4A0-D03 Questions and Answers
Question # 1
Consider the exhibit.
All connected leaf routers have the same Ethernet segment configuration. The IP-VRF is configured properly and is operational.
Which of the following statements is FALSE?
A.
This Ethernet segment is configured for Layer 3 multi-homing.
B.
The EVI for the IP-VRF using this segment is 1000.
C.
A LAG must be configured on the connected leaf routers and the host.
D.
The redundancy mode for this Ethernet segment is all-active.
Answer:
C
Explanation:
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.
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Question # 2
An IRB sub-interface that is being used to interconnect a MAC-VRF to an IP-VRF, is configured with anycast-gw set to true and anycast-gw enabled.
Which of the following statements is FALSE?
A.
The last octet of the default virtual MAC assigned to the sub-interface is derived from the last octet of the chassis MAC.
B.
The same IP address used on this sub-interface can be used by other IRB sub-interfaces on remote PEs participating in the IP-VRF.
C.
The host IP address of the sub-interface appears in the IP-VRF route table along with the prefix for the entire sub-net.
D.
Two MAC addresses associated to the sub-interface are shown in the forwarding table of the MAC-VRF that contains the IRB sub-interface.
Answer:
C
Explanation:
Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:
An anycast-gateway IRB allows multiple PEs to present the same default-gateway IP address to hosts in the same subnet. This is the mechanism that enables distributed gateway behavior in EVPN fabrics. The same anycast gateway IP may be configured on equivalent IRB subinterfaces across remote PEs participating in the same IP-VRF, allowing hosts to use the nearest leaf as their default gateway without changing their gateway address. SR Linux also associates gateway MAC information with the IRB, including virtual gateway MAC behavior used inside the MAC-VRF forwarding table. Option C is false because the anycast gateway IP is not treated as a normal unique host route that appears in the IP-VRF route table alongside the subnet prefix. The subnet route is installed for the connected network, but the shared anycast gateway address is a gateway function, not a separately advertised host endpoint that should appear as ordinary routed host reachability. Treating the anycast IP as a regular host route would undermine the distributed gateway model and create ambiguous ownership across PEs. Reference: IRB anycast gateway, MAC-VRF/IP-VRF interconnection, distributed default-gateway operation.
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Question # 3
Consider the exhibit.
Which of the following statements about the proxy ARP entry for the neighbor IP 192.168.100.1 is FALSE?
A.
The state is pending because this MAC address was originally associated with a different IP address.
B.
The traffic will be forwarded to a blackhole if the state changes to duplicate.
C.
The MAC address will be changed to 00:00:00:00:DE:AD if the state changes to duplicate.
D.
All traffic destined to 192.168.100.1 will be discarded for 9 minutes if the state changes to duplicate.
Answer:
D
Explanation:
Comprehensive and Detailed 150 to 250 words of Explanation From [SR Linux EVPN and Data Center Interconnect/Course Guide/topics]:
Proxy ARP in a Layer 2 EVPN service allows the leaf to answer ARP requests locally using learned IP/MAC bindings, reducing broadcast flooding across the overlay. SR Linux can also monitor IP duplication and MAC/IP inconsistencies in the proxy ARP table. A pending state indicates that the system has detected suspicious or conflicting information and is monitoring the binding before declaring it duplicate. If the entry becomes duplicate, SR Linux can use a blackhole behavior to prevent forwarding traffic toward a conflicted endpoint, and a special discard MAC such as 00:00:00:00:DE:AD can be associated with the duplicate entry. Option D is false because it incorrectly states that all traffic destined to 192.168.100.1 will be discarded for exactly 9 minutes. The exhibit references monitoring and hold-down behavior, but the answer key rejects the fixed “9 minutes†traffic-discard statement. The key concept is that duplicate handling protects the EVPN service from unstable or conflicting IP/MAC bindings, but the specific discard duration in option D is not correct. Reference: proxy ARP, IP duplication monitoring, duplicate-state blackhole behavior.
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