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 <TBD> 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 <TBD>
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 |
<TBD> 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
<TBD> 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
