4A0-D03 Reviews Questions

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

When a new Layer 2 EVPN MAC-VRF instance is enabled, the PE advertises an Inclusive Multicast Ethernet Tag route, commonly called an IMET route or EVPN route type 3. The IMET route is used to auto-discover remote PEs that participate in the same EVPN service and to build the BUM flooding list for that MAC-VRF. In this topology, all leaf routers peer with the route reflector on Spine-1. Leaf-1 therefore advertises its IMET route to the route reflector, not directly to Leaf-2 and Leaf-3. The route reflector then reflects the EVPN update to the other client leaves. Leaf-2 and Leaf-3 import the route based on matching route-target policy and add Leaf-1 to the replication list for broadcast, unknown unicast, and multicast traffic. Option B is the step that is not taken because it incorrectly describes direct leaf-to-leaf EVPN advertisement. In a route-reflector design, the RR centralizes EVPN route distribution and avoids the need for a full mesh of MP-BGP EVPN sessions between leaves. Reference: EVPN RT-3 IMET route, route-reflector operation, BUM flooding-list auto-discovery.

================

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

The scenario describes Layer 3 EVPN multi-homing with an IP-VRF service and an external CE VNF advertising the 40.40.40.0/24 prefix through BGP. A DF election can occur among the leaf routers participating in the Ethernet Segment, and the active/primary forwarding node is used for the relevant service behavior. The AD per EVI route can participate in identifying service-level reachability for the Ethernet Segment, and the prefix traffic follows the valid advertised path toward the CE VNF. Because Leaf3 has the BGP connection to the CE VNF, traffic for 40.40.40.0/24 is forwarded through Leaf3. Option B is false because it incorrectly states that all connected leaf routers will use single-active redundancy. The exhibit and answer context indicate a more specific forwarding/primary selection for the service, not a blanket statement that every connected leaf operates using single-active redundancy. In L3 multi-homing, redundancy behavior depends on the ES mode, prefix advertisement, next-hop association, and CE connectivity. The forwarding decision for the customer prefix is tied to the active/valid route advertisement, not to every leaf uniformly acting as single-active. Reference: L3 EVPN multi-homing, DF election, AD per EVI role, PE-CE BGP prefix forwarding.

================

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.

================

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.

================