Network Working Group W A Simpson, Editor Internet Draft Daydreamer expires in six months July 1994 IP Mobility Support draft-ietf-mobileip-protocol-05.txt | Status of this Memo This document is a submission to the Mobile-IP Working Group of the Internet Engineering Task Force (IETF). Comments should be submitted to the mobile-ip@ossi.com mailing list. Distribution of this memo is unlimited. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts. Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress.'' Please check the 1id-abstracts.txt listing contained in the internet-drafts Shadow Directories on nic.ddn.mil, ds.internic.net, venera.isi.edu, nic.nordu.net, or munnari.oz.au to learn the current status of any Internet Draft. Abstract This document specifies protocol enhancements that allow transparent routing of IP datagrams to Mobile Nodes in the Internet. The Mobile Node is always identified by its Home-Address, regardless of its current point of attachment to the Internet. While situated away from its home, a Mobile Node is also associated with a Care-Of- Address, which provides information about its current point of attachment to the Internet. The protocol provides for registering the Care-Of-Address with a Home Agent. The Home Agent sends traffic destined for the Mobile Node through a tunnel to the Care-Of-Address. Simpson expires in six months [Page i] DRAFT IP Mobility July 1994 1. Introduction Current versions of the Internet Protocol make an implicit assumption that a node's point of attachment remains fixed. Datagrams are sent to a node based on the location information contained in the node's IP address. If a node moves while keeping its IP address unchanged, its network number will not reflect its new point of attachment. The routing protocols will not be able to route datagrams to it correctly. This document defines new functions that allow a node to roam on the Internet, without changing its IP address. The following entities are defined: Mobile Node A host or router that changes its point of attachment from one | network or subnetwork to another. Home Agent A router that advertises reachability for a Mobile Node, maintains a registry of the current Mobility Bindings for that Mobile Node, and encapsulates datagrams for delivery to the Mobile Node while it is away from home. Foreign Agent A router that assists a locally reachable Mobile Node that is away from its home network. The following support services are defined: Agent Discovery All Agents advertise their availability on each link for which they provide service. A newly arrived Mobile Node can send a solicitation on the link to learn if any prospective Agents are present. Care-Of-Address Assignment The Care-Of-Address terminates the end of a tunnel toward a Mobile Node. Depending on the foreign network configuration, the Care- Of-Address may be either dynamically assigned to the Mobile Node Simpson expires in six months [Page 1] DRAFT IP Mobility July 1994 or associated with a Foreign Agent. Registration When the Mobile Node is away from home, it registers the Care-Of- Address with a Home Agent. Depending on its method of attachment, the Mobile Node will register either directly with a Home Agent, or through a Foreign Agent which forwards the registration to the Home Agent. Encapsulation Once a Mobile Node has registered a Care-Of-Address with a Home Agent, the Home Agent intercepts datagrams destined for the Mobile Node, formulates another datagram with the intercepted datagram enclosed within, and forwards the resulting datagram to the Care- Of-Address. Decapsulation At the Care-Of-Address, the enclosed datagram is extracted. When the Mobile Node has its own Care-Of-Address, it decapsulates its own datagrams. When the Care-Of-Address is associated with a Foreign Agent, the Foreign Agent decapsulates the datagrams. If the datagram is addressed to a Mobile Node which the Foreign Agent is currently serving, it will deliver the datagram to the Mobile Node. * 1.1. Requirements A Mobile Node using its Home-Address shall be able to communicate with other nodes after having been disconnected from the Internet, and then reconnected at a different point of attachment. A Mobile Node shall continue to be capable of communicating directly with existing nodes which do not implement the mobility functions | described in this document. A Mobile Node shall provide authentication in its registration messages. Simpson expires in six months [Page 2] DRAFT IP Mobility July 1994 1.2. Goals The Mobile Node's directly attached link is likely to be bandwidth limited. Few administrative messages are sent between a Mobile Node and an Agent. The size of these messages are kept as short as possible. 1.3. Assumptions The protocols defined in this document place no additional requirements on assignment of IP addresses. That is, a Mobile Node will be assigned an IP address by the organization that owns the machine, and will be able to use that IP address regardless of the current point of attachment. Mobile Nodes are able to change their point of attachment to the Internet no more frequently than once per second. No protocol enhancements are required in hosts or routers that are not serving any of the mobility functions. Similarly, no additional protocols are needed by a router (that is not acting as a Home Agent or a Foreign Agent) to route datagrams to or from a Mobile Node. The operation of this specification assumes that IP datagrams are | routed to a Destination without regard to the Source of the datagram. If desired, the Mobile Node can create tunnel(s) to its Home Agent. The definition of such mechanisms is outside the scope of this | document. 1.4. Specification Language In this document, several words are used to signify the requirements of the specification. These words are often capitalized. MUST This word, or the adjective "required", means that the definition is an absolute requirement of the specification. MUST NOT This phrase means that the definition is an absolute prohibition of the specification. SHOULD This word, or the adjective "recommended", means that there may exist valid reasons in particular circumstances to ignore this item, but the full implications must be Simpson expires in six months [Page 3] DRAFT IP Mobility July 1994 understood and carefully weighed before choosing a different course. MAY This word, or the adjective "optional", means that this item is one of an allowed set of alternatives. An implementation which does not include this option MUST be prepared to interoperate with another implementation which does include the option. silently discard The implementation discards the packet without further processing, and without indicating an error to the sender. The implementation SHOULD provide the capability of logging the error, including the contents of the discarded packet, and SHOULD record the event in a statistics counter. 