4A0-D03 Nokia SR Linux EVPN and Data Center Interconnect Free Practice Exam Questions (2026 Updated)

Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

In interface-less symmetric L3 EVPN routing, hosts in a subnet may be attached to different leaf routers, while inter-subnet forwarding is performed through the IP-VRF using VXLAN routed interfaces. The ingress and egress PEs both participate in L3 forwarding, and the routed VXLAN interface provides the per-IP-VRF overlay data-plane construct needed for symmetric routing. The IRB interfaces on the local MAC-VRFs must advertise learned local host routes so that remote PEs have the necessary host reachability information. The MAC-VRFs also need the appropriate EVPN control-plane configuration so host MAC/IP information can be exchanged, while the IP-VRF participates in L3 VPN-style route exchange for routed reachability. Option A is false because anycast gateway is not optional in this design for Leaf1 and Leaf2. Anycast gateway allows the same default-gateway IP and virtual MAC behavior to exist consistently on multiple leaves serving the same subnet. Without it, host default-gateway behavior would be inconsistent and traffic mobility across the fabric would break expected distributed gateway operation. Reference: interface-less symmetric routing, IRB, anycast gateway, routed VXLAN interface.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

Designated Forwarder election determines which PE forwards BUM traffic from the EVPN overlay toward a multi-homed Ethernet Segment for a given service. In this scenario, all leaf routers share the same DF candidate list for mac-vrf103, but the election configuration is not identical. Leaf1 and Leaf2 use the default algorithm, while Leaf3 and Leaf4 use the preference-based algorithm. Under preference-based DF election, the candidate with the highest configured preference is selected over lower-preference candidates, assuming the candidate list is valid and consistent. The question states that Leaf3 has the higher preference value compared with Leaf4. Therefore, Leaf3 becomes the DF for mac-vrf103. This is the correct outcome because the preference-based election explicitly overrides simple default behavior by assigning operator-defined priority to a PE. In production designs, this is useful when the operator wants deterministic forwarding placement, maintenance control, or service-specific primary-path selection rather than relying only on the default modulo-based DF selection process. Reference: EVPN DF election, preference-based algorithm, MAC-VRF service forwarding.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

A BGP route target is an extended community used to control which EVPN routes are imported into which MAC-VRF or IP-VRF. It is carried with EVPN updates and acts as the import/export policy tag for tenant service membership. The statement that it is a BGP extended community is correct. It is also correct that route targets support multi-tenant operation, because they allow different EVPN instances to carry potentially overlapping MAC or IP information while importing only the routes intended for that service. However, option D is false in the wording used here. The route target does not itself identify the EVPN instance in the control plane as a unique route identifier. That role is more closely associated with the route distinguisher and EVPN NLRI construction, while the route target determines import eligibility. A route target tells a receiving PE whether the route belongs in a local service instance, but it is not the unique identity of the EVPN route. This distinction is critical: route distinguishers make routes unique; route targets control route distribution and service membership. Reference: EVPN route targets, BGP extended communities, route import/export policy, RD versus RT function.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

In interface-less symmetric routing, the EVPN fabric exchanges host forwarding information using EVPN route type 2 MAC/IP advertisements. RT-2 carries the host MAC address and, when present, the associated host IP address, allowing remote PEs to build the forwarding state needed for distributed gateway operation. Unlike asymmetric routing, interface-less symmetric routing does not require every MAC-VRF to be instantiated on every PE. The design scales better because each leaf only needs the locally attached MAC-VRFs plus the shared IP-VRF/routed VXLAN construct for inter-subnet forwarding. Option B describes an asymmetric forwarding pattern more than a symmetric one; in symmetric routing, both ingress and egress PEs perform routed forwarding functions through the IP-VRF. Option C is also incorrect because anycast gateway is fundamental when multiple leaves provide the same default-gateway service for a subnet. Therefore, the true statement is that forwarding information is exchanged using EVPN route type 2 updates. Reference: interface-less symmetric routing, EVPN RT-2 host MAC/IP signaling, distributed IRB operation.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

Symmetric L3 EVPN routing uses an IP-VRF-based overlay model in which both ingress and egress PEs participate in routed forwarding. The ingress PE receives the frame from the local MAC-VRF, routes it into the IP-VRF, and sends it across the VXLAN routed interface. The egress PE receives the routed overlay packet, performs the corresponding IP-VRF lookup, and then forwards it into the locally attached destination MAC-VRF. Because the routed overlay is built per IP-VRF, a routed-VXLAN interface is required for that IP-VRF. EVPN route type 5 support is also required because RT-5 carries IP prefix reachability across the EVPN control plane. The false statement is option D. Symmetric routing specifically removes the requirement for every MAC-VRF to exist on every PE. A PE only needs the MAC-VRFs for locally attached subnets, plus the shared IP-VRF and routed overlay state. This is the major scaling advantage of symmetric routing compared with designs that require broad MAC-VRF instantiation across the fabric. Reference: symmetric L3 EVPN routing, routed VXLAN interface, RT-5 prefix reachability, MAC-VRF scaling.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

