RFC2207 - RSVP Extensions for IPSEC Data Flows

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　　Network Working Group L. Berger
Request for Comments: 2207 FORE Systems
Category: Standards Track T. O'Malley
BBN
September 1997

RSVP Extensions for IPSEC Data Flows

Status of this Memo

This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.

Abstract

This document presents extensions to Version 1 of RSVP. These
extensions permit support of individual data flows using RFC1826, IP
Authentication Header (AH) or RFC1827, IP Encapsulating Security
Payload (ESP). RSVP Version 1 as currently specified can support the
IPSEC protocols, but only on a per address, per protocol basis not on
a per flow basis. The presented extensions can be used with both
IPv4 and IPv6.

Table of Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 2
2 Overview of Extensions . . . . . . . . . . . . . . . . . . 3
3 Object Definition. . . . . . . . . . . . . . . . . . . . . 4
3.1 SESSION Class . . . . . . . . . . . . . . . . . . . . 5
3.2 FILTER_SPEC Class . . . . . . . . . . . . . . . . . . 5
3.3 SENDER_TEMPLATE Class . . . . . . . . . . . . . . . . 6
4 Processing Rules . . . . . . . . . . . . . . . . . . . . . 6
4.1 Required Changes. . . . . . . . . . . . . . . . . . . 6
4.2 Merging Flowspecs . . . . . . . . . . . . . . . . . . 7
4.2.1 FF and SE Styles. . . . . . . . . . . . . . . . . . 7
4.2.2 WF Styles . . . . . . . . . . . . . . . . . . . . . 8
5 IANA Considerations. . . . . . . . . . . . . . . . . . . . 8
6 Security Considerations. . . . . . . . . . . . . . . . . . 8
7 References . . . . . . . . . . . . . . . . . . . . . . . .10
8 Acknowledgments . . . . . . . . . . . . . . . . . . . . .10
9 Authors' Addresses . . . . . . . . . . . . . . . . . . . .10
A Options Considered . . . . . . . . . . . . . . . . . . . .11
A.1 UDP Encapsulation . . . . . . . . . . . . . . . . . .11
A.2 FlowID Header Encapsulation . . . . . . . . . . . . .12
A.3 IPSEC Protocol Modification . . . . . . . . . . . . .12
A.4 AH Transparency . . . . . . . . . . . . . . . . . . .13

1 Introduction

Recently published Standards Track RFCs specify protocol mechanisms
to provide IP level security. These IP Security, or IPSEC, protocols
support packet level authentication, [RFC1826], and integrity and
confidentiality [RFC1827]. A number of interoperable
implementations already exist and several vendors have announced
commercial products that will use these mechanisms.

The IPSEC protocols provide service by adding a new header between a
packet's IP header and the transport (e.g. UDP) protocol header. The
two security headers are the Authentication Header (AH), for
authentication, and the Encapsulating Security Payload (ESP), for
integrity and confidentiality.

RSVP is being developed as a resource reservation (dynamic QoS setup)
protocol. RSVP as currently specified [RFC2205] is tailored towards
IP packets carrying protocols that have TCP or UDP-like ports.
Protocols that do not have such UDP/TCP-like ports, such as the IPSEC
protocols, can be supported, but only with limitations.
Specifically, for flows of IPSEC data packets, flow definition can
only be done on per IP address, per protocol basis.

This memo proposes extensions to RSVP so that data flows containing
IPSEC protocols can be controlled at a granularity similar to what is
already specified for UDP and TCP. The proposed extensions can be
used with both IPv4 and IPv6. Section 2 of this memo will provide an
overview of extensions. Section 3 contains a description of extended
protocol mechanisms. Section 4 presents extended protocol processing
rules. Section 5 defines the additional RSVP data objects.

2 Overview of Extensions

The basic notion is to extend RSVP to use the IPSEC Security
Parameter Index, or SPI, in place of the UDP/TCP-like ports. This
will require a new FILTER_SPEC object, which will contain the IPSEC
SPI, and a new SESSION object.

While SPIs are allocated based on destination address, they will
typically be associated with a particular sender. As a result, two
senders to the same unicast destination will usually have different
SPIs. In order to support the control of multiple independent flows
between source and destination IP addresses, the SPI will be included
as part of the FILTER_SPEC. When using WF, however, all flows to the
same IP destination address using the same IP protocol ID will share
the same reservation. (This limitation exists because the IPSEC
transport headers do not contain a destination demultiplexing value
like the UDP/TCP destination port.)

