VPC network overview
A Virtual Private Cloud (VPC) network is a virtual version of a physical network, implemented inside of Google's production network, using Andromeda. A VPC network provides the following:
- Provides connectivity for your Compute Engine virtual machine (VM) instances, including Google Kubernetes Engine (GKE) clusters, App Engine flexible environment instances, and other Google Cloud products built on Compute Engine VMs.
- Offers native Internal TCP/UDP Load Balancing and proxy systems for Internal HTTP(S) Load Balancing.
- Connects to on-premises networks using Cloud VPN tunnels and Cloud Interconnect attachments.
- Distributes traffic from Google Cloud external load balancers to backends.
Projects can contain multiple VPC networks. Unless you create an organizational policy that prohibits it, new projects start with a default network (an auto mode VPC network) that has one subnetwork (subnet) in each region.
Networks and subnets
The terms subnet and subnetwork are synonymous. They are used
interchangeably in the Google Cloud console,
gcloud commands, and API
A subnet is not the same thing as a (VPC) network. Networks and subnets are different types of resources in Google Cloud.
For more information about subnets, see Subnets overview.
VPC networks have the following properties:
VPC networks, including their associated routes and firewall rules, are global resources. They are not associated with any particular region or zone.
Subnets are regional resources.
Each subnet defines a range of IPv4 addresses. Subnets in custom mode VPC networks can also have a range of IPv6 addresses.
Traffic to and from instances can be controlled with network firewall rules. Rules are implemented on the VMs themselves, so traffic can only be controlled and logged as it leaves or arrives at a VM.
Resources within a VPC network can communicate with one another by using internal IPv4 addresses, internal IPv6 addresses, or external IPv6 addresses, subject to applicable network firewall rules. For more information, see communication within the network.
Network administration can be secured by using Identity and Access Management (IAM) roles.
An organization can use Shared VPC to keep a VPC network in a common host project. Authorized IAM principals from other projects in the same organization can create resources that use subnets of the Shared VPC network.
VPC networks can be connected to other VPC networks in different projects or organizations by using VPC Network Peering.
VPC networks support GRE traffic, including traffic on Cloud VPN and Cloud Interconnect. VPC networks do not support GRE for Cloud NAT or for forwarding rules for load balancing and protocol forwarding. Support for GRE allows you to terminate GRE traffic on a VM from the internet (external IP address) and Cloud VPN or Cloud Interconnect (internal IP address). The decapsulated traffic can then be forwarded to a reachable destination. GRE enables you to use services such as Secure Access Service Edge (SASE) and SD-WAN.
For more information about IPv6, see Subnets overview.
Organization policy constraints
Each new project starts with a default VPC network. You can disable the creation of default networks by creating an organization policy with the
compute.skipDefaultNetworkCreationconstraint. Projects that inherit this policy won't have a default network.
You can control the following IPv6 configurations using organization policies:
Disable VPC External IPv6 usage: If set to true, the
constraints/compute.disableVpcExternalIpv6constraint prevents you from configuring dual-stack subnets with external IPv6 ranges.
Disable VPC Internal IPv6 usage: If set to true, the
constraints/compute.disableVpcInternalIpv6constraint prevents you from configuring dual-stack subnets with internal IPv6 ranges.
Disable All IPv6 usage: If set to true, the
constraints/compute.disableAllIpv6constraint disables the creation of, or update to, any resources involved in IPv6 usage.
For more information about constraints, see Organization policy constraints.
Subnet creation mode
Google Cloud offers two types of VPC networks, determined by their subnet creation mode:
When an auto mode VPC network is created, one subnet from each region is automatically created within it. These automatically created subnets use a set of predefined IPv4 ranges that fit within the
10.128.0.0/9CIDR block. As new Google Cloud regions become available, new subnets in those regions are automatically added to auto mode VPC networks by using an IP range from that block. In addition to the automatically created subnets, you can add more subnets manually to auto mode VPC networks in regions that you choose by using IP ranges outside of
When a custom mode VPC network is created, no subnets are automatically created. This type of network provides you with complete control over its subnets and IP ranges. You decide which subnets to create in regions that you choose by using IP ranges that you specify.
You can switch a VPC network from auto mode to custom mode. This is a one-way conversion; custom mode VPC networks cannot be changed to auto mode VPC networks. To help you decide which type of network meets your needs, see the considerations for auto mode VPC networks.
Unless you choose to disable it, each new project starts with a default network. The default network is an auto mode VPC network with pre-populated IPv4 firewall rules. The default network does not have pre-populated IPv6 firewall rules.
Considerations for auto mode VPC networks
Auto mode VPC networks are easy to set up and use, and they are well suited for use cases with these attributes:
Having subnets automatically created in each region is useful.
