Cisco APIC Layer 2 Networking Configuration Guide, Release 6.2(x)

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Cisco APIC Layer 2 Networking Configuration Guide, Release 6.2(x)

Proxy ARP

Updated: July 7, 2026

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Describes how Proxy ARP in Cisco ACI facilitates endpoint communication within a subnet by responding to ARP requests on behalf of unknown MAC addresses, illustrating the ARP request and response process between virtual machines and the ACI fabric.

Proxy ARP in Cisco ACI enables endpoints within a network or subnet to communicate with other endpoints without knowing the real MAC address of the endpoints. Proxy ARP is aware of the location of the traffic destination, and offers its own MAC address as the final destination instead.

VM1 to VM2 communication is desired.

Device

State

VM1

IP = * MAC = *

ACI fabric

IP = * MAC = *

VM2

IP = * MAC = *

VM1 sends an ARP request with a broadcast MAC address to VM2.

Device

State

VM1

IP = VM2 IP; MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

VM2

IP = * MAC = *

The ACI fabric floods the proxy ARP request within the bridge domain (BD).

Device

State

VM1

IP = VM2 IP; MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

VM2

IP = VM1 IP; MAC = BD MAC

VM2 sends an ARP response to the ACI fabric.

Device

State

VM1

IP = VM2 IP; MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

VM2

IP = VM1 IP; MAC = BD MAC

VM2 is learned.

Device

State

VM1

IP = VM2 IP; MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

VM2

IP = VM1 IP; MAC = BD MAC

VM1 sends an ARP request with a broadcast MAC address to VM2.

Device

State

VM1

IP = VM2 IP MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

VM2

IP = VM1 IP; MAC = BD MAC

The ACI fabric sends a proxy ARP response to VM1.

Device

State

VM1

IP = VM2 IP; MAC = BD MAC

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

VM2

IP = VM1 IP; MAC = BD MAC

  1. VM1 to VM2 communication is desired.

    Figure 1. VM1 to VM2 Communication is Desired.
    Table 1. ARP Table State

    Device

    State

    VM1

    IP = * MAC = *

    ACI fabric

    IP = * MAC = *

    VM2

    IP = * MAC = *

  2. VM1 sends an ARP request with a broadcast MAC address to VM2.

    Figure 2. VM1 sends an ARP Request with a Broadcast MAC address to VM2
    Table 2. ARP Table State

    Device

    State

    VM1

    IP = VM2 IP; MAC = ?

    ACI fabric

    IP = VM1 IP; MAC = VM1 MAC

    VM2

    IP = * MAC = *

  3. The ACI fabric floods the proxy ARP request within the bridge domain (BD).

    Figure 3. ACI Fabric Floods the Proxy ARP Request within the BD
    Table 3. ARP Table State

    Device

    State

    VM1

    IP = VM2 IP; MAC = ?

    ACI fabric

    IP = VM1 IP; MAC = VM1 MAC

    VM2

    IP = VM1 IP; MAC = BD MAC

  4. VM2 sends an ARP response to the ACI fabric.

    Figure 4. VM2 Sends an ARP Response to the ACI Fabric
    Table 4. ARP Table State

    Device

    State

    VM1

    IP = VM2 IP; MAC = ?

    ACI fabric

    IP = VM1 IP; MAC = VM1 MAC

    VM2

    IP = VM1 IP; MAC = BD MAC

  5. VM2 is learned.

    Figure 5. VM2 is Learned
    Table 5. ARP Table State

    Device

    State

    VM1

    IP = VM2 IP; MAC = ?

    ACI fabric

    IP = VM1 IP; MAC = VM1 MAC

    IP = VM2 IP; MAC = VM2 MAC

    VM2

    IP = VM1 IP; MAC = BD MAC

  6. VM1 sends an ARP request with a broadcast MAC address to VM2.

    Figure 6. VM1 Sends an ARP Request with a Broadcast MAC Address to VM2
    Table 6. ARP Table State

    Device

    State

    VM1

    IP = VM2 IP MAC = ?

    ACI fabric

    IP = VM1 IP; MAC = VM1 MAC

    IP = VM2 IP; MAC = VM2 MAC

    VM2

    IP = VM1 IP; MAC = BD MAC

  7. The ACI fabric sends a proxy ARP response to VM1.

    Figure 7. ACI Fabric Sends a Proxy ARP Response to VM1
    Table 7. ARP Table State

    Device

    State

    VM1

    IP = VM2 IP; MAC = BD MAC

    ACI fabric

    IP = VM1 IP; MAC = VM1 MAC

    IP = VM2 IP; MAC = VM2 MAC

    VM2

    IP = VM1 IP; MAC = BD MAC
Table 8. ARP Table State

Device

State

VM1

IP = * MAC = *

ACI fabric

IP = * MAC = *

VM2

IP = * MAC = *
Table 9. ARP Table State

Device

State

VM1

IP = VM2 IP; MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

VM2

IP = * MAC = *
Table 10. ARP Table State

Device

State

VM1

IP = VM2 IP; MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

VM2

IP = VM1 IP; MAC = BD MAC
Table 11. ARP Table State

Device

State

VM1

IP = VM2 IP; MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

VM2

IP = VM1 IP; MAC = BD MAC
Table 12. ARP Table State

Device

State

VM1

IP = VM2 IP; MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

IP = VM2 IP; MAC = VM2 MAC

VM2

IP = VM1 IP; MAC = BD MAC
Table 13. ARP Table State

Device

State

VM1

IP = VM2 IP MAC = ?

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

IP = VM2 IP; MAC = VM2 MAC

VM2

IP = VM1 IP; MAC = BD MAC
Table 14. ARP Table State

Device

State

VM1

IP = VM2 IP; MAC = BD MAC

ACI fabric

IP = VM1 IP; MAC = VM1 MAC

IP = VM2 IP; MAC = VM2 MAC

VM2

IP = VM1 IP; MAC = BD MAC