Introduction

Network Address Translation is an Internet standard that allows hosts on local area networks to use one set of IP addresses for internal communications and another set of IP addresses for external communications. A LAN that uses NAT is ascribed as anattednetwork. For NAT to function, there should be a NAT gateway in eachnattednetwork. The NAT gateway (NAT router) performs IP address rewriting on the way packet travel from/to LAN.

Nat matches only the first packet of the connection, connection tracking remembers the action and performs on all other packets belonging to the same connection.

Whenever NAT rules are changed or added, the connection tracking table should be cleared otherwise NAT rules may seem to be not functioning correctly until connection entry expires.

Types of NAT:

  • source NAT or srcnat.This type of NAT is performed onpackets that are originatedfrom a natted network. A NAT router replaces the private source address of an IP packet with a new public IP address as it travels through the router. A reverse operation is applied to the reply packets traveling in the other direction.
  • destination NAT or dstnat.This type of NAT is performed onpackets that are destinedfor the natted network. It is most commonly used to make hosts on a private network to be accessible from the Internet. A NAT router performing dstnat replaces the destination IP address of an IP packet as it travels through the router towards a private network.

Since RouterOS v7 the firewall NAT has two newINPUTandOUTPUTchains which are traversed for packets delivered to and sent from applications running on the local machine:

  • input- used to process packetsentering the routerthrough one of the interfaces with the destination IP address which is one of the router's addresses. Packets passing through the router are not processed against the rules of the input chain.
  • output- used to process packetsthatoriginated from the routerand leave it through one of the interfaces. Packets passing through the router are not processed against the rules of the output chain.

Destination NAT

Network address translation works by modifying network address information in the packets IP header. Let`s take a look at the common setup where a network administrator wants to access an office server from the internet.

We want to allow connections from the internet to the office server whose local IP is 10.0.0.3. In this case, we have to configure a destination address translation rule on the office gateway router:

/ip firewall nat add chain=dstnat action=dst-nat dst-address=172.16.16.1 dst-port=22 to-addresses=10.0.0.3 protocol=tcp

The rule above translates: when an incoming connection requests TCP port 22 with destination address 172.16.16.1, use thedst-nat行动和离开包与本地设备IP address 10.0.0.3 and port 22.

To allow access only from the PC at home, we can improve ourdst-natrule with"src-address=192.168.88.1"which is a Home`s PC public (this example) IP address. It is also considered to be more secure!

Source NAT

If you want to hide your local devices behind your public IP address received from ISP, you should configure the source network address translation (masquerading) feature of the MikroTik router.
Let`s assume you want to hide both office computer and server behind the public IP 172.16.16.1, the rule will look like the following one:

nat / ip防火墙添加链= srcnat src-address = 10.0.0.0/24 action=src-nat to-addresses=172.16.16.1 out-interface=WAN

Now your ISP will see all the requests coming with IP 172.16.16.1 and they will not see your LAN network IP addresses.

Masquerade

Firewall NATaction=masqueradeis a unique subversion ofaction=srcnat,it was designed for specific use in situations when public IP can randomly change, for example, DHCP server change assigned IP or PPPoE tunnel after disconnect gets different IP, in short -when public IP is dynamic.

nat / ip防火墙添加链= srcnat src-address = 10.0.0.0/24 action=masquarade out-interface=WAN

Every time when interface disconnects and/or its IP address changes, the router will clear all masqueraded connection tracking entries related to the interface, this way improving system recovery time after public IP change. Ifsrcnatis used instead ofmasquerade,connection tracking entries remain and connections can simply resume after a link failure.

Unfortunately, this can lead to some issues with unstable links when the connection gets routed over different links after the primary link goes down. In such a scenario following things can happen:

  • on disconnect, all related connection tracking entries are purged;
  • next packet from every purged (previously masqueraded) connection will come into the firewall asnew, and, if a primary interface is not back, a packet will be routed out via an alternative route (if you have any) thus creating a new masqueraded connection;
  • the primary link comes back, routing is restored over the primary link, so packets that belong to existing connections are sent over the primary interface without being masqueraded, that way leaking local IPs to a public network.

To work around this situationblackholeroute can be created as an alternative to the route that might disappear on disconnect.

Hosts behind a NAT-enabled router do not have true end-to-end connectivity. Therefore some Internet protocols might not work in scenarios with NAT. Services that require the initiation of TCP connection from outside the private network or stateless protocols such as UDP, can be disrupted.

To overcome these limitations RouterOS includes a number of so-called NAT helpers, that enable NAT traversal for various protocols. Whenaction=srcnatis used instead, connection tracking entries remain and connections can simply resume.

尽管源NAT和伪装执行山姆e fundamental function: mapping one address space into another one, the details differ slightly. Most noticeably, masquerading chooses the source IP address for the outbound packet from the IP bound to the interface through which the packet will exit.

