Transport Working Group F. Baker
Internet-Draft Cisco Systems
Intended status: Informational P. Bose
Expires: March 30, 2007 Lockheed Martin
September 26, 2006
QoS Signaling in a Nested Virtual Private Network
draft-ietf-tsvwg-vpn-signaled-preemption-01
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Copyright (C) The Internet Society (2006).
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Abstract
Some networks require communication between an interior and exterior
portion of a VPN, but have sensitivities about what information is
communicated across the boundary. This note seeks to outline the
issues and the nature of the proposed solutions.
Table of Contents
1. QoS in a nested VPN . . . . . . . . . . . . . . . . . . . . . 3
1.1. Nested VPNs . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Signaled QoS technology . . . . . . . . . . . . . . . . . 7
1.3. The Resource Reservation Protocol (RSVP) . . . . . . . . . 8
1.4. Logical structure of a VPN Router . . . . . . . . . . . . 10
2. Reservation and Preemption in a nested VPN . . . . . . . . . . 13
2.1. Reservation in a nested VPN . . . . . . . . . . . . . . . 14
2.2. Preemption in a nested VPN . . . . . . . . . . . . . . . . 16
2.3. Working through an example . . . . . . . . . . . . . . . . 17
2.3.1. Initial routine reservations - generating network
state . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.2. Initial routine reservations - request reservation . . 19
2.3.3. Installation of a reservation using precedence . . . . 20
2.3.4. Installation of a reservation using preemption . . . . 21
3. Data flows within a VPN Router . . . . . . . . . . . . . . . . 24
3.1. VPN Routers that carry data across the cryptographic
boundary . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.1.1. Plaintext to Ciphertext Data Flows . . . . . . . . . . 24
3.1.2. Ciphertext to Plaintext Data Flows . . . . . . . . . . 26
3.2. VPN Routers that use the Network Guard for signaling
across the cryptographic boundary . . . . . . . . . . . . 27
3.2.1. Signaling Flow . . . . . . . . . . . . . . . . . . . . 28
3.2.2. Use case with Network Guard . . . . . . . . . . . . . 29
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
5. Security Considerations . . . . . . . . . . . . . . . . . . . 33
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35
7.1. Normative References . . . . . . . . . . . . . . . . . . . 35
7.2. Informative References . . . . . . . . . . . . . . . . . . 36
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1. QoS in a nested VPN
More and more networks wish to guarantee secure transmission of IP
traffic across public LANs or WANs and therefore use Virtual Private
Networks. Some networks require communication between an interior
and exterior portion of a VPN, but have sensitivities about what
information is communicated across the boundary. This note seeks to
outline the issues and the nature of the proposed solutions. The
outline of the QoS solution for real-time traffic has been described
at a high level in [RFC4542]. The key characteristics of this
proposal are that
o it uses standardized protocols,
o It includes reservation setup and teardown for guaranteed and
controlled load services using the standardized protocols,
o it is independent of link delay, and therefore consistent with
high delay*bandwidth networks as well as the more common variety,
o it has no single point of failure, such as a central reservation
manager,
o It provides for the preemption of established data flows,
o In that preemption, it not only permits a policy-admitted data
flow in, but selects a specific data flow to exclude based upon
control input rather than simply accepting a loss of service
dictated at the discretion of the network control function, and
o interoperates directly with SIP Proxies, H.323 Gatekeepers, or
other call management subsystems to present the other services
required in a preemptive or preferential telephone network.
The thrust of the memo surrounds VPNs that use encryption in some
form, such as IPsec. As a result, we will discuss the VPN Router
supporting "plaintext" and "ciphertext" interfaces. However, the
concept extends readily to any form of aggregation, including the
concept proposed in [RFC3175] of the IP traffic entering and leaving
a network at identified points, and the use of other kinds of tunnels
including GRE, IP/IP, MPLS, and so on.
A note on the use of the words "priority" and "precedence" in this
document is in order. The term "priority" has been used in this
context with a variety of meanings, resulting in a great deal of
confusion. The term "priority" is used in this document to identify
one of several possible datagram scheduling algorithms. A scheduler
is used when deciding which datagram will be sent next on a computer
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interface; a priority scheduler always chooses a datagram from the
highest priority class (queue) that is occupied, shielding one class
of traffic from most of the jitter by passing jitter it would
otherwise have experienced to another class. [RFC3181] applies the
term to a reservation, in a sense that this document will refer to as
"precedence". The term "precedence" is used in the sense implied in
the phrase "Multi-Level Precedence and Preemption"[ITU.MLPP.1990] ;
some classes of sessions take precedence over others, which may
result in bandwidth being admitted that might not otherwise have been
or may result in the prejudicial termination of a lower precedence
session under a stated set of circumstances. For the purposes of the
present discussion, "priority" is a set of algorithms applied to
datagrams, where "precedence" is a policy attribute of sessions. The
techniques of priority comparisons are used in a router or a policy
decision point to implement precedence, but they are not the same
thing.
Along the same lines, it is important for the reader to understand
the difference between QoS policies and policies based on the
"precedence" or "importance" of data to the person or function using
it. Voice, regardless of the precedence level of the call, is
impeded by high levels of variation in network-induced delay. As a
result, voice is often serviced using a priority queue, transferring
jitter from that application's traffic to other applications. This
is as true of voice for routine calls as it is for flash traffic.
There are classes of application traffic that require bounded delay.
That is a different concept than "no jitter"; they can accept jitter
within stated bounds. Routing protocols such as OSPF or BGP are
critical to the correct functioning of network infrastructure. While
they are designed to work well with moderate loss levels, they are
not helped by them, and even a short period of high loss can result
in dramatic network events. Variation in delay, however, is not at
all an issue if it is within reasonable bounds. As a result, it is
common for routers to treat routing protocol datagrams in a way that
limits the probability of loss, accepting relatively high delay in
some cases, even though the traffic is absolutely critical to the
network. Telephone call setup exchanges have this characteristic as
well: faced with a choice between loss and delay, protocols like SIP
and H.323 far prefer the latter, as the call setup time is far less
than it would be if datagrams had to be retransmitted, and this is
true regardless of whether the call is routine or of high precedence.
As such, QoS markings tell us how to provide good service to an
application independent of how "important" it may be at the current
time, while "importance" can be conveyed separately in many cases.
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1.1. Nested VPNs
One could describe such a network in terms of three network diagrams.
Figure 1 shows a simple network stretched across a VPN connection.
The VPN Router (where, following [RFC2460] a "router" is "a node that
forwards packets not explicitly addressed to itself"), performs the
following steps: it
o receives an IP datagram from a plain text interface,
o determines what remote enclave and therefore other VPN Router to
forward it to,
o ensures that it has a tunnel mode security association (as
generally defined in [RFC2401] section 4) with that router,
o encloses the encrypted datagram within another VPN (e.g. IPsec)
and IP header, and
o forwards the encapsulated datagram toward the remote VPN Router.
The receiving VPN Router reverses the steps: it
o determines what security association the datagram was received
from,
o decrypts the interior datagram,
o forwards the now-decapsulated datagram on a plain text interface.
The use of IPsec in this manner is described as the tunnel mode of
[RFC2401] and [RFC4303].
Host Host Host Host Host Host
/------------------/ /------------------/
Router -------Router
|
VPN-Router
||
|| IPsec Tunnel through routed network
||
VPN-Router
|
Router -------Router
/------------------/ /------------------/
Host Host Host Host Host Host
Figure 1: VPN-connected enclave
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An important point to understand is that the VPN tunnel, like other
features of the routed network, are invisible to the host. The host
can infer that "something out there" is affecting the Path MTU,
introducing delay, or otherwise affecting its data stream, but if
properly implemented it should be able to adapt to these. The words
"if properly implemented" are the bane of every network manager,
however; substandard implementations do demonstrably exist.
