modified on 17 April 2014 at 08:30 ••• 368,871 views

Manual:IP/Firewall/Filter

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Applies to RouterOS: v3, v4

Contents

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:
  • accept - accept the packet. Packet is not passed to next firewall rule.
  • add-dst-to-address-list - add destination address to address list specified by address-list parameter
  • add-src-to-address-list - add source address to address list specified by address-list parameter
  • drop - silently drop the packet
  • jump - jump to the user defined chain specified by the value of jump-target parameter
  • log - add a message to the system log containing following data: in-interface, out-interface, src-mac, protocol, src-ip:port->dst-ip:port and length of the packet. After packet is matched it is passed to next rule in the list, similar as passthrough
  • passthrough - ignore this rule and go to next one (useful for statistics).
  • reject - drop the packet and send an ICMP reject message
  • return - passes control back to the chain from where the jump took place
  • tarpit - captures and holds TCP connections (replies with SYN/ACK to the inbound TCP SYN packet)
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 actions
Value 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,netmask; Default: ) Restrict connection limit per address or address block
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. Read more >>
connection-state (estabilished | invalid | new | related; Default: ) Interprets the connection tracking analysis data for a particular packet:
  • established - a packet which belongs to an existing connection
  • invalid - a packet which could not be identified for some reason
  • new - the packet has started a new connection, or otherwise associated with a connection which has not seen packets in both directions.
  • related - a packet which is related to, but not part of an existing connection, such as ICMP errors or a packet which begins FTP data 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:
  • unicast - IP address used for point to point transmission
  • local - if dst-address is assigned to one of router's interfaces
  • broadcast - packet is sent to all devices in subnet
  • multicast - packet is forwarded to 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 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].
  • count - maximum average packet rate measured in packets per time interval
  • time - specifies the time interval in which the packet rate is measured (optional)
  • burst - number of packets which are not counted by packet rate
  • mode - the classifier for packet rate limiting
  • expire - specifies interval after which recored ip address /port will be deleted (optional)
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. Works only if use-ip-firewall is enabled in bridge settings.
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 (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 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 strict source routing option
  • timestamp - match packets with timestamp
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 following format: count[/time],burst.
  • count - maximum average packet rate measured in packets per time interval
  • time - specifies the time interval in which the packet rate is measured (optional, 1s will be used if not specified)
  • burst - number of packets which are not counted by packet rate
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. Works only if use-ip-firewall is enabled in bridge settings.
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 (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. 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. Parameters are in following format WeightThreshold, DelayThreshold, LopPortWeight, 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 - weight of the packets with privileged (<=1024) destination port
  • HighPortWeight - weight of the packet with non-priviliged destination port
random (integer: 1..99; Default: ) Matches packets randomly with given probability.
reject-with (; Default: ) Specifies error to be sent back if packet is rejected. Applicable if action=reject
routing-mark (string; Default: ) Matches packets marked by mangle facility with particular routing mark
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:

  • unicast - IP address used for point to point transmission
  • local - if address is assigned to one of router's interfaces
  • broadcast - packet is sent to all devices in subnet
  • multicast - packet is forwarded to defined group of devices
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
  • 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
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
ttl (integer: 0..255; Default: ) Matches packets TTL value

Stats

/ip firewall filter print stats will show additional read-only properties

Property Description
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

Property Description
reset-counters (id) Reset statistics counters for specified firewall rules.
reset-counters-all () Reset statistics counters for all firewall rules.


Basic examples

Router protection

Lets say our private network is 192.168.0.0/24 and public (WAN) interface is ether1. We will set up firewall to allow connections to router itself only from our local network and drop the rest. Also we will allow ICMP protocol on any interface so that anyone can ping your router from internet.

