Strongswan
Strongswan is an open source IPSec-based VPN solution. Most Linux distributions include Strongswan or make it easy to install. You can install it on hosts in either your on-premises network or a cloud provider network.
This topic provides configuration for CPE running Strongswan. The Strongswan 5.x branch supports both the IKEv1 and IKEv2 key exchange protocols with the native NETKEY IPSec stack of the Linux kernel.
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.
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.
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.
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.
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.
Supported IPSec Parameters
For a vendor-neutral list of supported IPSec parameters for all regions, see Supported IPSec Parameters.
The Oracle BGP ASN for the commercial cloud realm is 31898. If you're configuring Site-to-Site VPN for the US Government Cloud, see Required Site-to-Site VPN Parameters for Government Cloud and also Oracle's BGP ASN. For the United Kingdom Government Cloud, see Regions.
CPE Configuration
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.
Default Strongswan Configuration Files
The default Strongswan installation creates the following files:
etc/strongswan/ipsec.conf: The root of the Strongswan configuration./etc/strongswan/ipsec.secrets: The root of the location where Strongswan looks for secrets (the tunnel pre-shared keys).
The default etc/strongswan/ipsec.conf file includes this line:
Include /etc/strongswan/*.confThe default etc/strongswan/ipsec.secrets file includes this line:
include /etc/strongswan/ipsec.d/*.secretsThe preceding lines automatically merge all the .conf and
.secrets files in the /etc/strongswan directory into the
main configuration and secrets files that Strongswan 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
The following configuration process discusses how a route-based tunnel is configured on Strongswan. The Oracle VPN headends use route-based tunnels. Oracle recommends that you configure Strongswan with the Virtual Tunnel Interface (VTI) configuration syntax.
For details about the specific parameters used in this document, see Supported IPSec Parameters.
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 Strongswan. 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).
If you're using multiple interfaces, configure lines 5 and 7 for that interface as well.
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.ens3.send_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.ens3.accept_redirects = 0
The Strongswan configuration uses the following variables. Determine the values before proceeding with the configuration.
${cpeLocalIP}: The IP address of your Strongswan device.${cpePublicIpAddress}: The public IP address for Strongswan, also 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.${oracleHeadend2}: For the second tunnel, the Oracle public IP endpoint obtained from the Oracle Console.${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.
Strongswan 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 Strongswan configuration) can be left or right, but the configuration for that connection must be consistent. In this example:
- left: Your local Strongswan CPE
- right: The Oracle VPN headend
Use the following template for your /etc/strongswan/ipsec.conf file. The
file defines the two tunnels that Oracle creates when you set up the IPSec connection.
If your CPE is behind a one-to-one NAT device, uncomment the leftid
parameter and set it equal to the ${cpePublicIpAddress}.
# basic configuration
config setup
conn %default
ikelifetime=28800s
keylife=3600s
rekeymargin=3m
keyingtries=%forever
mobike=no
ike=aes256-sha2_384-ecp384!
esp=aes256gcm16-modp1536!
conn oci-tunnel-1
left=${cpeLocalIP}
#leftid=${cpePublicIpAddress} # See preceding note about 1-1 NAT device
leftsubnet=0.0.0.0/0
leftauth=psk
right=${oracleHeadend1}
rightid=${oracleHeadend1}
rightsubnet=0.0.0.0/0
rightauth=psk
type=tunnel
keyexchange=ikev1 # To use IKEv2, change to ikev2
auto=start
dpdaction=restart
mark=13 # Needs to be unique across all tunnels
conn oci-tunnel-2
left={cpeLocalIP}
#leftid=${cpePublicIpAddress}
leftsubnet=0.0.0.0/0
leftauth=psk
right=${oracleHeadend2}
rightid=${oracleHeadend2}
rightsubnet=0.0.0.0/0
rightauth=psk
type=tunnel
keyexchange=ikev1 # To use IKEv2, change to ikev2
auto=start
dpdaction=restart
mark=14 # Needs to be unique across all tunnels
Statements like ike= and esp= can be modified for
specific parameters based on the Supported IPSec Parameters.
Use the following template for your /etc/strongswan/ipsec.secrets file. It
contains two lines per IPSec connection (one line per tunnel).
${cpePublicIpAddress} ${oracleHeadend1}: PSK "${sharedSecret1}"
${cpePublicIpAddress} ${oracleHeadend2}: PSK "${sharedSecret2}"
The following command creates a VTI interface with the defined name and binds it to the tunnel using local and remote IPs.
ip tunnel add <name> local <local IP> remote <remote IP> mode vti key <mark><name>can be any valid device name (ipsec0, vti0, and so on). The ip command treats names starting withvtias special in some instances (such as when retrieving device statistics). The IP addresses are the endpoints of the IPSec tunnel. A private IP can be used when your CPE is behind a NAT device.-
<mark>has to match the mark configured for the connection.
After creating the VTI, it has to be enabled (use ip link set <name> up)
and then you may install routes and use routing protocols as shown in the following example.
ip tunnel add vti1 mode vti local 10.0.3.78 remote 193.123.68.187 key 13
ip link set vti1 upThe route installation by the IKE daemon must be disabled. To do this, modify
charon.conf as shown.
Directory - /etc/strongswan/strongswan.d/Charon.conf
#Uncomment below statement
install_routes = no
After setting up your configuration and secrets files, you must restart the Strongswan service. Use the following command:
Strongswan restart
Restarting the Strongswan service might impact existing tunnels.
