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S12700 V200R010C00 Configuration Guide - Ethernet Switching

This document describes the configuration of Ethernet services, including configuring link aggregation, VLANs, Voice VLAN, VLAN mapping, QinQ, GVRP, MAC table, STP/RSTP/MSTP, SEP, and so on.
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Link-type Negotiation Protocol (LNP) dynamically negotiates the link type of an Ethernet interface. The negotiated link type can be access or trunk.
  • When the link type on an Ethernet interface is negotiated as access, the interface joins VLAN 1 by default.
  • When the link type on an Ethernet interface is negotiated as trunk, the interface joins VLANs 1 to 4094.


The switch supports the following link types on an Ethernet interface: access, hybrid, trunk, and dot1q tunnel. The four link types are applicable to different network positions and are manually specified. If the network topology changes, link types of Ethernet interfaces also need to be reconfigured which can be complicated. To simplify configuration, LNP supports auto-negotiation of the link types on Ethernet interfaces and allows Ethernet interfaces to join VLANs after the auto-negotiation.


When the Layer 2 device on the network shown in Figure 4-10 are successfully connected, the physical status of their interfaces becomes Up. After LNP negotiation is complete, user-side interfaces on Switch4, Switch5, Switch6, and Switch7 join VLAN 1 as access interfaces. Interfaces between switches become trunk interfaces and allow all VLANs.

Figure 4-10  Typical LNP networking
  • LNP negotiation conditions

    After LNP is enabled, LNP negotiation is triggered in the following situations:

    • The local device receives LNP packets from the remote device.
    • The local configuration or interface status changes.

    In addition to access, hybrid, trunk, and dot1q tunnel, LNP provides an additional two link types:

    • negotiation-desirable: The local device actively sends LNP packets.
    • negotiation-auto: The local device does not actively send LNP packets.

    An interface that is negotiated as a trunk interface allows all VLANs by default; therefore, a loop prevention protocol needs to be deployed to prevent loops.

    If a loop prevention protocol (for example, STP, RSTP, MSTP, or VBST) is deployed on a Layer 2 network, LNP negotiation can succeed on a blocked interface regardless of the link type.

  • LNP negotiation

    The link type of a Layer 2 Ethernet interface determines the negotiation result. Table 4-3 describes LNP negotiation results on a Layer 2 interface in Up state.

    • If the ends of an Eth-Trunk link have a different number of member interfaces, the LNP negotiation may fail.

    • If the link type of the Layer 2 Ethernet interface is set to access, hybrid, trunk, or Dot1q tunnel, LNP negotiation does not take effect on the interface.
    • If the negotiation fails, the link type of an interface will be set to. access.
    Table 4-3  LNP negotiation

    Local LNP Negotiation Mode

    Remote Link Type or LNP Negotiation Mode

    Negotiated Local Link Type

    Status of Remote Link Type


    Access (LNP negotiation enabled)



    Hybrid (LNP negotiation enabled)



    Dot1q tunnel (LNP negotiation enabled)


    Dot1q tunnel

    Trunk (LNP negotiation enabled)



    LNP negotiation not supported or disabled















    LNP negotiation depends on the communication between both ends. When the communication is delayed, the link type may be incorrectly negotiated. Only after three rounds of communication are complete will the link type be considered in a stable negotiation state; otherwise, the link type of the interface remains in a negotiation state. Before the link type enters a stable negotiation state, the interface is blocked and does not forward packets to prevent forwarding errors.

    The VLAN Central Management Protocol (VCMP) domain name affects LNP negotiation. The link type can be negotiated as trunk only when domain names at both ends are consistent; otherwise, the link type is negotiated as access.

Updated: 2019-08-21

Document ID: EDOC1000142081

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