Chapter 5. Setting up an IPsec VPN

Procedure

1. Install the libreswan packages:

   # yum install libreswan

2. If you are re-installing Libreswan, remove its old database files and create a new database:

   # systemctl stop ipsec
   # rm /etc/ipsec.d/*db
   # ipsec initnss

3. Start the ipsec service, and enable the service to be started automatically on boot:

   # systemctl enable ipsec --now

4. Configure the firewall to allow 500 and 4500/UDP ports for the IKE, ESP, and AH protocols by adding the ipsec service:

   # firewall-cmd --add-service="ipsec"
   # firewall-cmd --runtime-to-permanent

Procedure

1. Generate a raw RSA key pair on each host:

   # ipsec newhostkey

2. The previous step returned the generated key’s ckaid. Use that ckaid with the following command on left, for example:

   # ipsec showhostkey --left --ckaid 2d3ea57b61c9419dfd6cf43a1eb6cb306c0e857d

   The output of the previous command generated the leftrsasigkey= line required for the configuration. Do the same on the second host (right):

   # ipsec showhostkey --right --ckaid a9e1f6ce9ecd3608c24e8f701318383f41798f03

3. In the /etc/ipsec.d/ directory, create a new my_host-to-host.conf file. Write the RSA host keys from the output of the ipsec showhostkey commands in the previous step to the new file. For example:

   conn mytunnel
       leftid=@west
       left=192.1.2.23
       leftrsasigkey=0sAQOrlo+hOafUZDlCQmXFrje/oZm [...] W2n417C/4urYHQkCvuIQ==
       rightid=@east
       right=192.1.2.45
       rightrsasigkey=0sAQO3fwC6nSSGgt64DWiYZzuHbc4 [...] D/v8t5YTQ==
       authby=rsasig

4. After importing keys, restart the ipsec service:

   # systemctl restart ipsec

5. Load the connection:

   # ipsec auto --add mytunnel

6. Establish the tunnel:

   # ipsec auto --up mytunnel

7. To automatically start the tunnel when the ipsec service is started, add the following line to the connection definition:

   auto=start

Procedure

1. Copy the file with the configuration of your host-to-host VPN to a new file, for example:

   # cp /etc/ipsec.d/my_host-to-host.conf /etc/ipsec.d/my_site-to-site.conf

2. Add the subnet configuration to the file created in the previous step, for example:

   conn mysubnet
        also=mytunnel
        leftsubnet=192.0.1.0/24
        rightsubnet=192.0.2.0/24
        auto=start
   
   conn mysubnet6
        also=mytunnel
        leftsubnet=2001:db8:0:1::/64
        rightsubnet=2001:db8:0:2::/64
        auto=start
   
   # the following part of the configuration file is the same for both host-to-host and site-to-site connections:
   
   conn mytunnel
       leftid=@west
       left=192.1.2.23
       leftrsasigkey=0sAQOrlo+hOafUZDlCQmXFrje/oZm [...] W2n417C/4urYHQkCvuIQ==
       rightid=@east
       right=192.1.2.45
       rightrsasigkey=0sAQO3fwC6nSSGgt64DWiYZzuHbc4 [...] D/v8t5YTQ==
       authby=rsasig

Procedure

1. On each node, import PKCS #12 files. This step requires the password used to generate the PKCS #12 files:

   # ipsec import nodeXXX.p12

2. Create the following three connection definitions for the IPsec required (private), IPsec optional (private-or-clear), and No IPsec (clear) profiles:

   # cat /etc/ipsec.d/mesh.conf
   conn clear
   	auto=ondemand 1
   	type=passthrough
   	authby=never
   	left=%defaultroute
   	right=%group
   
   conn private
   	auto=ondemand
   	type=transport
   	authby=rsasig
   	failureshunt=drop
   	negotiationshunt=drop
   	ikev2=insist
   	left=%defaultroute
   	leftcert=nodeXXXX
   	leftid=%fromcert 2
   	rightid=%fromcert
   	right=%opportunisticgroup
   
   conn private-or-clear
   	auto=ondemand
   	type=transport
   	authby=rsasig
   	failureshunt=passthrough
   	negotiationshunt=passthrough
   	# left
   	left=%defaultroute
   	leftcert=nodeXXXX 3
   	leftid=%fromcert
   	leftrsasigkey=%cert
   	# right
   	rightrsasigkey=%cert
   	rightid=%fromcert
   	right=%opportunisticgroup

