Internet Engineering Task Force G. Montenegro
INTERNET DRAFT Sun Microsystems, Inc.
M. Borella
3Com Corporation
February 2000
RSIP Support for End-to-end IPsec
draft-ietf-nat-rsip-ipsec-02.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 document proposes mechanisms that enable "Realm-Specific
IP" (RSIP) to handle end-to-end IPsec.
Expires June 2000 [Page 1]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
Table of Contents
1. Introduction ................................................... 3
2. Model .......................................................... 3
3. Implementation Notes ........................................... 4
4. IKE Handling and Demultiplexing ................................ 5
5. IPsec Handling and Demultiplexing .............................. 6
6. RSIP Protocol Extensions ....................................... 6
6.1 IKE Support in RSIP ........................................ 7
6.2 IPsec Support in RSIP ...................................... 8
7. IANA Considerations ............................................ 10
8. Security Considerations ........................................ 10
9. Acknowledgements ............................................... 11
Appendix A: On Optional Port Allocation to RSIP Clients ........... 11
Appendix B: RSIP Error Numbers for IKE and IPsec Support .......... 12
Appendix C: Message Type Values for IPsec Support ................. 12
Appendix D: A Note on Flow Policy Enforcement ..................... 13
Appendix E: Remote Host Rekeying .................................. 13
Appendix F: Example Application Scenarios ......................... 14
Appendix G: Thoughts on Supporting Incoming Connections ........... 15
References ........................................................ 17
Author addresses .................................................. 18
Expires June 2000 [Page 2]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
1. Introduction
This document specifies RSIP extensions to enable end-to-end
IPsec. It assumes the RSIP framework as presented in [RSIP-FW],
and specifies extensions to the RSIP protocol defined in
[RSIP-P]. Other terminology follows [NAT-TERMS].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described
in RFC 2119.
2. Model
For clarity, the discussion below assumes this model:
RSIP client RSIP server Host
Xa Na Nb Yb
+------------+ Nb1 +------------+
[X]------| Addr space |----[N]-----| Addr space |-------[Y]
| A | Nb2 | B |
+------------+ ... +------------+
Hosts X and Y belong to different address spaces A and B,
respectively, and N is an RSIP server. N has two addresses: Na
on address space A, and Nb on address space B. For example, A
could be a private address space, and B the public address space
of the general Internet. Additionally, N may have a pool of
addresses in address space B which it can assign to or lend to
X.
This document proposes RSIP extensions and mechanisms to enable
an RSIP client X to initiate IKE and IPsec sessions to a legacy
IKE and IPsec node Y. In order to do so, X exchanges RSIP
protocol messages with the RSIP server N. This document does not
yet address IKE/IPsec session initiation from Y to an RSIP
client X. For some thoughts on this matter see Appendix G.
The discussion below assumes that the RSIP server N is examining
a packet sent by Y, destined for X. This implies that "source"
refers to Y and "destination" refers to Y's peer, namely, X's
presence at N.
This document assumes the use of the RSAP-IP flavor of RSIP
(except that port number assignments are optional), on top of
which SPI values are used for demultiplexing. Because of this,
Expires June 2000 [Page 3]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
more than one RSIP client may share the same global IP address.
3. Implementation Notes
The RSIP server N is not required to have more than one address
on address space B. RSIP allows X (and any other hosts on
address space A) to reuse Nb. Because of this, Y's SPD SHOULD
NOT be configured to support address-based keying. Address-based
keying implies that only one RSIP client may, at any given point
in time, use address Nb when exchanging IPsec packets with Y.
Instead, Y's SPD SHOULD be configured to support
session-oriented keying, or user-oriented keying [Kent98c]. In
addition to user-oriented keying, other types of identifications
within the IKE Identification Payload are equally effective at
disambiguating who is the real client behind the single address
Nb [Piper98].
