Neighbor Discovery in RouterOS

Neighbor Discovery in RouterOS

Summary

Neighbor Discovery protocols enable MikroTik routers to discover compatible devices within the same Layer 2 broadcast domain. RouterOS supports three discovery protocols: MNDP (MikroTik Neighbor Discovery Protocol), CDP (Cisco Discovery Protocol), and LLDP (Link Layer Discovery Protocol). These protocols exchange device information including identity, platform, IP addresses, and capabilities, enabling network administrators to map out their network topology automatically.

The neighbor discovery mechanism operates at Layer 2, broadcasting discovery packets to identify nearby devices running compatible protocols. This functionality proves invaluable for network documentation, troubleshooting, and management tasks where knowing what devices exist on each network segment is essential. Unlike traditional network scanning methods that actively probe IP addresses, neighbor discovery works passively by listening for broadcasted announcements from other devices.

MNDP is MikroTik’s proprietary protocol designed specifically for RouterOS devices, providing the most detailed information including RouterOS version, board model, and uptime. CDP and LLDP offer interoperability with non-MikroTik equipment, making them suitable for heterogeneous network environments. RouterOS can simultaneously run all three protocols, discovering devices regardless of their manufacturer or discovery protocol preference.

Neighbor List

The neighbor list displays all discovered devices within the Layer 2 broadcast domains that the router can reach. Each entry shows the interface through which the neighbor was discovered, its IP and MAC addresses, identity, version, and platform information. The list updates automatically as discovery packets are received and ages out as devices become unreachable.

Sub-menu: /ip/neighbor

Viewing the Neighbor List

Display all discovered neighbors:

/ip/neighbor/print

Example output showing various device types:

Columns: INTERFACE, ADDRESS, MAC-ADDRESS, IDENTITY, VERSION, BOARD
#  INTERFACE  ADDRESS         MAC-ADDRESS       IDENTITY    VERSION  BOARD
0  ether13    192.168.33.2    00:0C:42:00:38:9F MikroTik    6.49     RB1100AHx2
1  ether11    1.1.1.4         00:0C:42:40:94:25 test-host   6.48     RB1000
2  Local      10.0.11.203     00:02:B9:3E:AD:E0 c2611-r1    Cisco     IOS
3  Local      10.0.11.47      00:0C:42:84:25:BA 11.47-750   6.47     RB750
4  Local      10.0.11.254     00:0C:42:70:04:83 tsys-sw1    6.48     RB750G
5  Local      10.0.11.202     00:17:5A:90:66:08 c7200       Cisco     IOS

The neighbor list includes MikroTik devices running RouterOS, Cisco equipment using CDP, and any LLDP-capable devices from various manufacturers. The “Local” interface designation indicates that the device discovered itself, typically when connected through a bridge or bonding interface.

Neighbor Entry Properties

Property	Type	Description
address	IP	The highest IP address configured on the discovered device
address6	IPv6	IPv6 address configured on the discovered device
age	time	Time elapsed since the last discovery packet was received
board	string	RouterBOARD model name (RouterOS devices only)
discovered-by	cdp | lldp | mndp	Protocol(s) that discovered this neighbor (RouterOS 7.7+)
identity	string	System identity configured on the neighbor device
interface	string	Local interface through which the neighbor was discovered
interface-name	string	Interface name on the neighbor device (CDP-specific)
ipv6	yes | no	Whether the device has IPv6 enabled
mac-address	MAC	MAC address of the remote device; enables MAC-telnet access
platform	string	Device platform name (MikroTik, Cisco, etc.)
software-id	string	RouterOS software ID (RouterOS devices only)
system-caps	string	LLDP system capabilities
system-caps-enabled	string	LLDP enabled capabilities
unpack	none | simple | uncompressed-headers | uncompressed-all	Discovery packet compression type
uptime	time	Uptime of the remote device (RouterOS devices only)
version	string	Software version running on the remote device
running	string array	Features running on the neighbor (e.g., CAPsMAN)

Memory Management

Starting from RouterOS v6.45, the number of neighbor entries per interface is limited to (total RAM in megabytes) × 16 to prevent memory exhaustion. This limit applies individually to each interface, meaning a router with 128MB of RAM can store up to 2048 neighbor entries per interface. When the limit is reached, older entries are removed to make space for new discoveries.