Although the RESV message format will not change, RESV processing
will require modification. Processing of the new IPSEC FILTER_SPEC
will depend on the use of the new SESSION object and on the protocol
ID contained in the session definition. When the new FILTER_SPEC
object is used, the complete four bytes of the SPI will need to be
extracted from the FILTER_SPEC for use by the packet classifier. The
location of the SPI in the transport header of the IPSEC packets is
dependent on the protocol ID field.

The extension will also require a change to PATH processing,
specifically in the usage of the port field in a session definition.
An RSVP session is defined by the triple: (DestAddress, protocol ID,
DstPort). [RFC2205] includes the definition of one type of SESSION
object, it contains UDP/TCP destination ports, specifically "a 16-bit
quantity carried at the octet offset +2 in the transport header" or
zero for protocols that lack such a field. The IPSEC protocols do

not contain such a field, but there remains a requirement for
demultiplexing sessions beyond the IP destination address. In order
to satisfy this requirement, a virtual destination port, or vDstPort,
is introduced. The vDstPort value will be carried in the new SESSION
object but not in the IPSEC transport header. The vDstPort allows
for the differentiation of multiple IPSEC sessions destined to the
same IP address. See Section 5 for a discussion of vDstPort ranges.

In PATH messages, the SENDER_TEMPLATE for IPSEC flows will have the
same format as the modified FILTER_SPEC. But, a new SESSION object
will be used to unambiguously distinguish the use of a virtual
destination port.

Traffic will be mapped (classified) to reservations based on SPIs in
FILTER_SPECs. This, of course, means that when WF is used all flows
to the same IP destination address and with the same IP protocol ID
will share the same reservation.

The advantages to the described approach are that no changes to
RFC1826 and 1827 are required and that there is no additional per
data packet overhead. Appendix A contains a discussion of the
advantages of this approach compared to several other alternatives.
This approach does not take advantage of the IPv6 Flow Label field,
so greater efficiency may be possible for IPv6 flows. The details of
IPv6 Flow Label usage is left for the future.

3 Object Definition

The FILTER_SPEC and SENDER_TEMPLATE used with IPSEC protocols will
contain a four byte field that will be used to carry the SPI. Rather
than label the modified field with an IPSEC specific label, SPI, the
label "Generalized Port Identifier", or GPI, will be so that these
object may be reused for non-IPSEC uses in the future. The name for
these objects are the IPv4/GPI FILTER_SPEC, IPv6/GPI FILTER_SPEC,
IPv4/GPI SENDER_TEMPLATE, and IPv6/GPI SENDER_TEMPLATE. Similarly,
the new SESSION objects will be the IPv4/GPI SESSION and the IPv6/GPI
SESSION. When referring to the new objects, IP version will not be
included unless a specific distinction between IPv4 and IPv6 is being
made.

3.1 SESSION Class

SESSION Class = 1.

o IPv4/GPI SESSION object: Class = 1, C-Type = 3

+-------------+-------------+-------------+-------------+
| IPv4 DestAddress (4 bytes) |
+-------------+-------------+-------------+-------------+
| Protocol ID | Flags | vDstPort |
+-------------+-------------+-------------+-------------+

o IPv6/GPI SESSION object: Class = 1, C-Type = 4

+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 DestAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Protocol ID | Flags | vDstPort |
+-------------+-------------+-------------+-------------+

3.2 FILTER_SPEC Class

FILTER_SPEC class = 10.

o IPv4/GPI FILTER_SPEC object: Class = 10, C-Type = 4

+-------------+-------------+-------------+-------------+
| IPv4 SrcAddress (4 bytes) |
+-------------+-------------+-------------+-------------+
| Generalized Port Identifier (GPI) |
+-------------+-------------+-------------+-------------+

o IPv6/GPI FILTER_SPEC object: Class = 10, C-Type = 5

+-------------+-------------+-------------+-------------+
| |
+ +
| |
+ IPv6 SrcAddress (16 bytes) +
| |
+ +
| |
+-------------+-------------+-------------+-------------+
| Generalized Port Identifier (GPI) |
+-------------+-------------+-------------+-------------+

3.3 SENDER_TEMPLATE Class

SENDER_TEMPLATE class = 11.

o IPv4/GPI SENDER_TEMPLATE object: Class = 11, C-Type = 4

Definition same as IPv4/GPI FILTER_SPEC object.

o IPv6/GPI SENDER_TEMPLATE object: Class = 11, C-Type = 5

Definition same as IPv6/GPI FILTER_SPEC object.

