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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                         Cisco Systems Inc
Expires: September 6, 2009                                 March 5, 2009


           Applicability of Keying Methods for RSVP Security
           draft-ietf-tsvwg-rsvp-security-groupkeying-03.txt

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   This Internet-Draft is submitted to IETF in full conformance with the
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   This Internet-Draft will expire on September 6, 2009.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Abstract

   The Resource reSerVation Protocol (RSVP) allows hop-by-hop
   authentication of RSVP neighbors.  This requires messages to be
   cryptographically signed using a shared secret between participating



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   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 present document also discusses applicability
   of group keying to RSVP encryption.


Table of Contents

   1.  Introduction and Problem Statement . . . . . . . . . . . . . .  3
   2.  The RSVP Hop-by-Hop Trust Model  . . . . . . . . . . . . . . .  3
   3.  Applicability of Key Types for RSVP  . . . . . . . . . . . . .  5
     3.1.  Interface and neighbor based keys  . . . . . . . . . . . .  5
     3.2.  Group keys . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Key Provisioning Methods for RSVP  . . . . . . . . . . . . . .  7
     4.1.  Static Key Provisioning  . . . . . . . . . . . . . . . . .  7
     4.2.  Dynamic Keying . . . . . . . . . . . . . . . . . . . . . .  8
       4.2.1.  Neighbor and Interface Based Key Negotiation . . . . .  8
       4.2.2.  Dynamic Group Key Distribution . . . . . . . . . . . .  8
   5.  Specific Cases . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.1.  RSVP Notify Messages . . . . . . . . . . . . . . . . . . .  8
     5.2.  RSVP-TE and GMPLS  . . . . . . . . . . . . . . . . . . . .  8
   6.  Applicability of IPsec for RSVP  . . . . . . . . . . . . . . . 10
     6.1.  General Considerations Using IPsec . . . . . . . . . . . . 10
     6.2.  Using IPsec ESP  . . . . . . . . . . . . . . . . . . . . . 10
     6.3.  Using IPsec AH . . . . . . . . . . . . . . . . . . . . . . 11
     6.4.  Applicability of Tunnel Mode . . . . . . . . . . . . . . . 11
     6.5.  Applicability of Transport Mode  . . . . . . . . . . . . . 12
     6.6.  Applicability of Tunnel Mode with Address Preservation . . 12
   7.  End Host Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  Applicability to Other Architectures and Protocols . . . . . . 13
   9.  Summary  . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 14
     10.1. Subverted RSVP Nodes . . . . . . . . . . . . . . . . . . . 15
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
   12. Changes to Previous Version  . . . . . . . . . . . . . . . . . 15
     12.1. changes from behringer-00 to behringer-01  . . . . . . . . 15
     12.2. changes from behringer-01 to ietf-00 . . . . . . . . . . . 16
     12.3. changes from ietf-00 to ietf-01  . . . . . . . . . . . . . 16
     12.4. changes from ietf-01 to ietf-02  . . . . . . . . . . . . . 16
     12.5. changes from ietf-02 to ietf-03  . . . . . . . . . . . . . 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 authenticity 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 key per router pair across an entire network is
   operationally hard, especially for key changes.  Effectively, many
   users of RSVP therefore resort to the same key throughout their RSVP
   network, and change it rarely if ever, because of the operational
   burden.  [RFC3562] however recommends regular key changes, at least
   every 90 days.

   The present document discusses the various keying methods and their
   applicability to different RSVP deployment environments, for both
   message integrity and encryption.  It does not recommend any
   particular method or protocol (e.g., RSVP authentication versus IPsec
   AH), but is meant as a comparative guideline to understand where each
   RSVP keying method is best deployed, and its limitations.
   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].


2.  The RSVP Hop-by-Hop Trust Model

   Many protocol security mechanisms used in networks require and use
   per peer authentication.  Each hop authenticates 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



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   own peers and so on.  See also the document "RSVP security
   properties" [RFC4230] for more background.

   The keys used for generating the RSVP messages can, in particular, be
   group keys (for example distributed via GDOI [RFC3547], as discussed
   in [I-D.weis-gdoi-mac-tek]).

   The trust an RSVP node has to another RSVP node 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 each other node with which
   it has a trust relationship established via the mechanisms here to
   adhere to the protocol specifications laid out by the various
   standards.  Note that in any group keying scheme like GDOI a node
   trusts explicitly as well as implicitly all the other members of the
   group.

   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.  However, 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.

                       ----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



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   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.

