Manual:Interface/Bridge

Applies to RouterOS: v3, v4+

Summary

Sub-menu: /interface bridge
Standards: IEEE 802.1D , IEEE 802.1Q

Ethernet-like networks (Ethernet, Ethernet over IP, IEEE 802.11 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 MAC address of first bridge port which comes up will be chosen automatically).

Properties

Property	Description
add-dhcp-option82 (yes | no; Default: no)	Whether to add DHCP Option-82 information (Agent Remote ID and Agent Circuit ID) to DHCP packets. Can be used together with Option-82 capable DHCP server to assign IP addresses and implement policies. This property only has effect when dhcp-snooping is set to yes.
admin-mac (MAC address; Default: none)	Static MAC address of the bridge. This property only has effect when auto-mac is set to 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.
arp-timeout (auto | integer; Default: auto)	ARP timeout is time how long ARP record is kept in ARP table after no packets are received from IP. Value auto equals to the value of arp-timeout in IP/Settings, default is 30s.
auto-mac (yes | no; Default: yes)	Automatically select one MAC address of bridge ports as a bridge MAC address.
comment (string; Default: )	Short description of the interface.
dhcp-snooping (yes | no; Default: no)	Enables or disables DHCP Snooping on the bridge.
disabled (yes | no; Default: no)	Changes whether the bridge is disabled.
ether-type (0x9100 | 0x8100 | 0x88a8; Default: 0x8100)	Changes the EtherType, which will be used to determine if a packet has a VLAN tag. Packets that have a matching EtherType are considered as tagged packets. This property only has effect when vlan-filtering is set to yes.
fast-forward (yes | no; Default: yes)	Special and faster case of FastPath which works only on bridges with 2 interfaces (enabled by default only for new bridges). More details can be found in the Fast Forward section.
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.
frame-types (admit-all | admit-only-untagged-and-priority-tagged | admit-only-vlan-tagged; Default: admit-all)	Specifies allowed ingress frame types on a bridge port. This property only has effect when vlan-filtering is set to yes.
igmp-snooping (yes | no; Default: no)	Enables multicast group and port learning to prevent multicast traffic from flooding all interfaces in a bridge.
igmp-version (2 | 3; Default: 2)	Selects the IGMP version in which IGMP general membership queries will be generated. This property only has effect when igmp-snooping is set to yes.
ingress-filtering (yes | no; Default: no)	Enables or disables ingress filtering, which checks if an entry exists for the ingress port and the VLAN ID in the bridge VLAN table. Should be used with frame-types to specify if the ingress traffic should be tagged or untagged. This property only has effect when vlan-filtering is set to yes.
last-member-interval (time; Default: 1s)	If a port has fast-leave set to no and a bridge port receives a IGMP Leave message, then a IGMP Snooping enabled bridge will send a IGMP query to make sure that no devices has subscribed to a certain multicast stream on a bridge port. If a IGMP Snooping enabled bridge does not receive a IGMP membership report after amount of last-member-interval, then the bridge considers that no one has subscribed to a certain multicast stream and can stop forwarding it. This property only has effect when igmp-snooping is set to yes.
last-member-query-count (integer: 0..4294967295; Default: 2)	How many times should last-member-interval pass until a IGMP Snooping bridge will stop forwarding a certain multicast stream. This property only has effect when igmp-snooping is set to yes.
max-hops (integer: 6..40; Default: 20)	Bridge count which BPDU can pass in a MSTP enabled network in the same region before BPDU is being ignored. This property only has effect when protocol-mode is set to mstp.
max-message-age (time; Default: 00:00:20)	How long to remember Hello messages received from other STP/RSTP enabled bridges. This property only has effect when protocol-mode is set to stp or rstp.
membership-interval (time; Default: 4m20s)	Amount of time after an entry in the Multicast Database (MDB) is removed if a IGMP membership report is not received on a certain port. This property only has effect when igmp-snooping is set to yes.
mtu (integer; Default: 1500)	Maximum Transmission Unit
multicast-querier (yes | no; Default: no)	Multicast querier generates IGMP general membership queries to which all IGMP capable devices respond with a IGMP membership report, usually a PIM (multicast) router generates these queries. By using this property you can make a IGMP Snooping enabled bridge to generate IGMP general membership queries. This property should be used whenever there is no PIM (multicast) router in a Layer2 network or IGMP packets must be sent through multiple IGMP Snooping enabled bridges to reach a PIM (multicast) router. Without a multicast querier in a Layer2 network the Multicast Database (MDB) is not being updated and IGMP Snooping will not function properly. This property only has effect when igmp-snooping is set to yes.
multicast-router (disabled | permanent | temporary-query; Default: temporary-query)	Changes the state of a bridge itself if IGMP membership reports are going to be forwarded to it. This property can be used to forward IGMP membership reports to the bridge for statistics or to analyse them. disabled - IGMP membership reports are not forwarded to the bridge itself regardless what is connected to it. permanent - IGMP membership reports are forwarded through this the bridge itself regardless what is connected to it. temporary-query - automatically detect multicast routers and IGMP Snooping enabled bridges. This property only has effect when igmp-snooping is set to yes.
name (text; Default: bridgeN)	Name of the bridge interface
priority (integer: 0..65535 decimal format or 0x0000-0xffff hex format; Default: 32768 / 0x8000)	Bridge priority, used by STP to determine root bridge, used by MSTP to determine CIST and IST regional root bridge. This property only has effect when protocol-mode is not set to none.
protocol-mode (none | rstp | stp | mstp; 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. Select MSTP to ensure loop-free topology across multiple VLANs. Since RouterOS v6.43 it is possible to forward Reserved MAC addresses that are in 01:80:C2:XX:XX:XX range, this can be done by setting the protocol-mode to none.
pvid (integer: 1..4094; Default: 1)	Port VLAN ID (pvid) specifies which VLAN the untagged ingress traffic is assigned to. It applies e.g. to frames sent from bridge IP and destined to a bridge port. This property only has effect when vlan-filtering is set to yes.
querier-interval (time; Default: 4m15s)	Used to change the interval how often a bridge checks if it is the active multicast querier. This property only has effect when igmp-snooping and multicast-querier is set to yes.
query-interval (time; Default: 2m5s)	Used to change the interval how often IGMP general membership queries are sent out. This property only has effect when igmp-snooping and multicast-querier is set to yes.
query-response-interval (time; Default: 10s)	Interval in which a IGMP capable device must reply to a IGMP query with a IGMP membership report. This property only has effect when igmp-snooping and multicast-querier is set to yes.
region-name (text; Default: )	MSTP region name. This property only has effect when protocol-mode is set to mstp.
region-revision (integer: 0..65535; Default: 0)	MSTP configuration revision number. This property only has effect when protocol-mode is set to mstp.
startup-query-count (integer: 0..4294967295; Default: 2)	Specifies how many times must startup-query-interval pass until the bridge starts sending out IGMP general membership queries periodically. This property only has effect when igmp-snooping and multicast-querier is set to yes.
startup-query-interval (time; Default: 31s250ms)	Used to change the amount of time after a bridge starts sending out IGMP general membership queries after the bridge is enabled. This property only has effect when igmp-snooping and multicast-querier is set to yes.
transmit-hold-count (integer: 1..10; Default: 6)	The Transmit Hold Count used by the Port Transmit state machine to limit transmission rate.
vlan-filtering (yes | no; Default: no)	Globally enables or disables VLAN functionality for bridge.