Verification

1. Open an IPsec tunnel by using the ping command:

   # ping <nodeYYY>

2. Display the NSS database with the imported certification:

   # certutil -L -d sql:/etc/ipsec.d
   
   Certificate Nickname    Trust Attributes
                           SSL,S/MIME,JAR/XPI
   
   west                    u,u,u
   ca                      CT,,

3. See which tunnels are open on the node:

   # ipsec trafficstatus
   006 #2: "private#10.15.0.0/16"[1] ...<nodeYYY>, type=ESP, add_time=1691399301, inBytes=512, outBytes=512, maxBytes=2^63B, id='C=US, ST=NC, O=Example Organization, CN=east'

Procedure

1. Install the libreswan packages:

   # yum install libreswan

2. If you are re-installing Libreswan, remove its old NSS database:

   # systemctl stop ipsec
   # rm /etc/ipsec.d/*db

3. Start the ipsec service, and enable the service to be started automatically on boot:

   # systemctl enable ipsec --now

4. Configure the firewall to allow 500 and 4500 UDP ports for the IKE, ESP, and AH protocols by adding the ipsec service:

   # firewall-cmd --add-service="ipsec"
   # firewall-cmd --runtime-to-permanent

5. Switch the system to FIPS mode:

   # fips-mode-setup --enable

6. Restart your system to allow the kernel to switch to FIPS mode:

   # reboot

Verification

1. Confirm Libreswan is running in FIPS mode:

   # ipsec whack --fipsstatus
   000 FIPS mode enabled

2. Alternatively, check entries for the ipsec unit in the systemd journal:

   $ journalctl -u ipsec
   ...
   Jan 22 11:26:50 localhost.localdomain pluto[3076]: FIPS Product: YES
   Jan 22 11:26:50 localhost.localdomain pluto[3076]: FIPS Kernel: YES
   Jan 22 11:26:50 localhost.localdomain pluto[3076]: FIPS Mode: YES

3. To see the available algorithms in FIPS mode:

   # ipsec pluto --selftest 2>&1 | head -11
   FIPS Product: YES
   FIPS Kernel: YES
   FIPS Mode: YES
   NSS DB directory: sql:/etc/ipsec.d
   Initializing NSS
   Opening NSS database "sql:/etc/ipsec.d" read-only
   NSS initialized
   NSS crypto library initialized
   FIPS HMAC integrity support [enabled]
   FIPS mode enabled for pluto daemon
   NSS library is running in FIPS mode
   FIPS HMAC integrity verification self-test passed

4. To query disabled algorithms in FIPS mode:

   # ipsec pluto --selftest 2>&1 | grep disabled
   Encryption algorithm CAMELLIA_CTR disabled; not FIPS compliant
   Encryption algorithm CAMELLIA_CBC disabled; not FIPS compliant
   Encryption algorithm SERPENT_CBC disabled; not FIPS compliant
   Encryption algorithm TWOFISH_CBC disabled; not FIPS compliant
   Encryption algorithm TWOFISH_SSH disabled; not FIPS compliant
   Encryption algorithm NULL disabled; not FIPS compliant
   Encryption algorithm CHACHA20_POLY1305 disabled; not FIPS compliant
   Hash algorithm MD5 disabled; not FIPS compliant
   PRF algorithm HMAC_MD5 disabled; not FIPS compliant
   PRF algorithm AES_XCBC disabled; not FIPS compliant
   Integrity algorithm HMAC_MD5_96 disabled; not FIPS compliant
   Integrity algorithm HMAC_SHA2_256_TRUNCBUG disabled; not FIPS compliant
   Integrity algorithm AES_XCBC_96 disabled; not FIPS compliant
   DH algorithm MODP1024 disabled; not FIPS compliant
   DH algorithm MODP1536 disabled; not FIPS compliant
   DH algorithm DH31 disabled; not FIPS compliant

5. To list all allowed algorithms and ciphers in FIPS mode:

   # ipsec pluto --selftest 2>&1 | grep ESP | grep FIPS | sed "s/^.*FIPS//"
   {256,192,*128}  aes_ccm, aes_ccm_c
   {256,192,*128}  aes_ccm_b
   {256,192,*128}  aes_ccm_a
   [*192]  3des
   {256,192,*128}  aes_gcm, aes_gcm_c
   {256,192,*128}  aes_gcm_b
   {256,192,*128}  aes_gcm_a
   {256,192,*128}  aesctr
   {256,192,*128}  aes
   {256,192,*128}  aes_gmac
   sha, sha1, sha1_96, hmac_sha1
   sha512, sha2_512, sha2_512_256, hmac_sha2_512
   sha384, sha2_384, sha2_384_192, hmac_sha2_384
   sha2, sha256, sha2_256, sha2_256_128, hmac_sha2_256
   aes_cmac
   null
   null, dh0
   dh14
   dh15
   dh16
   dh17
   dh18
   ecp_256, ecp256
   ecp_384, ecp384
   ecp_521, ecp521

Procedure

1. Enable password protection for the NSS database for Libreswan:

   # certutil -N -d sql:/etc/ipsec.d
   Enter Password or Pin for "NSS Certificate DB":
   Enter a password which will be used to encrypt your keys.
   The password should be at least 8 characters long,
   and should contain at least one non-alphabetic character.
   
