Google Cloud Platform (GCP) firewall rules let you allow or deny traffic to and from your virtual machine (VM) instances based on a configuration you specify. Enabled GCP firewall rules are always enforced, protecting your instances regardless of their configuration and operating system, even if they have not started up.
Every VPC network functions as a distributed firewall. While firewall rules are defined at the network level, connections are allowed or denied on a per-instance basis. You can think of the GCP firewall rules as existing not only between your instances and other networks, but between individual instances within the same network. See Using Firewall Rules for instructions on creating and working with firewall rules.
Firewall rules in GCP
When you create a GCP firewall rule, you specify a VPC network and a set of components that define what the rule will do. The components enable you to target certain types of traffic, based on the traffic's protocol, ports, sources, and destinations. Refer to firewall rule components for details.
You create or modify GCP firewall rules through the
Google Cloud Platform Console,
gcloud command line tool,
and REST API. When you create or modify
a firewall rule, you can specify the instances to which it is intended to apply
by using the target component of the rule.
In addition to firewall rules that you create, GCP has other rules that can affect incoming and outgoing traffic:
GCP always allows communication between a VM instance and its corresponding metadata server at
169.254.169.254. Refer to always allowed traffic for details.
Every network has two implied firewall rules which permit outgoing connections and block incoming connections. Firewall rules that you create can override these implied rules.
defaultnetwork is pre-populated with firewall rules that you can delete or modify.
GCP firewall rules have the following characteristics:
Firewall rules only support IPv4 traffic. When specifying a source for an ingress rule or a destination for an egress rule by address, you can only use an IPv4 address or IPv4 block in CIDR notation.
Each firewall rule applies to incoming (
ingress) or outgoing (
egress) traffic, not both. Refer to the direction of traffic for more information.
When you create a firewall rule, you must select a VPC network. While the rule is enforced at the instance level, its configuration is associated with a VPC network. This means you cannot share firewall rules among VPC networks, including networks connected by VPC Network Peering or by using Cloud VPN tunnels.
GCP firewall rules are stateful. If a connection is allowed between a source and a target or a target and a destination, all subsequent traffic in either direction will be allowed as long as the connection is active. In other words, firewall rules allow bidirectional communication once a session is established. The connection is considered active if at least one packet is sent every 10 minutes. Firewall rules cannot allow traffic in one direction while denying the associated return traffic.
GCP firewall rules do not reassemble fragmented TCP packets. Consequently, a firewall rule applicable to the TCP protocol can only apply to the first fragment because it contains the TCP header. Firewall rules applicable to the TCP protocol do not apply to the subsequent TCP fragments.
The maximum number of tracked connections in the firewall rule table depends on the number of stateful connections supported by the machine type of the instance:
|Instance Machine Type||Maximum Number of Stateful Connections|
|Shared-core machine types||130,000|
|Instances with 1 to 8 vCPUs||130,000 connections per vCPU|
|Instances with more than 8 vCPUs||1,040,000 (130,000×8) connections total|
Every VPC network has two implied firewall rules. These rules exist, but are not shown in the Cloud Console:
The implied allow egress rule: An
egressrule whose action is
allow, destination is
0.0.0.0/0, and priority is the lowest possible (
65535) lets any instance send traffic to any destination, except for traffic blocked by GCP. Outbound access may be restricted by a higher priority firewall rule. Internet access is allowed if no other firewall rules deny outbound traffic and if the instance has an external IP address or uses a NAT instance. Refer to Internet access requirements for more details.
The implied deny ingress rule: An
ingressrule whose action is
deny, source is
0.0.0.0/0, and priority is the lowest possible (
65535) protects all instances by blocking incoming traffic to them. Incoming access may be allowed by a higher priority rule. Note that the
defaultnetwork includes some additional rules that override this one, allowing certain types of incoming traffic.
The implied rules cannot be removed, but they have the lowest possible
priorities. Rules you create can override them as long as your rules have higher
priorities (priority numbers less than
deny rules take
allow rules of the same priority, an ingress
with a priority of
65535 never takes effect.
Pre-populated rules in the
default network is pre-populated with
firewall rules that allow incoming traffic to instances. These rules can be
deleted or modified as necessary:
Allows ingress connections for all protocols and ports among instances in the network. This rule has the second-to-lowest priority of
65534, and it effectively permits incoming connections to VM instances from others in the same network.
Allows ingress connections on TCP port 22 from any source to any instance in the network. This rule has a priority of
Allows ingress connections on TCP port 3389 from any source to any instance in the network. This rule has a priority of
65534, and it enables connections to instances running the Microsoft Remote Desktop Protocol (RDP).
