You have an L2VPN connecting two CEs across a provider network.

Layer 2 VPNs don’t support fragmentation in the provider network. It is critical that the provider network supports the largest frame that the CE devices can generate after the MPLS and virtual routing and forwarding (VRF) labels are added by the PE devices. This example leaves the CE devices at the default 1500-byte maximum transmission unit (MTU) while configuring the provider core to support a 4000 byte MTU. This configuration avoids discards by ensuring the CE devices cannot exceed the MTU in the provider’s network.