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:

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.


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 IP 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, subject to applicable network firewall rules. For more information, see communication within the network.

  • Instances with internal IP addresses can communicate with Google APIs and services. For more information, see Private access options for services.

  • 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 members 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 can be securely connected in hybrid environments by using Cloud VPN or Cloud Interconnect.

  • VPC networks support GRE traffic (beta) except traffic on Cloud VPN, Cloud Interconnect, Cloud NAT, and forwarding rules for load balancing and protocol forwarding. GRE enables you to use services such as secure access service edge (SASE) and SD-WAN.

  • VPC networks only support IPv4 unicast traffic. They do not support broadcast, multicast, or IPv6 traffic within the network; VMs in the VPC network can only send to IPv4 destinations and only receive traffic from IPv4 sources. However, it is possible to create an IPv6 address for a global load balancer.

Network and subnet terminology

The terms subnet and subnetwork are synonymous. They are used interchangeably in the Google Cloud Console, gcloud commands, and API documentation.

A subnet is not the same thing as a (VPC) network. Networks and subnets are different types of objects in Google Cloud.

Networks and subnets

Each VPC network consists of one or more useful IP range partitions called subnets. Each subnet is associated with a region. VPC networks do not have any IP address ranges associated with them. IP ranges are defined for the subnets.

A network must have at least one subnet before you can use it. Auto mode VPC networks create subnets in each region automatically. Custom mode VPC networks start with no subnets, giving you full control over subnet creation. You can create more than one subnet per region. For information about the differences between auto mode and custom mode VPC networks, see types of VPC networks.

When you create a resource in Google Cloud, you choose a network and subnet. For resources other than instance templates, you also select a zone or a region. Selecting a zone implicitly selects its parent region. Because subnets are regional objects, the region that you select for a resource determines the subnets that it can use:

  • The process of creating an instance involves selecting a zone, a network, and a subnet. The subnets available for selection are restricted to those in the selected region. Google Cloud assigns the instance an IP address from the range of available addresses in the subnet.

  • The process of creating a managed instance group involves selecting a zone or region, depending on the group type, and an instance template. The instance templates available for selection are restricted to those whose defined subnets are in the same region selected for the managed instance group.

    • Instance templates are global resources. The process of creating an instance template involves selecting a network and a subnet. If you select an auto mode VPC network, you can choose to use auto subnets to defer subnet selection to one that is available in the selected region of any managed instance group that would use the template. Auto mode VPC networks have a subnet in every region by definition.
  • The process of creating a Kubernetes container cluster involves selecting a zone or region (depending on the cluster type), a network, and a subnet. The subnets available for selection are restricted to those in the selected region.

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 IP ranges that fit within the CIDR 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.

Default network

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 firewall rules.

You can disable the creation of default networks by creating an organization policy with the compute.skipDefaultNetworkCreation constraint. Projects that inherit this policy won't have a default network.

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.

Subnet ranges

When you create a subnet, you must define its primary IP 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.

Each primary or secondary IP range for all subnets in a VPC network must be a unique valid CIDR block. Refer to the per network limits for the number of secondary IP ranges you can define.

Your 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.

For more information, see working with subnets.

Valid ranges

A subnet's primary and secondary IP address ranges are regional internal IP addresses. The following table describes valid ranges.

Range Description
Private IP addresses RFC 1918 Shared address space RFC 6598 IETF protocol assignments RFC 6890 (TEST-NET-1) (TEST-NET-2) (TEST-NET-3)
Documentation RFC 5737 IPv6 to IPv4 relay (deprecated) RFC 7526 Benchmark testing RFC 2544

Reserved for future use (Class E) as noted in RFC 5735 and RFC 1112.

Some operating systems do not support the use of this range, so verify that your OS supports it before creating subnets that use this range.

Privately used public IP addresses

Includes IP addresses that are not part of the RFC ranges listed in this table and not part of the restricted set. When you use these addresses as subnet ranges, Google Cloud does not announce these routes to the internet and does not route traffic from the internet to them.

For VPC Network Peering, subnet routes for public IP addresses are not automatically exchanged. The subnet routes are automatically exported by default, but peer networks must be explicitly configured to import them in order to use them.

Subnet ranges have the following constraints:

  • Subnet ranges cannot match, be narrower, or be broader than a restricted range. For example, is not a valid subnet range because it overlaps with the link-local range (RFC 3927), which is a restricted range.

  • Subnet ranges cannot span an RFC range (described in the previous table) and a privately used public IP address range. For example, is not a valid subnet range because it overlaps with RFC 1918 and public IP addresses.

  • Subnet ranges cannot span multiple RFC ranges. For example, isn't a valid subnet range because it includes both (from RFC 1918) and (from RFC 6890). However, you can create two subnets with different primary ranges, one with and one with Or, you could use both of these ranges on the same subnet if you make one of them a secondary range.

Restricted ranges

Restricted ranges include Google public IP addresses and commonly reserved RFC ranges, as described in the following table. These ranges cannot be used for subnet ranges.