   By contrast, 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 sign a Path message addressed to the
   receiver and forwards it to R2.  Being a non-RSVP node, R2 and 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 it successfully with the group key.


3.  Applicability of Key Types for RSVP

3.1.  Interface and neighbor based keys

   Most current RSVP authentication implementations support interface
   based RSVP keys.  When the interface is point-to-point (and therefore
   an RSVP router only has a single RSVP neighbor on each interface),
   this is equivalent to neighbor based keys in the sense that a
   different key is used for each neighbor.  However, when the interface
   is multipoint, all RSVP speakers on a given subnet have to share the
   same key in this model, which makes it unsuitable for deployment
   scenarios where different trust groups share a subnet, for example
   Internet exchange points.  In such a case, neighbor based keys are
   required.

   With neighbor based keys, an RSVP key is bound to an interface plus a
   neighbor on that interface.  It allows the distinction of different
   trust groups on a single subnet.  (Assuming that layer-2 security is
   correctly implemented to prevent layer-2 attacks.)

   Per interface and per neighbor keys can be used within a single
   security domain.  As mentioned above, per interface keys are only
   applicable when all the nodes reachable on the specific interface
   belong to the same security domain.

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



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   level keys can only be deployed safely when all the reachable
   neighbors on the interface belong to the same security domain.

   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

   Here, 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, since
   all RSVP nodes implicitly trust each other.  Using group keys, they
   extend this trust to the group key server.  This is represented in
   Figure 2.

         ......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 however, because by definition the different domains do not
   trust each other and would 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,



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   is to use a separate group key server for each security domain, and
   to use per interface or per neighbor authentication between the two
   domains.  Figure 4 shows this set-up.

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

             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.


4.  Key Provisioning Methods for RSVP

4.1.  Static Key Provisioning

   The simplest way to implement RSVP authentication is to use static,
   preconfigured keys.  Static keying can be used with interface based
   keys, neighbor based keys or group keys.

   However, such static key provisioning is expensive on the operational
   side, since no secure automated mechanism can be used, and initial
   provisioning as well as key updates require configuration.  This
   method is therefore mostly useful for small deployments, where key
   changes can be carried out manually, or for deployments with
   automated configuration tools which support key changes.

   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, manually configured keys may be applicable to inter-domain RSVP
   authentication.

   Since it is not feasible to carry out the key change at the exact
   same time on both sides, 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.  (Note that
   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



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   manual keying tends to be significantly longer than with dynamic key
   rollover schemes.)

4.2.  Dynamic Keying

4.2.1.  Neighbor and Interface Based 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 interface or neighbor based keys.  However, existing
   key negotiation protocols such as IKEv1 [RFC2409] or IKEv2 [RFC4306]
   may not be appropriate in all environments because of the relative
   complexity of the protocols and related operations.

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 [RFC3547].  In this solution, a key server authenticates
   each of the RSVP nodes independently, and then distributes a group
   key to the entire group.


5.  Specific Cases

5.1.  RSVP Notify Messages

   [RFC3473] introduces the Notify message and allows such Notify
   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.  We observe that, alternatively,
   in some environments, group keying may allow use of regular RSVP
   authentication ([RFC2747]) for protection of non-hop-by-hop Notify
   messages.  For example, this may be applicable to controlled
   environments where nodes invoking notification requests are known to
   belong to the same key group as nodes generating Notify messages.

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



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   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
   (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."  We
   observe that 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 a PLR and MP authenticate messages from
   each other, 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.  In its security considerations section,
   [RFC4875] points out that RSVP message integrity mechanisms for hop-
   by-hop RSVP signaling apply to the hop-by-hop P2MP RSVP-TE signaling.
   In turn, we observe that the considerations in this document on
   keying methods apply equally to P2MP RSVP-TE for the hop-by-hop
   signaling.

   [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.  We note that the observation in section 3.1 of this
   document about use of group keying for protection of non-hop-by-hop
   messages apply to protection of non-hop-by-hop signaling for LSP
   Hierarchy and P2MP RSVP- TE.