/ip firewall filter
add chain=input connection-state=invalid action=drop \
	comment="Drop Invalid connections"  
add chain=input connection-state=established action=accept \
	comment="Allow Established connections"  
add chain=input protocol=icmp action=accept \
	comment="Allow ICMP" 
add chain=input src-address=192.168.0.0/24 action=accept \
	in-interface=!ether1 
add chain=input action=drop comment="Drop everything else"  

Customer protection

To protect the customer's network, we should check all traffic which goes through router and block unwanted. For icmp, tcp, udp traffic we will create chains, where will be droped all unwanted packets:

/ip firewall filter
add chain=forward protocol=tcp connection-state=invalid \
 	action=drop comment="drop invalid connections"  
add chain=forward connection-state=established action=accept \ 
 	comment="allow already established connections"  
add chain=forward connection-state=related action=accept \
 	comment="allow related connections"  

Block "bogon" IP addresses

add chain=forward src-address=0.0.0.0/8 action=drop  
add chain=forward dst-address=0.0.0.0/8 action=drop  
add chain=forward src-address=127.0.0.0/8 action=drop 
add chain=forward dst-address=127.0.0.0/8 action=drop 
add chain=forward src-address=224.0.0.0/3 action=drop 
add chain=forward dst-address=224.0.0.0/3 action=drop 

Make jumps to new chains:

add chain=forward protocol=tcp action=jump jump-target=tcp  
add chain=forward protocol=udp action=jump jump-target=udp  
add chain=forward protocol=icmp action=jump jump-target=icmp 

Create tcp chain and deny some tcp ports in it:

add chain=tcp protocol=tcp dst-port=69 action=drop \
 	comment="deny TFTP" 
add chain=tcp protocol=tcp dst-port=111 action=drop \
 	comment="deny RPC portmapper"  
add chain=tcp protocol=tcp dst-port=135 action=drop \
 	comment="deny RPC portmapper"  
add chain=tcp protocol=tcp dst-port=137-139 action=drop \
 	comment="deny NBT"  
add chain=tcp protocol=tcp dst-port=445 action=drop \
 	comment="deny cifs"  
add chain=tcp protocol=tcp dst-port=2049 action=drop comment="deny NFS"  
add chain=tcp protocol=tcp dst-port=12345-12346 action=drop comment="deny NetBus"  
add chain=tcp protocol=tcp dst-port=20034 action=drop comment="deny NetBus"  
add chain=tcp protocol=tcp dst-port=3133 action=drop comment="deny BackOriffice"  
add chain=tcp protocol=tcp dst-port=67-68 action=drop comment="deny DHCP" 

Deny udp ports in udp chain:

add chain=udp protocol=udp dst-port=69 action=drop comment="deny TFTP"  
add chain=udp protocol=udp dst-port=111 action=drop comment="deny PRC portmapper"  
add chain=udp protocol=udp dst-port=135 action=drop comment="deny PRC portmapper"  
add chain=udp protocol=udp dst-port=137-139 action=drop comment="deny NBT"  
add chain=udp protocol=udp dst-port=2049 action=drop comment="deny NFS"  
add chain=udp protocol=udp dst-port=3133 action=drop comment="deny BackOriffice"  

Allow only needed icmp codes in icmp chain:

add chain=icmp protocol=icmp icmp-options=0:0 action=accept \
 	comment="echo reply"  
add chain=icmp protocol=icmp icmp-options=3:0 action=accept \
 	comment="net unreachable"  
add chain=icmp protocol=icmp icmp-options=3:1 action=accept \
 	comment="host unreachable"
add chain=icmp protocol=icmp icmp-options=3:4 action=accept \
 	comment="host unreachable fragmentation required"  
add chain=icmp protocol=icmp icmp-options=4:0 action=accept \
 	comment="allow source quench"  
add chain=icmp protocol=icmp icmp-options=8:0 action=accept \
 	comment="allow echo request"  
add chain=icmp protocol=icmp icmp-options=11:0 action=accept \
 	comment="allow time exceed"  
add chain=icmp protocol=icmp icmp-options=12:0 action=accept \ 
 	comment="allow parameter bad"  
add chain=icmp action=drop comment="deny all other types"  

other ICMP codes are found here.

Brute force protection

Bruteforce_login_prevention_(FTP_&_SSH)


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