Internet DRAFT - draft-trammell-plus-statefulness
draft-trammell-plus-statefulness
Network Working Group M. Kuehlewind
Internet-Draft B. Trammell
Intended status: Informational ETH Zurich
Expires: May 17, 2018 J. Hildebrand
November 13, 2017
Transport-Independent Path Layer State Management
draft-trammell-plus-statefulness-04
Abstract
This document describes a simple state machine for stateful network
devices on a path between two endpoints to associate state with
traffic traversing them on a per-flow basis, as well as abstract
signaling mechanisms for driving the state machine. This state
machine is intended to replace the de-facto use of the TCP state
machine or incomplete forms thereof by stateful network devices in a
transport-independent way, while still allowing for fast state
timeout of non-established or undesirable flows.
Status of This Memo
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This Internet-Draft will expire on May 17, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. State Machine . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Uniflow States . . . . . . . . . . . . . . . . . . . . . 7
3.2. Biflow States . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Additional States and Actions . . . . . . . . . . . . . . 8
4. Abstract Signaling Mechanisms . . . . . . . . . . . . . . . . 8
4.1. Flow Identification . . . . . . . . . . . . . . . . . . . 9
4.2. Association and Confirmation Signaling . . . . . . . . . 9
4.2.1. Start-of-flow versus continual signaling . . . . . . 10
4.3. Bidirectional Stop Signaling . . . . . . . . . . . . . . 11
4.3.1. Authenticated Stop Signaling . . . . . . . . . . . . 12
4.4. Separate Utility . . . . . . . . . . . . . . . . . . . . 12
5. Deployment Considerations . . . . . . . . . . . . . . . . . . 12
5.1. Middlebox Deployment . . . . . . . . . . . . . . . . . . 12
5.2. Endpoint Deployment . . . . . . . . . . . . . . . . . . . 13
6. Signal mappings for transport protocols . . . . . . . . . . . 13
6.1. Signal mapping for TCP . . . . . . . . . . . . . . . . . 13
6.2. Signal mapping for QUIC . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
The boundary between the network and transport layers was originally
defined to be that between information used (and potentially
modified) hop-by-hop, and that used end-to-end. End-to-end
information in the transport layer is associated with state at the
endpoints, but processing of network-layer information was assumed to
be stateless.
The widespread deployment of stateful middleboxes in the Internet,
such as network address and port translators (NAPT), firewalls that
model the TCP state machine to distinguish packets belonging from
desirable flows from backscatter and random attack traffic, and
devices which keep per-flow state for reporting and monitoring
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purposes (e.g. IPFIX [RFC7011] Metering Processes), has broken this
assumption, and made it more difficult to deploy non-TCP transport
protocols in the Internet.
The deployment of new transport protocols encapsulated in UDP with
encrypted transport headers (such as QUIC [I-D.ietf-quic-transport])
will present a challenge to the operation of these devices, and their
ubquity likewise threatens to impair the deployability of these
protocols. There are two main causes for this problem: first,
stateful devices often use an internal model of the TCP state machine
to determine when TCP flows start and end, allowing them to manage
state for these flows; for UDP flows, they must rely on timeouts.
These timeouts are generally short relative to those for TCP
[IMC-GATEWAYS], requiring UDP- encapsulated transports either to
generate unproductive keepalive traffic for long-lived sessions, or
to tolerate connectivity problems and the necessity of reconnection
due to loss of on-path state.
This document presents an abstract solution to this problem by
defining a transport-independent state machine to be implemented at
per-flow state- keeping middleboxes as a replacement for incomplete
TCP state modeling. A key concept behind this approach is that
encryption of transport protocol headers allows a transport protocol
to separate its wire image - what it looks like to devices on path -
from its internal semantics. We advocate the creation of a minimal
wire image for these protocols that exposes enough information to
drive the state machine presented. Present and future evolution of
encrypted transport protocols can then happen behind this wire image,
and Middleboxes implementing this state machine can use signals from
a UDP encapsulation common to a set of encrypted transport protocols
can have equivalent state information to that provided by TCP,
reducing the friction between deployed middleboxes and these new
transport protocols.
2. Terminology
In this document, the term "flow" is defined to be compatible with
the definition given in [RFC7011]: A flow is defined as a set of
packets passing a device on the network during a certain time
interval. All packets belonging to a particular Flow have a set of
common properties. Each property is defined as the result of
applying a function to the values of:
1. one or more network layer header fields (e.g., destination IP
address) or transport layer header fields (e.g., destination port
number) that the device has access to;
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2. one or more characteristics of the packet itself (e.g., number of
MPLS labels, etc.);
3. one or more of the fields derived from packet treatment at the
device (e.g., next-hop IP address, the output interface, etc.).
