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Basic Bridge Configuration

Basic Bridge Configuration

Section titled “Basic Bridge Configuration”

TL;DR (Quick Start)

Section titled “TL;DR (Quick Start)”

For the impatient: here’s the 30-second version.

# Create bridge and add ports
/interface bridge add name=bridge-lan
/interface bridge port add bridge=bridge-lan interface=ether2
/interface bridge port add bridge=bridge-lan interface=ether3
/ip address add address=192.168.99.1/24 interface=bridge-lan

Overview

Section titled “Overview”

This guide demonstrates how to create a bridge on MikroTik RouterOS to combine multiple interfaces into a single broadcast domain.

Prerequisites

Section titled “Prerequisites”
  • A MikroTik router running RouterOS 7.x or later
  • Access to the router via SSH, WinBox, or WebFig

Configuration Steps

Section titled “Configuration Steps”

Step 1: Create a Bridge Interface

Section titled “Step 1: Create a Bridge Interface”

Create a new bridge named “bridge-lan”:

/interface bridge add name=bridge-lan comment="LAN Bridge"

Step 2: Add First Port to Bridge

Section titled “Step 2: Add First Port to Bridge”

Add ether2 to the bridge:

/interface bridge port add bridge=bridge-lan interface=ether2 comment="LAN Port 1"

Step 3: Assign IP Address to Bridge

Section titled “Step 3: Assign IP Address to Bridge”

Assign an IP address to the bridge interface:

/ip address add address=192.168.99.1/24 interface=bridge-lan comment="Bridge IP"

Verification

Section titled “Verification”

Verify your bridge configuration:

Check 1: Bridge Interface

Section titled “Check 1: Bridge Interface”
/interface bridge print

Expected Output:

Flags: X - disabled, R - running
 0  R name="bridge-lan" mtu=auto actual-mtu=1500 l2mtu=1598 arp=enabled
      arp-timeout=auto mac-address=DC:2C:6E:XX:XX:XX protocol-mode=rstp
      fast-forward=yes igmp-snooping=no auto-mac=yes ageing-time=5m
      priority=0x8000 max-message-age=20s forward-delay=15s
      transmit-hold-count=6 vlan-filtering=no comment="LAN Bridge"

Check 2: Bridge Ports

Section titled “Check 2: Bridge Ports”
/interface bridge port print

Expected Output:

Flags: X - disabled, I - inactive, D - dynamic, H - hw-offload
 #     INTERFACE  BRIDGE      HW   PVID  PRIORITY  PATH-COST  INTERNAL...
 0   H ether2     bridge-lan  yes     1  0x80             10         10

Check 3: IP Address

Section titled “Check 3: IP Address”
/ip address print where interface=bridge-lan

Expected Output:

Flags: X - disabled, I - invalid, D - dynamic
 #   ADDRESS            NETWORK         INTERFACE
 0   192.168.99.1/24    192.168.99.0    bridge-lan

Troubleshooting

Section titled “Troubleshooting”

Problem: No connectivity between bridged ports

Section titled “Problem: No connectivity between bridged ports”

Symptoms: Devices on bridged ports cannot communicate with each other.

Causes & Solutions:

  1. STP blocking ports - Check port status:

    /interface bridge port print

    Look for ports with role=disabled-port or role=alternate-port. Wait for STP convergence or check for network loops.

  2. Interface not running - Verify interfaces are up:

    /interface print where name~"ether"

    Ensure physical cables are connected and interfaces show R (running) flag.

  3. Hardware offloading issues - Try disabling hw-offload:

    /interface bridge port set [find interface=ether2] hw=no

Problem: Bridge IP address not reachable

Section titled “Problem: Bridge IP address not reachable”

Symptoms: Cannot ping or access router via bridge IP.

Causes & Solutions:

  1. Firewall blocking traffic - Check input chain rules:

    /ip firewall filter print chain=input

    Ensure ICMP and management traffic is allowed.

  2. Wrong subnet - Verify client IP is in same subnet as bridge:

    /ip address print where interface=bridge-lan

Problem: Slow performance or high CPU

Section titled “Problem: Slow performance or high CPU”

Symptoms: Network throughput is low, router CPU is high.

Causes & Solutions:

  1. Hardware offloading disabled - Enable hw-offload for supported switches:

    /interface bridge port set [find] hw=yes

  2. Too many MAC addresses - Check bridge host table:

    /interface bridge host print count-only

    Consider increasing max-learned-entries or investigating rogue devices.

Problem: MAC address flapping warnings in logs

Section titled “Problem: MAC address flapping warnings in logs”

Symptoms: Log shows “MAC flapping” messages.

Causes & Solutions:

  1. Network loop detected - This indicates the same MAC is seen on multiple ports. Check for:
    • Misconfigured redundant links without STP
    • Devices connected to multiple bridge ports
    /log print where message~"flapping"
Section titled “Related Topics”

Next Steps

Section titled “Next Steps”

Advanced Topics

Section titled “Advanced Topics”
Section titled “Related Concepts”

References

Section titled “References”