Range Description
Public IP addresses for Google APIs and services, including Google Cloud netblocks. You can find these IP addresses at https://gstatic.com/ipranges/goog.txt. and Private Google Access-specific virtual IP addresses Current (local) network RFC 1122 Local host RFC 1122 Link-local RFC 3927 Multicast (Class D) RFC 5771 Limited broadcast destination address RFC 8190 and RFC 919

Reserved IP addresses in a subnet

Every subnet has four reserved IP addresses in its primary IP range. There are no reserved IP addresses in the secondary IP ranges.

Reserved IP address Description Example
Network First address in the primary IP range for the subnet in
Default gateway Second address in the primary IP range for the subnet in
Second-to-last address Second-to-last address in the primary IP range for the subnet that is reserved by Google Cloud for potential future use in
Broadcast Last address in the primary IP range for the subnet in

Auto mode IP ranges

This table lists the IP ranges for the automatically created subnets in an auto mode VPC network. IP ranges for these subnets fit inside the CIDR block. Auto mode VPC networks are built with one subnet per region at creation time and automatically receive new subnets in new regions. Unused portions of are reserved for future Google Cloud use.

Region IP range (CIDR) Default gateway Usable addresses (inclusive)
asia-east1 to
asia-east2 to
asia-northeast1 to
asia-northeast2 to
asia-northeast3 to
asia-south1 to
asia-southeast1 to
asia-southeast2 to
australia-southeast1 to
europe-north1 to
europe-west1 to
europe-west2 to
europe-west3 to
europe-west4 to
europe-west6 to
northamerica-northeast1 to
southamerica-east1 to
us-central1 to
us-east1 to
us-east4 to
us-west1 to
us-west2 to
us-west3 to
us-west4 to

Routes and firewall rules


Routes define paths for packets leaving instances (egress traffic). Routes in Google Cloud are divided into two categories: system-generated and custom.

Every new network starts with two types of system-generated routes:

  • The default route defines a path for traffic to leave the VPC network. It provides general internet access to VMs that meet the internet access requirements. It also provides the typical path for Private Google Access.

  • A subnet route is created for each of the IP ranges associated with a subnet. Every subnet has at least one subnet route for its primary IP range. Additional subnet routes are created for a subnet if you add secondary IP ranges to it. Subnet routes define paths for traffic to reach VMs that use the subnets. You cannot remove subnet routes manually.

Custom routes are either static routes that you create manually or dynamic routes maintained automatically by one or more of your Cloud Routers. For more information, see custom routes.

For complete details about routing in Google Cloud, see the routes overview.

Dynamic routing mode

Each VPC network has an associated dynamic routing mode that controls the behavior of all of its Cloud Routers. Cloud Routers share routes to your VPC network and learn custom dynamic routes from connected networks when you connect your VPC network to another network by using a Cloud VPN tunnel that uses dynamic routing, or by using Dedicated Interconnect or Partner Interconnect.

  • Regional dynamic routing is the default. In this mode, routes to on-premises resources learned by a given Cloud Router in the VPC network only apply to the subnets in the same region as the Cloud Router. Unless modified by custom advertisements, each Cloud Router only shares the routes to subnets in its region with its on-premises counterpart.

  • Global dynamic routing changes the behavior of all Cloud Routers in the network such that the routes to on-premises resources that they learn are available in all subnets in the VPC network, regardless of region. Unless modified by custom advertisements, each Cloud Router shares routes to all subnets in the VPC network with its on-premises counterpart.

For information about how the set of routes shared by a Cloud Router can be customized, see custom advertisements.

The dynamic routing mode can be set when you create or modify a VPC network. You can change the dynamic routing mode from regional to global and vice-versa without restriction. For instructions, see Changing the dynamic routing mode.

Firewall rules

Firewall rules apply to both outgoing (egress) and incoming (ingress) traffic in the network. Firewall rules control traffic even if it is entirely within the network, including communication among VM instances.

Every VPC network has two implied firewall rules. One implied rule allows most egress traffic, and the other denies all ingress traffic. You cannot delete the implied rules, but you can override them with your own. Google Cloud always blocks some traffic, regardless of firewall rules; for more information, see blocked traffic.

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, including the 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 ( 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:

    • The instance must have an external IP address. An external IP address can be assigned to an instance when it is created or after it has been created.

    • The instance must be able to use Cloud NAT or an instance-based proxy that is the target for a static route.

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 traceroute and mtr might provide incomplete results because the TTL doesn't expire on some of the hops. Hops that are inside and outside of Google's network might be hidden in these circumstances:

  • When you send packets from Compute Engine instances to external IP addresses, including external IP addresses of other Google Cloud resources or destinations on the internet.

  • When you send packets to the external IP address associated with a Compute Engine instance or other Google Cloud resource.

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 traceroute or 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 caps

Network throughput information is available in the Network bandwidth section.

Packet size

Information about packet size is in the maximum transmission unit (MTU) section.

