Understanding EVPN (Ethernet VPN) and ARP Request Handling
# What is EVPN?
* EVPN (Ethernet VPN) is a BGP-based control plane for VXLAN that improves Layer 2 & Layer 3 network scalability.
* Eliminates flood-and-learn behavior using BGP MAC/IP advertisement routes.
# Why is an ARP Request Sent?
* When CE1 (192.168.1.1/24) wants to communicate with CE2 (192.168.1.2/24), it sends an ARP request to discover the MAC address of CE2.
# How Does EVPN Process the ARP Request?1## PE1 receives the ARP request from CE1.2## PE1 sends a MAC/IP advertisement route (Type 2 EVPN route) to inform PE2 and PE3 of CE1's MAC address.3## PE1 forwards the ARP request as BUM (Broadcast, Unknown unicast, and Multicast) traffic to PE2 and PE3.4## PE3 (Designated Forwarder - DF) forwards the packet to CE2.5## PE2 (Non-DF) does NOT forward the packet to avoid loops.
Analysis of the Answer Choices:
# A. When forwarding the packet to PE3, PE1 needs to add the BUM traffic label allocated by PE3 to the packet.
* Correct:
* BUM (Broadcast, Unknown Unicast, Multicast) traffic in EVPN is encapsulated with a special label assigned by the receiving PE.
* PE1 adds the BUM traffic label for PE3 before sending the ARP request.
# B. PE1 sends a MAC/IP advertisement route carrying the MAC address of CE1.
* Correct:
* EVPN Type 2 MAC/IP advertisement routes are sent to inform other PEs of CE1's MAC/IP binding.
# C. PE2 forwards the packet to CE1.
* Incorrect:
* PE2 is the Non-Designated Forwarder (Non-DF) and does NOT forward BUM traffic to avoid loops.
# D. PE3 forwards the packet to CE1.
* Correct:
* PE3 is the Designated Forwarder (DF) for this segment, meaning it forwards the ARP request to CE2.
# Reference: Huawei HCIE-Datacom Guide - EVPN BGP MAC/IP Advertisement and BUM Traffic Handling Real-World Application:
* Data Center Interconnect (DCI): EVPN prevents excessive ARP flooding across VXLAN networks.
* Enterprise Campus Networks: Uses EVPN VXLAN to scale Layer 2 connectivity across multiple locations.