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OpenVPN server

When configured as an OpenVPN server, the Endian UTM Appliance can accept remote connections from the uplink and allow a VPN client to be set up and interact with the local resources as if it were a local workstation or server.

The OpenVPN server on the Endian UTM Appliance allows the simultaneous presence of several server instances. Each instance listens on a different port, and accepts incoming connections to that port only.

Moreover, when the hardware on which Endian UTM Appliance is installed has multiple CPU cores, every instance may be assigned more that one core, thus resulting in an increase of the throughput and data processing of that instance. It is nevertheless also possible to have multiple instances of OpenVPN running on a device equipped with a single-core CPU, though this results in possibly reduced performances since the CPU carries the load of all instances.

The OpenVPN server settings page is composed of two tabs: Server configuration and VPN client download.

Server configuration

This page shows a switch called Enable OpenVPN server swoff, that will start the OpenVPN server and all services related to it (like e.g., the VPN firewall if enabled) once clicked.

Below, there are two boxes, OpenVPN settings -that allows to set up some global settings shared by all the instances- and OpenVPN Instances - that containes the list of the OpenVPN server instances defined on the Endian UTM Appliance

Right below, the Add new OpenVPN server instance link allows to define a new server instance.

Note

When starting the OpenVPN server for the first time, the root and host certificates are generated automatically.

OpenVPN settings

The box on the top shows the current OpenVPN settings, which concern the authentication method, and are:

Authentication type

There are three available authentication methods to connect clients to the OpenVPN server running on the Endian UTM Appliance:

  • PSK (username and password). Connection is established after providing correct username and password.
  • X.509 certificate. A valid certificate only is needed to connect.
  • X.509 certificate & PSK (two factor). Both a valid certificate, and a username/passwords combination are needed.

Warning

When employing certificate-only authentication, a client with a valid certificate will be granted access to the OpenVPN server even if it has no valid account!

Endian UTM Appliance‘s default method is PSK (username/password): The client authenticates using username and password. To use this method, no additional change is needed, while the other two methods are described below.

Certificate configuration

This drop-down menu is used to select the method of creation of a new certificate. The available options are:

  • Generate a new certificate. Create a new certificate from scratch. This option is only available if no host certificate has already been generated. A form will open where to specify all options necessary to create a new certificate. These are the same found in the new certificates generation editor, with two slight changes: Common name becomes System hostname and Organizational unit name becomes Department name.

  • Use selected certificate. Select one certificate from those available, shown on the right-hand side of the drop-down menu. It is possible to see the full details of this certificate by clicking on the View details hyperlink.

    Hint

    The name of the certificate selected appears right above the hyperlink.

  • Use an existing certificate. A second drop-down menu on the left allows to select a certificate that has already been created and stored on the Endian UTM Appliance.

  • Upload a certificate. By clicking on the Browse... button that appears underneath the drop-down menu it will be possible to select from the workstation and to upload an existing certificate. The password for the certificate, if needed, can be provided in the textfield on the right-hand side.

  • Upload a certificate signing request. The Browse... button that appears underneath the drop-down menu can be clicked to select from the workstation and upload an existing certificate signing request. The validity of the certificate in days can be provided in the textfield on the right-hand side.

On the right of the Certificate configuration drop-down menu, the name of the currently used certificate is shown, above the info icon and the View details link. The latter will show all information about the certificate when clicked.

Below the Certificate configuration drop-down menu, there is the download icon , with the name of the Certificate Authority and the Download certificate link to download the cerrtificate needed for the client connections.

In the Advanced options panel, a few options are available to customise the OpenVPN server.

Delay triggers
A tick on the checkbox will allow to delay the triggers launched whenever a client connects to or disconnects from the OpenVPN server. Since triggers are mostly a reload of routing and firewall rules, this option proves useful when many clients connect or disconnect at the same time.
Log verbosity

This option allows to increase or decrease the amount of messages written in the log file. The default value is 1, which means that only the most relevant messages are written to the log file, and can be increased up to 5.

Hint

A good value for debugging is 4.

Create a DNS entry for each connected client
When this option is ticked, whenever a client connect, it will receive an entry in the local DNS server, for other clients to be able to connect easily to it. The next option will appear.
Clients DNS entry prefix

A custom prefix that will be prefixed to the username of a client to uniquely identify it when using the local DNS.