Connecting via MAC-Address

The neighbor list provides MAC addresses that enable direct connections using MAC-telnet:

/tool mac-telnet 00:0C:42:00:38:9F interface=ether13

This capability proves especially useful when IP connectivity is unavailable but Layer 2 reachability exists.

Discovery Configuration

Neighbor discovery behavior is controlled through the discovery settings sub-menu. These settings determine which interfaces participate in discovery, which protocols are used, and how frequently discovery packets are transmitted.

Sub-menu: /ip/neighbor/discovery-settings

Discovery Settings Properties

Property	Type	Description	Default
discover-interface-list	string	Interface list containing interfaces that participate in discovery	static
discover-interval	time: 5s..9h6m8s	Frequency of discovery packet transmission; affects TTL for CDP/LLDP (RouterOS 7.16+)	30s
lldp-dcbx	yes | no	Send DCBX TLVs for QoS coordination (CRS3xx, CRS5xx, CCR2116, CCR2216)	no
lldp-mac-phy-config	yes | no	Send MAC/PHY Configuration/Status TLV in LLDP	no
lldp-max-frame-size	yes | no	Send Maximum Frame Size TLV in LLDP	no
lldp-poe-power	yes | no	Send Power Via MDI TLV for PoE management (RouterOS 7.15+)	yes
lldp-med-net-policy-vlan	integer: 0..4094	VLAN ID for LLDP-MED Network Policy TLV	disabled
lldp-vlan-info	yes | no	Send IEEE 802.1 VLAN TLVs in LLDP (RouterOS 7.16+)	no
mode	rx-only | tx-only | tx-and-rx	Discovery packet sending and receiving mode (RouterOS 7.7+)	tx-and-rx
protocol	cdp | lldp | mndp	List of discovery protocols to use	cdp,lldp,mndp

Basic Discovery Configuration

Set the interface list for neighbor discovery:

/ip/neighbor/discovery-settings/set discover-interface-list=LAN

Configure which protocols to use:

/ip/neighbor/discovery-settings/set protocol=mndp,lldp

Disable CDP to avoid conflicts with LLDP-MED:

/ip/neighbor/discovery-settings/set protocol=mndp,lldp

Discovery Mode Selection

The mode property controls how the router participates in discovery:

• tx-and-rx: Sends discovery announcements and listens for neighbors (default)
• rx-only: Only listens for neighbors without sending announcements
• tx-only: Only announces itself without listening for others

Use rx-only mode when you want to discover other devices without revealing your own presence:

/ip/neighbor/discovery-settings/set mode=rx-only

Interface List Management

Discovery operates on interfaces included in the specified interface list. Interfaces not in the list do not participate in discovery and cannot discover or be discovered.

Create and configure an interface list for discovery:

/interface/list/add name=discovery-list
/interface/list/member/add interface=ether1 list=discovery-list
/interface/list/member/add interface=ether2 list=discovery-list
/ip/neighbor/discovery-settings/set discover-interface-list=discovery-list

Limiting Discovery to Specific Slave Interfaces

Since RouterOS v6.44, neighbor discovery works on individual slave interfaces of bridges and bonds. Include the specific slave interface in the discovery list while excluding the master interface:

/interface/bonding/add name=bond1 slaves=ether5,ether6
/interface/list/add name=only-ether5
/interface/list/member/add interface=ether5 list=only-ether5
/ip/neighbor/discovery-settings/set discover-interface-list=only-ether5

The neighbor list will show the master interface name along with the specific slave interface where the discovery was received:

#  INTERFACE  ADDRESS         MAC-ADDRESS       IDENTITY    VERSION  BOARD
0  ether5     192.168.88.1    CC:2D:E0:11:22:33 R1          6.45.4   CCR1036-8G-2S+
   bond1

LLDP Configuration

Link Layer Discovery Protocol (LLDP) is a vendor-neutral protocol for advertising capabilities and devices to neighboring equipment. RouterOS sends various Type-Length-Value (TLV) elements in LLDP messages, providing detailed information about the device and its interfaces.

