Troubleshooting

This troubleshooting guide can help you monitor and solve common issues with Cloud VPN.

To interpret status messages and IKE cipher references, see the Reference section.

To find logging and monitoring information, see Viewing logs and metrics.

To find definitions for terminology used on this page, see Cloud VPN key terms.

Error messages

To check error messages, follow these steps:

  1. In the Google Cloud Console, go to the VPN page.

    Go to VPN

  2. If you see a status icon, hover over it to see the error message.

Often, the error message can help you pinpoint the issue. If not, check your logs for more information. You can find detailed status information in the Cloud Console on the Tunnel details page.

VPN logs

Cloud VPN logs are stored in Cloud Logging. Logging is automatic, so you do not need to enable it.

For information about viewing logs for the peer gateway side of your connection, see your product documentation.

Often, the gateways are configured correctly, but there's a problem in the peer network between the hosts and the gateway, or there is a problem with the network between the peer gateway and the Cloud VPN gateway.

To check the logs, follow these steps:

  1. In the Cloud Console, go to the Logs Explorer page.

    Go to Logs Explorer

  2. Check the logs for the following information:

    1. Verify that the remote peer IP address configured on the Cloud VPN gateway is correct.
    2. Verify that traffic flowing from your on-premises hosts is reaching the peer gateway.
    3. Verify that traffic is flowing between the two VPN gateways in both directions. In the VPN logs, check for reported incoming messages from the other VPN gateway.
    4. Check that the configured IKE versions are the same on both sides of the tunnel.
    5. Check that the shared secret is the same on both sides of the tunnel.
    6. If your peer VPN gateway is behind one-to-one NAT, ensure that you have properly configured the NAT device to forward UDP traffic to your peer VPN gateway on ports 500 and 4500. Configure your peer gateway to use the external IP address of the NAT device to identify itself. For details, see on-premises gateways behind NAT.
    7. If the VPN logs show a no-proposal-chosen error, this error indicates that Cloud VPN and your peer VPN gateway were unable to agree on a set of ciphers. For IKEv1, the set of ciphers must match exactly. For IKEv2, there must be at least one common cipher proposed by each gateway. Make sure that you use supported ciphers to configure your peer VPN gateway.
    8. Make sure that you configure your peer and Google Cloud routes and firewall rules so that traffic can traverse the tunnel. You might need to contact your network administrator for help.

  3. To find specific problems, you can search your logs for the following strings:

    1. In the Query builder pane, enter one of the advanced queries listed in the following table to search for a particular event, and click Run Query.

    2. Adjust the timeframe in the Histogram pane as necessary, and then click Run within the pane. For more details about using Logs Explorer for queries, see Building log queries.

      To view Use this Logging search
      Cloud VPN initiates Phase 1 (IKE SA) 
      resource.type="vpn_gateway"
("initiating IKE_SA" OR "generating IKE_SA_INIT request")
      Cloud VPN cannot contact remote peer 
      resource.type="vpn_gateway"
"establishing IKE_SA failed, peer not responding"
      IKE (Phase 1) authentication events 
      resource.type="vpn_gateway"
("generating IKE_AUTH request" OR "parsed IKE_AUTH response")
      Successful IKE authentication 
      resource.type="vpn_gateway"
("authentication of" AND "with pre-shared key successful")
      Phase 1 (IKE SA) established 
      resource.type="vpn_gateway"
("IKE_SA" AND "established between")
      All Phase 2 (Child SA) events, including re-key events 
      resource.type="vpn_gateway"
"CHILD_SA"
      Peer asks for Phase 2 re-key 
      resource.type="vpn_gateway"
detected rekeying of CHILD_SA
      Peer asks to terminate Phase 2 (Child SA) 
      resource.type="vpn_gateway"
received DELETE for ESP CHILD_SA
      Cloud VPN asks to terminate Phase 2 (Child SA) 
      resource.type="vpn_gateway"
sending DELETE for ESP CHILD_SA
      Cloud VPN closes Phase 2 (Child SA), perhaps in response to the peer 
      resource.type="vpn_gateway" closing CHILD_SA
      Cloud VPN closed Phase 2 itself 
      resource.type="vpn_gateway" CHILD_SA closed
      If remote traffic selectors don't match 
      resource.type="vpn_gateway"
Remote traffic selectors narrowed
      If local traffic selectors don't match 
      resource.type="vpn_gateway"
Local traffic selectors narrowed

