Introduction
Mangle is a kind of 'marker' that marks packets for future processing with special marks. Many other facilities in RouterOS make use of these marks, e.g. queue trees, NAT, routing. They identify a packet based on its mark and process it accordingly. The mangle marks exist only within the router, they are not transmitted across the network.
Additionally, the mangle facility is used to modify some fields in the IP header, like TOS (DSCP) and TTL fields.
Firewall mangle rules consist of five predefined chains that cannot be deleted:
- The PREROUTING chain: Rules in this chain apply to packets as they just arrive on the network interface;
- The INPUT chain: Rules in this chain apply to packets just before they’re given to a local process;
- The OUTPUT chain: The rules here apply to packets just after they’ve been produced by a process;
- The FORWARD chain: The rules here apply to any packets that are routed through the current host;
- The POSTROUTING chain: The rules in this chain apply to packets as they just leave the network interface;
Properties
| Property | Description |
|---|---|
| action (action name; Default: accept) | Action to take if a packet is matched by the rule:
|
| address-list (string; Default: ) | Name of the address list to be used. Applicable if action is add-dst-to-address-list or add-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 by address-list parameter. Used in conjunction with add-dst-to-address-list or add-src-to-address-list actions
|
| chain (name; Default: ) | Specifies to which chain the 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 example connection-bytes=2000000-0 means that the rule matches if more than 2MB (upload and download) 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. If no-mark is set, the rule will match any unmarked connection. |
| connection-nat-state (srcnat | dstnat; Default: ) | Can match connections that are srcnatted, dstnatted, or both. Note that connection-state=related connections connection-nat-state is determined by the direction of the first packet. and if connection tracking needs to use dst-nat to deliver this connection to the same hosts as the main connection it will be in connection-nat-state=dstnat even if there are no dst-nat rules at all. |
| connection-rate (Integer 0..4294967295; Default: ) | Connection Rate is a firewall matcher that allows the capture of traffic based on the present speed of the connection. |
| connection-state (established | invalid | new | related; Default: ) | Interprets the connection tracking analytics data for a particular packet:
|
| 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 where the 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-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 its own limit. Parameters are written in the following format: count[/time],burst,mode[/expire].
|
| dst-port (integer[-integer]: 0..65535; Default: ) | List of destination port numbers or port number ranges |
| 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 matches.
|
| 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. Read more |
| 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.
For example, if a router receives an 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 action=jump |
| 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 the following format: count[/time],burst.
|
| 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 if action=log or log=yes configured. |
| new-dscp (integer: 0..63; Default: ) | Sets a new DSCP value for a packet |
| new-mss (integer; Default: ) | Sets a new MSS for a packet. Clampt-to-pmtu feature sets (DF) bit in the IP header to dynamically discover the PMTU of a path. Host sends all datagrams on that path with the DF bit set until receives ICMP Destination Unreachable messages with a code meaning "fragmentation needed and DF set". Upon receipt of such a message, the source host reduces its assumed PMTU for the path. |
| new-packet-mark (string; Default: ) | Sets a new packet-mark value |
| new-priority (integer | from-dscp | from-dscp-high-3-bits | from-ingress; Default: ) | Sets a new priority for a packet. This can be the VLAN, WMM, DSCP or MPLS EXP priority Read more. This property can also be used to set an internal priority. |
| new-routing-mark (string; Default: ) | Sets a new routing-mark value (in RouterOS v7 routing mark must be created before as a new Routing table) |
| new-ttl (decrement | increment | set:integer; Default: ) | Sets a new Time to live value |
| nth (integer,integer; Default: ) | Matches every nth packet: nth=2,1 rule will match every first packet of 2, hence, 50% of all the traffic that is matched by the rule |
| 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. If no-mark is 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 |
| passthrough (yes|no; Default: yes) | whether to let the packet to pass further (like action passthrough) into the firewall or not (property only valid some actions) |
| per-connection-classifier (ValuesToHash:Denominator/Remainder; Default: ) | PCC matcher allows division of 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 if protocol is 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 format WeightThreshold, DelayThreshold, LowPortWeight, HighPortWeight
|
| 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 |
| route-dst (IP, Default:) | Matches packets with a specific gateway |
| 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 internal priority that has been set using the set-priority action |
| src-address (IP/Netmask, IP range; Default: ) | Matches packets where the 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-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 a 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[-integer]: 0..65535; Default: ) | Matches TCP MSS value of an IP packet |
| time (time-time,sat | fri | thu | wed | tue | mon | sun; Default: ) | Allows creation of a filter based on the packets' arrival time and date or, for locally generated packets, departure time and date |
| tls-host (string; Default: ) | Allows matching traffic based on TLS hostname. Accepts GLOB syntax for wildcard matching. Note that the matcher will not be able to match the hostname if the TLS handshake frame is fragmented into multiple TCP segments (packets). |
| ttl (equal | greater-than | less-than | not-equal : integer(0..255); Default: ) | Matches packets TTL value. |
Stats
To show additional read-only properties:
| 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 print out stats:
[admin@MikroTik] > ip firewall mangle print stats all Flags: X - disabled, I - invalid, D - dynamic # CHAIN ACTION BYTES PACKETS 0 D ;;; special dummy rule to show fasttrack counters prerouting passthrough 18 176 176 30 562 1 D ;;; special dummy rule to show fasttrack counters forward passthrough 18 176 176 30 562 2 D ;;; special dummy rule to show fasttrack counters postrouting passthrough 18 176 176 30 562 3 forward change-mss 18 512 356
Configuration example
Change MSS
It is a known fact that VPN links have a smaller packet size due to encapsulation overhead. A large packet with MSS that exceeds the MSS of the VPN link should be fragmented prior to sending it via that kind of connection. However, if the packet has a Don't Fragment flag set, it cannot be fragmented and should be discarded. On links that have broken path MTU discovery (PMTUD), it may lead to a number of problems, including problems with FTP and HTTP data transfer and e-mail services.
In the case of a link with broken PMTUD, a decrease of the MSS of the packets coming through the VPN link resolves the problem. The following example demonstrates how to decrease the MSS value via mangle:
/ip firewall mangle add out-interface=pppoe-out protocol=tcp tcp-flags=syn action=change-mss new-mss=1300 chain=forward tcp-mss=1301-65535
Overview
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