Allows ingress ICMP traffic from any source to any instance in the network. This rule has a priority of
65534, and it enables tools like
Always blocked traffic
Google Cloud Platform always blocks the following traffic. Your firewall rules cannot be used to allow any of the following traffic described in the table below.
|Always blocked traffic||Applies to|
|GRE traffic||All sources, all destinations, including among instances using internal IP addresses|
|Protocols other than TCP, UDP, ICMP, and IPIP||Traffic between:
• instances and the Internet
• instances if they are addressed with external IP addresses
• instances if a load balancer with an external IP address is involved
|Egress traffic on TCP port 25 (SMTP)||Traffic from:|
• instances to the Internet
• instances to other instances addressed by external IP address
Always allowed traffic
Google runs a local metadata server alongside each instance at
169.254.169.254. This server is essential to the operation of the instance, so
the instance can access it regardless of any firewall rules you configure. The
metadata server provides the following basic services to the instance:
- DNS resolution, following the name resolution order for the VPC network. Unless you have configured an alternative name server, DNS resolution includes looking up Compute Engine Internal DNS, querying Cloud DNS zones, and public DNS names.
- Instance metadata
Firewall rule components
Each firewall rule consists of the following configuration components:
A numerical priority, which is used to determine if the rule will be applied. Only the highest priority (lowest priority number) rule whose other components match traffic is applied; conflicting rules with lower priorities are ignored.
The direction of traffic:
ingressrules apply to incoming connections from specified sources to GCP targets, and
egressrules apply to traffic going to specified destinations from targets.
An action on match, either
deny, which determines if the rule permits or blocks traffic.
A target, which defines the instances (including GKE clusters and App Engine Flex instances) to which the rule will apply.
The enforcement status of the firewall rule: You can enable and disable firewall rules without deleting them.
|Ingress (inbound) rule|
|Priority||Action||Enforcement||Target (defines the destination)||Source||Protocols and Ports|
||The target parameter specifies the destination. It can be one of the
• All instances in the
• Instances by
• Instances by network tag
|One of the following:
• Range of IPv4 addresses;
default is any (
• Instances by
• Instances by network tag
|Specify a protocol or protocol and a port.
If not set, the rule applies to all protocols.
|Egress (outbound) rule|
|Priority||Action||Enforcement||Target (defines the source)||Destination||Protocols and Ports|
||The target parameter specifies the source. It can be one of the
• All instances in the
• Instances by
• Instances by network tag
|Any network or a specific range of IPv4 addresses; default is any (
||Specify a protocol or protocol and a port.
If not set, the rule applies to all protocols.
The firewall rule priority is an integer from
65535, inclusive. Lower
integers indicate higher priorities. If you do not specify a priority when
creating a rule, it is assigned a priority of
The relative priority of a firewall rule determines if it is applicable when evaluated against others. The evaluation logic works as follows:
The highest priority rule applicable to a target for a given type of traffic takes precedence. Target specificity does not matter. For example, a higher priority
ingressrule for certain ports and protocols intended for all targets overrides a similarly defined rule for the same ports and protocols intended for specific targets.
The highest priority rule applicable for a given protocol and port definition takes precedence, even when the protocol and port definition is more general. For example, a higher priority
ingressrule allowing traffic for all protocols and ports intended for given targets overrides a lower priority
ingressrule denying TCP 22 for the same targets.
A rule with a
denyaction overrides another with an
allowaction only if the two rules have the same priority. Using relative priorities, it is possible to build
allowrules that override
denyrules, and vice versa.
Rules with the same priority and the same action have the same result. However, the rule that is used during the evaluation is indeterminate. Normally, it doesn't matter which rule is used except when you enable firewall rule logging. If you want your logs to show firewall rules being evaluated in a consistent and well-defined order, assign them unique priorities. For more information about logging, see the Firewall Rules Logging Overview.
Consider the following example where two firewall rules exist:
ingressrule from sources
0.0.0.0/0(anywhere) applicable to all targets, all protocols, and all ports, having a
denyaction and a priority of
ingressrule from sources
0.0.0.0/0(anywhere) applicable to specific targets with the tag
webserver, for traffic on TCP 80, with an
The priority of the second rule determines whether TCP traffic on port 80 is
allowed for the
If the priority of the second rule is set to a number greater than
1000, it will have a lower priority, so the first rule denying all traffic will apply.
