Connecting multiple environments

Inter-Configuration Network Routing (ICNR) lets you connect multiple environments together. VMs in one environment can communicate with VMs in another environment, or VMs in multiple environments can communicate with shared services in dedicated environments.


  • It's possible to create up to 100 ICNR connections for an environment but multiple active connections can significantly slow power-state changes for the connected environments.
  • Environments must be in the same region to connect using ICNR.

ICNR overview

By default, each environment is isolated from other environments in your account. ICNR connects the networks in multiple Skytap environments, which allows VMs on those networks to communicate with one another. It can also be used to split large environments up into smaller environments so that you can restrict access to sets of servers.

When you set up ICNR, be sure to avoid IP overlap between networks. Either enable Network Address Translation (NAT) on the Skytap networks or manually design environment networks to avoid overlaps (see Avoiding overlapping IP address spaces).

The figure below shows the conceptual view of the environments with and without ICNR.

ICNR Diagram

Enabling ICNR

Step 1: Create a visible network in the environment with your centralized servers

By default, a network in an environment isn’t visible to networks outside of the environment.

To make a network visible to other networks
  1. Navigate to the Network Settings tab of the Settings page. The Network Settings page displays.

    Network Settings

  2. Click the Edit Network button next to the network. The Edit network window displays.
  3. Check the Visible to other networks checkbox.

    Edit Network

  4. While you’re editing the network, you may also want to enable Network Address Translation (NAT), detailed in the next step. Otherwise, click Save Changes.

Step 2: Enable Network Address Translation (optional)

Network Address Translation (NAT) is a process that maps each internal Skytap network address (such as in a network to an external network address (such as Other networks detect and send data to the external network addresses. Enabling NAT means that you don’t have to manually change the subnets of connecting networks to avoid overlaps. For more information, see Using Network Address Translation (NAT) to avoid IP address conflicts.

NAT can only be enabled for automatic networks that have been made visible to other networks (as in Step 1, above).

To enable NAT
  1. In the Edit network window, click the checkbox labeled Apply NAT for connecting networks.

    Edit Network Window

  2. The NAT Subnet field is automatically filled with a subnet that has no overlaps with any other networks that you have access to. When you use ICNR, this prevents overlap between connected networks, as even networks with identical IP addresses are assigned separate, unique addresses. You can manually enter a NAT subnet of your choosing.
  3. Click Save Changes.

Step 3: Connect the networks in other environments to the visible network

To connect a network to visible network in another environment
  1. Navigate to the Network Settings page of the environment you want to connect to the centralized servers.
  2. Click on the Connect to a network link for the network you want to connect (Network 1 in the example below).

    Network Settings - Connect to a Network

  3. A dialog box displays that contains all visible networks in the same region. In this example, it’s the network in the centralized environment:

    Connect Networks

  4. Click the Connect to Network button. The networks are connected to each other and able to exchange data.
  5. Repeat this process for each additional environment you want to connect using ICNR.

    Networks in an environment are automatically connected to each other. You don’t need to do anything to connect networks in the same environment. You can control whether traffic flows through a connection between networks in the same environment with the Allow all traffic between networks in this environment setting. For more information, see Routing between networks in the same environment.

Viewing network connections

To help you keep track of your network connections, you can see a list of all the networks a network is connected to.

To view a list of network connections
  1. Navigate to the Network Settings page.
  2. Click on the Show connected networks link to display all of the networks that connect to this network.

    Network Settings

Deleting a network connection

To delete a connection between a network in your environment and another network
  1. Navigate to the Network Settings page in your environment.
  2. Click on the Show connected networks link for the network want to change.

    Network Settings

  3. Click Disconnect network Disconnect next to the network connection you want to remove.

Avoiding overlapping IP address spaces

Enable NAT to prevent IP address space overlap. The information below applies only if you’re not using NAT on your linked environments.

A connection between networks doesn’t work if their IP address spaces overlap. Overlapping IP address spaces may prevent traffic from being routed to the correct network. In this case, Skytap prevents you from creating the connection.

There are two ways IP address spaces can overlap:

  • The address spaces are identical. For instance, the IP address with subnet size of 16 (written in CIDR Classless Inter-Domain Routing – a compact representation of an IP address and its associated routing prefix. notation as can’t be connected to another network with the IP address of and a subnet mask of 16.
  • One of the network address spaces is fully contained within the address space of another network. For instance, the address space is fully contained within (the /24 subnet represents a portion of the address space available in the /16 subnet).

Skytap checks for overlap whenever you edit a network, create a new network, or create a connection between networks using ICNR. When you connect networks from different environments together, Skytap checks that none of the networks connected to either environment have IP address overlaps. This means that additional networks connected to one of the two connecting networks can cause the connection to fail if its IP address overlaps. If Skytap detects an overlap, it displays an error message. Examples of the most likely errors, and recommended steps to fix them, are described below.

Network connection error types

Error type 1: Direct overlap

Network A ( has overlapping address space with Network B (

Possible resolution

Change the IP address space of Network A or Network B (for example, to

Direct Overlap

Error type 2: Indirect overlap with a network in the same environment

Network A ( has overlapping address space with Network C (, which is in the same environment as Network B. Networks in the same environment are automatically connected to each other.

Possible resolution

Change the IP address space of Network A or Network C

Indirect Overlap Within Environment

Error type 3: Indirect overlap with a network in another environment

Network A ( has overlapping address space with Network C (, which is in a third environment that is already connected to Network B.

Possible resolution
  • Change the IP address space of Network A or Network C
  • Disconnect Network C from Network B

Indirect Overlap

Error type 4: Editing a network

Networks within an environment are already connected to each other. While editing a network you can encounter errors if you choose an IP address space that overlaps with that of another network in the same environment; a network in another environment that is connected to the network you’re editing; or a network in another environment that is connected to another network in the this environment

Possible resolution

Choose a different, non-overlapping, IP address space for the network you’re editing.

Error type 5: Overlap with network across a VPN connection

This error condition occurs when trying to connect networks that are connected to other networks over a VPN connection. The figure below illustrates the error condition.

Network B is connected to the corporate network over the VPN connection. Remote network, Network C has the address space When you try to connect Network A to Network B in Skytap, Network A overlaps with Network C.

Possible resolution

Change the subnet of Network A and attempt the connection again

Overlap Across VPN