4.1.1. Optional Header Elements

The AVP header contains one optional field. This field is only present if the respective bit-flag is enabled.

Vendor-ID

The Vendor-ID field is present if the 'V' bit is set in the AVP Flags field. The optional four-octet Vendor-ID field contains the IANA-assigned "SMI Network Management Private Enterprise Codes" [ENTERPRISE] value, encoded in network byte order. Any vendors or standardization organizations that are also treated like vendors in the IANA-managed "SMI Network Management Private Enterprise Codes" space wishing to implement a vendor-specific Diameter AVP MUST use their own Vendor-ID along with their privately managed AVP address space, guaranteeing that they will not collide with any other vendor's vendor-specific AVP(s) or with future IETF AVPs.

A Vendor-ID value of zero (0) corresponds to the IETF-adopted AVP values, as managed by IANA. Since the absence of the Vendor-ID field implies that the AVP in question is not vendor specific, implementations MUST NOT use the value of zero (0) for the Vendor-ID field.