4 Processing Rules

This section presents additions to the Processing Rules presented in
[RFC2209]. These additions are required in order to properly
process the GPI SESSION and FILTER_SPEC objects. Values for
referenced error codes can be found in [RFC2205]. As in with the
other RSVP documents, values for internally reported (API) errors are
not defined.

4.1 Required Changes

Both RESV and PATH processing will need to be changed to support the
new objects. The changes ensure consistency and extend port
processing.

The following PATH message processing changes are required:

o When a session is defined using the GPI SESSION object, only
the GPI SENDER_TEMPLATE may be used. When this condition is
violated, end-stations should report a "Conflicting C-Type" API
error to the application.

o For PATH messages that contain the GPI SESSION object,
end-stations must verify that the protocol ID corresponds to a
protocol known to use the GPI SESSION object. Values 51 (AH)
or 50 (ESP) must be supported by implementations supporting
the described IPSEC extensions. If an unknown protocol ID is
used, then the API should report an "API Error" to the
application.

o For such messages, the vDstPort value should be recorded.
The vDstPort value forms part of the recorded state and is used
to match Resv messages, but it is not passed to traffic control.
Non-zero values of vDstPort are required. This requirement
ensures that a non-GPI SESSION object will never merge with a
GPI SESSION object. Violation of this condition causes an
"Invalid Destination Port" API error.

The changes to RESV message processing are:

o When a RESV message contains a GPI FILTER_SPEC, the session
must be defined using the GPI SESSION object. Otherwise, this is
a message formatting error.

o The GPI contained in the FILTER_SPEC must match the GPI
contained in the SENDER_TEMPLATE. Otherwise, a "No sender
information for this Resv message" error is generated.

o When the GPI FILTER_SPEC is used, each node must create
a data classifier for the flow described by the quadruple:
(DestAddress, protocol ID, SrcAddress, GPI). The data classifier
will need to look for the four byte GPI at transport header
offset +4 for AH, and at transport header offset +0 for ESP.

4.2 Merging Flowspecs

When using this extension for IPSEC data flows, RSVP sessions are
defined by the triple: (DestAddress, protocol Id, vDstPort).
Similarly, a sender is defined by the tuple: (SrcAddress, GPI), where
the GPI field will be a four byte representation of a generalized
source port. These extensions have some ramifications depending upon
the reservation style.

4.2.1 FF and SE Styles

In the FF and SE Styles, the FILTER_SPEC object contains the
(SrcAddress, GPI) pair. This allows the receiver to uniquely
identify senders based on both elements of the pair. When merging
explicit sender descriptors, the senders may only be considered
identical when both elements are identical.

4.2.2 WF Styles

These extensions provide very limited service when used with WF style
reservations. As described, the SENDER_TEMPLATE and FILTER_SPEC each
contain the GPI. In a WF style reservation, the RESV message does
NOT contain a FILTER_SPEC (after all, it is a wildcard filter), and
the SENDER_TEMPLATE is ignored (again, because any sender is
allowed). As a result, classifiers may match all packets which
contain both the session's destination IP address and protocol ID to
such WF reservations.

Although a solution for this limitation is not proposed, this issue
is not seen as significant since IPSEC applications are less likely
to use WF style reservations.

5 IANA Considerations

The range of possible vDstPort values is broken down into sections,
in a fashion similar to the UDP/TCP port ranges.

0 Illegal Value
1 - 10 Reserved. Contact authors.
11 - 8191 Assigned by IANA
8192 - 65535 Dynamic

IANA is directed to assign the well-known vDstPorts using the
following criteria: Anyone who asks for an assigned vDstPort must
provide a) a Point of Contact, b) a brief description of intended
use, and c) a short name to be associated with the assignment (e.g.
"ftp").

6 Security Considerations

The same considerations stated in [RFC2205], [RFC1826], and [RFC
1827] apply to the extensions described in this note. There are two
additional issue related to these extensions.

First, the vDstPort mechanism represents another data element about
the IP Flow that might be available to an adversary. Such data might
be useful to an adversary engaging in traffic analysis by monitoring
not only the data packets of the IP Flow but also the RSVP control
messages associated with that Flow. Protection against traffic
analysis attacks is outside the scope of this mechanism. One
possible approach to precluding such attacks would be deployment and
use of appropriate link-layer confidentiality mechansisms, such as
encryption.

