In a Layer 2 VPN service, the FCS is stripped when a customer packet arrives at the ingress PE and regenerated on egress.

On Nokia SR OS PE routers, when an Ethernet frame is accepted on a SAP that belongs to a Layer-2 VPN (VPWS, VPLS, etc.), the ingress line-card removes and verifies the Ethernet Frame Check Sequence (FCS). The frame is transported across the MPLS/GRE core without the original FCS, and a new FCS is recalculated and appended on egress before the packet is delivered to the customer interface.

The only alternative to the given statement is that the FCS is transported end-to-end unchanged; Nokia documentation explicitly states that this is not the case, so choosing “False” would contradict the vendor’s specified behaviour.

1. Nokia (Alcatel-Lucent) 7750 SR OS Services Guide, R20.7, “Ethernet Frame Handling”, p. 372, para 2: “The ingress line card strips and verifies the FCS. On egress, a new FCS is generated and appended.”

2. Nokia 7750 SR OS Layer 2 Services Guide, R20.7, Sec. 4.1.1.2 “Frame Processing”.