Configure L2VPN MTU Negotiation

As defined in relevant standards, nodes negotiate MTU values before they establish virtual circuits (VCs) or pseudo wires (PWs) on Layer 2 virtual private networks (L2VPNs), such as Pseudowire Emulation Edge-to-Edge (PWE3), virtual leased line (VLL), and virtual private LAN service (VPLS) networks. An MTU inconsistency will cause two nodes to fail to establish a VC or PW.

Type	MTU Configuration Methods	MTU Value Selection Rules
PWE3	Specify MTU parameter in the mpls switch-l2vc command. Configure the mtu mtu-value command in the PW template view.	One of the following MTUs with priorities in descending order is selected: MTU parameter specified in the mpls l2vc command or mpls switch-l2vc command MTU configured in PW template Interface MTU of the AC interface Default MTU value (1500 bytes)
BGP VLL	Configure the mtu mtu-value command in MPLS-L2VPN instance view.	One of the following MTUs with priorities in descending order is selected: MTU configured in MPLS-L2VPN instance view Default MTU value (1500 bytes)
VPLS	Configure the mtu mtu-value command in VSI view.	One of the following MTUs with priorities in descending order is selected: MTU configured in VSI instance view Default MTU value (1500 bytes)

Type

MTU Configuration Methods

MTU Value Selection Rules

PWE3

Specify MTU parameter in the mpls switch-l2vc command.
Configure the mtu mtu-value command in the PW template view.

One of the following MTUs with priorities in descending order is selected:

MTU parameter specified in the mpls l2vc command or mpls switch-l2vc command
MTU configured in PW template
Interface MTU of the AC interface
Default MTU value (1500 bytes)

BGP VLL

Configure the mtu mtu-value command in MPLS-L2VPN instance view.

One of the following MTUs with priorities in descending order is selected:

MTU configured in MPLS-L2VPN instance view
Default MTU value (1500 bytes)

VPLS

Configure the mtu mtu-value command in VSI view.

One of the following MTUs with priorities in descending order is selected:

MTU configured in VSI instance view
Default MTU value (1500 bytes)

By default, Huawei routers implement MTU negotiation for VCs or PWs. Two nodes must use the same MTU to ensure that a VC or PW is established successfully. L2VPN MTUs are only used to establish VCs and PWs and do not affect packet forwarding.

The default VPLS MTU is 1500 bytes, which is not subject to changes on the interface MTU because the MTU is configured in the VSI view.

To communicate with non-Huawei devices that do not verify L2VPN MTU consistency, L2VPN MTU consistency verification can be disabled on NetEngine 8000 F. This allows NetEngine 8000 F to establish VCs and PWs with the non-Huawei devices.