Connectivity Tests can drop a test packet for any of the following reasons.
For a full list of possible reasons, see Configuration analysis states.
Foreign IP address disallowed
The packet is dropped because a Compute Engine instance can send or receive packets with a foreign IP address only when IP forwarding is enabled.
Probable cause
The VM instance doesn't have IP forwarding enabled, but the source or destination IP address of the packet going through it doesn't match the instance's IP addresses. This might happen, for example, when the packet is delivered to the instance using a static route with the VM instance as a next hop.
Recommendations
Create a Compute Engine instance with IP forwarding enabled, or set the corresponding attribute for the existing instance. For more information, see Enable IP forwarding for instances.
Dropped due to a firewall rule
The packet can be dropped because of a firewall rule, except when the packet is allowed due to connection tracking.
Probable cause
Connectivity Tests might deny a test packet because the packet matches a blocking firewall rule or a firewall policy rule. However, the actual data plane might allow the packet through due to connection tracking on the firewall rule. Connection tracking allows packets for an existing connection to return despite the firewall rule.
Every VPC network has two implied firewall rules that allow egress traffic to everywhere and block incoming traffic from everywhere. You might also have a higher priority deny egress firewall rule.
For connectivity to succeed, you need an egress firewall rule at the source allowing access to the destination endpoint, and an ingress firewall rule at the destination to allow this connection.
VPC firewall rules are stateful. If the specified destination endpoint is normally the side that initiates the communication, response traffic is automatically allowed with connection tracking and there is no need for an ingress firewall rule.
Recommendations
Delete the deny rule or create an allow rule based on the details in the Connectivity Tests results. For more information, see Firewall policies and Use VPC firewall rules.
Dropped due to no matching route
The packet is dropped due to no matching routes.
Probable cause
There is no active route matching the packet attributes (like a destination IP address) in the packet network and region.
Recommendations
Verify the list of effective routes in the Google Cloud console. If you have just created a new route, note that it might take some time for Connectivity Tests to receive a configuration update and incorporate it into analysis.
If you try to access the destination endpoint by using its internal IP address, make sure that the source and destination networks are connected (for example, using the VPC Network Peering, Network Connectivity Center, or a hybrid connectivity solution such as Cloud VPN).
Note that transitive VPC peering is not supported. Consider connecting the source and destination networks directly or by using a hybrid connectivity solution.
If you try to access the destination endpoint through the internet, make sure that you have a route for the destination IP address with the next hop internet gateway.
If the packet is going through the hybrid connectivity network endpoint group, consider additional requirements for routes applicability. Some routes you see in the route view table might not be available for traffic from hybrid NEGs.
For more information, see Routes and Use routes.
The packet is sent to a wrong network
The packet is sent to an unintended network. For example, you execute a
test from a Compute Engine instance in the network-1 network to the
Compute Engine instance in the network-2 network, but the packet
is sent to the network-3 network.
Probable cause
The network-1 network has a route with a destination range that includes the
destination instance IP address with the next hop in a different network
(network-3 in the example above).
Recommendations
Verify the list of effective routes and the list of routes applicable to the source instance, in the Google Cloud console. For more information about route creation and applicability, see Routes and Use routes.
Route next hop IP address is not resolved
The packet is sent to a destination using an invalid route with the next hop IP address not assigned to any resource.
Probable cause
If this is a route with next-hop-address, the next hop address must be
a primary internal IPv4 address or an IPv6 address of the Compute Engine
instance in the route's VPC network. Addresses in peered networks are not
supported.
If this is a route with next-hop-ilb, the next hop address must be an
address of the internal passthrough Network Load Balancer (forwarding rules used by other load balancers,
protocol forwarding, or as Private Service Connect endpoints are not
supported). The IP address must be assigned to a resource in the route's VPC
network, or in a network connected to it with VPC Network Peering.
Recommendations
Verify the next hop IP address belongs to a supported resource. For more information, see Considerations for next hop instances and Considerations for internal passthrough Network Load Balancer next hops.
Route next hop instance has a NIC in the wrong network
The packet is sent to a destination using an invalid route with the next hop Compute Engine instance not having a network interface controller (NIC) in the route's network.
Probable cause
The Compute Engine instance used as a route next hop must have a NIC in the route's network (not a peered VPC network).
Recommendations
Verify that the next hop Compute Engine instance has a NIC in the route's network. For more information, see Considerations for next hop instances.
