vyos-documentation/docs/configuration/vpn/ipsec/ipsec_general.rst

.. _ipsec_general:

#########################
IPsec General Information
#########################

***********************
Information about IPsec
***********************

IPsec is the framework used to secure data.
IPsec accomplishes these goals by providing authentication,
encryption of IP network packets, key exchange, and key management.
VyOS uses Strongswan package to implement IPsec.

**Authentication Header (AH)** is defined in  :rfc:`4302`. It creates
a hash using the IP header and data payload, and prepends it to the
packet. This hash is used to validate that the data has not been
changed during transfer over the network.

**Encapsulating Security Payload (ESP)** is defined in :rfc:`4303`.
It provides encryption and authentication of the data.


There are two IPsec modes:
    **IPsec Transport Mode**:
        In transport mode, an IPSec header (AH or ESP) is inserted
        between the IP header and the upper layer protocol header.

    **IPsec Tunnel Mode:**
        In tunnel mode, the original IP packet is encapsulated in
        another IP datagram, and an IPsec header (AH or ESP) is
        inserted between the outer and inner headers.

.. figure:: /_static/images/ESP_AH.png
   :scale: 80 %
   :alt: AH and ESP in Transport Mode and Tunnel Mode

***************************
IKE (Internet Key Exchange)
***************************
The default IPsec method for secure key negotiation is the Internet Key
Exchange (IKE) protocol. IKE is designed to provide mutual authentication
of systems, as well as to establish a shared secret key to create IPsec
security associations. A security association (SA) includes all relevant
attributes of the connection, including the cryptographic algorithm used,
the IPsec mode, the encryption key, and other parameters related to the
transmission of data over the VPN connection.

IKEv1
=====

IKEv1 is the older version and is still used today. Nowadays, most
manufacturers recommend using IKEv2 protocol.

IKEv1 is described in the next RFCs: :rfc:`2409` (IKE), :rfc:`3407`
(IPsec DOI), :rfc:`3947` (NAT-T), :rfc:`3948` (UDP Encapsulation
of ESP Packets), :rfc:`3706` (DPD)

IKEv1 operates in two phases to establish these IKE and IPsec SAs:
    * **Phase 1** provides mutual authentication of the IKE peers and
      establishment of the session key. This phase creates an IKE SA (a
      security association for IKE) using a DH exchange, cookies, and an
      ID exchange. Once an IKE SA is established, all IKE communication
      between the initiator and responder is protected with encryption
      and an integrity check that is authenticated. The purpose of IKE
      phase 1 is to facilitate a secure channel between the peers so that
      phase 2 negotiations can occur securely. IKE phase 1 offers two modes:
      Main and Aggressive.

        * **Main Mode** is used for site-to-site VPN connections.
        
        * **Aggressive Mode** is used for remote access VPN connections.

    * **Phase 2** provides for the negotiation and establishment of the
      IPsec SAs using ESP or AH to protect IP data traffic.

IKEv2
=====

IKEv2 is described in :rfc:`7296`. The biggest difference between IKEv1 and
IKEv2 is that IKEv2 is much simpler and more reliable than IKEv1 because
fewer messages are exchanged during the establishment of the VPN and
additional security capabilities are available.


IKE Authentication
==================

VyOS supports 3 authentication methods.
    * **Pre-shared keys**: In this method, both peers of the IPsec
      tunnel must have the same preshared keys.
    * **Digital certificates**: PKI is used in this method.
    * **RSA-keys**: If the RSA-keys method is used in your IKE policy,
      you need to make sure each peer has the other peer’s public keys.

*************************
DPD (Dead Peer Detection)
*************************

This is a mechanism used to detect when a VPN peer is no longer active.
This mechanism has different algorithms in IKEv1 and IKEv2 in VyOS.
DPD Requests are sent as ISAKMP R-U-THERE messages and DPD Responses
are sent as ISAKMP R-U-THERE-ACK messages. In IKEv1, DPD sends messages
every configured interval. The remote peer is considered unreachable
if no response to these packets is received within the DPD timeout.
In IKEv2, DPD sends messages every configured interval. If one request
is not responded, Strongswan execute its retransmission algorithm with
its timers.  `IKEv2 Retransmission`_

*****************
Configuration IKE
*****************

IKE (Internet Key Exchange) Attributes
======================================

VyOS IKE group has the next options:

.. cfgcmd:: set vpn ipsec ike-group <name> close-action <action>

  Defines the action to take if the remote peer unexpectedly
  closes a CHILD_SA:

 * **none** - Set action to none (default),
 * **trap** - Installs a trap policy (IPsec policy without Security
   Association) for the CHILD_SA and traffic matching these policies
   will trigger acquire events that cause the daemon to establish the
   required IKE/IPsec SAs.
 * **start** - Tries to immediately re-create the CHILD_SA.

