Virtual IP Addresses¶
pfSense® software enables the use of multiple IP addresses in conjunction with NAT or local services through Virtual IPs (VIPs).
There are four types of Virtual IP addresses available in pfSense: IP Alias, CARP, Proxy ARP, and Other. Each is useful in different situations. In most circumstances, pfSense software will need to answer ARP request for a VIP which means that IP Alias, Proxy ARP or CARP must be used. In situations where ARP is not required, such as when additional public IP addresses are routed by a service provider to the WAN IP address on the firewall, use Other type VIPs.
pfSense software will not respond to pings destined to Proxy ARP and Other type VIPs regardless of firewall rule configuration. With Proxy ARP and Other VIPs, NAT must be present on the firewall, forwarding traffic to an internal host for ping to function. See Network Address Translation for more information.
IP Aliases work like any other IP address on an interface, such as the actual interface IP address. They will respond to layer 2 (ARP) and can used as binding addresses by services on the firewall. They can also be used to handle multiple subnets on the same interface. pfSense software will respond to ping on an IP Alias, and services on the firewall that bind to all interfaces will also respond on IP Alias VIPs unless the VIP is used to forward those ports in to another device (e.g. 1:1 NAT).
IP Alias VIPs can use Localhost as their interface to bind services using IP addresses from a block of routed addresses without specifically assigning the IP addresses to an interface. This is primarily useful in HA with CARP scenarios so that IP addresses do not need to be consumed by a CARP setup (one IP each per node, then the rest as CARP VIPs) when the subnet exists only inside the firewall (e.g. NAT or firewall services such as VPNs).
IP Aliases on their own do not synchronize to XMLRPC Configuration Synchronization peers because that would result in an IP address conflict. One exception to this is IP Alias VIPs using a CARP VIP “interface” for their interface. Those do not result in a conflict so they will synchronize. Another exception is IP Alias VIPs bound to Localhost as their interface. Because these are not active outside of the firewall itself, there is no chance of a conflict so they will also synchronize.
CARP VIPs are primarily used with High Availability redundant deployments utilizing CARP. CARP VIPs each have their own unique MAC address derived from their VHID, which can be useful even outside of a High Availability deployment.
For information on using CARP VIPs, see High Availability.
CARP VIPs may also be used with a single firewall. This is typically done in cases where the pfSense deployment will eventually be converted into an HA cluster node, or when having a unique MAC address is a requirement. In rare cases a provider requires each unique IP address on a WAN segment to have a distinct MAC address, which CARP VIPs provide.
CARP VIPs and IP Alias VIPs can be combined in two ways:
Proxy ARP VIPs function strictly at layer 2, providing ARP replies for the specified IP address or CIDR range of IP addresses. This allows pfSense software to accept traffic targeted at those addresses inside a shared subnet. For example, pfSense software can forward traffic sent to an additional address inside its WAN subnet according to its NAT configuration. The address or range of addresses are not assigned to any interface on pfSense, because they don’t need to be. This means no services on pfSense software itself can respond on these IP addresses.
Proxy ARP VIPs do not sync to XML-RPC Configuration Sync peers because doing so would cause an IP address conflict.
Other type VIPs define additional IP addresses for use when ARP replies for the IP address are not required. The only function of adding an Other type VIP is making that address available in the NAT configuration drop-down selectors. This is convenient when the firewall has a public IP block routed to its WAN IP address, IP Alias, or a CARP VIP.