INTERNET DRAFT Michael Borella
Expires August 1999 David Grabelsky
3Com Corp.
Jeffrey Lo
Kunihiro Tuniguchi
NEC USA
Realm Specific IP: Protocol Specification
<draft-ietf-nat-rsip-protocol-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
This draft presents a protocol that enables an alternative to network
address translation (NAT). Realm-Specific IP (RSIP) defines an
architecture in which an RSIP server is a multi-homed host connecting
two routing realms. An RSIP client in the first routing realm may be
assigned a plurality of routing parameters from the second routing
realm. The RSIP client will be allowed to create packets using these
parameters, and tunnel them across the first routing realm. For
example, more than one host from a private address space using RSIP
may share one or more public address. Unlike NAT, RSIP does not
break the end-to-end integrity of protocols. We present a general,
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extensible negotiation protocol to be operated between RSIP clients
and servers which facilitates the assignment of parameters and
resources from the server to the client. This draft is a
generalization of the techniques introduced in the drafts <draft-
borella-aatn-dnat-01.txt> (DNAT) and <draft-ietf-nat-hnat-00.txt>
(Host-NAT).
1. Introduction
Network Address Translation (NAT) has gained popularity as a method
of separating public and private address spaces, and alleviating
network address shortages. A NAT translates the addresses of packets
leaving a first routing realm to an address from a second routing
realm, and performs the reverse function for packets entering the
first routing realm from the second routing realm. This translation
is performed transparently to the hosts in either space, and may
include modification of TCP/UDP port numbers as well as IP addresses.
While a NAT does not require hosts to be aware of the translation, it
will require an application layer gateway (ALG) for any protocol that
transmits IP addresses or port numbers in packet payloads (such as
FTP). Additionally, a NAT will not work with protocols that require
IP addresses and ports to remain unmodified between the source and
destination hosts or protocols that prevent such modifications to
occur (such as some IPSec modes).
An alternative to a transparent NAT is an architecture that allows
the clients within the first (e.g., private) routing realm to
directly use addresses and other routing parameters from the second
(e.g., public) routing realm. This form of Realm-Specific IP (RSIP)
requires that an RSIP-server (a router or gateway between the two
realms) assign at least one address from the second routing realm,
and perhaps some other resources, to each RSIP-client host in the
first routing realm that needs to establish end-to-end connectivity
to a host, entity or device in the second routing realm. Thus, the
second routing realm is not transparent to RSIP-client, but this
system allows packets to maintain their integrity from RSIP-client to
destination. In order to resolve addressing and routing ambiguities
in the first routing realm, all publicly routed packets are tunneled
between RSIP-client and the RSIP-server, or tunneled such that the
RSIP-server can perform a NAT function on the outer IP header only.
ALGs are not required in the RSIP-server.
A disadvantage to RSIP is that it requires that hosts be modified so
that they tunnel externally-bound packets and place some number of
layer three, layer four or other values from those assigned by the
RSIP-server in each packet bound for the second routing realm.
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This draft discusses a method for assigning parameters to an RSIP-
client from an RSIP-server. In particular, this method is a
generalization of the techniques introduced in the drafts <draft-
borella-aatn-dnat-01.txt> (DNAT) and <draft-ietf-nat-hnat-00.txt>
(Host-NAT).
1.1. Specification of Requirements
The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD
NOT", "SHALL", and "SHALL NOT", and "MAY" that appear in this
document are to be interpreted as described in [1].
2. Architecture
For simplicity, for the remainder of this document we will assume
that the RSIP-clients in the first routing realm (network) use
private (network 10) IP addresses, and that the second routing realm
(network) uses public IP addresses. The RSIP-server connects the
public and private realms and contains interfaces to both. Other NAT
terminology found in this document is defined in [2].
