Manual:IP/Firewall/Filter
Summary
Sub-menu: /ip firewall filter
The firewall implements packet filtering and thereby provides security functions that are used to manage data flow to, from and through the router. Along with the Network Address Translation it serves as a tool for preventing unauthorized access to directly attached networks and the router itself as well as a filter for outgoing traffic.
Network firewalls keep outside threats away from sensitive data available inside the network. Whenever different networks are joined together, there is always a threat that someone from outside of your network will break into your LAN. Such break-ins may result in private data being stolen and distributed, valuable data being altered or destroyed, or entire hard drives being erased. Firewalls are used as a means of preventing or minimizing the security risks inherent in connecting to other networks. Properly configured firewall plays a key role in efficient and secure network infrastrure deployment.
MikroTik RouterOS has very powerful firewall implementation with features including:
- stateful packet inspection
- Layer-7 protocol detection
- peer-to-peer protocols filtering
- traffic classification by:
- source MAC address
- IP addresses (network or list) and address types (broadcast, local, multicast, unicast)
- port or port range
- IP protocols
- protocol options (ICMP type and code fields, TCP flags, IP options and MSS)
- interface the packet arrived from or left through
- internal flow and connection marks
- DSCP byte
- packet content
- rate at which packets arrive and sequence numbers
- packet size
- packet arrival time
- and much more!
Chains
The firewall operates by means of firewall rules. Each rule consists of two parts - the matcher which matches traffic flow against given conditions and the action which defines what to do with the matched packet.
Firewall filtering rules are grouped together in chains. It allows a packet to be matched against one common criterion in one chain, and then passed over for processing against some other common criteria to another chain. For example a packet should be matched against the IP address:port pair. Of course, it could be achieved by adding as many rules with IP address:port match as required to the forward chain, but a better way could be to add one rule that matches traffic from a particular IP address, e.g.: /ip firewall filter add src-address=1.1.1.2/32 jump-target="mychain" and in case of successfull match passes control over the IP packet to some other chain, id est mychain in this example. Then rules that perform matching against separate ports can be added to mychain chain without specifying the IP addresses.
There are three predefined chains, which cannot be deleted:
- input - used to process packets entering the router through 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
- forward - used to process packets passing through the router
- output - used to process packets originated from the router and leaving it through one of the interfaces. Packets passing through the router are not processed against the rules of the output chain
Packet flow diagrams illustrate how packets are processed in RouterOS.
When processing a chain, rules are taken from the chain in the order they are listed there from top to bottom. If a packet matches the criteria of the rule, then the specified action is performed on it, and no more rules are processed in that chain (the exception is the passthrough action). If a packet has not matched any rule within the chain, then it is accepted.
Properties
| Property | Description |
|---|---|
| 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 add-dst-to-address-list or add-src-to-address-list |
| address-list-timeout (time; Default: 00:00:00) | 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 actionsValue of 00:00:00 will leave the address in the address list forever |
| 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-bytes=2000000-0 means that the rule matches if more than 2MB has been transfered through the relevant connection |
| connection-limit (integer,netmaks; Default: ) | Restrict connection limit per address or address block/td> |
| connection-mark (string; Default: ) | Matches packets marked via mangle facility with particular connection mark |
| connection-rate (Integer 0..4294967295; Default: ) | Connection Rate is a firewall matcher that allow to capture traffic based on present speed of the connection. more> |
| connection-state (estabilished | invalid | new | related; Default: ) | Interprets the connection tracking analysis 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 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 if 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: 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. 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. Read more> |
| ipv4-options (; Default: ) | |
| 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 if given pps limit is exceeded. Parameters are written in following format: count,time,burst.
|
| log-prefix (string; Default: ) | Adds specified text at the beginning of every log message. Applicable if action=log |
| nth (integer,integer; Default: ) | Matches every nth packet. Read more |
| 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 |
| p2p (all-p2p | bit-torrent | blubster | direct-connect | edonkey | fasttrack | gnutella | soulseek | warez | winmx; Default: ) | Matches packets from various peer-to-peer (P2P) protocols. Does not work on encrypted p2p packets. |
| packet-mark (string; Default: ) | Matches packets marked via mangle facility with particular packet mark |
| 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. Read more >> |
| 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 |
| random (; Default: ) | |
| reject-with (; Default: ) | |
| routing-mark (; Default: ) | |
| src-address (; Default: ) | |
| src-address-list (; Default: ) | |
| src-address-type (; Default: ) | |
| src-port (; Default: ) | |
| tcp-flags (; Default: ) | |
| tcp-mss (; Default: ) | |
| time (; Default: ) | |
| ttl (; Default: ) |
Stats
Basic examples