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			29 KiB
		
	
	
	
		
			ReStructuredText
		
	
	
	
	
	
| .. _nat44:
 | ||
| 
 | ||
| #####
 | ||
| NAT44
 | ||
| #####
 | ||
| 
 | ||
| :abbr:`NAT (Network Address Translation)` is a common method of
 | ||
| remapping one IP address space into another by modifying network address
 | ||
| information in the IP header of packets while they are in transit across
 | ||
| a traffic routing device. The technique was originally used as a
 | ||
| shortcut to avoid the need to readdress every host when a network was
 | ||
| moved. It has become a popular and essential tool in conserving global
 | ||
| address space in the face of IPv4 address exhaustion. One
 | ||
| Internet-routable IP address of a NAT gateway can be used for an entire
 | ||
| private network.
 | ||
| 
 | ||
| IP masquerading is a technique that hides an entire IP address space,
 | ||
| usually consisting of private IP addresses, behind a single IP address
 | ||
| in another, usually public address space. The hidden addresses are
 | ||
| changed into a single (public) IP address as the source address of the
 | ||
| outgoing IP packets so they appear as originating not from the hidden
 | ||
| host but from the routing device itself. Because of the popularity of
 | ||
| this technique to conserve IPv4 address space, the term NAT has become
 | ||
| virtually synonymous with IP masquerading.
 | ||
| 
 | ||
| As network address translation modifies the IP address information in
 | ||
| packets, NAT implementations may vary in their specific behavior in
 | ||
| various addressing cases and their effect on network traffic. The
 | ||
| specifics of NAT behavior are not commonly documented by vendors of
 | ||
| equipment containing NAT implementations.
 | ||
| 
 | ||
| The computers on an internal network can use any of the addresses set
 | ||
| aside by the :abbr:`IANA (Internet Assigned Numbers Authority)` for
 | ||
| private addressing (see :rfc:`1918`). These reserved IP addresses are
 | ||
| not in use on the Internet, so an external machine will not directly
 | ||
| route to them. The following addresses are reserved for private use:
 | ||
| 
 | ||
| * 10.0.0.0 to 10.255.255.255 (CIDR: 10.0.0.0/8)
 | ||
| * 172.16.0.0 to 172.31.255.255 (CIDR: 172.16.0.0/12)
 | ||
| * 192.168.0.0 to 192.168.255.255 (CIDR: 192.168.0.0/16)
 | ||
| 
 | ||
| 
 | ||
| If an ISP deploys a :abbr:`CGN (Carrier-grade NAT)`, and uses
 | ||
| :rfc:`1918` address space to number customer gateways, the risk of
 | ||
| address collision, and therefore routing failures, arises when the
 | ||
| customer network already uses an :rfc:`1918` address space.
 | ||
| 
 | ||
| This prompted some ISPs to develop a policy within the :abbr:`ARIN
 | ||
| (American Registry for Internet Numbers)` to allocate new private
 | ||
| address space for CGNs, but ARIN deferred to the IETF before
 | ||
| implementing the policy indicating that the matter was not a typical
 | ||
| allocation issue but a reservation of addresses for technical purposes
 | ||
| (per :rfc:`2860`).
 | ||
| 
 | ||
| IETF published :rfc:`6598`, detailing a shared address space for use in
 | ||
| ISP CGN deployments that can handle the same network prefixes occurring
 | ||
| both on inbound and outbound interfaces. ARIN returned address space to
 | ||
| the :abbr:`IANA (Internet Assigned Numbers Authority)` for this
 | ||
| allocation.
 | ||
| 
 | ||
| The allocated address block is 100.64.0.0/10.
 | ||
| 
 | ||
| Devices evaluating whether an IPv4 address is public must be updated to
 | ||
| recognize the new address space. Allocating more private IPv4 address
 | ||
| space for NAT devices might prolong the transition to IPv6.
 | ||
| 
 | ||
| Overview
 | ||
| ========
 | ||
| 
 | ||
| Different NAT Types
 | ||
| -------------------
 | ||
| 
 | ||
| .. _source-nat:
 | ||
| 
 | ||
| SNAT
 | ||
| ^^^^
 | ||
| 
 | ||
| :abbr:`SNAT (Source Network Address Translation)` is the most common
 | ||
| form of :abbr:`NAT (Network Address Translation)` and is typically
 | ||
| referred to simply as NAT. To be more correct, what most people refer
 | ||
| to as :abbr:`NAT (Network Address Translation)` is actually the process
 | ||
| of :abbr:`PAT (Port Address Translation)`, or NAT overload. SNAT is
 | ||
| typically used by internal users/private hosts to access the Internet
 | ||
| - the source address is translated and thus kept private.