Outside of the enclave, the hosts are essentially invisible. The
communicating enclaves look like a simple data exchange between peer
hosts across a routed network, as shown in Figure 2.
VPN-Router | Router | VPN-Router
Figure 2: VPN-connected enclave from exterior perspective
Such networks can be nested and re-used in a complex manner. As
shown in Figure 3 a pair of enclaves might communicate across a
cipher text network which, for various reasons, is itself re-
encrypted and transmitted across a larger cipher text network. The
reasons for doing this vary, but they relate to information-hiding in
the wider network, different levels of security required for
different enclosed enclaves, and so on.
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Host Host Host Host Host Host
/------------------/ /------------------/
Router -------Router
|
VPN-Router VPN-Router VPN-Router
/---------------------/ /----------/
Router -------------Router
|
VPN-Router VPN-Router
/-----------/ /----------/
Router -------Router
|
|
Router -------Router
/-----------/ /----------/
VPN-Router VPN-Router
|
Router ------------Router
/---------------------/ /----------/
VPN-Router VPN-Router VPN-Router
|
Router -------Router
/------------------/ /------------------/
Host Host Host Host Host Host
Figure 3: Nested VPN
The key question this document explores is "how do reservations, and
preemption of reservations, work in such an environment?"
1.2. Signaled QoS technology
The Integrated Services model for networking was originally proposed
in [RFC1633]. In short, it divides all applications into two broad
classes: those that will adapt themselves to any available bandwidth,
and those that will not or cannot. In its own words,
One class of applications needs the data in each packet by a
certain time and, if the data has not arrived by then, the data
is essentially worthless; we call these "real-time"
applications. Another class of applications will always wait
for data to arrive; we call these "elastic" applications.
The Integrated Services model defines data flows supporting
applications as either "real-time" or "elastic". It should be noted
that "real-time" traffic is also referred to as "inelastic" traffic,
and that elastic traffic is occasionally referred to as "non-real-
time."
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In this view, the key issue is the so-called "playback point": a
real-time application is considered to have a certain point in time
at which data describing the next sound, picture, or whatever to be
delivered to a display device or forfeit its utility, while an
elastic application has no such boundary. Another way to look at the
difference is that real-time applications have an irreducible lower
bound on their bandwidth requirements. For example, the typical
G.711 payload is delivered in 160 byte samples (plus 40 bytes of IP/
UDP/RTP headers) at 20 millisecond intervals. This will yield 80
KBPS of bandwidth, without silence suppression, and not accounting
for the layer 2 overhead. To operate in real-time, a G.711 codec
requires the network over which its data will be delivered to support
communications at 80 KBPS at the IP layer with roughly constant end
to end delay and nominal or no loss. If this is not possible (if
there is significant loss or wide variations in delay), voice quality
will suffer. On the other hand, if many megabits of capacity are
available, the G.711 codec will not increase its bandwidth
requirements either. Although adaptive codecs exist, (e.g., G.722.2
or G.726), the adaptive mechanism can either require greater or
lesser bandwidth and can adapt only within a certain range of
bandwidth requirements beyond which the quality of the data flow
required is not met. Elastic applications, however, will generally
adapt themselves to any network: if the bottleneck provides 9600 bits
per second, a web transfer or electronic mail exchange will happen at
9600 bits per second, and if hundreds of megabits are available, the
TCP (or SCTP) transport will increase their transfer rate in an
attempt to reduce the time required to accomplish the transfer.
For real-time applications, those that require data to be delivered
end to end with at least a certain rate and with delays varying
between stated bounds, the Integrated Services architecture proposes
the use of a signaling protocol that allows the communicating
applications and the network to communicate about the application
requirements and the network's capability to deliver them. Several
such protocols have been developed or are under development, notably
including RSVP and NSIS. The present discussion is limited to RSVP,
although any protocol that delivers a similar set of capabilities
could be considered.
1.3. The Resource Reservation Protocol (RSVP)
RSVP is initially defined in [RFC2205] with a set of datagram
processing rules defined in [RFC2209] and datagram details for
Integrated Services [RFC2210]. Conceptually, this protocol specifies
a way to identify data flows from a source application to a
destination application and request specific resources for them. The
source may be a single machine or a set of machines listed explicitly
or implied, whereas the destination may be a single machine or a
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multicast group (and therefore all of the machines in it). Each
application is specified by a transport protocol number in the IP
protocol field, or may additionally include destination and perhaps
source port numbers. The protocol is defined for both IPv4 [RFC0791]
and IPv6 [RFC2460]. It was recognized immediately that it was also
necessary to provide a means to perform the same function for various
kinds of tunnels, which implies a relationship between what is inside
and what is outside the tunnel. Definitions were therefore developed
for IPsec [RFC2207] and [I-D.ietf-tsvwg-rsvp-ipsec] and for more
generic forms of tunnels [RFC2746]. With the later development of
the Differentiated Services Architecture [RFC2475], definitions were
added to specify the DSCP [RFC2474] to be used by a standard RSVP
data flow in [RFC2996] and to use a pair of IP addresses and a DSCP
as the identifying information for a data flow [RFC3175].
In addition, the initial definition of the protocol included a
placeholder for policy information, and for preemption of
reservations. This placeholder was later specified in detail in
[RFC2750] with a view to associating a policy [RFC2872] with an
identity [RFC3182] and thereby enabling the network to provide a
contracted service to an authenticated and authorized user. This was
integrated with the Session Initiation Protocol [RFC3261] in
[RFC3312]. Preemption of a reservation is specified in the context,
in [RFC3181] which in essence specifies that a reservation installed
in the network using an Preemption Priority and retained using a
separate Defending Priority may be removed by the network via an RESV
Error signal that removes the entire reservation. This has issues,
however, in that the matter is often not quite so black and white.
If the issue is that an existing reservation for 80 KBPS can no
longer be sustained but a 60 KBPS reservation could, it is possible
that a VoIP sender could change from a G.711 codec to a G.729 codec
and achieve that. Or, if there are multiple sessions in a tunnel or
other aggregate, one of the calls could be eliminated leaving
capacity for the others. [RFC4495] seeks to address this issue.
In a similar way, a capability was added to limit the possibility of
control signals being spoofed or otherwise attacked [RFC2747]
[RFC3097].
[RFC3175] describes several features that are unusual in RSVP, being
specifically set up to handle aggregates in a service provider
network. It describes three key components:
o The RFC 3175 session object, which identifies not the IP addresses
of the packets that are identified, but the IP addresses of the
ingress and egress devices in the network, and the DSCP that the
traffic will use,
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o The function of a reservation "aggregator", which operates in the
ingress router and accepts individual reservations from the
"customer" network which it aggregates into the ISP core in a
tunnel, an MPLS LSP, or as a traffic stream that it known to leave
at the deaggregator,
o The function of a reservation "deaggregator", which operates in
the egress router and breaks the aggregate reservation and data
streams back out into individual data streams that may be passed
to other networks.
In retrospect, the Session Object specified by RFC 3175 is useful but
not intrinsically necessary. If the ISP network uses tunnels, such
as MPLS LSPs, IP/IP or GRE tunnels or enclosing IPsec Security
Associations, the concepts of an aggregator and a deaggregator work
in the same manner, although the reservation mechanism would be that
of [RFC3473] and [RFC3474] [RFC2207] [I-D.ietf-tsvwg-rsvp-ipsec] or
[RFC2746].
