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Configuration Guide - VXLAN

CloudEngine 12800 and 12800E V200R003C00

This document describes the configurations of VXLAN.
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BD-based Layer 2 Proxy ARP

BD-based Layer 2 Proxy ARP

Background

On a VXLAN, after a Layer 2 gateway receives an ARP request packet, it broadcasts the packet within the BD. If the Layer 2 gateway receives a large number of ARP request packets within a period and broadcasts the packets, excessive ARP request packets are forwarded on the VXLAN, consuming excessive network resources and causing network congestion. As a result, the network performance deteriorates, and user services are affected. To resolve this problem, BD-based Layer 2 proxy ARP can be deployed on the Layer 2 gateway.

Layer 2 proxy ARP is an effective mechanism that helps minimize the number of broadcast ARP packets. After receiving an ARP request packet, the Layer 2 gateway with Layer 2 proxy ARP enabled preferentially sends an ARP reply packet. It broadcasts the packet only when it fails to respond to the packet.

NOTE:

This function is supported for IPv4 over IPv4 and IPv4 over IPv6 networks but not for IPv6 over IPv4 or IPv6 over IPv6 networks.

Implementation

As shown in Figure 5-16, BD-based Layer 2 proxy ARP is enabled on the Layer 2 gateways. After the user access-side interface receives an ARP request packet, the involved Layer 2 gateway listens to the packet for ARP source information and records the source IP address, source MAC address, inbound interface information in a local ARP snooping binding entry, which provides references for Layer 2 proxy ARP. Additionally, if the VXLAN tunnel is established in BGP EVPN mode, BGP EVPN can be enabled to collect host information per BD on the Layer 2 gateways. This configuration allows Layer 2 gateways to synchronize listened user ARP information with each other through BGP EVPN routes (MAC/IP routes). Then the local Layer 2 gateway adds the synchronized source IP address, source MAC address, and source VTEP IP address to another local ARP snooping binding entry.

When a Layer 2 gateway receives another ARP request packet, the gateway searches its local ARP snooping binding entries (including the locally listened entries and those synchronized with the other gateway) for an entry that matches the packet's destination IP address:
  • If the matching entry exits, the gateway directly sends an ARP reply packet based on the found information.

  • If no matching entry exits, the gateway broadcasts the ARP request packet.

In this way, the number of broadcast ARP packets is minimized on the VXLAN.
Figure 5-16 BD-based Layer 2 proxy ARP

Deployment Scenario

BD-based Layer 2 proxy ARP is applicable if a VXLAN tunnel is established in BGP EVPN mode to implement Layer 2 interconnection, and it is deployed only on Layer 2 gateways.

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Updated: 2019-05-05

Document ID: EDOC1100004207

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