Connectivity

Consider the following suggestions when using ping to verify connectivity between on-premises systems and Google Cloud virtual machine (VM) instances:

  • Ensure that the firewall rules in your Google Cloud network allow incoming ICMP traffic. The implied allow egress rule permits outgoing ICMP traffic from your network unless you have overridden it. Similarly, make sure that your on-premises firewall rules are also configured to allow incoming and outgoing ICMP traffic.

  • Use internal IP addresses to ping Google Cloud VMs and on-premises systems. Pinging external IP addresses of VPN gateways does not test connectivity through the tunnel.

  • When testing connectivity from on-premises to Google Cloud, it's best to initiate a ping from a system on your network, not from your VPN gateway. Pinging from a gateway is possible if you set the appropriate source interface, but pinging from an instance on your network has the added benefit of testing your firewall configuration.

  • Ping tests do not verify that TCP or UDP ports are open. After you have established that systems have basic connectivity, you can use ping to perform additional tests.

Calculating network throughput

You can calculate network throughput within Google Cloud and to your on-premises or third-party cloud locations. This resource includes information about how to analyze results, explanations of variables that can affect network performance, and troubleshooting tips.

Common problems and solutions

Tunnel regularly goes down for a few seconds

By default, Cloud VPN negotiates a replacement security association (SA) before the existing one expires (also known as rekeying). Your peer VPN gateway might not be rekeying. Instead, it might negotiate a new SA only after deleting the existing SA, causing interruptions.

To check whether your peer gateway rekeys, view the Cloud VPN logs. If the connection drops and then re-establishes right after a Received SA_DELETE log message, your on-premises gateway didn't rekey.

To verify tunnel settings, refer to the Supported IKE ciphers document. In particular, make sure that the Phase 2 lifetime is correct, and that a Diffie-Hellman (DH) group is set to one of the recommended values.

To search for events in your Cloud VPN tunnel, you can use a Logging advanced log filter. For example, the following advanced filter searches for DH group mismatches:

resource.type="vpn_gateway"
"Peer proposal: DOES NOT HAVE DIFFIE_HELLMAN_GROUP"

On-premises gateways behind NAT

Cloud VPN can work with on-premises or peer VPN gateways that are behind NAT. This is made possible by UDP encapsulation and NAT-T. Only one-to-one NAT is supported.

As part of the authentication process, Cloud VPN checks the identity of the peer gateway. Cloud VPN expects every peer gateway to identify itself by using the ID_IPV4_ADDR identity type as specified in RFC 7815, with the external IP (peer gateway) address configured for the Cloud VPN tunnel.

The following log messages indicate that the peer VPN gateway is incorrectly identifying itself with an internal IP address. In this example, PEER_GATEWAY_INTERNAL_IP is an internal IP address, and PEER_GATEWAY_EXTERNAL_IP is the external IP address of the NAT device between the peer VPN gateway and the internet.

authentication of PEER_GATEWAY_INTERNAL_IP with pre-shared key successful
constraint check failed: identity PEER_GATEWAY_EXTERNAL_IP required
selected peer config 'vpn_PEER_GATEWAY_EXTERNAL_IP' inacceptable: constraint checking failed

When using one-to-one NAT, your on-premises VPN gateway must identify itself by using the same external IP address of the NAT device:

  • The identity type must be ID_IPV4_ADDR (RFC 7815).

  • Not all Cisco devices support setting a device identity to an IP address different from the one that the device is using (its internal IP address). For example, Cisco ASA devices do not support assignment of different (external) IP addresses for their identities. Thus, Cisco ASA devices cannot be configured to use one-to-one NAT with Cloud VPN.

  • For Juniper devices, you can set the identity of the device by using set security ike gateway NAME local-identity inet EXTERNAL_IP, where NAME is your VPN gateway name and EXTERNAL_IP is your external IP address. For more details, see this Juniper TechLibrary article.