CGNAT (NAT444)

To combat IPv4 address exhaustion, a new RFC 6598 was deployed. The idea is to use shared 100.64.0.0/10 address space inside the carrier's network and perform NAT on the carrier's edge router to a single public IP or public IP range.

因为这样设置的本质,它也是called NAT444, as opposed to a NAT44 network for a 'normal' NAT environment, three different IPv4 address spaces are involved.

CGNAT configuration on RouterOS does not differ from any other regular source NAT configuration:

/ip firewall nat add chain=src-nat action=srcnat src-address=100.64.0.0/10 to-address=2.2.2.2 out-interface=

Where:

  • 2.2.2.2 - public IP address,
  • public_if - interface on providers edge router connected to the internet

The advantage of NAT444 is obvious, fewer public IPv4 addresses are used. But this technique comes with major drawbacks:

  • The service provider router performing CGNAT needs to maintain a state table for all the address translations: this requires a lot of memory and CPU resources.
  • Console gaming problems. Some games fail when two subscribers using the same outside public IPv4 address try to connect to each other.
  • Tracking users for legal reasons means extra logging, as multiple households go behind one public address.
  • Anything requiring incoming connections is broken. While this already was the case with regular NAT, end-users could usually still set up port forwarding on their NAT router. CGNAT makes this impossible. This means no web servers can be hosted here, and IP Phones cannot receive incoming calls by default either.
  • Some web servers only allow a maximum number of connections from the same public IP address, as a means to counter DoS attacks like SYN floods. Using CGNAT this limit is reached more often and some services may be of poor quality.
  • 6to4 requires globally reachable addresses and will not work in networks that employ addresses with a limited topological span.


Packets with Shared Address Space source or destination addresses MUST NOT be forwarded across Service Provider boundaries. Service Providers MUST filter such packets on ingress links. In RouterOS this can be easily done with firewall filters on edge routers:

/ip firewall filter add chain=input src-address=100.64.0.0/10 action=drop in-interface= add chain=output dst-address=100.64.0.0/10 action=drop out-interface= add chain=forward src-address=100.64.0.0/10 action=drop in-interface= add chain=forward src-address=100.64.0.0/10 action=drop out-interface= add chain=forward dst-address=100.64.0.0/10 action=drop out-interface=

Service providers may be required to log of MAPed addresses, in a large CGN deployed network that may be a problem. Fortunately, RFC 7422 suggests a way to manage CGN translations in such a way as to significantly reduce the amount of logging required while providing traceability for abuse response.

RFC states that instead of logging each connection, CGNs could deterministically map customer private addresses (received on the customer-facing interface of the CGN, a.k.a., internal side) to public addresses extended with port ranges.

In RouterOS described algorithm can be done with few script functions. Let's take an example:

Inside IP Outside IP/Port range
100.64.1.1 2.2.2.2:2000-2099
100.64.1.2 2.2.2.2:2100-2199
100.64.1.3 2.2.2.2:2200-2299
100.64.1.4 2.2.2.2:2300-2399
100.64.1.5 2.2.2.2:2400-2499
100.64.1.6 2.2.2.2:2500-2599

Instead of writing NAT mappings by hand, we could write a function that adds such rules automatically.

:全球√6 ={:因为我从= 0 = 1美元={:如果(我* i > $1) do={ :return ($i - 1) } } } :global addNatRules do={ /ip firewall nat add chain=srcnat action=jump jump-target=xxx \ src-address="$($srcStart)-$($srcStart + $count - 1)" :local x [$sqrt $count] :local y $x :if ($x * $x = $count) do={ :set y ($x + 1) } :for i from=0 to=$x do={ /ip firewall nat add chain=xxx action=jump jump-target="xxx-$($i)" \ src-address="$($srcStart + ($x * $i))-$($srcStart + ($x * ($i + 1) - 1))" } :for i from=0 to=($count - 1) do={ :local prange "$($portStart + ($i * $portsPerAddr))-$($portStart + (($i + 1) * $portsPerAddr) - 1)" /ip firewall nat add chain="xxx-$($i / $x)" action=src-nat protocol=tcp src-address=($srcStart + $i) \ to-address=$toAddr to-ports=$prange /ip firewall nat add chain="xxx-$($i / $x)" action=src-nat protocol=udp src-address=($srcStart + $i) \ to-address=$toAddr to-ports=$prange } }

After pasting the above script in the terminal function "addNatRules" is available. If we take our example, we need to map 6 shared network addresses to be mapped to 2.2.2.2 and each address uses a range of 100 ports starting from 2000. So we run our function:

$addNatRules count=6 srcStart=100.64.1.1 toAddr=2.2.2.2 portStart=2000 portsPerAddr=100

Now you should be able to get a set of rules:

