modified on 17 July 2014 at 07:14 ••• 260,399 views

Manual:Interface/Bridge

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Applies to RouterOS: v3, v4+

Contents

Summary

Sub-menu: /interface bridge
Standards: IEEE802.1D


Ethernet-like networks (Ethernet, Ethernet over IP, IEEE802.11 in ap-bridge or bridge mode, WDS, VLAN) can be connected together using MAC bridges. The bridge feature allows the interconnection of hosts connected to separate LANs (using EoIP, geographically distributed networks can be bridged as well if any kind of IP network interconnection exists between them) as if they were attached to a single LAN. As bridges are transparent, they do not appear in traceroute list, and no utility can make a distinction between a host working in one LAN and a host working in another LAN if these LANs are bridged (depending on the way the LANs are interconnected, latency and data rate between hosts may vary).

Network loops may emerge (intentionally or not) in complex topologies. Without any special treatment, loops would prevent network from functioning normally, as they would lead to avalanche-like packet multiplication. Each bridge runs an algorithm which calculates how the loop can be prevented. STP and RSTP allows bridges to communicate with each other, so they can negotiate a loop free topology. All other alternative connections that would otherwise form loops, are put to standby, so that should the main connection fail, another connection could take its place. This algorithm exchanges configuration messages (BPDU - Bridge Protocol Data Unit) periodically, so that all bridges are updated with the newest information about changes in network topology. (R)STP selects a root bridge which is responsible for network reconfiguration, such as blocking and opening ports on other bridges. The root bridge is the bridge with the lowest bridge ID.

Bridge Interface Setup

Sub-menu: /interface bridge


To combine a number of networks into one bridge, a bridge interface should be created (later, all the desired interfaces should be set up as its ports). One MAC address will be assigned to all the bridged interfaces (the smallest MAC address will be chosen automatically).

Properties

Property Description
admin-mac (MAC address; Default: ) Static MAC address of the bridge (takes effect if auto-mac=no)
ageing-time (time; Default: 00:05:00) How long a host's information will be kept in the bridge database
arp (disabled | enabled | proxy-arp | reply-only; Default: enabled) Address Resolution Protocol setting
  • disabled - the interface will not use ARP
  • enabled - the interface will use ARP
  • proxy-arp - the interface will use the ARP proxy feature
  • reply-only - the interface will only reply to requests originated from matching IP address/MAC address combinations which are entered as static entries in the "/ip arp" table. No dynamic entries will be automatically stored in the "/ip arp" table. Therefore for communications to be successful, a valid static entry must already exist.
auto-mac (yes | no; Default: yes) Automatically select the smallest MAC address of bridge ports as a bridge MAC address
forward-delay (time; Default: 00:00:15) Time which is spent during the initialization phase of the bridge interface (i.e., after router startup or enabling the interface) in listening/learning state before the bridge will start functioning normally
l2mtu (integer; read-only) Layer2 Maximum transmission unit. read more»
max-message-age (time; Default: 00:00:20) How long to remember Hello messages received from other bridges
mtu (integer; Default: 1500) Maximum Transmission Unit
name (text; Default: bridgeN) Name of the bridge interface
priority (integer: 0..65535 decimal format or 0x0000-0xffff hex format; Default: 32768 / 0x8000)

Spanning tree protocol priority for bridge interface. Bridge with the smallest (lowest) bridge ID becomes a Root-Bridge. Bridge ID consists of two numbers - priority and MAC address of the bridge. To compare two bridge IDs, the priority is compared first. If two bridges have equal priority, then the MAC addresses are compared.

protocol-mode (none | rstp | stp; Default: rstp) Select Spanning tree protocol (STP) or Rapid spanning tree protocol (RSTP) to ensure a loop-free topology for any bridged LAN. RSTP provides for faster spanning tree convergence after a topology change.
transmit-hold-count (integer: 1..10; Default: 6) The Transmit Hold Count used by the Port Transmit state machine to limit transmission rate

(Rapid) Spanning Tree Protocol

http://en.wikipedia.org/wiki/Spanning_Tree_Protocol

Example

To add and enable a bridge interface that will forward all the protocols:

[admin@MikroTik] /interface bridge> add 
[admin@MikroTik] /interface bridge> print 
Flags: X - disabled, R - running 
 0  R name="bridge1" mtu=1500 l2mtu=65535 arp=enabled 
      mac-address=00:00:00:00:00:00 protocol-mode=none priority=0x8000 
      auto-mac=yes admin-mac=00:00:00:00:00:00 max-message-age=20s 
      forward-delay=15s transmit-hold-count=6 ageing-time=5m 
[admin@MikroTik] /interface bridge>

