/ip firewall nat
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 referred as natted network. For NAT to function, there should be a NAT gateway in each natted network. The NAT gateway (NAT router) performs IP address rewriting on the way a packet travel from/to LAN.
There are two types of NAT:
- source NAT or srcnat. This type of NAT is performed on packets that are originated from 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 travelling in the other direction.
- destination NAT or dstnat. This type of NAT is performed on packets that are destined to the natted network. It is most comonly used to make hosts on a private network to be acceesible from the Internet. A NAT router performing dstnat replaces the destination IP address of an IP packet as it travel through the router towards a private network.
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. Moreover, some protocols are inherently incompatible with NAT, a bold example is AH protocol from the IPsec suite.
To overcome these limitations RouterOS includes a number of so-called NAT helpers, that enable NAT traversal for various protocols.
|action (action name; Default: accept)||Action to take if packet is matched by the rule:
|address-list (string; Default: )||Name of the address list to be used. Applicable if action is
|address-list-timeout (time; Default: 00:00:00)||Time interval after which the address will be removed from the address list specified by
|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 transfered through the particular connection. 0 - means infinity, for example
|connection-limit (integer,netmaks; Default: )||Restrict connection limit per address or address block/td>|
|connection-mark (no-mark | string; Default: )||Matches packets marked via mangle facility with particular connection mark. If no-mark is set, rule will match any unmarked connection.|
|connection-rate (Integer 0..4294967295; Default: )||Connection Rate is a firewall matcher that allow to capture traffic based on 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 which destination is equal to specified IP or falls into specified IP range.|
|dst-address-list (name; Default: )||Matches destination address of a packet against user-defined address list|
|dst-address-type (unicast | local | broadcast | multicast; Default: )||Matches destination address type:
|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 the limit matcher, every destination IP address / destination port has it's own limit. Parameters are written in following format:
|dst-port (integer[-integer]: 0..65535; Default: )||List of destination port numbers or port number ranges|
|fragment (yes|no; Default: )||Matches fragmented packets. First (starting) fragment does not count. If connection tracking is enabled there will be no fragments as system automatically assembles every packet|
|hotspot (auth | from-client | http | local-dst | to-client; Default: )|
|icmp-options (integer:integer; Default: )||Matches ICMP type:code fileds|
|in-bridge-port (name; Default: )||Actual interface the packet has entered the router, if incoming interface is bridge|
|in-interface (name; Default: )||Interface the packet has entered the router|
|ingress-priority (integer: 0..63; Default: )||Matches ingress 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 following format:
For example, if router receives Ipsec encapsulated Gre packet, then rule
|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.
|jump-target (name; Default: )||Name of the target chain to jump to. Applicable only if
|layer7-protocol (name; Default: )||Layer7 filter name defined in layer7 protocol menu.|
|limit (integer,time,integer; Default: )||Matches packets until a given pps limit is exceeded. Parameters are written in following format:
|log-prefix (string; Default: )||Adds specified text at the beginning of every log message. Applicable if
|nth (integer,integer; Default: )||Matches every nth packet.
|out-bridge-port (name; Default: )||Actual interface the packet is leaving the router, if outgoing interface is 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. If no-mark is set, 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 to divide traffic into equal streams with ability to keep packets with 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 if
|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 following format
|random (integer: 1..99; Default: )||Matches packets randomly with 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 if
|src-address (Ip/Netmaks, Ip range; Default: )||Matches packets which source is equal to specified IP or falls into specified IP range.|
|src-address-list (name; Default: )||Matches source address of a packet against user-defined address list|
|src-address-type (unicast | local | broadcast | multicast; Default: )||
Matches source address type:
|src-port (integer[-integer]: 0..65535; Default: )||List of source ports and ranges of source ports. Applicable only if protocol is TCP or UDP.|
|src-mac-address (MAC address; Default: )||Matches source MAC address of the packet|
|tcp-flags (ack | cwr | ece | fin | psh | rst | syn | urg; Default: )||Matches specified TCP flags
|tcp-mss (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 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 original address with specified one. Applicable if action is dst-nat, netmap, same, src-nat|
|to-ports (integer[-integer]: 0..255; Default: )||Replace original port with specified one. Applicable if action is dst-nat, redirect, netmap, same, src-nat|
|ttl (integer: 0..255; Default: )||Matches packets TTL value|
/ip firewall nat print stats will show additional read-only properties
|bytes (integer)||Total amount of bytes matched by the rule|
|packets (integer)||Total amount of packets matched by the rule|
By default print is equivalent to print static and shows only static rules.
[admin@dzeltenais_burkaans] /ip firewall mangle> print stats Flags: X - disabled, I - invalid, D - dynamic # CHAIN ACTION BYTES PACKETS 0 prerouting mark-routing 17478158 127631 1 prerouting mark-routing 782505 4506
To print also dynamic rules use print all.