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>

Spanning Tree Protocol

RouterOS bridge interfaces are capable of running Spanning Tree Protocol to ensure a loop-free and redundant topology. For small networks with just 2 bridges STP does not bring much benefits, but for larger networks properly configured STP is very crucial, leaving STP related values to default may result in completely unreachable network in case of a even single bridge failure. To achieve a proper loop-free and redundant topology, it is necessary to properly set bridge priorities, port path costs and port priorities.

Warning: In RouterOS it is possible to set any value for bridge priority between 0 and 65535, the IEEE 802.1W standard states that the bridge priority must be in steps of 4096. This can cause incompatibility issues between devices that does not support such values. To avoid compatibility issues, it is recommended to use only these priorities: 0, 4096, 8192, 12288, 16384, 20480, 24576, 28672, 32768, 36864, 40960, 45056, 49152, 53248, 57344, 61440

STP has multiple variants, currently RouterOS supports STP, RSTP and MSTP. Depending on needs, either one of them can be used, some devices are able to run some of these protocols using hardware offloading, detailed information about which device support it can be found in the Hardware Offloading section. STP is considered to be outdated and slow, it has been almost entirely replaced in all network topologies by RSTP, which is backwards compatible with STP. For network topologies that depend on VLANs, it is recommended to use MSTP since it is a VLAN aware protocol and gives the ability to do load balancing per VLAN groups. There are a lot of considerations that should be made when designing a STP enabled network, more detailed case studies can be found in the Spanning Tree Protocol section.

Note: By the IEEE 802.1ad standard the BPDUs from bridges that comply with IEEE 802.1Q are not compatible with IEEE 802.1ad bridges, this means that the same bridge VLAN protocol should be used across all bridges in a single Layer2 domain, otherwise (R/M)STP will not function properly.

Per port STP

There might be certain situations where you want to limit STP functionality on a single or multiple ports. Below you can find some examples for different use cases.

Warning: Be careful when changing the default (R/M)STP functionality, make sure you understand the working principles of STP and BPDUs. Misconfigured (R/M)STP can cause unexpected behaviour.

• Don't send out BPDUs from a certain port

/interface bridge
add name=bridge1
/interface bridge port
add bridge=bridge1 interface=ether1
add bridge=bridge1 interface=ether2
add bridge=bridge1 interface=ether3
/interface bridge filter
add action=drop chain=output dst-mac-address=01:80:C2:00:00:00/FF:FF:FF:FF:FF:FF out-interface=ether1

In this example BPDUs will not be sent out through ether1. In case the bridge is the root bridge, then loop detection will not work on this port. If another bridge is connected to ether1, then the other bridge will not receive any BPDUs and therefore might become as a second root bridge. You might want to consider blocking received BPDUs as well.

Note: You can use Interface Lists to specify multiple interfaces.

• Drop received BPDUs on a certain port

/interface bridge
add name=bridge1
/interface bridge port
add bridge=bridge1 interface=ether1
add bridge=bridge1 interface=ether2
add bridge=bridge1 interface=ether3
/interface bridge filter
add action=drop chain=input dst-mac-address=01:80:C2:00:00:00/FF:FF:FF:FF:FF:FF in-interface=ether1

This can also be done on some switch chips using ACL rules (for example, on CRS3xx):

/interface ethernet switch rule
add dst-mac-address=01:80:C2:00:00:00/FF:FF:FF:FF:FF:FF new-dst-ports="" ports=ether1 switch=switch1

Or on CRS1xx/CRS2xx:

/interface ethernet switch acl
add action=drop mac-dst-address=01:80:C2:00:00:00 src-ports=ether1

In this example all received BPDUs on ether1 are dropped. This will prevent other bridges on that port becoming a root bridge.

Warning: If you intend to drop received BPDUs on a port, then make sure to prevent BPDUs from being sent out from the interface that this port is connected to. A root bridge always sends out BPDUs and under normal conditions is waiting for a more superior BPDU (from a bridge with a lower bridge ID), but the bridge must temporarily disable the new root-port when transitioning from a root bridge to designated bridge. If you have blocked BPDUs only on one side, then a port will flap continuously.

• Don't allow BPDUs on a port

/interface bridge
add name=bridge1
/interface bridge port
add bridge=bridge1 interface=ether1 bpdu-guard=yes
add bridge=bridge1 interface=ether2
add bridge=bridge1 interface=ether3

In this example if ether1 receives a BPDU, it will block the port and will require you to manually re-enable it.

Bridge Settings

Sub-menu: /interface bridge settings

Property	Description
use-ip-firewall (yes | no; Default: no)	Force bridged traffic to also be processed by prerouting, forward and postrouting sections of IP routing ( Packet Flow). This does not apply to routed traffic.
use-ip-firewall-for-pppoe (yes | no; Default: no)	Send bridged un-encrypted PPPoE traffic to also be processed by IP/Firewall. This property only has effect when use-ip-firewall is set to yes.
use-ip-firewall-for-vlan (yes | no; Default: no)	Send bridged VLAN traffic to also be processed by IP/Firewall. This property only has effect when use-ip-firewall is set to yes.
allow-fast-path (yes | no; Default: yes)	Allows FastPath.
bridge-fast-path-active (yes | no; Default: )	Shows whether Bridge FastPath is active.
bridge-fast-path-packets (integer; Default: )	Shows packet count forwarded by Bridge FastPath.
bridge-fast-path-bytes (integer; Default: )	Shows byte count forwarded by Bridge Fast Path.
bridge-fast-forward-packets (integer; Default: )	Shows packet count forwarded by Bridge Fast Forward.
bridge-fast-forward-bytes (integer; Default: )	Shows byte count forwarded by Bridge Fast Forward.

