Dynamic Prefix Allocation for NEMOv4

The following extension is defined according to this specification.

defines that the prefix field of the mobile network request extension can not be set to zero. This mechanism works only in combination with the explicit mode of operation defined in . According to this specification, a mobile client MAY include one or more mobile network request extensions with the prefix field set to zero. Such mobile network request extensions indicate that the mobile client requests mobile network prefix(es) to be assigned to it by the home agent. In this case, the mobile client MAY set the prefix length field of such extensions to zero or to a length of its choice as a hint to the home agent. According to this specification, mobile network request extensions with the prefix field set to zero MAY be included in a registration request message either during initial registration or during a subsequent registration. When a mobile client receives a registration reply it MUST process it as defined in MIPv4 and . If one or more network acknowledgement extension are included with the Code field set to “Success” the mobile client SHOULD treat the prefixes in the corresponding prefix fields as allocated prefixes and create the appropriate bindings as defined in . If in response to a registration request with a mobile network request extension with the prefix field set to zero, a mobile client receives a registration reply with a network acknowledgement extensiona including Code field set to 1 “invalid prefix", it may use it as a hint that the home agent does not support dynamic prefix allocation.

A home agent receiving a mobile network request extension with the prefix field set to zero MAY return a mobile network acknowledgement extension with the prefix field set to the prefix allocated to the mobile client. The length of that prefix is at the discretion of the home agent. The home agent MAY take into account the prefix length hint if one is included in the mobile network request extension. Once the home agent allocates a prefix it MUST maintain the prefix registration table as defined in . Alternatively the home agent MAY return a mobile network acknowledgement extension with the Code field set to one of the negative codes defined in . Dynamic mobile prefix allocation as defined in this specification MAY be combined with dynamic home address allocation as defined in . In other words the home address field of the registration request message MAY be set to zero while the message also includes one or more mobile network request extensions with the prefix field also set to zero. Once the home agent allocates a prefix it MUST maintain the prefix registration table as defined in . The lifetime of the allocated prefix will be equal to the lifetime of the binding cache entry For dynamic prefix allocation the mobile client’s home address MAY be used to identify the client if it is not set to zero. Otherwise, as defined in the NAI extension of MIPv4 , the NAI extension needs to be included in the registration request, in which case the same extension SHOULD be used to identify the mobile client for prefix allocation purposes.