Route next hop address is not a VM primary IP address
The packet is sent to a destination using an invalid route with the next hop IP
address (next-hop-address) not being a primary IP address of the
Compute Engine instance.
Probable cause
The route's next hop IP address (next-hop-address) must be a primary internal
IPv4 address of the Compute Engine instance.
Alias IP address ranges are not supported.
Recommendations
Verify that the next hop IP address is a primary internal IPv4 address of the Compute Engine instance. For more information, see Considerations for next hop instances.
Route next hop forwarding rule type is invalid
The packet is sent to a destination using an invalid route with the next hop
forwarding rule (next-hop-ilb) not being a forwarding rule of the
internal passthrough Network Load Balancer.
Probable cause
The route's next hop forwarding rule must be a forwarding rule of the internal passthrough Network Load Balancer. For more information, see Considerations for internal passthrough Network Load Balancer next hops.
Recommendations
Create a route targeting a supported forwarding rule instead of the invalid route.
Private traffic to internet
A packet with an internal destination address was sent to an internet gateway.
Probable cause
The packet destination IP address is a private IP address, which cannot be reached through the internet. However, the packet leaves the source Compute Engine instance, and matches a route with the next hop internet gateway.
Recommendations
If you'd like to access the destination through the internet, make sure that the source Compute Engine instance has internet connectivity—for example, it has an external IP address or uses Cloud NAT— and use the destination endpoint's external IP address in the test.
If you'd like to access the destination through its internal IP address, you need to establish connectivity (create routes) between the source and destination networks. You can do this in any of the following ways:
- If your destination endpoint is within an on-premises network, use a Network Connectivity Center solution or a hybrid connectivity solution, such as Cloud VPN or Cloud Interconnect.
- If your destination endpoint is within Google Cloud:
- Configure VPC Network Peering between VPC networks.
- Configure Cloud VPN between VPC networks.
- Configure network connectivity using Network Connectivity Center VPC spokes.
If you already have a connection to the destination network:
- The source endpoint network doesn't have a route through this connection or uses the default route that goes through the internet gateway. Verify the list of effective routes, and the list of routes applicable to the source instance in the Google Cloud console. For more information about route creation and applicability, see Routes and Use routes.
If you are testing connectivity to an on-premises network from a peered network, see this example for custom advertisement, network routing mode, and exchanging custom routes.
Transitive VPC Network Peering is not supported. You can use VPN or peering for these two VPC networks.
Private Google Access is disallowed
Compute Engine instance with only an internal IP address tries to reach the external IP address of Google APIs and services, but Private Google Access is not enabled in the instance's subnet.
Recommendations
You can allow the Compute Engine VM instance to reach the external IP address of Google APIs and services in any of the following ways:
- Enable Private Google Access for the instance's subnet.
- Assign an external IP address to the Compute Engine NIC.
- Enable Cloud NAT for the VM instance's subnet.
Private Google Access through VPN tunnel is not supported
A source endpoint with an internal IP address tries to reach the external IP address of Google APIs and services through the VPN tunnel to another network, but Private Google Access needs to be enabled in the source endpoint network.
Probable cause
The packet from the source endpoint to the external IP address of the Google APIs and services is routed through the Cloud VPN tunnel, but such a configuration is not supported.
Recommendations
If the source endpoint is a Google Cloud endpoint (like a Compute Engine VM instance), consider enabling Private Google Access in its source subnet.
If the source endpoint is an on-premises endpoint, refer to the Private Google Access for on-premises hosts for detailed instructions.
Forwarding rule mismatch
The forwarding rule's protocol and ports don't match the packet header.
Probable cause
The packet is sent using a protocol that isn't supported by the forwarding rule, or the packet is sent to a destination port that doesn't match the ports supported by the forwarding rule.
Recommendations
Confirm the destination forwarding rule protocol and ports.
Forwarding rule region mismatch
The forwarding rule doesn't have global access enabled, and its region doesn't match the packet's region.
Probable cause
Depending on the load balancer and its tier, a forwarding rule is either global or regional. For more details, see the load balancer types table.
If the forwarding rule is regional, the client (for example, the VM or the VPC connector) should be in the same region as the load balancer.
Recommendations
If you connect to the load balancer from a Google Cloud endpoint such as a Compute Engine VM instance, make sure it's located in the same region as the forwarding rule.