Port Settings

Sub-menu: /interface bridge port

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

Property	Description
auto-isolate (yes | no; Default: no)	Prevents STP blocking port from erroneously moving into a forwarding state if no BPDUs are received on the bridge. This property only has effect when protocol-mode is not set to none.
bpdu-guard (yes | no; Default: no)	Enables or disables BPDU Guard feature on a port. This feature disables a port if it receives a BPDU and requires the port to be manually re-enabled if a BPDU was received. Should be used to prevent a bridge from BPDU related attacks. This property only has effect when protocol-mode is not set to none.
bridge (name; Default: none)	The bridge interface the respective interface is grouped in.
broadcast-flood (yes | no; Default: yes)	When enabled, bridge floods broadcast traffic to all bridge egress ports. When disabled, drops broadcast traffic on egress ports. Can be used to filter all broadcast traffic on an egress port. Broadcast traffic is considered as traffic that uses FF:FF:FF:FF:FF:FF as destination MAC address, such traffic is crucial for many protocols such as DHCP, ARP, NDP, BOOTP (Netinstall) and others. This option does not limit traffic flood to the CPU.
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. An edge port will skip the learning and the listening state in STP and will transition directly to forwarding state, this reduces the STP initialization time. This property only has effect when protocol-mode is not set to none.
external-fdb (auto | no | yes; Default: auto)	Whether to use wireless registration table to speed up bridge host learning. If there are no Wireless interfaces in a bridge, then setting external-fdb to yes will disable MAC learning and the bridge will act as a hub (disables hardware offloading). Replaced with learn parameter in RouterOS v6.42
fast-leave (yes | no; Default: no)	Enables IGMP Fast leave feature on the port. Bridge will stop forwarding traffic to a bridge port whenever a IGMP Leave message is received for appropriate multicast stream. This property only has effect when igmp-snooping is set to yes.
frame-types (admit-all | admit-only-untagged-and-priority-tagged | admit-only-vlan-tagged; Default: admit-all)	Specifies allowed ingress frame types on a bridge port. This property only has effect when vlan-filtering is set to yes.
ingress-filtering (yes | no; Default: no)	Enables or disables ingress filtering, which checks if an entry exists for the ingress port and the VLAN ID in the bridge VLAN table. Should be used with frame-types to specify if the ingress traffic should be tagged or untagged. This property only has effect when vlan-filtering is set to yes.
learn (auto | no | yes; Default: auto)	Changes MAC learning behaviour on a bridge port yes - enables MAC learning no - disables MAC learning auto - detects if bridge port is a Wireless interface and uses Wireless registration table instead of MAC learning, will use Wireless registration table if the Wireless interface is set to one of ap-bridge,bridge,wds-slave mode and bridge mode for the Wireless interface is disabled.
multicast-router (disabled | permanent | temporary-query; Default: temporary-query)	Changes the state of a bridge port whether IGMP membership reports are going to be forwarded to this port. By default IGMP membership reports (most importantly IGMP Join messages) are only forwarded to ports that have a multicast router or a IGMP Snooping enabled bridge connected to. Without at least one port marked as a multicast-router IPTV might not work properly, it can be either be detected automatically or forced manually. disabled - IGMP membership reports are not forwarded through this port regardless what is connected to it. permanent - IGMP membership reports are forwarded through this port regardless what is connected to it. temporary-query - automatically detect multicast routers and IGMP Snooping enabled bridges. You can improve security by forcing ports that have IPTV boxes connected to never become ports marked as multicast-router. This property only has effect when igmp-snooping is set to yes.
horizon (integer 0..429496729; Default: none)	Use split horizon bridging to prevent bridging loops. Set the same value for group of ports, to prevent them from sending data to ports with the same horizon value. Split horizon is a software feature that disables hardware offloading. Read more about Bridge split horizon.
internal-path-cost (integer: 0..65535; Default: 10)	Path cost to the interface for MSTI0 inside a region. This property only has effect when protocol-mode is set to mstp.
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, used by MSTP to determine "best" path between regions. This property only has effect when protocol-mode is not set to none.
point-to-point (auto | yes | no; Default: auto)	Specifies if a bridge port is connected to a bridge using a point-to-point link for faster convergence in case of failure. This property only has effect when protocol-mode is not set to none.
priority (integer: 0..240; Default: 128)	The priority of the interface, used by STP to determine the root port, used by MSTP to determine root port between regions.
pvid (integer 1..4094; Default: 1)	Port VLAN ID (pvid) specifies which VLAN the untagged ingress traffic is assigned to. This property only has effect when vlan-filtering is set to yes.
restricted-role (yes | no; Default: no)	Enable the restricted role on a port, used by STP to forbid a port becoming a root port. This property only has effect when protocol-mode is not set to none.
restricted-tcn (yes | no; Default: no)	Disable topology change notification (TCN) sending on a port, used by STP to forbid network topology changes to propagate. This property only has effect when protocol-mode is not set to none.
tag-stacking (yes | no; Default: no)	Forces all packets to be treated as untagged packets. Packets on ingress port will be tagged with another VLAN tag regardless if a VLAN tag already exists, packets will be tagged with a VLAN ID that matches the pvid value and will use EtherType that is specified in ether-type. This property only has effect when vlan-filtering is set to yes.
trusted (yes | no; Default: no)	When enabled, it allows to forward DHCP packets towards DHCP server through this port. Mainly used to limit unauthorized servers to provide malicious information for users. This property only has effect when dhcp-snooping is set to yes.
unknown-multicast-flood (yes | no; Default: yes)	When enabled, bridge floods unknown multicast traffic to all bridge egress ports. When disabled, drops unknown multicast traffic on egress ports. Multicast addresses that are in /interface bridge mdb are considered as learned multicasts and therefore will not be flooded to all ports. Without IGMP Snooping all multicast traffic will be dropped on egress ports. Has effect only on an egress port. This option does not limit traffic flood to the CPU. Note that local multicast addresses (224.0.0.0/24) are not flooded when unknown-multicast-flood is disabled, as a result some protocols that rely on local multicast addresses might not work properly, such protocols are RIPv2m OSPF, mDNS, VRRP and others. Some protocols do send a IGMP join request and therefore are compatible with IGMP Snooping, some OSPF implementations are compatible with RFC1584, RouterOS OSPF implementation is not compatible with IGMP Snooping. This property should only be used when igmp-snooping is set to yes.
unknown-unicast-flood (yes | no; Default: yes)	When enabled, bridge floods unknown unicast traffic to all bridge egress ports. When disabled, drops unknown unicast traffic on egress ports. If a MAC address is not learned in /interface bridge host, then the traffic is considered as unknown unicast traffic and will not be flooded to all ports. MAC address is learnt as soon as a packet on a bridge port is received, then the source MAC address is added to the bridge host table. Since it is required for the bridge to receive at least one packet on the bridge port to learn the MAC address, it is recommended to use static bridge host entries to avoid packets being dropped until the MAC address has been learnt. Has effect only on an egress port. This option does not limit traffic flood to the CPU.