 | ||
| 
 | ||
| .. _destination-nat:
 | ||
| 
 | ||
| DNAT
 | ||
| ^^^^
 | ||
| 
 | ||
| :abbr:`DNAT (Destination Network Address Translation)` changes the
 | ||
| destination address of packets passing through the router, while
 | ||
| :ref:`source-nat` changes the source address of packets. DNAT is
 | ||
| typically used when an external (public) host needs to initiate a
 | ||
| session with an internal (private) host. A customer needs to access a
 | ||
| private service behind the routers public IP. A connection is
 | ||
| established with the routers public IP address on a well known port and
 | ||
| thus all traffic for this port is rewritten to address the internal
 | ||
| (private) host.
 | ||
| 
 | ||
| .. _bidirectional-nat:
 | ||
| 
 | ||
| Bidirectional NAT
 | ||
| ^^^^^^^^^^^^^^^^^
 | ||
| 
 | ||
| This is a common scenario where both :ref:`source-nat` and
 | ||
| :ref:`destination-nat` are configured at the same time. It's commonly
 | ||
| used when internal (private) hosts need to establish a connection with
 | ||
| external resources and external systems need to access internal
 | ||
| (private) resources.
 | ||
| 
 | ||
| NAT, Routing, Firewall Interaction
 | ||
| ----------------------------------
 | ||
| 
 | ||
| There is a very nice picture/explanation in the Vyatta documentation
 | ||
| which should be rewritten here.
 | ||
| 
 | ||
| NAT Ruleset
 | ||
| -----------
 | ||
| 
 | ||
| :abbr:`NAT (Network Address Translation)` is configured entirely on a
 | ||
| series of so called `rules`. Rules are numbered and evaluated by the
 | ||
| underlying OS in numerical order! The rule numbers can be changes by
 | ||
| utilizing the :cfgcmd:`rename` and :cfgcmd:`copy` commands.
 | ||
| 
 | ||
| .. note:: Changes to the NAT system only affect newly established
 | ||
|    connections. Already established connections are not affected.
 | ||
| 
 | ||
| .. hint:: When designing your NAT ruleset leave some space between
 | ||
|    consecutive rules for later extension. Your ruleset could start with
 | ||
|    numbers 10, 20, 30. You thus can later extend the ruleset and place
 | ||
|    new rules between existing ones.
 | ||
| 
 | ||
| Rules will be created for both :ref:`source-nat` and
 | ||
| :ref:`destination-nat`.
 | ||
| 
 | ||
| For :ref:`bidirectional-nat` a rule for both :ref:`source-nat` and
 | ||
| :ref:`destination-nat` needs to be created.
 | ||
| 
 | ||
| .. _traffic-filters:
 | ||
| 
 | ||
| Traffic Filters
 | ||
| ---------------
 | ||
| 
 | ||
| Traffic Filters are used to control which packets will have the defined
 | ||
| NAT rules applied. Five different filters can be applied within a NAT
 | ||
| rule.
 | ||
| 
 | ||
| * **outbound-interface** - applicable only to :ref:`source-nat`. It
 | ||
|   configures the interface which is used for the outside traffic that
 | ||
|   this translation rule applies to. Interface groups, inverted
 | ||
|   selection and wildcard, are also supported.
 | ||
| 
 | ||
|   Examples:
 | ||
| 
 | ||
|   .. code-block:: none
 | ||
| 
 | ||
|     set nat source rule 20 outbound-interface name eth0
 | ||
|     set nat source rule 30 outbound-interface name bond1*
 | ||
|     set nat source rule 20 outbound-interface name !vtun2
 | ||
|     set nat source rule 20 outbound-interface group GROUP1
 | ||
|     set nat source rule 20 outbound-interface group !GROUP2
 | ||
| 
 | ||
| 
 | ||
| * **inbound-interface** - applicable only to :ref:`destination-nat`. It
 | ||
|   configures the interface which is used for the inside traffic the
 | ||
|   translation rule applies to. Interface groups, inverted
 | ||
|   selection and wildcard, are also supported.
 | ||
| 
 | ||
|   Example:
 | ||
| 
 | ||
|   .. code-block:: none
 | ||
| 
 | ||
|     set nat destination rule 20 inbound-interface name eth0
 | ||
|     set nat destination rule 30 inbound-interface name bond1*
 | ||
|     set nat destination rule 20 inbound-interface name !vtun2
 | ||
|     set nat destination rule 20 inbound-interface group GROUP1
 | ||
|     set nat destination rule 20 inbound-interface group !GROUP2
 | ||
| 
 | ||
| 
 | ||
| * **protocol** - specify which types of protocols this translation rule
 | ||
|   applies to. Only packets matching the specified protocol are NATed.
 | ||
|   By default this applies to `all` protocols.
