Network Working Group M. Behringer
Internet-Draft F. Le Faucheur
Intended status: Informational B. Weis
Expires: April 25, 2011 Cisco Systems
October 22, 2010
Applicability of Keying Methods for RSVP Security
draft-ietf-tsvwg-rsvp-security-groupkeying-08.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
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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. 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 regularly change keys due to network operational
requirements.
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].
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
own peers and so on. See also the document "RSVP security
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properties" [RFC4230] for more background.
The keys used for protecting RSVP messages can, in particular, be
group keys (for example distributed via GDOI [RFC3547], 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 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 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. 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.
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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." We
note that 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 it
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. However, when the
interface is multipoint, all RSVP speakers on a given subnet have to
share the same key in this model. This makes it unsuitable for
deployment scenarios where nodes from different security domains are
present on a subnet, for example Internet exchange points. A
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security domain is defined here as a set of nodes that shares a
common RSVP security policy. In such cases, per neighbor keys are
required.
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. 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
level keys can be deployed safely only when all the reachable
neighbors on the interface belong to the same security domain.
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. Using group keys, they extend this trust to the
group key server. 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.
Figure 4 shows this setup.
....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.
Because a group key may be used to verify messages from different
peers, monotonically increasing sequence number methods are not
appropriate. Time based anti-replay methods (e.g., the INTEGITY
sequence numbers based on a clock [RFC2747]) can be used with group
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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.
(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 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 [RFC3547]. In this solution, a key server authenticates
each of the RSVP nodes independently, and then distributes a group
key to the group as part of an encrypted and integrity protected key
agreement protocol. 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. 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, 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." 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 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. 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 analyses in this document of 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.
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. 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. Nevertheless, IPsec
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can be used to protect RSVP. Note that the 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 SPD should 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
[RFC3547] 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 should use only the 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). 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 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. 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 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 should 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. Note that 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 should be
detected and RSVP reservations will not proceed along an unintended
path.
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
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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., 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 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 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): [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
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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
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
benefit from a group keying approach.
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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
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 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
can be removed if this document is published as an RFC.
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13. Informative References
[I-D.ietf-pcn-architecture]
Eardley, P., "Pre-Congestion Notification (PCN)
Architecture", draft-ietf-pcn-architecture-11 (work in
progress), April 2009.
[I-D.ietf-tsvwg-rsvp-proxy-approaches]
Faucheur, F., Manner, J., Wing, D., and L. Faucheur, "RSVP
Proxy Approaches",
draft-ietf-tsvwg-rsvp-proxy-approaches-09 (work in
progress), March 2010.
[I-D.weis-gdoi-mac-tek]
Weis, B. and S. Rowles, "GDOI Generic Message
Authentication Code Policy", draft-weis-gdoi-mac-tek-01
(work in progress), June 2010.
[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.
[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,
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Internet-Draft RSVP Keying Applicability October 2010
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.
[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.
[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
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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