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> 

Interface lists

Starting with RouterOS v6.41 it possible to add interface lists as a bridge port and sort them. Interface lists are useful for creating simpler firewall rules, you can read more about interface lists at the Interface List section. Below is an example how to add interface list to a bridge:

/interface list member
add interface=ether1 list=LAN1
add interface=ether2 list=LAN1
add interface=ether3 list=LAN2
add interface=ether4 list=LAN2
/interface bridge port
add bridge=bridge1 interface=LAN1
add bridge=bridge1 interface=LAN2

Ports from a interface list added to a bridge will show up as dynamic ports:

[admin@MikroTik] > /interface bridge port print 
Flags: X - disabled, I - inactive, D - dynamic, H - hw-offload 
 #     INTERFACE                                      BRIDGE
 0     LAN1                                           bridge1
 1  D  ether1                                         bridge1
 2  D  ether2                                         bridge1
 3     LAN2                                           bridge1
 4  D  ether3                                         bridge1
 5  D  ether4                                         bridge1 

It is also possible to sort the order of lists in which they appear in the /interface bridge port menu. This can be done using the move command. Below is an example how to sort interface lists:

[admin@MikroTik] > /interface bridge port move 3 0
[admin@MikroTik] > /interface bridge port print 
Flags: X - disabled, I - inactive, D - dynamic, H - hw-offload 
 #     INTERFACE                                      BRIDGE
 0     LAN2                                           bridge1
 1  D  ether3                                         bridge1
 2  D  ether4                                         bridge1
 3     LAN1                                           bridge1
 4  D  ether1                                         bridge1
 5  D  ether2                                         bridge1

Note: The second parameter when moving interface lists is considered as "before id", the second parameter specifies before which interface list should be the selected interface list moved. When moving first interface list in place of the second interface list, then the command will have no effect since the first list will be moved before the second list, which is the current state either way.

Hosts Table

MAC addresses that have been learned on a bridge interface can be viewed in the /interface bridge host menu. Below is a table of parameters and flags that can be viewed.

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
dynamic (read-only: flag)	Dynamically created entry
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

Monitoring

To get the active hosts 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                  

Static entries

Since RouterOS v6.42 it is possible to add a static MAC address entry into the hosts table. This can be used to forward a certain type of traffic through a specific port. Below is a table of possible parameters that can be set when adding a static MAC address entry into the hosts table.

Sub-menu: /interface bridge host

Property	Description
bridge (name; Default: none)	The bridge interface to which the MAC address is going to be assigned to.
disabled (yes | no; Default: no)	Disables/enables static MAC address entry.
interface (name; Default: none)	Name of the interface.
mac-address (MAC address; Default: )	MAC address that will be added to the hosts table statically.
vid (integer: 1..4094; Default: )	VLAN ID for the statically added MAC address entry.

For example, if it was required that all traffic destined to 4C:5E:0C:4D:12:43 is forwarded only through ether2, then the following commands can be used:

/interface bridge host
add bridge=bridge interface=ether2 mac-address=4C:5E:0C:4D:12:43

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 VLAN Filtering

Bridge VLAN Filtering since RouterOS v6.41 provides VLAN aware Layer2 forwarding and VLAN tag modifications within the bridge. This set of features makes bridge operation more like a traditional Ethernet switch and allows to overcome Spanning Tree compatibilty issues compared to configuration when tunnel-like VLAN interfaces are bridged. Bridge VLAN Filtering configuration is highly recommended to comply with STP (IEEE 802.1D), RSTP (IEEE 802.1W) standards and is mandatory to enable MSTP (IEEE 802.1s) support in RouterOS.

The main VLAN setting is vlan-filtering which globally controls vlan-awareness and VLAN tag processing in the bridge. If vlan-filtering=no, bridge ignores VLAN tags, works in a shared-VLAN-learning (SVL) mode and cannot modify VLAN tags of packets. Turning on vlan-filtering enables all bridge VLAN related functionality and independent-VLAN-learning (IVL) mode. Besides joining the ports for Layer2 forwarding, bridge itself is also an interface therefore it has Port VLAN ID (pvid).

Sub-menu: /interface bridge vlan

Bridge VLAN table represents per-VLAN port mapping with an egress VLAN tag action. tagged ports send out frames with a learned VLAN ID tag. untagged ports remove VLAN tag before sending out frames if the learned VLAN ID matches the port pvid.

Property	Description
bridge (name; Default: none)	The bridge interface which the respective VLAN entry is intended for.
disabled (yes | no; Default: no)	Enables or disables Bridge VLAN entry.
tagged (interfaces; Default: none)	Interface list with a VLAN tag adding action in egress. This setting accepts comma separated values. E.g. tagged=ether1,ether2.
untagged (interfaces; Default: none)	Interface list with a VLAN tag removing action in egress. This setting accepts comma separated values. E.g. tagged=ether3,ether4
vlan-ids (integer 1..4094; Default: 1)	The list of VLAN IDs for certain port configuration. This setting accepts VLAN ID range as well as comma separated values. E.g. vlan-ids=100-115,120,122,128-130.

Sub-menu: /interface bridge host

Bridge Host table allows monitoring learned MAC addresses and when vlan-filtering is enabled shows learned VLAN ID as well.

[admin@MikroTik] > interface bridge host print where !local
Flags: L - local, E - external-fdb 
  BRIDGE                          VID MAC-ADDRESS       ON-INTERFACE                   AGE                 
  bridge1                         200 D4:CA:6D:77:2E:F0 ether3                         7s                  
  bridge1                         200 E4:8D:8C:1B:05:F0 ether2                         2s                  
  bridge1                         300 D4:CA:6D:74:65:9D ether4                         3s                  
  bridge1                         300 E4:8D:8C:1B:05:F0 ether2                         2s                  
  bridge1                         400 4C:5E:0C:4B:89:5C ether5                         0s                  
  bridge1                         400 E4:8D:8C:1B:05:F0 ether2                         0s                  
[admin@MikroTik] > 

Note: Make sure you have added all needed interfaces to the bridge VLAN table when using bridge VLAN filtering. For routing functions to work properly on the same device through ports that use bridge VLAN filtering, you will need to allow access to the CPU from those ports, this can be done by adding the bridge interface itself to the VLAN table, for tagged traffic you will need to add the bridge interface as a tagged port and create a VLAN interface on the bridge interface. Examples can be found at the Management port section.