If the priority of the second rule is set to
1000, the two rules will have identical priorities, so the first rule denying all traffic will apply.
If the priority of the second rule is set to a number less than
1000, it will have a higher priority, thus allowing traffic on TCP 80 for the
webservertargets. Absent other rules, the first rule would still deny other types of traffic to the
webservertargets, and it would also deny all traffic, including TCP 80, to instances without the
The previous example demonstrates how you can use priorities to create selective
allow rules and global
deny rules to implement a security best practice of
Direction of traffic
The direction of a firewall rule can be either
direction is always defined from the perspective of the
ingressdirection describes traffic sent from a source to a target. Ingress rules apply to packets for new sessions where the destination of the packet is the target.
egressdirection describes traffic sent from a target to a destination. Egress rules apply to packets for new sessions where the source of the packet is the target.
If you don't specify a direction, GCP uses
Consider an example connection between two VMs in the same network. Traffic from VM1 to VM2 can be controlled using either of these firewall rules:
ingressrule with a target of VM2 and a source of VM1.
egressrule with a target of VM1 and a destination of VM2.
Action on match
The action component of a firewall rule determines if it will permit or block traffic, subject to the other components of the rule:
allowaction permits connections matching the other specified components.
denyaction blocks connections matching the other specified components.
You can change whether or not a firewall rule is enforced by setting its state to enabled or disabled. Disabling a rule is useful for troubleshooting or to grant temporary access to instances. It's much easier to disable a rule, test, and then re-enable it, than it is to delete and re-create the rule.
Unless you specify otherwise, all firewall rules are enabled when they are created. You can also choose to create a rule in a disabled state.
The enforcement state for firewall rules can be changed from enabled to disabled and back by updating the rule.
Consider disabling a firewall rule for situations like these:
- For troubleshooting: If you're not sure whether a firewall rule is blocking or allowing traffic, disable it temporarily to determine if traffic is allowed or blocked. This is useful to troubleshoot the effect of one rule in conjunction with others.
- For maintenance: Disabling firewall rules can make periodic maintenance simpler. Suppose you have a firewall rule that blocks incoming SSH to targets (for example, instances by target tag), and that rule is usually enabled. When you need to perform maintenance, you can disable the rule. After you finish, enable the rule again.
For an ingress (inbound) rule, the target parameter designates the destination VM instances, including GKE clusters and App Engine Flex instances. For an egress (outbound) rule, the target designates the source instances. Thus, the target parameter is always used to designate GCP instances, but whether a target is a destination of traffic or a source for traffic depends on the direction of the rule.
You specify a target by using exactly one of the following options:
All instances in the network: The firewall rule applies to all instances in the network.
Instances by target tags: The firewall rule applies only to instances with a matching network tag.
Instances by target service accounts: The firewall rule applies only to instances that use a specific service account. See VPC Quotas and Limits for the maximum number of target service accounts you can apply per firewall rule.
For details about the benefits and limitations of target tags and target service accounts, see filtering by service account vs. network tag
Targets and IP addresses
The target of an ingress firewall rule applies to all traffic arriving on an instance's network interface in the VPC network, regardless of how the target is specified. An ingress firewall rule takes effect on packets whose destination matches one of the following IP addresses:
The primary internal IP address assigned to the instance's network interface in the VPC network.
Any configured alias IP ranges on the instance's network interface in the VPC network.
The external IP address that's associated with the instance's network interface in the VPC network.
A GCP load balancer if the instance is a backend of the load balancer.
The target of an egress firewall rule applies to all traffic leaving an instance's network interface in the VPC network, regardless of how the target is specified. An egress firewall rule takes effect on packets whose source matches either the primary internal IP address or any configured alias IP ranges on the instance's network interface in the VPC network.
Source or destination
You specify either a source or a destination, but not both, depending on the direction of the firewall you create:
For ingress (inbound) rules, the target parameter specifies the destination instances for traffic; you cannot use the destination parameter. You specify the source by using the source parameter.
For egress (outbound) rules, the target parameter specifies the source instances for traffic; you cannot use the source parameter. You specify the destination by using the destination parameter.
The source parameter is only applicable to ingress rules. It must be exactly one of the following:
Source IP ranges: You can specify ranges of IP addresses as sources for packets. The ranges can include addresses inside your VPC network and those outside of it. Source IP ranges can be used to define sources both inside and outside of GCP.