   Enter new password:

2. Create the /etc/ipsec.d/nsspassword file that containins the password you have set in the previous step, for example:

   # cat /etc/ipsec.d/nsspassword
   NSS Certificate DB:_<password>_

   The nsspassword file use the following syntax:

   <token_1>:<password1>
   <token_2>:<password2>

   The default NSS software token is NSS Certificate DB. If your system is running in FIPS mode, the name of the token is NSS FIPS 140-2 Certificate DB.

3. Depending on your scenario, either start or restart the ipsec service after you finish the nsspassword file:

   # systemctl restart ipsec

Verification

1. Check that the ipsec service is running after you have added a non-empty password to its NSS database:

   # systemctl status ipsec
   ● ipsec.service - Internet Key Exchange (IKE) Protocol Daemon for IPsec
      Loaded: loaded (/usr/lib/systemd/system/ipsec.service; enabled; vendor preset: disable>
      Active: active (running)...

Procedure

1. Add the following option to the /etc/ipsec.conf file in the config setup section:

   listen-tcp=yes

2. To use TCP encapsulation as a fallback option when the first attempt over UDP fails, add the following two options to the client’s connection definition:

   enable-tcp=fallback
   tcp-remoteport=4500

   Alternatively, if you know that UDP is permanently blocked, use the following options in the client’s connection configuration:

   enable-tcp=yes
   tcp-remoteport=4500

Procedure

1. Edit the Libreswan configuration file in the /etc/ipsec.d/ directory of the connection that should use automatic detection of ESP hardware offload support.
2. Ensure the nic-offload parameter is not set in the connection’s settings.

3. If you removed nic-offload, restart the ipsec service:

   # systemctl restart ipsec

Verification

1. Display the tx_ipsec and rx_ipsec counters of the Ethernet device the IPsec connection uses:

   # ethtool -S enp1s0 | egrep "_ipsec"
        tx_ipsec: 10
        rx_ipsec: 10

2. Send traffic through the IPsec tunnel. For example, ping a remote IP address:

   # ping -c 5 remote_ip_address

3. Display the tx_ipsec and rx_ipsec counters of the Ethernet device again:

   # ethtool -S enp1s0 | egrep "_ipsec"
        tx_ipsec: 15
        rx_ipsec: 15

   If the counter values have increased, ESP hardware offload works.

Procedure

1. Enable ESP hardware offload support on the network bond:

   # nmcli connection modify bond0 ethtool.feature-esp-hw-offload on

   This command enables ESP hardware offload support on the bond0 connection.

2. Reactivate the bond0 connection:

   # nmcli connection up bond0

3. Edit the Libreswan configuration file in the /etc/ipsec.d/ directory of the connection that should use ESP hardware offload, and append the nic-offload=yes statement to the connection entry:

   conn example
       ...
       nic-offload=yes

4. Restart the ipsec service:

   # systemctl restart ipsec

1. Display the active port of the bond:

   # grep "Currently Active Slave" /proc/net/bonding/bond0
   Currently Active Slave: enp1s0

2. Display the tx_ipsec and rx_ipsec counters of the active port:

   # ethtool -S enp1s0 | egrep "_ipsec"
        tx_ipsec: 10
        rx_ipsec: 10

3. Send traffic through the IPsec tunnel. For example, ping a remote IP address:

   # ping -c 5 remote_ip_address

4. Display the tx_ipsec and rx_ipsec counters of the active port again:

   # ethtool -S enp1s0 | egrep "_ipsec"
        tx_ipsec: 15
        rx_ipsec: 15

   If the counter values have increased, ESP hardware offload works.

1. Reload the vpn.example.com connection:

   # ipsec auto --add vpn.example.com
   002 added connection description "vpn.example.com"

2. Next, initiate the VPN connection:

   # ipsec auto --up vpn.example.com

Procedure

1. Press the Super key, type Settings, and press Enter to open the control-center application.
2. Select the Network entry on the left.
3. Click the + icon.
4. Select VPN.