1.4. Logical structure of a VPN Router
The conceptual structure of a VPN Router is similar to that of any
other router. In its simplest form, it is physically a two or more
port device, similar to that shown in Figure 4 which has one or more
interfaces to the protected enclave(s) and one or more interfaces to
the outside world. On the latter, it structures some number of
tunnels (in the case of an IPsec tunnel, having security
associations) that it can treat as point to point interfaces from a
routing perspective.
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+---------+ +-------+ +----+----+ +---------+
| RSVP | |Routing| |Net Guard| |IPsec Mgr|
+----+----+ +---+---+ +----+----+ +----+----+
| | | |
+----+-----------+------------+-----------------+----+
| IP |
+-----------+--------------------+------------+------+
| | |
| +-----+-----+ +----+------+
| | Encrypt/ | | Encrypt/ |
| |Decrypt for| |Decrypt for|
| | Security | | Security |
| |Association| |Association|
| +-----+-----+ +----+------+
| | |
+-----------+------------+ +-----+------------+------+
| Plain text | | Cipher text |
| Interface | | Interface |
+------------------------+ +-------------------------+
Figure 4: Logical structure of a VPN Router
The encrypt/decrypt unit may be implemented as a function of the
plain text router, as a function on its interface card, or as a
function of an external device with a private interface to the IP
routing functionality of the plain text router. These are
conceptually equivalent, although there are practical differences in
implementation. The key issue is that when IP routing presents a
message to the encrypt/decrypt unit for transmission, it must also be
presented with the IP address of the plain text routing peer, whether
host or router, to which the security association must be
established. This IP Address is used to select (and perhaps create)
the security association, and in turn select the appropriate set of
security parameters. This could also be implemented by presenting
the local Security Parameter Index (SPI) for the data, if it has been
created out of band by the Network Management Process.
In addition, it is necessary for aggregated signaling to be generated
for the cipher text domain. This may be accomplished in several
ways:
o by having the RSVP process on the plain text router generate the
messages and having the encrypt/decrypt unit bypass them into the
cipher text network
o by having the plain text RSVP Process advise a process in the
encrypt/decrypt implementation of what needs to be generated using
some local exchange, and having it generate such messages, or
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o by having a separate parallel network management system
intermediate between the plain text and cipher text routers, in
which case the encrypt/decrypt unit and the parallel network
system must use the same address and the cipher text router must
distinguish between traffic for them based on SPI or the presence
of encryption.
Control plane signaling using this additional path is described in
Section 3.2. The information flow between the plain text and cipher
text domains includes
o IP datagrams via the encrypt/decrypt unit,
o RSVP signaling via the bypass path,
o Control information coordinating security associations, and
o precious little else.
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2. Reservation and Preemption in a nested VPN
/ \
( +--+ +--+ enclave ) ,---------.
.----------. \ |H2+---+R2| / ,-' `
+--+ +--+`--.\ +--+ ++-+ / / +--+ +--+
|H1+---+R1| \`. | ,' / |R3+---+H3|
+--+ +-++ ) '--. +----++ _.-' ( ++-+ +--+
| / _.`---|VPN2||''-. \ |
enclave +----+-i.--'' +----++ `----.\ +----+ enclave
--------|VPN1|' | ``|VPN3| ,
,+----+ | +----+------'
,' --+-------+----------+------------------+---`.
,' ++-+ `.
,' |R7+--------+ `.
/ interface +--+ | \
domain 1 +-+--+ \
_.--------|VPN7|--------.
,-----'' +--+-+ `------. .
`-. ,-' | `-. .-'
`-: inner domain +-++ `.'
( |R9| )
.'. ++-+ ;-.
.' `-. | ,-' `-.
' `------. +-+--+ _.-----' `
interface `---------|VPN8|-------''
domain 2 +-+--+ /
\ | +--+ /
`. +----------+R8| ,'
`. ++-+ ,'
`. --+------------------+-----------+------+-- ,'
,-----+----+ | +----+------.
,' |VPN6|. | _.|VPN4| `
+----+.`----. +----+ _.--'' ,+----+
| \ `--=.-|VPN5|---:' / |
+--+ ++-+ : ,-'' +----+ `--. ; ++-+ +--+
|H6+---+R6| | ,' | `.| |R4+---+H4|
+--+ +--+ ;/ +--+ ++-+ : +--+ +--+
// |H5+---+R5| \
enclave ,'( +--+ +--+ `. enclave
`. ,' \ enclave / '-. ,
`-------' \ / `-------'
Figure 5: Reservations in a nested VPN
Let us discuss how a resource reservation protocol, and specifically
RSVP, might be used in a nested virtual private network.
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2.1. Reservation in a nested VPN
A reservation in a nest VPN is very much like a reservation in any
other network, with one exception: it is composed of multiple
reservations that must be coordinated. These include a reservation
within the originating and receiving enclaves and a reservation at
each layer of the VPN, as shown in Figure 5.
Thus, when a host in one enclave opens a reservation to a host in
another enclave, a reservation of the appropriate type and size is
created end to end. As it traverses the VPN Router leaving its
enclave, the reservation information and the data are placed within
the appropriate tunnel (e. g., the IPsec Security Association for its
precedence level to the appropriate remote VPN Router). At the
remote VPN Router, it is extracted from the tunnel and passed on its
way to the target system. The data in the enclave will be marked
with a DSCP appropriate to its application and (if there is a
difference) precedence level, and the signaling datagrams (PATH and
RESV) are marked with a DCLASS object indicating that value. RSVP
signaling datagrams (PATH and RESV) are marked with a DCLASS object
indicating the value used for the corresponding data. The DSCP on
the signaling datagrams, however, is a DSCP for signaling, and has
the one provision that if routing varies by DSCP then it must be a
DSCP that is routed the same way as the relevant data. The [RFC2872]
policy object specifies the applicable policy (e. g., "routine
service for voice traffic") and asserts a [RFC3182] credential
indicating its user (which may be a person or a class of persons).
As specified in [RFC3181] it also specifies its Preemption Priority
and its Defending Priority; these enable the Preemption Priority of a
new session to be compared with the Defending Priority of previously
admitted sessions.
On the cipher text side of the VPN Router, no guarantees result
unless the VPN Router likewise sets up a reservation to the peer VPN
Router across the cipher text domain. Thus, the VPN Router sets up
an [RFC2207] [I-D.ietf-tsvwg-rsvp-ipsec] or [RFC3175] reservation to
its peer.
The Session Object defined by [RFC2207] or
[I-D.ietf-tsvwg-rsvp-ipsec] contains a field called a "virtual
destination port", which allows the multiplexing of many reservations
over a common security association, and in the latter case, a common
DSCP value. Thus, the voice traffic at every precedence level might
use the EF DSCP and service as described in [RFC3246], but the
reservations would be for "the aggregate of voice sessions at
precedence Pn between these VPN Routers". This would allow the
network administration to describe policies with multiple thresholds,
such as "a new session at precedence Pn may be accepted if the total
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reserved bandwidth does not exceed threshold Qn; if it is necessary
and sufficient to accept the reservation, existing reservations at
lower precedences may be preemptively reduced to make acceptance of
the new session possible."
In the [RFC3175] case, since the DSCP must be used to identify both
the reservation and the corresponding data stream, the aggregate
reservations for different precedence levels require different DSCP
values.