[admin@dzeltenais_burkaans] /ip firewall mangle> print all stats Flags: X - disabled, I - invalid, D - dynamic # CHAIN ACTION BYTES PACKETS 0 prerouting mark-routing 17478158 127631 1 prerouting mark-routing 782505 4506 2 D forward change-mss 0 0 3 D forward change-mss 0 0 4 D forward change-mss 0 0 5 D forward change-mss 129372 2031
Or to print only dynamic rules use print dynamic
[admin@dzeltenais_burkaans] /ip firewall mangle> print stats dynamic Flags: X - disabled, I - invalid, D - dynamic # CHAIN ACTION BYTES PACKETS 0 D forward change-mss 0 0 1 D forward change-mss 0 0 2 D forward change-mss 0 0 3 D forward change-mss 132444 2079
Menu specific commands
|reset-counters (id)||Reset statistics counters for specified firewall rules.|
|reset-counters-all ()||Reset statistics counters for all firewall rules.|
If you want to "hide" the private LAN 192.168.0.0/24 "behind" one address 10.5.8.109 given to you by the ISP, you should use the source network address translation (masquerading) feature of the MikroTik router. The masquerading will change the source IP address and port of the packets originated from the network 192.168.0.0/24 to the address 10.5.8.109 of the router when the packet is routed through it.
To use masquerading, a source NAT rule with action 'masquerade' should be added to the firewall configuration:
/ip firewall nat add chain=srcnat action=masquerade out-interface=Public
All outgoing connections from the network 192.168.0.0/24 will have source address 10.5.8.109 of the router and source port above 1024. No access from the Internet will be possible to the Local addresses. If you want to allow connections to the server on the local network, you should use destination Network Address Translation (NAT).
Forward all traffic to internal host
If you want to link Public IP 10.5.8.200 address to Local one 192.168.0.109, you should use destination address translation feature of the MikroTik router. Also if you want allow Local server to initiate connections to outside with given Public IP you should use source address translation, too.
Add Public IP to Public interface:
/ip address add address=10.5.8.200/32 interface=Public
Add rule allowing access to the internal server from external networks:
/ip firewall nat add chain=dstnat dst-address=10.5.8.200 action=dst-nat \ to-addresses=192.168.0.109
Add rule allowing the internal server to initate connections to the outer networks having its source address translated to 10.5.8.200:
/ip firewall nat add chain=srcnat src-address=192.168.0.109 action=src-nat \ to-addresses=10.5.8.200
If you would like to direct requests for a certain port to an internal machine (sometimes called opening a port, port mapping), you can do it like this:
/ip firewall nat add chain=dstnat dst-port=1234 action=dst-nat protocol=tcp to-address=192.168.1.1 to-port=1234
This rule translates to: when an incoming connection requests TCP port 1234, use the DST-NAT action and redirect it to local address 192.168.1.1 and the port 1234
Port forwarding to internal FTP server
As you can see from illustration above FTP uses more than one connection, but only command channel should be forwarded by Destination nat. Data channel is considered as related connection and should be accepted with "accept related" rule if you have strict firewall. Note that for related connections to be properly detected FTP helper has to be enabled.
/ip firewall nat add chain=dstnat dst-address=10.5.8.200 dst-port=21 protocol=tcp action=dst-nat to-addresses=192.168.0.109
/ip firewall filter add chain=forward connection-state=established,related action=accept
Note that active FTP might not work if client is behind dumb firewall or NATed router, because data channel is initiated by the server and cannot directly access the client.
If client is behind Mikrotik router, then make sure that FTP helper is enabled
[admin@3C22-atombumba] /ip firewall service-port> print Flags: X - disabled, I - invalid # NAME PORTS 0 ftp 21 1 tftp 69 2 irc 6667 3 h323 4 sip 5060 5061 5 pptp
If you want to link Public IP subnet 18.104.22.168/24 to local one 22.214.171.124/24, you should use destination address translation and source address translation features with action=netmap.
/ip firewall nat add chain=dstnat dst-address=126.96.36.199/24 \ action=netmap to-addresses=188.8.131.52/24 /ip firewall nat add chain=srcnat src-address=184.108.40.206/24 \ action=netmap to-addresses=220.127.116.11/24
Same can be written using different address notation, that still have to match with the described network
/ip firewall nat add chain=dstnat dst-address=18.104.22.168-22.214.171.124 \ action=netmap to-addresses=126.96.36.199-188.8.131.52 /ip firewall nat add chain=srcnat src-address=184.108.40.206-220.127.116.11 \ action=netmap to-addresses=18.104.22.168-22.214.171.124