The diagram below describes an exemplary reference architecture for
RSIP. Some number of RSIP-clients are attached via a private network
to an RSIP-server, which also acts as a router or gateway between the
private and public networks. This router has been assigned some
number of public addresses that it may use or allocate for use on the
public network.
+-------------+
| RSIP-client |
| 1 +--+
| 10.0.0.2 | | +-------------+
+-------------+ | 10.0.0.1 | | 149.112.240.0/24
+-----------------+ RSIP-server +-------------------
+-------------+ | | |
| RSIP-client | | +-------------+
| 2 +--+ private public
| 10.0.0.3 | | network network
+-------------+ |
|
|
...
RSIP MAY be based on either the Basic NAT or the NAPT model. In the
Basic NAT model, a unique public IP address is assigned to each
private NAT client that is actively communicating with the public
network. Only one NAT client uses a given public address. In the
NAPT model, one public address is shared by one or more NAT clients.
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One or more NAT clients may use the same public address by limiting
the ports that they use to disjoint subsets of the port space. The
NAT server assigns these disjoint port sets to each host, along with
the public IP address. For the remainder of this document we will
assume the NAPT model.
For purposes of illustration, we will provide a brief example of the
transport operation of RSIP with respect to the above architecture.
We assume that RSIP-client 10.0.0.2 has been assigned public address
149.112.240.10 and port set 10000-10015 (the actual mechanism for
this assignment is discussed below). Packets transmitted from this
client to a WWW server at the external address of 128.153.4.3 will be
appear as follows on the private network:
Outer IP Inner IP TU Ports
+--------------+----------------+----------+
Src: | 10.0.0.2 | 149.112.240.10 | 10000 |
+--------------+----------------+----------+
Dst: | 10.0.0.1 | 128.153.4.3 | 80 |
+--------------+----------------+----------+
Note that 10000 was chosen arbitrarily from the port set by the
kernel port selection code of the RSIP-client. Upon reaching the
RSIP-server, the outer IP header is stripped off, and the remaining
packet is transmitted on the public network. Incoming packets to the
RSIP-client may be demultiplexed based on layer three, layer four, or
other parameters, and tunneled from the RSIP-server to the RSIP-
client.
Note that the architecture and protocols for RSIP may allow for
cascading of RSIP-servers. For example, RSIP-server A may assign
some number of public IP addresses and port sets to RSIP-server B,
which is entirely inside of the private network. RSIP-server B will
then assign some of these addresses and port sets to private hosts.
This architecture conforms to the model in which a corporation (in
charge of RSIP-server B) buys public network access from an ISP (in
charge of RSIP-server A). In this scenario, RSIP-server B and end
hosts within the corporation could be considered the RSIP-client of
RSIP-server A and RSIP-server B respectively.
2.1. RSIP Parameter Negotiation
An RSIP-client initiates a binding request with an RSIP-server by
transmitting a REGISTER message. This allows the RSIP-server to
become aware of the RSIP-client. The RSIP-server will assign a
unique identifier to the RSIP-client. Negotiation of tunnel type
may also occur.
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An RSIP client must then use the ASSIGN message to request one or
more IP addresses, port sets and/or other parameters from the
public realm. Upon these parameters will be assigned with a lease
time, after which their assignment must be renewed.
At this point, the RSIP-client may use the assigned parameters to
transmit packets to the public network.
If an RSIP-client no longer needs some parameters, that it has
been assigned, it may release them by transmitting a FREE message
to the RSIP-server, and specifying the parameters to release
within that message.
If an RSIP-client no longer needs to communicate with the public
network, it may use the DE_REGISTER message to notify the RSIP-
server of such. Use of the DE-REGISTER message effectively
releases all of the RSIP-client's parameters. It must register
and be assigned parameters once more before it transmits packets
to the public network again.
The ERROR message may be used at any time by the RSIP-server to
indicate that an RSIP-client's request was denied or malformed.