VPC network example

The following example illustrates a custom mode VPC network with three subnets in two regions:

VPC network example (click to enlarge)
VPC network example (click to enlarge)
  • Subnet1 is defined as in 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 in 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, 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

VPC networks have a default maximum transmission unit (MTU) of 1460 bytes. However, you can configure your VPC networks to have an MTU of 1500 bytes.

The MTU is the size, in bytes, of the largest packet supported by a network layer protocol, including both headers and data. In Google Cloud, you set the MTU for each VPC network, and VM instances that use that network must also be configured to use that MTU for their interfaces. The network's MTU setting is communicated to a VM when that VM requests an IP address using DHCP. DHCP Option 26 contains the network's MTU.

The MTU impacts both UDP and TCP traffic:

  • If a UDP packet is sent that is larger than the destination can receive or that exceeds the MTU on some network link on the path to the destination, then the packet is dropped if the Don't-Fragment flag is set. When it gets dropped, an ICMP packet of the type Fragmentation-Needed is sent back to the sender. For more information on path discovery, see PMTUD.
  • If a UDP packet is sent that is larger than the destination can receive or that exceeds the MTU on some network link towards the destination, then it is (generally) fragmented if the Don't-Fragment flag is not set. This fragmentation is done where a mismatch is detected: this could be at an intermediate router or even at the sender itself if a packet is sent that is larger than the MTU.
  • TCP negotiates the maximum segment size (MSS) during connection setup time. Packets are then segmented into the smaller MTU size of both endpoints of the connection.

VMs and MTU settings

Linux VMs based on Google-provided OS images automatically have their interface MTU set to the MTU of the VPC network when they are created. If a VM has multiple network interfaces, each interface is set to the MTU of the attached network. If you change the MTU of a VPC that has running VMs, you must stop and then start those VMs to pick up the new MTU. When the VMs start up again, the changed network MTU is communicated to them from DHCP.

Windows VMs do not automatically configure their interfaces to use the VPC network's MTU when they start. Instead, Windows VMs based on Google-provided OS images are configured with a fixed MTU of 1460. To set Windows VMs based on Google-provided OS images to an MTU of 1500, run the following command on each Windows VM:

netsh interface ipv4 set subinterface VM_NAME mtu=1500 store=persistent

You can also use this command to set the MTU of custom Windows VMs, either to 1460 or 1500, as appropriate to the network.

Verify MTU settings on any VMs that use custom images. It is possible that they might honor the VPC network's MTU, but it is also possible that their MTUs might be set to a fixed value.

See Changing the MTU of a network for instructions.

Migrating services to a different MTU network

You might decide to migrate your services to new VMs in a new network rather than changing the MTU of your existing network. In such a case, you might have a server, such as a database server, that needs to be accessible to all VMs during the migration. If so, the following general approach might help you migrate cleanly:

  1. Create the new network with the new MTU.
  2. Create any necessary firewall rules and routes in the new network.
  3. Create a VM with multiple network interfaces in the old network. One interface connects to the new network using the new MTU and the other connects to the old network using the old MTU.
  4. Configure this new VM as a secondary server for the existing one.
  5. Fail the primary server over to the secondary one.
  6. Either Migrate VMs to the new network or create new VMs in the new network. If you create new VMs, ou can create them from scratch, from an existing image, or by creating a snapshot of the existing VMs and using that to populate the new persistent disks.
  7. Configure these VMs to use the operational server in that network.
  8. Migrate traffic to the new VMs.
  9. If you intend to delete the old network, create a new server in the new network, get it in sync with the existing server, and fail over to it.
  10. Delete the old server and old network.

Consequences of mismatched MTUs

A mismatched MTU is defined as two communicating VM instances that have different MTU settings. This can, in a limited number of cases, cause connectivity problems. Specific cases involve the use of instances as routers and the use of Kubernetes inside VMs.

In most common scenarios, TCP connections established between instances with different MTUs are successful due to the MSS negotiation, where both ends of a connection will agree to use the lower of the two MTUs.

MTU differences between peered VPC networks

For information about how VPC Network Peering handles differences between the MTUs of networks, see Consequences of mismatched MTUs.

MTU differences with Cloud VPN

For information about Cloud VPN and MTU, see Tunnel MTU.

MTU differences with Cloud Interconnect

Cloud Interconnect can have an MTU of 1440 or 1500.

If the communicating VMs have an MTU of 1500 and the Interconnect connection has an MTU of 1440, MSS clamping reduces the MTU of TCP connections to 1440 and TCP traffic proceeds.

MSS clamping does not affect UDP packets, so if the VPC network has an MTU of 1500 and the Interconnect connection has an MTU of 1440, then UDP datagrams with more than 1412 bytes of data (1412 bytes UDP data + 8 byte UDP header + 20 byte IPv4 header = 1440) are dropped. In such a case, you can do one of the following:

  • Lower the MTU of the attached VPC network to 1460.
  • Adjust your application to send smaller UDP packets.
  • Create a new Interconnect connection of 1500 bytes

For more information about Cloud Interconnect and MTU, see Cloud Interconnect MTU.

Network performance


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.

Packet loss

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.

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