Because it cannot rely on address-based keying, RSIP support for
IPsec is similar to the application of IPsec for remote access
using dynamically assigned addresses. Both cases impose
additional requirements which are not met by minimally compliant
IPsec implementations [Gupta]:
Note that a minimally-compliant IKE implementation (which
only implements Main mode with Pre-shared keys for Phase I
authentication) cannot be used on a remote host with a
dynamically assigned address. The IKE responder (gateway)
needs to look up the initiator's (mobile node's) pre-shared
key before it can decrypt the latter's third main mode
message (fifth overall in Phase I). Since the initiator's
identity is contained in the encrypted message, only its IP
address is available for lookup and must be predictable.
Other options, such as Main mode with digital signatures/RSA
encryption and Aggressive mode, can accomodate IKE peers with
dynamically assigned addresses.
IKE packets are typically carried on UDP port 500 for both
source and destination, although the use of ephemeral source
ports is not precluded [ISAKMP]. IKE implementations for use
with RSIP SHOULD employ ephemeral ports, and should handle
them as follows [IPSEC-MSG]:
IKE implementations MUST support UDP port 500 for both
source and destination, but other port numbers are also
allowed. If an implementation allows other-than-port-500
for IKE, it sets the value of the port numbers as reported
in the ID payload to 0 (meaning "any port"), instead of
Expires June 2000 [Page 4]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
500. UDP port numbers (500 or not) are handled by the
common "swap src/dst port and reply" method.
It is important to note that IPsec implementations MUST be aware
of RSIP, at least in some peripheral sense, in order to receive
assigned SPIs and perhaps other parameters from an RSIP client.
Therefore, bump-in-the-stack (BITS) implementations of IPsec are
not expected to work "out of the box" with RSIP.
4. IKE Handling and Demultiplexing
If an RSIP client requires the use of port 500 as its IKE
source, this prevents that field being used for demultiplexing.
Instead, the "Initiator Cookie" field in the IKE header fields
must be used for this purpose. This field is appropriate as
it is guaranteed to be present in every IKE exchange (Phase
1 and Phase 2), and is guaranteed to be in the clear (even
if subsequent IKE payloads are encrypted). However, it is
protected by the Hash payload in IKE [IKE]. Because of this,
an RSIP client and server must agree upon a valid value for
the Initiator Cookie.
Once X and N arrive at a mutually agreeable value for the
Initiator Cookie, X uses it to create an IKE packet and tunnels
it the RSIP server N. N decapsulates the IKE packet and sends
it on address space B.
The minimum tuple negotiated via RSIP, and used for
demultiplexing incoming IKE responses from Y at the RSIP server
N, is:
- IKE destination port number
- Initiator Cookie
- Destination IP address
One problem still remains: how does Y know that it is supposed
to send packets to X via Nb? Y is not RSIP-aware, but it is
definitely IKE-aware. Y sees IKE packets coming from address Nb.
To prevent Y from mistakenly deriving the identity of its IKE
peer based on the source address of the packets (Nb), X MUST
exchange client identifiers with Y:
- IDii, IDir if in Phase 1, and
- IDci, IDcr if in Phase 2.
Expires June 2000 [Page 5]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
The proper use of identifiers allows the clear separation
between those identities and the source IP address of the
packets.
5. IPsec Handling and Demultiplexing
The RSIP client X and server N must arrive at an SPI value to
denote the incoming IPsec security association from Y to X.
Once N and X make sure that the SPI is unique within both of
their SPI spaces, X communicates its value to Y as part of
the IPsec security association establishment process, namely,
Quick Mode in IKE [IKE] or manual assignment.
This ensures that Y sends IPsec packets (protocols 51 and
50 for AH and ESP, respectively) [Kent98a,Kent98b] to X via
address Nb using the negotiated SPI.
IPsec packets from Y destined for X arrive at RSIP server N.
They are demultiplexed based on the following minimum tuple
of demultiplexing fields:
- protocol (50 or 51)
- SPI
- destination IP address
If N is able to find a matching mapping, it tunnels the packet
to X according to the tunneling mode in effect. If N cannot
find an appropriate mapping, it MUST discard the packet.
6. RSIP Protocol Extensions
The next two sections specify how the RSIP protocol [RSIP-P] is
extended to support both IKE (a UDP application) and the
IPsec-defined AH and ESP headers (layered directly over IP with
their own protocol numbers).