[admin@rack1_b18_450] /ip firewall nat> print Flags: X - disabled, I - invalid, D - dynamic 0 chain=srcnat action=jump jump-target=xxx src-address=100.64.1.1-100.64.1.6 log=no log-prefix="" 1 chain=xxx action=jump jump-target=xxx-0 src-address=100.64.1.1-100.64.1.2 log=no log-prefix="" 2 chain=xxx action=jump jump-target=xxx-1 src-address=100.64.1.3-100.64.1.4 log=no log-prefix="" 3 chain=xxx action=jump jump-target=xxx-2 src-address=100.64.1.5-100.64.1.6 log=no log-prefix="" 4 chain=xxx-0 action=src-nat to-addresses=2.2.2.2 to-ports=2000-2099 protocol=tcp src-address=100.64.1.1 log=no log-prefix="" 5 chain=xxx-0 action=src-nat to-addresses=2.2.2.2 to-ports=2000-2099 protocol=udp src-address=100.64.1.1 log=no log-prefix="" 6 chain=xxx-0 action=src-nat to-addresses=2.2.2.2 to-ports=2100-2199 protocol=tcp src-address=100.64.1.2 log=no log-prefix="" 7 chain=xxx-0 action=src-nat to-addresses=2.2.2.2 to-ports=2100-2199 protocol=udp src-address=100.64.1.2 log=no log-prefix="" 8 chain=xxx-1 action=src-nat to-addresses=2.2.2.2 to-ports=2200-2299 protocol=tcp src-address=100.64.1.3 log=no log-prefix="" 9 chain=xxx-1 action=src-nat to-addresses=2.2.2.2 to-ports=2200-2299 protocol=udp src-address=100.64.1.3 log=no log-prefix="" 10 chain=xxx-1 action=src-nat to-addresses=2.2.2.2 to-ports=2300-2399 protocol=tcp src-address=100.64.1.4 log=no log-prefix="" 11 chain=xxx-1 action=src-nat to-addresses=2.2.2.2 to-ports=2300-2399 protocol=udp src-address=100.64.1.4 log=no log-prefix="" 12 chain=xxx-2 action=src-nat to-addresses=2.2.2.2 to-ports=2400-2499 protocol=tcp src-address=100.64.1.5 log=no log-prefix="" 13 chain=xxx-2 action=src-nat to-addresses=2.2.2.2 to-ports=2400-2499 protocol=udp src-address=100.64.1.5 log=no log-prefix="" 14 chain=xxx-2 action=src-nat to-addresses=2.2.2.2 to-ports=2500-2599 protocol=tcp src-address=100.64.1.6 log=no log-prefix="" 15 chain=xxx-2 action=src-nat to-addresses=2.2.2.2 to-ports=2500-2599 protocol=udp src-address=100.64.1.6 log=no log-prefix=""


Hairpin NAT

Hairpin network address translation (NAT Loopback) is where the device on the LAN is able to access another machine on the LAN via the public IP address of the gateway router.



In the above example the gateway router has the followingdst-natconfiguration rule:

/ip firewall nat add chain=dstnat action=dst-nat dst-address=172.16.16.1 dst-port=443 to-addresses=10.0.0.3 to-ports=443 protocol=tcp

When a user from the PC at home establishes a connection to the webserver, the router performs DST NAT as configured:

  1. the client sends a packet with a source IP address of 192.168.88.1 to a destination IP address of 172.16.16.1 on port 443 to request some web resources;
  2. the router destination NAT`s the packet to 10.0.0.3 and replaces the destination IP address in the packet accordingly. The source IP address stays the same: 192.168.88.1;
  3. the server replies to the client's request and the reply packet have a source IP address of 10.0.0.3 and a destination IP address of 192.168.88.1.
  4. the router determines that the packet is part of a previous connection and undoes the destination NAT, and puts the original destination IP address into the source IP address field. The destination IP address is 192.168.88.1, and the source IP address is 172.16.16.1;
  5. The client receives the reply packet it expects, and the connection is established;


But, there will be aproblem, when a client on the same network as the web server requests a connection to the web server'spublicIP address:

  1. the client sends a packet with a source IP address of 10.0.0.2 to a destination IP address of 172.16.16.1 on port 443 to request some web resources;
  2. the router destination NATs the packet to 10.0.0.3 and replaces the destination IP address in the packet accordingly. The source IP address stays the same: 10.0.0.2;
  3. the server replies to the client's request. However, the source IP address of the request is on the same subnet as the web server. The web server does not send the reply back to the router but sends it back directly to 10.0.0.2 with a source IP address in the reply of 10.0.0.3;
  4. The client receives the reply packet, but it discards it because it expects a packet back from 172.16.16.1, and not from 10.0.0.3;

To resolve this issue, we will configure a newsrc-natrule (the hairpin NAT rule) as follows:

