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Versions: (draft-behringer-tsvwg-rsvp-security-groupkeying) 00 01 02 03 04 05 06 07 08 09 10 11 RFC 6411

Network Working Group                                       M. Behringer
Internet-Draft                                            F. Le Faucheur
Intended status: Informational                                   B. Weis
Expires: March 12, 2012                                    Cisco Systems
                                                       September 9, 2011


           Applicability of Keying Methods for RSVP Security
           draft-ietf-tsvwg-rsvp-security-groupkeying-11.txt

Abstract

   The Resource reSerVation Protocol (RSVP) allows hop-by-hop integrity
   protection of RSVP neighbors.  This requires messages to be
   cryptographically protected using a shared secret between
   participating nodes.  This document compares group keying for RSVP
   with per neighbor or per interface keying, and discusses the
   associated key provisioning methods as well as applicability and
   limitations of these approaches.  The document also discusses
   applicability of encrypting RSVP messages.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on March 12, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction and Problem Statement . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  The RSVP Hop-by-Hop Trust Model  . . . . . . . . . . . . . . .  4
   3.  Applicability of Key Types for RSVP  . . . . . . . . . . . . .  5
     3.1.  Per interface and per neighbor keys  . . . . . . . . . . .  5
     3.2.  Group keys . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Key Provisioning Methods for RSVP  . . . . . . . . . . . . . .  8
     4.1.  Static Key Provisioning  . . . . . . . . . . . . . . . . .  8
     4.2.  Dynamic Keying . . . . . . . . . . . . . . . . . . . . . .  8
       4.2.1.  Per Neighbor and Per Interface Key Negotiation . . . .  8
       4.2.2.  Dynamic Group Key Distribution . . . . . . . . . . . .  9
   5.  Specific Cases Supporting Use of Group Keying  . . . . . . . .  9
     5.1.  RSVP Notify Messages . . . . . . . . . . . . . . . . . . .  9
     5.2.  RSVP-TE and GMPLS  . . . . . . . . . . . . . . . . . . . .  9
   6.  Applicability of IPsec for RSVP  . . . . . . . . . . . . . . . 10
     6.1.  General Considerations Using IPsec . . . . . . . . . . . . 10
     6.2.  Comparing AH and the INTEGRITY Object  . . . . . . . . . . 11
     6.3.  Applicability of Tunnel Mode . . . . . . . . . . . . . . . 12
     6.4.  Non-Applicability of Transport Mode  . . . . . . . . . . . 12
     6.5.  Applicability of Tunnel Mode with Address Preservation . . 13
   7.  End Host Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  Applicability to Other Architectures and Protocols . . . . . . 14
   9.  Summary  . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 16
     10.1. Subverted Nodes  . . . . . . . . . . . . . . . . . . . . . 16
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   13. Informative References . . . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18














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1.  Introduction and Problem Statement

   The Resource reSerVation Protocol [RFC2205] allows hop-by-hop
   authentication of RSVP neighbors, as specified in [RFC2747].  In this
   mode, an integrity object is attached to each RSVP message to
   transmit a keyed message digest.  This message digest allows the
   recipient to verify the identity of the RSVP node that sent the
   message, and to validate the integrity of the message.  Through the
   inclusion of a sequence number in the scope of the digest, the digest
   also offers replay protection.

   [RFC2747] does not dictate how the key for the integrity operation is
   derived.  Currently, most implementations of RSVP use a statically
   configured key, per interface or per neighbor.  However, to manually
   configure a key per router pair across an entire network is
   operationally hard, especially when key changes are to be performed
   on a regular basis.  Effectively, many users of RSVP therefore resort
   to using the same key throughout their RSVP network, and they change
   it rarely if ever, because of the operational burden.  It is however
   often necessary to change keys due to network operational
   requirements (e.g., change of operational staff).

   This document discusses a variety of keying methods and their
   applicability to different RSVP deployment environments, for both
   message integrity and encryption.  It is meant as a comparative guide
   to understand where each RSVP keying method is best deployed, and the
   limitations of each method.  Furthermore, it discusses how RSVP hop
   by hop authentication is impacted in the presence of non-RSVP nodes,
   or subverted nodes, in the reservation path.

   The document "RSVP Security Properties" ([RFC4230]) provides an
   overview of RSVP security, including RSVP Cryptographic
   Authentication [RFC2747], but does not discuss key management.  It
   states that "RFC 2205 assumes that security associations are already
   available".  The present document focuses specifically on key
   management with different key types, including group keys.  Therefore
   this document complements [RFC4230].