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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 to protect RSVP.  Note that
   [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.  However, when using group
   keying, IPsec can be used to protect RSVP.  The potential issues and
   solutions using group keying are:

   o  [RFC2747] specifies in section 4.2, bullet 3, that both the key
      identifier and the sending system address are used to uniquely
      determine the key.  In a group keying scenario it would be
      necessary to either store a list of senders to do this, or to not
      use the sending system address to determine the key.  Both methods
      are valid, and one of the two approaches must be chosen.  The pros
      and cons are beyond the scope of this document.
   o  Anti-replay protection in a group keying scenario requires some
      changes to the way [RFC2747] defines anti-replay.  Possible
      solutions are discussed in detail in [I-D.weis-gdoi-mac-tek]).
      For example, when using counter-based methods with various senders
      in a single SA, the same counter may be received more than once,
      this conflicts with [RFC2747], which states that each counter
      value may only be accepted once.  Time based approaches are a
      solution for group keying scenarios.

   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
   [RFC3547] contains all relevant policy options to secure RSVP with
   IPsec, and no extensions are necessary.  An example GDOI policy would
   be to encrypt all packets of the RSVP protocol itself (IP protocol
   46).  A router implementing GDOI and IPsec protocols is therefore
   able to implement RSVP encryption.

6.2.  Using IPsec ESP

   In both tunnel mode and transport mode, ESP does not protect the
   header (in tunnel mode the outer header).  This is an issue with
   group keying when using ESP to secure the RSVP packets: the packet
   header could be modified by a man-in-the-middle attack, replacing the
   destination address with another RSVP router in the network.  This
   router will receive the packet, use the group key to decrypt the
   encapsulated packet, and then act on the RSVP packet.  This way an
   attacker cannot create new reservations or affect existing ones, but



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   he can "re-direct" reservations to parts of the network off the
   actual reservation path, thereby potentially denying resources to
   other applications on that part of the network.

6.3.  Using IPsec AH

   The INTEGRITY object defined by [RFC2747] provides integrity
   protection for RSVP also in a group keying context, as discussed
   above.  IPsec 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).  IPsec AH tunnel mode (transport mode
   is not appliable, see section 6.5) protects the entire original IP
   packet, including the IP header, IP options or extension headers,
   plus the entire RSVP packet.  The difference between the two schemes
   in terms of covered fields is therefore whether the IP header and IP
   options or extension headers are protected (as is the case with AH)
   or not (as is the case with the INTEGRITY object).

   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.  This document focuses on keying
   approaches only; a general security comparison of these approaches is
   outside the scope of this document.

6.4.  Applicability of Tunnel Mode

   IPsec tunnel mode encapsulates the original packet, prepending a new
   IP tunnel header plus an ESP or AH sub-header.  The entire original
   packet plus the ESP/AH subheader is secured.  In the case of ESP the
   new, outer IP header however is not cryptographically secured in this
   process.  This leads to the problem described in Section 6.2.  AH
   tunnel mode also secures the outer header, and is therefore not
   subject to these man-in-the-middle attacks.

   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.  Note that 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 can not be applied,
   because a router upstream a non-RSVP hop does not know the next RSVP



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   hop, and can thus not apply the correct tunnel header.  This is
   independent of the key type used.

6.5.  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.

6.6.  Applicability of Tunnel Mode with Address Preservation

   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.

   Tunnel mode with address preservation, in conjunction with group
   keying, allows the use of IPsec 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.


7.  End Host Considerations

   Unless RSVP Proxy entities ([I-D.ietf-tsvwg-rsvp-proxy-approaches]
   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 Point (or directly to the first
   hop router).  Host-based security relies on the same mechanisms as
   between routers (i.e.  INTEGRITY object) as specified in [RFC2747].



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   For host-based security, interface or neighbor based keys may be
   used, however, key management with pre-shared 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 zone of trust as the network
   itself, 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 only discusses 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): [I-D.ietf-pcn-architecture]
      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 initial end-to-end Path message.  Note
      that from the viewpoint of securing end-to-end RSVP, there are a
      lot of similarities in scenarios involving RSVP Aggregation over



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      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 RSVP authentication or IPsec AH) and/ or for RSVP encryption
   (e.g., using IPsec ESP in tunnel mode).

   +-----------------------------+--------------------+----------------+
   |                             | Neighbor/interface |   Group keys   |
   |                             |     based keys     |                |
   +-----------------------------+--------------------+----------------+
   | Works intra-domain          |         Yes        |       Yes      |
   | Works inter-domain          |         Yes        |       No       |
   | Works over non-RSVP hops    |         No         |     Yes (1)    |
   | Dynamic keying              |      Yes (IKE)     |  Yes (eg GDOI) |
   +-----------------------------+--------------------+----------------+

      Table 1: Overview of keying approaches and their applicability

   (1): RSVP authentication with group keys works over non-RSVP nodes;
   RSVP encryption with IPsec ESP Tunnel mode does not.