/ip firewall nat add action=masquerade chain=srcnat dst-address=10.0.0.3 out-interface=LAN protocol=tcp src-address=10.0.0.0/24

After configuring the rule above:

  1. the client sends a packet with a source IP address of 10.0.0.2 to a destination IP address of 172.16.16.1 on port 443 to request some web resources;
  2. the router destination NATs the packet to 10.0.0.3 and replaces the destination IP address in the packet accordingly. It also source NATs the packet and replaces the source IP address in the packet with the IP address on its LAN interface. The destination IP address is 10.0.0.3, and the source IP address is 10.0.0.1;
  3. the web server replies to the request and sends the reply with a source IP address of 10.0.0.3 back to the router's LAN interface IP address of 10.0.0.1;
  4. the router determines that the packet is part of a previous connection and undoes both the source and destination NAT, and puts the original destination IP address of 10.0.0.3 into the source IP address field, and the original source IP address of 172.16.16.1 into the destination IP address field

Endpoint-Independent NAT

Endpoint-independent NAT creates mapping in the source NAT and uses the same mapping for all subsequent packets with the same source IP and port. This mapping is created with the following rule:

/ip firewall nat add action=endpoint-independent-nat chain=srcnat out-interface=WAN protocol=udp

This mapping allows running source-independent filtering, which allows forwarding packets from any source from WAN to mapped internal IP and port. Following rule enables filtering:

/ip firewall nat add action=endpoint-independent-nat chain=dstnat in-interface=WAN protocol=udp


Endpoint-independent NAT works only with UDP protocol.


Additionally, endpoint-independent-nat can take a few other parameters:

  • randomize-port- randomize to which public port connections will be mapped.