If a server implements RSIP support for IKE and IPsec as defined
in this document, it MAY include the RSIP Method parameter for
RSIP with IPsec in the REGISTER_RESPONSE method sent to the client.
This method is assigned a value of 3:
3 RSIP with IPsec (RSIPSEC)
Unless otherwise specified, requirements of micro and macro
Expires June 2000 [Page 6]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
flow-based policy are handled according to [RSIP-P].
6.1 IKE Support in RSIP
As discussed above, if X's IPsec implementation allows use of
an ephemeral source port for IKE, then incoming IKE traffic
can be demultiplexed by N based on the destination address and
port tuple. This is the simplest and most desirable way of
supporting IKE, and IPsec implementations that interact with
RSIP SHOULD allow it.
However, if X must use source port 500 for IKE, there are two
techniques with which X and N can arrive at a mutually unique
Initiator Cookie.
- Trial and error.
- Negotiation via an extension of the RSIP protocol.
The trial and error technique consists of X first obtaining
resources with which to use IPsec (via ASSIGN_REQUEST_RSIPSEC,
defined below), and then randomly choosing an Initiator Cookie
and transmitting the first packet to Y. Upon arrival at N,
the RSIP server examines the Initiator Cookie for uniqueness
per X's assigned address (Nb). If the cookie is unique,
N allows the use of this cookie for this an all subsequent
packets between X and Y on this RSIP binding. If the cookie
is not unique, N drops the packet.
When an IKE packet is determined to be lost, the IKE client will
attempt to retransmit at least three times [IKE]. An RSIP-aware
IKE client SHOULD use different Initiator Cookies for each of
these retransmissions.
The probability of an Initiator Cookie collision at N and
subsequent retransmissions by X, is infinitessimal given the
64-bit cookie space. According to the birthday paradox, in a
population of 640 million RSIP clients going through the same
RSIP server, the chances of a first collision is just 1%. Thus,
it is desirable to use the trial and error method over
negotiation, for these reasons:
- Simpler implementation requirements
- It is highly unlikely that more than one round trip
between X and N will be necessary.
Expires June 2000 [Page 7]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
6.2 IPsec Support in RSIP
This section defines the protocol extensions required for
RSIP to support AH and ESP. The required message types are
ASSIGN_REQUEST_RSIPSEC and ASSIGN_RESPONSE_RSIPSEC:
ASSIGN_REQUEST_RSIPSEC
The ASSIGN_REQUEST_RSIPSEC message is used by an RSIP client
to request IPsec parameter assignments. An RSIP client MUST
request an IP address and SPIs in one message.
If the RSIP client wishes to use IPsec to protect a TCP or
UDP application, it MUST use the port range parameter (see
Appendix A). Otherwise, it MUST set the port parameters to
the "don't need" value. This is accomplished by setting the
length field to 0, and by omitting both the number field and
the port field. This informs the server that the client does
not actually need any port assignments.
The client may initialize the SPI parameter to the "don't
care" value (see below). In this case, it is requesting
the server to assign it a valid SPI value to use.
Alternatively, the client may initialize the SPI parameter to
a value it considers valid. In this case, it is suggesting
that value to the server. Of course, the server may choose
to reject that suggestion and return an appropriate error
message.
The format of this message is:
<ASSIGN_REQUEST_RSIPSEC> ::= <Version>
<Message Type>
<Client ID>
<Address (local)>
<Ports (local)>
<Address (remote)>
<Ports (remote)>
<SPI>
[Lease Time]
[Tunnel Type]
The following message-specific error conditions exist. The
error behavior of ASSIGN_REQUEST_RSIP_IPSEC follows that
of ASSIGN_REQUEST_RSAP-IP for all non-IPsec errors.
Expires June 2000 [Page 8]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
- If the client is not allowed to use IPsec through the
server, the server MUST respond with an ERROR_RESPONSE
containing the IPSEC_UNALLOWED parameter.
- If the SPI parameter is a "don't care" value and the
RSIP server cannot allocate ANY SPIs, the RSIP server
MUST respond with an ERROR_RESPONSE containing the
IPSEC_SPI_UNAVAILABLE error.