Warning: When allowing access to the CPU, you are allowing access from a certain port to the actual router/switch, this is not always desirable. Make sure you implement proper firewall filter rules to secure your device when access to the CPU is allowed from a certain VLAN ID and port, use firewall filter rules to allow access to only certain services.

VLAN Example #1 (Trunk and Access Ports)

Trunk and Access Ports

• Create a bridge with disabled vlan-filtering to avoid losing access to the router before VLANs are completely configured.

/interface bridge
add name=bridge1 vlan-filtering=no

• Add bridge ports and specify pvid for VLAN access ports to assign their untagged traffic to the intended VLAN.

/interface bridge port
add bridge=bridge1 interface=ether2
add bridge=bridge1 interface=ether6 pvid=200
add bridge=bridge1 interface=ether7 pvid=300
add bridge=bridge1 interface=ether8 pvid=400

• Add Bridge VLAN entries and specify tagged and untagged ports in them.

/interface bridge vlan
add bridge=bridge1 tagged=ether2 untagged=ether6 vlan-ids=200
add bridge=bridge1 tagged=ether2 untagged=ether7 vlan-ids=300
add bridge=bridge1 tagged=ether2 untagged=ether8 vlan-ids=400

• In the end, when VLAN configuration is complete, enable Bridge VLAN Filtering.

/interface bridge set bridge1 vlan-filtering=yes

VLAN Example #2 (Trunk and Hybrid Ports)

Trunk and Hybrid Ports

• Create a bridge with disabled vlan-filtering to avoid losing access to the router before VLANs are completely configured.

/interface bridge
add name=bridge1 vlan-filtering=no

• Add bridge ports and specify pvid on hybrid VLAN ports to assign untagged traffic to the intended VLAN.

/interface bridge port
add bridge=bridge1 interface=ether2
add bridge=bridge1 interface=ether6 pvid=200
add bridge=bridge1 interface=ether7 pvid=300
add bridge=bridge1 interface=ether8 pvid=400

• Add Bridge VLAN entries and specify tagged and untagged ports in them. In this example egress VLAN tagging is done on ether6,ether7,ether8 ports too, making them into hybrid ports.

/interface bridge vlan
add bridge=bridge1 tagged=ether2,ether7,ether8 untagged=ether6 vlan-ids=200
add bridge=bridge1 tagged=ether2,ether6,ether8 untagged=ether7 vlan-ids=300
add bridge=bridge1 tagged=ether2,ether6,ether7 untagged=ether8 vlan-ids=400

• In the end, when VLAN configuration is complete, enable Bridge VLAN Filtering.

/interface bridge set bridge1 vlan-filtering=yes

Warning: The PVID value is set to all traffic that enters the bridge and adds the port dynamically to the bridge VLAN table for VLAN ID that matches the PVID value. If you are trying to isolate tagged traffic from untagged traffic, then make sure you have set a PVID to a bridge port that is different from the bridge's PVID value, otherwise these ports will be dynamically added to the bridge VLAN table and will be able to forward traffic from untagged ports.

VLAN Example #3 (InterVLAN Routing by Bridge)

InterVLAN Routing by Bridge

• Create a bridge with disabled vlan-filtering to avoid losing access to the router before VLANs are completely configured.

/interface bridge
add name=bridge1 vlan-filtering=no

• Add bridge ports and specify pvid for VLAN access ports to assign their untagged traffic to the intended VLAN.

/interface bridge port
add bridge=bridge1 interface=ether6 pvid=200
add bridge=bridge1 interface=ether7 pvid=300
add bridge=bridge1 interface=ether8 pvid=400

• Add Bridge VLAN entries and specify tagged and untagged ports in them. In this example bridge1 interface is the VLAN trunk that will send traffic further to do InterVLAN routing.

/interface bridge vlan
add bridge=bridge1 tagged=bridge1 untagged=ether6 vlan-ids=200
add bridge=bridge1 tagged=bridge1 untagged=ether7 vlan-ids=300
add bridge=bridge1 tagged=bridge1 untagged=ether8 vlan-ids=400

• Configure VLAN interfaces on the bridge1 to allow handling of tagged VLAN traffic at routing level and set IP addresses to ensure routing between VLANs as planned.

/interface vlan
add interface=bridge1 name=vlan200 vlan-id=200
add interface=bridge1 name=vlan300 vlan-id=300
add interface=bridge1 name=vlan400 vlan-id=400

/ip address
add address=20.0.0.1/24 interface=vlan200 network=20.0.0.0
add address=30.0.0.1/24 interface=vlan300 network=30.0.0.0
add address=40.0.0.1/24 interface=vlan400 network=40.0.0.0

• In the end, when VLAN configuration is complete, enable Bridge VLAN Filtering.

/interface bridge set bridge1 vlan-filtering=yes

Management port

There are multiple ways to setup management port on a device that uses bridge VLAN filtering. Below are some of the most popular approaches to properly enable access to a router/switch. Start by creating a bridge without VLAN filtering enabled:

/interface bridge
add name=bridge1 vlan-filtering=no

• In case VLAN filtering will not be used and access with untagged traffic is desired

The only requirement is to create an IP address on the bridge interface.

/ip address
add address=192.168.99.1/24 interface=bridge1

• In case VLAN filtering is used and access from trunk and/or access ports with tagged traffic is desired

In this example VLAN 99 will be used to access the device, a VLAN interface on the bridge must be created and an IP address must be assigned to it.

/interface vlan
add interface=bridge1 name=MGMT vlan-id=99
/ip address
add address=192.168.99.1/24 interface=MGMT

For example, if you want to allow access to the router/switch from access ports ether3,ether4 and from trunk port sfp-sfpplus1, then you must add this entry to the VLAN table:

/interface bridge vlan
add bridge=bridge1 tagged=bridge1,ether3,ether4,sfp-sfpplus1 vlan-ids=99

After that you can enable VLAN filtering:

/interface bridge set bridge1 vlan-filtering=yes

• In case VLAN filtering is used and access from trunk and/or access ports with untagged traffic is desired

To allow untagged traffic to access the router/switch, start by creating an IP address on the bridge interface.