In asymmetric EVPN IRB, the ingress PE performs routing from the source subnet into the destination subnet, then forwards the packet across the VXLAN overlay using the destination MAC-VRF/VNI. The egress PE does not perform another IP-VRF lookup for that packet; it performs Layer 2 forwarding in the destination MAC-VRF. In this scenario, Host-2 sends traffic toward Host-1. After the ingress routing decision, the traffic arrives at Leaf-2 in the context of the destination MAC-VRF, mac-vrf-1. Leaf-2 then performs a MAC lookup in mac-vrf-1 and forwards the frame to Host-1. Option D is therefore correct. Option A reverses the forwarding direction and misidentifies the leaf action. Option B incorrectly sends mac-vrf-2 traffic toward the IP-VRF on Leaf-2, even though Leaf-2 is acting as the egress PE for Host-1. Option C is also incorrect because the egress forwarding action is based on the MAC table in the destination MAC-VRF, not an IP-VRF ARP lookup at that stage. Reference: asymmetric L3 EVPN IRB data-plane operation, ingress routing and egress MAC forwarding.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

When Host-1 sends its first Ethernet frame into MAC VRF-1, Leaf-1 performs normal local data-plane MAC learning on the access interface and installs Host-1's MAC address into the MAC forwarding table. In an L2 EVPN MAC-VRF, host MAC reachability is then advertised into the EVPN control plane using EVPN route type 2, the MAC/IP Advertisement route. Route type 5 is not used for host MAC advertisement; RT-5 is used for IP prefix advertisement in Layer 3 EVPN services. Therefore, option B is false because it incorrectly states that Leaf-1 generates an EVPN RT-5 update with the host MAC address. In this topology, Leaf-1 sends the correct EVPN update to the route reflector, Spine-1. The route reflector then reflects the update to Leaf-2 and Leaf-3, and those remote leaves import the route if the route target matches their MAC VRF-1 import policy. The route target controls service membership, ensuring that only PEs participating in the same EVPN instance import the MAC route. Reference: L2 EVPN MAC learning, RT-2 MAC/IP advertisement, route-reflector distribution, route-target import.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

EVPN route type 2 carries MAC/IP advertisement information. It is central to host-based routing and to designs where the fabric must distribute host MAC-to-IP bindings for integrated routing and bridging. In host routing, RT-2 is required because individual host reachability is signaled through MAC/IP advertisements. In interface-less prefix routing, RT-2 is still needed because the system relies on host or gateway MAC/IP information associated with the IRB and distributed gateway behavior. Interface-ful unnumbered designs may also require RT-2-style information to resolve next-hop or adjacency behavior because the routed interface does not use a conventional numbered next-hop model. Prefix routing with interface-ful numbered operation is different. In that model, the routed interface has explicit IP addressing and prefix reachability can be carried with L3 prefix routes without requiring EVPN RT-2 host MAC/IP advertisement as a dependency. Therefore, the symmetric routing option that does not require EVPN route type 2 is prefix routing interface-ful numbered. Reference: symmetric L3 EVPN routing models, RT-2 MAC/IP advertisements, prefix routing behavior.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

In asymmetric L3 EVPN routing, each participating PE must have the MAC-VRFs needed to forward traffic in the destination bridge domain. However, the specific exhibit describes two MAC-VRFs interconnected through IP-VRF3, with Leaf-1 hosting MAC-VRF1 and Leaf-2 hosting MAC-VRF2. The false statement is that Leaf-1 and Leaf-2 must both have instances of MAC-VRF1 and MAC-VRF2. That requirement is not true for this described deployment. Each local MAC-VRF connects to IP-VRF3 using an IRB interface, and host MAC/IP information is advertised using EVPN route type 2 so remote PEs can learn endpoint reachability. The question's answer also implies that IP prefix advertisement using route type 5 is part of the control-plane exchange between the leaves for the routed service context. What matters is that the fabric can resolve host and prefix reachability through EVPN without forcing every PE to instantiate every MAC-VRF in this topology. Option B overstates the MAC-VRF placement requirement and is therefore false. Reference: asymmetric L3 EVPN routing, RT-2 host advertisements, RT-5 IP prefix routes, IRB attachment.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

A Gratuitous ARP is an ARP message a host sends to announce or refresh its own IP-to-MAC binding without waiting for another host to request it. In a traditional Ethernet subnet, the GARP is sent as a broadcast so that other hosts can update their ARP caches with the sender's current MAC address. This is useful after a host boots, changes NICs, moves to another attachment point, or takes over an IP address in a redundancy scenario. In EVPN environments, GARPs are also important because a leaf can snoop the ARP information and update local proxy ARP and EVPN MAC/IP state. Option D is false because recipients do not acknowledge a gratuitous ARP with a reply. GARP is an announcement mechanism, not a request/response transaction. If every receiving host acknowledged a broadcast GARP, the result would be unnecessary ARP traffic amplification. The correct behavior is passive update of ARP state by receiving systems and, in EVPN, potential control-plane propagation of the learned binding by the local PE. Reference: GARP behavior, proxy ARP learning, Layer 2 EVPN endpoint update procedures.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