The predefined IP ranges of the subnets do not overlap with IP ranges that you would use for different purposes (for example, Cloud VPN connections to on-premises resources).
However, custom mode VPC networks are more flexible and are better suited to production. The following attributes highlight use cases where custom mode VPC networks are recommended or required:
Having one subnet automatically created in each region isn't necessary.
Having new subnets automatically created as new regions become available could overlap with IP addresses used by manually created subnets or static routes, or could interfere with your overall network planning.
You need complete control over the subnets created in your VPC network, including regions and IP address ranges used.
You plan to connect VPC networks by using VPC Network Peering or Cloud VPN. Because the subnets of every auto mode VPC network use the same predefined range of IP addresses, you cannot connect auto mode VPC networks to one another.
You want to create subnets with IPv6 ranges. Auto mode VPC networks do not support dual-stack subnets.
IPv4 subnet ranges
Each subnet has a primary IPv4 address range. The primary internal addresses for the following resources come from the subnet's primary range: VM instances, internal load balancers, and internal protocol forwarding. You can optionally add secondary IP address ranges to a subnet, which are only used by alias IP ranges. However, you can configure alias IP ranges for instances from the primary or secondary range of a subnet.
Your IPv4 subnets don't need to form a predefined contiguous CIDR block, but you can do that if desired. For example, auto mode VPC networks do create subnets that fit within a predefined auto mode IP range.
There are four unusable IP addresses in every primary IPv4 subnet range. For more information, see reserved IP addresses in a subnet.
Auto mode VPC networks are created with one subnet per region at
creation time and automatically receive new subnets in new regions. The subnets
have IPv4 ranges only, and all subnet ranges fit inside the
block. Unused portions of
10.128.0.0/9 are reserved for future
Google Cloud use. For information about what IPv4 range is used in which
region, see Auto mode IPv4 subnet ranges.
IPv6 subnet ranges
When you create a dual-stack subnet in a custom mode VPC network, you choose whether the subnet is configured with an internal IPv6 subnet range, or an external IPv6 subnet range.
Internal IPv6 subnet ranges use unique local addresses (ULAs).
- ULAs are used for VM to VM communication within VPC networks. ULAs for IPv6 are analogous to RFC 1918 addresses for IPv4. ULAs cannot be reached from the internet, and are not publicly routable.
External IPv6 subnet ranges use global unicast addresses (GUAs).
- GUAs can be used for VM to VM communication within VPC networks, and are also routable on the internet.
For more information about IPv6 subnet ranges, see Subnets overview.
Networks that support dual-stack subnets
You can create dual-stack subnets in a custom mode VPC network.
Dual-stack subnets are not supported on auto mode VPC networks, including the default network. Dual-stack subnets are not supported on legacy networks.
If you have an auto mode VPC network that you would like to add dual-stack subnets to, you can do the following:
Routes and firewall rules
Routes define paths for packets leaving instances (egress traffic). For details about Google Cloud route types, see the routes overview.
Dynamic routing mode
For a description of dynamic routing mode options, see Effects of dynamic routing mode in the Cloud Router documentation.
Route advertisements and internal IP addresses
The following IP addresses are advertised within a VPC network:
Regional internal IPv4 addresses
Used for primary and secondary IPv4 subnet address ranges
Regional internal and external IPv6 addresses
Used for internal and external IPv6 subnet address ranges
Global internal IPv4 addresses
If you connect VPC networks using VPC Network Peering, subnet ranges using private IPv4 addresses are always exchanged. You can control whether subnet ranges using privately used public IPv4 addresses are exchanged. Global internal IPv4 addresses are never exchanged using peering. For additional details, see the VPC Network Peering documentation.
When you connect a VPC network to another network, such as an on-premises network, using a Google Cloud connectivity product like Cloud VPN, Cloud Interconnect, or Router appliance:
- You can advertise the VPC network's internal IP addresses to another network (such as an on-premises network).
- Though connectivity between a VPC network and another network (such as an on-premises network) can use private routing provided by a Google Cloud connectivity product, the other network's IP addresses might also be publicly routable. Keep this in mind if an on-premises network uses publicly routable IP addresses.
- VM instances in a VPC network containing subnet ranges with privately used public IP addresses are not able to connect to external resources which use those same public IP addresses.
- Take extra care when advertising privately used public IP addresses to another network (such as an on-premises network), especially when the other network can advertise those public IP addresses to the internet.
Both hierarchical firewall policies and VPC firewall rules apply to packets sent to and from VM instances (and resources that depend on VMs, such as Google Kubernetes Engine nodes). Both types of firewalls control traffic even if it is between VMs in the same VPC network.
To monitor which firewall rule allowed or denied a particular connection, see Firewall Rules Logging.
Communications and access
Communication within the network
The system-generated subnet routes define the paths for sending traffic among instances within the network by using internal IP addresses. For one instance to be able to communicate with another, appropriate firewall rules must also be configured because every network has an implied deny firewall rule for ingress traffic.
