Dynamic Prefix Allocation for Network Mobility for Mobile IPv4 (NEMOv4)
updates
- rfc-5177 — Network Mobility (NEMO) Extensions for Mobile IPv4
Extracted elements (18)
The Mobile Router's home address MAY be used to identify the client for prefix allocation; when the home address is zero (dynamic home address allocation), the NAI extension is used instead. This allows dynamic prefix allocation to work even when the home address is not yet known.
Dynamic mobile prefix allocation MAY be combined with dynamic home address allocation (RFC5177): the home address field of the registration request MAY be set to zero while also including Mobile Network Request extensions with Prefix set to zero.
If a Mobile Router receives a registration reply with a network acknowledgement extension Code set to 1 ('invalid prefix') in response to a zero-Prefix request, this may be used 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 Router.
For a Mobile Network Prefix for which the assignment was unsuccessful, the Code field in the corresponding Mobile Network Acknowledgement extension should be set to 4 (MOBNET_UNASSIGNED).
Home agent implementations SHOULD take steps to prevent address exhaustion attacks, for example by limiting the number and size of prefixes any one Mobile Router can be allocated.
If one or more network acknowledgement extensions are included with Code set to 'Success', the Mobile Router SHOULD treat the prefixes in the corresponding Prefix fields as allocated prefixes and create the appropriate bindings as defined in RFC5177.
Mobile Network Request extensions with the Prefix field set to zero MAY be included in a registration request during initial registration or during a subsequent registration.
Once the home agent allocates a prefix, it MUST maintain the prefix registration table as defined in RFC5177. The lifetime of the allocated prefix equals the lifetime of the binding cache entry.
The Mobile Router MAY set the prefix length field of a zero-Prefix Mobile Network Request extension to zero or to a length of its choice as a hint to the home agent about the desired prefix size.
The Prefix field of the Mobile Network Request extension MUST be set to zero to indicate that the Mobile Router is requesting dynamic mobile network prefix assignment by the home agent.
When a Mobile Router receives a registration reply, it MUST process it as defined in Mobile IPv4 (RFC5944) and RFC5177.
When the Mobile Router's home address is zero, the NAI extension (RFC2794) needs to be included in the registration request, and the same extension SHOULD be used to identify the Mobile Router for prefix allocation purposes.
MOBNET_UNASSIGNED (Code 4) is a new Mobile Network Acknowledgement Extension code value meaning 'Home Agent cannot assign a mobile network prefix'. It is used when prefix assignment is unsuccessful.
The Mobile Network Acknowledgement extension returned by the home agent carries a Prefix field set to the allocated prefix and a Code field indicating success or failure of the allocation.
The Mobile Network Request extension carries a Prefix field that, when set to zero, signals a request for dynamic prefix assignment. An optional prefix length hint field allows the Mobile Router to indicate a preferred prefix size.
A new value has been assigned in the Mobile Network Acknowledgement Extension registry: Code 4 — 'Home Agent cannot assign a mobile network prefix' (MOBNET_UNASSIGNED).
This specification operates within the security constraints of Mobile IPv4 (RFC5944), NAI (RFC2794), and RFC5177. Home agents SHOULD limit the number and size of prefixes assignable to a single Mobile Router to prevent address exhaustion attacks.