While connecting from an on-premises network, make sure that the client accesses the load balancer through Cloud VPN tunnels or VLAN attachments that are in the same region as the load balancer. For more details, see Internal Application Load Balancers and connected networks.
You can enable global access on internal Application Load Balancers and regional internal proxy Network Load Balancers to access clients in any region. By default, clients for these load balancers must be in the same region as the load balancer. For more information, see Enable global access for internal Application Load Balancers and Enable global access for regional internal proxy Network Load Balancers.
Firewall blocking load balancer backend health check
Firewalls block health check probes to the backends and cause backends to be unavailable for traffic from the load balancer.
Probable cause
For health checks to work, you must create ingress allow firewall rules that allow traffic from Google Cloud probers to reach your backends. Otherwise, the backends are considered unhealthy.
Recommendations
Create ingress allow firewall rules according to the probe IP ranges and firewall rules table. For more information, see Required firewall rules.
No external address available
A VM instance with only an internal IP address tried to access external hosts through a route whose next hop is the default internet gateway. Expected when Cloud NAT is not enabled in the subnet or when there's no other default route that uses a different type of next hop (such as a proxy VM).
Probable cause
An instance with only an internal IP address tried to access an external host but it did not have an external IP address or Cloud NAT was not enabled in the subnet.
Recommendations
If you'd like to access external endpoints, you can assign an external IP address to your instance. Alternatively, you can enable Cloud NAT on its subnet unless the connection goes through a proxy instance that gives access to the internet.
Forwarding rule with no instances
The forwarding rule does not have backends configured.
Probable cause
The forwarding rule you are trying to reach does not have any backends configured.
Recommendations
Check the load balancer configuration and make sure that the backend service of the load balancer has backends configured.
Traffic type is blocked
The type of traffic is blocked and you cannot configure a firewall rule to enable it. For more details, see Always blocked traffic.
Probable cause
This traffic type is blocked by default and can't be enabled by creating firewall rules. Common scenarios are as follows:
- Sending egress traffic to an external destination with TCP port 25 (SMTP). For more details, see Always blocked traffic.
- Sending traffic to an unsupported port on a Cloud SQL instance. For example, sending traffic to TCP port 3310 to a MySQL Cloud SQL instance with port 3306 open.
- Sending egress traffic from an App Engine standard environment version, a Cloud Function, or a Cloud Run revision that uses a protocol other than TCP or UDP.
Recommendations
For egress SMTP (egress traffic to an external destination with TCP port 25) traffic, see Sending email from an instance.
For DHCP protocol, including UDP IPv4 packets to destination port 68 (DHCPv4 responses) and UDP IPv6 packets to destination port 546 (DHCPv6 responses), DHCP traffic is only allowed from the metadata server (169.254.169.254).
For Cloud SQL connectivity, make sure the port used is correct.
Serverless VPC Access connector is not configured
The packet was dropped because the App Engine standard environment version, the Cloud Function, or the Cloud Run revision does not have a Serverless VPC Access connector configured.
Probable cause
The destination IP address is a private IP address, which cannot be reached through the internet. The packet leaves the source, but there is no Serverless VPC Access connector configured for the App Engine standard environment version, the Cloud Function, or the Cloud Run revision.
Recommendations
If you try to access the destination endpoint by using its private IP address, make sure that you have configured a Serverless VPC Access connector for the App Engine standard environment version, the Cloud Function, or the Cloud Run revision.
Serverless VPC Access connector is not running
The packet was dropped because the Serverless VPC Access connector is not running.
Probable cause
The packet was dropped because all the Serverless VPC Access connector instances are stopped.
Recommendations
For a list of troubleshooting steps, see Troubleshooting.
Private Service Connect connection is not accepted
The packet was dropped because the Private Service Connect connection was not accepted.
Probable cause
The Private Service Connect endpoint is in a project that is not approved to connect to the service. For more information, see View endpoint details.
Recommendations
Make sure that the Private Service Connect endpoint is in a project that is approved to connect to the managed service.
Private Service Connect endpoint is accessed from a peered network
The packet is sent to the Private Service Connect endpoint in the peered network, but such a configuration is not supported.
Recommendations
Consider using one of the connectivity patterns described on the Private Service Connect deployment patterns page. You can also access Google APIs and published services by using Private Service Connect backends.