Bridge Settings

Sub-menu: /interface bridge settings


Property Description
allow-fast-path (yes | no; Default: yes) Allows fast path
use-ip-firewall (yes | no; Default: no) Send bridged traffic to also be processed by 'IP firewall'
use-ip-firewall-for-pppoe (yes | no; Default: no) Send bridged un-encrypted PPPoE traffic to also be processed by 'IP firewall' (requires use-ip-firewall=yes to work)
use-ip-firewall-for-vlan (yes | no; Default: no) Send bridged VLAN traffic to also be processed by 'IP firewall' (requires use-ip-firewall=yes to work)

Port Settings

Sub-menu: /interface bridge port


Port submenu is used to enslave interfaces in a particular bridge interface.

Property Description
bridge (name; Default: none) The bridge interface the respective interface is grouped in
edge (auto | no | no-discover | yes | yes-discover; Default: auto) Set port as edge port or non-edge port, or enable automatic detection. Edge ports are connected to a LAN that has no other bridges attached. If the port is configured to discover edge port then as soon as the bridge detects a BPDU coming to an edge port, the port becomes a non-edge port.
external-fdb (auto | no | yes; Default: auto) Whether to use wireless registration table to speed up bridge host learning
horizon (none | integer 0..429496729; Default: none) Use split horizon bridging to prevent bridging loops. read more»
interface (name; Default: none) Name of the interface
path-cost (integer: 0..65535; Default: 10) Path cost to the interface, used by STP to determine the "best" path
point-to-point (auto | yes | no; Default: auto)
priority (integer: 0..255; Default: 128) The priority of the interface in comparison with other going to the same subnet

Example

To group ether1 and ether2 in the already created bridge1 bridge

[admin@MikroTik] /interface bridge port> add bridge=bridge1 interface=ether1
[admin@MikroTik] /interface bridge port> add bridge=bridge1 interface=ether2
[admin@MikroTik] /interface bridge port> print 
Flags: X - disabled, I - inactive, D - dynamic 
 #    INTERFACE              BRIDGE              PRIORITY PATH-COST  HORIZON   
 0    ether1                 bridge1             0x80     10         none      
 1    ether2                 bridge1             0x80     10         none      
[admin@MikroTik] /interface bridge port> 

Bridge Monitoring

Sub-menu: /interface bridge monitor


Used to monitor the current status of a bridge.

Property Description
current-mac-address (MAC address) Current MAC address of the bridge
designated-port-count (integer) Number of designated bridge ports
port-count (integer) Number of the bridge ports
root-bridge (yes | no) Shows whether bridge is the root bridge of the spanning tree
root-bridge-id (text) The root bridge ID, which is in form of bridge-priority.bridge-MAC-address
root-path-cost (integer) The total cost of the path to the root-bridge
root-port (name) Port to which the root bridge is connected to
state (enabled | disabled) State of the bridge

Example

To monitor a bridge:

[admin@MikroTik] /interface bridge> monitor bridge1 
                  state: enabled
    current-mac-address: 00:0C:42:52:2E:CE
            root-bridge: yes
         root-bridge-id: 0x8000.00:00:00:00:00:00
         root-path-cost: 0
              root-port: none
             port-count: 2
  designated-port-count: 0

[admin@MikroTik] /interface bridge>

Bridge Port Monitoring

Sub-menu: /interface bridge port monitor


Statistics of an interface that belongs to a bridge.

Property Description
edge-port (yes | no) Whether port is an edge port or not
edge-port-discovery (yes | no) Whether port is set to automatically detect edge ports
external-fdb (yes | no) Shows whether registration table is used instead of forwarding data base
forwarding (yes | no) Port state
learning (yes | no) Port state
port-number (integer 1..4095) Port identifier
point-to-point-port (yes | no)
role (designated | root port | alternate | backup | disabled)

(R)STP algorithm assigned role of the port:

  • Disabled port - not strictly part of STP, a network administrator can manually disable a port
  • Root port – a forwarding port that is the best port from Nonroot-bridge to Rootbridge
  • Alternative port – an alternate path to the root bridge. This path is different than using the root port
  • Designated port – a forwarding port for every LAN segment
  • Backup port – a backup/redundant path to a segment where another bridge port already connects.
sending-rstp (yes | no) Whether the port is sending BPDU messages
status (in-bridge | inactive) Port status

Example

To monitor a bridge port:

[admin@MikroTik] /interface bridge port> monitor 0     
               status: in-bridge
          port-number: 1
                 role: designated-port
            edge-port: no
  edge-port-discovery: yes
  point-to-point-port: no
         external-fdb: no
         sending-rstp: no
             learning: yes
           forwarding: yes