1.1.  Terminology

   A security domain is defined in this document as two or more nodes
   that share a common RSVP security policy.

   When a key is mentioned in this document, it is a symmetric key.  A
   symmetric key best meets the operational requirements of RSVP
   deployments, and is the only type of key currently explicitly
   supported for protecting RSVP messages.




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2.  The RSVP Hop-by-Hop Trust Model

   Many protocol security mechanisms used in networks require and use
   per peer authentication.  Each hop authenticates messages from its
   neighbor with a shared key or certificate.  This is also the model
   used for RSVP.  Trust in this model is transitive.  Each RSVP node
   trusts explicitly only its RSVP next hop peers, through the message
   digest contained in the INTEGRITY object.  The next hop RSVP speaker
   in turn trusts its own peers and so on.  See also the document "RSVP
   security properties" [RFC4230] for more background.

   The keys used for protecting RSVP messages can, in particular, be
   group keys (for example distributed via the Group Domain of
   Interpretations (GDOI) [I-D.ietf-msec-gdoi-update], as discussed in
   [I-D.weis-gdoi-mac-tek]).  If a group key is used, the authentication
   granularity becomes group membership of devices, not (individual)
   peer authentication between devices.

   The trust an RSVP node has to another RSVP node within a common
   security domain has an explicit and an implicit component.
   Explicitly the node trusts the other node to maintain the RSVP
   messages intact or confidential, depending on whether authentication
   or encryption (or both) is used.  This means only that the message
   has not been altered or seen by another, non-trusted node.
   Implicitly each node trusts the other node to maintain the level of
   protection specified within that security domain.  In any group
   keying scheme like GDOI a node trusts all the other members of the
   group (because the authentication is now based on group membership,
   as noted above).

   The RSVP protocol can operate in the presence of a non-RSVP router in
   the path from the sender to the receiver.  The non-RSVP hop will
   ignore the RSVP message and just pass it along.  The next RSVP node
   can then process the RSVP message.  For RSVP authentication or
   encryption to work in this case, the key used for computing the RSVP
   message digest needs to be shared by the two RSVP neighbors, even if
   they are not IP neighbors.  In the presence of non-RSVP hops, while
   an RSVP node always knows the next IP hop before forwarding an RSVP
   Message, it does not always know the RSVP next hop.  In fact, part of
   the role of a Path message is precisely to discover the RSVP next hop
   (and to dynamically re-discover it when it changes, for example
   because of a routing change).  Thus, the presence of non-RSVP hops
   impacts operation of RSVP authentication or encryption and may
   influence the selection of keying approaches.

   Figure 1 illustrates this scenario.  R2 in this picture does not
   participate in RSVP, the other nodes do.  In this case, R2 will pass
   on any RSVP messages unchanged, and will ignore them.



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                       ----R3---
                      /         \
     sender----R1---R2(*)       R4----receiver
                      \         /
                       ----R5---
   (*) Non-RSVP hop

                   Figure 1: A non-RSVP Node in the path

   This creates a challenge for RSVP authentication and encryption.  In
   the presence of a non-RSVP hop, with some RSVP messages such as a
   PATH message, an RSVP router does not know the RSVP next hop for that
   message at the time of forwarding it.  For example, in Figure 1, R1
   knows that the next IP hop for a Path message addressed to the
   receiver is R2, but it does necessarily not know if the RSVP next hop
   is R3 or R5.  This means that per interface and per neighbor keys
   cannot easily be used in the presence of non-RSVP routers on the path
   between senders and receivers.

   Section 4.3 of [RFC2747] states that "... the receiver MAY initiate
   an integrity handshake with the sender."  If this handshake is taking
   place, it can be used to determine the identity of the next RSVP hop.
   In this case, non-RSVP hops can be traversed also using per interface
   or per neighbor keys.

   Group keying will naturally work in the presence of non-RSVP routers.
   Referring back to Figure 1, with group keying, R1 would use the group
   key to protect a Path message addressed to the receiver and forwards
   it to R2.  Being a non-RSVP node, R2 will ignore and forward the Path
   message to R3 or R5 depending on the current shortest path as
   determined by routing.  Whether it is R3 or R5, the RSVP router that
   receives the Path message will be able to authenticate the message
   successfully using the group key.