 | ||
| 
 | ||
|   Example:
 | ||
| 
 | ||
|   * Set SNAT rule 20 to only NAT TCP and UDP packets
 | ||
|   * Set DNAT rule 20 to only NAT UDP packets
 | ||
| 
 | ||
|   .. code-block:: none
 | ||
| 
 | ||
|     set nat source rule 20 protocol tcp_udp
 | ||
|     set nat destination rule 20 protocol udp
 | ||
| 
 | ||
| * **source** - specifies which packets the NAT translation rule applies
 | ||
|   to based on the packets source IP address and/or source port. Only
 | ||
|   matching packets are considered for NAT.
 | ||
| 
 | ||
|   Example:
 | ||
| 
 | ||
|   * Set SNAT rule 20 to only NAT packets arriving from the 192.0.2.0/24
 | ||
|     network
 | ||
|   * Set SNAT rule 30 to only NAT packets arriving from the 203.0.113.0/24
 | ||
|     network with a source port of 80 and 443
 | ||
| 
 | ||
|   .. code-block:: none
 | ||
| 
 | ||
|     set nat source rule 20 source address 192.0.2.0/24
 | ||
|     set nat source rule 30 source address 203.0.113.0/24
 | ||
|     set nat source rule 30 source port 80,443
 | ||
| 
 | ||
| 
 | ||
| * **destination** - specify which packets the translation will be
 | ||
|   applied to, only based on the destination address and/or port number
 | ||
|   configured.
 | ||
| 
 | ||
|   .. note:: If no destination is specified the rule will match on any
 | ||
|      destination address and port.
 | ||
| 
 | ||
|   Example:
 | ||
| 
 | ||
|   * Configure SNAT rule (40) to only NAT packets with a destination
 | ||
|     address of 192.0.2.1.
 | ||
| 
 | ||
|   .. code-block:: none
 | ||
| 
 | ||
|     set nat source rule 40 destination address 192.0.2.1
 | ||
| 
 | ||
| 
 | ||
| Address Conversion
 | ||
| ------------------
 | ||
| 
 | ||
| Every NAT rule has a translation command defined. The address defined
 | ||
| for the translation is the address used when the address information in
 | ||
| a packet is replaced.
 | ||
| 
 | ||
| Source Address
 | ||
| ^^^^^^^^^^^^^^
 | ||
| 
 | ||
| For :ref:`source-nat` rules the packets source address will be replaced
 | ||
| with the address specified in the translation command. A port
 | ||
| translation can also be specified and is part of the translation
 | ||
| address.
 | ||
| 
 | ||
| .. note:: The translation address must be set to one of the available
 | ||
|    addresses on the configured `outbound-interface` or it must be set to
 | ||
|    `masquerade` which will use the primary IP address of the
 | ||
|    `outbound-interface` as its translation address.
 | ||
| 
 | ||
| .. note:: When using NAT for a large number of host systems it
 | ||
|    recommended that a minimum of 1 IP address is used to NAT every 256
 | ||
|    private host systems. This is due to the limit of 65,000 port numbers
 | ||
|    available for unique translations and a reserving an average of
 | ||
|    200-300 sessions per host system.
 | ||
| 
 | ||
| Example:
 | ||
| 
 | ||
| * Define a discrete source IP address of 100.64.0.1 for SNAT rule 20
 | ||
| * Use address `masquerade` (the interfaces primary address) on rule 30
 | ||
| * For a large amount of private machines behind the NAT your address
 | ||
|   pool might to be bigger. Use any address in the range 100.64.0.10 -
 | ||
|   100.64.0.20 on SNAT rule 40 when doing the translation
 | ||
| 
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat source rule 20 translation address 100.64.0.1
 | ||
|   set nat source rule 30 translation address 'masquerade'
 | ||
|   set nat source rule 40 translation address 100.64.0.10-100.64.0.20
 | ||
| 
 | ||
| 
 | ||
| Destination Address
 | ||
| ^^^^^^^^^^^^^^^^^^^
 | ||
| 
 | ||
| For :ref:`destination-nat` rules the packets destination address will be
 | ||
| replaced by the specified address in the `translation address` command.
 | ||
| 
 | ||
| Example:
 | ||
| 
 | ||
| * DNAT rule 10 replaces the destination address of an inbound packet
 | ||
|   with 192.0.2.10
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat destination rule 10 translation address 192.0.2.10
 | ||
| 
 | ||
| 
 | ||
| Also, in :ref:`destination-nat`, redirection to localhost is supported.
 | ||
| The redirect statement is a special form of dnat which always translates
 | ||
| the destination address to the local host’s one.
 | ||
| 
 | ||
| Example of redirection:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat destination rule 10 translation redirect port 22
 | ||
| 
 | ||
| NAT Load Balance
 | ||
| ----------------
 | ||
| 
 | ||
| Advanced configuration can be used in order to apply source or destination NAT,
 | ||
| and within a single rule, be able to define multiple translated addresses,
 | ||
| so NAT balances the translations among them.
