Oracle Cloud Infrastructure Documentation

Libreswan

Libreswan is an open source IPSec implementation that is based on FreeS/WAN and Openswan. Most Linux distributions include Libreswan or make it easy to install. You can install it on hosts in either your on-premises network or a cloud provider network. For an example of setting up a Libreswan host in another cloud provider to connect to your Oracle Cloud Infrastructure virtual cloud network (VCN), see Access to Other Clouds with Libreswan.

This topic provides configuration for CPE that is running Libreswan. Virtual tunnel interface (VTI) support for this route-based configuration requires minimum Libreswan version 3.18 and a recent Linux 3.x or 4.x kernel. This configuration was validated using Libreswan version 3.29.

Important

Oracle provides configuration instructions for a tested set of vendors and devices. Use the correct configuration for your vendor and software version.

If the device or software version that Oracle used to verify the configuration does not exactly match your device or software, you might still be able to create the necessary configuration on your device. Consult your vendor's documentation and make any necessary adjustments.

If your device is for a vendor not in the list of verified vendors and devices, or if you're already familiar with configuring your device for IPSec, see the list of supported IPSec parameters and consult your vendor's documentation for assistance.

Oracle Cloud Infrastructure offers Site-to-Site VPN, a secure IPSec connection between your on-premises network and a virtual cloud network (VCN).

The following diagram shows a basic IPSec connection to Oracle Cloud Infrastructure with redundant tunnels. IP addresses used in this diagram are an example only.

This image summarizes the general layout of your on-premises network, Site-to-Site VPN IPSec tunnels, and VCN.

Best Practices

This section covers general best practices and considerations for using Site-to-Site VPN.

Configure All Tunnels for Every IPSec Connection

Oracle deploys two IPSec headends for each of your connections to provide high availability for your mission-critical workloads. On the Oracle side, these two headends are on different routers for redundancy purposes. Oracle recommends configuring all available tunnels for maximum redundancy. This is a key part of the "Design for Failure" philosophy.

Have Redundant CPEs in Your On-Premises Network Locations

Each of your sites that connects with IPSec to Oracle Cloud Infrastructure should have redundant edge devices (also known as customer-premises equipment (CPE)). You add each CPE to the Oracle Console and create a separate IPSec connection between your dynamic routing gateway (DRG)  and each CPE. For each IPSec connection, Oracle provisions two tunnels on geographically redundant IPSec headends. For more information, see the Connectivity redundancy guide (PDF).

Routing Protocol Considerations

When you create a Site-to-Site VPN IPSec connection, it has two redundant IPSec tunnels. Oracle encourages you to configure your CPE to use both tunnels (if your CPE supports it). In the past, Oracle created IPSec connections that had up to four IPSec tunnels.

The following three routing types are available, and you choose the routing type separately for each tunnel in the Site-to-Site VPN:

  • BGP dynamic routing: The available routes are learned dynamically through BGP. The DRG dynamically learns the routes from your on-premises network. On the Oracle side, the DRG advertises the VCN's subnets.
  • Static routing: When you set up the IPSec connection to the DRG, you specify the particular routes to your on-premises network that you want the VCN to know about. You also must configure your CPE device with static routes to the VCN's subnets. These routes are not learned dynamically.
  • Policy-based routing: When you set up the IPSec connection to the DRG, you specify the particular routes to your on-premises network that you want the VCN to know about. You also must configure your CPE device with static routes to the VCN's subnets. These routes are not learned dynamically.

For more information about routing with Site-to-Site VPN, including Oracle recommendations on how to manipulate the BGP best path selection algorithm, see Routing for Site-to-Site VPN.

Other Important CPE Configurations

Ensure that access lists on your CPE are configured correctly to not block necessary traffic from or to Oracle Cloud Infrastructure.

If you have multiple tunnels up simultaneously, you might experience asymmetric routing. To allow for asymmetric routing, ensure that your CPE is configured to handle traffic coming from your VCN on any of the tunnels. For example, you need to disable ICMP inspection, configure TCP state bypass . For more details about the appropriate configuration, contact your CPE vendor's support. To configure routing to be symmetric, refer to Routing for Site-to-Site VPN.

Caveats and Limitations

This section covers general important characteristics and limitations of Site-to-Site VPN to be aware of. See Service Limits for a list of applicable limits and instructions for requesting a limit increase.

Asymmetric Routing

Oracle uses asymmetric routing across the multiple tunnels that make up the IPSec connection. Configure your firewalls accordingly. Otherwise, ping tests or application traffic across the connection don't work reliably.