3.  Applicability of Key Types for RSVP

3.1.  Per interface and per neighbor keys

   Most current RSVP authentication implementations support per
   interface RSVP keys.  When the interface is point-to-point (and
   therefore an RSVP router has only a single RSVP neighbor on each
   interface), this is equivalent to per neighbor keys in the sense that
   a different key is used for each neighbor.  In the point-to-point
   case, the security domain is simply between the router and its
   neighbor.  However, when the interface is multipoint, all RSVP
   speakers on a given subnet have to belong to the same security domain
   and share the same key in this model.  This makes it unsuitable for



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   deployment scenarios where nodes from different security domains are
   present on a subnet, for example Internet exchange points.  In such
   cases, per neighbor keys are required and the security domain is
   between the router and its neighbor.

   With per neighbor keys, each RSVP key is bound to an interface plus a
   neighbor on that interface.  It allows for the existence of different
   security domains on a single interface and subnet.

   Per interface and per neighbor keys can be used within a single
   security domain.

   These key types can also be used between security domains, since they
   are specific to a particular interface or neighbor.

   Both monotonically increasing sequence number (e.g., the INTEGRITY
   object simple sequence numbers [RFC2747], or the ESP and AH anti-
   replay service [RFC4301] sequence numbers) and time based anti-replay
   methods (e.g., the INTEGRITY sequence numbers based on a clock
   [RFC2747]) can be used with per neighbor and per interface keys.

   As discussed in the previous section, per neighbor and per interface
   keys can not be used in the presence of non-RSVP hops.

3.2.  Group keys

   In the case of group keys, all members of a group of RSVP nodes share
   the same key.  This implies that a node uses the same key regardless
   of the next RSVP hop that will process the message (within the group
   of nodes sharing the particular key).  It also implies that a node
   will use the same key on the receiving as on the sending side (when
   exchanging RSVP messages within the group).

   Group keys apply naturally to intra-domain RSVP authentication, where
   all RSVP nodes are part of the same security domain and implicitly
   trust each other.  The nodes also extended trust to a group key
   server (GKS), which administers group membership and provides group
   keys.  This is represented in Figure 2.













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         ......GKS1.............
         :    :   :   :        :
         :    :   :   :        :
     source--R1--R2--R3-----destination
     |                                |
     |<-----domain 1----------------->|

        Figure 2: Group Key Server within a single security domain

   A single group key cannot normally be used to cover multiple security
   domains, because by definition the different domains do not trust
   each other.  They would therefore not be willing to trust the same
   group key server.  For a single group key to be used in several
   security domains, there is a need for a single group key server,
   which is trusted by both sides.  While this is theoretically
   possible, in practice it is unlikely that there is a single such
   entity trusted by both domains.  Figure 3 illustrates this setup.

         ...............GKS1....................
         :    :   :   :        :   :   :       :
         :    :   :   :        :   :   :       :
     source--R1--R2--R3--------R4--R5--R6--destination
     |                  |    |                      |
     |<-----domain 1--->|    |<-------domain 2----->|

        Figure 3: A Single Group Key Server across security domains

   A more practical approach for RSVP operation across security domains,
   is to use a separate group key server for each security domain, and
   to use per interface or per neighbor keys between the two domains
   (thus comprising a third security domain).  Figure 4 shows this
   setup.

         ....GKS1......        ....GKS2.........
         :    :   :   :        :   :   :       :
         :    :   :   :        :   :   :       :
     source--R1--R2--R3--------R4--R5--R6--destination
     |                  |    |                      |
     |<-----domain 1--->|    |<-------domain 2----->|
                        |<-->|
                       domain 3

             Figure 4: A group Key Server per security domain

   As discussed in Section 2, group keying can be used in the presence
   of non-RSVP hops.

   Because a group key may be used to verify messages from different



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   peers, monotonically increasing sequence number methods are not
   appropriate.  Time based anti-replay methods (e.g., the INTEGRITY
   sequence numbers based on a clock [RFC2747]) can be used with group
   keys.


4.  Key Provisioning Methods for RSVP

4.1.  Static Key Provisioning

   Static keys are preconfigured, either manually, or through a network
   management system.  The simplest way to implement RSVP authentication
   is to use static keys.  Static keying can be used with per interface
   keys, per neighbor keys or group keys.

   The provisioning of static keys requires either manual operator
   intervention on each node, or a network management system performing
   the same task.  Time synchronization of static key provisioning and
   changes is critical, to avoid inconsistent keys within a security
   domain.

   Static key provisioning is therefore not an ideal model in a large
   network.