 | ||
| 
 | ||
| NAT Load Balance uses an algorithm that generates a hash and based on it, then
 | ||
| it applies corresponding translation. This hash can be generated randomly, or 
 | ||
| can use data from the ip header: source-address, destination-address,
 | ||
| source-port and/or destination-port. By default, it will generate the hash
 | ||
| randomly.
 | ||
| 
 | ||
| When defining the translated address, called ``backends``, a ``weight`` must
 | ||
| be configured. This lets the user define load balance distribution according
 | ||
| to their needs. Them sum of all the weights defined for the backends should
 | ||
| be equal to 100. In oder words, the weight defined for the backend is the
 | ||
| percentage of the connections that will receive such backend.
 | ||
| 
 | ||
| .. cfgcmd:: set nat [source | destination] rule <rule> load-balance hash
 | ||
|    [source-address | destination-address | source-port | destination-port
 | ||
|    | random]
 | ||
| .. cfgcmd:: set nat [source | destination] rule <rule> load-balance backend
 | ||
|   <x.x.x.x> weight <1-100>
 | ||
| 
 | ||
| 
 | ||
| Configuration Examples
 | ||
| ======================
 | ||
| 
 | ||
| To setup SNAT, we need to know:
 | ||
| 
 | ||
| * The internal IP addresses we want to translate
 | ||
| * The outgoing interface to perform the translation on
 | ||
| * The external IP address to translate to
 | ||
| 
 | ||
| In the example used for the Quick Start configuration above, we
 | ||
| demonstrate the following configuration:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat source rule 100 outbound-interface name 'eth0'
 | ||
|   set nat source rule 100 source address '192.168.0.0/24'
 | ||
|   set nat source rule 100 translation address 'masquerade'
 | ||
| 
 | ||
| Which generates the following configuration:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   rule 100 {
 | ||
|       outbound-interface {
 | ||
|           name eth0
 | ||
|       }
 | ||
|       source {
 | ||
|           address 192.168.0.0/24
 | ||
|       }
 | ||
|       translation {
 | ||
|           address masquerade
 | ||
|       }
 | ||
|   }
 | ||
| 
 | ||
| In this example, we use **masquerade** as the translation address
 | ||
| instead of an IP address. The **masquerade** target is effectively an
 | ||
| alias to say "use whatever IP address is on the outgoing interface",
 | ||
| rather than a statically configured IP address. This is useful if you
 | ||
| use DHCP for your outgoing interface and do not know what the external
 | ||
| address will be.
 | ||
| 
 | ||
| When using NAT for a large number of host systems it recommended that a
 | ||
| minimum of 1 IP address is used to NAT every 256 host systems. This is
 | ||
| due to the limit of 65,000 port numbers available for unique
 | ||
| translations and a reserving an average of 200-300 sessions per host
 | ||
| system.
 | ||
| 
 | ||
| Example: For an ~8,000 host network a source NAT pool of 32 IP addresses
 | ||
| is recommended.
 | ||
| 
 | ||
| A pool of addresses can be defined by using a hyphen between two IP
 | ||
| addresses:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat source rule 100 translation address '203.0.113.32-203.0.113.63'
 | ||
| 
 | ||
| .. _avoidng_leaky_nat:
 | ||
| 
 | ||
| Avoiding "leaky" NAT
 | ||
| --------------------
 | ||
| 
 | ||
| Linux netfilter will not NAT traffic marked as INVALID. This often
 | ||
| confuses people into thinking that Linux (or specifically VyOS) has a
 | ||
| broken NAT implementation because non-NATed traffic is seen leaving an
 | ||
| external interface. This is actually working as intended, and a packet
 | ||
| capture of the "leaky" traffic should reveal that the traffic is either
 | ||
| an additional TCP "RST", "FIN,ACK", or "RST,ACK" sent by client systems
 | ||
| after Linux netfilter considers the connection closed. The most common
 | ||
| is the additional TCP RST some host implementations send after
 | ||
| terminating a connection (which is implementation-specific).
 | ||
| 
 | ||
| In other words, connection tracking has already observed the connection
 | ||
| be closed and has transition the flow to INVALID to prevent attacks from
 | ||
| attempting to reuse the connection.
 | ||
| 
 | ||
| You can avoid the "leaky" behavior by using a firewall policy that drops
 | ||
| "invalid" state packets.
 | ||
| 
 | ||
| Having control over the matching of INVALID state traffic, e.g. the
 | ||
| ability to selectively log, is an important troubleshooting tool for
 | ||
| observing broken protocol behavior. For this reason, VyOS does not
 | ||
| globally drop invalid state traffic, instead allowing the operator to
 | ||
| make the determination on how the traffic is handled.
