Network Working Group W A Simpson, Editor Internet Draft Daydreamer expires in six months May 1994 IP Mobility Support draft-ietf-mobileip-protocol-02.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 the Home Agent. The Home Agent tunnels traffic destined for the Mobile Node to the Care-Of-Address. Simpson expires in six months [Page i] DRAFT IP Mobility May 1994 1. Introduction Current versions of the Internet Protocol make an implicit assumption that a node's attachment point remains fixed. Datagrams are sent to a node based on the network and subnet number 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 An IP host or router that changes connections from one network or | subnetwork to another. Home Agent A router on a network that advertises reachability for a Mobile Node, maintains a registry of the current Mobility Bindings for that node while it is away from home, and tunnels datagrams for delivery to a Mobile Node. 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 Agents advertise their availability on each link. 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 dynamically assigned to the Mobile Node, or | associated with a Foreign Agent. Simpson expires in six months [Page 1] DRAFT IP Mobility May 1994 Registration When the Mobile Node is away from home, it registers the Care-Of- | Address with the 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. | Otherwise, 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. 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. A Mobile Node shall continue to be capable of communicating directly with existing nodes that 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 May 1994 1.2. Goals As few administrative messages as possible are sent between a Mobile Node and a Foreign Agent. The link is likely to be bandwidth limited. The size of messages on the Mobile Node's directly attached link are to be kept as short as possible. The link is likely to be bandwidth limited. 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 as frequently as 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 tunnel to its Home Agent. The definition of such tunneling mechanisms is outside the scope of this specification. 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. Simpson expires in six months [Page 3] DRAFT IP Mobility May 1994 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 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 Host The peer with which a Mobile Node is communicating. The Correspondent Host 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. The Home-Address is 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. Simpson expires in six months [Page 4] DRAFT IP Mobility May 1994 Routing Prefix The high-order bits in an address, which are used by 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 tunneled by the Home Agent. Simpson expires in six months [Page 5] DRAFT IP Mobility May 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 must learn if there are any prospective Foreign Agents available to serve it while it is away from home. If the Mobile Node is returning home, it must learn if its Home Agent is available. 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. | Simpson expires in six months [Page 6] DRAFT IP Mobility May 1994 When multiple methods are in use, the Mobile Node SHOULD first 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 link-layer identification has been received. Any Foreign Agent and Home Agent which is not identified by a link- layer protocol MUST implement 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 May 1994 Any Foreign Agent and Home Agent which is not identified by a link- layer protocol MUST implement 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 Mobility Extension is required, and indicates that the router is | an Agent. Other extensions, such as the Short Encapsulation | Extension 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. | The Mobile Node chooses a Care-Of-Address from among advertising | Agents in the same fashion as it would choose a first hop router. | The Care-Of-Address chosen is the most preferred Router Address | listed. Simpson expires in six months [Page 8] DRAFT IP Mobility May 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 the Care-Of-Address currently used by the Mobile Node. When assigned a transient Care-Of-Address, a Mobile Node can act without a Foreign Agent. When registering or deregistering directly with the Home Agent, the registration process involves the exchange of only 2 messages. a) The Mobile Node sends a Registration Request to the Home Agent, | to ask the 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 Foreign Agent, the Foreign Agent acts as a relay between the Mobile Node and Home Agent. The 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 the 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 May 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 well-known port is used. | 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 May 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 The Home-Address of the Mobile Node. 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: Type | 1 when sent by the Mobile Node 2 when sent by the Foreign Agent Simpson expires in six months [Page 11] DRAFT IP Mobility May 1994 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. The LifeTime SHOULD NOT be set to greater than the LifeTime learned in an Agent Advertisement. Home Agent The IP address of the Home Agent. | Home-Address The Home 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 subnet 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. Authenticator A hash value taken over a stream of bytes consisting of the shared secret between the Mobile Node and Home Agent, 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. The Mobile-Foreign or Foreign-Home Authentication Extension is | Simpson expires in six months [Page 12] DRAFT IP Mobility May 1994 optional, and immediately follows the Mobile-Home Authentication Extension. * When forwarded by a Foreign Agent, fields and extensions are copied | from the Registration Request without modification. Simpson expires in six months [Page 13] DRAFT IP Mobility May 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 May 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 [2]. 