IP Discovery uses DHCP and DHCPv6 snooping, ARP (Address Resolution Protocol) snooping, ND (Neighbor Discovery) snooping, and VM Tools to learn MAC and IP addresses.
The discovered MAC and IP addresses are used to achieve ARP/ND suppression, which minimizes traffic between VMs connected to the same logical switch. The addresses are also used by the SpoofGuard and distributed firewall (DFW) components. DFW uses the address bindings to determine the IP address of objects in firewall rules.
DHCP/DHCPv6 snooping inspects the DHCP/DHCPv6 packets exchanged between the DHCP/DHCPv6 client and server to learn the IP and MAC addresses.
ARP snooping inspects the outgoing ARP and GARP (gratuitous ARP) packets of a VM to learn the IP and MAC addresses.
VM Tools is software that runs on an ESXi-hosted VM and can provide the VM's configuration information including MAC and IP or IPv6 addresses. This IP discovery method is available for VMs running on ESXi hosts only.
ND snooping is the IPv6 equivalent of ARP snooping. It inspects neighbor solicitation (NS) and neighbor advertisement (NA) messages to learn the IP and MAC addresses.
Duplicate address detection checks whether a newly discovered IP address is already present on the realized binding list for a different port. This check is performed for ports on the same segment. If a duplicate address is detected, the newly discovered address is added to the discovered list, but is not added to the realized binding list. All duplicate IPs have an associated discovery timestamp. If the IP that is on the realized binding list is removed, either by adding it to the ignore binding list or by disabling snooping, the duplicate IP with the oldest timestamp is moved to the realized binding list. The duplicate address information is available through an API call.
By default, the discovery methods ARP snooping and ND snooping operate in a mode called trust on first use (TOFU). In TOFU mode, when an address is discovered and added to the realized bindings list, that binding remains in the realized list forever. TOFU applies to the first 'n' unique <IP, MAC, VLAN> bindings discovered using ARP/ND snooping, where 'n' is the binding limit that you can configure. You can disable TOFU for ARP/ND snooping. The methods will then operate in trust on every use (TOEU) mode. In TOEU mode, when an address is discovered, it is added to the realized bindings list and when it is deleted or expired, it is removed from the realized bindings list. DHCP snooping and VM Tools always operate in TOEU mode
For each port, NSX Manager maintains an ignore bindings list, which contains IP addresses that cannot be bound to the port. By navigating to and selecting a port, you can add discovered bindings to the ignore bindings list. You can also delete an existing discovered or realized binding by copying it to Ignore Bindings.
For Linux VMs, the ARP flux problem might cause ARP snooping to obtain incorrect information. The problem can be prevented with an ARP filter. For more information, see http://linux-ip.net/html/ether-arp.html#ether-arp-flux.