In either case, the fundamental necessity is for one VPN Router to
act as what [RFC3175] calls the "aggregator" and another to act as
the "deaggregator", and extend a VPN tunnel between them. If the VPN
Tunnel is an IPsec Security Association between the VPN Routers and
the IP packet is entirely contained within (such as is used to cross
a firewall), then the behavior of [RFC2746] is required of the
tunnel. That bearer will have the following characteristics:
o it will have a DSCP corollary or the same as the DSCP for the data
it carries,
o the reservations and data will be carried in security associations
between the VPN Routers, and
o the specification for the reservation for the tunnel itself will
not be less than the sum of the requirements of the aggregated
reservations.
The following requirements relationships apply between the set of
enclosed reservations and the tunnel reservation:
o The sum of the average rates of the contained reservations, having
been adjusted for the additional IP headers, will be less than or
equal to the average rate of the tunnel reservation.
o The sum of the peak rates of the contained reservations, having
been adjusted for the additional IP headers, will be less than or
equal to the peak rate of the tunnel reservation.
o The sum of the burst sizes of the contained reservations, having
been adjusted for the additional IP headers, will be less than or
equal to the burst size of the tunnel reservation.
o The Preemption Priority of a tunnel reservation is identical to
that of the individual reservations it aggregates.
o The Defending Priority of a tunnel reservation is identical to
that of the individual reservations it aggregates.
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This would differ only in the case that measurement-based admission
is in use in the tunnel but not in the end system. In that case, the
tunnel's average bandwidth specification would be greater than or
equal to the actual average offered traffic. Such systems are beyond
the scope of this specification.
As a policy matter, it may be useful to note a quirk in the way
Internet QoS works. If the policies for various precedence levels
specify different thresholds (e. g., "to accept a new routine call,
the total reserved bandwidth after admission may not exceed X; to
accept a higher precedence level call, the total reserved bandwidth
after admission may not exceed X+Y, and this may be achieved by
preempting a lower precedence level call"), the bandwidth Y
effectively comes from the bandwidth in use by elastic traffic rather
than forcing a preemption event.
2.2. Preemption in a nested VPN
As discussed in Section 1.3 preemption is specified in [RFC3181] and
further addressed in [RFC4495]. The issue is that in many cases the
need is to reduce the bandwidth of a reservation due to a change in
the network, not simply to remove the reservation. In the case of an
end system originated reservation, the end system might be able to
accommodate the need through a change of codec; in the case of an
aggregate of some kind, it could reduce the bandwidth it is sending
by dropping one or more reservations entirely.
In a nested VPN or other kind of aggregated reservation, this means
that the deaggregator (the VPN Router initiating the RESV signal for
the tunnel) must
o receive the RESV Error signaling it to reduce its bandwidth,
o re-issue its RESV accordingly,
o identify one or more of its aggregated reservations, enough to do
the job, and
o signal them to reduce their bandwidth accordingly.
It is possible, of course, that it is signaling them to reduce their
bandwidth to zero, which is functionally equivalent to removing the
reservation as described in [RFC3181].
In the routers in the core, an additional case arises. One could
imagine that some enclave presents the VPN with a single session, and
that session has a higher precedence level. If some interior link is
congested (e. g., the reserved bandwidth will exceed policy if the
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call is admitted), a session between a different pair of VPN Routers
must be preempted. More generally, in selecting a reservation to
preempt, the core router must always select a reservation at the
lowest available Defending Priority. This is the reason that various
precedence levels must be kept separate in the core.
2.3. Working through an example
The network in Figure 5 shows three security layers: six plain text
enclaves around the periphery, two cipher text domains connecting
them at one layer (referred to in the diagram as an "interface
domain"), and a third cipher text domain connecting the first two
(referred to in the diagram as an "inner domain"). The following
distribution of information exists:
o Each enclave has access to general routing information concerning
other enclaves it is authorized to communicate with: systems in it
can translate a DNS name for a remote host or domain and obtain
the corresponding address or prefix.
o Each enclave router also has specific routing information
regarding its own enclave.
o A default route is distributed within the enclave, pointing to its
VPN Router.
o VPN Routers 1-6 are able to translate remote enclave prefixes to
the appropriate remote enclave's VPN Router addresses.
o Each interface domain has access to general routing information
concerning the other interface domains, but not the enclaves.
Systems in an interface domain can translate a DNS name for a
remote interface domain and obtain the corresponding address or
prefix.
o Each interface domain router also has specific routing information
regarding its own interface domain.
o A default route is distributed within the interface domain,
pointing to the "inner" VPN Router.
o VPN Routers 7 and 8 are able to translate remote interface domain
prefixes to remote VPN Router addresses.
o Routers in the inner domain have routing information for that
domain only.
While the example shows three levels, there is nothing magic about
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the number three. The model can be extended to any number of
concentric layers.
Note that this example places unidirectional reservations in the
forward direction. In voice and video applications, one generally
has a reservation in each direction. The reverse direction is not
discussed, for the sake of clarity, but operates in the same way in
the reverse direction and uses the same security associations.
2.3.1. Initial routine reservations - generating network state
Now let us install a set of reservations from H1 to H4, H2 to H5, and
H3 to H6, and for the sake of argument let us presume that these are
at the "routine" precedence. H1, H2, and H3 each initiate an PATH
signal describing their traffic. For the sake of argument, let us
presume that H1's reservation is for an [RFC2205] session, H2's
reservation is for a session encrypted using IPsec, and therefore
depends on [RFC2207] and H3 (which is a PSTN Gateway) sends an
[RFC3175] reservation comprising a number of distinct sessions.
Since these are going to H4, H5, and H6 respectively, the default
route leads them to VPN1, VPN2, and VPN3 respectively.
The VPN Routers each ensure that they have an appropriate security
association or tunnel open to the indicated remote VPN Router (VPN4,
VPN5, or VPN6). This will be a security association or tunnel for
the indicated application at the indicated precedence level. Having
accomplished that, it will place the PATH signal into the security
association and forward it. If such does not already exist,
following [RFC3175] 's aggregation model, it will now open a
reservation (send a PATH signal) for the tunnel/SA within the
interface domain; if the reservation does exist, the VPN Router will
increase the bandwidth indicated in the ADSPEC appropriately. In
this example, these tunnel/SA reservations will follow the default
route to VPN7.
VPN7 ensures that it has an appropriate security association or
tunnel open to VPN8. This will be a security association or tunnel
for the indicated application at the indicated precedence level.
Having accomplished that, it will place the PATH signal into the
security association and forward it. If such does not already exist,
following [RFC3175] 's aggregation model, it will now open a
reservation (send a PATH signal) for the tunnel/SA within the
interface domain; if the reservation does exist, the VPN Router will
increase the bandwidth indicated in the ADSPEC appropriately. In
this example, this tunnel/SA reservation is forwarded to VPN8.
VPN8 acts as an [RFC3175] deaggregator for the inner domain. This
means that it receives the PATH signal for the inner domain
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reservation and stores state, decrypts the data stream from VPN7,
operates on the RSVP signals as an RSVP-configured router, and
forwards the received IP datagrams (including the updated PATH
signals) into its interface domain. The PATH signals originated by
VPN1, VPN2, and VPN3 are therefore forwarded towards VPN4, VPN5, and
VPN6 according to the routing of the interface domain.
VPN4, VPN5, and VPN6 each act as an [RFC3175] deaggregator for the
interface domain. This means that it receives the PATH signal for
the interface domain reservation and stores state, decrypts the data
stream from its peer, operates on the RSVP signals as an RSVP-
configured router, and forwards the received IP datagrams (including
the updated PATH signals) into its enclave. The PATH signals
originated by H1, H2, and H3 are therefore forwarded towards H4, H5,
and H6 according to the routing of the enclave.