   We also make the following observations:

   o  All key types can be used statically, or with dynamic key
      negotiation.  This impacts the managability of the solution, but
      not the applicability itself.
   o  For encryption of RSVP messages IPsec ESP in tunnel mode can be
      used.  There is however a security concern, see Section 6.2.
   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
      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





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10.1.  Subverted RSVP Nodes

   A subverted node is defined here as an untrusted node, for example
   because an intruder has gained control over it.  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,
   independently whether per-interface, per-neighbor or group keys are
   used.


11.  Acknowledgements

   The authors would like to thank everybody who provided feedback on
   this document.  Specific thanks to Bob Briscoe, Hannes Tschofenig,
   Brian Weis and Ran Atkinson .


12.  Changes to Previous Version

   This section provides a change log.  It will be removed in the final
   document:

12.1.  changes from behringer-00 to behringer-01

   o  New section "Applicability to Other Architectures and Protocols":
      Goal is to clarify the scope of this document: The idea presented
      here is also applicable to other architectures
      (PCN[I-D.ietf-pcn-architecture], RFC3175 and RFC4860, etc.




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   o  Clarified the scope of this document versus RFC4230 (in the
      introduction, last paragraph).
   o  Added a section on "End Host Considerations".
   o  Expanded section 5.5 (RSVP Encryption) to clarify that GDOI
      contains all necessary mechanisms to do RSVP encrpytion.
   o  Tried to clarify the "trust to do what?" question raised by Bob
      Briscoe in a mail on 26 Jul 2007.  See the section on trust model.
   o  Lots of small editorial changes (references, typos, figures, etc).
   o  Added an Acknowledgements section.

12.2.  changes from behringer-01 to ietf-00

   o  various edits to make it clearer that draft-weis-gdoi-for-rsvp is
      an example of how dynamic group keying could be achieved for RSVP
      and not necessarily the recommended solution

12.3.  changes from ietf-00 to ietf-01

   o  Significant re-structuring of the entire document, to improve the
      flow, and provide more consistency in various sections.
   o  Moved the "Subverted RSVP nodes" discussion into the security
      considerations section.
   o  Added a "summary" section.
   o  Complete re-write of the old section 5.5 (RSVP encryption), and
      "promotion" to a separate section.
   o  Changed reference ID.weis-gdoi-for-rsvp to the new draft ID.weis-
      gdoi-mac-tek
   o  in several places, explicitly mentioned "encryption" for RSVP (in
      parallel to authentication).
   o  Various minor edits.

12.4.  changes from ietf-01 to ietf-02

   o  Re-wrote and re-structured the section on IPsec (section 6).
   o  Re-wrote the section on RSVP-TE and GMPLS (section 5.2).
   o  Various editorial changes.

12.5.  changes from ietf-02 to ietf-03

   o  Extension of section 6.3 (Using IPsec AH), to address comments
      received from Ran Atkinson.  Included a comparison of what AH
      protects vs what the INTEGRITY object protects.
   o  Added section 6.5 on "tunnel mode with address preservation.
   o  Some minor edits.







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13.  Informative References

   [I-D.ietf-pcn-architecture]
              Eardley, P., "Pre-Congestion Notification (PCN)
              Architecture", draft-ietf-pcn-architecture-09 (work in
              progress), January 2009.

   [I-D.ietf-tsvwg-rsvp-proxy-approaches]
              Faucheur, F., Manner, J., Wing, D., and A. Guillou, "RSVP
              Proxy Approaches",
              draft-ietf-tsvwg-rsvp-proxy-approaches-06 (work in
              progress), October 2008.

   [I-D.weis-gdoi-mac-tek]
              Weis, B. and S. Rowles, "GDOI Generic Message
              Authentication Code Policy", draft-weis-gdoi-mac-tek-00
              (work in progress), July 2008.

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

   [RFC2409]  Harkins, D. and D. Carrel, "The Internet Key Exchange
              (IKE)", RFC 2409, November 1998.

   [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.

   [RFC3547]  Baugher, M., Weis, B., Hardjono, T., and H. Harney, "The
              Group Domain of Interpretation", RFC 3547, July 2003.

   [RFC3562]  Leech, M., "Key Management Considerations for the TCP MD5
              Signature Option", RFC 3562, July 2003.

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



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   [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.

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

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

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

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, 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.











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Authors' Addresses

   Michael H. Behringer
   Cisco Systems Inc
   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 Inc
   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





























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