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This page provides an overview of subnets in Google Distributed Cloud (GDC) air-gapped and
their role in your load balancing efforts. A subnet, or subnetwork, represents a
logical subdivision of an IP network. This segmentation enhances network
efficiency, security, and manageability. For more information on subnets, see
Subnets and IP addresses in
GDC.
This page is for developers within the application operator group who want to
establish a secure air-gapped connection and balance workloads across zones. For
more information, see Audiences for GDC air-gapped
documentation.
Global subnets for load balancing
A global subnet is a subnet created within the global API server. These
subnets are required for global external load balancers (ELB) and internal load
balancers (ILB). Global subnets enable the allocation of IP addresses that are
accessible across different parts of a global infrastructure, spanning multiple
GDC zones.
You use global subnets to complete the following tasks:
Provide parent CIDRs for ILB IP addresses: A global parent subnet
of type Branch can be created to manage a pool of IP addresses
specifically for internal load balancers.
Allocate single IP addresses for ILB and ELB services: Global leaf subnets
are used to reserve a single Virtual IP (VIP) address for a specific ILB or ELB.
Enable anycast IPs for ELBs: For ELBs, a specific global parent
subnet is used to allocate anycast IP addresses, which are essential for
global external accessibility.
Subnets and forwarding rules
The direct link between a global subnet and a load balancer's functionality is
established through the forwarding rule resource. A forwarding rule references a
global leaf subnet to obtain the VIP address that clients use to
access the load balancing service.
Here's an example showing how the configuration works:
A global leaf subnet is created with a prefixLength value of 32,
indicating that the subnet allocates a single IP address.
This allocated IP address, identified by the name of the leaf subnet, is
then specified in the cidrRef field of either a ForwardingRuleInternal
resource for ILBs or ForwardingRuleExternal resource for ELBs.
This link makes the load balancer's forwarding rule use a dedicated
and globally managed IP address provided by the subnet.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-29 UTC."],[],[],null,["# About subnets for load balancing\n\nThis page provides an overview of subnets in Google Distributed Cloud (GDC) air-gapped and\ntheir role in your load balancing efforts. A subnet, or subnetwork, represents a\nlogical subdivision of an IP network. This segmentation enhances network\nefficiency, security, and manageability. For more information on subnets, see\n[Subnets and IP addresses in\nGDC](/distributed-cloud/hosted/docs/latest/gdch/platform/pa-user/subnets-overview).\n\nThis page is for developers within the application operator group who want to\nestablish a secure air-gapped connection and balance workloads across zones. For\nmore information, see [Audiences for GDC air-gapped\ndocumentation](/distributed-cloud/hosted/docs/latest/gdch/resources/audiences).\n\nGlobal subnets for load balancing\n---------------------------------\n\nA *global subnet* is a subnet created within the global API server. These\nsubnets are required for global external load balancers (ELB) and internal load\nbalancers (ILB). Global subnets enable the allocation of IP addresses that are\naccessible across different parts of a global infrastructure, spanning multiple\nGDC zones.\n\nYou use global subnets to complete the following tasks:\n\n- **Provide parent CIDRs for ILB IP addresses:** A global parent subnet of type `Branch` can be created to manage a pool of IP addresses specifically for internal load balancers.\n- **Allocate single IP addresses for ILB and ELB services:** Global leaf subnets are used to reserve a single Virtual IP (VIP) address for a specific ILB or ELB.\n- **Enable anycast IPs for ELBs:** For ELBs, a specific global parent subnet is used to allocate anycast IP addresses, which are essential for global external accessibility.\n\nSubnets and forwarding rules\n----------------------------\n\nThe direct link between a global subnet and a load balancer's functionality is\nestablished through the forwarding rule resource. A forwarding rule references a\nglobal leaf subnet to obtain the VIP address that clients use to\naccess the load balancing service.\n\nHere's an example showing how the configuration works:\n\n1. A global leaf subnet is created with a `prefixLength` value of `32`, indicating that the subnet allocates a single IP address.\n2. This allocated IP address, identified by the name of the leaf subnet, is then specified in the `cidrRef` field of either a `ForwardingRuleInternal` resource for ILBs or `ForwardingRuleExternal` resource for ELBs.\n3. This link makes the load balancer's forwarding rule use a dedicated and globally managed IP address provided by the subnet.\n\nWhat's next\n-----------\n\n- [Create a global subnet for internal load balancing](/distributed-cloud/hosted/docs/latest/gdch/platform/pa-user/create-global-subnet-ilb)\n- [Create a global subnet for external load balancing](/distributed-cloud/hosted/docs/latest/gdch/platform/pa-user/create-global-subnet-elb)"]]
