A customer requests that their Layer 2 Ethernet service be configured to forward frames up to 9000 bytes. The service provider is using MPLS encapsulation. What is the minimum MTU setting for the network ports?

To calculate the minimum required MTU for the network ports, all encapsulation overhead must be added to the customer's maximum frame size. The customer frame (9000 bytes) is encapsulated within an MPLS packet, which is then encapsulated by the Layer 2 protocol on the network port (typically Ethernet). Calculation: Customer Frame Size: 9000 bytes MPLS Overhead (2 labels: Transport + Service): 4 + 4 = 8 bytes Network Port Ethernet Header (DMAC, SMAC, EtherType): 14 bytes Total Minimum MTU = 9000 + 8 + 14 = 9022 bytes.

A. 9000: This is only the customer's frame size and does not account for any of the service provider's MPLS or Ethernet encapsulation overhead.
B. 9004: This value does not correspond to a correct calculation of standard MPLS and Ethernet overhead. It might account for one MPLS label but ignores other headers.
C. 9008: This accounts for the customer frame plus the MPLS label stack (9000 + 8), but it omits the underlying network port's Layer 2 header (14 bytes for Ethernet).
E. 9036: This value is too high. It may incorrectly include extra overhead, such as a control word (4 bytes) and a network VLAN tag (4 bytes), which are not always present.

1. Nokia 7750 SR OS Services Configuration Guide, Release 21.10.R1, "MTU Configuration Guidelines". This section details the need to account for service and transport overhead. It states, "The network port MTU must be large enough to accommodate the service payload plus any overhead."

2. Nokia 4A0-104 Courseware, Module 3: "Layer 2 Services". The module explains that the network-facing port MTU must be the sum of the service MTU plus all encapsulation headers (e.g., MPLS labels, underlying Ethernet).