/ip address
add address=192.168.88.1/24 interface=bridge1

It is required to add VLAN 1 to ports from which you want to allow the access to the router/switch, for example, to allow access from access ports ether3,ether4 add this entry to the VLAN table:

/interface bridge vlan
add bridge=bridge1 untagged=ether3,ether4 vlan-ids=1

Make sure that PVID on the bridge interface matches the PVID value on these ports:

/interface bridge set bridge1 pvid=1
/interface bridge port set ether3,ether4 pvid=1

After that you can enable VLAN filtering:

/interface bridge set bridge1 vlan-filtering=yes

Note: If connection to the router/switch through an IP address is not required, then steps adding this IP address can be skipped since connection to the router/switch through Layer2 protocols (e.g. MAC-telnet) will be working either way.

VLAN Tunneling (Q-in-Q)

Since RouterOS v6.43 the RouterOS bridge is IEEE 802.1ad compliant and it is possible to filter VLAN IDs based on Service VLAN ID (0x88A8) rather than Customer VLAN ID (0x8100). The same principals can be applied as with IEEE 802.1Q VLAN filtering (the same setup examples can be used). Below is a topology for a common Provider bridge:

Provider bridge topology

In this example R1, R2, R3 and R4 might be sending any VLAN tagged traffic by 802.1Q (CVID), but SW1 and SW2 needs isolate traffic between routers in a way that R1 is able to communicate only with R3 and R2 is only able to communicate with R4. To do so, you can tag all ingress traffic with a SVID and only allow these VLANs on certain ports. Start by enabling 802.1ad VLAN protocol on the bridge, use these commands on SW1 and SW2:

/interface bridge
add name=bridge1 vlan-filtering=no ether-type=0x88a8

In this setup ether1 and ether2 are going to be access ports (untagged), use the pvid parameter to tag all ingress traffic on each port, use these commands on SW1 and SW2:

/interface bridge port
add interface=ether1 bridge=bridge1 pvid=200
add interface=ether2 bridge=bridge1 pvid=300
add interface=ether3 bridge=bridge1

Specify tagged and untagged ports in the bridge VLAN table, use these commands on SW1 and SW2:

/interface bridge vlan
add bridge=bridge1 tagged=ether3 untagged=ether1 vlan-ids=200
add bridge=bridge1 tagged=ether3 untagged=ether2 vlan-ids=300

When bridge VLAN table is configured, you can enable bridge VLAN filtering, use these commands on SW1 and SW2

/interface bridge set bridge1 vlan-filtering=yes

Warning: By enabling vlan-filtering you will be filtering out traffic destined to the CPU, before enabling VLAN filtering you should make sure that you set up a Management port. The difference between using different EtherTypes is that you must use a Service VLAN interface. Service VLAN interfaces can be created as regular VLAN interface, but the use-service-tag parameter toggles if the interface will use Service VLAN tag.

Note: Currently only CRS3xx series switches are capable of hardware offloading VLAN filtering based on SVID (Service VLAN ID) tag when ether-type is set to 0x88a8.

Warning: When ether-type is set to 0x8100, then the bridge checks the outer VLAN tag if it is using EtherType 0x8100. If the bridge receives a packet with an outer tag that has a different EtherType, it will mark the packet as untagged. Since RouterOS only checks the outer tag of a packet, it is not possible to filter 802.1Q packets when 802.1ad protocol is used.

Tag stacking

Since RouterOS v6.43 it is possible to forcefully add a new VLAN tag over any existing VLAN tags, this feature can be used to achieve a CVID stacking setup, where a CVID (0x8100) tag is added before an existing CVID tag. This type of setup is very similar to Provider bridge setup, to achieve the same setup but with multiple CVID tags (CVID stacking) we can use the same topology:

Tag stacking topology

In this example R1, R2, R3 and R4 might be sending any VLAN tagged traffic, it can be 802.1ad, 802.1Q or any other type of traffic, but SW1 and SW2 needs isolate traffic between routers in a way that R1 is able to communicate only with R3 and R2 is only able to communicate with R4. To do so, you can tag all ingress traffic with a new CVID tag and only allow these VLANs on certain ports. Start by selecting the proper EtherType, use these commands on SW1 and SW2:

/interface bridge
add name=bridge1 vlan-filtering=no ether-type=0x8100

In this setup ether1 and ether2 will ignore any VLAN tags that are present and add a new VLAN tag, use the pvid parameter to tag all ingress traffic on each port and allow tag-stacking on these ports, use these commands on SW1 and SW2:

/interface bridge port
add interface=ether1 bridge=bridge1 pvid=200 tag-stacking=yes
add interface=ether2 bridge=bridge1 pvid=300 tag-stacking=yes
add interface=ether3 bridge=bridge1

Specify tagged and untagged ports in the bridge VLAN table, you only need to specify the VLAN ID of the outer tag, use these commands on SW1 and SW2:

/interface bridge vlan
add bridge=bridge1 tagged=ether3 untagged=ether1 vlan-ids=200
add bridge=bridge1 tagged=ether3 untagged=ether2 vlan-ids=300

When bridge VLAN table is configured, you can enable bridge VLAN filtering, which is required in order for the PVID parameter have any effect, use these commands on SW1 and SW2

/interface bridge set bridge1 vlan-filtering=yes

Warning: By enabling vlan-filtering you will be filtering out traffic destined to the CPU, before enabling VLAN filtering you should make sure that you set up a Management port.

Fast Forward

Fast Forward allows to forward packets faster under special conditions. When Fast Forward is enabled, then the bridge can process packets even faster since it can skip multiple bridge related checks, including MAC learning. Below you can find a list of conditions that MUST be met in order for Fast Forward to be active:

• Bridge has fast-forward set to yes
• Bridge has only 2 running ports
• Both bridge ports support Fast Path and Fast Path is active on ports and globally
• Bridge Hardware Offloading is disabled
• protocol-mode is set to none
• Bridge VLAN Filtering is disabled
• unknown-multicast-flood is set to yes
• unknown-unicast-flood is set to yes
• broadcast-flood is set to yes
• MAC address for the bridge matches with a MAC address from one of the bridge slaves
• horizon for both ports is set to none

Note: Fast Forward disables MAC learning, this is by design to achieve faster packet forwarding. MAC learning prevents traffic from flooding multiple interfaces, but MAC learning is not needed when a packet can only be sent out trough just one interface.

Warning: Fast Forward is disabled when hardware offloading is enabled. Hardware offloading can achieve full write-speed performance when it is active since it will use the built-in switch chip (if such exists on your device), fast forward uses the CPU to forward packets. When comparing throughput results, you would get such results: Hardware offloading > Fast Forward > Fast Path > Slow Path.

