Forwarding rules overview

A forwarding rule specifies how to route network traffic to the backend services of a load balancer. A forwarding rule includes an IP address, an IP protocol, and one or more ports on which the load balancer accepts traffic. Some Google Cloud load balancers limit you to a predefined set of ports, and others let you specify arbitrary ports.

A forwarding rule and its corresponding IP address represent the frontend configuration of a Google Cloud load balancer.

Depending on the load balancer type, the following is true:

In addition, a regional forwarding rule can be a resource that's designated as a service in App Hub, which is in preview.

Internal forwarding rules

Internal forwarding rules forward traffic that originates inside a Google Cloud network. The clients can be in the same Virtual Private Cloud (VPC) network as the backends, or the clients can be in a connected network.

Internal forwarding rules are used by the following Google Cloud load balancers:

  • Internal passthrough Network Load Balancer
  • Internal Application Load Balancer
  • Internal proxy Network Load Balancer

Internal passthrough Network Load Balancer

With an internal passthrough Network Load Balancer, the supported traffic types are either IPv4 or IPv6. For information about the supported protocols, see Forwarding rule protocols.

Each internal passthrough Network Load Balancer has at least one regional internal forwarding rule. The regional internal forwarding rules point to the load balancer's regional internal backend service. The following diagram shows how a forwarding rule fits into the internal passthrough Network Load Balancer architecture.

Internal passthrough Network Load Balancer forwarding rule.
Internal passthrough Network Load Balancer forwarding rule (click to enlarge).

The following diagram shows how the load balancer components fit within a subnet and region.

The internal forwarding rule must be defined in a region and a subnet. The backend service only needs to correspond to that region.

High-level internal passthrough Network Load Balancer example.
High-level internal passthrough Network Load Balancer example (click to enlarge).

For more information about internal passthrough Network Load Balancers, see the following pages:

Internal Application Load Balancer

With an internal Application Load Balancer, the supported traffic type is IPv4, and the supported protocol can be HTTP, HTTPS, or HTTP/2. The scope of the forwarding rule depends on the type of load balancer:

  • Each regional internal Application Load Balancer has at least one regional internal forwarding rule. The regional internal forwarding rule points to the load balancer's regional target HTTP or HTTPS proxy. The forwarding rule is associated with a regional internal IP address.

  • Each cross-region internal Application Load Balancer has at least one global internal forwarding rule. The global internal forwarding rule points to the load balancer's global target HTTP or HTTPS proxy. The global forwarding rule is configured with a regional internal IP address and associated with a regional subnet; whereas, a global external Application Load Balancer has a global forwarding rule that has a global anycast IP address.

Internal managed forwarding rules connected to a target HTTP(S) proxy support any port number between 1 and 65535 inclusive.

As an example, the following diagram shows how a forwarding rule fits into the regional internal Application Load Balancer architecture.

Regional internal Application Load Balancer forwarding rule.
Regional internal Application Load Balancer forwarding rule (click to enlarge).

For more information about internal Application Load Balancers, see the following pages:

Internal proxy Network Load Balancer

With an internal proxy Network Load Balancer, the supported traffic type is IPv4, and the supported protocol is TCP.

  • Each regional internal proxy Network Load Balancer has at least one regional internal forwarding rule. The forwarding rule specifies an internal IP address, port, and regional target TCP proxy. Clients use the IP address and port to connect to the load balancer's Envoy proxies—the forwarding rule's IP address is the IP address of the load balancer (sometimes called a virtual IP address or VIP).

  • Each cross-region internal proxy Network Load Balancer has at least one global internal forwarding rule. The global internal forwarding rule points to the load balancer's global target TCP proxy. The global forwarding rule is configured with a regional internal IP address and associated with a regional subnet.

Internal managed forwarding rules connected to a target TCP proxy support any port number between 1 and 65535 inclusive.

