Nokia SR Linux EVPN and Data Center Interconnect 4A0-D03 Exam Questions

Answer : D

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

This setup represents a Layer 2 EVPN multi-homing attachment where the host is connected to Leaf1 and Leaf2 through an Ethernet Segment named ES-1. In SR Linux EVPN multi-homing, the Ethernet Segment must be associated with the physical or logical attachment interfaces facing the host. This allows the PEs to advertise Ethernet Segment information into EVPN, participate in DF election, and apply the appropriate forwarding behavior for single-active or all-active redundancy. Option D is therefore correct. Option A is not necessarily true because the exhibit indicates an active/standby style attachment, not all-active operation. Option B is also incorrect because ECMP on the remote MAC-VRF is not the mechanism that defines the local ES association or single-active behavior. Option C is wrong in this setup because a host LAG is required for common all-active L2 multi-homing with LACP, but the shown design uses an active/standby-style attachment where the Ethernet Segment is bound to the host-facing ports. The technical anchor is that ES-1 must be associated to the access ports connecting the host into the multi-homed MAC-VRF service. Reference: L2 EVPN multi-homing, Ethernet Segment interface association, DF behavior.

Answer : C

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.

Answer : C

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

The exhibit describes a Layer 3 multi-homing scenario where the Ethernet Segment is associated with an IP-VRF and the configuration references an EVI value of 1000. The segment is configured with all-active multi-homing, allowing multiple attached leaf routers to advertise reachability for the same external L3 next-hop or third-party prefix attachment. In this model, the Ethernet Segment represents the shared L3 attachment and is used by EVPN to associate remote prefix reachability with the multi-homed segment. The incorrect statement is that a LAG must be configured on the connected leaf routers and the host. That requirement is specific to many Layer 2 all-active host attachment designs, where the host commonly uses LACP toward multiple leaf routers and the leaf LAG subinterfaces are associated with the Ethernet Segment. In Layer 3 multi-homing, the attached device can be a router or VNF, and the EVPN ES association can be used for L3 prefix reachability without mandating that the host side be configured as a LAG. Reference: L3 EVPN multi-homing, EVI association, all-active Ethernet Segment behavior.

Answer : B

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

For Layer 2 all-active EVPN multi-homing on SR Linux, the Ethernet Segment configuration is the control-plane anchor that binds the redundant access attachment to EVPN. The relevant LAG subinterfaces must be associated with the Ethernet Segment so that the PE can advertise the segment correctly and apply split-horizon and aliasing behavior. The Ethernet Segment must also be administratively enabled; otherwise, the PE will not participate properly in ES discovery and DF procedures. The multi-homing mode must be set to all-active to permit forwarding through multiple attached leaf routers and support host-side LAG operation. The false statement is option B. The Ethernet Segment Identifier has a defined structure, and the blanket statement that the 2nd through 7th octets ''must not be all zeros'' is not a valid requirement as stated. What matters operationally is that the ESI uniquely identifies the same multi-homed Ethernet Segment across participating PEs and is consistently configured where required. The ESI must be non-zero as a meaningful segment identifier, but the specific octet restriction in the option is not the SR Linux all-active configuration rule. Reference: SR Linux L2 EVPN all-active multi-homing, Ethernet Segment configuration, LAG association.

Answer : D

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

In an integrated gateway-based DCI design, the same physical or logical router performs both the data center gateway role and the WAN PE role. This is why option D is correct. The device terminates or participates in the data center-side EVPN service and also handles the WAN-side VPN transport, including route translation or re-advertisement where needed. This approach avoids exposing every data center leaf router to the WAN and avoids requiring route reflector reachability between data centers. It also avoids building VXLAN tunnels directly between all leaf routers in separate data centers. Those characteristics belong to gateway-less DCI, where the EVPN overlay stretches more directly across the WAN and the WAN must carry the underlay or overlay reachability required by the data center leaves. Integrated gateway design is more controlled: the gateway is the interworking point, which makes it suitable when the provider or operator wants a strong service boundary and centralized DCI policy enforcement. Reference: integrated gateway-based DCI, single-router gateway/WAN PE function, EVPN/VPN interworking.

Answer : D

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.

Answer : D

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

In active-standby, or single-active, Layer 2 EVPN multi-homing, only one PE is active for the Ethernet Segment and MAC-VRF at a time. Leaf1 and Leaf2 participate in DF election, and the elected DF becomes the active forwarding PE for that service attachment. Because this is not all-active multi-homing, the non-DF must not forward traffic to the host for the protected service. This prevents duplicate frames, incorrect MAC learning, and loops on the access side. The DF accepts traffic from the host and forwards BUM traffic received from remote PEs toward the host-facing segment. Option D is false because it claims that the non-DF can forward unicast traffic from remote PEs to the host. In single-active operation, remote peers must direct traffic to the active PE, and the standby PE remains ready to take over only after DF state changes. This is the operational distinction from all-active multi-homing, where more than one PE may be used for forwarding depending on the traffic type and aliasing behavior. Reference: single-active L2 EVPN multi-homing, DF role, non-DF forwarding suppression.