Connectivity works for some VMs, but not for others

If ping, traceroute, or other methods of sending traffic work from only some VMs to your on-premises systems, or from only some on-premises systems to some Google Cloud VMs, and you verified that both Google Cloud and on-premises firewall rules are not blocking the traffic that you are sending, you might have traffic selectors that exclude certain sources or destinations.

Traffic selectors define the ranges of IP addresses for a VPN tunnel. In addition to routes, most VPN implementations only pass packets through a tunnel if both of the following are true:

  • Their sources fit within the IP ranges specified in the local traffic selector.
  • Their destinations fit within the IP ranges specified in the remote traffic selector.

You specify traffic selectors when you create a Classic VPN tunnel by using policy-based routing or a route-based VPN. You also specify traffic selectors when you create the corresponding peer tunnel.

Some vendors use terms such as local proxy, local encryption domain, or left side network as synonyms for local traffic selector. Similarly, remote proxy, remote encryption domain, or right side network are synonyms for remote traffic selector.

To change traffic selectors for a Classic VPN tunnel, you must delete and re-create the tunnel. These steps are required because the traffic selectors are an integral part of tunnel creation, and tunnels cannot be edited later.

Use the following guidelines when defining traffic selectors:

  • The local traffic selector for the Cloud VPN tunnel should cover all subnets in your Virtual Private Cloud (VPC) network that you need to share with your peer network.
  • The local traffic selector for your peer network should cover all on-premises subnets that you need to share with your VPC network.
  • For a given VPN tunnel, traffic selectors have the following relationship:
    • The Cloud VPN local traffic selector should match the remote traffic selector for the tunnel on your peer VPN gateway.
    • The Cloud VPN remote traffic selector should match the local traffic selector for the tunnel on your peer VPN gateway.

Connecting Classic VPN and HA VPN gateways

Google Cloud does not support creating a tunnel from an HA VPN gateway that connects to a Classic VPN gateway. If you attempt to create an externalVpnGateway resource that has the external IP address of a Classic VPN gateway, Google Cloud returns the following error message:

  You cannot provide an interface with an IP address owned by Google Cloud.
  You can only create tunnels from an HA gateway to an HA gateway
  or create tunnels from an HA gateway to an ExternalVpnGateway.

This is expected behavior. Instead, create a VPN tunnel that connects an HA VPN gateway to another HA VPN gateway.

Troubleshooting reference

This section includes information about status icons, status messages, and supported IKE ciphers.

Status icons

Cloud VPN uses the following status icons in the Cloud Console.

Icon graphic Color Description Applies to messages
Green success icon
 Green Success ESTABLISHED
Yellow warning icon
 Yellow Warning ALLOCATING RESOURCES, FIRST HANDSHAKE, WAITING FOR FULL CONFIG, PROVISIONING
Red error icon
 Red Error All remaining messages

Status messages

To indicate VPN gateway and tunnel states, Cloud VPN uses the following status messages. The VPN tunnel is billed for the states indicated.

Message Description Tunnel billed in this state?
ALLOCATING RESOURCES Allocating resources to set up the tunnel. Yes
PROVISIONING Waiting to receive all configs to set up the tunnel. No
WAITING FOR FULL CONFIG Full config received, but a tunnel is not yet established. Yes
FIRST HANDSHAKE Establishing the tunnel. Yes
ESTABLISHED A secure communication session is successfully established. Yes
NETWORK ERROR
(replaced by NO INCOMING PACKETS)		 Bad IPsec authorization. Yes
AUTHORIZATION ERROR Handshake failed. Yes
NEGOTIATION FAILURE The tunnel configuration was rejected; can be due to being added to a denylist. Yes
DEPROVISIONING The tunnel is being shut down. No
NO INCOMING PACKETS The gateway is not receiving any packets from the on-premises VPN. Yes
REJECTED The tunnel configuration was rejected; contact Support. Yes
STOPPED The tunnel is stopped and not active; can be due to the deletion of one or more required forwarding rules for the VPN tunnel. Yes

IKE cipher reference

Cloud VPN supports ciphers and configuration parameters for peer VPN devices or VPN services. Cloud VPN auto-negotiates the connection as long as the peer side uses a supported IKE cipher setting.

For the full IKE cipher reference, see Supported IKE ciphers.

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