To detect maximum transmission unit (MTU) mismatches, Intermediate System-to-Intermediate System (IS-IS) pads hello packets to the full interface MTU. All hello packets on Fabric Extend network-to-network interface (NNI) links are padded . On non-Fabric Extend point-to-point NNI links, hello packets are padded until a hello packet is received from the other side.
Note
If you downgrade to a release that does not support this feature, you must disable the feature and save the configuration before you downgrade. You must have a compatible configuration file if you downgrade to an earlier release.