When you use multiple tunnels to Oracle Cloud Infrastructure, Oracle recommends that you configure your routing to deterministically route traffic through the preferred tunnel. If you want to use one IPSec tunnel as primary and another as backup, configure more-specific routes for the primary tunnel (BGP) and less-specific routes (summary or default route) for the backup tunnel (BGP/static). Otherwise, if you advertise the same route (for example, a default route) through all tunnels, return traffic from your VCN to your on-premises network routes to any of the available tunnels. This is because Oracle uses asymmetric routing.

For specific Oracle routing recommendations about how to force symmetric routing, see Routing for Site-to-Site VPN.

Route-Based or Policy-Based Site-to-Site VPN

The IPSec protocol uses Security Associations (SAs) to determine how to encrypt packets. Within each SA, you define encryption domains to map a packet's source and destination IP address and protocol type to an entry in the SA database to define how to encrypt or decrypt a packet.

Note

Other vendors or industry documentation might use the term proxy ID, security parameter index (SPI), or traffic selector when referring to SAs or encryption domains.

There are two general methods for implementing IPSec tunnels:

  • Route-based tunnels: Also called next-hop-based tunnels. A route table lookup is performed on a packet's destination IP address. If that route's egress interface is an IPSec tunnel, the packet is encrypted and sent to the other end of the tunnel.
  • Policy-based tunnels: The packet's source and destination IP address and protocol are matched against a list of policy statements. If a match is found, the packet is encrypted based on the rules in that policy statement.

The Oracle Site-to-Site VPN headends use route-based tunnels but can work with policy-based tunnels with some caveats listed in the following sections.

Libreswan 3.25 Caveat

If your CPE device uses Libreswan 3.25 or earlier and you attempt to set up an IKEv1 connection with your CPE as a responder, you need to explicitly set the phase 2 parameter in your CPE configuration for the IPSec tunnel to come up. For example, using the current recommended encryption algorithm AES-256-gcm and PFS group5, you must configure the phase 2 parameter phase2alg="aes_gcm256;modp1536" on the CPE device.

This problem is not seen in later Libreswan releases.

Encryption domain for route-based tunnels

If your CPE supports route-based tunnels, use that method to configure the tunnel. It's the simplest configuration with the most interoperability with the Oracle VPN headend.

Route-based IPSec uses an encryption domain with the following values:

  • Source IP address: Any (0.0.0.0/0)
  • Destination IP address: Any (0.0.0.0/0)
  • Protocol: IPv4

If you need to be more specific, you can use a single summary route for your encryption domain values instead of a default route.

Encryption domain for policy-based tunnels

When you use policy-based tunnels, every policy entry (a CIDR block on one side of the IPSec connection) that you define generates an IPSec security association (SA) with every eligible entry on the other end of the tunnel. This pair is referred to as an encryption domain.

In this diagram, the Oracle DRG end of the IPSec tunnel has policy entries for three IPv4 CIDR blocks and one IPv6 CIDR block. The on-premises CPE end of the tunnel has policy entries two IPv4 CIDR blocks and two IPv6 CIDR blocks. Each entry generates an encryption domain with all possible entries on the other end of the tunnel. Both sides of an SA pair must use the same version of IP. The result is a total of eight encryption domains.

Diagram showing multiple encryption domains and how to determine their number.
Important

If the CPE only supports policy-based tunnels, be aware of the following restrictions.

  • Site-to-Site VPN supports multiple encryption domains, but has an upper limit of 50 encryption domains.
  • If you had a situation similar to the prior example and only configured three of the six possible IPv4 encryption domains on the CPE side, the link would be listed in a "Partial UP" state because all possible encryption domains are always created on the DRG side.
  • Depending on when a tunnel was created you might not be able to edit an existing tunnel to use policy-based routing and might need to replace the tunnel with a new IPSec tunnel.
  • The CIDR blocks used on the Oracle DRG end of the tunnel can't overlap the CIDR blocks used on the on-premises CPE end of the tunnel.
  • An encryption domain must always be between two CIDR blocks of the same IP version.

If Your CPE Is Behind a NAT Device

In general, the CPE IKE identifier configured on your end of the connection must match the CPE IKE identifier that Oracle is using. By default, Oracle uses the CPE's public IP address, which you provide when you create the CPE object in the Oracle Console. However, if your CPE is behind a NAT device, the CPE IKE identifier configured on your end might be the CPE's private IP address, as show in the following diagram.

This image shows the CPE behind a NAT device, the public and private IP addresses, and the CPE IKE identifier.
Note

Some CPE platforms do not allow you to change the local IKE identifier. If you cannot, you must change the remote IKE ID in the Oracle Console to match your CPE's local IKE ID. You can provide the value either when you set up the IPSec connection, or later, by editing the IPSec connection. Oracle expects the value to be either an IP address or a fully qualified domain name (FQDN) such as cpe.example.com. For instructions, see Changing the CPE IKE Identifier That Oracle Uses.