Hint

If the prefix written here is vpn, the entry will be vpn-username, like e.g., vpn-johndoe.

OpenVPN server instances

The list of already defined OpenVPN instances is shown in this panel, above which is present the Add new OpenVPN server instance hyperlink. A click on this link will open an editor in which toq provide all the necessary configuration values for a new VPN instance.

Note

When the number of OpenVPN instances in greater than the cores, a yellow callout informs that the performances may degrade.

In the editor, the following configuration options are shown.

Name
The name given to the OpenVPN server instance.
Remark
A comment for this instance.
Bind only to
The IP address to which the instance should listen to.
Port
The port on which the instance waits for incoming connections.
Device type
The device used by the instance, chosen between TUN and TAP from the drop-down menu. TUN devices require that the traffic be routed, hence the option Bridged below is not available for TUN devices.
Protocol
The protocol used, chosen between TCP and UDP from the drop-down menu.
Bridged

Tick this option to run the OpenVPN server in bridged mode, i.e., within one of the existing zones.

Note

If the OpenVPN server is not bridged (i.e., it is routed), the clients will receive their IP addresses from a dedicated subnet. In this case, appropriate firewall rules in the VPN firewall should be created, to make sure the clients can access any zone, or some server/resource (e.g., a source code repository). If the OpenVPN server is bridged, it inherits the firewall settings of the zone it is defined in.

VPN subnet
This option is the only available if bridged mode is disabled. It allows the OpenVPN server to run in its own, dedicated subnet, that can be specified in the text box and should be different from the subnets of the other zones.
Bridged to
The zone to which the OpenVPN server should be bridged. The drop-down menu shows only the available zones.
Dynamic IP pool start address
The first possible IP address in the network of the selected zone that should be used for the OpenVPN clients.
Dynamic IP pool end address
The last possible IP address in the network of the selected zone that should be used for the OpenVPN clients.

Routed and bridged OpenVPN server, static and dynamic IP addresses.

When configuring a pool of IP addresses to be reserved for clients connecting via OpenVPN, it is necessary to keep in mind a few guidelines that help both the prevention of future malfunctioning and the cleaner and easier design and set up.

Before starting the configuration of the server, there is a golden rule to remember, concerning the implementation of the VPN multicore architecture: Regardless of the bridged or routed mode used for a multicore VPN server instance, the reservation of static IP addresses is neglected. In other words, a client connecting to this VPN server, will receive a dynamic IP address, even though in her configuration there is a static IP assignment.

The first choice is to define whether the OpenVPN server should act in routed or bridged mode. In the former case, it is necessary to define a suitable VPN subnet that will provide the IP addresses for the clients. The traffic directed to this subnet has to be filtered, if necessary, using the VPN firewall. In the latter case, the OpenVPN server is configured to consider the clients, upon connecting, as they were physically connected to that zone, i.e., the server bridges the client to one of the zones. In this case, a pool of IP addresses must be defined within that zone using the two option that appear right before this box. This pool must be entirely contained in the zone’s subnet and smaller than that one. It is also important to make sure that this pool does conflict with other pools defined in that zone, like e.g., a DHCP server.

In a bridged OpenVPN server it is possible to assign to some (or even to all) user a static IP address. When planning this possibility, it is a good practice that these static IP addresses do not belong to any of the IP pools defined in that zone, to prevent any conflicts of address and wrong routing. Traffic to this particular client can then be filtered using the VPN (or IPsec) user as source or destination of traffic in the Firewall rules.

Certificate configuration
This option allows to select a certificate for the instance, that is different from the default one defined in the global options. The choices for this options are the same as in the global section of the OpenVPN configuration.

In the Advanced options box, additional options can be configured.

Number of cores
The drop-down menu allows to chose how many CPUs of the Endian UTM Appliance can be used by the instance, hence the options in the drop-down menu may vary.
Allow multiple connections from one account:
Normally, one client is allowed to connect from one location at a time. Selecting this option permits multiple client logins, even from different locations. However, when the same client is connect twice or more, the VPN firewall rules do not apply anymore.
Block DHCP responses coming from tunnel
Tick this checkbox when receiving DHCP responses from the LAN at the other side of the VPN tunnel that conflict with the local DHCP server.
Client to client connections

Select from the drop-dow menu the modalities of the communications between clients of the OpenVPN server. This option is only available on single-process servers, i.e., on servers running only one instance of the OpenVPN server.