In EVPN PE-CE routing, the PE exchanges ordinary IPv4 or IPv6 unicast routing information with the CE. When the PE learns CE prefixes, it imports them into the tenant IP-VRF and advertises them to other EVPN PEs as EVPN route type 5 IP Prefix routes. Conversely, when the PE receives EVPN routes from remote PEs, it can advertise corresponding IPv4/IPv6 BGP updates toward the CE, subject to policy. Import and export policies are essential because they control which customer routes are accepted, which EVPN-learned routes are advertised, and how attributes are modified. Option C is false because iBGP is not the preferred PE-CE model in this context. eBGP is typically preferred between PE and CE because it creates a clean administrative routing boundary between the provider/data-center edge and the customer or external router. Using eBGP also simplifies route policy, loop prevention, and operational separation. The CE does not need to participate in the EVPN overlay; it speaks standard BGP unicast with the PE, while the PE performs the EVPN RT-5 advertisement into the fabric. Reference: EVPN PE-CE BGP routing, eBGP preference, RT-5 prefix advertisement, import/export policy.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

The exhibit describes an EVPN IRB environment where MAC-VRF100 and IP-VRF-100 exchange host reachability through local learning and EVPN advertisements. Leaf-1 can advertise EVPN route type 2 updates containing host MAC/IP information for MAC-VRF100. This is the normal mechanism used to distribute endpoint bindings learned from local hosts. If IP-VRF-100 is not configured for prefix advertisement, Leaf-1 will not generate EVPN route type 5 updates for that IP-VRF, so option A is consistent. The ARP cache in the IP-VRF is normally required for local subnet host resolution; remote host reachability can be learned through EVPN rather than requiring every remote ARP entry to be learned by local data-plane ARP. Option B is false because ARP/GARP snooping is not performed by the IRB interface in the manner stated. ARP/GARP learning for proxy ARP and MAC/IP advertisement is associated with the MAC-VRF bridge-domain behavior and the local access side, not with the IRB subinterface indiscriminately snooping all ARP/GARP messages as described. Reference: EVPN IRB operation, RT-2 host MAC/IP advertisement, RT-5 behavior, ARP/GARP learning scope.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

An IRB interface is the logical connection point between a Layer 2 MAC-VRF and a Layer 3 IP-VRF. It provides the routed gateway function for hosts in the bridge domain while allowing traffic to move into the routed VRF for inter-subnet forwarding. The correct statement is that when an IRB sub-interface has multiple IP addresses, one can be designated as the primary. This is important because the primary address is used for normal gateway or subnet behavior when more than one address is present on the same routed interface context. Option A is inaccurate because the question is about an IRB sub-interface, not a generic subinterface selection between bridge or routed access modes. Option B is not the defining multi-homing model; EVPN multi-homing is implemented through Ethernet Segment association and MAC-VRF attachment behavior, not by adding multiple IRB subinterfaces for multi-homing. Option D is also wrong because the IRB is the shared logical link between the MAC-VRF and IP-VRF; the design does not require separate IRB subinterfaces on each side as independent constructs. Reference: SR Linux IRB configuration, MAC-VRF to IP-VRF interconnection, primary IP addressing.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

In SR Linux BGP configuration, parameters defined at a more specific hierarchy level can override broader protocol-level settings. Therefore, if a `local-as` value is configured within the BGP group used for EVPN MP-BGP route-reflector sessions, that value overrides the AS number configured directly under the BGP protocol for that group's sessions. Option A is correct. Option B is false because the cluster ID is configured on the route reflector, not on every participating client. The cluster ID identifies the RR cluster and helps prevent route-reflection loops. Option C is false because redundant route reflectors normally operate in parallel rather than as strict primary/backup devices; clients can peer with both for resilience. Option D is misleading because EVPN route reflectors are used to avoid a full mesh of overlay MP-BGP EVPN sessions between leaves, not to replace ordinary underlay eBGP leaf-spine routing sessions. In a clean fabric design, the underlay provides IP reachability, while the EVPN overlay uses MP-BGP sessions, often via route reflectors, to distribute tenant reachability. Reference: SR Linux BGP hierarchy, EVPN route reflector sessions, local-AS override, cluster ID behavior.

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Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:

A decoupled gateway-based DCI model separates the data center border-leaf function from the WAN PE function. This separation is the key design point. The border leaf remains part of the data center EVPN/VXLAN environment, while the WAN PE participates in WAN VPN transport and policy enforcement. Because the roles are split across two devices, the handoff between the border leaf and WAN PE provides a clean administrative and operational boundary. That boundary is useful for security policy, QoS marking, traffic classification, and troubleshooting ownership. The WAN does not need direct reachability to every leaf and route reflector as in a gateway-less model. The WAN PE also does not peer directly with the data center route reflector in a decoupled model; route exchange occurs through the border-leaf/WAN-PE handoff. VXLAN tunnels between leaf routers across different data centers are characteristic of gateway-less extension, not decoupled gateway operation. Therefore, the statement about clear demarcation between the data center border leaf and WAN PE is the accurate description. Reference: decoupled gateway-based DCI, security/QoS demarcation, WAN PE separation.

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