H4, H5, and H6 now receive the original PATH signals and deliver them
to their application.
2.3.2. Initial routine reservations - request reservation
The application in H4, H5, and H6 decides to install the indicated
reservations, meaning that they now reply with RESV signals. These
signals request the bandwidth reservation. Following the trail left
by the PATH signals, the RESV signals traipse back to their
respective sources. The state left by the PATH signals leads them to
VPN4, VPN5, and VPN6 respectively. If the routers in the enclaves
are configured for RSVP, this will be explicitly via R4, R5, or R6;
if they are not, routing will lead them through those routers.
The various RSVP-configured routers en route in the enclave
(including the VPN Router on the "enclave" side) will verify that
there is sufficient bandwidth on their links and that any other
stated policy is also met. Having accomplished that, each will
update its reservation state and forward the RESV signal to the next.
The VPN Routers will also each generate an RESV for the reservation
within the interface domain, attempting to set or increase the
bandwidth of the reservation appropriately.
The various RSVP-configured routers en route in the interface domain
(including VPN8) will verify that there is sufficient bandwidth on
their links and that any other stated policy is also met. Having
accomplished that, each will update its reservation state and forward
the RESV signal to the next. VPN8 will also generate an RESV for the
reservation within the inner domain, attempting to set or increase
the bandwidth of the reservation appropriately. This gets the
reservation to the inner deaggregator, VPN8.
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The various RSVP-configured routers en route in the inner domain
(including VPN7) will verify that there is sufficient bandwidth on
their links and that any other stated policy is also met. Having
accomplished that, each will update its reservation state and forward
the RESV signal to the next. This gets the signal to VPN7.
VPN7 acts as an [RFC3175] aggregator for the inner domain. This
means that it receives the RESV signal for the inner domain
reservation and stores state, decrypts the data stream from VPN8,
operates on the RSVP signals as an RSVP-configured router, and
forwards the received IP datagrams (including the updated RESV
signals) into its interface domain. The RESV signals originated by
VPN4, VPN5, and VPN6 are therefore forwarded towards VPN1, VPN2, and
VPN3 through the interface domain.
VPN1, VPN2, and VPN3 each act as an [RFC3175] aggregator for the
interface domain. This means that it receives the RESV signal for
the interface domain reservation and stores state, decrypts the data
stream from its peer, operates on the RSVP signals as an RSVP-
configured router, and forwards the received IP datagrams (including
the updated RESV signals) into its enclave. The RESV signals
originated by H4, H5, and H6 are therefore forwarded towards H1, H2,
and H3 according to the routing of the enclave.
H1, H2, and H3 now receive the original RESV signals and deliver them
to their application.
2.3.3. Installation of a reservation using precedence
Without going through the details called out in Section 2.3.1 and
Section 2.3.2 if sufficient bandwidth exists to support them,
reservations of other precedence levels or other applications may
also be installed across this network. If the "routine" reservations
already described are for voice, for example, and sufficient
bandwidth is available under the relevant policy, a reservation for
voice at the "priority" precedence level might be installed. Due to
the mechanics of preemption, however, this would not expand the
existing "routine" reservations in the interface and inner domains,
as doing this causes loss of information - how much of the
reservation is now "routine" and how much is "priority"? Rather,
this new reservation will open up a separate set of tunnels or
security associations for traffic of its application class at its
precedence between that aggregator and deaggregator.
As a side note, there is an opportunity here that does not exist in
the PSTN. In the PSTN, all circuits are potentially usable by any
PSTN application under a certain set of rules (H channels, such as
are used by video streams, must be contiguous and ordered). As such,
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if a channel is not made available to routine traffic but is made
available to priority traffic, the operator is potentially losing
revenue on the reserved bandwidth and deserves remuneration.
However, in the IP Internet, some bandwidth must be kept for basic
functions such as routing, and in general policies will not permit
100% of the bandwidth on an interface to be allocated to one
application at one precedence. As a result, it may be acceptable to
permit a certain portion (e. g. 50%) to be used by routine voice and
a larger amount (e. g. 60%) to be used by voice at a higher
precedence level. Under such a policy, a higher precedence
reservation for voice might not result in the preemption of a routine
call, but rather impact elastic traffic, and might be accepted at a
time that a new reservation of lower precedence might be denied.
In microwave networks, such as satellite or mobile ad hoc, one could
also imagine network management intervention that could change the
characteristics of the radio signal to increase the bandwidth under
some appropriate policy.
2.3.4. Installation of a reservation using preemption
So we now have a number of reservations across the network described
in Figure 5 including several reservations at "routine" precedence
and one at "priority" precedence. For sake of argument, let us
presume that the link from VPN7 to R9 is now fully utilized - all of
the bandwidth allocated by policy to voice at the routine or priority
level has been reserved. Let us further imagine that a new
"priority" reservation is now placed from H3 to H6.
The process described in Section 2.3.1 is followed, resulting in PATH
state across the network for the new reservation. This is installed
even though it is not possible to install a new reservation on
VPN7-R9, as it does not install any reservation and the network does
not know whether H6 will ultimately require a reservation.
The process described in Section 2.3.2 is also followed. The
application in H6 decides to install the indicated reservation,
meaning that it now replies with an RESV signal. Following the trail
left by the PATH signal, the RESV signal traipses back towards H3.
VPN6 and (if RSVP was configured) R6 verify that there is sufficient
bandwidth on their links and that any other stated policy is also
met. Having accomplished that, each will update its reservation
state and forward the RESV signal to the next. VPN6 also generates
an RESV for the reservation within the interface domain, attempting
to set or increase the bandwidth of the reservation appropriately.
VPN6, R8, and VPN8's "interface domain" side now verify that there is
sufficient bandwidth on their links and that any other stated policy
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is also met. Having accomplished that, each will update its
reservation state and forward the RESV signal to the next. VPN8 will
also generate an RESV for the reservation within the inner domain,
attempting to set or increase the bandwidth of the reservation
appropriately. This gets the reservation to the inner deaggregator,
VPN8.
VPN8's "inner domain" side and R9 now verify that there is sufficient
bandwidth on their links and that any other stated policy is also
met. At R9, a problem is detected - there is not sufficient
bandwidth under the relevant policy. In the absence of precedence,
R9 would now return an RESV Error indicating that the reservation
could not be increased or installed. In such a case, if a pre-
existing reservation of lower bandwidth already existed, the previous
reservation would remain in place but the new bandwidth would not be
granted, and the originator (H6) would be informed. Let us clarify
what it means to be at a stated precedence: it means that the
POLICY_DATA object in the RESV contains a Preemption Priority and a
Defending Priority with values specified in some memo. With
precedence, [RFC4495]'s algorithm would have the Preemption Priority
of the new reservation compared to the Defending Priority of extant
reservations in the router, of which there are two: one VPN7->VPN8 at
"routine" precedence and one VPN7->VPN8 at "priority" precedence.
Since the Defending Priority of routine reservation is less than the
Preemption Priority of a "priority" reservation, the "routine"
reservation is selected. R9 determines that it will accept the
increase in its "priority" reservation VPN7->VPN8 and reduce the
corresponding "routine" reservation. Two processes now occur in
parallel:
o The routine reservation is reduced following the algorithms in
[RFC4495] and
o The priority reservation continues according to the usual rules.