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. | May be modified by the Home Agent. 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. Authenticator A hash value taken over a stream of bytes consisting of the shared secret between the Mobile Node and Home Agent, followed by (concatenated with) all of 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. Note that the Care-Of-Address and Home Agent are not | present in the message. This provides a separate calculation value for mutual authentication from the Home Agent to the Mobile Node. Simpson expires in six months [Page 15] DRAFT IP Mobility May 1994 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 are copied | from the Registration Reply without modification. Simpson expires in six months [Page 16] DRAFT IP Mobility May 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. | 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 [2]. | 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 17] DRAFT IP Mobility May 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R| Reserved | +-+-+-+-+-+-+-+-+ Extension 16 | Length 3 | Sequence Number Contains the number of advertisement messages sent | since the node was initialized. This number MUST | include this advertisement. 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. | R Registration required bit. When this bit is set to | 1, registration with the Foreign Agent is required, | even when the Mobile Node has acquired a transient | Care-Of-Address. | Reserved Sent as zero; ignored on reception. | 4.2. Authentication Extensions | 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 | Simpson expires in six months [Page 18] DRAFT IP Mobility May 1994 32 Mobile-Home 33 Mobile-Foreign 34 Foreign-Home Length The number of data bytes in the Extension (16 when | MD5 is used). | Authenticator Variable length (128 bits for MD5). | For Mobile-Home authentication, the value differs | depending on the direction the message is sent. | These calculations are defined in the Registration | Request and Reply messages. | For Mobile-Foreign and Foreign-Home authentication, | 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 | Length of this extension, but not including the | Authenticator field itself, and finally the shared | secret again. | 4.3. 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 | Simpson expires in six months [Page 19] DRAFT IP Mobility May 1994 5. Forwarding Datagrams to the Mobile Node | 5.1. IP in IP Encapsulation | Support for IP in IP encapsulated tunneling is required. Use of | other tunneling methods is optional. | The full 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 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. | When the Home Agent encapsulates the datagram, it sets the IP Time To | Live (TTL) field 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 20] DRAFT IP Mobility May 1994 5.2. Minimal Encapsulation | A minimal forwarding header is defined for datagrams which are not | fragmented prior to tunneling. When a datagram is already fragmented | prior to tunneling, IP in IP is used. | 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. S Source field present bit, which indicates that the Correspondent Source Address field is present. Simpson expires in six months [Page 21] DRAFT IP Mobility May 1994 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. Tunneling 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. Unfortunately, ICMP only requires IP routers to return 8 bytes (64 | Simpson expires in six months [Page 22] DRAFT IP Mobility May 1994 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, a | Home Agent can return accurate ICMP messages in most cases. The Home | Agent 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 Home Agent 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 Home Agent 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 Home Agents | will not always match up one-to-one with errors encountered within | the tunnel, but they will accurately reflect the state of the | network. Simpson expires in six months [Page 23] DRAFT IP Mobility May 1994 6. Mobile Node Considerations | A Mobile Node listens for Beacons 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. Whenever a Mobile Node changes its point of attachment to the Internet, it must initiate the registration process. If it is away from home, it must register with a Foreign Agent. If it is returning home, it must deregister 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 change in the Incarnation Number of a Foreign Agent with which it is registered, it SHOULD re-register with that Agent. A Mobile Node SHOULD re-register with its Foreign Agent(s) before the LifeTime of its registration expires. The Mobile Node MAY re- register with its Foreign Agent(s) at any time. Simpson expires in six months [Page 24] DRAFT IP Mobility May 1994 A Mobile Node can ask the Home Agent to terminate forwarding service through 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. Thus, the registration function and the tunnel decapsulation function can be co-located in a single node. This eliminates the need to deploy separate entities as Foreign Agents. The direct registration process involves the exchange of only two messages: a) The Mobile Node sends a Registration Request to the Home Agent, | to ask the Home Agent to provide the requested service. b) The Home Agent sends a Registration Reply to the Mobile Node to grant or deny service. All communication between the Mobile Node and its Home Agent is direct, and there is no need to use the Agent Solicitation, Agent Advertisement, and Registration Request. | 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 will attach itself to its home link. Since a Mobile Node that is at home needs no forwarding, a de-registration procedure MAY 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 Simpson expires in six months [Page 25] DRAFT IP Mobility May 1994 entries. b) The Home Agent sends a Registration Reply to the Mobile Node to grant or deny service. In this special case, for Authenticator calculation, 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 with 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 Incarnation Number occurs, or the Advertisement LifeTime expires, since the Mobile Node is not seeking tunneling 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, 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. Simpson expires in six months [Page 26] DRAFT IP Mobility May 1994 6.6. 