Source tags: You can define the source for packets as the primary internal IP address of the network interface of VM instances in the same VPC network, identifying those source instances by a matching network tag. Source tags only apply to traffic sent from the network interface of another applicable instance in your VPC network. A source tag cannot control packets whose sources are external IP addresses, even if the external IP addresses belong to instances. See VPC Quotas and Limits for the maximum number of source tags you can apply per firewall rule.
Source service accounts: You can define the source for packets as the primary internal IP address of the network interface of instances in the same VPC network, identifying those source instances by the service accounts they use. Source service accounts only apply to traffic sent from the network interface of another applicable instance in your VPC network. A source service account cannot control packets whose sources are external IP addresses, even if the external IP addresses belong to instances. See VPC Quotas and Limits for the maximum number of source service accounts you can apply per firewall rule.
A combination of source IP ranges and source tags can be used.
A combination of source IP ranges and source service accounts can be used.
If all of source IP ranges, source tags, and source service accounts are omitted, GCP defines the source as any IP address (
The destination parameter is only applicable to egress rules. The destination parameter only accepts IP address ranges. The ranges can include addresses inside your VPC network and those outside of it.
If you do not specify a destination range, GCP defines the
destination to be all IP addresses (
Protocols and ports
You can narrow the scope of a firewall rule by specifying protocols or protocols and ports. You can specify a protocol or a combination of protocols and their ports. If you omit both protocols and ports, the firewall rule is applicable for all traffic on any protocol and any port.
In order to make a firewall rule specific, you must first specify a protocol. If the protocol supports ports, you can optionally specify a port number or port range. Not all protocols support ports, though. For example, ports exist for TCP and UDP, but not for ICMP. (ICMP does have different ICMP types, but they are not ports.)
You can specify a protocol using its name (
ipip) or its decimal IP protocol
GCP firewall rules use port information to reference the destination port of a packet, not its source port:
For ingress (inbound) firewall rules, destination ports are ports on systems identified by the rule's target parameter. (For ingress rules, the target parameter specifies the destination VMs for traffic.)
For egress (outbound) firewall rules, destination ports represent ports on the systems identified by the rule's destination parameter.
The following table summarizes valid protocol and port specification combinations for GCP firewall rules:
|No protocol and port||—||If you do not specify a protocol, the firewall rule applies to all protocols and their applicable ports.|
||If you specify a protocol without any port information, the firewall rule applies to that protocol and all of its applicable ports.|
|Protocol and single port||
||If you specify a protocol and a single port, the firewall rule applies to just that port of the protocol.|
|Protocol and port range||
||If you specify a protocol and a port range, the firewall rule applies to just the port range for the protocol.|
||If you specify a comma-delimited list of protocols or protocols and ports, the firewall rule applies to each of the specified protocols and ports. For more information, see creating firewall rules.|
Source and target filtering by service account
You can use service accounts to create firewall rules that are more specific in nature:
For both ingress and egress rules, you can use service accounts to specify targets.
For ingress rules, you can specify the source for incoming packets as the primary internal IP address of any VM in the network where the VM uses a particular service account.
The service account must be created before you create a firewall rule that relies on it.
Firewall rules that use service accounts to identify instances apply to both new instances created and associated with the service account and existing instances if you change their service accounts. Changing the service account associated with an instance requires that you stop and restart it. You can associate service accounts with individual instances and with instance templates used by managed instance groups.
Filtering by service account vs. network tag
This section highlights key points to consider when deciding if you should use service accounts or network tags to define targets and sources (for ingress rules).
If you need strict control over how firewall rules are applied to VMs, use target service accounts and source service accounts instead of target tags and source tags:
A network tag is an arbitrary attribute. One or more network tags can be associated with an instance by any IAM member who has permission to edit it. IAM members with the Compute Engine Instance Admin role to a project have this permission. IAM members who can edit an instance can change its network tags, which could change the set of applicable firewall rules for that instance.
A service account represents an identity associated with an instance. Only one service account can be associated with an instance. You control access to the service account by controlling the grant of the Service Account User role for other IAM members. For an IAM member to start an instance using a service account, that member must have the Service Account User role to at least that service account as well as appropriate permissions to create instances (for example, having the Compute Engine Instance Admin role to the project).
You cannot mix and match service accounts and network tags in any firewall rule:
You cannot use target service accounts and target tags together in any firewall rule (ingress or egress).
The following are invalid sources for ingress firewall rules if you specify targets by target tag or target service account:
|Target tags||Source service accounts
Combination of source IP ranges and source service accounts
|Target service account||Source tags
Combination of source IP ranges and source tags
Operational considerations for service accounts and network tags are:
Changing a service account for an instance requires stopping and restarting it. Adding or removing tags can be done while the instance is running.