LLDP TLV Elements

RouterOS advertises the following TLVs in LLDP messages:

• Chassis ID: MAC address of the device
• Port ID: Interface name or combined name (e.g., “bridge/ether1”)
• Time To Live: Validity period for the LLDP information
• System Name: Router identity from /system/identity
• System Description: Platform, RouterOS version, and RouterBOARD name
• Management Address: All IP addresses configured on the port
• System Capabilities: Enabled capabilities (bridge, router, etc.)
• Port Description: Interface description including bridge/bond membership
• Port VLAN ID: IEEE 802.1 PVID from bridge port settings
• Port And Protocol VLAN ID: Protocol VLAN status
• VLAN Name: Up to 10 active VLANs from bridge VLAN table
• MAC/PHY Configuration/Status: Duplex, bit rate, auto-negotiation
• Power Via MDI: PoE capabilities and status
• Maximum Frame Size: L2MTU + 18 bytes
• LLDP-MED Media Capabilities: MED endpoint classification
• LLDP-MED Network Policy: VLAN ID for voice traffic
• LLDP-MED Extended Power via MDI: PoE power details
• Port Extender: Port Extender and Controller Bridge advertisement

Configuring LLDP VLAN Information

Enable IEEE 802.1 VLAN TLVs for interfaces using bridge VLAN filtering:

/ip/neighbor/discovery-settings/set lldp-vlan-info=yes

This advertises the Port VLAN ID, active VLAN names from /interface/bridge/vlan, and protocol VLAN status to neighboring LLDP-capable devices.

Configuring LLDP-MED Network Policy

Assign a VLAN for LLDP-MED capable devices such as VoIP phones:

/ip/neighbor/discovery-settings/set lldp-med-net-policy-vlan=100

The TLV includes predefined values that cannot be modified:

• Application Type: Voice
• VLAN Type: Tagged
• L2 Priority: 0
• DSCP Priority: 0

When used with a bridge interface, enable R/MSTP with protocol-mode setting and exclude other discovery protocols to avoid misconfiguration.

LLDP PoE Power TLV

RouterOS 7.15+ includes LLDP PoE power TLVs for PoE-out port management:

/ip/neighbor/discovery-settings/set lldp-poe-power=yes

This sends two TLVs:

• IEEE 802.3 Organizationally Specific Power Via MDI TLV
• TIA-1057 (LLDP-MED) Extended Power via MDI TLV (auto-included when remote device supports MED power)

These TLVs apply only to Ethernet interfaces with PoE-Out capability.

DCBX Configuration

Data Center Bridging Capabilities Exchange Protocol (DCBX) enables QoS coordination with neighboring devices. Available on CRS3xx, CRS5xx, CCR2116, and CCR2216 devices:

/ip/neighbor/discovery-settings/set lldp-dcbx=yes

When enabled, DCBX advertises:

• ETS Configuration TLV: Willingness bit, priority assignment, bandwidth allocation, TSA
• ETS Recommendation TLV: Recommended ETS configuration from neighboring devices
• Priority-based Flow Control Configuration TLV: PFC settings and willingness
• Application Priority TLV: Application prioritization
• Application Priority TLV: VLAN configurations for applications

The willingness bit is always disabled, meaning the device does not accept remote QoS configurations.

Protocol Comparison

Understanding the differences between MNDP, CDP, and LLDP helps in selecting the appropriate protocols for your network environment.

MNDP (MikroTik Neighbor Discovery Protocol)

MNDP provides the richest information for RouterOS-to-RouterOS communication. It reveals detailed hardware and software information including RouterBOARD model, RouterOS version, uptime, and installed features like CAPsMAN. MNDP packets are compact and optimized for MikroTik equipment. Use MNDP when your network consists primarily of RouterOS devices and you need maximum visibility into device details.

