVPN instance. A remote host's MAC address is learned via BGP Type 2 routes, but when the local host sends traffic to it, the packet drops. The engineer runs 'show route table bgp.evpn.0' and sees the route. What is the most likely reason the packet is dropping in the data plane?

Accepted Answer

The data-plane VNI mapping or tunnel next-hop resolution is incomplete.. Even if the control plane has learned the EVPN Type 2 route, if the data plane tunnel encapsulation (such as a missing VNI mapping or incomplete VXLAN next-hop resolution) is misconfigured, data plane forwarding will fail.

Answer

Type-4 routes have not been exchanged yet.

Answer

The BGP route target import policy is rejecting the route.

Answer

The local router's BGP router ID is misconfigured.

Question 12

Which BGP address family must be enabled under the BGP neighbor configuration to exchange EVPN routes between PE routers?

Accepted Answer

evpn signaling (or l2vpn evpn). To exchange EVPN routing information, the 'evpn signaling' or 'l2vpn evpn' address family must be configured under the BGP protocol hierarchy and neighbor sessions.

Answer

inet-unicast

Answer

vpls-signaling

Answer

iso-unicast

Question 13

Which EVPN route type is known as the Ethernet Segment Route and is advertised by a PE router to signal its connectivity to a multi-homed Ethernet segment?

Accepted Answer

Route Type 4. EVPN Route Type 4 is the Ethernet Segment Route, used for discovering other PEs attached to the same Ethernet segment and executing the Designated Forwarder (DF) election.

Answer

Route Type 2

Answer

Route Type 3

Answer

Route Type 1

Question 14

Which Junos configuration hierarchy is used to define an EVPN routing instance of type 'evpn'?

Accepted Answer

routing-instances instance-type evpn. In Junos OS, EVPN instances are defined under 'routing-instances instance-type evpn'.

Answer

bridge-domains <name> evpn

Answer

protocols evpn

Answer

interfaces xe-0/0/0 unit 0 family evpn

Question 15

You are integrating an EVPN-VXLAN fabric with an existing MPLS L3VPN backbone using a data center gateway. Which route type allows seamless translation and communication of prefix routes between the EVPN instance and the IP-VRF MPLS VPN backbone?

Accepted Answer

Route Type 5. EVPN Route Type 5 (IP Prefix Route) permits the advertising of IP prefixes that can be easily imported into IP-VRFs, bridging EVPN and classical MPLS L3VPN domains.

Answer

Route Type 3

Answer

Route Type 1

Answer

Route Type 2

Question 16

An engineer is troubleshooting a newly configured EVPN-VXLAN multi-homed setup where the Designated Forwarder (DF) is constantly toggling between two PE routers. What is the most likely cause of this DF churn?

Accepted Answer

Mismatched Ethernet Segment Identifiers (ESIs) or unstable BGP connectivity between PEs.. DF churn typically occurs when BGP sessions or reachability between the PE routers flapping, or when the timers (such as wait-for-timer) are misconfigured, causing conflicting DF election states.

Answer

Incorrect MAC mobility sequence numbers.

Answer

Exceeding the maximum MAC address table limit.

Answer

Using VXLAN instead of MPLS data plane encapsulation.

Question 17

Which EVPN route type is responsible for advertising MAC addresses combined with IP addresses (MAC/IP Advertisement Route)?

Accepted Answer

Route Type 2. Route Type 2 is the MAC/IP Advertisement Route, which carries a MAC address and optionally an IP address, facilitating both L2 bridging and L3 host routing.

Answer

Route Type 3

Answer

Route Type 4

Answer

Route Type 1

Question 18

You are designing an EVPN network with active-active multi-homing. A host sends traffic to a multi-homed PE. The PE receives the traffic on a designated link. How does EVPN suppress unnecessary flooding across the core for unknown unicast traffic originating from a multi-homed site?

Accepted Answer

By dynamically learning MAC addresses via control-plane Type 2 routes, turning unknown unicast into known unicast.. EVPN suppresses unknown unicast flooding by performing MAC learning via control-plane advertisement (Type 2 routes) upon first contact, so subsequent traffic is unicast-forwarded rather than flooded.

Answer

By utilizing Spanning Tree Protocol to block redundant ports across the core.

Answer

By dropping all packets with unknown destination MAC addresses at the ingress leaf.

Answer

By enforcing ingress replication drop filters on Type 3 routes.

Question 19

You are analyzing BGP EVPN updates and observe an Extended Community attached to a Type-2 route containing a sequence number. What is the primary function of this MAC Mobility Extended Community?

Accepted Answer

It facilitates loop-free MAC movement tracking by incrementing sequence numbers when a host changes attachment PEs.. The MAC Mobility Extended Community carries a sequence number used to resolve MAC moves. If a host moves from one PE to another, the new PE advertises the MAC with an incremented sequence number, causing all other PEs to update their tables to point to the new location.

Answer

It signals the EVPN split-horizon label for BUM traffic.

Answer

It determines the Designated Forwarder for multi-homed Ethernet segments.

Answer

It defines the VXLAN Network Identifier (VNI) mapping for data-plane decapsulation.

Question 20

An administrator wishes to configure VXLAN data plane encapsulation on an MX Series router with an EVPN instance. Which statement under the routing-instances hierarchy defines the local VTEP source interface?

Accepted Answer

vtep-source-interface lo0.0;. In Junos OS, the VXLAN source interface is defined using the 'vtep-source-interface' statement under the EVPN routing instance or switch-options hierarchy.

Answer

encapsulation-source-interface fxp0.0;

Answer

vxlan-source-ip lo0.0;

Answer

tunnel-source loopback 0;