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copyright
years
2020, 2025
lastupdated 2025-10-01
keywords editing, managing, manage, edit, add, connection
subcollection transit-gateway

{{site.data.keyword.attribute-definition-list}}

Creating a GRE tunnel connection

{: #gre-connection}

You can connect endpoints using a Generic Routing Encapsulation (GRE) tunnel transit gateway connection. This connection allows a transit gateway to connect to overlay networks hosted on classic infrastructure resources. {: shortdesc}

This form of GRE tunnel is now deprecated. Use of unbound GRE tunnels is recommended. For more information, see Creating an unbound GRE tunnel. {: deprecated}

Unbound GRE tunnels provide the following benefits:

  • The ability to receive classic network subnets from a classic connection.
  • The ability to communicate through other unbound GRE tunnels on the same transit gateway in the same availability zone.
  • Does not require a classic connection on the transit gateway. As a result, the classic network's subnets will not be advertised to the connections on the transit gateway (and vice versa).

Migrating your GRE tunnels to unbound GRE tunnels requires deleting any existing GRE tunnels before creating new unbound ones. Migration will also cause a network disruption for anything that uses the old GRE tunnel until you create the new one.

To migrate from a GRE tunnel to an unbound GRE tunnel:

  1. Gather the existing GRE tunnel's configuration information for use on the new unbound GRE tunnel.

  2. Delete your old GRE tunnel.

  3. Delete any classic connections if need be.

    Classic connections can't be deleted if they are being used by other GRE tunnels. {: note}

  4. Create the new unbound GRE tunnel.

Transit gateway GRE connections require the gateway owner to specifically configure HA for their needs. A GRE connection is a point to point connection, has no built in redundancy, and is a single point of failure. When configuring a GRE connection on a transit gateway, you must specify the availability zone. For a robust HA solution, configure multiple GRE connections using different availability zones. {: note}

Before you begin

{: #gre-begin}

The following prerequisites must be met before you can create a GRE tunnel connection:

  • Ensure that you have an existing classic infrastructure connection, or create one. For more information, see Adding a connection. The GRE tunnel connection connects with an endpoint only on classic infrastructure.
  • Review the GRE connection considerations for additional prerequisites.

Creating a GRE tunnel connection in the UI

{: #tg-ui-adding-gre-connection-transit-gateway} {: ui}

Only unbound GRE tunnels can be created in the UI. For more information, see Creating an unbound GRE tunnel.

Creating a GRE tunnel connection from the CLI

{: #tg-cli-adding-gre-connection-transit-gateway} {: cli}

Create a Generic Routing Encapsulation (GRE) tunnel connection on the given transit gateway.

ibmcloud tg connection-create-gre|ccgre GATEWAY_ID --name NAME --zone ZONE --base-connection-id BASE_CONNECTION_ID --local-gateway-ip LOCAL_GATEWAY_IP --local-tunnel-ip LOCAL_TUNNEL_IP --remote-gateway-ip REMOTE_GATEWAY_IP --remote-tunnel-ip REMOTE_TUNNEL_IP [--remote-bgp-asn REMOTE_BGP_ASN] [--output json]

{: pre}

Where:

  • GATEWAY_ID: ID of the gateway where the new connection is bound.

  • --name: Name of the new connection.

  • --zone: Availability zone for the GRE tunnel. Example: us-south-1

  • --base-connection-id: ID of the classic network connection that will be the underlay for the GRE tunnel.

  • --local-gateway-ip: Local gateway IP address for the GRE tunnel connection.

  • --local-tunnel-ip: Local tunnel IP address for the GRE tunnel connection.

  • --remote-gateway-ip: Remote gateway IP address for the GRE tunnel connection.

  • --local-tunnel-ip: Remote tunnel IP address for the GRE tunnel connection.

  • --remote-bgp-asn: Optional: If the remote BGP ASN is not specified, one is generated.

  • --output json: Optional: Shows the output in JSON format.

  • --help | -h: Optional: Get help on this command.

