Vendors or operators often require that proprietary extensions to a protocol be defined to provide unique features or simply for diagnostic or versioning reasons. For this reason, Mobile IP vendor-/organization-specific extensions have been defined in [RFC3115]. There are two types of vendor-specific extensions:
Normal (NVSE) vendor-/organization-specific extensions
One basic difference between critical and normal extensions is that when the critical extension is encountered but not recognized, the message containing the extension must be silently discarded. On the other hand, when a normal, vendor-/organization-specific extension is encountered but not recognized, the extension should be ignored, but the rest of the extensions and message data must still be processed. Another difference is that a critical, vendor/organization extension has a length field of 2 octets, whereas the NVSE has a length field of only 1 octet. Figures A.5 and A.6 describe the CVSE and NVSE, respectively.