- If an SPI parameter is not a "don't care" value
and the RSIP server cannot allocate it because the
requested address and SPI tuple is in use, the RSIP
server MUST respond with an ERROR_RESPONSE containing
the IPSEC_SPI_INUSE error.
ASSIGN_RESPONSE_RSIPSEC
The ASSIGN_RESPONSE_RSIPSEC message is used by an RSIP
server to assign parameters to an IPsec-enabled RSIP client.
The format of this message is:
<ASSIGN_RESPONSE_RSIPSEC> ::= <Version>
<Message Type>
<Client ID>
<Bind ID>
<Address (local)>
<Ports (local)>
<Address (remote)>
<Ports (remote)>
<SPI>
<Lease Time>
<Tunnel Type>
If the port parameters were set to the "don't need" value
in the request (see above), the RSIP server must do the
same in the response.
Additionally, RSIP support for IPsec requires the following
new parameter:
SPI
Code Length Number SPI SPI
+------+--------+---------+---------+ +---------+
| 22 | 2 | 2 bytes | 4 bytes | ... | 4 bytes |
+------+--------+---------+---------+ +---------+
Sent by the RSIP client in ASSIGN_REQUEST_RSIPSEC messages to
Expires June 2000 [Page 9]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
ask for a particular number of SPIs to be assigned. Also sent
by the RSIP server to the client in ASSIGN_RESPONSE_RSIPSEC
messages.
The "SPI" fields encode one or more SPIs. When a single SPI is
specified, the value of the number field is 1 and there is one
SPI field following the number field. When more than one SPI
is specified, the value of the number field will indicate the
total number of SPIs contained, and the parameter may take one
of two forms. If there is one SPI field, the SPIs specified are
considered to be contiguous starting at the SPI number specified
in the SPI field. Alternatively, there may be a number of SPI
fields equal to the value of the number field. The number of
SPI fields can be extrapolated from the value of the length
field.
In some cases, it is necessary to specify a "don't care"
value for one or more SPIs. This is accomplished by setting
the length field to 2 (to account for the 2 bytes in the
Number field), setting the number field to the number of SPIs
necessary, and omitting all SPI fields. The value of the
number field MUST be greater than or equal to one.
7. IANA Considerations
All of the designations below are tentative.
- RSIP IPsec error codes (see below).
- ASSIGN_REQUEST_RSIP_IPSEC message type code.
- SPI parameter code.
8. Security Considerations
This document does not add any security issues to those already
posed by NAT, or normal routing operations. Current routing
decisions typically are based on a tuple with only one element:
destination IP address. This document just adds more elements
to the tuple. Furthermore, by allowing an end-to-end mode of
operation and by introducing a negotiation phase to address
reuse, the mechanisms described here are more secure and less
arbitrary than NAT.
A word of caution is in order: SPI values are meant to be
semi-random, and, thus serve also as anti-clogging tokens
Expires June 2000 [Page 10]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
to reduce off-the-path denial-of-service attacks. However,
RSIP support for IPsec, renders SPI's a negotiated item: in
addition to being unique values at the receiver X, they must
also be unique at the RSIP server, N. Limiting the range of
the SPI values available to the RSIP clients reduces their
entropy slightly.
9. Acknowledgements
Many thanks to Bernard Aboba, Vipul Gupta, Jeffrey Lo, Dan
Nessett and Gary Jaszewski for helpful discussions.
Appendix A: On Optional Port Allocation to RSIP Clients
Despite the fact that SPIs rather than ports are used to
demultiplex packets at the RSIP server, the RSIP server may
still allocate mutually exclusive port numbers to the RSIP
clients. If this does not happen, there is the possibility that
two RSIP clients using the same IP address attempt an IPsec
session with the same server using the same source port
numbers.