2.2. Operation
In the case of Basic-NAT-Like operation, the number of IP
addresses requested in an ASSIGN may be more than one, but an
RSIP-client MAY NOT be assigned port sets.
In the case of NAPT-like operation, an RSIP-client MUST request
one or more port sets in ASSIGN messages that contain an IP
address, but only one IP address may be requested per ASSIGN
message. If more than one IP address is desired, the request MUST
be issued as two independent ASSIGN requests, and each will be
given a different binding.
If the resources requested are temporarily unavailable, an RSIP-
server MAY either commit a subset of the resources requested or
return an ERROR message indicating that the requested resource was
temporarily unavailable. An RSIP-client is free to attempt
another ASSIGN request for the same resource after an interval of
time.
An RSIP-server MAY allow freeing to be done on a subset of an
assigned range, address range in the case of traditional NAT-like
operation and port range in the case of NAPT-like operation. Child
ranges as a result of a subset free MUST retain the same binding.
If an RSIP-server receives a FREE message that refers to
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parameters not assigned to the originating RSIP-client, an ERROR
message indicating that the parameter range was invalid MUST be
returned. If an RSIP server receives a FREE message referring to
an unknown binding, an ERROR message indicating that the binding
is unknown MUST be returned.
If an RSIP-client wishes to extend the duration of an existing
binding, an ASSIGN request with the same Bind ID and the desired
extension duration MAY be sent. The RSIP-server SHOULD either
grant the request, grant a smaller duration than that requested or
deny the request. If a smaller duration is granted, this duration
MUST be included in the response message to the ASSIGN request. In
the case when the request is denied, the appropriate error
response MUST be sent.
2.3. Subnet Query
In some cases it is not possible for an RSIP-client to know
whether a packet should be tunneled to the RSIP-server or
transmitted using the local (private) routing realm only. The RSIP
protocol provides a subnet query mechanism through which an RSIP-
client may query an RSIP-server to ask whether a particular subnet
falls within the private domain. An RSIP-client queries the
server using the QUERY message with the subnet included in the IP
address field of the message. The RSIP-server MAY confirm the
subnet queried or MAY return the whole range of subnets supported
so as to enable the RSIP-client to cache the entries. The RSIP-
server may be manually configured to know the topology of the
private domain.
2.4. Unreliable Transport
A sequence number field SHOULD be included in all messages if UDP,
or some other unreliable transport mechanism, is used. The
sequence number starts with zero in the client's REGISTER message
and end with a maximum value in the server's DE_REGISTER message.
This field SHOULD be incremented by one for every request issued.
Responses MUST include the same sequence number as that of the
request which it acknowledges.
If an RSIP-client does not receive a response from the RSIP-server
for a request, a new request with the same sequence number MAY be
issued after an interval of time. An RSIP-server receiving a
request with a sequence number smaller than what it previously
received SHOULD ignore the request. Pipelining of requests and
aggregation of responses are not allowed.
Sequence number wraparound is highly unlikely, however it must be
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considered in both the RSIP clients and servers.
2.5. Parameter Assignment Transport and Mechanisms
In order to assign parameters to the RSIP-client from the RSIP-
server, a transport protocol and an assignment mechanism must be
used. Design of the end-to-end NAT protocol aims to be transport
independent, so that existing transport protocols such as UDP or
TCP can be used.
The assignment mechanisms MAY be DHCP, COPS, DIAMETER or some
similar protocol. While these protocols would allow nearly-
arbitrary parameters to be assigned to the RSIP-clients, our
current goal is to determine the parameters that are necessary for
RSIP to operate in full generality, and define a basic protocol
with which these parameters can be negotiated and assigned. Once
the fundamental requirements of RSIP parameter assignment are
specified, it may either be integrated into an existing protocol
or left alone as its own protocol.
3. General Message and Parameter Formats
In this section we define the general message and parameter format.
Codes for each parameter and message types will be discussed the
following sections. Within an RSIP control packet, the parameters
MAY appear in any order, but it is recommended that required
parameters precede all optional parameters.