R9 reduces its "routine" reservation by sending an RESV Error
updating its internal state to reflect the reduced reservation and
sending an RESV Error to VPN8 requesting that it reduce its
reservation to a number less than or equal to the relevant threshold
less the sum of the competing reservations. VPN8, acting as a de-
aggregator, makes two changes. On the "inner domain" side, it marks
its reservation down to the indicated rate (the most it is now
permitted to reserve), so that if an RESV Refresh event happens it
will request the specified rate. On the "interface domain" side it
selects one or more of the relevant reservations by an algorithm of
its choosing and requests that it likewise reduce its rate. For sake
of argument, let us imagine that the selected reservation is the one
to VPN5. The RESV Error now makes its way through R8 to VPN5, which
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similarly reduces its bandwidth request to the stated amount and
passes a RESV Error signal on the "enclave" side requesting that the
reservation be appropriately reduced.
H5 is now faced with a decision. If the request is to reduce its
reservation to zero, that is equivalent to tearing down the
reservation. In this simple case, it sends an RESV Tear to tear down
the reservation entirely and advises its application to adjust its
expectations of the session accordingly, which may mean shutting down
the session. If the request is to reduce it below a certain value,
however, it may be possible for the application to do so and remain
viable. For example, if a VoIP application using a G. 711 codec (80
KBPS) is asked to reduce its bandwidth below 70 KBPS, it may be
possible to renegotiate the codec in use to G. 729 or some other
codec. In such a case, the originating application should re-reserve
at the stated bandwidth (in this case, 70 KBPS), initiate the
application level change, and let the application change the
reservation again (perhaps to 60 KBPS) when it has completed that
process.
For the "priority" reservation, at the same time, R9 believes that it
has sufficient bandwidth and that any other stated policy is also
met, it forwards the RESV to VPN7. Each will update its reservation
state and forward the RESV signal to the next. VPN7 now acts as an
[RFC3175] aggregator for the inner domain. This means that it
receives the RESV signal for the inner domain reservation and stores
state, decrypts the data stream from VPN8, operates on the RSVP
signals as an RSVP-configured router, and forwards the received IP
datagrams (including the updated RESV signals) into its interface
domain. The RESV signals originated by VPN4, VPN5, and VPN6 are
therefore forwarded towards VPN1, VPN2, and VPN3 through the
interface domain.
VPN3 now acts as an [RFC3175] aggregator for the interface domain.
This means that it receives the RESV signal for the interface domain
reservation and stores state, decrypts the data stream from its peer,
operates on the RSVP signals as an RSVP-configured router, and
forwards the received IP datagrams (including the updated RESV
signals) into its enclave. The RESV signal originated by H6 is
therefore forwarded towards H3 according to the routing of the
enclave.
H3 now receives the original RESV signals and deliver it to the
relevant application.
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3. Data flows within a VPN Router
This section details the data flows within a VPN Router, in the
context of sessions as described in Section 2.
3.1. VPN Routers that carry data across the cryptographic boundary
3.1.1. Plaintext to Ciphertext Data Flows
+-----------------------+ +----------------------+
| +--------------------+| |+--------------------+|
| |RSVP || ||Aggregate RSVP ||
| | || || ||
| |Per session: || ID ||Agg. Session ||
| | Destination ||--->|| Agg. Destination ||
| | Source || || Agg. Source= self ||
| | potential SPI || || Agg. SPI generated||
| | DSCP ---------> DSCP ||
| | vPort or protocol---------> vPort ||
| | and port || || ||
| | Mean rate ---------> Sum of mean rates ||
| | Peak rate ---------> f(Peak rates) ||
| | Burst Size ---------> Sum of Burst sizes||
| | || || ||
| +--------------------+| |+--------------------+|
| +--------------------+| |+--------------------+|
| | IP || || IP ||
| +--------------------+| |+--------------------+|
| +--------------------+| |+--------------------+|
| | Plain text Interface|| ||Cipher text Interface||
| +--------------------+| |+--------------------+|
+-----------------------+ +----------------------+
Figure 6: Data Flows in a VPN Router Outbound
Parameters on a reservation include:
Destination Address: On the plain text side, the VPN Router
participates in the end to end reservations being installed for
plain text sessions. These may include individual flows as
described in [RFC2205] IPsec data flows [RFC2207] aggregate
reservations [RFC3175] or other types. It passes an identifier
for the cipher text side of the deaggregator to its cipher text
unit.
DSCP: The DSCP of the plain text data flow is provided to the cipher
text side.
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Virtual Port: The virtual destination port is provided to the cipher
text side. This may be derived from an [RFC2207] session object
or from policy information.
Mean Rate: The sum of the plain text mean rates is provided to the
cipher text unit.
Peak Rate: A function of the plain text peak rates is provided to
the cipher text unit. This function is less than or equal to the
sum of the peak rates.
Burst Size: The sum of the burst sizes is provided to the cipher
text unit.
Messages include:
Path: The Plain text PATH message is sent as encrypted data to the
cipher text unit. In parallel, a trigger needs to be sent to the
cipher text unit that results in it generating the corresponding
aggregated PATH message for the cipher text side.
Path Error: This indicates that a PATH message sent to the remote
enclave was in error. In the error case, the message itself is
sent on as encrypted data, but a signal is sent to the cipher text
side in case the error affects the cipher text reservation (such
as removing or changing state).
Path Tear: The PATH Tear message is sent as encrypted data to the
cipher text unit. In parallel, a signal is sent to the cipher
text side which will trigger a Path Tear on its reservation in the
event that this is the last aggregated session, or change the
SENDER_TSPEC of the aggregated session.
RESV: The Plain text RESV message is sent as encrypted data to the
cipher text unit. In parallel, a trigger needs to be sent to the
cipher text unit that results in it generating the corresponding
aggregated RESV message for the cipher text side.
RESV Error: This indicates that a RESV message received as data and
forwarded into the enclave was in error or needed to be preempted
as described in [RFC3181] or [RFC4495]. In the error case, the
message itself is sent on as encrypted data, but a signal is sent
to the cipher text side in case the error affects the cipher text
reservation (such as removing or changing state).
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RESV Tear: The RESV Tear message is sent as encrypted data to the
cipher text unit. In parallel, a signal is sent to the cipher
text side which will trigger a RESV Tear on its reservation in the
event that this is the last aggregated session, or reduce the
bandwidth of an existing reservation.
RESV Confirm: This indicates that a RESV message received as data
and forwarded into the enclave, and is now being confirmed. This
message is sent as encrypted data to the cipher text side, and in
parallel a signal is sent to potentially trigger an RESV Confirm
on the aggregate reservation.
3.1.2. Ciphertext to Plaintext Data Flows
+-----------------------+ +----------------------+
| +--------------------+| |+--------------------+|
| |RSVP || ||Aggregate RSVP ||
| | || || terminated ||
| |Per session: |+ || ||
| | Destination || || ||
| | Source <---------Decrypted RSVP ||
| | potential SPI || || message sent to ||
| | DSCP || || Plain text unit ||
| | vPort or protocol || || *as data* for ||
| | and port || || normal processing ||
| | Mean rate || || ||
| | Peak rate || || ||
| | Burst Size || || ||
| | || || ||
| +--------------------+| |+--------------------+|
| +--------------------+| |+--------------------+|
| | IP || || IP ||
| +--------------------+| |+--------------------+|
| +--------------------+| |+--------------------+|
| |Plain text Interface|| ||Cipher text Interface||
| +--------------------+| |+--------------------+|
+-----------------------+ +----------------------+
Figure 7: Data Flows in a VPN Router Inbound
The aggregate reservation is terminated by the cipher text side of
the VPN Router. The RSVP messages related to the subsidiary sessions
are carried in the encrypted tunnel as data, and therefore arrive at
the plain text side with other data. As the plain text side
participates in these reservations, some information is returned to
the cipher text size to parameterize the aggregate reservation as
described in Section 3.1.1 in the processing of the outbound
messages.