.. cfgcmd:: set vpn ipsec ike-group <name> ikev2-reauth

  Whether rekeying of an IKE_SA should also reauthenticate
  the peer. In IKEv1, reauthentication is always done.
  Setting this parameter enables remote host re-authentication
  during an IKE rekey.

.. cfgcmd:: set vpn ipsec ike-group <name> key-exchange

  Which protocol should be used to initialize the connection
  If not set both protocols are handled and connections will
  use IKEv2 when initiating, but accept any protocol version
  when responding:

 * **ikev1** - Use IKEv1 for Key Exchange.
 * **ikev2** - Use IKEv2 for Key Exchange.

.. cfgcmd:: set vpn ipsec ike-group <name> lifetime

  IKE lifetime in seconds <0-86400> (default 28800).

.. cfgcmd:: set vpn ipsec ike-group <name> mode

  IKEv1 Phase 1 Mode Selection:

 * **main** - Use Main mode for Key Exchanges in the IKEv1 Protocol
   (Recommended Default).
 * **aggressive** - Use Aggressive mode for Key Exchanges in the IKEv1
   protocol aggressive mode is much more insecure compared to Main mode.

.. cfgcmd:: set vpn ipsec ike-group <name> proposal <number> dh-group <dh-group number>

  Dh-group. Default value is **2**.

.. cfgcmd:: set vpn ipsec ike-group <name> proposal <number> encryption <encryption>

  Encryption algorithm. Default value is **aes128**.

.. cfgcmd:: set vpn ipsec ike-group <name> proposal <number> hash <hash>

  Hash algorithm. Default value is **sha1**.

.. cfgcmd:: set vpn ipsec ike-group <name> proposal <number> prf <prf>

  Pseudo-random function.


DPD (Dead Peer Detection) Configuration
=======================================

.. cfgcmd:: set vpn ipsec ike-group <name> dead-peer-detection action <action>

  Action to perform for this CHILD_SA on DPD timeout.

  * **trap** - Installs a trap policy (IPsec policy without Security
    Association), which will catch matching traffic and tries to
    re-negotiate the tunnel on-demand.
  * **clear** - Closes the CHILD_SA and does not take further action
    (default).
  * **restart** - Immediately tries to re-negotiate the CHILD_SA
    under a fresh IKE_SA.

.. cfgcmd:: set vpn ipsec ike-group <name> dead-peer-detection interval <interval>

  Keep-alive interval in seconds <2-86400> (default 30).

.. cfgcmd:: set vpn ipsec ike-group <name> dead-peer-detection timeout <timeout>

  Keep-alive timeout in seconds <2-86400> (default 120) **IKEv1 only**

ESP (Encapsulating Security Payload) Attributes
===============================================

In VyOS, ESP attributes are specified through ESP groups.
Multiple proposals can be specified in a single group.

VyOS ESP group has the next options:

.. cfgcmd:: set vpn ipsec esp-group <name> compression

  Enables the  IPComp(IP Payload Compression) protocol which allows
  compressing the content of IP packets.

.. cfgcmd:: set vpn ipsec esp-group <name> disable-rekey

  Do not locally initiate a re-key of the SA, remote peer must
  re-key before expiration.

.. cfgcmd:: set vpn ipsec esp-group <name> life-bytes <bytes>

  ESP life in bytes <1024-26843545600000>. Number of bytes
  transmitted over an IPsec SA before it expires.

.. cfgcmd:: set vpn ipsec esp-group <name> life-packets <packets>

  ESP life in packets <1000-26843545600000>.
  Number of packets transmitted over an IPsec SA before it expires.

.. cfgcmd:: set vpn ipsec esp-group <name> lifetime <timeout>

  ESP lifetime in seconds <30-86400> (default 3600).
  How long a particular instance of a connection (a set of
  encryption/authentication keys for user packets) should last,
  from successful negotiation to expiry.