More infohttps://www.ietf.org/rfc/rfc5128.txtsection 2.2.3 and 2.2.5


IPv4

Properties

Property Description
action(action name; Default:accept) Action to take if a packet is matched by the rule:
  • accept- accept the packet. A packet is not passed to the next NAT rule.
  • add-dst-to-address-list- add the destination address tothe address listspecified byaddress-listparameter
  • add-src-to-address-list- add the source address tothe address listspecified byaddress-listparameter
  • dst-nat- replaces the destination address and/or port of an IP packet with values specified byto-addressesandto-portsparameters
  • jump- jump to the user-defined chain specified by the value ofjump-targetparameter
  • log- add a message to the system log containing the following data: in-interface, out-interface, src-mac, protocol, src-ip:port->dst-ip:port and length of the packet. After a packet is matched it is passed to the next rule in the list, similar aspassthrough
  • masquerade- replaces the source port of an IP packet with one specified byto-portsparameter and replace the source address of an IP packet to the IP determined by the routing facility.
  • netmap- creates a static 1:1 mapping of one set of IP addresses to another one. Often used to distribute public IP addresses to hosts on private networks
  • passthrough- if a packet is matched by the rule, increase the counter and go to the next rule (useful for statistics).
  • redirect- replaces the destination port of an IP packet with one specified byto-portsparameter and destination address to one of the router's local addresses
  • return- passes control back to the chain from where the jump took place
  • same- gives a particular client the same source/destination IP address from a supplied range for each connection. This is most frequently used for services that expect the same client address for multiple connections from the same client
  • src-nat- replaces the source address of an IP packet with values specified byto-addressesandto-portsparameters
  • endpoint-independent-nat- uses endpoint-independent mapping and filtering. Works only with UDP protocol.
address-list(string; Default: ) Name of the address list to be used. Applicable if action isadd-dst-to-address-listoradd-src-to-address-list
address-list-timeout(none-dynamic | none-static | time; Default:none-dynamic) Time interval after which the address will be removed from the address list specified byaddress-listparameter. Used in conjunction withadd-dst-to-address-listoradd-src-to-address-listactions
  • Value ofnone-dynamic(00:00:00) will leave the address in the address list till the reboot
  • Value ofnone-staticwill leave the address in the address list forever and will be included in the configuration export/backup
chain(name; Default: ) Specifies to which chain rule will be added. If the input does not match the name of an already defined chain, a new chain will be created
comment(string; Default: ) Descriptive comment for the rule
connection-bytes(integer-integer; Default: ) Matches packet only if a given amount of bytes has been transferred through the particular connection. 0 - means infinity, for exampleconnection-bytes=2000000-0如果更多的th意味着规则匹配an 2MB has been transferred through the relevant connection
connection-limit(integer,netmask; Default: ) Matches connections per address or address block after a given value is reached
connection-mark(no-mark | string; Default: ) Matches packets marked via mangle facility with particular connection mark. Ifano-markis set, the rule will match any unmarked connection
connection-rate(Integer 0..4294967295; Default: ) Connection Rate is a firewall matcher that allows capturing traffic based on the present speed of the connection
connection-type(ftp | h323 | irc | pptp | quake3 | sip | tftp; Default: ) Matches packets from related connections based on information from their connection tracking helpers. A relevant connection helper must be enabled under/ip firewall service-port
content(string; Default: ) Match packets that contain specified text
dscp(integer: 0..63; Default: ) Matches DSCP IP header field.
dst-address(IP/netmask | IP range; Default: ) Matches packets whose destination is equal to specified IP or falls into a specified IP range.
dst-address-list(name; Default: ) Matches the destination address of a packet against a user-definedaddress list
dst-address-type(unicast | local | broadcast | multicast; Default: ) Matches destination address type:
  • unicast- IP address used for point-to-point transmission
  • local- if dst-address is assigned to one of the router's interfaces
  • broadcast- packet is sent to all devices in a subnet
  • multicast- packet is forwarded to a defined group of devices
dst-limit(integer[/time],integer,dst-address | dst-port | src-address[/time]; Default: ) Matches packets until a given PPS limit is exceeded. As opposed to thelimitmatcher, every destination IP address/destination port has its own limit. Parameters are written in the following format:count[/time],burst,mode[/expire].
  • count- maximum average packet rate measured in packets pertimeinterval
  • time- specifies the time interval in which the packet rate is measured (optional)
  • burst- number of packets that are not counted by packet rate
  • mode- the classifier for packet rate limiting
  • expire- specifies interval after which recorded IP address /port will be deleted (optional)
dst-port(integer[-integer]: 0..65535; Default: ) List of destination port numbers or port number ranges in formatRange[,Port], for example,dst-port=123-345,456-678
fragment(yes|no; Default: ) Matches fragmented packets. The first (starting) fragment does not count. If connection tracking is enabled there will be no fragments as the system automatically assembles every packet
hotspot(auth | from-client | http | local-dst | to-client; Default: ) Matches packets received from HotSpot clients against various HotSpot matchers.
  • auth- matches authenticated HotSpot client packets
  • from-client- matches packets that are coming from the HotSpot client
  • http- matches HTTP requests sent to the HotSpot server
  • local-dst- matches packets that are destined to the HotSpot server
  • to-client- matches packets that are sent to the HotSpot client
icmp-options(integer:integer; Default: ) Matches ICMP type: code fields
in-bridge-port(name; Default: ) Actual interface the packet has entered the router if the incoming interface is a bridge
in-interface(name; Default: ) Interface the packet has entered the router
ingress-priority(integer: 0..63; Default: ) Matches ingress the priority of the packet. Priority may be derived from VLAN, WMM or MPLS EXP bit.
ipsec-policy(in | out, ipsec | none; Default: ) Matches the policy used by IPSec. Value is written in the following format:direction, policy. The direction is Used to select whether to match the policy used for decapsulation or the policy that will be used for encapsulation.
  • in- valid in the PREROUTING, INPUT, and FORWARD chains
  • out- valid in the POSTROUTING, OUTPUT, and FORWARD chains
  • ipsec- matches if the packet is subject to IPsec processing;
  • none——比赛不受IPsec proc的包essing (for example, IPSec transport packet).