The following diagram shows how a forwarding rule fits into the regional internal proxy Network Load Balancer architecture.

Regional internal proxy Network Load Balancer forwarding rule.
Regional internal proxy Network Load Balancer forwarding rule (click to enlarge).

For more details about internal proxy Network Load Balancers, see the following pages:

External forwarding rules

External forwarding rules accept traffic from client systems that have internet access, including:

  • A client outside of Google Cloud
  • A Google Cloud VM with an external IP address
  • A Google Cloud VM without an external IP address using Cloud NAT or an instance-based NAT system

External forwarding rules are used by the following Google Cloud load balancer types:

  • External Application Load Balancer
  • External proxy Network Load Balancer
  • External passthrough Network Load Balancer

Global external Application Load Balancer

For global external Application Load Balancers, the forwarding rule and IP address depend on the load balancer mode, and the Network Service Tiers that you select for the load balancer.

  • The global external Application Load Balancer supports only Premium Tier.
  • Each classic Application Load Balancer can be Premium Tier or Standard Tier.
  • The regional external Application Load Balancer supports both Premium and Standard Tier.

In an external Application Load Balancer, a forwarding rule points to a target proxy.

  • In Premium Tier, global external Application Load Balancers and classic Application Load Balancers use a global external IP address, which can be either IPv4 or IPv6, and a global external forwarding rule. You can provide a globally accessible application that directs end users to backends in the closest region and distributes traffic among multiple regions. Because a global external forwarding rule uses a single external IP address, you don't need to maintain separate DNS records in different regions or wait for DNS changes to propagate.

    You can have two different global external IP addresses pointing to the same global external Application Load Balancer. For example, in Premium Tier, the global external IP address for one forwarding rule can be IPv4, and the global external IP address for a second forwarding rule can be IPv6. Both forwarding rules can point to the same target proxy. As a result, you can provide both an IPv4 and an IPv6 address for the same external Application Load Balancer. For more information, see the IPv6 termination documentation.

  • In Premium Tier, regional external Application Load Balancers use a regional external IPv4 address and a regional external forwarding rule.

  • In Standard Tier, regional external Application Load Balancers and classic Application Load Balancers, use a regional external IP address, which must be IPv4, and a regional external forwarding rule. A load balancer in Standard Tier can only distribute traffic to backends within a single region.

External forwarding rules connected to a target HTTP(S) proxy support any port number between 1 and 65535 inclusive.

The following diagram shows how a global forwarding rule fits into the architecture for a global external Application Load Balancer. The same architecture also applies to the classic Application Load Balancer in Premium Tier.

Global external Application Load Balancer forwarding rule.
Global external Application Load Balancer forwarding rule (click to enlarge).

For more information about external Application Load Balancers, see the External Application Load Balancer overview.

External proxy Network Load Balancer

An external proxy Network Load Balancer offers TCP proxying capability, with optional SSL offload. An external proxy Network Load Balancer is similar to an external Application Load Balancer because it can terminate SSL (TLS) sessions. However, these load balancers don't support path-based redirection like external Application Load Balancers, so they're better suited for handling SSL for protocols other than HTTPS, such as IMAP or WebSockets over SSL.

External proxy Network Load Balancers support both Premium Tier and Standard Tier. The forwarding rule and IP address depend on the type of load balancer mode and the Network Service Tiers that you select for the load balancer:

  • The classic proxy Network Load Balancer can be Premium Tier or Standard Tier.
  • The global external proxy Network Load Balancer supports only Premium Tier.
  • The regional external proxy Network Load Balancer supports only Standard Tier.

In an external proxy Network Load Balancer, a forwarding rule points to either a TCP or an SSL target proxy.

  • In Premium Tier, global external proxy Network Load Balancers and classic proxy Network Load Balancers use a global external IP address, which can be either IPv4 or IPv6, and a global external forwarding rule. You can provide a globally accessible application that directs end users to backends in the closest region and distributes traffic among multiple regions. Because a global external forwarding rule uses a single external IP address, you don't have to maintain separate DNS records in different regions or wait for DNS changes to propagate.