.. cfgcmd:: set vpn ipsec esp-group <name> mode <mode>

  The type of the connection:

  * **tunnel** - Tunnel mode (default).
  * **transport** - Transport mode.

.. cfgcmd:: set vpn ipsec esp-group <name> pfs < dh-group>

  Whether Perfect Forward Secrecy of keys is desired on the
  connection's keying channel and defines a Diffie-Hellman group for
  PFS:

 * **enable** - Inherit Diffie-Hellman group from IKE group (default).
 * **disable** - Disable PFS.
 * **<dh-group>** - Defines a Diffie-Hellman group for PFS.

.. cfgcmd:: set vpn ipsec esp-group <name> proposal <number> encryption <encryption>

  Encryption algorithm. Default value is **aes128**.

.. cfgcmd:: set vpn ipsec esp-group <name> proposal <number> hash <hash>

  Hash algorithm. Default value is **sha1**.

Global IPsec Settings
=====================

.. cfgcmd:: set vpn ipsec interface <name>

  Interface name to restrict outbound IPsec policies. There is a possibility
  to specify multiple interfaces. If an interfaces are not specified, IPsec
  policies apply to all interfaces.


.. cfgcmd:: set vpn ipsec log level <number>

  Level of logging. Default value is **0**.

.. cfgcmd:: set vpn ipsec log subsystem <name>

  Subsystem of the daemon.

Options
=======

.. cfgcmd:: set vpn ipsec options disable-route-autoinstall

  Do not automatically install routes to remote
  networks.

.. cfgcmd:: set vpn ipsec options flexvpn

  Allows FlexVPN vendor ID payload (IKEv2 only). Send the Cisco
  FlexVPN vendor ID payload (IKEv2 only), which is required in order to make
  Cisco brand devices allow negotiating a local traffic selector (from
  strongSwan's point of view) that is not the assigned virtual IP address if
  such an address is requested by strongSwan. Sending the Cisco FlexVPN
  vendor ID prevents the peer from narrowing the initiator's local traffic
  selector and allows it to e.g. negotiate a TS of 0.0.0.0/0 == 0.0.0.0/0
  instead. This has been tested with a "tunnel mode ipsec ipv4" Cisco
  template but should also work for GRE encapsulation.

.. cfgcmd:: set vpn ipsec options interface <name>

  Interface Name to use. The name of the interface on which
  virtual IP addresses should be installed. If not specified the addresses
  will be installed on the outbound interface.

.. cfgcmd:: set vpn ipsec options virtual-ip

  Allows the installation of virtual-ip addresses.

IKEv2 Retransmission
====================

If the peer does not respond on DPD packet, the router starts retransmission procedure.

The following formula is used to calculate the timeout:

.. code-block:: none

  relative timeout = timeout * base ^ (attempts-1)

.. cfgcmd:: set vpn ipsec options retransmission attempts

  Number of attempts before the peer is considered to be in the down state.
  Default value is **5**.

.. cfgcmd:: set vpn ipsec options retransmission base

  Base number of exponential backoff. Default value is **1.8**.

.. cfgcmd:: set vpn ipsec options retransmission timeout

  Timeout in seconds before the first retransmission. Default value is **4**.

Using the default values, packets are retransmitted as follows:

+-----------+-------------+------------------+------------------+
| Attempts  | Formula     | Relative timeout | Absolute timeout |
+-----------+-------------+------------------+------------------+
| 1         | 4 * 1.8 ^ 0 | 4s               | 4s               |
+-----------+-------------+------------------+------------------+
| 2         | 4 * 1.8 ^ 1 | 7s               | 11s              |
+-----------+-------------+------------------+------------------+
| 3         | 4 * 1.8 ^ 2 | 13s              | 24s              |
+-----------+-------------+------------------+------------------+
| 4         | 4 * 1.8 ^ 3 | 23s              | 47s              |
+-----------+-------------+------------------+------------------+
| 5         | 4 * 1.8 ^ 4 | 42s              | 89s              |
+-----------+-------------+------------------+------------------+
| peer down | 4 * 1.8 ^ 5 | 76s              | 165s             |
+-----------+-------------+------------------+------------------+