CDP (Cisco Discovery Protocol)

CDP offers compatibility with Cisco equipment and some third-party devices. It provides basic device information including hostname, platform, and interface details. CDP proves useful in mixed-vendor environments where Cisco equipment must be discovered. RouterOS CDP implementation supports receiving and sending CDP announcements, making it suitable for Cisco-centric networks with MikroTik equipment.

LLDP (Link Layer Discovery Protocol)

LLDP is the IEEE standard (802.1AB) protocol, providing vendor-neutral device discovery. It offers extensive customization through TLV selection and integrates with LLDP-MED for IP telephony and network policy advertisement. LLDP is ideal for multi-vendor environments requiring standardized network mapping and supports advanced features like VLAN assignment for VoIP devices.

Common Configuration Scenarios

Scenario 1: Router-Only Network

For networks containing only MikroTik routers, use MNDP exclusively for optimal information:

/ip/neighbor/discovery-settings/set protocol=mndp

This minimizes broadcast traffic while providing complete device visibility.

Scenario 2: Mixed Vendor Environment

In networks with multiple vendors, enable all protocols:

/ip/neighbor/discovery-settings/set protocol=cdp,lldp,mndp

This ensures discovery of all equipment regardless of the protocol they use.

Scenario 3: VoIP Deployment with LLDP-MED

Deploy LLDP-MED for automatic VLAN assignment to IP phones:

/ip/neighbor/discovery-settings/set protocol=lldp lldp-med-net-policy-vlan=100

Configure the bridge to accept the LLDP-assigned VLAN:

/interface/bridge/vlan/add bridge=bridge1 tagged=bridge1 vlan-ids=100

Scenario 4: Secure Discovery Mode

Prevent your router from being discovered while still discovering others:

/ip/neighbor/discovery-settings set mode=rx-only

This is useful in security-sensitive environments where you want to inventory devices without revealing your presence.

Monitoring and Management

Scheduled Neighbor Checks

Create a scheduler to log neighbor changes periodically:

/system/scheduler/add name=log-neighbors interval=1m on-event=":log info \"Neighbors: \$[/ip/neighbor/print count-only]\""

Exporting Neighbor Information

Save neighbor list to a file for documentation:

/ip/neighbor/print file=neighbors-backup

Resetting Discovery Cache

Clear all discovered neighbors:

/ip/neighbor/remove [find]

Troubleshooting

Neighbors Not Appearing

1. Verify the interface is in the discovery interface list: /interface/list/member/print where list=discovery-list
2. Check that the neighbor device supports at least one enabled protocol
3. Confirm Layer 2 connectivity between devices (same VLAN, no blocking)
4. Verify the interface is not disabled: /interface/print
5. Test with a known working MikroTik device to rule out remote device issues

LLDP TLVs Not Received

1. Confirm both ends support LLDP and have it enabled
2. Verify the specific TLV is enabled in discovery settings
3. Check for LLDP-MED compatibility issues with non-LLDP-MED devices
4. Ensure VLANs are properly configured if using LLDP-MED VLAN policy

CDP Incompatibility

1. CDP is not supported on all RouterOS platforms; verify compatibility
2. Some Cisco devices require specific CDP timers; adjust discover-interval
3. Check that CDP is not blocked by firewall rules on the remote device

Discovery Intervals Too Long

Reduce the discovery interval for faster convergence:

/ip/neighbor/discovery-settings/set discover-interval=5s

Lower intervals increase network traffic but provide faster neighbor detection.

Memory Usage Concerns

Monitor neighbor entry counts per interface:

:foreach i in=[/interface/find] do={ :local n [/interface/get $i name]; :put ($n . ": " . [/ip/neighbor/print count-only where interface=$n]) }

If limits are approached, consider increasing RAM or reducing discovery scope to specific interfaces.

See Also

• System Identity — configure router identity for neighbor announcements
• Interface Lists — manage interface lists for discovery scope
• MAC-Telnet — connect to neighbors using discovered MAC addresses
• Bridge VLAN Filtering — configure VLANs for LLDP VLAN TLVs
• PoE-Out — manage PoE settings with LLDP PoE TLVs