[admin@MikroTik] /interface bridge port>

Bridge Host Monitoring

Sub-menu: /interface bridge host


Property Description
age (read-only: time) The time since the last packet was received from the host
bridge (read-only: name) The bridge the entry belongs to
external-fdb (read-only: flag) Whether the host was learned using wireless registration table
local (read-only: flag) Whether the host entry is of the bridge itself (that way all local interfaces are shown)
mac-address (read-only: MAC address) Host's MAC address
on-interface (read-only: name) Which of the bridged interfaces the host is connected to

Example

To get the active host table:

[admin@MikroTik] /interface bridge host> print 
Flags: L - local, E - external-fdb 
  BRIDGE           MAC-ADDRESS       ON-INTERFACE          AGE                 
  bridge1          00:00:00:00:00:01 ether2                3s                  
  bridge1          00:01:29:FF:1D:CC ether2                0s                  
L bridge1          00:0C:42:52:2E:CF ether2                0s                  
  bridge1          00:0C:42:52:2E:D0 ether2                3s                  
  bridge1          00:0C:42:5C:A5:AE ether2                0s                  
[admin@MikroTik] /interface bridge host>

Bridge Firewall

Sub-menu: /interface bridge filter, /interface bridge nat


The bridge firewall implements packet filtering and thereby provides security functions that are used to manage data flow to, from and through bridge.

Packet flow diagram shows how packets are processed through router. It is possible to force bridge traffic to go through /ip firewall filter rules (see: Bridge Settings)

There are two bridge firewall tables:

  • filter - bridge firewall with three predefined chains:
    • input - filters packets, where the destination is the bridge (including those packets that will be routed, as they are destined to the bridge MAC address anyway)
    • output - filters packets, which come from the bridge (including those packets that has been routed normally)
    • forward - filters packets, which are to be bridged (note: this chain is not applied to the packets that should be routed through the router, just to those that are traversing between the ports of the same bridge)
  • nat - bridge network address translation provides ways for changing source/destination MAC addresses of the packets traversing a bridge. Has two built-in chains:
    • srcnat - used for "hiding" a host or a network behind a different MAC address. This chain is applied to the packets leaving the router through a bridged interface
    • dstnat - used for redirecting some packets to other destinations

You can put packet marks in bridge firewall (filter and NAT), which are the same as the packet marks in IP firewall put by '/ip firewall mangle'. In this way, packet marks put by bridge firewall can be used in 'IP firewall', and vice versa.

General bridge firewall properties are described in this section. Some parameters that differ between nat and filter rules are described in further sections.

Properties

Property Description
802.3-sap (integer) DSAP (Destination Service Access Point) and SSAP (Source Service Access Point) are 2 one byte fields, which identify the network protocol entities which use the link layer service. These bytes are always equal. Two hexadecimal digits may be specified here to match a SAP byte
802.3-type (integer) Ethernet protocol type, placed after the IEEE 802.2 frame header. Works only if 802.3-sap is 0xAA (SNAP - Sub-Network Attachment Point header). For example, AppleTalk can be indicated by SAP code of 0xAA followed by a SNAP type code of 0x809B
arp-dst-address (IP address; default: ) ARP destination address
arp-dst-mac-address (MAC address; default: ) ARP destination MAC address
arp-gratuitous (yes | no; default: ) Matches ARP gratuitous packets
arp-hardware-type (integer; default: 1) ARP hardware type. This is normally Ethernet (Type 1)
arp-opcode (arp-nak | drarp-error | drarp-reply | drarp-request | inarp-reply | inarp-request | reply | reply-reverse | request | request-reverse)

ARP opcode (packet type)