The general message format is shown below.
1 byte Variable Variable
+-----------+---------------+-------------------
| Type | Parameter 1 | Parameter 2 ...
+-----------+---------------+-------------------
The type field indicates how the parameters are to be interpreted
(e.g., request, response, error, etc.).
The general format of all parameters is shown below.
1 byte 2 bytes 'Length' bytes
+------+----------+----------------------
| Code | Length | Parameter value ...
+------+----------+----------------------
All parameters consist of a fixed portion and a variable portion.
The fixed portion is a 1 byte code value and a 2 byte length. The
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remaining portion of the parameter is the parameter value, the length
which is the number of bytes indicated by the length field.
4. Parameter Types and Formats
Number of IP Addresses
Code Length Number of Addresses
+------+--------+----------------------+
| 0 | 1 | (1 byte) |
+------+--------+----------------------+
Used in ASSIGN messages to request a particular number of public
addresses to be assigned.
Number of Ports
Code Length Number of Ports
+------+--------+-------------------+
| 1 | 1 | (1 byte) |
+------+--------+-------------------+
Used in ASSIGN messages to request a particular number of ports to
be assigned.
IP Address
Code Length IP Address
+------+-------------------------+-------------------------------+
| 2 | Multiple of 4 | (Multiple of 4 bytes) |
+------+-------------------------+-------------------------------+
This field represents the IPv4 address(es) negotiated. More than
one IP addresses MAY be included after the length field; thus, the
length field MUST be a multiple of 4.
IP Address Range
Code Length Low Address High Address
(May repeat)
+------+------------------------+-----------------------------+
| 3 | Multiple of 8 | (4 bytes) | (4 bytes) |
+------+------------------------+-----------------------------+
In cases where the number of IPv4 addresses negotiated is large
and contiguous, the IPv4 address range parameter is used to
represent the range. Multiple ranges MAY be represented within a
single IP Address Range parameter.
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Port Range
Code Length Low Port High Port
(May Repeat)
+------+-----------------------+-----------------------+
| 4 | Multiple of 4 | (2 bytes) | (2 bytes) |
+------+-----------------------+-----------------------+
The port range MUST be contiguous and is inclusive. Multiple
ranges MAY be represented within a port range parameter.
Lease Time
Code Length Lease Time
+------+--------+-------------------+
| 5 | 4 | (4 bytes) |
+------+--------+-------------------+
Number of seconds that an RSIP-client may retain the parameters
assigned by an RSIP-server.
Error
Code Length Error
+------+--------+-------------------+
| 6 | 2 | (2 bytes) |
+------+--------+-------------------+
These error codes allow an RSIP-server to inform an RSIP-client
why a particular request has failed.
0 Unknown Error - An error that cannot be identified has occurred
1 Bind ID Not Found - The request refers to an invalid Bind ID.
2 Client ID Not Found - The request refers to an invalid Client ID.
3 Invalid Message - The request does not contain an mandatory
parameter or cannot be parsed.
4 NAT Type Not Supported - The request refers to a NAT type not
supported by this NAT-server.
5 Not Authorized - The RSIP-client is not authorized to make the
request.
6 Resource Temporarily Unavailable - The request has asked for a
resource (e.g., addresses, ports) that the RSIP-server
is not currently able to grant.
7 Tunnel Type Not Supported - The request refers to a tunnel type
that the RSIP-server does not support.
8 Wrong Sequence Number - The request used a sequence number that
the RSIP-server did not expect.
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Client ID
Code Length Client ID
+------+--------+-------------------+
| 7 | 4 | (4 bytes) |
+------+--------+-------------------+
A unique number assigned by an RSIP-server when an RSIP-client
registers with the server. It is used to identify the RSIP-client.