For example, if a router receives an IPsec encapsulated Gre packet, then ruleipsec-policy=in,ipsecwill match Gre packet, but the ruleipsec-policy=in,nonewill match the ESP packet.
ipv4-options(any | loose-source-routing | no-record-route | no-router-alert | no-source-routing | no-timestamp | none | record-route | router-alert | strict-source-routing | timestamp; Default: ) Matches IPv4 header options.
  • any- match packet with at least one of the ipv4 options
  • loose-source-routing- match packets with a loose source routing option. This option is used to route the internet datagram based on information supplied by the source
  • no-record-route- match packets with no record route option. This option is used to route the internet datagram based on information supplied by the source
  • no-router-alert- match packets with no router alter option
  • no-source-routing- match packets with no source routing option
  • no-timestamp- match packets with no timestamp option
  • record-route- match packets with record route option
  • router-alert- match packets with router alter option
  • strict-source-routing- match packets with a strict source routing option
  • timestamp- match packets with a timestamp
jump-target(name; Default: ) Name of the target chain to jump to. Applicable only ifaction=jump
layer7-protocol(name; Default: ) Layer7 filter name defined inlayer7 protocol menu.
limit(integer,time,integer; Default: ) Matches packets until a given PPS limit is exceeded. Parameters are written in the following format:count[/time],burst.
  • count- maximum average packet rate measured in packets pertimeinterval
  • time- specifies the time interval in which the packet rate is measured (optional, 1s will be used if not specified)
  • burst- number of packets that are not counted by packet rate
log(yes | no; Default:no) Add a message to the system log containing the following data: in-interface, out-interface, src-mac, protocol, src-ip:port->dst-ip:port, and length of the packet.
log-prefix(string; Default: ) Adds specified text at the beginning of every log message. Applicable ifaction=logorlog=yesconfigured.
out-bridge-port(name; Default: ) Actual interface the packet is leaving the router if the outgoing interface is a bridge
out-interface(; Default: ) Interface the packet is leaving the router
packet-mark(no-mark | string; Default: ) Matches packets marked via mangle facility with particular packet mark. Ifno-markis set, the rule will match any unmarked packet
packet-size(integer[-integer]:0..65535; Default: ) Matches packets of specified size or size range in bytes
per-connection-classifier(ValuesToHash:Denominator/Remainder; Default: ) PCC matcher allows dividing traffic into equal streams with the ability to keep packets with a specific set of options in one particular stream
port(integer[-integer]: 0..65535; Default: ) Matches if any (source or destination) port matches the specified list of ports or port ranges. Applicable only ifprotocolis TCP or UDP
protocol(name or protocol ID; Default:tcp) Matches particular IP protocol specified by protocol name or number
psd(integer,time,integer,integer; Default: ) Attempts to detect TCP and UDP scans. Parameters are in the following formatWeightThreshold, DelayThreshold, LowPortWeight, HighPortWeight
  • WeightThreshold- total weight of the latest TCP/UDP packets with different destination ports coming from the same host to be treated as port scan sequence
  • DelayThreshold- delay for the packets with different destination ports coming from the same host to be treated as possible port scan subsequence
  • LowPortWeight- the weight of the packets with privileged (<1024) destination port
  • HighPortWeight- the weight of the packet with a non-privileged destination port
random(integer: 1..99; Default: ) Matches packets randomly with a given probability
routing-mark(string; Default: ) Matches packets marked by mangle facility with particular routing mark
same-not-by-dst(yes | no; Default: ) Specifies whether to take into account or not destination IP address when selecting a new source IP address. Applicable ifaction=same
src-address(Ip/Netmaks, Ip range; Default: ) Matches packets whose source is equal to specified IP or falls into a specified IP range.
src-address-list(name; Default: ) Matches source address of a packet against user-definedaddress list
src-address-type(unicast | local | broadcast | multicast; Default: )

Matches source address type:

  • unicast- IP address used for point-to-point transmission
  • local- if an address is assigned to one of the router's interfaces
  • broadcast- packet is sent to all devices in a subnet
  • multicast- packet is forwarded to a defined group of devices
src-port(integer[-integer]: 0..65535; Default: ) List of source ports and ranges of source ports. Applicable only if a protocol is TCP or UDP.
src-mac-address(MAC address; Default: ) Matches source MAC address of the packet
tcp-mss(integer[-integer]: 0..65535; Default: ) Matches TCP MSS value of an IP packet
time(time-time,sat | fri | thu | wed | tue | mon | sun; Default: ) Allows to create a filter based on the packets' arrival time and date or, for locally generated packets, departure time and date
to-addresses(IP address[-IP address]; Default:0.0.0.0) Replace the original address with the specified one. Applicable if action is dst-nat, netmap, same, src-nat
to-ports(integer[-integer]: 0..65535; Default: ) Replace the original port with the specified one. Applicable if action is dst-nat, redirect, masquerade, netmap, same, src-nat
ttl(integer: 0..255; Default: ) Matches packets TTL value

Stats

Property Description
bytes(integer) The total amount of bytes matched by the rule
packets(integer) The total amount of packets matched by the rule

To show additionalread-onlyproperties:

[admin@MikroTik] > ip firewall nat print stats all Flags: X - disabled, I - invalid, D - dynamic # CHAIN ACTION BYTES PACKETS 0 srcnat masquerade 265 659 987

IPv6

NAT66 is supported since RouterOS v7.1.