1.5. Terminology This document frequently uses the following terms: Authentication Type This includes the algorithm and algorithm mode. Note that a single algorithm (such as DES) might have several modes (for example, CBC and ECB). Correspondent A peer with which a Mobile Node is communicating. The Correspondent may be either mobile or stationary. Home-Address A long-term IP address that is assigned to a Mobile Node. It remains unchanged regardless of where the node is attached to the Internet. Datagrams addressed to the Home-Address are intercepted by the Home Agent while the Mobile Node is registered with that Home Agent. Link A communication facility or medium over which nodes can communicate at the link layer; underlying the network layer. Mobility Binding The association of a Home-Address with a Care-Of-Address, and the remaining LifeTime of the association. Routing Prefix The high-order bits in an address, which are used by Simpson expires in six months [Page 4] DRAFT IP Mobility July 1994 routers to locate a link for delivery of a datagram. Mobility Security Association The security relationship between two nodes that is used with Mobile IP protocol messages. This relationship includes the authentication type (including algorithm and algorithm mode), the secret (such as a shared key, or appropriate public/private key pair), and possibly other information such as labelling. Triangle Routing A path followed by a datagram destined for a Mobile Node, when that datagram arrives first at the Home Agent, and then is encapsulated and forwarded by the Home Agent. Simpson expires in six months [Page 5] DRAFT IP Mobility July 1994 2. Agent Discovery To communicate with a Foreign or Home Agent, a Mobile Node must learn either the IP address or the link address of that Agent. It is assumed that a link-layer connection has been established between the Agent and the Mobile Node. The method used to establish such a link-layer connection is not specified in this document. After establishing a link-layer connection that supports the attachment of Mobile Nodes, the node learns whether there are any Agents available. If the Home Agent is recognized, the Mobile Node is at home. There are often several methods of learning the availability of an Agent. Those described here are recommended. Point-to-Point Link-Layers The Point-to-Point-Protocol (PPP) [RFC-1548] Internet Protocol Control Protocol (IPCP) [RFC-1332], negotiates the use of IP addresses. When the Home-Address is not accepted, but a transient IP address is dynamically assigned, that address is used as the Care-Of- Address in registration. When no transient IP address is dynamically assigned, but an IP address is advertised by the peer, that address is assumed to be the IP address of an Agent. Multi-Point Link-Layers Another link establishment protocol, IEEE 802.11, might yield the link address of an agent. This link-layer address is used to attempt registration. ICMP Router Discovery An Agent which is not identified by a link-layer protocol MUST implement ICMP Router Discovery [RFC-1256]. The Router Advertisements indicate whether the router is also an Agent. It is recommended that as few messages as possible which duplicate functionality be sent on mobile links. This is particularly important on wireless and congested links. When multiple methods are in use, the Mobile Node SHOULD first Simpson expires in six months [Page 6] DRAFT IP Mobility July 1994 attempt registration with routers sending Router Advertisements in preference to those sending link-layer advertisements. This ordering maximizes the likelihood that the registration will be recognized, thereby minimizing the number of registration attempts. An Administrative Domain MAY require registration with a Foreign Agent even when another registration method is in use. This facility is envisioned for service providers with packet filtering fire-walls, or visiting policies (such as accounting) which require exchanges of authorization. 2.1. Authentication No authentication is required for the advertisement and solicitation process. These messages MAY be authenticated using a future IP Authentication Header, which is external to the messages described here. Further work on authentication of advertisement and solicitation is outside of the scope of this document. Whenever an externally authenticated message fails authentication, the message is silently discarded. 2.2. Agent Solicitation Every Mobile Node is required to implement ICMP Router Solicitation. However, the Router Solicitation is only sent when no Care-Of-Address has been determined through a link-layer protocol or Router Advertisement. Any Foreign Agent and Home Agent which is not identified by a link- layer protocol MUST respond to ICMP Router Solicitation. | The same procedures, defaults, and constants are used as described in "ICMP Router Discovery Messages" [RFC-1256]. 2.3. Agent Advertisement Every Mobile Node is required to correctly process ICMP Router Advertisements. Simpson expires in six months [Page 7] DRAFT IP Mobility July 1994 Any Foreign Agent and Home Agent which is not identified by a link- layer protocol MUST send ICMP Router Advertisements. An Agent which is identified by a link-layer protocol SHOULD also implement Router Advertisements. However, the Router Advertisements need not be sent, except when the site policy requires registration with the Agent, or as a response to a specific Router Solicitation. The same procedures, defaults, and constants are used as described in "ICMP Router Discovery Messages" [RFC-1256], except as specified herein. The Router Advertisements are extended by examining the number of advertised addresses. When the IP total length indicates that the ICMP message is longer than needed for the number of addresses present, the remainder is interpreted as extensions. The extensions are described in the "Mobility Message Extensions" chapter. The Mobility Extension is required, and indicates that the router is an Agent. Other extensions indicate optionally supported features. | The Code field of the ICMP Router Advertisement is interpreted as follows: 0 If the Mobility Extension is present, the router supports mobility registration. The router is participating in routing common traffic. 16 A Home or Foreign Agent which supports registration, but is not participating in routing common traffic. A Foreign Agent includes the Care-Of-Address as a Router Address. The Mobile Node examines the Agent Advertisement. If any Router Address listed exactly matches a Home Agent in its list, the Mobile Node is at home. Otherwise, the Care-Of-Address is chosen from among advertising Agents in the same fashion as the Mobile Node would choose a first hop router. The highest preference Router Address which falls within a subnet that the Mobile Node has configured on its mobile interface(s) is used for the Care-Of-Address. | It is very likely that no Routing-Prefix matches when the Mobile Node | is not at home. In this case, the highest preference non-matching Router Address is used for the Care-Of-Address. Simpson expires in six months [Page 8] DRAFT IP Mobility July 1994 3. Registration The registration function exchanges information between Mobile Nodes and Home Agents. This function creates a Mobility Binding, linking the Home-Address with a Care-Of-Address to be used to reach the Mobile Node. When assigned a transient Care-Of-Address, a Mobile Node can act without a Foreign Agent, and register or de-register directly with a Home Agent. This registration process involves the exchange of only 2 messages: a) The Mobile Node sends a Registration Request to a Home Agent, to ask that Home Agent to provide the requested service. b) The Home Agent sends a Registration Reply to the Mobile Node to grant or deny service. An Administrative Domain MAY require registration through a Foreign Agent, as indicated in Agent Advertisements. When the Care-Of-Address is associated with a Foreign Agent, the Foreign Agent acts as a relay between the Mobile Node and Home Agent. This extended registration process involves the exchange of 4 messages: a) The Mobile Node sends a Registration Request to the prospective Foreign Agent to begin the registration process. b) The Foreign Agent relays the request by sending a Registration Request to the Home Agent, to ask that Home Agent to provide the requested service. c) The Home Agent sends a Registration Reply to the Foreign Agent to grant or deny service. d) The Foreign Agent sends a copy of the Registration Reply to the Mobile Node to inform it of the disposition of its request. 