+-------------+
| RSIP client |
| X1 +--+
| | | +-------------+
+-------------+ | | |Nb
+---------+ RSIP server +----------------
+-------------+ | | N |
| RSIP client | | +-------------+
| X2 +--+ private public
| | | network network
+-------------+ |
|
|
For example, consider hosts X1 and X2 depicted above. Assume
that they both are using public address Nb, and both are
contacting an external server Y at port 80. If they are using
IPsec but are not allocated mutually exclusive port numbers,
they may both choose the same ephemeral port number to use when
contacting Y at port 80. Assume client X1 does so first, and
after engaging in an IKE negotiation begins communicating with
the public server using IPsec.
When Client X2 starts its IKE session, it sends its
Expires June 2000 [Page 11]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
identification to the public server. The latter's SPD requires
that different identities use different flows (port numbers).
Because of this, the IKE negotiation will fail. Client X2 will
be forced to try another ephemeral port until it succeeds in
obtaining one which is currently not in use by any other
security association between the public server and any of the
RSIP clients in the private network.
Each such iteration is costly in terms of round-trip times and
CPU usage. Hence --and as a convenience to its RSIP clients--,
an RSIP server may also assign mutually exclusive port numbers
to its IPsec RSIP clients.
Despite proper allocation of port numbers, an RSIP server cannot
prevent their misuse because it cannot examine the port fields
in packets that have been encrypted by the RSIP clients.
Presumably, if the RSIP clients have gone through the trouble of
negotiating ports numbers, it is in their best interest to
adhere to these assignments.
Appendix B: RSIP Error Numbers for IKE and IPsec Support
This section provides descriptions for the error values in
the RSIP error parameter beyond those defined in [RSIP-P].
401: IPSEC_UNALLOWED. The server will not allow the client
to use end-to-end IPsec.
402: IPSEC_SPI_UNAVAILABLE. The server does not have an SPI
available for client use.
403: IPSEC_SPI_INUSE. The client has requested an SPI that
another client is currently using.
Appendix C: Message Type Values for IPsec Support
This section defines the values assigned to RSIP message types
beyond those defined in [RSIP-P].
22 ASSIGN_REQUEST_RSIPSEC
23 ASSIGN_RESPONSE_RSIPSEC
Expires June 2000 [Page 12]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
Appendix D: A Note on Flow Policy Enforcement
An RSIP server may not be able to enforce local or remote
micro-flow policy when a client uses ESP for end-to-end
encryption, since all TCP/UDP port numbers will be encrypted.
However, if AH without ESP is used, micro-flow policy is
enforceable. Macro-flow policy will always be enforceable.
Appendix E: Remote Host Rekeying
Occasionally, a remote host with which an RSIP client has
established an IPsec security association (SA) will rekey
[Jenkins]. SA rekeying is only an issue for RSIP when IKE port
500 is used by the client and the rekey is of ISAKMP phase 1
(the ISAKMP SA). The problem is that the remote host will
transmit IKE packets to port 500 with a new initiator cookie.
The RSIP server will not have a mapping for the cookie, and
SHOULD drop the the packets. This will cause the ISAKMP SA
between the RSIP client and remote host to be deleted, and may
lead to undefined behavior given that current implementations
handle rekeying in a number of different ways.
If the RSIP client uses an ephemeral source port, rekeying
will not be an issue for RSIP. If this cannot be done, there
are a number of RSIP client behaviors that may reduce the
number of occurances of this problem, but are not guaranteed
to eliminate it.
- The RSIP client's IKE implementation is given a smaller
ISAKMP SA lifetime than is typically implemented.
This would likely cause the RSIP client to rekey the
ISAKMP SA before the remote host. Since the RSIP client
chooses the Initiator Cookie, there will be no problem
routing incoming traffic at the RSIP server.
- The RSIP client terminates the ISAKMP SA as soon as the
first IPsec SA is established. This may alleviate the
situation to some degree if the SA is coarse-grained. On
the other hand, this exacerbates the problem if the SA
is fine-grained (such that it cannot be reused by other
application-level connections), and the remote host needs
to initialize sockets back to the RSIP client.
Note that the unreliability of UDP essentially makes the
ephemeral source approach the only robust solution.