It is possible to check how many packets where processed by Fast Forward:

[admin@MikroTik] > /interface bridge settings print 
              use-ip-firewall: no
     use-ip-firewall-for-vlan: no
    use-ip-firewall-for-pppoe: no
              allow-fast-path: yes
      bridge-fast-path-active: yes
     bridge-fast-path-packets: 0
       bridge-fast-path-bytes: 0
  bridge-fast-forward-packets: 1279812
    bridge-fast-forward-bytes: 655263744

Note: If packets are processed by Fast Path, then Fast Forward is not active. Packet count can be used as an indicator whether Fast Forward is active or not.

IGMP Snooping

IGMP Snooping which controls multicast streams and prevents multicast flooding is implemented in RouterOS starting from version 6.41.
It's settings are placed in bridge menu and it works independently in every bridge interface.
Software driven implementation works on all devices with RouterOS but CRS1xx/2xx/3xx series switches also support IGMP Snooping with hardware offloading.

Sub-menu: /interface bridge /interface bridge mdb

• Enabling IGMP Snooping on Bridge.

/interface bridge set bridge1 igmp-snooping=yes

• Monitoring multicast groups in the Bridge Multicast Database

[admin@MikroTik] > interface bridge mdb print 
BRIDGE                   VID GROUP                                              PORTS           
bridge1                  200 229.1.1.2                                          ether3          
                                                                                ether2          
                                                                                ether1          
bridge1                  300 231.1.3.3                                          ether4          
                                                                                ether3          
                                                                                ether2          
bridge1                  400 229.10.10.4                                        ether4          
                                                                                ether3          
bridge1                  500 234.5.1.5                                          ether5          
                                                                                ether1          

• Monitoring ports that are connected to a multicast router

[admin@MikroTik] > /interface bridge port monitor [f]
              interface: ether1          ether2
                 status: in-bridge       in-bridge
            port-number: 1               2
                   role: designated-port designated-port
              edge-port: yes             yes
    edge-port-discovery: yes             yes
    point-to-point-port: yes             yes
           external-fdb: no              no
           sending-rstp: yes             yes
               learning: yes             yes
             forwarding: yes             yes
       multicast-router: yes              no

Note: IGMP membership reports are only forwarded to ports that are connected to a multicast router or to another IGMP Snooping enabled bridge. If no port is marked as a multicast-router then IGMP membership reports will not be forwarded to any port.

Note: CRS series switches are capable of running IGMP Snooping along with hardware offloading, but CRS1xx and CRS2xx series switches will not work properly with IGMP Snooping if VLAN switching is configured on the switch chip. It is possible to use IGMP Snooping along with VLAN switching, but then you must make sure that IGMP packets are sent out with the correct VLAN tag using egress ACL rules.

DHCP Snooping and DHCP Option 82

Sub-menu: /interface bridge /interface bridge port

Starting from RouterOS version 6.43, bridge supports DHCP Snooping and DHCP Option 82. The DHCP Snooping is a Layer2 security feature, that limits unauthorized DHCP servers from providing a malicious information to users. In RouterOS you can specify which bridge ports are trusted (where known DHCP server resides and DHCP messages should be forwarded) and which are untrusted (usually used for access ports, received DHCP server messages will be dropped). The DHCP Option 82 is an additional information (Agent Circuit ID and Agent Remote ID) provided by DHCP Snooping enabled devices that allows identifying the device itself and DHCP clients.

DHCP Snooping and Option 82 setup

In this example, SW1 and SW2 are DHCP Snooping and Option 82 enabled devices. First, we need to create a bridge, assign interfaces and mark trusted ports. Use these commands on SW1:

/interface bridge
add name=bridge
/interface bridge port
add bridge=bridge interface=ether1
add bridge=bridge interface=ether2 trusted=yes

For SW2 configuration will be similar, but we also need to mark ether1 as trusted, because this interface is going to receive DHCP messages with Option 82 already added. You need to mark all ports as trusted if they are going to receive DHCP messages with added Option 82, otherwise these messages will be dropped. Also, we add ether3 to the same bridge and leave this port untrusted, imagine there is an unauthorized (rogue) DHCP server. Use these commands on SW2:

/interface bridge
add name=bridge
/interface bridge port
add bridge=bridge interface=ether1 trusted=yes
add bridge=bridge interface=ether2 trusted=yes
add bridge=bridge interface=ether3

Then we need to enable DHCP Snooping and Option 82. In case your DHCP server does not support DHCP Option 82 or you do not implement any Option 82 related policies, this option can be disabled. Use these commands on SW1 and SW2:

/interface bridge
set [find where name="bridge"] dhcp-snooping=yes add-dhcp-option82=yes

Now both devices will analyze what DHCP messages are received on bridge ports. The SW1 is responsible for adding and removing the DHCP Option 82. The SW2 will limit rogue DHCP server form receiving any discovery messages and drop malicious DHCP server messages from ether3.

Note: Currently only CRS3xx devices fully support hardware DHCP Snooping and Option 82. For CRS1xx and CRS2xx series switches it is possible to use DHCP Snooping along with VLAN switching, but then you must make sure that DHCP packets are sent out with the correct VLAN tag using egress ACL rules. Other devices are capable of using DHCP Snooping and Option 82 features along with hardware offloading, but you must make sure that there is no VLAN related configuration applied on the device, otherwise DHCP Snooping and Option 82 might not work properly. See Bridge Hardware Offloading section with supported features.