    It is possible to have two different global external IP addresses pointing to the same external proxy Network Load Balancer. For example, in Premium Tier, the global external IP address for one forwarding rule can be IPv4, and the global external IP address for a second forwarding rule can be IPv6. Both forwarding rules can point to the same target proxy. As a result, you can provide both an IPv4 and an IPv6 address for the same external proxy Network Load Balancer. For more information, see the IPv6 termination documentation.

  • In Premium Tier, regional external proxy Network Load Balancers use a regional external IPv4 address and a regional external forwarding rule.

  • In Standard Tier, regional external proxy Network Load Balancers and classic proxy Network Load Balancers use a regional external IP address, which must be IPv4, and a regional external forwarding rule. A load balancer in Standard Tier can only distribute traffic to backends within a single region.

External forwarding rules connected to a target TCP or SSL proxy support any port number between 1 and 65535 inclusive.

The following diagram shows how a forwarding rule fits into the external proxy Network Load Balancer architecture.

External proxy Network Load Balancer forwarding rule.
External proxy Network Load Balancer forwarding rule (click to enlarge).

For more information about external proxy Network Load Balancers, see the External proxy Network Load Balancer overview. For information about configuring external proxy Network Load Balancers, see Set up an external proxy Network Load Balancer.

External passthrough Network Load Balancer

External passthrough Network Load Balancers is a pass-through load balancer that distributes traffic among backend instances in a single region. An external passthrough Network Load Balancer uses a regional external forwarding rule and a regional external IP address. The regional external IP address can be accessed from anywhere on the internet and by Google Cloud VMs with internet access.

For backend service-based external passthrough Network Load Balancers, the regional external forwarding rule points to a backend service. Backend service-based external passthrough Network Load Balancers support TCP, UDP, ESP, GRE, ICMP, and ICMPv6 traffic. For details, see Forwarding rule protocols for backend service-based external passthrough Network Load Balancers. Forwarding rules for backend service-based load balancers can be configured with either IPv4 or IPv6 addresses. Forwarding rules for backend service-based external passthrough Network Load Balancers support the following advanced features:

  • Direct traffic coming from a specific range of source IP addresses to a specific backend service. For more information, see Traffic steering.
  • Distribute traffic across the load balancer's backend instances based on the weights reported by an HTTP health check using Weighted load balancing.

For target pool-based external passthrough Network Load Balancers, the forwarding rule points to a target pool. A target pool-based external passthrough Network Load Balancer supports only TCP or UDP traffic. Forwarding rules for target pool-based external passthrough Network Load Balancer support only IPv4 addresses.

For regional external IPv4 addresses, the external passthrough Network Load Balancer supports both Standard Tier and Premium Tier. Regional external IPv6 addresses are only available in the Premium Tier.

To support backend instances in more than one region, you must create a external passthrough Network Load Balancer in each region. This is the case regardless of whether the IP address of the load balancer is in the Premium Tier or the Standard Tier.

The following figure shows an external passthrough Network Load Balancer which has a regional external forwarding rule with the IP address, 120.1.1.1. The load balancer is serving requests from backends in the us-central1 region.

External passthrough Network Load Balancer example.
External passthrough Network Load Balancer example (click to enlarge).

For more information about external passthrough Network Load Balancers, see the External passthrough Network Load Balancer overview. For information about configuring external passthrough Network Load Balancers, see one of the following:

How Network Service Tiers affect load balancers

In Network Service Tiers, the distinction between Standard Tier and Premium Tier depends on how far traffic is routed over the public internet:

  • Standard Tier: Offloads traffic as close as possible to the data center. This means that traffic is typically routed over the public internet for a longer distance, compared with Premium Tier.