 | ||
| 
 | ||
| .. _hairpin_nat_reflection:
 | ||
| 
 | ||
| Hairpin NAT/NAT Reflection
 | ||
| --------------------------
 | ||
| 
 | ||
| A typical problem with using NAT and hosting public servers is the
 | ||
| ability for internal systems to reach an internal server using it's
 | ||
| external IP address. The solution to this is usually the use of
 | ||
| split-DNS to correctly point host systems to the internal address when
 | ||
| requests are made internally. Because many smaller networks lack DNS
 | ||
| infrastructure, a work-around is commonly deployed to facilitate the
 | ||
| traffic by NATing the request from internal hosts to the source address
 | ||
| of the internal interface on the firewall.
 | ||
| 
 | ||
| This technique is commonly referred to as NAT Reflection or Hairpin NAT.
 | ||
| 
 | ||
| Example:
 | ||
| 
 | ||
| * Redirect Microsoft RDP traffic from the outside (WAN, external) world
 | ||
|   via :ref:`destination-nat` in rule 100 to the internal, private host
 | ||
|   192.0.2.40.
 | ||
| 
 | ||
| * Redirect Microsoft RDP traffic from the internal (LAN, private)
 | ||
|   network via :ref:`destination-nat` in rule 110 to the internal,
 | ||
|   private host 192.0.2.40. We also need a :ref:`source-nat` rule 110 for
 | ||
|   the reverse path of the traffic. The internal network 192.0.2.0/24 is
 | ||
|   reachable via interface `eth0.10`.
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat destination rule 100 description 'Regular destination NAT from external'
 | ||
|   set nat destination rule 100 destination port '3389'
 | ||
|   set nat destination rule 100 inbound-interface name 'pppoe0'
 | ||
|   set nat destination rule 100 protocol 'tcp'
 | ||
|   set nat destination rule 100 translation address '192.0.2.40'
 | ||
| 
 | ||
|   set nat destination rule 110 description 'NAT Reflection: INSIDE'
 | ||
|   set nat destination rule 110 destination port '3389'
 | ||
|   set nat destination rule 110 inbound-interface name 'eth0.10'
 | ||
|   set nat destination rule 110 protocol 'tcp'
 | ||
|   set nat destination rule 110 translation address '192.0.2.40'
 | ||
| 
 | ||
|   set nat source rule 110 description 'NAT Reflection: INSIDE'
 | ||
|   set nat source rule 110 destination address '192.0.2.0/24'
 | ||
|   set nat source rule 110 outbound-interface name 'eth0.10'
 | ||
|   set nat source rule 110 protocol 'tcp'
 | ||
|   set nat source rule 110 source address '192.0.2.0/24'
 | ||
|   set nat source rule 110 translation address 'masquerade'
 | ||
| 
 | ||
| Which results in a configuration of:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   vyos@vyos# show nat
 | ||
|    destination {
 | ||
|        rule 100 {
 | ||
|            description "Regular destination NAT from external"
 | ||
|            destination {
 | ||
|                port 3389
 | ||
|            }
 | ||
|            inbound-interface {
 | ||
|                name pppoe0
 | ||
|            }
 | ||
|            protocol tcp
 | ||
|            translation {
 | ||
|                address 192.0.2.40
 | ||
|            }
 | ||
|        }
 | ||
|        rule 110 {
 | ||
|            description "NAT Reflection: INSIDE"
 | ||
|            destination {
 | ||
|                port 3389
 | ||
|            }
 | ||
|            inbound-interface {
 | ||
|                name eth0.10
 | ||
|            }
 | ||
|            protocol tcp
 | ||
|            translation {
 | ||
|                address 192.0.2.40
 | ||
|            }
 | ||
|        }
 | ||
|    }
 | ||
|    source {
 | ||
|        rule 110 {
 | ||
|            description "NAT Reflection: INSIDE"
 | ||
|            destination {
 | ||
|                address 192.0.2.0/24
 | ||
|            }
 | ||
|            outbound-interface {
 | ||
|                name eth0.10
 | ||
|            }
 | ||
|            protocol tcp
 | ||
|            source {
 | ||
|                address 192.0.2.0/24
 | ||
|            }
 | ||
|            translation {
 | ||
|                address masquerade
 | ||
|            }
 | ||
|        }
 | ||
|    }
 | ||
| 
 | ||
| 
 | ||
| Destination NAT
 | ||
| ---------------
 | ||
| 
 | ||
| DNAT is typically referred to as a **Port Forward**. When using VyOS as
 | ||
| a NAT router and firewall, a common configuration task is to redirect
 | ||
| incoming traffic to a system behind the firewall.
 | ||
| 
 | ||
| In this example, we will be using the example Quick Start configuration
 | ||
| above as a starting point.