3.1. Authentication Each Mobile Node, Foreign Agent, and Home Agent MUST support an internal table holding a list of IP addresses, and the Mobility Security Association for each address. Mobile Node to Home Agent registration messages are required to be Simpson expires in six months [Page 9] DRAFT IP Mobility July 1994 authenticated with the Mobile-Home Authentication Extension. The Mobile Node and Home Agent MUST support authentication using keyed MD5 and key sizes of 128 bits or greater, with manual key distribution. Additional authentication algorithms, algorithm modes, and key distribution methods MAY also be supported. In addition, the Foreign Agent SHOULD support authentication using keyed MD5 and key sizes of 128 bits or greater, with manual key distribution. Additional authentication algorithms, algorithm modes, and key distribution methods MAY also be supported. Only one Mobility Security Association exists between any given pair of participating nodes at any given time. Whenever a Mobility Security Association exists between a pair of nodes, all registration messages between these nodes MUST be authenticated, using the appropriate authentication extension. 3.2. UDP The Registration messages defined herein use the User Datagram Protocol header [RFC-768]. The UDP checksum is required. Any mobility message with an incorrect or zero UDP checksum is silently discarded. Simpson expires in six months [Page 10] DRAFT IP Mobility July 1994 3.3. Registration Request The UDP Header is followed by the fields shown below: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | LifeTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home Agent | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home-Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Care-Of-Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Prefix-Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + TimeStamp + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions ... +-+-+-+-+-+-+-+- IP fields: Source An IP address belonging to the interface on which this message is sent. | A Mobile Node MUST use the transient Care-Of- | Address when assigned; otherwise, the Home- | Address is used. Destination The IP address of the Agent, when known. When the IP address is unknown (the agent was discovered via a link-layer protocol), the "all Mobile Agents" multicast address. The link-layer unicast address is used to deliver the datagram to the correct Agent. UDP fields: Source Port variable Destination Port MobileIP fields: Simpson expires in six months [Page 11] DRAFT IP Mobility July 1994 Type 1 when sent by the Mobile Node 2 when sent by the Foreign Agent Code Optional capabilities: 0 - remove prior registrations 1 - retain prior registrations LifeTime The seconds remaining before the registration is considered expired. A value of zero indicates a request for de-registration. A value of all ones indicates infinity. Home Agent The IP address of a Home Agent. Home-Address The IP address of the Mobile Node. | Care-Of-Address The IP address for the decapsulation end of a tunnel. Reserved Sent as zero; ignored on reception. Prefix-Size The size of the left-justified bit-mask that is applied to the Home-Address to determine the IP Routing-Prefix. Ranges from 0 to 30. Set to zero by Mobile Nodes which are not routers. TimeStamp 64 bits. A sequence number assigned by the Mobile Node. A Network Time Protocol [RFC-1305] value is preferred, but the elapsed time since system startup, or any other monotonically increasing counter MAY be used. The value MUST NOT be the same as an immediately preceeding request. The Mobile-Home Authentication Extension is required, and immediately follows all non-authentication extensions. The Mobile-Foreign or Foreign-Home Authentication Extension is optional, and immediately follows the Mobile-Home Authentication Extension. When forwarded by a Foreign Agent, fields and extensions which are specific to the Foreign Agent are removed. All others are copied Simpson expires in six months [Page 12] DRAFT IP Mobility July 1994 without modification. Simpson expires in six months [Page 13] DRAFT IP Mobility July 1994 3.4. Registration Reply The UDP Header is followed by the fields shown below: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | LifeTime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home-Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Prefix-Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + TimeStamp + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extensions ... +-+-+-+-+-+-+-+- IP fields: The Source and Destination of the Request message are swapped for the Reply message. Note that the Source of the original Registration Request must be saved in order for the Foreign Agent to return the reply to the correct Mobile Node. UDP fields: The Source Port and Destination Port of the Request message are swapped for the Reply message. Note that the Source Port of the original Registration Request must be saved in order for the Foreign Agent to return the reply to the correct Mobile Node port. MobileIP fields: Type 3 Code One of the following codes: 0 service will be provided. denied by Foreign Agent, 16 reason unspecified. Simpson expires in six months [Page 14] DRAFT IP Mobility July 1994 17 administratively prohibited. 18 insufficient resources. 19 Mobile Node failed authentication. 20 Home Agent failed authentication. 21 Request LifeTime too long. denied by Home Agent, 32 reason unspecified. 33 administratively prohibited. 34 insufficient resources. 35 Mobile Node failed authentication. 36 Foreign Agent failed authentication. Up-to-date values of the Code field are specified | in the most recent "Assigned Numbers" [RFC-1310]. LifeTime The seconds remaining before the registration is considered expired. A value of zero confirms a request for de-registration. A value of all ones indicates infinity. Home-Address Copied from the Request message. Reserved Copied from the Request message. Prefix-Size Copied from the Request message. TimeStamp Copied from the Request message. The Mobile-Home Authentication Extension is required, and immediately follows all non-authentication extensions. The Mobile-Foreign or Foreign-Home Authentication Extension is optional, and immediately follows the Mobile-Home Authentication Extension. Note that the Care-Of-Address and Home Agent are not present in the message. This provides a separate calculation value for mutual authentication. When forwarded by a Foreign Agent, fields and extensions which are specific to the Foreign Agent are removed. All others are copied without modification. Simpson expires in six months [Page 15] DRAFT IP Mobility July 1994 4. Mobility Message Extensions To promote extensibility, each message begins with a short fixed part, which is followed by one or more extensions in Type-Length- Value format. Extensions allow variable amounts of information to be carried within each datagram. The end of the list of Extensions is indicated by the Total Length of the IP datagram. These extensions apply to messages in both preceding chapters. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- | Extension | Length | Data ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- Extension Current values are assigned as follows: 16 Mobility 32 Mobile-Home Authentication 33 Mobile-Foreign Authentication 34 Foreign-Home Authentication 64 Minimal Encapsulation 65 GRE Encapsulation Up-to-date values are specified in the most recent | "Assigned Numbers" [RFC-1310]. Length Indicates the length of the Data field. The Length does not include the Extension and Length bytes. Data This field is zero or more bytes and contains the value(s) for this Extension. The format and length of the Data field is determined by the Extension and Length fields. When an extension is encountered which is not recognized, it is ignored. The length field is used to skip the data field in searching for the next extension. Simpson expires in six months [Page 16] DRAFT IP Mobility July 1994 4.1. Mobility Extension 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extension | Length | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |F| Reserved | +-+-+-+-+-+-+-+-+ Extension 16 Length 3 Sequence Number Contains the number of advertisement messages sent since the node was initialized. This number MUST count this advertisement; that is, it begins with one (1) and wraps to zero (0). When this value decreases, the Mobile Node MUST assume that any current registration has been lost. This field cannot roll over in less than 2**16 seconds, and rollover is unambiguously indicated by the value zero (0). F Foreign Agent bit. When this bit is set to 1, registration through the Foreign Agent is required, even when the Mobile Node has acquired a transient Care-Of-Address. Reserved Sent as zero; ignored on reception. The Mobility Extension is found in Agent Advertisements. 4.2. Mobile-Home Authentication Extension 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extension | Length | Authenticator ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Simpson expires in six months [Page 17] DRAFT IP Mobility July 1994 Extension 32 Length The number of data bytes in the Extension (16 when MD5 is used). Authenticator Variable length (128 bits for MD5). A hash value taken over a stream of bytes consisting of the shared secret, followed by (concatenated with) the fields in the message beginning with the Code field, including all prior extensions, and the Type and Length of this extension, but not including the Authenticator field itself, and finally the shared secret again. This Authentication Extension is found in all Registration Requests and Replies. The value differs depending on the direction the message is sent, since the Registration Request and Reply have different fields. 4.3. Mobile-Foreign Authentication Extension 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extension | Length | Authenticator ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Extension 33 Length The number of data bytes in the Extension (16 when MD5 is used). Authenticator Variable length (128 bits for MD5). A hash value taken over a stream of bytes consisting of the shared secret, followed by (concatenated Simpson expires in six months [Page 18] DRAFT IP Mobility July 1994 with) the Source, the Destination, the remaining fields in the message beginning with the UDP header, including all prior extensions, and the Type and Length of this extension, but not including the Authenticator field itself, and finally the shared secret again. This Authentication Extension is found in Registration Requests and Replies where a Mobility Security Association exists between the Mobile Node and a Foreign Agent. The value differs depending on the direction the message is sent, since the Registration Request and Reply have different fields. 4.4. Foreign-Home Authentication Extension 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extension | Length | Nonce | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Authenticator ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Extension 34 Length The number of data bytes in the Extension (18 when MD5 is used). Nonce A number to distinguish the authentication. With respect to a TimeStamp of a given Mobile Node and Home Agent pair, the number SHOULD be unique. The number MAY be unpredictable (random). Authenticator Variable length (128 bits for MD5). A hash value taken over a stream of bytes consisting of the shared secret, followed by (concatenated with) the Source, the Destination, the remaining fields in the message beginning with the UDP header, including all prior extensions, and the Type and Simpson expires in six months [Page 19] DRAFT IP Mobility July 1994 Length of this extension, but not including the Authenticator field itself, and finally the shared secret again. This Authentication Extension is found in Registration Requests and Replies where a Mobility Security Association exists between the Foreign Agent and the Home Agent. The value differs depending on the direction the message is sent, since the Registration Request and Reply have different fields. 4.5. Minimal Encapsulation Extension 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Extension | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Extension 64 Length 0 The Minimal Encapsulation Extension is found in Agent Advertisements and Registration Requests. Simpson expires in six months [Page 20] DRAFT IP Mobility July 1994 5. Forwarding Datagrams to the Mobile Node 5.1. IP in IP Encapsulation Support for IP in IP encapsulated datagrams is required. An outer, full-sized IP fragmentation header is inserted before the datagram's IP header: +---------------------------+ | Outer IP Header | +---------------------------+ +---------------------------+ | IP Header | | IP Header | +---------------------------+ ====> +---------------------------+ | | | | | IP Payload | | IP Payload | | | | | +---------------------------+ +---------------------------+ The format of the IP header is as described in [RFC-791]. The outer IP header Source and Destination addresses identify the "endpoints" of the tunnel. The inner IP header Source and Destination addresses identify the sender and recipient of the datagram. The Protocol field in the outer IP header is set to protocol number for the encapsulation protocol. The Destination field in the outer IP header set to the Care-Of- Address of the Mobile Node. The Source field in the outer IP header is set to the IP address of the encapsulating agent. When the datagram is encapsulated, the Time To Live (TTL) field in the outer IP header is set to be the same as the original datagram. When decapsulating, the outer IP TTL minus one is inserted into the inner IP TTL. Thus, IP hops are counted, but the actual routers interior to the tunnel are not identified. Simpson expires in six months [Page 21] DRAFT IP Mobility July 1994 5.2. Minimal Encapsulation A minimal forwarding header is defined for datagrams which are not fragmented prior to encapsulating. When a datagram is already fragmented prior to encapsulating, IP in IP is used. Use of this encapsulating method is optional. The minimal header is inserted between the datagram's IP header and the rest of the datagram: +---------------------------+ +---------------------------+ | IP Header | | Modified IP Header | +---------------------------+ ====> +---------------------------+ | | | Forwarding Header | | IP Payload | +---------------------------+ | | | | +---------------------------+ | IP Payload | | | +---------------------------+ A Foreign Agent which is capable of decapsulating the minimal header will include the Minimal Encapsulation Extension in its Router Advertisements. A Mobile Node indicates the capability of decapsulating the minimal header at the Care-Of-Address by the inclusion of the Minimal Encapsulation Extension in its Registration Request. The Minimal Encapsulation Extension is not included in the Registration Reply. The use of the minimal header is entirely at the discretion of the Home Agent. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Protocol |S| Reserved | Header Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Home-Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Correspondent Source Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Protocol Copied from the Protocol field in the original IP header. Simpson expires in six months [Page 22] DRAFT IP Mobility July 1994 S Source field present bit, which indicates that the Correspondent Source Address field is present. 0 not present. 