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Configuration Guide - Ethernet Switching

S1720, S2700, S5700, and S6720 V200R012(C00 and C20)

This document describes the configuration of Ethernet services, including configuring MAC address table, link aggregation, VLANs, VLAN aggregation, MUX VLAN, VLAN termination, Voice VLAN, VLAN mapping, QinQ, GVRP, VCMP, STP/RSTP/MSTP, VBST, SEP, RRPP, ERPS, LBDT, and Layer 2 protocol transparent transmission.
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Link-type Negotiation Protocol (LNP) dynamically negotiates the link type of an Ethernet interface. The negotiated link type affects the VLAN the interface joins, which is described as follows:
  • 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 a VLAN between VLAN 1 and VLAN 4094 by default.


The switch supports the following link types on an Ethernet interface: access, hybrid, trunk, and QinQ. The four link types are applicable to different network positions and are manually specified. When the network topology changes, link types of Ethernet interfaces also need to be reconfigured. If this is done manually, configuration is time-consuming and complex. To simplify the configuration, LNP supports auto-negotiation of the link types on Ethernet interfaces and allows Ethernet interfaces to join VLANs after the auto-negotiation. This eliminates the need to manually configure link types of Ethernet interfaces, reducing the workload.


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

Figure 4-10  Typical LNP networking
  • 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 the following 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 (for example, STP, RSTP, MSTP, or VBST) needs to be deployed to prevent loops.

    If a loop prevention protocol is deployed on a Layer 2 network, LNP negotiation can succeed even on a blocked interface.

  • LNP negotiation

    The link type of the remote 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 two ends of an Eth-Trunk link have different numbers of member interfaces, the LNP negotiation may fail (the link type of an interface will be set to access when the negotiation fails).

    • 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.
    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 communication between both ends. When the communication is delayed, the link type may be incorrectly negotiated. After three rounds of communication are complete, the link type is in stable negotiation state. Otherwise, the link type of the interface stays in negotiation state. Before the link type enters the stable negotiation state, the interface in blocking state does not forward packets. This prevents forwarding errors.

    The VLAN Central Management Protocol (VCMP) domain name affects LNP negotiation. The link type can be set to trunk only when domain names at both ends are consistent or the domain name of at least one end is empty; otherwise, the link type is set to access.

Updated: 2018-12-24

Document ID: EDOC1100038339

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