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3.2. VPN Routers that use the Network Guard for signaling across the
cryptographic boundary
As described in Section 1.4 the Network Guard provides an additional
path for the reservation signaling between the plain text and cipher
text domains.
_.------------.
,--'' Plain text Domain--.
,-' +--------+ +--------+ `-.
,' | Host | | Host | `.
,' +--------+ +--------+ `.
; :
| +----------------------+ |
: | +--------+ | |
`. | | Router | | ,'
`. | +---+----+ | ,'
`- | +----------+ | ,'
---| +-+--+ +-+--+--+ |'
|----|E/D |--|Net Grd| | VPN Router
,-'| +-+--+ +-+--+--+ |\
, | +----------+ | \
,' | +---+----+ | `.
,' | | Router | | |
/ | +--------+ | \
; +----------------------+ :
| |
: Cipher text Domain ;
Figure 8: RSVP passage via Network Guard
In this context, the VPN Router is composed of a plaintext router, a
ciphertext router, an encrypt/decrypt implementation (such as a line
card or interface device) and a network management process that
manages the encrypt/decrypt implementation and potentially passes
defined information flows between the plaintext and ciphertext
domains. If the Network Guard is implemented as software process
that exchanges configuration instructions between the routers, this
is simple to understand. If it is built as separate systems
exchanging datagrams, it is somewhat more complex, but conceptually
equivalent. For example, the ciphertext router would consider an IP
datagram received via the Network Guard (control plane) as having
been received from and concerning the interface used in the data
plane to the encrypt/decrypt unit.
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3.2.1. Signaling Flow
Encrypt/Decrypt units may not be capable of terminating and
originating flows as described in Section 3.1, and policy may prevent
knowledge of the cipher text network addresses in the plain text
router. In such a case the plain text and cipher text routers may
use the Network Guard as the path for the signaling flows. The
Network Guard performs the following functions to enable the flow of
reservation signaling across the cryptographic domain
o Transform plain text session identifiers into cipher text session
identifiers and vice-versa in IP datagrams and RSVP objects (e.g.
IP addresses)
o Resource management of aggregated reservations (e.g. including
cipher text encapsulation overhead to resources requested)
o Read and write configuration on the Encrypt/Decrypt units as
necessary (e.g. read plain text to cipher text IP address mapping)
In addition the plain text and cipher text routers must support a
routing function or local interface which ensures that aggregated
RSVP messages flow via the Network Guard. The signaling flow across
the entire VPN Router at cryptographic boundary however remains
identical to the description in Section 3.1.
A reader may note that the VPN Router described in Figure 8 can be
collapsed into a single router with two halves or the Network Guard
and the Encrypt/Decrypt units can be part of the plain text router.
The details of alternate logical and physical architectures for the
VPN router are beyond the scope of this document.
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3.2.2. Use case with Network Guard
........................................
: VPN Router A :
: :
:+-----------++----------++-----------+:
+------+ RSVP :| || NetGrd-A || |:
|Host-A|<---->:|PT-Router-A|+----------+|CT-Router-A|::::::::
+------+ :| || E/D-A || |: ::
:+-----------++----------++-----------+: ::
: A-RSVP : ::
: <:::::::::::::> : ::
:......................................: ::
A-RSVP ::
,---.
,' `.
/ \
; Interface :
| Domain |
: ;
\ /
`. ,'
'---'
A-RSVP ::
........................................ ::
: VPN Router B : ::
: : ::
:+-----------++----------++-----------+: ::
+------+ RSVP :| || NetGrd-B || |: ::
|Host-B|<---->:|PT-Router-B|+----------+|CT-Router-B|::::::::
+------+ :| || E/D-B || |:
:+-----------++----------++-----------+:
: A-RSVP :
: <:::::::::::::> :
:......................................:
Figure 9: Aggregated RSVP via Network Guard
The above figure depicts a simple use case for aggregated signaling
with the Network Guard. In this scenario, Host A initiates RSVP
signaling to Host B for a reservation. The RSVP signaling between
the hosts is encapsulated by the VPN Router Instances into encrypted
tunnels. Aggregated RSVP signaling is triggered by VPN Router
Instances, and flows into the CT-Routers as well as the interface
domains to reserve resources at RSVP capable routers on the path.
The aggregation/deaggregation point for RSVP reservations in this use
case are the PT-Routers. The signaling aggregation of RSVP into
A-RSVP at the PT-Router is similar to the data flow described in
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Section 3.1. The Network Guard performs the additional functions
described in Section 3.2.1 to transform plaintext A-RSVP messages
into suitable ciphertext A-RSVP messages. A typical reservation set
up in this case would follow these steps
o Host-A sends RSVP PATH message to Host B
o PT-Router-A encapsulates RSVP PATH message in encrypted tunnel to
VPN Router Instance B
o CT Routers and Interface domain carry encrypted RSVP PATH message
(like any other encrypted data message)
o PT-Router-B decrypts RSVP Path Message and sends an E2E PathErr
message to PT-Router-A in the encrypted tunnel.
o PT-Router-B forwards decrypted plaintext RSVP PATH message to
Host-B.
o PT-Router-A receives E2E PathErr and sends an aggregated RSVP PATH
message towards PT-Router-B via the Network Guard.
o The NetGrd-A transforms the plaintext aggregate RSVP into the
ciphertext aggregate RSVP message as described in Section 3.2.1
and sends it to the CT-Router-A.
o The ciphertext aggregated RSVP message travels through ciphertext
routers in the interface domain.
o CT-Router-B receives the ciphertext aggregate RSVP message and
sends it to the NetGrd-B.
o The NetGrd-B transforms the ciphertext aggregate RSVP into the
plaintext aggregate RSVP message as described in Section 3.2.1 and
sends it to the PT-Router-B.
The subsequent RSVP and Aggregate RSVP signaling follows a similar
flow, as described in detail in [RFC3175] and
[I-D.ietf-tsvwg-rsvp-ipsec]to aggregate each plaintext reservation
into a corresponding ciphertext reservation. This ensures that RSVP
capable ciphertext routers reserve the required resources for a
plaintext end to end reservation. Subsequent mechanisms such as
preemption or the increase and decrease of resources reserved may be
applied to these reservations as described before in this document.
The RSVP data flow as described in Section 3.1 within the VPN router
(from the plaintext router to the ciphertext router via the Guard)
provides necessary and sufficient information to routers in the
ciphertext domain to implement the QoS solution presented in the
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document.
In this description, we have described the Network Guard as being
separate from the Encrypt/Decrypt unit. This separation exists
because in certain implementations it is mandated by those who
specify the devices. The separation does not come for free, however;
the separation of the devices for system engineering purposes is
expensive, and it imposes architectural problems. For example, when
the Guard is used to aggregate RSVP messages or PIM routing, the
traffic is destined to the remote VPN Router. This means that the
Guard must somehow receive and respond to, on behalf of the VPN
Router, messages that are not directed to it. There are several
possible solutions:
o The two devices could use a common MAC and IP address, so that
traffic destined to one is also received by the other
o The ciphertext interface of the Guard could be placed into
promiscuous mode, allowing it to receive all messages and discard
all but the few it is interested in.
o The Guard could be engineered to receive all from the ciphertext
router and pass the bulk of it on to the VPN Router through
another interface. In this case, the Guard and the VPN Router
would use the same IP address.
o The VPN Router could be engineered to receive all traffic from the
ciphertext router and pass any unencrypted traffic it receives to
the Guard through another interface. In this case, the Guard and
the VPN Router would use the same IP address.
o All the VPN router functions as shown in Figure 9 could be
incorporated into a single chassis, with appropriate internal
traffic management to send some traffic into the plaintext enclave
and some to the Guard. In this case, the Guard and the VPN Router
would at least functionally be the same system.