Expires June 2000 [Page 13]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
Appendix F: Example Application Scenarios
This section briefly describes some examples of how RSIP may be
used to enable applications of IPsec that are otherwise not
possible.
The SOHO (small office, home office) scenario
---------------------------------------------
+----------+
|RSIP |
|client X1 +--+
| | | +-------------+ +-------+
+----------+ | |NAPT gateway | |public |
+--+ and +--.......---+IPsec |
+----------+ | |RSIP server | |peer Y |
|RSIP | | +-------------+ +-------+
|client X2 +--+ private public
| | | "home" Internet
+----------+ | network
|
|
Suppose the private "home" network is a small installation in
somebody's home, and that the RSIP clients X1 and X2 must use
the RSIP server N as a gateway to the outside world. N is
connected via an ISP and obtains a single address which must be
shared by its clients. Because of this, N has NAPT,
functionality. Now, X1 wishes to establish an IPsec SA with
peer Y. This is possible because N is also an RSIP server
augmented with the IPsec support defined in this document. Y is
IPsec-capable, but is not RSIP aware. This is perhaps the most
typical application scenario.
The above is equally applicable in the ROBO (remote office,
branch office) scenario.
Expires June 2000 [Page 14]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
The Roadwarrior scenario
------------------------
+---------+ +------------+ +----------+
|RSIP | |Corporate | | IPsec |
|client X +--..........--+Firewall +---+ peer Y |
| | public | and | | (user's |
+---------+ Internet |RSIP server | | desktop) |
| N | | |
+------------+ +----------+
private corporate
network
In this example, a remote user with a laptop gains access to the
Internet, perhaps by using PPP or DHCP. The user wants to access
its corporation private network. Using mechanisms not specified
in this document, the RSIP client in the laptop engages in an
RSIP authentication and authorization phase with the RSIP server
at the firewall. After that phase is completed, the IPsec
extensions to RSIP defined here are used to establish an IPsec
session with a peer, Y, that resides within the corporation's
network. Y could be, for example, the remote user's usual
desktop when at the office. The corporate firewall complex would
use RSIP to selectively enable IPsec traffic between internal
and external systems.
Note that this scenario could also be reversed in order to allow
an internal system (Y) to initiate and establish an IPsec
session with an external IPsec peer (X).
Appendix G: Thoughts on Supporting Incoming Connections
Incoming IKE connections are much easier to support if the
peer Y can initiate IKE exchanges to a port other than 500.
In this case, the RSIP client would allocate that port at
the RSIP client via ASSIGN_REQUEST_RSAP-IP. Alternatively,
if the RSIP client is able to allocate an IP address at the
RSIP server via ASSIGN_REQUEST_RSA-IP, Y could simply initiate
the IKE exchange to port 500 at that address.
If there is only one address Nb that must be shared by the RSIP
server and all its clients, and if Y can only send to port
500, the problem is much more difficult. At any given time,
the combination of address Nb and UDP port 500 may only be
registered and used by only one RSIP system (including clients
and server).
Expires June 2000 [Page 15]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
Solving this issue would require demultiplexing the incoming
IKE connection request based on something other than the
port and address combination. It may be possible to do so
by first registering an identity with a new RSIP command of
LISTEN_RSIP_IKE. Note that the identity could not be that of
the IKE responder (the RSIP client), but that of the initiator
(Y). The reason is that the Phase 1 only allows the sender to
include its own identity, not that of the intended recipient
(both, by the way, are allowed in Phase 2). Furthermore, the
identity must be in the clear in the first incoming packet for
the RSIP server to be able to use it as a demultiplexor. This
rules out all variants of Main Mode and Aggressive Mode
with Public Key Encryption (and Revised Mode of Public Key
Encryption), since these encrypt the ID payload.
The only Phase 1 variants which enable incoming IKE sessions
are Aggressive Mode with signatures or with pre-shared keys.
Because this scheme involves the RSIP server demultiplexing
based on the identity of the IKE initiator, it is conceivable
that only one RSIP client at a time may register interest in
fielding requests from any given peer Y. Furthermore, this
precludes more than one RSIP client's being available to any
unspecified peer Y.
