Internet Draft L. Berger
Expiration: August 22, 1996 BBN
File: draft-berger-rsvp-ext-02.txt T. O'Malley
BBN
R. Atkinson
Cisco
Proposed
RSVP Extensions for IPSEC IPv4 Data Flows
February 22, 1996
Status of this Memo
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Abstract
This document presents extensions to Version 1 of RSVP. These
extensions permit support of individual data flows using RFC 1826 IP
Authentication Header (AH) or RFC 1827 IP Encapsulating Security
Payload (ESP). RSVP Version 1 as currently specified can support the
IPv4 IPSEC protocols, but only on a per address, per protocol basis
not on a per flow basis.
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Table of Contents
1 Introduction 3
2 Overview of Extensions 4
3 Mechanisms 5
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 7
5 Object Definition 8
5.1 SESSION Class 8
5.2 FILTER_SPEC Class 8
5.3 SENDER_TEMPLATE Class 8
6 Security Considerations 9
7 References 10
8 Acknowledgments and Authors' Information 10
8.1 Acknowledgments 10
8.2 Authors' Information 10
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Changes From Previous Version
The most significant changes from the previous version are:
o Introduced the notion of a virtual destination port. This
modification more clearly shows that the DstPort is not in the
transport header. In the SESSION object, now contains a vDstPort
field rather than a DstPort field.
o Fixed values of AH (51) and ESP (50), they were reversed.
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. For IPv4, RSVP as currently specified [RSVP96] is tailored
towards IP packets carrying protocols that have TCP or UDP-like
ports. Protocols that do not have such UDP/TCP-like ports can be
supported, but only with limitations. The IPSEC protocols do not
have UDP/TCP like ports, so they are not very well supported.
Specifically, for flows of IPSEC data packets, flow definition can
only be done on an 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. 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.
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2 Overview of Extensions
The basic notion is to extend RSVP to use the IPSEC Security
Parameter Index, or SPI, in place of UDP/TCP-like ports. This will
require a new FILTER_SPEC object, which will contain the IPSEC SPI,
and a new SESSION object.
The extension will require modifying RESV processing. 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 allow the receiver to share reservations among senders, the SPI
will be included as part of the FILTER_SPEC. This approach will
support the control of multiple independent flows between source and
destination IP addresses using FF and SE filter styles. With WF, all
flows to the same IP destination address using the same protocol will
share the same reservation. This limitation exists because the IPSEC
protocols do not contain either UDP/TCP-like destination ports or
some other alternative destination demultiplexing value in the
transport header.
Although the format of the RESV message will not change, RESV
processing will require modification. When the FILTER_SPEC is used
with IPSEC protocols, processing will need to be dependent on the use
of the new SESSION object and on the next protocol field contained in
the session definition. When the new SESSION 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
next protocol field. The SPI is located at transport header offset
+4 for AH (51), and at +0 for ESP (50).
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, ProtocolId,
DstPort). The DstPort field of the SESSION object is currently
defined as "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. To satisfy this requirement, a virtual destination port, or
vDstPort, is introduced. The vDstPort value will not be carried in
the IPSEC transport header. This change will allow control of
multiple IPSEC flows to a single destination. 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 protocol ID will share the same reservation.
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In PATH messages, the SENDER_TEMPLATE for IPSEC flows will match the
modified FILTER_SPEC. But, a new SESSION object will be used to
unambiguously distinguish the use of a virtual destination port.
Session definition and PATH processing will need to be modified to
support the new message class types.
To make use of this extension, communicating hosts will need to match
RSVP sessions and reservations to appropriate SPIs. To make best use
of reservations, the WF reservation style should be avoided and
multiple SPIs used when supporting multiple data flows between hosts.
The use of multiple SPIs is supported by the IPSEC protocols, so this
should not be an issue. Avoiding WF and only using SE and FF style
reservations should also not be a major issue since the IPSEC
protocols require receivers to identify all valid senders and their
associated SPIs.
End-stations will also need to track when the SPI value associated
with an RSVP flow changes. 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. This issue is also likely to be a
tolerable, since rekeying intervals are under the control of local
administrators.
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. The disadvantages to this approach are that we
have to modify RSVP and, to a lesser degree, that the use of SPI is
overloaded.
3 Mechanisms
This extension does not alter the mechanisms described in [RSVP96]
with the exception of Port Usage. For IPSEC data flows, UDP/TCP-like
ports are primarily replaced by IPSEC SPIs.
Implementations of RSVP that support IPSEC flows must recognize the
new SESSION object and the IPSEC ProtocolIds. When the new SESSION
object is used, for example, such systems must permit non-zero
destination port values even though the IPSEC protocols don't support
UDP/TCP-like ports.
Session definition for IPSEC flows will continue to use the triple:
(DestAddress, ProtocolId, vDstPort), where the vDstPort field will
represent a virtual destination port rather than a specific value in
the transport header. The ProtocolId field must be set to either AH
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(51) or ESP (50). Implementations of RSVP must require non-zero
vDstPort values when either IPSEC protocol is used. A zero value of
vDstPort is not valid and end-stations should give an error to an
application that specifies a zero value.
The FILTER_SPEC format will not contain a port field. Instead, it
will have a four byte field that will contain an SPI. The
SENDER_TEMPLATE format will match the FILTER_SPEC format, both
defined by the pair: (SrcAddress, SPI). When the new objects are
used, SPIs in SENDER_TEMPLATEs and FILTER_SPECs must match.