   Often, the number of interconnection points across two domains where
   RSVP is allowed to transit is relatively small and well controlled.
   Also, the different domains may not be in a position to use an
   infrastructure trusted by both domains to update keys on both sides.
   Thus, statically provisioned keys may be applicable to inter-domain
   RSVP authentication.

   Since it is not feasible to carry out a key change at the exact same
   time in communicating RSVP nodes, some grace period needs to be
   implemented during which an RSVP node will accept both the old and
   the new key.  Otherwise, RSVP operation would suffer interruptions.
   (Also with dynamic keying approaches there can be a grace period
   where two keys are valid at the same time; however, the grace period
   in manual keying tends to be significantly longer than with dynamic
   key rollover schemes.)

4.2.  Dynamic Keying

4.2.1.  Per Neighbor and Per Interface Key Negotiation

   To avoid the problem of manual key provisioning and updates in static
   key deployments, key negotiation between RSVP neighbors could be used
   to derive either per interface or per neighbor keys.




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4.2.2.  Dynamic Group Key Distribution

   With this approach, group keys are dynamically distributed among a
   set of RSVP routers.  For example, [I-D.weis-gdoi-mac-tek] describes
   a mechanism to distribute group keys to a group of RSVP speakers,
   using GDOI [I-D.ietf-msec-gdoi-update].  In this solution, each RSVP
   node requests a group key from a key server as part of an encrypted
   and integrity protected key agreement protocol.  Once the key server
   has authenticated and authorized the RSVP nodes it distributes a
   group key to the group member.  The authentication in this model can
   be based on public key mechanisms, thereby avoiding the need for
   static key provisioning.


5.  Specific Cases Supporting Use of Group Keying

5.1.  RSVP Notify Messages

   [RFC3473] introduces the Notify message and allows such messages to
   be sent in a non-hop-by-hop fashion.  As discussed in the Security
   Considerations section of [RFC3473], this can interfere with RSVP's
   hop-by-hop integrity and authentication model.  [RFC3473] describes
   how standard IPsec based integrity and authentication can be used to
   protect Notify messages.

   Group keying may allow use of regular RSVP authentication ([RFC2747])
   for protection of non-hop-by-hop Notify messages.  For example, RSVP
   Notify messages commonly used for traffic engineering in MPLS
   networks are non-hop-by-hop messages.  Such messages may be sent from
   an ingress node directly to an egress node.  Group keying in such a
   case avoids the establishment of node-to-node keying when node-to-
   node keying is not otherwise used.

5.2.  RSVP-TE and GMPLS

   Use of RSVP authentication for RSVP-TE [RFC3209] and for RSVP-TE Fast
   Reroute [RFC4090] deserves additional considerations.

   With the facility backup method of Fast Reroute, a backup tunnel from
   the Point of Local Repair (PLR) to the Merge Point (MP) is used to
   protect Label Switched Paths (protected LSPs) against the failure of
   a facility (e.g., a router) located between the PLR and the MP.
   During the failure of the facility, the PLR redirects a protected LSP
   inside the backup tunnel and as a result, the PLR and MP then need to
   exchange RSVP control messages between each other (e.g., for the
   maintenance of the protected LSP).  Some of the RSVP messages between
   the PLR and MP are sent over the backup tunnel (e.g., a Path message
   from PLR to MP) while some are directly addressed to the RSVP node



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   (e.g., a Resv message from MP to PLR).  During the rerouted period,
   the PLR and the MP effectively become RSVP neighbors, while they may
   not be directly connected to each other and thus do not behave as
   RSVP neighbors in the absence of failure.  This point is raised in
   the Security Considerations section of [RFC4090] that says: "Note
   that the facility backup method requires that a PLR and its selected
   merge point trust RSVP messages received from each other."  Such
   environments may benefit from group keying.  A group key can be used
   among a set of routers enabled for Fast Reroute thereby easily
   ensuring that PLR and MP authenticate messages from each other can be
   authenticated, without requiring prior specific configuration of
   keys, or activation of key update mechanism, for every possible pair
   of PLR and MP.

   Where RSVP-TE or RSVP-TE Fast Reroute is deployed across AS
   boundaries (see [RFC4216]), the considerations presented above in
   section 3.1 and 3.2 apply, such that per interface or per neighbor
   keys can be used between two RSVP neighbors in different ASes
   (independently of the keying method used by the RSVP router to talk
   to the RSVP routers in the same AS).

   [RFC4875] specifies protocol extensions for support of Point-to-
   Multipoint (P2MP) RSVP-TE.  RSVP message integrity mechanisms for
   hop-by-hop RSVP signaling apply to the hop-by-hop P2MP RSVP-TE
   signaling (see [RFC4875] Security Considerations) .