 | ||
| 
 | ||
| To setup a destination NAT rule we need to gather:
 | ||
| 
 | ||
| * The interface traffic will be coming in on;
 | ||
| * The protocol and port we wish to forward;
 | ||
| * The IP address of the internal system we wish to forward traffic to.
 | ||
| 
 | ||
| In our example, we will be forwarding web server traffic to an internal
 | ||
| web server on 192.168.0.100. HTTP traffic makes use of the TCP protocol
 | ||
| on port 80. For other common port numbers, see:
 | ||
| https://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
 | ||
| 
 | ||
| Our configuration commands would be:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat destination rule 10 description 'Port Forward: HTTP to 192.168.0.100'
 | ||
|   set nat destination rule 10 destination port '80'
 | ||
|   set nat destination rule 10 inbound-interface name 'eth0'
 | ||
|   set nat destination rule 10 protocol 'tcp'
 | ||
|   set nat destination rule 10 translation address '192.168.0.100'
 | ||
| 
 | ||
| Which would generate the following NAT destination configuration:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   nat {
 | ||
|       destination {
 | ||
|           rule 10 {
 | ||
|               description "Port Forward: HTTP to 192.168.0.100"
 | ||
|               destination {
 | ||
|                   port 80
 | ||
|               }
 | ||
|               inbound-interface {
 | ||
|                   name eth0
 | ||
|               }
 | ||
|               protocol tcp
 | ||
|               translation {
 | ||
|                   address 192.168.0.100
 | ||
|               }
 | ||
|           }
 | ||
|       }
 | ||
|   }
 | ||
| 
 | ||
| .. note:: If forwarding traffic to a different port than it is arriving
 | ||
|    on, you may also configure the translation port using
 | ||
|    `set nat destination rule [n] translation port`.
 | ||
| 
 | ||
| This establishes our Port Forward rule, but if we created a firewall
 | ||
| policy it will likely block the traffic.
 | ||
| 
 | ||
| Firewall rules for Destination NAT
 | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 | ||
| 
 | ||
| It is important to note that when creating firewall rules, the DNAT
 | ||
| translation occurs **before** traffic traverses the firewall. In other
 | ||
| words, the destination address has already been translated to
 | ||
| 192.168.0.100.
 | ||
| 
 | ||
| So in our firewall ruleset, we want to allow traffic which previously matched
 | ||
| a destination nat rule. In order to avoid creating many rules, one for each
 | ||
| destination nat rule, we can accept all **'dnat'** connections with one simple
 | ||
| rule, using ``connection-status`` matcher:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set firewall ipv4 forward filter rule 10 action accept
 | ||
|   set firewall ipv4 forward filter rule 10 connection-status nat destination
 | ||
|   set firewall ipv4 forward filter rule 10 state new enable
 | ||
| 
 | ||
| This would generate the following configuration:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   ipv4 {
 | ||
|       forward {
 | ||
|           filter {
 | ||
|               rule 10 {
 | ||
|                   action accept
 | ||
|                   connection-status {
 | ||
|                       nat destination
 | ||
|                   }
 | ||
|                   state {
 | ||
|                       new enable
 | ||
|                   }
 | ||
|               }
 | ||
|           }
 | ||
|       }
 | ||
|   }
 | ||
| 
 | ||
| 
 | ||
| 1-to-1 NAT
 | ||
| ----------
 | ||
| 
 | ||
| Another term often used for DNAT is **1-to-1 NAT**. For a 1-to-1 NAT
 | ||
| configuration, both DNAT and SNAT are used to NAT all traffic from an
 | ||
| external IP address to an internal IP address and vice-versa.
 | ||
| 
 | ||
| Typically, a 1-to-1 NAT rule omits the destination port (all ports) and
 | ||
| replaces the protocol with either **all** or **ip**.
 | ||
| 
 | ||
| Then a corresponding SNAT rule is created to NAT outgoing traffic for
 | ||
| the internal IP to a reserved external IP. This dedicates an external IP
 | ||
| address to an internal IP address and is useful for protocols which
 | ||
| don't have the notion of ports, such as GRE.
 | ||
| 
 | ||
| Here's an extract of a simple 1-to-1 NAT configuration with one internal
 | ||
| and one external interface:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set interfaces ethernet eth0 address '192.168.1.1/24'
 | ||
|   set interfaces ethernet eth0 description 'Inside interface'
 | ||
|   set interfaces ethernet eth1 address '192.0.2.30/24'
 | ||
|   set interfaces ethernet eth1 description 'Outside interface'
 | ||
|   set nat destination rule 2000 description '1-to-1 NAT example'
 | ||
|   set nat destination rule 2000 destination address '192.0.2.30'
 | ||
|   set nat destination rule 2000 inbound-interface name 'eth1'
 | ||
|   set nat destination rule 2000 translation address '192.168.1.10'
 | ||
|   set nat source rule 2000 description '1-to-1 NAT example'
 | ||
|   set nat source rule 2000 outbound-interface name 'eth1'
 | ||
|   set nat source rule 2000 source address '192.168.1.10'
 | ||
|   set nat source rule 2000 translation address '192.0.2.30'
 | ||
| 
 | ||
| Firewall rules are written as normal, using the internal IP address as
 | ||
| the source of outbound rules and the destination of inbound rules.