Once the IKE session is in place, IPsec is set up as discussed
in this document, namely, by the RSIP client and the RSIP server
agreeing on an incoming SPI value, which is then communicated
to the peer Y as part of Quick Mode.
The alternate address and port combination must be discovered
by the remote peer using methods such as manual configuration,
or the use of KX (RFC2230) or SRV (RFC2052) records. It may
even be possible for the DNS query to trigger the above
mechanisms to prepare for the incoming and impending IKE
session initiation. Such a mechanism would allow more than
one RSIP client to be available at any given time, and would
also enable each of them to respond to IKE initiations from
unspecified peers. Such a DNS query, however, is not guaranteed
to occur. For example, the result of the query could be cached
and reused after the RSIP server is no longer listening for
a given IKE peer's identity.
Because of the limitations implied by having to rely on the
identity of the IKE initiator, the only practical way of
supporting incoming connections is for the peer Y to initiate
the IKE session at a port other than 500.
Expires June 2000 [Page 16]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
References
[Gupta] Gupta, V., "Secure Remote Access over the
Internet using IPSec," -- work in progress,
draft-gupta-ipsec-remote-access-03.txt,
Oct, 1999.
[IKE] Harkins, D., Carrel, D., "The Internet Key
Exchange (IKE)," RFC 2409, November 1998.
[ISAKMP] Maughan, D., Schertler, M., Schneider, M.,
and Turner, J., "Internet Security Association
and Key Management Protocol (ISAKMP)," RFC 2408,
November 1998.
[IPSEC-MSG] Ted Ts'o, message to the IETF's
IPsec mailing list, Message-Id:
<199911232216.RAA01932@trampoline.thunk.org>,
November 23, 1999.
[Jenkins] T. Jenkins, "IPsec Rekeying Issues," -- work in
progress, draft-jenkins-ipsec-rekeying-03.txt,
January 2000.
[Kent98a] S. Kent, R. Atkinson, "IP Encapsulating
Payload," RFC 2406, November 1998 (obsoletes
RFC 1827, August 1995).
[Kent98b] S. Kent, R. Atkinson, "IP Authentication
Header," RFC 2402, November 1998 (obsoletes
RFC 1826, August 1995).
[Kent98c] S. Kent, R. Atkinson, "Security Architecture
for the Internet Protocol," RFC 2401, November
1998 (obsoletes RFC 1827, August 1995).
[Piper98] D. Piper, "The Internet IP Security Domain
of Interpretation for ISAKMP," RFC 2407,
November 1998.
[NAPT] P. Srisuresh and K. Egevang,
"Traditional IP Network Address Translator
(Traditional NAT)" -- work in progress,
draft-ietf-nat-traditional-03.txt, September
1999.
[NAT-TERMS] P. Srisuresh and M. Holdredge, "IP Network
Address Translator (NAT) Terminology and
Expires June 2000 [Page 17]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
Considerations," RFC 2663, August 1999.
[RSIP-FW] M. Borella, J. Lo, D. Grabelsky
and G. Montenegro, "Realm Specific
IP: A Framework" -- work in progress,
draft-ietf-nat-rsip-framework-03.txt,
December 1999.
[RSIP-P] M. Borella, D. Grabelsky, J. Lo,
K. Taniguchi, "Realm Specific IP: Protocol
Specification" -- work in progress,
draft-ietf-nat-rsip-protocol-05.txt, January
2000.
Author addresses
Questions about this document may be directed at:
Gabriel E. Montenegro
Sun Labs Networking and Security Center
Sun Microsystems, Inc.
901 San Antonio Road
Mailstop UMPK 15-214
Mountain View, California 94303
Voice: +1-415-786-6288
Fax: +1-415-786-6445
E-Mail: gab@sun.com
Michael Borella
3Com Corp.
1800 W. Central Rd.
Mount Prospect IL 60056
Voice: +1-847 342-6093
E-Mail: mike_borella@3com.com
Copyright (c) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
Expires June 2000 [Page 18]
INTERNET DRAFT RSIP Support for End-to-end IPsec February 2000
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Expires June 2000 [Page 19]