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A virtual address used for NAT does not necessarily behave like an address owned by a local service.

\n

Source facts

\n

Netgate distinguishes IP Alias, CARP, Proxy ARP, and Other virtual IPs. IP Alias addresses can answer ARP and bind local services. Proxy ARP provides Layer 2 replies, while Other suits addresses routed to the firewall without ARP. Proxy ARP and Other do not themselves answer ping without forwarding it to an internal target.

\n

Source: Netgate — Virtual IP Addresses.

\n

Applicability

\n

This concerns pfSense VIP types and provider addressing arrangements.

\n

DSE recommendation

\n

DSE recommends obtaining the provider’s subnet and routing design before selecting a VIP type. State whether the address must be owned by a firewall service, translated to another host, or shared through an HA design. Avoid using an unanswered ping alone to declare a Proxy ARP address unusable. Include service listeners bound to all addresses in the exposure review because a new locally owned address can change where those services respond. Ask the provider and firewall owners to sign off on the same address-delivery diagram. For each extra address, mark the intended responder and service owner. Reject an acceptance result that tests only ICMP when the requirement is a local listener or translated application.

\n

Verification

\n

For an approved spare address, inspect the expected ARP or routed delivery path and test the actual intended protocol. Check local service binding and NAT independently. Record the selected VIP type and why its behavior matches the provider’s design.

\n

Official reference

\n

Netgate — Virtual IP Addresses. Reviewed October 20, 2026.

", "content_text": "A virtual address used for NAT does not necessarily behave like an address owned by a local service.\nSource facts\nNetgate distinguishes IP Alias, CARP, Proxy ARP, and Other virtual IPs. IP Alias addresses can answer ARP and bind local services. Proxy ARP provides Layer 2 replies, while Other suits addresses routed to the firewall without ARP. Proxy ARP and Other do not themselves answer ping without forwarding it to an internal target.\nSource: Netgate — Virtual IP Addresses.\nApplicability\nThis concerns pfSense VIP types and provider addressing arrangements.\nDSE recommendation\nDSE recommends obtaining the provider’s subnet and routing design before selecting a VIP type. State whether the address must be owned by a firewall service, translated to another host, or shared through an HA design. Avoid using an unanswered ping alone to declare a Proxy ARP address unusable. Include service listeners bound to all addresses in the exposure review because a new locally owned address can change where those services respond. Ask the provider and firewall owners to sign off on the same address-delivery diagram. For each extra address, mark the intended responder and service owner. Reject an acceptance result that tests only ICMP when the requirement is a local listener or translated application.\nVerification\nFor an approved spare address, inspect the expected ARP or routed delivery path and test the actual intended protocol. Check local service binding and NAT independently. Record the selected VIP type and why its behavior matches the provider’s design.\nOfficial reference\nNetgate — Virtual IP Addresses. Reviewed October 20, 2026.", "content_markdown": "A virtual address used for NAT does not necessarily behave like an address owned by a local service.\n\n## Source facts\n\nNetgate distinguishes IP Alias, CARP, Proxy ARP, and Other virtual IPs. IP Alias addresses can answer ARP and bind local services. Proxy ARP provides Layer 2 replies, while Other suits addresses routed to the firewall without ARP. Proxy ARP and Other do not themselves answer ping without forwarding it to an internal target.\n\nSource: [Netgate — Virtual IP Addresses](https://docs.netgate.com/pfsense/en/latest/firewall/virtual-ip-addresses.html).\n\n## Applicability\n\nThis concerns pfSense VIP types and provider addressing arrangements.\n\n## DSE recommendation\n\nDSE recommends obtaining the provider’s subnet and routing design before selecting a VIP type. State whether the address must be owned by a firewall service, translated to another host, or shared through an HA design. Avoid using an unanswered ping alone to declare a Proxy ARP address unusable. Include service listeners bound to all addresses in the exposure review because a new locally owned address can change where those services respond. Ask the provider and firewall owners to sign off on the same address-delivery diagram. For each extra address, mark the intended responder and service owner. Reject an acceptance result that tests only ICMP when the requirement is a local listener or translated application.\n\n## Verification\n\nFor an approved spare address, inspect the expected ARP or routed delivery path and test the actual intended protocol. Check local service binding and NAT independently. Record the selected VIP type and why its behavior matches the provider’s design.\n\n## Official reference\n\n[Netgate — Virtual IP Addresses](https://docs.netgate.com/pfsense/en/latest/firewall/virtual-ip-addresses.html). 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