  • Premium Tier: Routes traffic through Google's production network as far as possible before leaving Google Cloud to get to the end user.

Load balancer Supported Network Service Tiers
  • Global external Application Load Balancer
  • Global external proxy Network Load Balancer
These load balancers are always Premium Tier. Their backend services, forwarding rules, and IP addresses are global.
  • Classic Application Load Balancer
  • Classic proxy Network Load Balancer

These load balancers can be Premium Tier or Standard Tier.

With Premium Tier, they are global. Their forwarding rules, IP addresses, and backend services are global.

In Standard Tier, these load balancers are effectively regional. Their backend services are global, but their forwarding rules and IP addresses are regional.

  • Regional external Application Load Balancer
  • Regional external proxy Network Load Balancer
These load balancers can be Premium or Standard Tier. Their backend services, forwarding rules, and IP addresses are always regional.
  • Cross-region internal Application Load Balancer
  • Regional internal Application Load Balancer
  • Regional internal proxy Network Load Balancer
  • Cross-region internal proxy Network Load Balancer
  • Internal passthrough Network Load Balancer
These load balancers support traffic within a VPC network (including networks connected to it). Traffic is Premium Tier because it is within a VPC network.
External passthrough Network Load Balancer

These load balancers must use regional external IPv4 or IPv6 addresses.

These load balancers can be either Premium or Standard Tier. IPv6 addresses require Premium Tier.

Only the backend service-based external passthrough Network Load Balancers can handle IPv6 traffic.

IP protocol specifications

Each forwarding rule has an associated IP protocol that the rule will serve. The default protocol value is TCP.

Product Load balancing scheme IP protocol options
Global external Application Load Balancer EXTERNAL_MANAGED TCP
Classic Application Load Balancer EXTERNAL TCP
Regional external Application Load Balancer EXTERNAL_MANAGED TCP
Cross-region internal Application Load Balancer INTERNAL_MANAGED TCP
Regional internal Application Load Balancer INTERNAL_MANAGED TCP
Global external proxy Network Load Balancer EXTERNAL_MANAGED TCP or SSL
Classic proxy Network Load Balancer EXTERNAL TCP or SSL
Regional external proxy Network Load Balancer EXTERNAL_MANAGED TCP
Regional internal proxy Network Load Balancer INTERNAL_MANAGED TCP
Cross-region internal proxy Network Load Balancer INTERNAL_MANAGED TCP
External passthrough Network Load Balancer EXTERNAL TCP, UDP, or L3_DEFAULT
Internal passthrough Network Load Balancer INTERNAL TCP, UDP, or L3_DEFAULT
Traffic Director INTERNAL_SELF_MANAGED TCP

IP address specifications

The forwarding rule must have an IP address that your customers use to reach your load balancer. The IP address can be static or ephemeral.

A static IP address provides a single reserved IP address that you can point your domain to. If you ever need to delete your forwarding rule and re-add it, you can continue using the same reserved IP address.

An ephemeral IP address remains constant while the forwarding rule exists. When you choose an ephemeral IP address, Google Cloud associates an IP address with your load balancer's forwarding rule. If you need to delete the forwarding rule and re-add it, the forwarding rule might receive a new IP address.

Depending on the load balancer type, the IP address can have various attributes. The following table summarizes the valid IP address configurations, based on the load balancing scheme and the target of the forwarding rule.