Of these, clearly the last is the simplest architecturally and the
one which most minimizes the attendant risk.
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4. IANA Considerations
This document makes no request of the IANA.
Note to RFC Editor: in the process assigning numbers and building
IANA registries prior to publication, this section will have served
its purpose. It may therefore be removed upon publication as an RFC.
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5. Security Considerations
The typical security concerns of datagram integrity, node and user
authentication are implicitly met by the security association that
exists between the VPN Routers. The secure data stream which flows
between the VPN Routers is also used for the reservation signaling
datagrams flowing between VPN Routers. Information that is contained
in these signaling datagrams receives the same level of encryption
that is received by the data streams.
One of the reasons cited for the nesting of VPN routes in Section 1.1
are the different levels of security across the nested VPN Routers.
If the security level decreases from one VPN Router to the next VPN
Router in the nested path, the reservation signaling datagrams will
by default receive the lower security level treatment. For most
cases, the lower security treatment is acceptable. In certain
networks, however, the reservation signaling across the entire nested
path must receive the highest security level treatment (e. g.
encryption, authentication of signaling nodes). For example the
highest precedence level may only be signaled to VPN Routers which
can provide the highest security levels. If any VPN Router in the
nested path is incapable of providing the highest security level, it
cannot participate in the reservation mechanism.
In the general case, the nested path may contain routers which are
either incapable of participating in VPNs or providing required
security levels. These routers can participate in the reservation
only if the lower security level is acceptable (as configured by
policy) for the signaling of reservation datagrams.
VPN Routers encapsulate encrypted IP packets and prepend an extra
header on each packet. These packets, whether used for signaling or
data, should be identifiable, at a minimum by the IP addresses and
DSCP value. The prepended header, therefore, should contain at a
minimum the DSCP value corresponding to the signaled reservation in
each packet. This may literally be the same DSCP as is used for the
data (forcing control plane traffic to receive the same QoS treatment
as its data), or a different DSCP that is routed identically
(separating control and data plane traffic QoS but not routing).
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6. Acknowledgements
Doug Marquis, James Polk, Mike Tibodeau, Pete Babendreier, Roger
Levesque, and Subha Dhesikan gave early review comments.
Comments by Sean O'Keefe, Tony De Simone, Julie Tarr, Chris Christou
and their associates resulted in Section 3.2.
Francois Le Faucheur, Bruce Davie, and Chris Christou (with Pratik
Bose) added [I-D.ietf-tsvwg-rsvp-ipsec], which clarified the
interaction of this approach with the DSCP.
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7. References
7.1. Normative References
[I-D.ietf-tsvwg-rsvp-ipsec] Faucheur, F., "Generic Aggregate RSVP
Reservations",
draft-ietf-tsvwg-rsvp-ipsec-01 (work in
progress), June 2006.
[RFC2205] Braden, B., Zhang, L., Berson, S.,
Herzog, S., and S. Jamin, "Resource
ReSerVation Protocol (RSVP) -- Version 1
Functional Specification", RFC 2205,
September 1997.
[RFC2207] Berger, L. and T. O'Malley, "RSVP
Extensions for IPSEC Data Flows",
RFC 2207, September 1997.
[RFC2746] Terzis, A., Krawczyk, J., Wroclawski,
J., and L. Zhang, "RSVP Operation Over
IP Tunnels", RFC 2746, January 2000.
[RFC2750] Herzog, S., "RSVP Extensions for Policy
Control", RFC 2750, January 2000.
[RFC2996] Bernet, Y., "Format of the RSVP DCLASS
Object", RFC 2996, November 2000.
[RFC3175] Baker, F., Iturralde, C., Le Faucheur,
F., and B. Davie, "Aggregation of RSVP
for IPv4 and IPv6 Reservations",
RFC 3175, September 2001.
[RFC4495] Polk, J. and S. Dhesikan, "A Resource
Reservation Protocol (RSVP) Extension
for the Reduction of Bandwidth of a
Reservation Flow", RFC 4495, May 2006.
[RFC4542] Baker, F. and J. Polk, "Implementing an
Emergency Telecommunications Service
(ETS) for Real-Time Services in the
Internet Protocol Suite", RFC 4542,
May 2006.
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7.2. Informative References
[ITU.MLPP.1990] International Telecommunications Union, "Multilevel
Precedence and Preemption Service", ITU-
T Recommendation I.255.3, 1990.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC1633] Braden, B., Clark, D., and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview",
RFC 1633, June 1994.
[RFC2209] Braden, B. and L. Zhang, "Resource ReSerVation
Protocol (RSVP) -- Version 1 Message Processing
Rules", RFC 2209, September 1997.
[RFC2210] Wroclawski, J., "The Use of RSVP with IETF
Integrated Services", RFC 2210, September 1997.
[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for
the Internet Protocol", RFC 2401, November 1998.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol,
Version 6 (IPv6) Specification", RFC 2460,
December 1998.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang,
Z., and W. Weiss, "An Architecture for
Differentiated Services", RFC 2475, December 1998.
[RFC2747] Baker, F., Lindell, B., and M. Talwar, "RSVP
Cryptographic Authentication", RFC 2747,
January 2000.
[RFC2872] Bernet, Y. and R. Pabbati, "Application and Sub
Application Identity Policy Element for Use with
RSVP", RFC 2872, June 2000.
[RFC3097] Braden, R. and L. Zhang, "RSVP Cryptographic
Authentication -- Updated Message Type Value",
RFC 3097, April 2001.
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[RFC3181] Herzog, S., "Signaled Preemption Priority Policy
Element", RFC 3181, October 2001.
[RFC3182] Yadav, S., Yavatkar, R., Pabbati, R., Ford, P.,
Moore, T., Herzog, S., and R. Hess, "Identity
Representation for RSVP", RFC 3182, October 2001.
[RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le
Boudec, J., Courtney, W., Davari, S., Firoiu, V.,
and D. Stiliadis, "An Expedited Forwarding PHB (Per-
Hop Behavior)", RFC 3246, March 2002.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G.,
Johnston, A., Peterson, J., Sparks, R., Handley, M.,
and E. Schooler, "SIP: Session Initiation Protocol",
RFC 3261, June 2002.
[RFC3312] Camarillo, G., Marshall, W., and J. Rosenberg,
"Integration of Resource Management and Session
Initiation Protocol (SIP)", RFC 3312, October 2002.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions",
RFC 3473, January 2003.
[RFC3474] Lin, Z. and D. Pendarakis, "Documentation of IANA
assignments for Generalized MultiProtocol Label
Switching (GMPLS) Resource Reservation Protocol -
Traffic Engineering (RSVP-TE) Usage and Extensions
for Automatically Switched Optical Network (ASON)",
RFC 3474, March 2003.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
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Authors' Addresses
Fred Baker
Cisco Systems
1121 Via Del Rey
Santa Barbara, California 93117
USA
Phone: +1-408-526-4257
Fax: +1-413-473-2403
EMail: fred@cisco.com
Pratik Bose
Lockheed Martin
700 North Frederick Ave
Gaithersburg, Maryland 20871
USA
Phone: +1-301-240-7041
Fax: +1-301-240-5748
EMail: pratik.bose@lmco.com
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Full Copyright Statement
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Funding for the RFC Editor function is provided by the IETF
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RFC-2629 XML format.
Baker & Bose Expires March 30, 2007 [Page 39]