1 present. Reserved Sent as zero; ignored on reception. Header Checksum The 16-bit one's complement of the one's complement sum of the encapsulation header. For computing the checksum, the Checksum field is set to 0. Home-Address Copied from the Destination field in the original IP header. Correspondent Source Address Copied from the Source field in the original IP header. Present only if the S-bit is set. The Protocol field in the IP header is replaced by protocol number for the encapsulation protocol. The Destination field in the IP header is replaced by the Care-Of- Address of the Mobile Node. If the encapsulating agent is not the original source of the datagram, the Source field in the IP header is replaced by the IP address of the encapsulating agent. Finally, the Don't Fragment bit is set in the IP header. When decapsulating a datagram, the fields in the forwarding header are restored to the IP header, and the forwarding header is removed from the datagram. 5.3. Tunnel Management It is possible that one of the routers along the tunnel interior might encounter an error while processing the datagram, causing it to return an IP ICMP error message to the source end of the tunnel. The three types of ICMP errors that can occur in this circumstance are: - Datagram too big. - Time Exceeded. - Destination Unreachable. Simpson expires in six months [Page 23] DRAFT IP Mobility July 1994 Unfortunately, ICMP only requires IP routers to return 8 bytes (64 bits) of the datagram beyond the IP header. This is not enough to include the encapsulated header, so it is not generally possible for the Home Agent to immediately reflect the ICMP message from the interior of a tunnel back to the source host. However, by carefully maintaining "soft state" about its tunnels, the encapsulating router can return accurate ICMP messages in most cases. The router SHOULD maintain at least the following soft state information about each tunnel: - MTU of the tunnel. - TTL (path length) of the tunnel - Reachability of the end of the tunnel. The router uses the ICMP messages it receives from the interior of a tunnel to update the soft state information for that tunnel. When subsequent datagrams arrive that would transit the tunnel, the router checks the soft state for the tunnel. If the datagram would violate the state of the tunnel (such as, the TTL is less than the tunnel TTL) the router sends an ICMP error message back to the source, but also forwards the datagram into the tunnel. Using this technique, the ICMP error messages sent by encapsulating routers will not always match up one-to-one with errors encountered within the tunnel, but they will accurately reflect the state of the network. The Don't Fragment bit is always set within the tunnel. This enables the proper MTU of the tunnel to be determined. Fragmentation which occurs because of the size of the encapsulation header is done before encapsulation, preventing more than one layer of fragmentation in a single datagram. Simpson expires in six months [Page 24] DRAFT IP Mobility July 1994 6. Mobile Node Considerations A Mobile Node listens for Agent Advertisements at all times that it has a link connection. In this manner, it can learn that its Foreign Agent has changed, or that it has arrived home. The determination that the point of attachment is at home or away from home is entirely at the discretion of the Mobile Node, based on the information obtained from Agent Advertisements. Whenever a Mobile Node detects a change in its point of attachment, it MUST initiate the registration process. If it is away from home, it MUST either register through a Foreign Agent where required, or directly with a Home Agent. If it is returning home, it MUST de- register with its Home Agent. A Mobile Node will operate without the support of mobility functions when it is at home. 6.1. Configuration and Registration Tables Each Mobile Node will need: - Home-Address - Prefix-Size - one or more Home Agents For each pending registration: - Media Address of Agent - Care-Of-Address - TimeStamp used - LifeTime For each Mobility Security Association: - Authentication Type - Authentication Key 6.2. Registration When Away From Home If a Mobile Node detects a reduction in the Sequence Number of an Agent Advertisement from a Foreign Agent through which it has registered, the Mobile Node SHOULD re-register. Such a reduction does not include the wrap of the Sequence Number to zero. Simpson expires in six months [Page 25] DRAFT IP Mobility July 1994 The LifeTime of the registration SHOULD NOT be set to greater than the LifeTime learned in an Agent Advertisement. When the method by which the Care-Of-Address is learned does not include a LifeTime, the default Router Advertisement LifeTime (1800 seconds) is used. The LifeTime MAY be modified by the Home Agent in its reply. A Mobile Node SHOULD re-register before the LifeTime of its registration expires. The Mobile Node MAY re-register at any time. A Mobile Node MAY ask a Home Agent to terminate forwarding service to a particular Care-Of-Address, by sending a registration with a LifeTime of zero. 6.3. Registration without a Foreign Agent In cases where a Mobile Node away from home is able to dynamically acquire a transient IP address, the Mobile Node can serve without a Foreign Agent, using the transient address as the Care-Of-Address. In these cases, all communication between the Mobile Node and its Home Agent is direct. This eliminates the need to deploy separate entities as Foreign Agents. The LifeTime of such a registration is chosen by the Mobile Node. By default, the Router Advertisement LifeTime (1800 seconds) is used. The LifeTime MAY be modified by the Home Agent in its reply. However, on those links where the Mobile Node detects an Agent Advertisement that has the "F" bit set in the Mobility Extension, the Mobile Node SHOULD register through an appropriate Foreign Agent, even when it could otherwise register directly with a Home Agent. It is assumed that such a Mobile Node has mechanisms to detect changes in its link-layer connectivity, and to initiate acquisition of a new transient address each time such a change occurs. The mechanisms will be specific to the particular link-layer technology, and are outside the scope of this document. 6.4. De-registration When At Home At times, a Mobile Node might attach itself to its home link. Since a Mobile Node that is at home needs no forwarding, a de-registration Simpson expires in six months [Page 26] DRAFT IP Mobility July 1994 procedure MUST be used between the Mobile Node and its Home Agent. The de-registration process involves the exchange of only two messages: a) The Mobile Node sends a Registration Request directly to its Home Agent, with the LifeTime set to zero, and the Code field set to 0, to indicate that the Home Agent remove all related entries. b) The Home Agent sends a Registration Reply to the Mobile Node to grant or deny service. In this special case, the Care-Of-Address is set to the Home-Address. This procedure is specified for the sake of convenience. The Mobile Node is not required to register with its Home Agent. It MAY de- register each Foreign Agent, or it MAY allow its Mobility Bindings to simply expire. It is not necessary to re-register with a Home Agent when a change of Sequence Number occurs, or the Advertisement LifeTime expires, since the Mobile Node is not seeking encapsulating service. 6.5. Registration Replies When a Mobile Node receives a Registration Reply which has a TimeStamp which is not the same as the TimeStamp of its most recent Registration Request to the putative sender, the message is silently discarded. When a Reply is received which has a Code indicating information from the Foreign Agent, the Mobile-Home Authenticator will be missing or invalid. However, if no other reply has as yet been received, the reason for denial SHOULD be accepted, and result in an appropriate action. If a later authenticated reply is received, that reply supercedes the unauthenticated reply. When a Reply is received which has a Code indicating that authentication failed with the Home Agent, the reason for denial SHOULD result in an appropriate action. Otherwise, when a Reply is received with an invalid Authenticator, the message is silently discarded. When the LifeTime of the reply is greater than the original request, Simpson expires in six months [Page 27] DRAFT IP Mobility July 1994 the excess time SHOULD be ignored. When the LifeTime of the reply is smaller than the original request, re-registration SHOULD occur before the LifeTime expires. The Mobile Node is not required to issue any message in reply to a Registration Reply. 