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 a Code set to 1. The return Code in the Registration Reply is the same. No error 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 copy of each arriving datagram to each Care-Of-Address, and the Mobile Node will receive multiple copies of its datagrams. 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 tunneled 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 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. * 7.1. Configuration and Registration Tables Each Foreign Agent will need: Simpson expires in six months [Page 27] DRAFT IP Mobility May 1994 - Care-Of-Address For each pending or current registration, the Foreign Agent will need a Visitor List: - Media Address of Mobile - Home-Address - Prefix-Size - Home Agent - 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, the Foreign Agent may: | - immediately deny service to the Mobile Node, by sending a Registration Reply with the appropriate Code set. - request permission from the Home Agent to provide service to the Mobile Node, by sending a Registration Request. | If the Foreign Agent is unable to satisfy the request for some | reason, such as the Mobile Node proposes a Lifetime longer than the | Foreign Agent has advertised, then the Foreign Agent sends a | Registration Reply with an appropriate Code, and does not forward the | request to the Home Agent. The Foreign Agent must maintain a list of pending Requests, which * includes the IP Source Address and UDP Source Port, in order that the Reply can be returned to the Mobile Node. * 7.3. Receiving Registration Replies A Registration Reply which does not relate to a pending Registration Request, or to a currently registered Mobile Node, is silently discarded. Simpson expires in six months [Page 28] DRAFT IP Mobility May 1994 If the Registration Reply granted permission to provide service to the Mobile Node, then the Foreign Agent updates its Visitor List accordingly. 8. Home Agent Considerations It is the intent that the Home Agent have primary responsibility for processing and coordinating 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. 8.1. Configuration and Registration Tables Each Home Agent will need: - an IP Address For each authorized Mobile Node, the Home Agent will need: - Home-Address * - Prefix-Size For each registered Mobile Node, the Home Agent will need a Forwarding List: - Home-Address - Prefix-Size - Care-Of-Address - LifeTime For each Mobility Security Association: | - Authentication Type - Authentication Key 8.2. Receiving Requests from the Foreign Agent | Upon receipt of a Registration Request from the Foreign Agent, 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. Simpson expires in six months [Page 29] DRAFT IP Mobility May 1994 When a Registration Request has an invalid Authenticator for the Mobile Node, a Reply is sent to the Foreign Agent, in order that the Foreign Agent can clear its pending request list. If permission is granted for the Foreign Agent to provide service to the Mobile Node, the Home Agent will update its Forwarding List with the Home-Address of the Mobile Node, and the Care-Of-Address of the tunnel. The Home Agent MAY shorten the LifeTime of the request. If the Request asks for termination of service by indicating a LifeTime of zero, the Home Agent removes the Mobility Binding for that Care-Of-Address from its Forwarding List. 8.3. Receiving Requests from the Mobile Node | Upon receipt of a Registration Request from the Mobile Node, 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. In this special case, for Authenticator calculation, the Care-Of- Address is a copy of the Home-Address. The Home Agent MAY shorten the LifeTime of the request. | 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. No special Reply is sent to associated Foreign Agents. The entries in their Visiting Lists are allowed to expire naturally. 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. Simpson expires in six months [Page 30] DRAFT IP Mobility May 1994 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 31] DRAFT IP Mobility May 1994 A. Mobile Networks 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 allows such a Mobile Router to register with a Foreign or Home Agent. Every Foreign Agent MUST be capable of passing all arriving encapsulated traffic for the routing-prefix to the correct Mobile Router. The Foreign Agent SHOULD NOT advertise the presence of the Mobile Router to other routers in its routing domain. When a transient IP address has been assigned, the Mobile Router can act as its own Foreign Agent, and register directly with the Home Agent, as described above. Such a Mobile Router MAY advertise to other routers in the foreign routing domain. The Mobile Router continues to participate in its home routing domain through the tunnel to the Home Agent. When the Mobile Router returns home, and de-registers with the Home Agent, it MAY participate in routing with other routers in its home routing domain. DISCUSSION: Dissatisfaction has been expressed that this restricts the roaming net to a single contiguous subnet. Language changes have been requested for "location privacy". B. 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. Special care has to be taken with handling ARP Requests from other nodes on the same link. 