Product and scheme Target Address type Address scope Address tier Reservable address Notes
Global external Application Load Balancer

EXTERNAL_MANAGED
Target HTTP proxy
Target HTTPS proxy
External Global Premium Tier: Global external IP address and forwarding rule Yes, optional IPv6 available
Classic Application Load Balancer

EXTERNAL
Target HTTP proxy
Target HTTPS proxy
External Regional or global, matching the forwarding rule Premium Tier: Global external IPv4 or IPv6 address and forwarding rule

Standard Tier: Regional external IPv4 address and forwarding rule
Yes, optional IPv6 available with a global external address (Premium Tier)
Regional external Application Load Balancer

EXTERNAL_MANAGED
Target HTTP proxy
Target HTTPS proxy
External Regional Standard Tier: Regional external IPv4 address and forwarding rule Yes, optional IPv6 not available
Cross-region internal Application Load Balancer

INTERNAL_MANAGED
Target HTTP proxy
Target HTTPS proxy
Internal Regional Premium Yes, optional Global forwarding rule is configured with a regional IP address within the primary IPv4 address range of the associated regional subnet. This is different from the global external Application Load Balancer where the global forwarding rule has a global anycast IP address.
Regional internal Application Load Balancer

INTERNAL_MANAGED
Target HTTP proxy
Target HTTPS proxy
Internal Regional Premium Yes, optional Forwarding rule address must be within the primary IPv4 address range of the associated subnet.
Global external proxy Network Load Balancer

EXTERNAL_MANAGED
Target SSL proxy
Target TCP proxy
External Global Premium Tier: Global external IP address and forwarding rule Yes, optional IPv6 available
Classic proxy Network Load Balancer

EXTERNAL
Target SSL proxy
Target TCP proxy
External Regional or global, matching the forwarding rule Premium Tier: Global external IPv4 or IPv6 address and forwarding rule

Standard Tier: Regional external IPv4 address and forwarding rule
Yes, optional IPv6 available with a global external address (Premium Tier)
Regional external proxy Network Load Balancer

EXTERNAL_MANAGED
Target TCP proxy External Regional Standard Tier: Regional external IPv4 address and forwarding rule Yes, optional IPv6 not available
Regional internal proxy Network Load Balancer

INTERNAL_MANAGED
Target TCP proxy Internal Regional Premium Yes, optional Forwarding rule address must be within the primary IPv4 address range of the associated subnet
Cross-region internal proxy Network Load Balancer

INTERNAL_MANAGED
Target TCP proxy Internal Regional Premium Yes, optional Forwarding rule address must be within the primary IPv4 address range of the associated subnet
External passthrough Network Load Balancer

EXTERNAL
Backend service
Target pool
External Regional Standard (IPv4 addresses)
Premium (IPv4 or IPv6 addresses)
Yes, optional IPv6 support requires a backend service-based external passthrough Network Load Balancer. Forwarding rule IPv6 address must be within a subnet's external IPv6 address range. The external IPv6 address is sourced from the subnet's external IPv6 address range and is therefore in Premium Tier.
Internal passthrough Network Load Balancer

INTERNAL
Backend service Internal Regional Premium Yes, optional Forwarding rule address must be within the primary IPv4 address range of the associated subnet.
Traffic Director

INTERNAL_SELF_MANAGED
Target HTTP proxy
Target gRPC proxy
Internal Global Not applicable No 0.0.0.0, 127.0.0.1, or any RFC 1918 address is allowed
Classic VPN

EXTERNAL
See the Classic VPN documentation External Regional Cloud VPN doesn't have Network Service Tiers Yes, required IPv6 not supported

Multiple forwarding rules with a common IP address

Two or more forwarding rules with the EXTERNAL or EXTERNAL_MANAGED load balancing scheme can share the same IP address if the following are true:

  • The ports used by each forwarding rule don't overlap.
  • The Network Service Tiers of each forwarding rule matches the Network Service Tiers of the external IP address.

Examples:

  • An external passthrough Network Load Balancer that accepts traffic on TCP port 79 and another external passthrough Network Load Balancer that accepts traffic on TCP port 80 can share the same regional external IP address.
  • You can use the same global external IP address for an external Application Load Balancer (HTTP and HTTPS).

If the forwarding rule's load balancing scheme is INTERNAL or INTERNAL_MANAGED, multiple forwarding rules can use the same IP address. For more information, see the following:

If the forwarding rule's load balancing scheme is INTERNAL_SELF_MANAGED for Traffic Director, it must have a unique IP address.