CPE Configuration

Important

The configuration instructions in this section are provided by Oracle Cloud Infrastructure for your CPE. If you need support or further assistance, contact your CPE vendor's support directly.

The following figure shows the basic layout of the IPSec connection.

This image summarizes the general layout of the IPSec connection and tunnels.

Default Libreswan Configuration Files

The default Libreswan installation creates the following files:

  • etc/ipsec.conf: The root of the Libreswan configuration.
  • /etc/ipsec.secrets: The root of the location where Libreswan looks for secrets (the tunnel pre-shared keys).
  • /etc/ipsec.d/: A directory for storing the .conf and .secrets files for your Oracle Cloud Infrastructure tunnels (for example: oci-ipsec.conf and oci-ipsec.secrets). Libreswan encourages you to create these files in this folder.

The default etc/ipsec.conf file includes this line:

include /etc/ipsec.d/*.conf

The default etc/ipsec.secrets file includes this line:

include /etc/ipsec.d/*.secrets

The preceding lines automatically merge all the.conf and .secrets files in the /etc/ipsec.d directory into the main configuration and secrets files that Libreswan uses.

About Using IKEv2

Oracle supports Internet Key Exchange version 1 (IKEv1) and version 2 (IKEv2). If you configure the IPSec connection in the Console to use IKEv2, you must configure your CPE to use only IKEv2 and related IKEv2 encryption parameters that your CPE supports. For a list of parameters that Oracle supports for IKEv1 or IKEv2, see Supported IPSec Parameters.

You specify the IKE version when setting up the IPSec configuration file in task 3 in the next section. In that example file, there's a comment showing how to configure IKEv1 versus IKEv2.

Configuration Process

Libreswan supports both route-based and policy-based tunnels. The tunnel types can coexist without interfering with each other. The Oracle VPN headends use route-based tunnels. Oracle recommends that you configure Libreswan with the Virtual Tunnel Interface (VTI) configuration syntax.

For details about the specific parameters used in this document, see Supported IPSec Parameters.

Task 1: Prepare the Libreswan instance

Depending on the Linux distribution you're using, you might need to enable IP forwarding on your interface to allow clients to send and receive traffic through Libreswan. In the /etc/sysctl.conf file, set the following values and apply the updates with sudo sysctl -p.

If you're using an interface other than eth0, change eth0 in the following example to your interface (lines 5 and 7).

net.ipv4.ip_forward=1
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.conf.eth0.send_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.eth0.accept_redirects = 0
Task 2: Determine the required configuration values

The Libreswan configuration uses the following variables. Determine the values before proceeding with the configuration.

  • ${cpeLocalIP}: The IP address of your Libreswan device.
  • ${cpePublicIpAddress}: The public IP address for Libreswan. This is the IP address of your outside interface. Depending on your network topology, the value might be different from ${cpeLocalIP}.
  • ${oracleHeadend1}: For the first tunnel, the Oracle public IP endpoint obtained from the Oracle Console.
  • ${oracleHeadend2}: For the second tunnel, the Oracle public IP endpoint obtained from the Oracle Console.
  • ${vti1}: The name of the first VTI used. For example, vti1.
  • ${vti2}: The name of the second VTI used. For example, vti2.
  • ${sharedSecret1}: The pre-shared key for the first tunnel. You can use the default Oracle-provided pre-shared key, or provide your own when you set up the IPSec connection in the Oracle Console.
  • ${sharedSecret2}: The pre-shared key for the second tunnel. You can use the default Oracle-provided pre-shared key, or provide your own when you set up the IPSec connection in the Oracle Console.
  • ${vcnCidrNetwork}: The VCN IP range.
Task 3: Set up the configuration file: /etc/ipsec.d/oci-ipsec.conf

Libreswan configuration uses the concept of left and right to define the configuration parameters for your local CPE device and the remote gateway. Either side of the connection (the conn in the Libreswan configuration) can be left or right, but the configuration for that connection must be consistent. In this example:

  • left: Your local Libreswan CPE
  • right: The Oracle VPN headend

Use the following template for your /etc/ipsec.d/oci-ipsec.conf file. The file defines the two tunnels that Oracle creates when you set up the IPSec connection.