  • Not allowed: The clients can not communicate one to the other.
  • Allow direct connections: The clients can communicate directly with each other but filtering is not possible.
  • Filter connections in the VPN firewall The clients can communicate with each other, but their traffic is redirected to the VPN Firewall and can be filtered using suitable rules there.

Note

In case of Appliances having multi-core CPUs, there is no selection possible and the option Filter connections in the VPN firewall is automatically activated

Renegotiation data channel key interval

This option allows to modify the time interval after which the data channel key will be renegotiated. The value is measured in seconds, with the default value set to 3600 seconds.
Push these nameservers
By ticking this checkbox, the nameserver specified in the textfield below are sent to the clients upon connection.
Nameservers
The nameservers specified in this textfield are sent to the connected clients, when the previous checkbox has been ticked.
Push these networks
By ticking this checkbox, the routes to the networks defined in the textfield below are sent to the connected clients.
Networks
The networks specified in this textfield are sent to the connected clients, when the previous checkbox has been ticked.
Push this domain
By ticking this checkbox, the search domain defined in the textfield on the right-hand side, is added to those of the connected clients.

Note

The options Push these nameservers and Push domain only work for clients running the Microsoft Windows operating system.

Domain
The domain that will be used to identify the servers and network resources in the VPN network (i.e., the search domain).
Authentication type
The authentication type for this instance of OpenVPN. By default it will inherit the global configuration. However, this can be overridden by specifying manually one of the available options here. They are: PSK (username/password), X.509 certificate and X.509 certificate & PSK (two factor). They are the same as in the global option
Cipher
This drop-down menu allows to choose the cipher that is used by the OpenVPN server. The default value is Auto, which means that the cipher is automatically negotiated.
Message digest algorithm
This drop-down menu allows to choose the message digest algorithm that is used by the OpenVPN server. The default value is Auto, which means that the cipher is automatically negotiated.
Disable channel encryption

When this option is ticked, the whole VPN traffic through this instance will NOT be encrypted, i.e., it will be in plain text. Moreover, the previous two options will disappear.

Warning

It is strongly suggested to not disable encryption on the OpenVPN server, as the whole traffic will not be encrypted and could be read in case the communication is intercepted.

The first time the service is started a new, self-signed CA certificate for this OpenVPN server is generated, an operation that may take a long time. After the certificate has been generated, it can be downloaded by clicking on the Download CA certificate link. This certificate must be used by all the clients that want to connect to this OpenVPN server, otherwise they will not be able to access.

After the server has been set up, it is possible to create and configure accounts for clients that can connect to the Endian UTM Appliance in the Authentication tab.

Enabled
Tick this checkbox to make sure the OpenVPN server is started.

Troubleshooting VPN connections.

While several problem with VPN connections can be easily spotted by looking at the configuration, one subtle source of connections hiccups is a wrong value of the MTU size. The Endian UTM Appliance sets a limit of 1450 bytes to the size of the VPN’s MTU, to prevent problems with the common MTU value used by the ISP, which is 1500. However, some ISP may use a MTU value lower that the commonly used value, making the Endian MTU value too large and causing therefore connection issues (the most visible one is probably the impossibility to download large files). This value can be modified by accessing the Endian UTM Appliance from the CLI and following these guidelines:

  1. Write down the MTU size used by the ISP (see link below).
  2. Login to the CLI, either from a shell or from Menubar ‣ System ‣ Web Console.
  3. Edit the OpenVPN template with an editor of choice: nano /etc/openvpn/openvpn.conf.tmpl.
  4. Search for the string mssfix 1450.
  5. Replace 1450 with a lower value, for example 1200.
  6. Restart OpenVPN by calling: jobcontrol restart openvpnjob.

See also

More information about the MTU size.

VPN client download

Click on the link to download the Endian VPN client for Microsoft Windows and MacOS X from the Endian Network. A valid account on Endian Network is required.

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