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 of
the objects will be IPv4/GPI FILTER_SPEC and IPv4/GPI
SENDER_TEMPLATE. Similarly, the name of the new SESSION object will
be IPv4/GPI SESSION.
4 Processing Rules
This section presents additions to the Processing Rules section of
the [RSVP96]. These additions are required in order to properly
process the new IPv4/GPI SESSION object and IPv4/GPI FILTER_SPEC.
4.1 Required Changes
Both RESV and PATH processing will need to be changed to support the
new IPv4/GPI 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 IPv4/GPI SESSION object,
only the IPv4/GPI SENDER_TEMPLATE may be used.
o For PATH messages that contain the IPv4/GPI SESSION object,
the value of the ProtocolId must correspond to a protocol
known to use the IPv4/GPI SESSION object. Values 51 (AH)
or 50 (ESP) must be supported by implementations supporting
the described IPSEC extensions.
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.
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(Non-zero values of vDstPort are required even though the IPSEC
protocols do not have UDP/TCP-like ports.)
The changes to RESV message processing are:
o When a RESV message contains an IPv4/GPI FILTER_SPEC, the
session must be defined using the IPv4/GPI SESSION object.
o When a RESV message contains an IPv4/GPI FILTER_SPEC, the
SENDER_TEMPLATE of the associated Path state must be an
IPv4/GPI SENDER_TEMPLATE object.
o The GPI contained in the FILTER_SPEC must match the GPI
contained in the SENDER_TEMPLATE.
o When the IPv4/GPI FILTER_SPEC is used, each node must create
a data classifier for the flow described by the quadruple:
(DestAddress, ProtocolId, SrcAddress, GPI). Specifically, the
data classifier must NOT include any UDP/TCP-like source or
destination ports! 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, ProtocolId, 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 on merging of
filter styles.
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 are likely to match all packets
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that contain both the session's destination IP address and next
protocol ID to such WF reservations. For this reason, it is
recommended that WF style reservations not be used with IPSEC
protocols.
A solution for this limitation is not proposed. This issue is not
seen as significant since IPSEC applications are unlikely to use WF
style reservations. Although, it would be nice to have a filter
style which specifies a wildcard sender but specific GPI. The
mechanism to support such a filter, however, seems non-trivial.
5 Object Definition
As previously mentioned, rather than label the modified FILTER_SPEC
and SENDER_TEMPLATE with IPSEC the specific fields, SPI, we use the
label "Generalized Port Identifier", or GPI, so that these object may
be reused for non-IPSEC uses in the future.
5.1 SESSION Class
SESSION Class = 1.
o IPv4/GPI SESSION object: Class = 1, C-Type = 3
+-------------+-------------+-------------+-------------+
| IPv4 DestAddress (4 bytes) |
+-------------+-------------+-------------+-------------+
| Protocol Id | Flags | vDstPort |
+-------------+-------------+-------------+-------------+
5.2 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) |
+-------------+-------------+-------------+-------------+
5.3 SENDER_TEMPLATE Class
SENDER_TEMPLATE class = 11.
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o IPv4/GPI SENDER_TEMPLATE object: Class = 11, C-Type = 3
Definition same as IPv4/GPI FILTER_SPEC object.
6 Security Considerations
The same considerations stated in [RSVP96], [RFC1826], and [RFC1827]
apply to the extensions described in this note. There are two
additional issues related to these extensions.
The first issue is that the use of SPIs to identify reservations may
introduce greater opportunity for traffic analysis. The significance
of the added traffic analysis threat will, of course, vary on a
case-by-case basis. Applications or users may choose to reduce the
threat by aggregating reservations and flows, or even aggregating all
traffic into a single flow and reservation.
The second issue is that 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). The frequency of key
changes will depend on duration and size of the flow, 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.
Many, if not most, RSVP sessions will not need to deal with this last
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.
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A way around this FF/SPI-change problem does exist, but it is not
elegant: 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 inelegant, but will provide
uninterrupted service for a set of applications.
7 References
[RSVP96] Braden, R., Ed., Zhang, L., Estrin, D., Herzog, S., and
S. Jamin, "Resource ReSerVation Protocol (RSVP) --
Version 1 Functional Specification. Internet Draft
draft-ietf-rsvp-spec-09.ps, February 1996.
[RFC1825] Atkinson, R., "Security Architecture for the Internet
Protocol", RFC 1825, NRL, August 1995.
[RFC1826] Atkinson, R., "IP Authentication Header", RFC 1826, NRL,
August 1995.
[RFC1827] Atkinson, R., "IP Encapsulating Security Payload", RFC
1827, NRL, August 1995.
8 Acknowledgments and Authors' Information
8.1 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 Fred
Baker <fred@cisco.com> for proposing a SPI FILTER_SPEC, Greg Troxel
<gdt@bbn.com> for proposing a solution that we didn't use, and both
John Krawczyk <jkrawczyk@BayNetworks.com> and Bob Braden
<braden@isi.edu> for their detailed feedback. 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.
8.2 Authors' Information
Lou Berger
BBN Corporation
1300 North 17th Street, Suite 1200
Arlington, VA 22209
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Phone: 703-284-4651
EMail: lberger@bbn.com
Tim O'Malley
BBN Corporation
10 Moulton Street
Cambridge, MA 02138
Phone: 617-873-3076
EMail: timo@bbn.com
Randall Atkinson
cisco Systems
170 West Tasman Drive
San Jose, CA 95134-1706
Phone: 408-526-6566
EMail: rja@cisco.com
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