  • arp-nak - negative ARP reply (rarely used, mostly in ATM networks)
  • drarp-error - Dynamic RARP error code, saying that an IP address for the given MAC address can not be allocated
  • drarp-reply - Dynamic RARP reply, with a temporaty IP address assignment for a host
  • drarp-request - Dynamic RARP request to assign a temporary IP address for the given MAC address
  • inarp-reply - InverseARP Reply
  • inarp-request - InverseARP Request
  • reply - standard ARP reply with a MAC address
  • reply-reverse - reverse ARP (RARP) reply with an IP address assigned
  • request - standard ARP request to a known IP address to find out unknown MAC address
  • request-reverse - reverse ARP (RARP) request to a known MAC address to find out unknown IP address (intended to be used by hosts to find out their own IP address, similarly to DHCP service)
arp-packet-type (integer: 0..65535 decimal format or 0x0000-0xffff hex format) ARP Packet Type
arp-src-address (IP address; default: ) ARP source address
arp-src-mac-address (MAC address; default: ) ARP source MAC address
chain (text) Bridge firewall chain, which the filter is functioning in (either a built-in one, or a user defined)
dst-address (IP address; default: ) Destination IP address (only if MAC protocol is set to IPv4)
dst-mac-address (MAC address; default: ) Destination MAC address
dst-port (integer 0..65535) Destination port number or range (only for TCP or UDP protocols)
in-bridge (name) Bridge interface through which the packet is coming in
in-interface (name) Physical interface (i.e., bridge port) through which the packet is coming in
ingress-priority (integer 0..63) Matches ingress priority of the packet. Priority may be derived from VLAN, WMM or MPLS EXP bit. read more»
ip-protocol (ddp | egp | encap | etherip | ggp | gre | hmp | icmp | icmpv6 | idpr-cmtp | igmp | ipencap | ipip | ipsec-ah | ipsec-esp | ipv6 | ipv6-frag | ipv6-nonxt | ipv6-opts | ipv6-route | iso-tp4 | l2tp | ospf | pim | pup | rdp | rspf | rsvp | st | tcp | udp | vmtp | vrrp | xns-idp | xtp)

IP protocol (only if MAC protocol is set to IPv4)

  • ddp - datagram delivery protocol
  • egp - exterior gateway protocol
  • encap - ip encapsulation
  • etherip -
  • ggp - gateway-gateway protocol
  • gre - general routing encapsulation
  • hmp - host monitoring protocol
  • icmp - IPv4 internet control message protocol
  • icmpv6 - IPv6 internet control message protocol
  • idpr-cmtp - idpr control message transport
  • igmp - internet group management protocol
  • ipencap - ip encapsulated in ip
  • ipip - ip encapsulation
  • ipsec-ah - IPsec AH protocol
  • ipsec-esp - IPsec ESP protocol
  • ipv6 -
  • ipv6-frag -
  • ipv6-nonxt -
  • ipv6-opts -
  • ipv6-route -
  • iso-tp4 - iso transport protocol class 4
  • l2tp -
  • ospf - open shortest path first
  • pim - protocol independent multicast
  • pup - parc universal packet protocol
  • rspf - radio shortest path first
  • rsvp -
  • rdp - reliable datagram protocol
  • st - st datagram mode
  • tcp - transmission control protocol
  • udp - user datagram protocol
  • vmtp - versatile message transport
  • vrrp - Virtual Router Redundancy Protocol
  • xns-idp - xerox ns idp
  • xtp – xpress transfer protocol
jump-target (name) If action=jump specified, then specifies the user-defined firewall chain to process the packet
limit (integer/time,integer)

Restricts packet match rate to a given limit.

  • count - maximum average packet rate, measured in packets per second (pps), unless followed by Time option
  • time - specifies the time interval over which the packet rate is measured
  • burst - number of packets to match in a burst
log-prefix (text) Defines the prefix to be printed before the logging information
mac-protocol (802.2 | arp | ip | ipv6 | ipx | length | mpls-multicast | mpls-unicast | pppoe | pppoe-discovery | rarp | vlan or integer: 0..65535 decimal format or 0x0000-0xffff hex format) Ethernet payload type (MAC-level protocol)
  • 802.2
  • arp - Type 0x0806 - ARP
  • ip - Type 0x0800 - IPv4
  • ipv6 - Type 0x86dd - IPv6
  • ipx - Type 0x8137 - "Internetwork Packet Exchange"
  • length
  • mpls-multicast - Type 0x8848 - MPLS Multicast
  • mpls-unicast - Type 0x8847 - MPLS Unicast
  • ppoe - Type 0x8864 - PPPoE Session
  • ppoe-discovery - Type 0x8863 - PPPoE Discovery
  • rarp - Type 0x8035 - Reverse ARP
  • vlan - Type 0x8100 - 802.1Q tagged VLAN
out-bridge (name) Outgoing bridge interface
out-interface (name) Interface that the packet is leaving the bridge through
packet-mark (name) Match packets with certain packet mark
packet-type (broadcast | host | multicast | other-host)

MAC frame type:

  • broadcast - broadcast MAC packet
  • host - packet is destined to the bridge itself
  • multicast - multicast MAC packet
  • other-host - packet is destined to some other unicast address, not to the bridge itself
src-address (IP address; default: ) Source IP address (only if MAC protocol is set to IPv4)
src-mac-address (MAC address; default: ) Source MAC address
src-port (integer 0..65535) Source port number or range (only for TCP or UDP protocols)
stp-flags (topology-change | topology-change-ack)

