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Feature Description - LAN Access and MAN Access 01

NE05E and NE08E V300R003C10SPC500

This is NE05E and NE08E V300R003C10SPC500 Feature Description - LAN Access and MAN Access
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Proxy ARP on an EVPN MPLS

Proxy ARP on an EVPN MPLS

Background

On an EVPN, when a user accesses a Layer 2 device through a BD or accesses a Layer 3 device through a VBDIF interface, an ARP request packet is broadcast in the BD. If the Layer 2 or Layer 3 device receives a large number of ARP request packets, broadcasting all these packets uses excessive network resources, causing network congestion. As a result, the network performance deteriorates, and user services are affected. To address the problem, BD-based Layer 2 proxy ARP can be configured on the Layer 2 device, or VBDIF interface-based Layer 3 proxy ARP can be configured on the Layer 3 device.

Proxy ARP on an EVPN MPLS is a mechanism of effectively reducing ARP broadcast packets.
  • After Layer 2 proxy ARP is enabled, a Layer 2 device takes the ARP entries learned in a specified BD. After receiving an ARP request packet, the Layer 2 device with proxy ARP enabled preferentially sends an ARP reply packet. It broadcasts the packet only when it fails to respond to the packet.
  • After Layer 3 proxy ARP is enabled, a Layer 3 device takes the ARP entries learned on a specified VBDIF interface. After receiving an ARP request packet, the Layer 3 device with proxy ARP enabled preferentially sends an ARP reply packet. It broadcasts the packet only when it fails to respond to the packet.

Implementation

  • BD-based Layer 2 Proxy ARP

    As shown in Figure 2-9, BD-based Layer 2 proxy ARP is enabled on Layer 2 devices. When the user access-side interface receives an ARP request packet, the involved Layer 2 device listens to the packet for ARP source information and records the source IP address, source MAC address, and inbound interface information in a local ARP snooping entry, which provides references for Layer 2 proxy ARP. In addition, Layer 2 devices can be enabled with EVPN to collect host information by BD. In this manner, the Layer 2 devices synchronize with each other and listen to ARP information through EVPN routes (MAC/IP routes). Such ARP information includes the source IP address and source MAC address.

    When a Layer 2 device receives another ARP request packet, it searches its local ARP snooping entries (including the locally listened entries and those synchronized with the other Layer 2 device) for an entry that matches the packet's destination IP address.

    • If such a matching entry exits, the Layer 2 device directly sends an ARP reply packet based on the found information.

    • If such a matching entry does not exit, the Layer 2 device broadcasts the ARP request packet.

    Figure 2-9 BD-based Layer 2 proxy ARP
  • VBDIF interface-based Layer 3 proxy ARP

    As shown in Figure 2-10, VBDIF interface-based Layer 3 proxy ARP is enabled on Layer 3 devices. When the user access-side interface receives an ARP request packet, the involved Layer 3 device listens to the packet for ARP source information and records the source IP address, source MAC address, and inbound interface information in a local ARP snooping entry, which provides references for Layer 3 proxy ARP. In addition, Layer 3 devices can be enabled with EVPN to collect host information by VBDIF interface. In this manner, the Layer 3 devices synchronize with each other and listen to ARP information through EVPN routes (MAC/IP routes). Such ARP information includes the source IP address and source MAC address.

    When a Layer 3 device receives another ARP request packet, it searches its local ARP snooping entries (including the locally listened entries and those synchronized with the other Layer 2 device) for an entry that matches the packet's destination IP address.

    • If such a matching entry exits, the Layer 3 device directly sends an ARP reply packet based on the found information.

    • If such a matching entry does not exit, the Layer 3 device broadcasts the ARP request packet.

    Figure 2-10 VBDIF interface-based Layer 3 proxy ARP

Usage Scenarios

  • BD-based Layer 2 proxy ARP applies to an EVPN MPLS accessed through a BD.

  • VBDIF interface-based Layer 3 proxy ARP applies to an EVPN MPLS accessed through a VBDIF interface.

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Updated: 2019-01-14

Document ID: EDOC1100058932

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