 | ||
| 
 | ||
| NAT before VPN
 | ||
| --------------
 | ||
| 
 | ||
| Some application service providers (ASPs) operate a VPN gateway to
 | ||
| provide access to their internal resources, and require that a
 | ||
| connecting organisation translate all traffic to the service provider
 | ||
| network to a source address provided by the ASP.
 | ||
| 
 | ||
| Load Balance
 | ||
| ------------
 | ||
| Here we provide two examples on how to apply NAT Load Balance.
 | ||
| 
 | ||
| First scenario: apply destination NAT for all HTTP traffic comming through
 | ||
| interface eth0, and user 4 backends. First backend should received 30% of
 | ||
| the request, second backend should get 20%, third 15% and the fourth 35%
 | ||
| We will use source and destination address for hash generation.
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat destination rule 10 inbound-interface name eth0
 | ||
|   set nat destination rule 10 protocol tcp
 | ||
|   set nat destination rule 10 destination port 80
 | ||
|   set nat destination rule 10 load-balance hash source-address
 | ||
|   set nat destination rule 10 load-balance hash destination-address
 | ||
|   set nat destination rule 10 load-balance backend 198.51.100.101 weight 30
 | ||
|   set nat destination rule 10 load-balance backend 198.51.100.102 weight 20
 | ||
|   set nat destination rule 10 load-balance backend 198.51.100.103 weight 15
 | ||
|   set nat destination rule 10 load-balance backend 198.51.100.104 weight 35
 | ||
| 
 | ||
| Second scenario: apply source NAT for all outgoing connections from
 | ||
| LAN 10.0.0.0/8, using 3 public addresses and equal distribution.
 | ||
| We will generate the hash randomly.
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat source rule 10 outbound-interface name eth0
 | ||
|   set nat source rule 10 source address 10.0.0.0/8
 | ||
|   set nat source rule 10 load-balance hash random
 | ||
|   set nat source rule 10 load-balance backend 192.0.2.251 weight 33
 | ||
|   set nat source rule 10 load-balance backend 192.0.2.252 weight 33
 | ||
|   set nat source rule 10 load-balance backend 192.0.2.253 weight 34
 | ||
| 
 | ||
| Example Network
 | ||
| ^^^^^^^^^^^^^^^
 | ||
| 
 | ||
| Here's one example of a network environment for an ASP.
 | ||
| The ASP requests that all connections from this company should come from
 | ||
| 172.29.41.89 - an address that is assigned by the ASP and not in use at
 | ||
| the customer site.
 | ||
| 
 | ||
| .. figure:: /_static/images/nat_before_vpn_topology.png
 | ||
|    :scale: 100 %
 | ||
|    :alt: NAT before VPN Topology
 | ||
| 
 | ||
|    NAT before VPN Topology
 | ||
| 
 | ||
| 
 | ||
| Configuration
 | ||
| ^^^^^^^^^^^^^
 | ||
| 
 | ||
| The required configuration can be broken down into 4 major pieces:
 | ||
| 
 | ||
| * A dummy interface for the provider-assigned IP;
 | ||
| * NAT (specifically, Source NAT);
 | ||
| * IPSec IKE and ESP Groups;
 | ||
| * IPSec VPN tunnels.
 | ||
| 
 | ||
| 
 | ||
| Dummy interface
 | ||
| """""""""""""""
 | ||
| 
 | ||
| The dummy interface allows us to have an equivalent of the Cisco IOS
 | ||
| Loopback interface - a router-internal interface we can use for IP
 | ||
| addresses the router must know about, but which are not actually
 | ||
| assigned to a real network.
