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