6.6. Registration Retransmission When no Reply has been received within a reasonable time, the Registration Request is re-transmitted. A new TimeStamp is chosen for each retransmission. The minimum retransmission time SHOULD be related to the speed of the link. The minimum value SHOULD be large enough to account for the size of the packets, twice the round trip time for transmission at the link speed, and at least an additional 100 milliseconds to allow for processing the packets before responding. Some circuits add another 200 milliseconds of satellite delay. The initial time MUST NOT be less than 1 second. At 9,600 bps or less, the recommended initial time is 3 seconds. At 1,200 bps or less, the recommended initial time is 5 seconds. Each successive value less than the maximum value SHOULD be at least twice the previous value. The maximum retransmission time SHOULD be no greater than the LifeTime of the Registration Request. 6.7. Simultaneous Registrations Under normal circumstances, sending a new Registration Request removes other unexpired registrations for a Mobile Node from the Home Agent. An optional capability is to allow multiple simultaneous registrations. For example, this is particularly useful when a Mobile Node is on a border between multiple cellular systems. In order to request simultaneous registrations, the Mobile Node sends the Registration Request with the Code set to 1. The return Code in the Registration Reply is the same. No error Simpson expires in six months [Page 28] DRAFT IP Mobility July 1994 occurs if the Home Agent is unable to fulfill the request. IP explicitly allows duplication of datagrams. When the Home Agent is able to fulfill the request, the Home Agent will encapsulate a separate copy of each arriving datagram to each Care-Of-Address, and the Mobile Node will receive multiple copies of its datagrams. When the need for multiple registrations has passed, the Mobile Node SHOULD re-register with the Code set to 0, to remove the other registrations. 6.8. Mobile Routers A Mobile Node can be a router, which is responsible for the mobility of an entire network moving together, such as on an airplane, a ship, a train, an automobile, a bicycle, or a kayak. Provision for a Routing-Prefix in registration messages is needed when a Mobile Node registers through a Foreign Agent. This allows a Foreign Agent to recognize all addresses attached to the Mobile Node when they are decapsulated at the Care-Of-Address. When a transient IP address has been assigned, the Mobile Node can register directly with the Home Agent, as described previously. Such a Mobile Node MAY advertise to other routers in the foreign routing domain. The Mobile Node MAY register multiple times with different Home- Addresses and Routing-Prefixes. This permits multiple prefixes to be routed through the Mobile Node. When the Mobile Node returns home, and de-registers with the Home Agent, it participates directly in routing with other routers in its home routing domain. 7. Foreign Agent Considerations It is the intent that Foreign Agent involvement be as minimal as possible. The role of the Foreign Agent is passive, passing registration requests to the Home Agent, and decapsulating datagrams to pass to the Mobile Node. When no Mobility Security Association exists, this also reduces the risks resulting from absence of authentication from Foreign Agent Simpson expires in six months [Page 29] DRAFT IP Mobility July 1994 messages. The Foreign Agent MUST NOT originate a Request or Reply that has not been prompted by the Mobile Node. No Request or Reply is generated to indicate that the service LifeTime has expired. A Foreign Agent MUST NOT originate a message which revokes the registration of a different Foreign Agent. A Foreign Agent SHOULD forward such revocations without modification when such revocation messages originated from an appropriate Mobile Node or Home Agent. The Foreign Agent SHOULD NOT advertise the presence of the Mobile Node which is a router to other routers in its routing domain. 7.1. Configuration and Registration Tables Each Foreign Agent will need: - Care-Of-Address For each pending or current registration, the Foreign Agent will need a Visitor List entry: - Media Address of Mobile - Home-Address - Prefix-Size - Home Agent - TimeStamp used - LifeTime A Foreign Agent that has implemented and is using authentication will also need to have the Mobility Security Association information for each pending or current authenticated registration. Even if a Foreign Agent implements authentication, it might not use authentication with each registration, because of the key management difficulties. 7.2. Receiving Registration Requests Upon receipt of a Registration Request, if the Foreign Agent is unable to satisfy the request for some reason, then the Foreign Agent sends a Registration Reply to the Mobile Node with an appropriate Code, and does not forward the request to the Home Agent. Simpson expires in six months [Page 30] DRAFT IP Mobility July 1994 Otherwise, the Foreign Agent will forward the Request to the Home Agent, modifying the Type, substituting the Foreign-Home Authenticator for the Mobile-Foreign Authenticator as necessary, and leaving the remaining fields unchanged. The Foreign Agent must maintain a list of pending Requests, which includes the IP Source Address and UDP Source Port, in order that a correctly addressed Reply can be returned to the Mobile Node. 7.3. Receiving Registration Replies The fields of the Registration Reply MUST be examined for validity. A Registration Reply which does not relate to a pending Registration Request, or to a currently registered Mobile Node, is silently discarded. If the Registration Reply granted permission to provide service to the Mobile Node, then the Foreign Agent updates its Visitor List accordingly. 7.4. Decapsulation Every Foreign Agent MUST examine all arriving encapsulated traffic for both the Home-Address and Routing-Prefix in order to forward to the correct Mobile Node. | When the Destination does not match any node currently in the Visitor | List, the datagram MUST be silently discarded (rather than being | further forwarded). ICMP Destination Unreachable MUST NOT be sent | when a Foreign Agent is unable to forward a datagram. 7.5. Mobility The Foreign Agent can be mobile, if the link identified by the Care- Of-Address is mobile. The Foreign Agent could be either a node on a mobile network, or another Mobile Node itself. 8. Home Agent Considerations It is the intent that the Home Agent have primary responsibility for Simpson expires in six months [Page 31] DRAFT IP Mobility July 1994 processing and coordinating mobility services. The Home Agent for a given Mobile Node SHOULD be located on the link identified by the Home-Address. This link MAY be virtual. The Home Agent SHOULD advertise the presence of the Mobile Node which is a router to other routers in its routing domain. 