   [RFC4206] defines LSP Hierarchy with GMPLS TE and uses non-hop-by-hop
   signaling.  Because it reuses LSP Hierarchy procedures for some of
   its operations, P2MP RSVP-TE also uses non-hop-by-hop signaling.
   Both LSP hierarchy and P2MP RSVP-TE rely on the security mechanisms
   defined in [RFC3473] and [RFC4206] for non hop-by-hop RSVP-TE
   signaling.  Group keying can simplify protection of non-hop-by-hop
   signaling for LSP Hierarchy and P2MP RSVP-TE.


6.  Applicability of IPsec for RSVP

6.1.  General Considerations Using IPsec

   The discussions about the various keying methods in this document are
   also applicable when using IPsec [RFC4301] to protect RSVP.
   [RFC2747] states in section 1.2 that IPsec is not an optimal choice
   to protect RSVP.  The key argument is that an IPsec SA and an RSVP SA
   are not based on the same parameters.  Nevertheless, IPsec can be
   used to protect RSVP.  The Security Policy Database (SPD) traffic
   selectors for related RSVP flows will not be constant.  In some
   cases, the source and destination addresses are end hosts, and
   sometimes they are RSVP routers.  Therefore, traffic selectors in the



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   SPD are expected to specify ANY for the source address and
   destination addresses, and specify IP protocol 46 (RSVP).

   The document "The Multicast Group Security Architecture" [RFC3740]
   defines in detail a "Group Security Association" (GSA).  This
   definition is also applicable in the context discussed here, and
   allows the use of IPsec for RSVP.  The existing GDOI standard
   [I-D.ietf-msec-gdoi-update] manages group security associations,
   which can be used by IPsec.  An example GDOI policy would be to
   encrypt or authenticate all packets of the RSVP protocol itself (IP
   protocol 46).  A router implementing GDOI and the AH and/or ESP
   protocols is therefore able to implement this policy.

   Because the traffic selectors for an SA cannot be predicted, SA
   lookup is expected to use only the Security Parameters Index (SPI)
   (or SPI plus protocol).

6.2.  Comparing AH and the INTEGRITY Object

   The INTEGRITY object defined by [RFC2747] provides integrity
   protection for RSVP also in a group keying context, as discussed
   above.  AH [RFC4302] is an alternative method to provide integrity
   protection for RSVP packets.

   The RSVP INTEGRITY object protects the entire RSVP message, but does
   not protect the IP header of the packet nor the IP options (in IPv4)
   or extension headers (in IPv6).

   AH tunnel mode (transport mode is not applicable, see section 6.4)
   protects the entire original IP packet, including the IP header of
   the original IP packet ("inner header"), IP options or extension
   headers, plus the entire RSVP packet.  It also protects the immutable
   fields of the outer header.

   The difference between the two schemes in terms of covered fields is
   therefore whether the IP header and IP options or extension headers
   of the original IP packet are protected (as is the case with AH) or
   not (as is the case with the INTEGRITY object).  Also, AH covers the
   immutable fields of the outer header.

   As described in the next section, IPsec tunnel mode can not be
   applied for RSVP traffic in the presence of non-RSVP nodes; therefore
   the security associations in both cases, AH and INTEGRITY object, are
   between the same RSVP neighbors.  From a keying point of view both
   approaches are therefore comparable.






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6.3.  Applicability of Tunnel Mode

   IPsec tunnel mode encapsulates the original packet, prepending a new
   IP header plus an ESP or AH sub-header.  The entire original packet
   plus the ESP/AH sub-header is secured.  In the case of ESP the new,
   outer IP header however is not cryptographically secured in this
   process.

   Protecting RSVP packets with IPsec tunnel mode works with any of the
   above described keying methods (interface, neighbor or group based),
   as long as there are no non-RSVP nodes on the path (however, see
   group keying considerations below).  For RSVP messages to be visible
   and considered at each hop, such a tunnel would not cross routers,
   but each RSVP node would establish a tunnel with each of its peers,
   effectively leading to link protection.

   In the presence of a non-RSVP hop, tunnel mode cannot be applied,
   because a router upstream from a non-RSVP hop does not know the next
   RSVP hop, and can thus not apply the correct tunnel header.  The same
   situation applies to a host attached to the network by a non-RSVP
   enabled first hop.  This is independent of the key type used.