Except for the default network, you must explicitly create higher priority
ingress firewall rules
to allow instances to communicate with one another. The default network includes
several firewall rules in addition to the implied ones,
default-allow-internal rule, which permits instance-to-instance
communication within the network. The default network also comes with ingress
rules allowing protocols such as RDP and SSH.
Rules that come with the default network are also presented as options for you to apply to new auto mode VPC networks that you create by using the Cloud console.
Internet access requirements
The following criteria must be satisfied for an instance to have outgoing internet access:
The network must have a valid default internet gateway route or custom route whose destination IP range is the most general (
0.0.0.0/0). This route defines the path to the internet. For more information, see Routes.
Firewall rules must allow egress traffic from the instance. Unless overridden by a higher priority rule, the implied allow rule for egress traffic permits outbound traffic from all instances.
One of the following must be true:
Communications and access for App Engine
VPC firewall rules apply to resources running in the VPC network, such as Compute Engine VMs. For App Engine instances, firewall rules work as follows:
App Engine standard environment: Only App Engine firewall rules apply to ingress traffic. Because App Engine standard environment instances do not run inside your VPC network, VPC firewall rules do not apply to them.
App Engine flexible environment: Both App Engine and VPC firewall rules apply to ingress traffic. Inbound traffic is only permitted if it is allowed by both types of firewall rules. For outbound traffic, VPC firewall rules apply.
For more information about how to control access to App Engine instances, see App security.
Traceroute to external IP addresses
For internal reasons, Google Cloud increases the TTL counter of packets
that traverse next hops in Google's network. Tools like
might provide incomplete results because the TTL doesn't expire on some of the
hops. Hops that are inside of Google's network might be hidden when you send
packets from Compute Engine instances to destinations on the internet.
The number of hidden hops varies based on the instance's Network Service Tiers,
region, and other factors. If there are only a few hops, it's possible for all
of them to be hidden. Missing hops from a
mtr result don't
mean that outbound traffic is dropped.
There is no workaround for this behavior. You must take it into account if you configure third-party monitoring that connects to an external IP address associated with a VM.
Egress throughput limits
Network throughput information is available on the Network bandwidth page in the Compute Engine documentation.
Information about packet size is in the maximum transmission unit overview.
VPC network example
The following example illustrates a custom mode VPC network with three subnets in two regions:
- Subnet1 is defined as
10.240.0.0/24in the us-west1 region.
- Two VM instances in the us-west1-a zone are in this subnet. Their IP addresses both come from the available range of addresses in subnet1.
- Subnet2 is defined as
192.168.1.0/24in the us-east1 region.
- Two VM instances in the us-east1-a zone are in this subnet. Their IP addresses both come from the available range of addresses in subnet2.
- Subnet3 is defined as
10.2.0.0/16, also in the us-east1 region.
- One VM instance in the us-east1-a zone and a second instance in the us-east1-b zone are in subnet3, each receiving an IP address from its available range. Because subnets are regional resources, instances can have their network interfaces associated with any subnet in the same region that contains their zones.
Maximum transmission unit
For more information about the maximum transmission unit (MTU) setting for a VPC network and its connected VMs, see the maximum transmission unit overview.
For information about changing the MTU of a VPC network, or migrating VMs between VPC networks with different MTU settings, see Change the MTU setting of a VPC network.
The measured inter-region latency for Google Cloud networks can be found in our live dashboard. The dashboard shows Google Cloud's median inter-region latency and throughput performance metrics and methodology to reproduce these results using PerfKit Benchmarker.
Google Cloud typically measures round-trip latencies less than 55 μs at the 50th percentile and tail latencies less than 80μs at the 99th percentile between c2-standard-4 VM instances in the same zone.
Google Cloud typically measures round-trip latencies less than 45μs at the 50th percentile and tail latencies less than 60μs at the 99th percentile between c2-standard-4 VM instances in the same low-latency network ("compact" placement policy). Compact placement policy lowers the network latency by ensuring that the VMs are located physically within the same low-latency network.
Methodology: Intra-zone latency is monitored via a blackbox prober that constantly runs netperf TCP_RR benchmark between a pair of c2-types VMs in every zone c2 instances are available. It collects P50 and P99 results for setup with and without compact placement policy. TCP_RR benchmark measures request/response performance by measuring the transaction rate. If your applications require best possible latency, c2 instances are recommended.
Google Cloud tracks cross-region packet loss by regularly measuring round-trip loss between all regions. We target the global average of those measurements to be lower than 0.01% .
Methodology: A blackbox vm-to-vm prober monitors the packet loss for every zone pair using pings and aggregates the results into one global loss metric. This metric is tracked with a one-day window.
Try it for yourself
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