There are a maximum number of target service accounts, source service accounts, target network tags, and source network tags that can be specified for firewall rules. Refer to VPC Resource Quotas for details.
If you identify instances by network tag, the firewall rule applies to the primary internal IP address of the instance.
The following use cases demonstrate how firewall rules work. Note that all of the firewall rules are enabled in these examples.
- A range of IPv4 addresses; the default is any (
- Other instances in your VPC network identified by service account
- Other instances in your VPC network identified by network tags
The default source is any IP address (
0.0.0.0/0). If you want to control
incoming connections for sources outside of your VPC network, including other
sources on the Internet, use a range of IPv4 addresses in CIDR format.
Ingress rules with an
allow action permit incoming traffic based on the other
components of the rule. In addition to specifying
the source and target for the rule, you can limit the rule to apply to specific
protocols and ports. Similarly, ingress rules with a
deny action can be used to protect instances by blocking incoming traffic
based on the firewall rule components.
The following diagram illustrates some examples of ingress connections which can be controlled by firewall rules. The examples use the target parameter in rule assignments to apply rules to specific instances.
An ingress rule with priority
1000is applicable to VM 1. This rule allows incoming TCP traffic from any source (
0.0.0.0/0). TCP traffic from other instances in the VPC network is allowed, subject to applicable egress rules for those other instances. VM 4 is able to communicate with VM 1 over TCP because VM 4 has no egress rule blocking such communication (only the implied allow egress rule is applicable). Because VM 1 has an external IP, this rule also permits incoming TCP traffic from external hosts on the Internet.
VM 2 has no specified ingress firewall rule, so the implied deny ingress rule rule blocks all incoming traffic. Connections from other instances in the network are blocked, regardless of egress rules for the other instances. Because VM 2 has an external IP, there is a path to it from external hosts on the Internet, but the implied deny rule blocks external incoming traffic as well.
An ingress rule with priority
1000is applicable to VM 3. This rule allows TCP traffic from instances in the network with the network tag
client, such as VM 4. TCP traffic from VM 4 to VM 3 is allowed because VM 4 has no egress rule blocking such communication (only the implied allow egress rule is applicable). Because VM 3 does not have an external IP, there is no path to it from external hosts on the Internet.
Egress firewall rules control outgoing connections from
target instances in your VPC network. Egress rules with an
allow action permit traffic from instances based on the other components of
the rule. For example, you can permit outbound
traffic to specific destinations, such
as a range of IPv4 addresses, on protocols and ports
you specify. Similarly, egress rules with a
deny action block traffic based on
the other components of the rule.
egress rule needs a destination. The default destination is any IP
0.0.0.0/0), but you can create a more specific destination by using a
range of IPv4 addresses in CIDR format. When specifying a range of IPv4
addresses, you can control traffic to instances in your network and to
destinations outside of your network, including destinations on the Internet.
The following diagram illustrates some examples of egress connections which can be controlled by firewall rules. The examples use the target parameter in rule assignments to apply rules to specific instances.
VM 1 has no specified egress firewall rule, so the implied allow egress rule rule lets it send traffic to any destination. Connections to other instances in the VPC network are allowed, subject to applicable ingress rules for those other instances. VM 1 is able to send traffic to VM 4 because VM 4 has an ingress rule allowing incoming traffic from any IP address range. Because VM 1 has an external IP address, it is able to send traffic to external hosts on the Internet. Incoming responses to traffic sent by VM 1 are allowed because firewall rules are stateful.
An egress rule with priority
1000is applicable to VM 2. This rule denies all outgoing traffic to all destinations (
0.0.0.0/0). Outgoing traffic to other instances in the VPC is blocked, regardless of the ingress rules applied to the other instances. Even though VM 2 has an external IP address, this firewall rule blocks its outgoing traffic to external hosts on the Internet.
An egress rule with priority
1000is applicable to VM 3. This rule blocks its outgoing TCP traffic to any destination in the
192.168.1.0/24IP range. Even though ingress rules for VM 4 permit all incoming traffic, VM 3 cannot send TCP traffic to VM 4. However, VM 3 is free to send UDP traffic to VM 4 because the egress rule only applies to the TCP protocol. Additionally, VM 3 can send any traffic to other instances in the VPC network outside of the
192.168.1.0/24IP range, as long as those other instances have ingress rules to permit such traffic. Because it does not have an external IP address, it has no path to send traffic outside of the VPC network.
- See Using Firewall Rules for instructions on creating and working with firewall rules.