8.1. Configuration and Registration Tables Each Home Agent will need: - an IP Address - Prefix-Size for the Home Network, if any For each authorized Mobile Node, the Home Agent will need: - Home-Address - Prefix-Size for the Mobile Network, if any For each registered Mobile Node, the Home Agent will need a Forwarding List entry: - Care-Of-Address - TimeStamp used - LifeTime For each Mobility Security Association: - Authentication Type - Authentication Key 8.2. Receiving Registration Requests Upon receipt of a Registration Request, the Home Agent grants or denies the service requested by sending a Registration Reply to the sender of the request, with the appropriate Code set. The Request is validated by checking that the TimeStamp is not the same as a preceeding Request, and the Mobile-Home Authentation Extension is correct. Other Authentication Extensions are also validated when present. The Home Agent MAY shorten the LifeTime of the request. Simpson expires in six months [Page 32] DRAFT IP Mobility July 1994 If service permission is granted, the Home Agent will update its Forwarding List with the Care-Of-Address of the tunnel. If the Request asks for termination of service by indicating a LifeTime of zero, and the Code field set to 1, the Home Agent removes the Mobility Binding for that Care-Of-Address from its Forwarding List. If the Request asks for termination of service by indicating a LifeTime of zero, and the Code field set to 0, the Home Agent removes the Mobility Bindings for all Foreign Agents associated with that Mobile Node from its Forwarding List. On termination, no special Reply is sent to additional associated Foreign Agents. The entries in their Visiting Lists are allowed to expire naturally. 8.3. Receiving Requests through a Foreign Agent When a Registration Request is invalid, a Reply is sent to the Foreign Agent, in order that the Foreign Agent can clear its pending request list. 8.4. Simultaneous Registrations When a Home Agent supports the optional capability of multiple simultaneous registrations, any datagrams forwarded are simply duplicated, and a copy is sent to each Care-Of-Address. The return Code in the Registration Reply is the same. No error occurs if the Home Agent is unable to fulfill the request, and earlier entries in the Forwarding List are removed. 8.5. Registration Expiration If the LifeTime for a given Mobile Node expires before the Home Agent has received a re-registration request, then the associated Mobility Binding is erased from the Forwarding List. No special Registration Reply is sent to the Foreign Agents. The entries in the Visiting Lists will expire naturally, and probably at the same time. Simpson expires in six months [Page 33] DRAFT IP Mobility July 1994 8.6. Encapsulation Every Home Agent MUST examine all arriving traffic for both the Home-Address and Routing-Prefix in order to forward to the correct Mobile Node. When previously encapsulated datagrams arrive which are associated with the Routing-Prefix of the Mobile Node, the Home Agent simply alters the Destination to the Care-Of-Address. This avoids recursive encapsulation. Previously encapsulated datagrams which are not associated with the Routing-Prefix are recursively encapsulated. 8.7. Mobility The Home Agent can be mobile, if the link identified by the Home- Address it serves is mobile. The Home Agent could be either a node on a mobile network, or another Mobile Node itself. A datagram would be encapsulated on its way to the mobile network, decapsulated for delivery to the Mobile Node, intercepted by the Home Agent, and re-encapsulated to the Mobile Node. Simpson expires in six months [Page 34] DRAFT IP Mobility July 1994 A. Gratuitous and Proxy ARP | Many people will use their computers for extended periods of time on | a single link, whether or not it is at their Home Network. When | doing so, they will expect the same level of service from their | infrastructure as they receive today on the Home Network. | A separate "virtual" IP address block is not required for Mobile | Hosts. This would require a small network to have an extra router | between the mobile and non-mobile nodes, which is an unacceptable | expense. | This section details the special care to be taken when using ARP | [RFC-826] with nodes on the same link as a Mobile Node. | A problem can arise if a Mobile Node which has previously answered an | ARP Request moves away from the link, leaving behind a stale entry in | another node's ARP cache. For example, if a router which forwards | datagrams into the Home Network has a stale ARP cache entry for the | Mobile Node, any datagrams arriving through that router for the | Mobile Node will be lost. Thus, it is important that ARP caches of | nodes populating the link be updated as soon as possible. | A gratuitous ARP is an ARP Reply that is broadcast to all nodes on a | link, which is not in response to any ARP Request. When an ARP Reply | is broadcast, all hosts are required to update their local ARP | caches, whether or not the ARP Reply was in response to an ARP | Request they had issued. | Therefore, a gratuitous proxy ARP is issued by the Home Agent on | behalf of a Mobile Node whenever the Home Agent receives a valid | registration. The gratuitous proxy ARP will indicate that all | remaining nodes should associate the Home-Address of the Mobile Node | with the link-layer address of the Home Agent which is now serving | the Mobile Node. | For this purpose, the source IP address would be the Home-Address, | the source link-layer address would be for the interface used, the | target IP address would be the all-systems multicast address, and the | target link-layer address would be the general broadcast. | Another proxy ARP will be sent in response to further Mobile Node | registration requests, or Correspondent ARP Requests. | While the Mobile Node is away from its Home Network, the Home Agent | performs proxy ARP Replies for the Mobile Node. | When a Mobile Node returns to its Home Network, it SHOULD issue a | Simpson expires in six months [Page 35] DRAFT IP Mobility July 1994 gratuitous ARP on its own behalf, immediately before sending the de- | registration request to the Home Agent. | Although the gratuitous ARP can be lost, this is not different from | the usual ARP Reply problems, which are outside the scope of this | document. An implementation MUST NOT repeat the gratuitous ARP | without a specific stimuli of the registration or de-registration | request. | B. TCP Timers * Most hosts and routers which implement TCP/IP do not permit easy configuration of the TCP Timer values. When high-delay (e.g. SATCOM) or low-bandwidth (e.g. High-Frequency Radio) links are in use, the default TCP Timer values in many systems will cause retransmissions or timeouts when the link and network is actually operating properly, though with greater than usual delays because of the media in use. This can cause an inability to create or maintain connections over such links, and can also cause unneeded retransmissions which consume already scarce bandwidth. Vendors are encouraged to make TCP Timers more configurable. Vendors of systems designed for the mobile computing markets should pick default timer values more suited to low-bandwidth, high-delay links. Users of Mobile Nodes should be sensitive to the possibility of timer-related difficulties. Simpson expires in six months [Page 36] DRAFT IP Mobility July 1994 Security Considerations The mobile computing environment is potentially very different from the ordinary computing environment. In many cases, mobile computers will be connected to the network via wireless links. Such links are particularly vulnerable to passive eavesdropping, active replay attacks, and other active attacks. The registration protocol described here will result in a host's traffic being source routed to its mobile location. Such traffic redirection could be a significant vulnerability when the registration were not authentic. Also, source routing is widely understood to be a security problem in the current Internet. [Bellovin89] The Address Resolution Protocol (ARP) is not