 | ||
| 
 | ||
| We only need a single step for this interface:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set interfaces dummy dum0 address '172.29.41.89/32'
 | ||
| 
 | ||
| NAT Configuration
 | ||
| """""""""""""""""
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set nat source rule 110 description 'Internal to ASP'
 | ||
|   set nat source rule 110 destination address '172.27.1.0/24'
 | ||
|   set nat source rule 110 source address '192.168.43.0/24'
 | ||
|   set nat source rule 110 translation address '172.29.41.89'
 | ||
|   set nat source rule 120 description 'Internal to ASP'
 | ||
|   set nat source rule 120 destination address '10.125.0.0/16'
 | ||
|   set nat source rule 120 source address '192.168.43.0/24'
 | ||
|   set nat source rule 120 translation address '172.29.41.89'
 | ||
| 
 | ||
| IPSec IKE and ESP
 | ||
| """""""""""""""""
 | ||
| 
 | ||
| The ASP has documented their IPSec requirements:
 | ||
| 
 | ||
| * IKE Phase:
 | ||
| 
 | ||
|   * aes256 Encryption
 | ||
|   * sha256 Hashes
 | ||
| 
 | ||
| * ESP Phase:
 | ||
| 
 | ||
|   * aes256 Encryption
 | ||
|   * sha256 Hashes
 | ||
|   * DH Group 14
 | ||
| 
 | ||
| 
 | ||
| Additionally, we want to use VPNs only on our eth1 interface (the
 | ||
| external interface in the image above)
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set vpn ipsec ike-group my-ike key-exchange 'ikev1'
 | ||
|   set vpn ipsec ike-group my-ike lifetime '7800'
 | ||
|   set vpn ipsec ike-group my-ike proposal 1 dh-group '14'
 | ||
|   set vpn ipsec ike-group my-ike proposal 1 encryption 'aes256'
 | ||
|   set vpn ipsec ike-group my-ike proposal 1 hash 'sha256'
 | ||
| 
 | ||
|   set vpn ipsec esp-group my-esp lifetime '3600'
 | ||
|   set vpn ipsec esp-group my-esp mode 'tunnel'
 | ||
|   set vpn ipsec esp-group my-esp pfs 'disable'
 | ||
|   set vpn ipsec esp-group my-esp proposal 1 encryption 'aes256'
 | ||
|   set vpn ipsec esp-group my-esp proposal 1 hash 'sha256'
 | ||
| 
 | ||
|   set vpn ipsec interface 'eth1'
 | ||
| 
 | ||
| IPSec VPN Tunnels
 | ||
| """""""""""""""""
 | ||
| 
 | ||
| We'll use the IKE and ESP groups created above for this VPN. Because we
 | ||
| need access to 2 different subnets on the far side, we will need two
 | ||
| different tunnels. If you changed the names of the ESP group and IKE
 | ||
| group in the previous step, make sure you use the correct names here
 | ||
| too.
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   set vpn ipsec authentication psk vyos id '203.0.113.46'
 | ||
|   set vpn ipsec authentication psk vyos id '198.51.100.243'
 | ||
|   set vpn ipsec authentication psk vyos secret 'MYSECRETPASSWORD'
 | ||
|   set vpn ipsec site-to-site peer branch authentication local-id '203.0.113.46'
 | ||
|   set vpn ipsec site-to-site peer branch authentication mode 'pre-shared-secret'
 | ||
|   set vpn ipsec site-to-site peer branch authentication remote-id '198.51.100.243'
 | ||
|   set vpn ipsec site-to-site peer branch connection-type 'initiate'
 | ||
|   set vpn ipsec site-to-site peer branch default-esp-group 'my-esp'
 | ||
|   set vpn ipsec site-to-site peer branch ike-group 'my-ike'
 | ||
|   set vpn ipsec site-to-site peer branch ikev2-reauth 'inherit'
 | ||
|   set vpn ipsec site-to-site peer branch local-address '203.0.113.46'
 | ||
|   set vpn ipsec site-to-site peer branch remote-address '198.51.100.243'
 | ||
|   set vpn ipsec site-to-site peer branch tunnel 0 local prefix '172.29.41.89/32'
 | ||
|   set vpn ipsec site-to-site peer branch tunnel 0 remote prefix '172.27.1.0/24'
 | ||
|   set vpn ipsec site-to-site peer branch tunnel 1 local prefix '172.29.41.89/32'
 | ||
|   set vpn ipsec site-to-site peer branch tunnel 1 remote prefix '10.125.0.0/16'
 | ||
| 
 | ||
| Testing and Validation
 | ||
| """"""""""""""""""""""
 | ||
| 
 | ||
| If you've completed all the above steps you no doubt want to see if it's
 | ||
| all working.
 | ||
| 
 | ||
| Start by checking for IPSec SAs (Security Associations) with:
 | ||
| 
 | ||
| .. code-block:: none
 | ||
| 
 | ||
|   $ show vpn ipsec sa
 | ||
| 
 | ||
|   Peer ID / IP                            Local ID / IP
 | ||
|   ------------                            -------------
 | ||
|   198.51.100.243                          203.0.113.46
 | ||
| 
 | ||
|       Tunnel  State  Bytes Out/In   Encrypt  Hash    NAT-T  A-Time  L-Time  Proto
 | ||
|       ------  -----  -------------  -------  ----    -----  ------  ------  -----
 | ||
|       0       up     0.0/0.0        aes256   sha256  no     1647    3600    all
 | ||
|       1       up     0.0/0.0        aes256   sha256  no     865     3600    all
 | ||
| 
 | ||
| That looks good - we defined 2 tunnels and they're both up and running.
 |