The BPDU (Bridge Protocol Data Unit) flags. Bridge exchange configuration messages named BPDU periodically for preventing loops

  • topology-change - topology change flag is set when a bridge detects port state change, to force all other bridges to drop their host tables and recalculate network topology
  • topology-change-ack - topology change acknowledgement flag is sen in replies to the notification packets
stp-forward-delay (time 0..65535) Forward delay timer
stp-hello-time (time 0..65535) STP hello packets time
stp-max-age (time 0..65535) Maximal STP message age
stp-msg-age (time 0..65535) STP message age
stp-port (integer 0..65535) STP port identifier
stp-root-address (MAC address) Root bridge MAC address
stp-root-cost (integer 0..65535) Root bridge cost
stp-root-priority (integer 0..65535) Root bridge priority
stp-sender-address (MAC address) STP message sender MAC address
stp-sender-priority (integer 0..65535) STP sender priority
stp-type (config | tcn)

The BPDU type:

  • config - configuration BPDU
  • tcn - topology change notification
vlan-encap (802.2 | arp | ip | ipv6 | ipx | length | mpls-multicast | mpls-unicast | pppoe | pppoe-discovery | rarp | vlan or integer: 0..65535 decimal format or 0x0000-0xffff hex format) the MAC protocol type encapsulated in the VLAN frame
vlan-id (integer 0..4095) VLAN identifier field
vlan-priority (integer 0..7) The user priority field

Notes

  • STP matchers are only valid if destination MAC address is 01:80:C2:00:00:00/FF:FF:FF:FF:FF:FF (Bridge Group address), also stp should be enabled.
  • ARP matchers are only valid if mac-protocol is arp or rarp
  • VLAN matchers are only valid for vlan ethernet protocol
  • IP-related matchers are only valid if mac-protocol is set as ipv4
  • 802.3 matchers are only consulted if the actual frame is compliant with IEEE 802.2 and IEEE 802.3 standards (note: it is not the industry-standard Ethernet frame format used in most networks worldwide!). These matchers are ignored for other packets.

Bridge Packet Filter

Sub-menu: /interface bridge filter


This section describes bridge packet filter specific filtering options, that are specific to '/interface bridge filter'.

Properties

Property Description
action (accept | drop | jump | log | mark-packet | passthrough | return | set-priority)
  • accept - accept the packet. No action, i.e., the packet is passed through without undertaking any action, and no more rules are processed in the relevant list/chain
  • drop - silently drop the packet (without sending the ICMP reject message)
  • jump - jump to the chain specified by the value of the jump-target argument
  • log - log the packet
  • mark - mark the packet to use the mark later
  • passthrough - ignore this rule and go on to the next one. Acts the same way as a disabled rule, except for ability to count packets
  • return - return to the previous chain, from where the jump took place
  • set-priority - set priority specified by the new-priority parameter on the packets sent out through a link that is capable of transporting priority (VLAN or WMM-enabled wireless interface). Read more>

Bridge NAT

Sub-menu: /interface bridge nat


This section describes bridge NAT options, that are specific to '/interface bridge nat'.

Properties

Property Description
action (accept | drop | jump | mark-packet | redirect | set-priority | arp-reply | dst-nat | log | passthrough | return | src-nat)
  • accept - accept the packet. No action, i.e., the packet is passed through without undertaking any action, and no more rules are processed in the relevant list/chain
  • arp-reply - send a reply to an ARP request (any other packets will be ignored by this rule) with the specified MAC address (only valid in dstnat chain)
  • drop - silently drop the packet (without sending the ICMP reject message)
  • dst-nat - change destination MAC address of a packet (only valid in dstnat chain)
  • jump - jump to the chain specified by the value of the jump-target argument
  • log - log the packet
  • mark - mark the packet to use the mark later
  • passthrough - ignore this rule and go on to the next one. Acts the same way as a disabled rule, except for ability to count packets
  • redirect - redirect the packet to the bridge itself (only valid in dstnat chain)
  • return - return to the previous chain, from where the jump took place
  • set-priority - set priority specified by the new-priority parameter on the packets sent out through a link that is capable of transporting priority (VLAN or WMM-enabled wireless interface). Read more>
  • src-nat - change source MAC address of a packet (only valid in srcnat chain)
to-arp-reply-mac-address (MAC address) Source MAC address to put in Ethernet frame and ARP payload, when action=arp-reply is selected
to-dst-mac-address (MAC address) Destination MAC address to put in Ethernet frames, when action=dst-nat is selected
to-src-mac-address (MAC address) Source MAC address to put in Ethernet frames, when action=src-nat is selected

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