Bind ID
Code Length Bind ID
+------+--------+-------------------+
| 8 | 4 | (4 bytes) |
+------+--------+-------------------+
The Bind ID is a unique number allocated for each new assignment.
It is returned as part of an ASSIGN response to a successful
ASSIGN request. Subsequent message exchanges pertaining a bind
MUST include its Bind ID. When a or range of parameters is
assigned to an RSIP-client, the parameter is said to be 'bound' to
that client. More than one bind with different Bind IDs may be
established between an RSIP-client and RSIP-server pair. A binding
will expire when its lease time runs out or when the RSIP-client
de-registers itself with the RSIP-server.
Sequence Number
Code Length Sequence Number
+------+--------+-------------------+
| 9 | 1 | (1 byte) |
+------+--------+-------------------+
If the transport protocol is connectionless. such as UDP, the
sequence number field MUST be included as a means to order the
messages and/or match requests and responses.
Tunnel Type
Code Length Tunnel Type
+------+--------+-------------+
| 10 | n | (n bytes) |
+------+--------+-------------+
The type of tunnel used between an RSIP-client and an RSIP-server.
Values are assigned as follows:
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0 Reserved
1 IP-IP
2 GRE
3 L2TP
4 IPSec
NOTE: More tunnel types should be defined, especially for the
different variations of IPSec.
NAT Type
Code Length NAT Type
+------+--------+-------------+
| 11 | n | (n bytes) |
+------+--------+-------------+
The type of NAT-like operation that the RSIP-server will perform.
The following values have been assigned:
1 Traditional NAT
2 NAPT
3 Twice NAT
Vendor Specific Parameter
Code Length Vendor ID Subcode Parameter
+------+----------+------------+-----------+-----------+
| 12 | n+4 | (2 bytes) | (2 bytes) | (n bytes) |
+------+----------+------------+-----------+-----------+
This parameter allows vendors to specify vendor specific
information. The Vendor ID field the vendor-specific ID assigned
by IANA. Subcodes are defined and used by each vendor.
5. Message Type
Apart from the message type field, which MUST appear at the beginning
of each message, other parameters MAY appear in any order. Note that
message sequencing MAY need to be introduced depending on the
transport. The following message types are defined in simple BNF.
Required parameters are enclosed in <> and MUST appear. Optional
parameters are enclosed in [] and MAY appear.
ERROR Response
An ERROR response is used to provide error responses to an RSIP-
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client message. The message type is 1.
<ERROR Response>::= <Message Type> <Error Parameter>
[<Sequence Number>][<Client ID>]
[<Bind ID>]
REGISTER
The REGISTER message is used by an RSIP-client to register with an
RSIP-server. An RSIP-client MUST register before it requests
parameters from the RSIP-server. The message type is 2. The RSIP-
client MAY list all of the tunnel types and NAT types supported.
The default tunnel type is IP-IP, and the default NAT type is
NAPT.
<REGISTER Request> ::= <Message Type>
[<Sequence Number>][<TunnelType>...]
[<NAT Type>...]
<REGISTER Response> ::= <Message Type> <Client ID>
[<Sequence Number>][<Tunnel Type>]
[<NAT Type>...]
DE_REGISTER
The DE_REGISTER message is used by an RSIP-client to de-register
with an RSIP-server. The message type is 3.
<DE_REGISTER Request> ::= <Message Type> <Client ID>
[<Sequence Number>]
<DE_REGISTER Response> ::= <Message Type> <Client ID>
[<Sequence Number>]
ASSIGN
The ASSIGN message is used by an RSIP-client to request parameter
assignments. The message type is 4. If a client is given a single
IP address, a port range MUST be specified if NAPT is the NAT
type. If a client is given a range of n IP addresses, this
parameter MUST be followed by exactly n port range parameters.
The Client ID field MUST be included, otherwise, an RSIP-server
MUST return an ERROR message with the "Client ID not found" error
parameter. The lease time parameter MAY be included in an
assignment request as an indication of a desired bind duration.