ipv6/firewall/nat/

Properties

Property Description
action(action name; Default:accept) Action to take if a packet is matched by the rule:
  • accept- accept the packet. A packet is not passed to the next NAT rule.
  • add-dst-to-address-list- add the destination address tothe address listspecified byaddress-listparameter
  • add-src-to-address-list- add the source address tothe address listspecified byaddress-listparameter
  • dst-nat- replaces destination address and/or port of an IP packet to values specified byto-addressesandto-portsparameters
  • jump- jump to the user-defined chain specified by the value ofjump-targetparameter
  • log- add a message to the system log containing the following data: in-interface, out-interface, src-mac, protocol, src-ip:port->dst-ip:port and length of the packet. After a packet is matched it is passed to the next rule in the list, similar aspassthrough
  • masquerade- replaces the source port of an IP packet with one specified byto-portsparameter and replace the source address of an IP packet to IP determined by the routing facility.
  • netmap- creates a static 1:1 mapping of one set of IP addresses to another one. Often used to distribute public IP addresses to hosts on private networks
  • passthrough- if a packet is matched by the rule, increase the counter and go to the next rule (useful for statistics).
  • redirect- replaces the destination port of an IP packet with one specified byto-portsparameter and destination address to one of the router's local addresses
  • return- passes control back to the chain from where the jump took place
  • src-nat- replaces the source address of an IP packet with values specified byto-addressesandto-portsparameters
address-list(string; Default: ) Name of the address list to be used. Applicable if action isadd-dst-to-address-listoradd-src-to-address-list
address-list-timeout(none-dynamic | none-static | time; Default:none-dynamic) Time interval after which the address will be removed from the address list specified byaddress-listparameter. Used in conjunction withadd-dst-to-address-listoradd-src-to-address-listactions
  • Value ofnone-dynamic(00:00:00) will leave the address in the address list till reboot
  • Value ofnone-staticwill leave the address in the address list forever and will be included in configuration export/backup
chain(name; Default: ) Specifies to which chain rule will be added. If the input does not match the name of an already defined chain, a new chain will be created
comment(string; Default: ) Descriptive comment for the rule
connection-bytes(integer-integer; Default: ) Matches packets only if a given amount of bytes has been transferred through the particular connection. 0 - means infinity, for exampleconnection-bytes=2000000-0如果更多的th意味着规则匹配an 2MB has been transferred through the relevant connection
connection-limit(integer,netmask; Default: ) Matches connections per address or address block after a given value is reached
connection-mark(no-mark | string; Default: ) Matches packets marked via mangle facility with particular connection mark. Ifno-markis set, the rule will match any unmarked connection
connection-rate(Integer 0..4294967295; Default: ) Connection Rate is a firewall matcher that allows capturing traffic based on the present speed of the connection
connection-state(established | invalid | new | related | untracked; Default: ) Interprets the connection tracking analytics data for a particular packet:
  • established- a packet that belongs to an existing connection
  • invalid- a packet that does not have a determined state in connection tracking (usually - severe out-of-order packets, packets with wrong sequence/ack number, or in case of a resource over usage on the router), for this reason, an invalid packet will not participate in NAT (as only connection-state=new packets do), and will still contain original source IP address when routed. We strongly suggest dropping allconnection-state=invalidpackets in firewall filter forward and input chains
  • new- the packet has started a new connection, or is otherwise associated with a connection that has not seen packets in both directions.
  • related- a packet that is related to, but not parts of an existing connection, such as ICMP errors or a packet that begins FTP data connection
  • an untracked- packet which was set to bypass connection tracking in firewallRAWtables.
connection-type(ftp | h323 | irc | pptp | quake3 | sip | tftp; Default: ) Matches packets from related connections based on information from their connection tracking helpers. A relevant connection helper must be enabled under/ip firewall service-port
content(string; Default: ) Match packets that contain specified text
dscp(integer: 0..63; Default: ) Matches DSCP IP header field.
dst-address(IP/netmask | IP range; Default: ) Matches packets whose destination is equal to specified IP or falls into a specified IP range.
dst-address-list(name; Default: ) Matches destination address of a packet against user-definedaddress list
dst-address-type(unicast | local | broadcast | multicast; Default: ) Matches destination address type:
  • unicast- IP address used for point-to-point transmission
  • local- if dst-address is assigned to one of the router's interfaces
  • broadcast- packet is sent to all devices in a subnet
  • multicast- packet is forwarded to a defined group of devices
dst-limit(integer[/time],integer,dst-address | dst-port | src-address[/time]; Default: ) Matches packets until a given PPS limit is exceeded. As opposed to thelimitmatcher, every destination IP address/destination port has its own limit. Parameters are written in the following format:count[/time],burst,mode[/expire].
  • count- maximum average packet rate measured in packets pertimeinterval
  • time- specifies the time interval in which the packet rate is measured (optional)
  • burst- number of packets that are not counted by packet rate
  • mode- the classifier for packet rate limiting
  • expire- specifies interval after which recorded IP address /port will be deleted (optional)
dst-port(integer[-integer]: 0..65535; Default: ) List of destination port numbers or port number ranges in formatRange[,Port], for example,dst-port=123-345,456-678
icmp-options(integer:integer; Default: ) Matches ICMP type: code fields
in-bridge-port(name; Default: ) Actual interface the packet has entered the router if the incoming interface is a bridge
in-bridge-port-list(name; Default: ) Set of interfaces defined ininterface list. Works the same asin-bridge-port
in-interface(name; Default: ) Interface the packet has entered the router
in-interface-list(name; Default: ) Set of interfaces defined ininterface list. Works the same asin-interface
ingress-priority(integer: 0..63; Default: ) Matches ingress the priority of the packet. Priority may be derived from VLAN, WMM or MPLS EXP bit.
ipsec-policy(in | out, ipsec | none; Default: ) Matches the policy used by IPSec. Value is written in the following format:direction, policy. The direction is Used to select whether to match the policy used for decapsulation or the policy that will be used for encapsulation.
  • in- valid in the PREROUTING, INPUT, and FORWARD chains
  • out- valid in the POSTROUTING, OUTPUT, and FORWARD chains
  • ipsec- matches if the packet is subject to IPsec processing;
  • none——比赛不受IPsec proc的包essing (for example, IPSec transport packet).

