Observe the following general rules when planning your service and physical MTU configurations:
The router must contend with MTU limitations at many service points. The physical (access and network) port, service, and SDP MTU values must be individually defined.
Identify the ports that are designated as network ports intended to carry service traffic.
MTU values should not be modified frequently.
MTU values must conform to both of the following conditions:
The service MTU must be less than or equal to the SDP path MTU.
The service MTU must be less than or equal to the access port (SAP) MTU.
When the network group encryption (NGE) feature is enabled, additional bytes because of NGE packet overhead must be considered. See the ‟NGE Packet Overhead and MTU Considerations” section in the 7450 ESS, 7750 SR, 7950 XRS, and VSR Services Overview Guide for more information.