   The use of group keying with ESP tunnel mode where a security gateway
   places a peer security gateway address as the destination of the ESP
   packet has consequences.  In particular, if a man-in-the-middle
   attacker re-directs the ESP-protected reservation to a different
   security gateway, the receiving security gateway cannot detect that
   the destination address was changed.  However, it has received and
   will act upon or route a RSVP reservation that will be routed along
   an unintended path.  Because RSVP routers encountering the RSVP
   packet path will not be aware that this is an unintended path, they
   will act upon it and the resulting RSVP state along both the intended
   path and unintended path will both be incorrect.  Therefore group
   keying is recommended not be used with ESP tunnel mode except with
   address preservation (see Section 6.5).

6.4.  Non-Applicability of Transport Mode

   IPsec transport mode, as defined in [RFC4303] is not suitable for
   securing RSVP Path messages, since those messages preserve the
   original source and destination.  [RFC4303] states explicitly that
   "the use of transport mode by an intermediate system (e.g., a
   security gateway) is permitted only when applied to packets whose
   source address (for outbound packets) or destination address (for
   inbound packets) is an address belonging to the intermediate system
   itself."  This would not be the case for RSVP Path messages.





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6.5.  Applicability of Tunnel Mode with Address Preservation

   When the identity of the next-hop RSVP peer is not known, it is not
   possible to use a tunnel-endpoint destination address in the Tunnel
   Mode outer IP header.  The document "Multicast Extensions to the
   Security Architecture for the Internet Protocol" [RFC5374] defines in
   section 3.1 a new tunnel mode: Tunnel mode with address preservation.
   This mode copies the destination and optionally the source address
   from the inner header to the outer header.  Therefore the
   encapsulated packet will have the same destination address as the
   original packet, and be normally subject to the same routing
   decisions.  While [RFC5374] is focusing on multicast environments,
   tunnel mode with address preservation can be used also to protect
   unicast traffic in conjunction with group keying.  In this tunnel
   mode the RSVP speakers act as security gateways, because they
   maintain the original end system addresses of the RSVP packets in the
   outer tunnel mode IP header.  This addressing scheme is used by RSVP
   to ensure that the packets continue along the routed path toward the
   destination end host.

   Tunnel mode with address preservation, in conjunction with group
   keying, allows the use of AH or ESP for protection of RSVP even in
   cases where non-RSVP nodes have to be traversed.  This is because it
   allows routing of the IPsec protected packet through the non-RSVP
   nodes in the same way as if it was not IPsec protected.

   When used with group keying, tunnel mode with address preservation
   can be used to mitigate re-direction attacks where a man-in-the-
   middle modifies the destination of the outer IP header of the tunnel
   mode packet.  The inbound processing rules for tunnel mode with
   address preservation (Section 5.2 of [RFC5374]) require that the
   receiver verify that the addresses in the outer IP header and the
   inner IP header are consistent.  Therefore, the attack can be
   detected and RSVP reservations will not proceed along an unintended
   path.


7.  End Host Considerations

   Unless RSVP Proxy entities ([RFC5945] are used, RSVP signaling is
   controlled by end systems and not routers.  As discussed in
   [RFC4230], RSVP allows both user-based security and host-based
   security.  User-based authentication aims at "providing policy based
   admission control mechanism based on user identities or application."
   To identify the user or the application, a policy element called
   AUTH_DATA, which is contained in the POLICY_DATA object, is created
   by the RSVP daemon at the user's host and transmitted inside the RSVP
   message.  This way, a user may authenticate to the Policy Decision



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   Point (or directly to the first hop router).  Host-based security
   relies on the same mechanisms as between routers (i.e., the INTEGRITY
   object) as specified in [RFC2747].  For host-based security, per
   interface or per neighbor keys may be used, however, key management
   with statically provisioned keys can be difficult in a large scale
   deployment, as described in section 4.  In principle an end host can
   also be part of a group key scheme, such as GDOI.  If the end systems
   are part of the same security domain as the RSVP hops in the network,
   group keying can be extended to include the end systems.  If the end
   systems and the network are in different zones of trust, group keying
   cannot be used.


