Create and manage a subnetwork

A subnetwork is a range of IP addresses in a cloud network. Addresses from this range will be assigned to Virtual Machines (VMs) in the cloud.  

Create a subnetwork

You can create a subnetwork in two ways: during the creation of a Gcore Virtual Machine or from the Networks page, which is described in the following section.

Create a subnetwork from the Networks page

1. In the Gcore Customer Portal, navigate to Cloud > Networking.

2. Find the network where you want to create a subnetwork and click its name to open it.

3. Click Create subnetwork.

4. A new Create subnetwork page will open. Here, you can customize subnetwork settings.

5. Enter the subnetwork name.

6. Set a CIDR within the specified range:

• 10.0.0.0/8
• 172.16.0.0/12
• 192.168.0.0/16
• fc00::/7

Set the mask between 16 and 24. You can find more information in the Set the IP range section.

7. (optional) Turn on the Enable DHCP toggle to assign IP addresses to machines in the subnet automatically.

For IPv6 networks, you can only enable or disable DHCP when creating a subnetwork. Changing this setting later is only possible via recreating the IPv6 subnetwork.

8. (optional) Turn on the Non-routable subnetwork toggle to block access to the subnet from external networks and other subnets. If you keep the network routable, you can specify the Gateway IP address. Otherwise, a random IP address will be assigned.

9. (optional) Specify custom DNS servers for the subnetwork. If you don’t need custom DNS settings, leave the field blank.

10. Define how your traffic will be distributed within a network:

• Destination: Specify the network or host where the traffic is intended to go.
• Next hop: Choose the intermediate device (e.g., a router or gateway) through which traffic must pass to reach the destination.

11. (optional) Turn on Add tags to add metadata to the subnetwork.

12. Click Create subnetwork.

Set the IP range

While creating a subnetwork, specify the address range in the CIDR format.

Your subnetwork's IP range must not overlap with others in the same network. Overlapping subnets cause network conflicts and break connectivity. Virtual machines in the same network communicate using private IP addresses, but subnetworks in different networks cannot communicate unless you configure routing.

The subnetwork size is set using the classless addressing (CIDR) method. You can use both private IPv6 and IPv4 addresses in subnetworks. 

Acceptable CIDR ranges for IPv4 addresses are as follows:

• 10.0.0.0 - 10.255.255.255 
• 172.16.0.0 - 172.31.255.255 
• 192.168.0.0 - 192.168.255.255

The valid subnet mask range is 16-29.

Comparison of IPv4 and IPv6 subnets

The table below outlines key networking features for IPv4 and IPv6, including supported CIDR ranges, subnet mask configurations, and connectivity options.

Feature	IPv4	IPv6
CIDR ranges	10.0.0.0/8 172.16.0.0/12 192.168.0.0/16	fc00::/7
Subnet mask range	/8 - /29 for 10.0.0.0/8 /12 - /29 for 172.16.0.0/12 /16 - /29 for 192.168.0.0/16	/7 - /126
Floating IP support	Yes	No
Internet access	Yes	No - private IPv6 subnets are not publicly routable Yes - public IPv6
DHCP configuration	Can be enabled or disabled	Cannot be changed after creation
Routing between subnets	Allowed within the same network	Allowed within the same network
UI availability	Available to all users	Available to all users

Gateway IP validation

Validation ensures proper configuration and prevents errors during creation or updates. The gateway IP address must belong to the defined CIDR range of the subnetwork. For example, if the CIDR is 192.168.0.0/24, the gateway IP must be within the 192.168.0.0 - 192.168.0.255 range.

Configure network routing

A routed network is a private network that's already connected to a router with a public interface. All Virtual Machines in such networks can access the internet through the router and accept incoming connections. 

By default, a subnetwork in the cloud is created with internet access, which means that it’s routable. If you need to restrict machines from external connections, you need to enable the Non-routable subnetwork option while creating a subnetwork.

Set up the default gateway

If your Gcore Virtual Machine or Gcore Bare Metal server has both public and private interfaces, disable the default gateway for all private subnetworks. Otherwise, there will be a conflict with the default gateway on the server, and you won’t be able to connect to the server.

If you need to configure a gateway in a private subnetwork, ensure that only one of your subnetworks is routable. To do this, check the subnetwork settings and verify that only one subnetwork has the Enable router gateway toggle active.

If you add a private interface (with or without a floating IP) after creating a server, some operating systems may not activate it automatically. This is especially common for Bare Metal servers. In such cases, configure the interface manually.

Manage subnetworks

You can view and manage subnetworks on the Networking page of the Gcore Customer Portal.

Rename a subnetwork

1. In the Gcore Customer Portal, navigate to Cloud > Networking.

2. Find the network where you want to rename a subnetwork. Click the network's name to open it.

3. Click the three-dot icon next to the subnetwork you want to rename, then click Edit.

4. Update the subnetwork’s name.

5. Click Edit subnetwork to save the changes.

The subnetwork has been renamed.

Delete a subnetwork

You can delete a subnetwork that’s not attached to a VM.

To delete a subnetwork:

1. In the Gcore Customer Portal, navigate to Cloud > Networking.

2. Find the network where you want to delete a subnetwork. Click the network's name to open it.

3. Click the three-dot icon next to the subnetwork you want to remove, then click Delete.

4. Confirm your action by clicking Delete again.

The subnetwork has been successfully removed.