LNP

Definition

Background

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.

Implementation

When the Layer 2 device on the network shown in Figure 4-10 is 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
  negotiation-desirable/negotiation-auto	Access (LNP negotiation enabled)	Access	Access
  	Hybrid (LNP negotiation enabled)	Trunk	Hybrid
  	Dot1q tunnel (LNP negotiation enabled)	Access	Dot1q tunnel
  	Trunk (LNP negotiation enabled)	Trunk	Trunk
  	LNP negotiation not supported or disabled	Access	Uncertain
  negotiation-desirable	negotiation-desirable	Trunk	Trunk
  negotiation-desirable	negotiation-auto	Trunk	Trunk
  negotiation-auto	negotiation-auto	Access	Access

  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.