For example, if a router receives an IPsec encapsulated Gre packet, then ruleipsec-policy=in,ipsecwill match Gre packet, but the ruleipsec-policy=in,nonewill match the ESP packet.
jump-target(name; Default: ) Name of the target chain to jump to. Applicable only ifaction=jump
layer7-protocol(name; Default: ) Layer7 filter name defined inlayer7 protocol menu.
limit(integer,time,integer; Default: ) Matches packets until a given PPS limit is exceeded. Parameters are written in the following format:count[/time],burst.
  • count- maximum average packet rate measured in packets pertimeinterval
  • time- specifies the time interval in which the packet rate is measured (optional, 1s will be used if not specified)
  • burst- number of packets that are not counted by packet rate
log(yes | no; Default:no) Add a message to the system log containing the following data: in-interface, out-interface, src-mac, protocol, src-ip:port->dst-ip:port, and length of the packet.
log-prefix(string; Default: ) Adds specified text at the beginning of every log message. Applicable ifaction=logorlog=yesconfigured.
out-bridge-port(name; Default: ) Actual interface the packet is leaving the router if the outgoing interface is a bridge
out-bridge-port-list(name; Default: ) Set of interfaces defined ininterface list. Works the same asout-bridge-port
out-interface(; Default: ) Interface the packet is leaving the router
out-interface-list(name; Default: ) Set of interfaces defined ininterface list. Works the same asout-interface
packet-mark(no-mark | string; Default: ) Matches packets marked via mangle facility with particular packet mark. Ifno-markis set, the rule will match any unmarked packet
packet-size(integer[-integer]:0..65535; Default: ) Matches packets of specified size or size range in bytes
per-connection-classifier(ValuesToHash:Denominator/Remainder; Default: ) PCC matcher allows dividing traffic into equal streams with the ability to keep packets with a specific set of options in one particular stream
port(integer[-integer]: 0..65535; Default: ) Matches if any (source or destination) port matches the specified list of ports or port ranges. Applicable only ifprotocolis TCP or UDP
protocol(name or protocol ID; Default:tcp) Matches particular IP protocol specified by protocol name or number
priority(integer: 0..63; Default:) Matches the packet's priority after a new priority has been set. Priority may be derived from VLAN, WMM, DSCP, MPLS EXP bit, or from the priority that has been set using theset-priorityaction.
random(integer: 1..99; Default: ) Matches packets randomly with a given probability
routing-mark(string; Default: ) Matches packets marked by mangle facility with particular routing mark
src-address(Ip/Netmaks, Ip range; Default: ) Matches packets whose source is equal to specified IP or falls into a specified IP range.
src-address-list(name; Default: ) Matches source address of a packet against user-definedaddress list
src-address-type(unicast | local | broadcast | multicast; Default: )

Matches source address type:

  • unicast- IP address used for point-to-point transmission
  • local- if an address is assigned to one of the router's interfaces
  • broadcast- packet is sent to all devices in a subnet
  • multicast- packet is forwarded to a defined group of devices
src-port(integer[-integer]: 0..65535; Default: ) List of source ports and ranges of source ports. Applicable only if a protocol is TCP or UDP.
tcp-flags(ack | cwr | ece | fin | psh | rst | syn | urg; Default: ) Matches specified TCP flags
  • ack- acknowledging data
  • cwr- congestion window reduced
  • ece- ECN-echo flag (explicit congestion notification)
  • fin- close connection
  • psh- push function
  • rst- drop connection
  • syn- new connection
  • urg- urgent data
src-mac-address(MAC address; Default: ) Matches source MAC address of the packet
tcp-mss(integer[-integer]: 0..65535; Default: ) Matches TCP MSS value of an IP packet
time(time-time,sat | fri | thu | wed | tue | mon | sun; Default: ) Allows to create a filter based on the packets' arrival time and date or, for locally generated packets, departure time and date
to-addresses(IP address[-IP address]; Default:0.0.0.0) Replace the original address with the specified one. Applicable if action is dst-nat, netmap, same, src-nat
to-ports(integer[-integer]: 0..65535; Default: ) Replace the original port with the specified one. Applicable if action is dst-nat, redirect, masquerade, netmap, same, src-nat

Stats

Property Description
bytes(integer) The total amount of bytes matched by the rule
packets(integer) The total amount of packets matched by the rule

To show additionalread-onlyproperties:

ipv6/firewall/nat/print stats
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