If a lease time is not requested by an RSIP-client, an RSIP-server
SHOULD assign a default lease time.
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<ASSIGN Request> ::= <Message Type> <Client ID>
[<Sequence Number>][<NAT Type>]
[<Number of Ports>] [<Number of IP Addr>]
[<Lease Time>]
<ASSIGN Response> ::= <Message Type> <Client ID> <BindID>
[<Sequence Number>][<Port Range>...]
[<IP Address>][<Lease Time>]
<ASSIGN Response> ::= <Message Type> <Client ID> <BindID>
[<Sequence Number>][<IP Address Range>]
[<Port Range 1>...<Port Range n>]
[<Lease Time>]
FREE
The FREE message is used by an RSIP-client to free parameter
assignments. The message type is 5. If no parameters are
specified in a FREE message, then all of the parameters associated
with the Bind ID MUST be freed.
<FREE Request> ::= <Message Type> <Client ID> <Bind ID>
[<Sequence Number>][<Port Range>...]
[<IP Address Range>...][<IP Address> ...]
<FREE Response> ::= <Message Type> <Client ID> <Bind ID>
[<Sequence Number>][<Port Range>]
[<IP Address Range>...][<IP Address>...]
QUERY
A QUERY message is used by an RSIP-client to request if a subnet
is supported by an RSIP-server. The message type is 6.
<QUERY Request> ::= <Message Type> <Client ID> <IP address>
[<Sequence Number>]
<QUERY Response> ::= <Message Type> <Client ID> <IP address>
[<Sequence Number>]
6. To Do
- Distinguish request and response messages
- Examples
7. Security Considerations
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RSIP, in and of itself, does not provide security. It may provide
the illusion of security or privacy by hiding a private address
space, but security and privacy can only be ensured by the proper use
of strong encryption.
An RSIP implementation must be guarded against potential denial- of-
service attacks. A malicious RSIP-client may be able to determine
the parameters associated with another RSIP-client via packet
sniffing. An attacker could free the resources allocated by the
RSIP-server by spoofing a FREE request. Negotiation between an RSIP
client and server should be secured with an appropriate
authentication mechanism.
RSIP-servers SHOULD NOT forward packets from a RSIP-client without
checking the validity of the source IP address and source port
number, as well as any other relevant parameters. Other necessary
policy based routing checks SHOULD also be made. Improper use of
source IP address, source port number, or any RSIP-client using a
resource or parameter assigned to a different RSIP-client are
auditable events. An RSIP-server SHOULD log negotiation transactions
in which a client attempts to use an improper Client ID or Bind ID.
8. References
[1] S. Bradner. "Key words for use in RFCs to indicate requirement
levels," RFC 2119, Mar. 1997.
[2] P. Srisuresh, Matt holdrege, "NAT: Terminology and
considerations" Internet Draft <draft-ietf-nat-
terminology-01.txt>, Work in progress.
9. Acknowledgements
The authors would like to thank Pyda Srisuresh and Rick Cobb for
their input.
10. Authors' Addresses
Michael Borella
3Com Corp.
Advanced Technologies Research Center
1800 W. Central Rd.
Mount Prospect IL 60056
(847) 342-6093
mike_borella@3com.com
David Grabelsky
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3Com Corp.
Advanced Technologies Research Center
1800 W. Central Rd.
Mount Prospect IL 60056
(847) 222-2483
david_grabelsky@3com.com
Jeffrey Lo
NEC USA
C&C Research Labs.
110 Rio Robles
San Jose, CA 95134
(408) 943 3033
jlo@ccrl.sj.nec.com
Kunihiro Taniguchi
NEC USA
C&C Research Labs.
110 Rio Robles
San Jose, CA 95134
(408) 943 3032
taniguti@ccrl.sj.nec.com
Copyright (c) The Internet Society (1999). All Rights Reserved.
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