Secondly, Changes in SPI values for a given flow will affect RSVP
flows and reservations. Changes will happen whenever that flow
changes its Security Association. Such changes will occur when a
flow is rekeyed (i.e. to use a new key). Rekeying intervals are
typically set based on traffic levels, key size, threat environment,
and crypto algorithm in use. When an SPI change occurs it will, in
most cases, be necessary to update (send) the corresponding
SENDER_TEMPLATEs and FILTER_SPECs. IPSEC implementations, RSVP
applications, and RSVP end-station implementations will need to take
the possibility of changes of SPI into account to ensure proper
reservation behavior. This issue is likely to be a tolerable, since
rekeying intervals are under the control of local administrators.

Many, if not most, RSVP sessions will not need to deal with this
rekeying issue. For those applications that do need to deal with
changes of SPIs during a session, the impact of sending new PATH and
RESV messages will vary based on the reservation style being used.
Builders of such applications may want to select reservation style
based on interaction with SPI changes.

The least impact of an SPI change will be to WF style reservations.
For such reservations, a new SENDER_TEMPLATE will need to be sent,
but no new RESV is required. For SE style reservations, both a new
SENDER_TEMPLATE and a new RESV will need to be sent. This will
result in changes to state, but should not affect data packet
delivery or actual resource allocation in any way. The FF style will
be impacted the most. Like with SE, both PATH and RESV messages will
need to be sent. But, since FF style reservations result in sender
receiving its own resource allocation, resources will be allocated
twice for a period of time. Or, even worse, there won't be enough
resources to support the new flow without first freeing the old flow.

A way around this FF/SPI-change problem does exist. Applications
that want FF style reservations can use multiple SE reservations.
Each real sender would have a separate SESSION (vDstPort) definition.
When it came time to switch SPIs, a shared reservation could be made
for the new SPI while the old SPI was still active. Once the new SPI
was in use, the old reservation could be torn down. This is less
than optimal, but will provide uninterrupted service for a set of
applications.

7 References

[RFC2205] Braden, R., Ed., Zhang, L., Estrin, D., Herzog, S.,
and S. Jamin, "Resource ReSerVation Protocol (RSVP)
-- Version 1 Functional Specification", RFC2205,
September 1997.

[RFC2209] Braden, R., Ed., Zhang, "Resource ReSerVation
Protocol (RSVP) -- Version 1 Message Processing
Rules", RFC2209, September 1997.

[RFC1825] Atkinson, R., "Security Architecture for the Internet
Protocol", RFC1825, NRL, August 1995.

[RFC1826] Atkinson, R., "IP Authentication Header", RFC1826, NRL,
August 1995.

[RFC1827] Atkinson, R., "IP Encapsulating Security Payload", RFC
1827, NRL, August 1995.

8 Acknowledgments

This note includes ideas originated and reviewed by a number of
individuals who did not participate in this note's writing. The
authors would like to acknowledge their contribution. We thank Ran
Atkinson <rja@cisco.com>, Fred Baker <fred@cisco.com>, Greg Troxel
<gdt@bbn.com>, John Krawczyk <jkrawczyk@BayNetworks.com> for much
appreciated input and feedback. Special appreciation goes to Bob
Braden <braden@isi.edu> for his detailed editorial and technical
comments. We also thank Buz Owen, Claudio Topolcic, Andy Veitch, and
Luis Sanchez for their help in coming up with the proposed approach.
If any brain-damage exists in this note, it originated solely from
the authors.

9 Authors' Addresses

Lou Berger Tim O'Malley
FORE Systems BBN Corporation
6905 Rockledge Drive 10 Moulton Street
Suite 800 Cambridge, MA 02138
Bethesda, MD 20817

Phone: 301-571-2534 Phone: 617-873-3076
EMail: lberger@fore.com EMail: timo@bbn.com

A Options Considered

This sections reviews other approaches that were explored in
developing the described extensions. They are included here to
provide additional context into the general problem. All listed
options were rejected by the working group.

Four other options were considered:

1. UDP Encapsulation
Add a UDP header between the IP and the IPSEC AH or ESP
headers.

2. FlowID Header Encapsulation
Add a new type of header between the IP and the IPSEC AH or
ESP headers.

3. IPSEC modification
Modify IPSEC headers so that there are appropriate fields in
same location as UDP and TCP ports.

4. AH Transparency
Skip over the Authentication Header packet classifier
processing.

A.1 UDP Encapsulation

Since current SESSION and FILTER object expect UDP or TCP ports, this
proposal says let's just give it to them. The basic concept is to
add a UDP port between the IP and AH/ESP headers. The UDP ports
would provide the granularity of control that is need to associate
specific flows with reservations.