8.  Applicability to Other Architectures and Protocols

   While, so far, this document discusses only RSVP security assuming
   the traditional RSVP model as defined by [RFC2205] and [RFC2747], the
   analysis is also applicable to other RSVP deployment models as well
   as to similar protocols:

   o  Aggregation of RSVP for IPv4 and IPv6 Reservations [RFC3175]: This
      scheme defines aggregation of individual RSVP reservations, and
      discusses use of RSVP authentication for the signaling messages.
      Group keying is applicable to this scheme, particularly when
      automatic Deaggregator discovery is used, since in that case, the
      Aggregator does not know ahead of time which Deaggregator will
      intercept the initial end-to-end RSVP Path message.
   o  Generic Aggregate Resource ReSerVation Protocol (RSVP)
      Reservations [RFC4860]: This document also discusses aggregation
      of individual RSVP reservations.  Here again, group keying applies
      and is mentioned in the Security Considerations section.
   o  Aggregation of Resource ReSerVation Protocol (RSVP) Reservations
      over MPLS TE/DS-TE Tunnels [RFC4804]([RFC4804]): This scheme also
      defines a form of aggregation of RSVP reservation but this time
      over MPLS TE Tunnels.  Similarly, group keying may be used in such
      an environment.
   o  Pre-Congestion Notification (PCN): [RFC5559] defines an
      architecture for flow admission and termination based on
      aggregated pre-congestion information.  One deployment model for
      this architecture is based on IntServ over DiffServ: the DiffServ
      region is PCN-enabled, RSVP signalling is used end-to-end but the
      PCN-domain is a single RSVP hop, i.e. only the PCN- boundary-nodes
      process RSVP messages.  In this scenario, RSVP authentication may
      be required among PCN-boundary-nodes and the considerations about
      keying approaches discussed earlier in this document apply.  In
      particular, group keying may facilitate operations since the
      ingress PCN-boundary-node does not necessarily know ahead of time
      which Egress PCN-boundary-node will intercept and process the



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      initial end-to-end Path message.  From the viewpoint of securing
      end-to-end RSVP in this scenario (from the end host to the ingress
      edge PCN node, to the egress PCN node, to the other end host),
      there are a lot of similarities in scenarios involving RSVP
      Aggregation over aggregate RSVP reservations ([RFC3175],
      [RFC4860]), RSVP Aggregation over MPLS-TE tunnels ([RFC4804]), and
      RSVP (Aggregation) over PCN ingress-egress aggregates.


9.  Summary

   The following table summarizes the various approaches for RSVP
   keying, and their applicability to various RSVP scenarios.  In
   particular, such keying can be used for RSVP authentication (e.g.,
   using the RSVP INTEGRITY object or AH) and/ or for RSVP encryption
   (e.g., using ESP in tunnel mode).

   +-------------------------------+-----------------+-----------------+
   |                               |       per       |    Group keys   |
   |                               |   neighbor/per  |                 |
   |                               |  interface keys |                 |
   +-------------------------------+-----------------+-----------------+
   | Works intra-domain            |       Yes       |       Yes       |
   | Works inter-domain            |       Yes       |        No       |
   | Works over non-RSVP hops      |        No       |     Yes (1)     |
   | Dynamic keying                |    Yes (IKE)    |    Yes (e.g.,   |
   |                               |                 |      GDOI)      |
   +-------------------------------+-----------------+-----------------+

      Table 1: Overview of keying approaches and their applicability

   (1): RSVP integrity with group keys works over non-RSVP nodes; RSVP
   encryption with ESP and RSVP authentication with AH work over non-
   RSVP nodes in 'Tunnel Mode with Address Preservation'; RSVP
   encryption with ESP & RSVP authentication with AH do not work over
   non-RSVP nodes in 'Tunnel Mode'.

   We also make the following observations:

   o  All key types can be used statically, or with dynamic key
      negotiation.  This impacts the manageability of the solution, but
      not the applicability itself.
   o  For encryption of RSVP messages, IPsec ESP in tunnel mode can be
      used.
   o  There are some special cases in RSVP, like non-RSVP hosts, the
      "Notify" message (as discussed in Section 5.1), the various RSVP
      deployment models discussed in Section 8 and MPLS Traffic
      Engineering and GMPLS discussed in section 5.2 , which would



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      benefit from a group keying approach.


10.  Security Considerations

   This entire document discusses RSVP security; this section describes
   a specific security considerations relating to subverted RSVP nodes.

10.1.  Subverted Nodes

   An undetected subverted node, for example one that an intruder has
   gained control over, it is still implicitly a trusted node.  However
   it is a threat to the security of RSVP.  Since RSVP authentication is
   hop-by-hop and not end-to-end, a subverted node in the path breaks
   the chain of trust.  This is to a large extent independent of the
   type of keying used.