Port specifications

The following table summarizes the valid port configurations, based on the load balancing scheme and the target of the forwarding rule.

Product Load balancing scheme Target Port requirements
Global external Application Load Balancer

Regional external Application Load Balancer
EXTERNAL_MANAGED Target HTTP proxy
Target HTTPS proxy
Can reference exactly one port from 1-65535
Classic Application Load Balancer EXTERNAL Target HTTP proxy
Target HTTPS proxy
Can reference exactly one port from 1-65535
Cross-region internal Application Load Balancer

Regional internal Application Load Balancer
INTERNAL_MANAGED Target HTTP proxy
Target HTTPS proxy
Can reference exactly one port from 1-65535
Global external proxy Network Load Balancer EXTERNAL_MANAGED Target TCP proxy
Target SSL proxy
Can reference exactly one port from 1-65535
Classic proxy Network Load Balancer EXTERNAL Target TCP proxy
Target SSL proxy
Can reference exactly one port from 1-65535
Regional external proxy Network Load Balancer EXTERNAL_MANAGED Target TCP proxy Can reference exactly one port from 1-65535
Regional internal proxy Network Load Balancer INTERNAL_MANAGED Target TCP proxy Can reference exactly one port from 1-65535
Cross-region internal proxy Network Load Balancer INTERNAL_MANAGED Target TCP proxy Can reference exactly one port from 1-65535
External passthrough Network Load Balancer EXTERNAL Backend service If the forwarding rule protocol is TCP or UDP, you can configure:
  • A list of up to five (contiguous or non-contiguous) ports, or,
  • A single port range (contiguous), or,
  • All ports. To configure all ports, either set --ports=ALL using the gcloud command line tool, or set allPorts to True using the API.

If the forwarding rule protocol is L3_DEFAULT, you must configure all ports.
  • To configure all ports, either set --ports=ALL using the gcloud command line tool, or set allPorts to True using the API.
Target pool

Must be a single port range (contiguous)

Specifying a port is optional for forwarding rules used with target pool-based external passthrough Network Load Balancers. If no port is specified, traffic from all ports (1-65535) is forwarded.

Internal passthrough Network Load Balancer INTERNAL Backend service Up to five (contiguous or non-contiguous) ports or you can configure all ports using one of these methods:
set --ports=ALL using the gcloud command line tool, or
set allPorts to True using the API.
Traffic Director INTERNAL_SELF_MANAGED Target HTTP proxy
Target HTTPS proxy
Must be a single value.

Within a VPC network, no two forwarding rules for Traffic Director can have the same IP address and port specification.
Classic VPN EXTERNAL Target VPN gateway Can reference exactly one of the following ports: 500, 4500

IAM conditions

With Identity and Access Management (IAM) Conditions, you can set conditions to control which roles are granted to principals. This feature lets you grant permissions to principals if configured conditions are met.

An IAM condition checks the load balancing scheme (for example, INTERNAL or EXTERNAL) in the forwarding rule and allows (or disallows) creation of the forwarding rule. If a principal tries to create a forwarding rule without permission, an error message appears.

For more information, see IAM Conditions.

Use forwarding rules

If you're using the Google Cloud console to set up a load balancer, the forwarding rule is set up implicitly as part of your frontend configuration. If you're using the Google Cloud CLI or the API, you need to configure the forwarding rule explicitly.

After creating a forwarding rule, you can make limited changes to it. For example, after a forwarding rule is defined, you can't change its IP address, port number, or protocol. However, you can update certain settings for forwarding rules by editing the frontend configuration of the load balancer they are associated with. Use either the gcloud CLI or the API to make any other changes.

APIs

For descriptions of the properties and methods available to you when working with forwarding rules through the REST API, see the following:

Google Cloud CLI

For the gcloud CLI reference documentation, see the following:

What's next