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.
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.
You can also enable OCI logging to get access to VPN logs.
Verifying the Tunnel Interface Status
Verify the current state of your Strongswan tunnels by using the following command.
strongswan statusIf the returned output is similar to the following example, the tunnel is established.
oci-tunnel-1[591]: ESTABLISHED 43 minutes ago, 10.0.3.78[129.148.216.212]...193.123.68.187[193.123.68.187]
oci-tunnel-1{399}: INSTALLED, TUNNEL, reqid 102, ESP in UDP SPIs: ce6a1525_i 4829c65c_o
oci-tunnel-1{399}: 0.0.0.0/0 === 0.0.0.0/0
In the future, if you need to open a support ticket with Oracle about your Strongswan
tunnel, include the complete output of the strongswan 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 Strongswan
implementation that shows the available VTIs.
ifconfig
<output trimmed>
vti1: flags=209<UP,POINTOPOINT,RUNNING,NOARP> mtu 8980
inet 10.10.10.1 netmask 255.255.255.252 destination 10.10.10.1
inet6 fe80::5efe:a00:34e prefixlen 64 scopeid 0x20<link>
tunnel txqueuelen 1000 (IPIP Tunnel)
RX packets 69209 bytes 4050022 (3.8 MiB)
RX errors 54 dropped 54 overruns 0 frame 0
TX packets 50453 bytes 3084997 (2.9 MiB)
TX errors 1016 dropped 0 overruns 0 carrier 1016 collisions 0
vti2: flags=209<UP,POINTOPOINT,RUNNING,NOARP> mtu 8980
inet 192.168.10.1 netmask 255.255.255.252 destination 192.168.10.1
inet6 fe80::5efe:a00:34e prefixlen 64 scopeid 0x20<link>
tunnel txqueuelen 1000 (IPIP Tunnel)
RX packets 101256 bytes 6494872 (6.1 MiB)
RX errors 12 dropped 12 overruns 0 frame 0
TX packets 70023 bytes 4443597 (4.2 MiB)
TX errors 2142 dropped 0 overruns 0 carrier 2142 collisions 0
Here's an example of the ip link show output:
ip link show
<output trimmed>
vti2@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 8980 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/ipip 10.0.3.78 peer 139.185.34.172
14: vti1@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 8980 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/ipip 10.0.3.78 peer 193.123.68.187
Configure Dynamic Routing with Strongswan
Oracle recommends using quagga to configure BGP. To install quagga, use the following Oracle Linux command (if you are using a different Linux distribution your commands might vary slightly):
sudo yum -y install quaggaChange the zebra configuration (/etc/quagga/zebra.conf) to define
the VTI IP address, which is required because BGP uses peering. Define the following
variables for zebra:
${vti_name1}: The name of the first VTI used. For example, vti1.${vti_name2}: The name of the second VTI used. For example, vti2.${vti_ipaddress1}: The IP address allocated to the first VTI used.${vti_ipaddress2}: The IP address allocated to the second VTI used.${local_subnet}: The local CPE subnet.
These variables are used in the following configuration file excerpt:
!
hostname strongswan-centos
log file /var/log/quagga/quagga.log
!
interface ens3
ipv6 nd suppress-ra
!
interface ens5
ipv6 nd suppress-ra
!
interface lo
!
interface <Vti_name1>
ip address ${vti_ipaddress1}
ipv6 nd suppress-ra
!
interface <Vti_name2>
ip address ${vti_ipaddress2}
ipv6 nd suppress-ra
!
ip route ${local_subnet} <Vti_name1>
ip route ${local_subnet} <Vti_name2>
!
ip forwarding
!
!
line vty
!
The bgpd config file is also required for BGP configuration. Define the following variables for bgpd:
${LOCAL_ASN}: The BGP ASN of your local network.${router-id_ipaddress}: The BGP ID of the local network.${local_subnet}: The local subnet that needs to be advertised.${bgp_peer-ip _network}: The /30 CIDR for the peer IP network in OCI.${neighbor_peer_ip_address}: The OCI BGP peer IP address.
These variables are used in the following configuration file excerpt from
/etc/quagga/bgpd.conf:
hostname <host-name>
router bgp ${LOCAL_ASN}
bgp router-id ${router-id_ipaddress}
network ${bgp_peer-ip _network}
network ${bgp_peer-ip _network}
network ${local_subnet}
neighbor ${neighbour_peer_ip_address} remote-as 31898
neighbor ${neighbour_peer_ip_address} ebgp-multihop 255
neighbor ${neighbour_peer_ip_address} next-hop-self
neighbor ${neighbour_peer_ip_address} remote-as 31898
neighbor ${neighbour_peer_ip_address} ebgp-multihop 255
neighbor ${neighbour_peer_ip_address} next-hop-self
log file bgpd.log
log stdout
Enabling strongswan to use routes and virtual IPs requires changes to
/etc/strongswan/strongswan.d/Charon.conf.
Uncomment the lines that read #install_routes = yes and
#install_virtual_ip = yes and change the values to "no" as
shown:
#Tunnels
install_routes = no
#Install virtual IP addresses.
install_virtual_ip = no
Use the following commands to enable and start service for zebra and BGPD:
systemctl start zebra
systemctl enable zebra
systemctl start bgpd
systemctl enable bgpd