Source and destination ports would be used, as normal, in RSVP
session definition and control. The port fields would also need to
be used to identify the real transport level protocol (e.g. ESP)
being used. Also since many UDP ports are assigned as well known
ports, use of port numbers would be limited. So, the port fields
would need to be used to unambiguously identify 1) the next level
protocol, 2) the RSVP session, and 3) the RSVP reservation.

The advantages of this option is that no RSVP changes are required.
The disadvantages is that, since the headers aren't in the expected
location, RFC1826 and RFC1827 are violated.

A.2 FlowID Header Encapsulation

[This option was originally proposed by Greg Troxel <gdt@bbn.com>.]

This option is very similar to option 1, but is more generic and
could be adopted as a standard solution. The notion is to use UDP
like ports for the sole purpose of flow identification. RSVP would
treat this new protocol exactly the same as UDP.

The difference between this and UDP encapsulation is in destination
host processing. The destination host would essentially ignore port
information and use a new field, protocol ID, to identify which
protocol should process the packet next. Some examples of protocol
IDs correspond to TCP, UDP, ESP, or AH.

The format of the FlowID Header would be:

+---------------+---------------+---------------+---------------+
| Source Port | Dest Port |
+---------------+---------------+---------------+---------------+
| Ver | Len | Protocol ID | Checksum |
+---------------+---------------+---------------+---------------+
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

2 bytes source port 4 bits length-32 (2)
2 bytes dest port 8 bits protocol ID
4 bits version (1) 16 bits checksum

The advantage of this protocol is that flow identification is
separated from all other protocol processing. The disadvantage is
that the addition of a header violates RFC1826 and 1827, and also
that applications using RSVP will need to add this extra header on
all data packets whose transport headers do not have UDP/TCP like
ports.

A.3 IPSEC Protocol Modification

The basic notion of this option is to leave RSVP as currently
specified and use the Security Association Identifier (SPI) found in
the IPSEC headers for flow identification. There are two issues with
using the SPI. The first is that the SPI is located in the wrong
location when using Authentication (AH). The second issue is how to
make use of the SPI.

The first issue is easy to fix, but violates RFC1826. UDP and TCP
have port assignments in the first 4 bytes of their headers, each is
two bytes long, source comes first, then destination. The ESP header
has the SPI in the same location as UDP/TCP ports, the AH doesn't.

The IP Authentication Header has the following syntax:

+---------------+---------------+---------------+---------------+
| Next Header | Length | RESERVED |
+---------------+---------------+---------------+---------------+
| Security Parameters Index |
+---------------+---------------+---------------+---------------+
| |
+ Authentication Data (variable number of 32-bit words) |
| |
+---------------+---------------+---------------+---------------+
1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8

Simply reversing the first 4 bytes with the SPI we will have the SPI
in the location that RSVP expects. This would be non-standard, or
require a major (i.e. not backward compatible) change to RSVP 1826.

The second issue is how to make use of the SPI. Per the current RSVP
specification, the first two bytes of a flow's SPI will need to be
carried in the PATH message and the second two bytes in the RESV
message. The biggest problem is that the SPI is normally selected by
the receiver and is likely to be different for EACH sender. (There
is a special case where the same SPI is used by all senders in a
multicast group. But this is a special case.) It is possible to
have the SPI selected prior to starting the RSVPsession. This will
work for unicast and the special multicast case. But using this
approach means that setup time will usually be extended by at least 1
round trip time. Its not clear how to support SE and WF style
reservations.

The advantage of this approach is no change to RSVP. The
disadvantages are modification to RFC1827 and limited support of RSVP
reservation styles.

A.4 AH Transparency

The source of the RSVP support of IPSEC protocols problem is that the
real transport header is not in the expected location. With ESP
packets, the real source and destination ports are encrypted and
therefore useless to RSVP. This is not the case for authentication.
For AH, the real header just follows the Authentication Header. So,
it would be possible to use the real transport header for RSVP
session definition and reservation.

To use the transport header, all that would need to be done is for
the flow classifier to skip over AHs before classifying packets. No
modification to RSVP formats or setup processing would be required.
Applications would make reservations based on transport (i.e., UDP or

TCP) ports as usual.

The advantages of this approach are no changes to either IPSEC
protocols or RSVP formats. The major disadvantage is that routers
and hosts must skip all AHs before classifying packets. The working
group decided that it was best to have a consistent solution for both
AH and ESP.

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