authenticated, and can potentially be used to steal another host's traffic. The use of "Gratuitous ARP" as described in this specification increases the risks of ARP because ARP is not authenticatable. This specification includes a strong authentication mechanism (keyed MD5) which precludes many potential attacks based on the Mobile IP registration protocol. However, because key distribution is difficult in the absence of a network key management protocol, not all messages with the Foreign Agent are authenticated. Vulnerabilities remain in the registration protocol whenever a registration message is not authenticated. For example, in a commercial environment it might be important to authenticate all messages between the Foreign Agent and the Home Agent, so that billing is possible, and service providers don't provide service to users that are not legitimate customers of that service provider. The strength of any authentication mechanism is dependent on several factors, including the innate strength of the authentication algorithm, the secrecy of the key used, the strength of the key used, and the quality of the particular implementation. This specification requires implementation of keyed MD5 for authentication, but does not preclude the use of other authentication algorithms and modes. For keyed MD5 authentication to be useful, the 128-bit key must be both secret (that is, known only to authorised parties) and pseudo-random. RFC-XXXX provides more information on generating pseudo-random numbers. Users who have sensitive data that they do not wish others to see | should use mechanisms outside the scope of this document (such as encryption) to provide appropriate protection. Users concerned about traffic analysis should consider appropriate use of link encryption. Simpson expires in six months [Page 37] DRAFT IP Mobility July 1994 References [Voydock83] | Voydock, V.L., S.T. Kent, "Security Mechanisms in High-level | Networks", ACM Computing Surveys, Vol. 15, No. 2, June 1983. | [Bellovin89] | Bellovin, S.M., "Security Problems in the TCP/IP Protocol | Suite", ACM Computer Communications Review, Vol. 19, No. 2, | March 1989. | [RFC-768] | [RFC-791] | [RFC-826] | [RFC-1122] | [RFC-1256] | [RFC-1310] | [RFC-1305] | [RFC-1321] | [RFC-1332] | [RFC-1548] | [RFC-XXXX] | Eastlake, D.E.3, S.D. Crocker, J.I. Schiller, "Randomness | Requirements for Security", work in progress. Acknowledgements | Special thanks to John Ioannidis (Columbia), for his inspiration and experimentation which began this most recent round of IP mobility development. Special thanks also to Steve Deering (Xerox PARC), for his early support as Chair of the Working Group. Many thanks to Charlie Perkins (IBM), who tirelessly proposed common definitions and summaries, without which we may still have Simpson expires in six months [Page 38] DRAFT IP Mobility July 1994 uncomparable proposals with different terminologies. Charlie also coalesed the Home and Foreign Agent objects. Security details are primarily the work of Randall Atkinson (NRL). Tunnel soft state was originally developed for the "IP Address Encapsulation (IPAE)" specification, by Robert E. Gilligan, Erik Nordmark, and Bob Hinden (all of Sun Microsystems). Much of the text of this specification is derived from earlier drafts by Charlie Kunzinger (IBM), the former Working Group Editor, who never put his name on the document. Thanks to the verbose members of the Working Group, particularly those who contributed text, including Dave Johnson (Carnegie Mellon University), Tony Li (Cisco Systems), Andrew Myles (Macquarie University), John Penners (US West), Fumio Taraoka (Sony), and John Zao (Harvard). Finally, the Editor wishes to thank Phil Karn (Qualcomm), whose decade of IP mobility experimentation in the amateur radio community, and widespread freeware dissemination of his KA9Q software, provided the impetus and availability for many thousands throughout the world to join the Internet community. Simpson expires in six months [Page 39] DRAFT IP Mobility July 1994 Chair's Address The working group can be contacted via the current chairs: Greg Minshall Kannan | 617-873-4153 | minshall@wc.novell.com | Editor's Address Questions about this memo can also be directed to: William Allen Simpson Daydreamer Computer Systems Consulting Services 1384 Fontaine Madison Heights, Michigan 48071 Bill.Simpson@um.cc.umich.edu bsimpson@MorningStar.com Simpson expires in six months [Page 40] DRAFT IP Mobility July 1994 Table of Contents 1. Introduction .......................................... 1 1.1 Requirements .................................... 2 1.2 Goals ........................................... 3 1.3 Assumptions ..................................... 3 1.4 Specification Language .......................... 3 1.5 Terminology ..................................... 4 2. Agent Discovery ....................................... 6 2.1 Authentication .................................. 7 2.2 Agent Solicitation .............................. 7 2.3 Agent Advertisement ............................. 7 3. Registration .......................................... 9 3.1 Authentication .................................. 9 3.2 UDP ............................................. 10 3.3 Registration Request ............................ 11 3.4 Registration Reply .............................. 14 4. Mobility Message Extensions ........................... 16 4.1 Mobility Extension .............................. 17 4.2 Mobile-Home Authentication Extension ............ 17 4.3 Mobile-Foreign Authentication Extension ......... 18 4.4 Foreign-Home Authentication Extension ........... 19 4.5 Minimal Encapsulation Extension ................. 20 5. Forwarding Datagrams to the Mobile Node ............... 21 5.1 IP in IP Encapsulation .......................... 21 5.2 Minimal Encapsulation ........................... 22 5.3 Tunnel Management ............................... 23 6. Mobile Node Considerations ............................ 25 6.1 Configuration and Registration Tables ........... 25 6.2 Registration When Away From Home ................ 25 6.3 Registration without a Foreign Agent ............ 26 6.4 De-registration When At Home .................... 26 6.5 Registration Replies ............................ 27 6.6 Registration Retransmission ..................... 28 6.7 Simultaneous Registrations ...................... 28 6.8 Mobile Routers .................................. 29 7. Foreign Agent Considerations .......................... 29 7.1 Configuration and Registration Tables ........... 30 7.2 Receiving Registration Requests ................. 30 7.3 Receiving Registration Replies .................. 31 7.4 Decapsulation ................................... 31 Simpson expires in six months [Page ii] DRAFT IP Mobility July 1994 7.5 Mobility ........................................ 31 8. Home Agent Considerations ............................. 31 8.1 Configuration and Registration Tables ........... 32 8.2 Receiving Registration Requests ................. 32 8.3 Receiving Requests through a Foreign Agent ...... 33 8.4 Simultaneous Registrations ...................... 33 8.5 Registration Expiration ......................... 33 8.6 Encapsulation ................................... 34 8.7 Mobility ........................................ 34 APPENDICES ................................................... 35 A. Gratuitous and Proxy ARP ..............................35 | B. TCP Timers ............................................ 36 SECURITY CONSIDERATIONS ...................................... 37 REFERENCES ................................................... 38 ACKNOWLEDGEMENTS ............................................. 38 CHAIR'S ADDRESS .............................................. 40 EDITOR'S ADDRESS ............................................. 40