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 Simpson expires in six months [Page 32] DRAFT IP Mobility May 1994 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 [RFC-826]. Therefore, a reasonably good solution is that 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 that 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. The gratuitous ARP SHOULD NOT be repeated. Another proxy ARP will be sent in response to further Mobile Node registration requests, or Correspondent Host 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 gratuitous ARP on its own behalf, just before de-registering itself from the Home Agent. After a Mobile Node de-registers, the Home Agent SHOULD issue ICMP Redirects when it receives a datagram from a Correspondent Host that could be sent directly to the Mobile Node. DISCUSSION This has pretty much the same set of problems (compounded by broken proxy ARP implementations) as gratuitous ARP. I would suggest to remove this as well. 1. The block of addresses (routing prefix) given to a HA shall be used *exclusively* for mobile hosts. A non-mobile host should not be assigned an address out of this block. If a mobile host is assigned address out of this block, then it may adversely impact its operations with mobile hosts. Simpson expires in six months [Page 33] DRAFT IP Mobility May 1994 2. Communication from CH to MH goes always through the HA associated with the MH (regardless of whether CH and MH are on a common subnet or not), unless triangular route elimination is employed. 3. From (2) it follows that the only IP <-> Link Layer address mapping an MH has to perform is for the MH's first hop router (usually the FA). In the case of a separate FA, MH learns FA's address as part of the registration, so MH doesn't need to do any ARP. In the case of an MH acting as its own tunnel end-point the MH acquires the IP address of its first hop router by means outside of the document (e.g. via DHCP), and that is the only IP address that MH may require ARP. So, a MH should be constrained NOT to use ARP if the MH doesn't act as its own tunnel end-point, and to use ARP to resolve ONLY the address of its first hop router if the MH acts as its own tunnel end-point. Specifically, it is well know that in real life packets (including ARP packets) can be lost. Thus a node that has a stale ARP cache may not receive the gratuitous ARP, and thus wouldn't purge its ARP entry. Since the gratuitous ARP mechanism is inherently unreliable and has unpredictable behaviour (you don't know whether a host would or wouldn't be able to receive such an ARP), it would be unwise to build any dependencies on it. As such all the text on gratuitous ARP should be removed from the document. COUNTER: Having a separate address block for mobile hosts would require a person with a home network to have a router between the laptop (which is mobile) and the non-mobile servers. This is bad. In fact, you can't STOP someone from doing this. You CAN indicate what features need to be in the MH and HA to enter and leave gracefully. C. 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 | Simpson expires in six months [Page 34] DRAFT IP Mobility May 1994 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 35] DRAFT IP Mobility May 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 specification (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 36] DRAFT IP Mobility May 1994 References [1] "V.L. Voydock & S.T. Kent, "Security Mechanisms in High-level | Networks", ACM Computing Surveys, Vol. 15, No. 2, June 1983." Also, the [Bellovin89] reference is: | "Steven M. Bellovin, "Security Problems in the TCP/IP Protocol | Suite", ACM Computer Communications Review, Vol. 19, No. 2, | March 1989." | RFC-1256, RFC-1305, RFC-1321, and RFC-1548 here. Acknowledgments Special thanks to John Ioannidis (Columbia), for his inspiration and experimentation which began this most recent round of IP mobility development. Many thanks to Charlie Perkins (IBM), who tirelessly proposed common definitions and summaries, without which we may still have 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 37] DRAFT IP Mobility May 1994 Chair's Address The working group can be contacted via the current chairs: Stephen Deering Greg Minshall 3333 Coyote Hill Road Palo Alto, CA 94304 415-812-4839 617-873-4153 Deering@PARC.Xerox.com 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 38] DRAFT IP Mobility May 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 ...........................17| 4.1 Mobility Extension ..............................18| 4.2 Authentication Extensions .......................18| 4.3 Minimal Encapsulation Extension .................19| 5. Forwarding Datagrams to the Mobile Node ...............20| 5.1 IP in IP Encapsulation ..........................20| 5.2 Minimal Encapsulation ...........................21| 5.3 Tunneling Management ............................22| 6. Mobile Node Considerations ............................ 24 6.1 Configuration and Registration Tables ........... 24 6.2 Registration When Away From Home ................ 24 6.3 Registration without a Foreign Agent ............ 25 6.4 De-registration When At Home .................... 25 6.5 Registration Replies ............................ 26 6.6 Simultaneous Registrations ...................... 27 7. Foreign Agent Considerations .......................... 27 7.1 Configuration and Registration Tables ........... 27 7.2 Receiving Registration Requests .................28| 7.3 Receiving Registration Replies .................. 28 8. Home Agent Considerations ............................. 29 8.1 Configuration and Registration Tables ........... 29 8.2 Receiving Requests from the Foreign Agent .......29| 8.3 Receiving Requests from the Mobile Node .........30| Simpson expires in six months [Page ii] DRAFT IP Mobility May 1994 8.4 Simultaneous Registrations ...................... 30 8.5 Registration Expiration ......................... 31 APPENDICES ................................................... 32 A. Mobile Networks ....................................... 32 B. Gratuitous and Proxy ARP .............................. 32 C. TCP Timers ............................................ 34 SECURITY CONSIDERATIONS ...................................... 36 REFERENCES ................................................... 37 ACKNOWLEDGEMENTS ............................................. 37 CHAIR'S ADDRESS .............................................. 38 EDITOR'S ADDRESS ............................................. 38