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; Default: )	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; Default: )	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.
action (accept | drop | jump | log | mark-packet | passthrough | return | set-priority; Default: )	Action to take if packet is matched by the rule: accept - accept the packet. Packet is not passed to next firewall rule 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 mark-packet - place a mark specified by the new-packet-mark parameter on a packet that matches the rule passthrough - if packet is matched by the rule, increase counter and go to next rule (useful for statistics) return - passes control back to the 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>
arp-dst-address (IP address; Default: )	ARP destination IP 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; Default: )	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 | hex 0x0000-0xffff; Default: )	ARP Packet Type.
arp-src-address (IP address; Default: )	ARP source IP address.
arp-src-mac-address (MAC addres; Default: )	ARP source MAC address.
chain (text; Default: )	Bridge firewall chain, which the filter is functioning in (either a built-in one, or a user-defined one).
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; Default: )	Destination port number or range (only for TCP or UDP protocols).
in-bridge (name; Default: )	Bridge interface through which the packet is coming in.
in-interface (name; Default: )	Physical interface (i.e., bridge port) through which the packet is coming in.
in-interface-list (name; Default: )	Set of interfaces defined in interface list. Works the same as in-interface.
ingress-priority (integer 0..63; Default: )	Matches the priority of an ingress packet. Priority may be derived from VLAN, WMM, DSCP or MPLS EXP bit. read more»
ip-protocol (dccp | 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 | sctp | st | tcp | udp | udp-lite | vmtp | vrrp | xns-idp | xtp; Default: )	IP protocol (only if MAC protocol is set to IPv4) dccp - Datagram Congestion Control Protocol ddp - Datagram Delivery Protocol egp - Exterior Gateway Protocol encap - Encapsulation Header etherip - Ethernet-within-IP Encapsulation ggp - Gateway-to-Gateway Protocol gre - Generic Routing Encapsulation hmp - Host Monitoring Protocol icmp - IPv4 Internet Control Message Protocol icmpv6 - IPv6 Internet Control Message Protocol idpr-cmtp - Inter-Domain Policy Routing Control Message Transport Protocol igmp - Internet Group Management Protocol ipencap - IP in IP (encapsulation) ipip - IP-within-IP Encapsulation Protocol ipsec-ah - IPsec Authentication Header ipsec-esp - IPsec Encapsulating Security Payload ipv6 - Internet Protocol version 6 ipv6-frag - Fragment Header for IPv6 ipv6-nonxt - No Next Header for IPv6 ipv6-opts - Destination Options for IPv6 ipv6-route - Routing Header for IPv6 iso-tp4 - ISO Transport Protocol Class 4 l2tp - Layer Two Tunneling Protocol ospf - Open Shortest Path First pim - Protocol Independent Multicast pup - PARC Universal Packet rdp - Reliable Data Protocol rspf - Radio Shortest Path First rsvp - Reservation Protocol sctp - Stream Control Transmission Protocol st - Internet Stream Protocol tcp - Transmission Control Protocol udp - User Datagram Protocol udp-lite - Lightweight User Datagram Protocol vmtp - Versatile Message Transaction Protocol vrrp - Virtual Router Redundancy Protocol xns-idp - Xerox Network Systems Internet Datagram Protocol xtp - Xpress Transport Protocol
jump-target (name; Default: )	If action=jump specified, then specifies the user-defined firewall chain to process the packet.
limit (integer/time,integer; Default: )	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; Default: )	Defines the prefix to be printed before the logging information.
mac-protocol (802.2 | arp | homeplug-av | ip | ipv6 | ipx | length | lldp | loop-protect | mpls-multicast | mpls-unicast | packing-compr | packing-simple | pppoe | pppoe-discovery | rarp | service-vlan | vlan | integer 0..65535 | hex 0x0000-0xffff; Default: )	Ethernet payload type (MAC-level protocol) 802.2 - 802.2 Frames (0x0004) arp - Address Resolution Protocol (0x0806) homeplug-av - HomePlug AV MME (0x88E1) ip - Internet Protocol version 4 (0x0800) ipv6 - Internet Protocol Version 6 (0x86DD) ipx - Internetwork Packet Exchange (0x8137) length - Packets with length field (0x0000-0x05DC) lldp - Link Layer Discovery Protocol (0x88CC) loop-protect - Loop Protect Protocol (0x9003) mpls-multicast - MPLS multicast (0x8848) mpls-unicast - MPLS unicast (0x8847) packing-compr - Encapsulated packets with compressed IP packing (0x9001) packing-simple - Encapsulated packets with simple IP packing (0x9000) pppoe - PPPoE Session Stage (0x8864) pppoe-discovery - PPPoE Discovery Stage (0x8863) rarp - Reverse Address Resolution Protocol (0x8035) service-vlan - Provider Bridging (IEEE 802.1ad) & Shortest Path Bridging IEEE 802.1aq (0x88A8) vlan - VLAN-tagged frame (IEEE 802.1Q) and Shortest Path Bridging IEEE 802.1aq with NNI compatibility (0x8100)
out-bridge (name; Default: )	Outgoing bridge interface.
out-interface (name; Default: )	Interface that the packet is leaving the bridge through.
out-interface-list (name; Default: )	Set of interfaces defined in interface list. Works the same as out-interface.
packet-mark (name; Default: )	Match packets with certain packet mark.
packet-type (broadcast | host | multicast | other-host; Default: )	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; Default: )	Source port number or range (only for TCP or UDP protocols).
stp-flags (topology-change | topology-change-ack; Default: )	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 sent in replies to the notification packets
stp-forward-delay (integer 0..65535; Default: )	Forward delay timer.
stp-hello-time (integer 0..65535; Default: )	STP hello packets time.
stp-max-age (integer 0..65535; Default: )	Maximal STP message age.
stp-msg-age (integer 0..65535; Default: )	STP message age.
stp-port (integer 0..65535; Default: )	STP port identifier.
stp-root-address (MAC address; Default: )	Root bridge MAC address.
stp-root-cost (integer 0..65535; Default: )	Root bridge cost.
stp-root-priority (integer 0..65535; Default: )	Root bridge priority.
stp-sender-address (MAC address; Default: )	STP message sender MAC address.
stp-sender-priority (integer 0..65535; Default: )	STP sender priority.
stp-type (config | tcn; Default: )	The BPDU type: config - configuration BPDU tcn - topology change notification
tls-host (string; Default: )	Allows to match https traffic based on TLS SNI hostname. Accepts GLOB syntax for wildcard matching. Note that matcher will not be able to match hostname if TLS handshake frame is fragmented into multiple TCP segments (packets).
vlan-encap (802.2 | arp | ip | ipv6 | ipx | length | mpls-multicast | mpls-unicast | pppoe | pppoe-discovery | rarp | vlan | integer 0..65535 | hex 0x0000-0xffff; Default: )	Matches the MAC protocol type encapsulated in the VLAN frame.
vlan-id (integer 0..4095; Default: )	MAtches the VLAN identifier field.
vlan-priority (integer 0..7; Default: )	Matches the VLAN priority

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; Default: accept)

Action to take if packet is matched by the rule: 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 - ladd a message to the system log containing following data: in-interface, out-interface, src-mac, dst-mac, eth-proto, 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 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; Default: accept)	Action to take if packet is matched by the rule: 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; Default: )	Source MAC address to put in Ethernet frame and ARP payload, when action=arp-reply is selected
to-dst-mac-address (MAC address; Default: )	Destination MAC address to put in Ethernet frames, when action=dst-nat is selected
to-src-mac-address (MAC address; Default: )	Source MAC address to put in Ethernet frames, when action=src-nat is selected

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