5. Select the Identity menu entry to see the basic configuration options:

   General

   Gateway — The name or IP address of the remote VPN gateway.

   Authentication

   Type

   • IKEv2 (Certificate)- client is authenticated by certificate. It is more secure (default).

   • IKEv1 (XAUTH) - client is authenticated by user name and password, or a pre-shared key (PSK).

     The following configuration settings are available under the Advanced section:

     Figure 5.1. Advanced options of a VPN connection

     
     Warning

     When configuring an IPsec-based VPN connection using the gnome-control-center application, the Advanced dialog displays the configuration, but it does not allow any changes. As a consequence, users cannot change any advanced IPsec options. Use the nm-connection-editor or nmcli tools instead to perform configuration of the advanced properties.

     Identification

   • Domain — If required, enter the Domain Name.

     Security

   • Phase1 Algorithms — corresponds to the ike Libreswan parameter — enter the algorithms to be used to authenticate and set up an encrypted channel.

   • Phase2 Algorithms — corresponds to the esp Libreswan parameter — enter the algorithms to be used for the IPsec negotiations.

     Check the Disable PFS field to turn off Perfect Forward Secrecy (PFS) to ensure compatibility with old servers that do not support PFS.

   • Phase1 Lifetime — corresponds to the ikelifetime Libreswan parameter — how long the key used to encrypt the traffic will be valid.

   • Phase2 Lifetime — corresponds to the salifetime Libreswan parameter — how long a particular instance of a connection should last before expiring.

     Note that the encryption key should be changed from time to time for security reasons.

   • Remote network — corresponds to the rightsubnet Libreswan parameter — the destination private remote network that should be reached through the VPN.

     Check the narrowing field to enable narrowing. Note that it is only effective in IKEv2 negotiation.

   • Enable fragmentation — corresponds to the fragmentation Libreswan parameter — whether or not to allow IKE fragmentation. Valid values are yes (default) or no.
   • Enable Mobike — corresponds to the mobike Libreswan parameter — whether to allow Mobility and Multihoming Protocol (MOBIKE, RFC 4555) to enable a connection to migrate its endpoint without needing to restart the connection from scratch. This is used on mobile devices that switch between wired, wireless, or mobile data connections. The values are no (default) or yes.

6. Select the IPv4 menu entry:

   IPv4 Method

   • Automatic (DHCP) — Choose this option if the network you are connecting to uses a DHCP server to assign dynamic IP addresses.
   • Link-Local Only — Choose this option if the network you are connecting to does not have a DHCP server and you do not want to assign IP addresses manually. Random addresses will be assigned as per RFC 3927 with prefix 169.254/16.
   • Manual — Choose this option if you want to assign IP addresses manually.

   • Disable — IPv4 is disabled for this connection.

     DNS

     In the DNS section, when Automatic is ON, switch it to OFF to enter the IP address of a DNS server you want to use separating the IPs by comma.

     Routes

     Note that in the Routes section, when Automatic is ON, routes from DHCP are used, but you can also add additional static routes. When OFF, only static routes are used.

   • Address — Enter the IP address of a remote network or host.
   • Netmask — The netmask or prefix length of the IP address entered above.
   • Gateway — The IP address of the gateway leading to the remote network or host entered above.

   • Metric — A network cost, a preference value to give to this route. Lower values will be preferred over higher values.

     Use this connection only for resources on its network

     Select this check box to prevent the connection from becoming the default route. Selecting this option means that only traffic specifically destined for routes learned automatically over the connection or entered here manually is routed over the connection.

7. To configure IPv6 settings in a VPN connection, select the IPv6 menu entry:

   IPv6 Method

   • Automatic — Choose this option to use IPv6 Stateless Address AutoConfiguration (SLAAC) to create an automatic, stateless configuration based on the hardware address and Router Advertisements (RA).
   • Automatic, DHCP only — Choose this option to not use RA, but request information from DHCPv6 directly to create a stateful configuration.
   • Link-Local Only — Choose this option if the network you are connecting to does not have a DHCP server and you do not want to assign IP addresses manually. Random addresses will be assigned as per RFC 4862 with prefix FE80::0.
   • Manual — Choose this option if you want to assign IP addresses manually.

   • Disable — IPv6 is disabled for this connection.

     Note that DNS, Routes, Use this connection only for resources on its network are common to IPv4 settings.

8. Once you have finished editing the VPN connection, click the Add button to customize the configuration or the Apply button to save it for the existing one.
9. Switch the profile to ON to active the VPN connection.