Example

{: #connection-create-gre-example}

Create a GRE tunnel connection named gre-connection using classic connection 9037f710-8dfb-4948-a2bd-847c8dde96d3 as the base connection:

ibmcloud tg connection-create-gre $gateway  --name gre-connection --base-connection-id 9037f710-8dfb-9999-a2bd-847c8dde96d3  --zone us-south-2 --local-gateway-ip 192.168.100.1 --local-tunnel-ip 192.168.101.1 --remote-gateway-ip 10.242.63.12 --remote-tunnel-ip 192.168.101.2

{: pre}

Creating a GRE tunnel connection with the API

{: #tg-api-adding-gre-connection-transit-gateway} {: api}

Example Request

{: #add-gre-connection-curl-api-request-example}

This example illustrates requesting a GRE connection:

curl -X POST "https://transit.cloud.ibm.com/v1/transit_gateways/test/connections?version=2022-01-27" -H "accept: application/json" -H "Content-Type: application/json" -d "{\"base_connection_id\":\"975f58c1-afe7-469a-9727-7f3d720f2d32\",\"local_gateway_ip\":\"192.168.100.1\",\"local_tunnel_ip\":\"192.168.129.2\",\"name\":\"Transit_Service_BWTN_SJ_DL\",\"network_type\":\"gre_tunnel\",\"remote_bgp_asn\":65010,\"remote_gateway_ip\":\"10.242.63.12\",\"remote_tunnel_ip\":\"192.168.129.1\"}"

{: pre}

The payload for this request is as follows:

{
  "base_connection_id": "975f58c1-afe7-469a-9727-7f3d720f2d32",
  "local_gateway_ip": "192.168.100.1",
  "local_tunnel_ip": "192.168.129.2",
  "name": "Transit_Service_BWTN_SJ_DL",
  "network_type": "gre_tunnel",
  "remote_bgp_asn": 65010,
  "remote_gateway_ip": "10.242.63.12",
  "remote_tunnel_ip": "192.168.129.1"
}

{: pre}

Example Response

{: #add-gre-connection-curl-api-response-example}

This example illustrates the response from creating a GRE tunnel:

{
  "created_at": "2020-03-31T12:08:05Z",
  "id": "1a15dca5-7e33-45e1-b7c5-bc690e569531",
  "name": "example-connection",
  "network_type": "gre_tunnel",
  "status": "pending",
  "updated_at": "2020-03-31T12:08:05Z"
}

{: screen}

For more information, see Adds a connection to a Transit Gateway in the Transit Gateway API reference. {: note}

Creating a GRE tunnel connection using Terraform

{: #tg-terraform-adding-gre-connection-transit-gateway} {: terraform}

You can specify the following argument references for your resource when creating a Generic Routing Encapsulation (GRE) tunnel connection:

Argument Details
base_connection_id \n Optional \n Forces new resource \n string The ID of a network_type classic connection a tunnel is configured over. \n This field only applies to network type gre_tunnel connections.
gateway \n Required \n Forces new resource \n string Enter the transit gateway identifier.
local_gateway_ip \n Optional \n Forces new resource \n string The local gateway IP address. \n This field is required for and only applicable to gre_tunnel and unbound_gre_tunnel connection types.
local_tunnel_ip \n Optional \n Forces new resource \n string The local tunnel IP address. \n This field is required for, and only applicable, to gre_tunnel and unbound_gre_tunnel type connections.
name \n Optional \n string Enter a name. If the name is not given, the default name is provided based on the network type, such as gre_tunnel.
network_type \n Required \n Forces new resource \n string The network type. Allowed values are gre_tunnel
remote_bgp_asn \n Optional \n Forces new resource \n integer The remote network BGP ASN. This will be generated for the connection if not specified. \n This field only applies to gre_tunnel and unbound_gre_tunnel type connections.
remote_gateway_ip \n Optional \n Forces new resource \n string The remote gateway IP address. This field only applies to gre_tunnel and unbound_gre_tunnel type connections.
remote_tunnel_ip \n Optional \n Forces new resource \n string The remote tunnel IP address. This field only applies to gre_tunnel and unbound_gre_tunnel type connections.
zone \n Optional \n Forces new resource \n string The location of the GRE tunnel. This field only applies to gre_tunnel and unbound_gre_tunnel type connections.
{: caption="Terraform argument references for creating a GRE" caption-side="bottom"}

Example

{: #tg-terraform-adding-gre-connection-transit-gateway-example}

This example illustrates requesting a GRE tunnel connection:

resource "ibm_tg_connection" "test_ibm_tg_connection" {
  gateway            = ibm_tg_gateway.test_tg_gateway.id
  network_type       = "gre_tunnel"
  name               = "myconnection"
  base_connection_id = testgretunnel
  local_gateway_ip   = 192.168.0.1
  local_tunnel_ip    = 10.0.0.1
  remote_bgp_asn     = 36361
  remote_gateway_ip  = 192.168.1.1
  remote_tunnel_ip   = 10.0.1.1
  zone               = us-east
}

{: pre}