ARP Suppression for BGP EVPN Overview

Address Resolution Protocol (ARP) suppression reduces the flooding of ARP messages in the EVPN network, leading to a more efficient use of core bandwidth.

ARP is responsible for mapping IPv4 addresses to MAC addresses in IP networks. ARP obtains endpoint MAC address information by utilizing the IP address information sent out in ARP broadcast requests. These broadcast requests are treated as multi-destination traffic, typically VXLAN-encapsulated, and sent to every VXLAN Tunnel End Point (VTEP) or edge device that is a member of the corresponding Layer 2 VXLAN network identifier (VNI). Responses to ARP broadcast requests are typically sent in the form of unicast packets to the requester, and the ARP traffic is scoped within the bounds of the broadcast domain represented by the Layer 2 VNI.

ARP broadcast requests are sent to the configured default gateway when a host needs to resolve the default gateway. This process facilitates the population of the MAC IP table for the edge device, ensuring that all MAC information is available in the BGP EVPN control plane protocol. Additionally, in a Route Type 2 advertisement, Layer 2, Layer 2 VNI, Route Distinguisher (RD), Route Target (RT), hosting VTEP, and associated IP information are populated. This is then distributed to all remote VTEPs.

Regular ARP broadcast requests are sent out to determine the IP-to-MAC binding of a destination endpoint. This ensures that a host device can learn information about an endpoint in the same subnet. ARP broadcast requests are flooded to all endpoints that are part of that Layer 2 VNI.

ARP snooping prevents flooding for known endpoints. When ARP snooping is employed, all ARP requests from an endpoint are redirected to the locally attached edge device. This allows for the determination of known endpoints. If the destination is known, the IP-to-MAC binding information is returned, and the local edge device performs an ARP proxy on behalf of the destination endpoint by sending a unicast ARP response toward the requester with the resolved MAC address of the known destination endpoint.

All ARP requests to known endpoints are terminated at the earliest possible point, typically the locally attached edge device, VTEP, or leaf. ARP suppression is possible because all information is known on all VXLAN VTEPs. ARP suppression differs from regular proxy ARP behavior; the router does not act as the proxy ARP endpoint in the response. Instead, the remote endpoint or host is used as the proxy, and the information is learned via either ARP snooping or the BGP EVPN control plane.

In this section:

  1. Configuring ARP Suppression for BGP EVPN
    You can enable ARP suppression for an EVPN instance. For BGP EVPN, when a VLAN is mapped to a VXLAN VNI, ARP suppression extends to corresponding EVPNs, VNIs, and EVIs. When ARP suppression is enabled, snooping MAC-IP bindings of any local endpoints for that VLAN is enabled. The information is maintained in a per-VLAN MAC-IP table. In addition to MAC-IP bindings learned through ARP snooping, any MAC-IP bindings learned via the BGP EVPN control plane are also stored in the same MAC-IP table.
Parent topic: BGP EVPN VXLAN