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IMPORTANT
SNS 3.x versions have reached End of Maintenance since July 1st, 2024.
We recommend that you update your SNS firewalls to a version with maintenance to guarantee the protection of your infrastructure.

# Creating or modifying a GRE interface

The GRE protocol allows encapsulating IP traffic in a point-to-point IP tunnel. This allows, for example, routing networks from one site to another through a GRE tunnel without having to declare this routing method on all routers in between.

GRE tunnels are not encrypted natively: they merely encapsulate. GRE traffic can however be made to go through an IPsec tunnel.

To create or modify a virtual GRE interface, click on the GRE interfaces tab.

## Button bar

Search | Search that covers interfaces.
Add | Adds an “empty” interface. An added interface (sending of a command) is effective only if its fields Name, IP address, Network mask, Tunnel source and Tunnel destination have been entered.
Delete | Deletes one or several selected interfaces. Use the keys Ctrl/Shift + Delete to delete several interfaces.
Check usage | Represented by the icon , this button indicates whether the selected interface is being used elsewhere in the configuration.

Apply | Sends the configuration of the IPsec interfaces.
Cancel | Cancels the configuration of the IPsec interfaces.

## Interactive features

Some operations listed in the taskbar can be performed by right-clicking on the table of GRE interfaces:

- Add,
- Delete,
- Check usage.

## Presentation of the table

The table sets out seven fields of information:

Status | Status of the interfaces: Enabled: Double-click to enable the created interface. Disabled: The interface is not in operation. The line will be grayed out in order to reflect this.
Name(mandatory) | Give the GRE interface a name.
IPv4 address (mandatory), | Enter the IP address assigned to the virtual interface created.
IPv4 mask (mandatory), | The default value suggested is 255.255.255.252. Since virtual GRE interfaces are meant for setting up point-to-point tunnels, a network that allows assigning two addresses is sufficient in theory. This value may however be customized.
Tunnel source (mandatory) | Select the outgoing interface of traffic using the tunnel. In general, this would be the firewall’s “out” interface or a bridge.
Tunnel destination (mandatory) | Select the object representing the tunnel’s remote endpoint. This is a host object that presents the public IP address of the remote firewall.
Comments(optional) | Any text.