   For interface or per neighbor keying, the subverted node can now
   introduce fake messages to its neighbors.  This can be used in a
   variety of ways, for example by changing the receiver address in the
   Path message, or by generating fake Path messages.  This allows path
   states to be created on every RSVP router along any arbitrary path
   through the RSVP domain.  That in itself could result in a form of
   Denial of Service by allowing exhaustion of some router resources
   (e.g. memory).  The subverted node could also generate fake Resv
   messages upstream corresponding to valid Path states.  In doing so,
   the subverted node can reserve excessive amounts of bandwidth thereby
   possibly performing a denial of service attack.

   Group keying allows the additional abuse of sending fake RSVP
   messages to any node in the RSVP domain, not just adjacent RSVP
   nodes.  However, in practice this can be achieved to a large extent
   also with per neighbor or interface keys, as discussed above.
   Therefore the impact of subverted nodes on the path is comparable for
   all keying schemes discussed here (per interface, per neighbor, group
   keys).


11.  Acknowledgements

   The authors would like to thank everybody who provided feedback on
   this document.  Specific thanks to Bob Briscoe, Hannes Tschofenig,
   Ran Atkinson, Stephen Kent, and Kenneth G. Carlberg.


12.  IANA Considerations

   There are no IANA considerations within this document.  This section



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   can be removed if this document is published as an RFC.


13.  Informative References

   [I-D.ietf-msec-gdoi-update]
              Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
              of Interpretation", draft-ietf-msec-gdoi-update-11 (work
              in progress), August 2011.

   [I-D.weis-gdoi-mac-tek]
              Weis, B. and S. Rowles, "GDOI Generic Message
              Authentication Code Policy", draft-weis-gdoi-mac-tek-02
              (work in progress), March 2011.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC2747]  Baker, F., Lindell, B., and M. Talwar, "RSVP Cryptographic
              Authentication", RFC 2747, January 2000.

   [RFC3175]  Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
              "Aggregation of RSVP for IPv4 and IPv6 Reservations",
              RFC 3175, September 2001.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

   [RFC3473]  Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Resource ReserVation Protocol-Traffic
              Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.

   [RFC3740]  Hardjono, T. and B. Weis, "The Multicast Group Security
              Architecture", RFC 3740, March 2004.

   [RFC4090]  Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
              Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              May 2005.

   [RFC4206]  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
              Hierarchy with Generalized Multi-Protocol Label Switching
              (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.

   [RFC4216]  Zhang, R. and J. Vasseur, "MPLS Inter-Autonomous System
              (AS) Traffic Engineering (TE) Requirements", RFC 4216,
              November 2005.



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   [RFC4230]  Tschofenig, H. and R. Graveman, "RSVP Security
              Properties", RFC 4230, December 2005.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              December 2005.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005.

   [RFC4804]  Le Faucheur, F., "Aggregation of Resource ReSerVation
              Protocol (RSVP) Reservations over MPLS TE/DS-TE Tunnels",
              RFC 4804, February 2007.

   [RFC4860]  Le Faucheur, F., Davie, B., Bose, P., Christou, C., and M.
              Davenport, "Generic Aggregate Resource ReSerVation
              Protocol (RSVP) Reservations", RFC 4860, May 2007.

   [RFC4875]  Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
              "Extensions to Resource Reservation Protocol - Traffic
              Engineering (RSVP-TE) for Point-to-Multipoint TE Label
              Switched Paths (LSPs)", RFC 4875, May 2007.

   [RFC5374]  Weis, B., Gross, G., and D. Ignjatic, "Multicast
              Extensions to the Security Architecture for the Internet
              Protocol", RFC 5374, November 2008.

   [RFC5559]  Eardley, P., "Pre-Congestion Notification (PCN)
              Architecture", RFC 5559, June 2009.

   [RFC5945]  Le Faucheur, F., Manner, J., Wing, D., and A. Guillou,
              "Resource Reservation Protocol (RSVP) Proxy Approaches",
              RFC 5945, October 2010.
















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Authors' Addresses

   Michael H. Behringer
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue Roumanille, Batiment T 3
   Biot - Sophia Antipolis  06410
   France

   Email: mbehring@cisco.com
   URI:   http://www.cisco.com


   Francois Le Faucheur
   Cisco Systems
   Village d'Entreprises Green Side
   400, Avenue Roumanille, Batiment T 3
   Biot - Sophia Antipolis  06410
   France

   Email: flefauch@cisco.com
   URI:   http://www.cisco.com


   Brian Weis
   Cisco Systems
   170 W. Tasman Drive
   San Jose, California  95134-1706
   USA

   Email: bew@cisco.com
   URI:   http://www.cisco.com



















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