Important

If your CPE is behind a 1-1 NAT device, uncomment the leftid parameter and set it equal to the ${cpePublicIpAddress}.

conn oracle-tunnel-1
     left=${cpeLocalIP}
     # leftid=${cpePublicIpAddress} # See preceding note about 1-1 NAT device
     right=${oracleHeadend1}
     authby=secret
     leftsubnet=0.0.0.0/0 
     rightsubnet=0.0.0.0/0
     auto=start
     mark=5/0xffffffff # Needs to be unique across all tunnels
     vti-interface=${vti1}
     vti-routing=no
     ikev2=no # To use IKEv2, change to ikev2=insist 
     ike=aes_cbc256-sha2_384;modp1536
     phase2alg=aes_gcm256;modp1536
     encapsulation=yes
     ikelifetime=28800s
     salifetime=3600s
conn oracle-tunnel-2
     left=${cpeLocalIP}
     # leftid=${cpePublicIpAddress} # See preceding note about 1-1 NAT device
     right=${oracleHeadend2}
     authby=secret
     leftsubnet=0.0.0.0/0
     rightsubnet=0.0.0.0/0
     auto=start
     mark=6/0xffffffff # Needs to be unique across all tunnels
     vti-interface=${vti2}
     vti-routing=no
     ikev2=no # To use IKEv2, change to ikev2=insist 
     ike=aes_cbc256-sha2_384;modp1536
     phase2alg=aes_gcm256;modp1536 
     encapsulation=yes
     ikelifetime=28800s
     salifetime=3600s
Task 4: Set up the secrets file: /etc/ipsec.d/oci-ipsec.secrets

Use the following template for your /etc/ipsec.d/oci-ipsec.secrets file. It contains two lines per IPSec connection (one line per tunnel).

${cpePublicIpAddress} ${oracleHeadend1}: PSK "${sharedSecret1}"
${cpePublicIpAddress} ${oracleHeadend2}: PSK "${sharedSecret2}"
Task 5: Restart the Libreswan configuration

After setting up your configuration and secrets files, you must restart the Libreswan service.

Important

Restarting the Libreswan service may impact existing tunnels.

The following command rereads the config file and restarts the Libreswan service. 

service ipsec restart
Task 6: Configure IP routing

Use the following ip command to create static routes that send traffic to your VCN through the IPSec tunnels. If you're logged in with an unprivileged user account, you might need to use sudo before the command.

Important

Static routes created with the ip route command do not persist through a reboot. To determine how to make your routes persist, refer to the documentation of your Linux distribution of choice.
ip route add ${VcnCidrBlock} nexthop dev ${vti1} nexthop dev ${vti2}
ip route show

Verification

A Monitoring service is also available from Oracle Cloud Infrastructure to actively and passively monitor your cloud resources. For information about monitoring your Site-to-Site VPN, see Site-to-Site VPN Metrics.

If you have issues, see Site-to-Site VPN Troubleshooting.

Verifying the Libreswan Status

Verify the current state of your Libreswan tunnels by using the following command.

ipsec status

The tunnel is established if you see a line that includes the following:

STATE_MAIN_I4: ISAKMP SA established

If you're using IKEv2, you see the following:

STATE_V2_IPSEC_I (IPsec SA established)

In the future, if you need to open a support ticket with Oracle about your Libreswan tunnel, include the output of the preceding ipsec status command.

Verifying the Tunnel Interface Status

Verify that the virtual tunnel interfaces are up or down by using the ifconfig command or the ip link show command. You can also use applications such as tcpdump with the interfaces.

Here's an example of the ifconfig output with a working Libreswan implementation that shows the available VTIs.

ifconfig
<output trimmed>
				
vti01: flags=209<UP,POINTOPOINT,RUNNING,NOARP> mtu 8980
     inet6 fe80::5efe:a00:2 prefixlen 64 scopeid 0x20<link>
     tunnel txqueuelen 1000 (IPIP Tunnel)
     RX packets 0 bytes 0 (0.0 B)
     RX errors 0 dropped 0 overruns 0 frame 0
     TX packets 0 bytes 0 (0.0 B)
     TX errors 10 dropped 0 overruns 0 carrier 10 collisions 0

vti02: flags=209<UP,POINTOPOINT,RUNNING,NOARP> mtu 8980
     inet6 fe80::5efe:a00:2 prefixlen 64 scopeid 0x20<link>
     tunnel txqueuelen 1000 (IPIP Tunnel)
     RX packets 0 bytes 0 (0.0 B)
     RX errors 0 dropped 0 overruns 0 frame 0
     TX packets 0 bytes 0 (0.0 B)
     TX errors 40 dropped 0 overruns 0 carrier 40 collisions 0

Here's an example of the ip link show output:

ip link show
<output trimmed>

9: vti01@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 8980 qdisc noqueue
state UNKNOWN mode DEFAULT group default qlen 1000
   link/ipip 10.0.0.2 peer 129.213.240.52

10: vti02@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 8980 qdisc noqueue
state UNKNOWN mode DEFAULT group default qlen 1000
   link/ipip 10.0.0.2 peer 129.213.240.51

Also, in the Oracle Console, each IPSec tunnel should now be in the UP state.