A packet is defined as belonging to a flow if it completely satisfies
all the defined properties of the flow.
A bidirectional flow or biflow is defined as compatible with
[RFC5103], by joining the "forward direction" flow with the "reverse
direction" flow, derived by reversing the direction of directional
fields (ports and IP addresses). Biflows are only relevant at
devices positioned so as to see all the packets in both directions of
the biflow, generally on the endpoint side of the service demarcation
point for either endpoint as defined in the reference path given in
[RFC7398].
3. State Machine
A transport-independent state machine for on-path devices is shown in
Figure 1. It was designed to have the following properties:
o A device on path that can see traffic in both directions between
two endpoints knows that each side of an association wishes that
association to continue. This allows firewalls to delegate policy
decisions about accepting or continuing an association to the
servers they protect.
o A device on path that can see traffic in both directions between
two endpoints knows that each device can receive traffic at the
source address it provides. This allows firewalls to provide
protection against trivially spoofed packets.
Both of these properties hold with current firewalls and network
address translation devices observing the flags and sequence/
acknowledgment numbers exposed by TCP.
It relies on six states, three configurable timeouts, and a set of
signals defined in Section 4. The states are defined as follows:
o zero: there is no state for a given flow at the device
o uniflow: at least one packet has been seen in one direction
o associating: at least one packet has been seen in one direction,
and an indication that the receiving endpoint wishes to continue
the association has been seen in the other direction.
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o associated: a flow in associating state has further demonstrated
that the initial sender can receive packets at its given source
address.
o stop-wait: one side of a connection has sent an explicit stop
signal, waiting for confirmation
o stopping: stop signal confirmed, association is stopping.
We refer to the zero and uniflow states as "uniflow states", as they
are relevant both for truly unidirectional flows, as well as in
situations where an on-path device can see only one side of a
communication. We refer to the remaining four states as "biflow
states", as they are only applicable to true bidirectional flows,
where the on-path device can see both sides of the communication.
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`- - - - - - - - - - - - - - - - - - - - - - - - - - - -'
` +============+ a->b +============+ '
` / \--------->/ \<-+ '
+--->( zero ) ( uniflow ) | a->b '
^ ` \ /<---------\ /--+ '
| ` +============+ TO_IDLE +============+ '
| `- - - - - - - - - - or - | association - - - - -'
| stop signal V signal
| +============+
| TO_IDLE / \
+<-----------------------( associating )
| \ /
| +============+
| | confirmation
| V signal
| +============+
| TO_ASSOCIATED / \<-+
+<-----------------------( associated ) | any packet
| \ /--+
| +============+
| | stop
| V signal
| +============+
| TO_ASSOCIATED / \<-+
+<-----------------( stop-wait ) | any packet
| \ /--+
| +============+
| | stop confirmation
| V signal
| +============+
| TO_STOP / \<-+
+------------( stopping ) | any packet
\ /--+
+============+
Figure 1: Transport-Independent State Machine for Stateful On-Path
Devices
The three timeouts are defined as follows:
o TO_IDLE, the unidirectional idle timeout, can be considered
equivalent to the idle timeout for transport protocols where the
device has no information about session start and end (e.g. most
UDP protocols).
o TO_ASSOCIATED, the bidirectional idle timeout, can be considered
equivalent to the timeout for transport protocols where the device
has information about session start and end (e.g. TCP).
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o TO_STOP is the teardown timeout: how long the device will account
additional packets to a flow after confirming a close signal,
ensuring retransmitted and/or reordered close signal don't lead to
the spurious creation of new flow state.
Selection of timeouts is a configuration and implementation detail,
but generally TO_STOP <= TO_IDLE << TO_ASSOCIATED; see [IMC-GATEWAYS]
for an analysis of the magnitudes of these timeouts in presently
deployed gateway devices.
3.1. Uniflow States
Every packet received by a device keeping per-flow state must
associate that packet with a flow (see Section 4.1). When a device
receives a packet associated with a flow it has no state for, and it
is configured to forward the packet instead of dropping it, it moves
that flow from the zero state into the uniflow state and starts a
timer TO_IDLE. It resets this timer for any additional packet it
forwards in the same direction as long as the flow remains in the
uniflow state. When timer TO_IDLE expires on a flow in the uniflow
state, the device drops state for the flow and performs any
processing associated with doing so: tearing down NAT bindings,
stopping associated firewall pinholes, exporting flow information,
and so on. The device may also drop state on a stop signal, if
observed.
Some devices will only see one side of a communication, e.g. if they
are placed in a portion of a network with asymmetric routing. These
devices use only the zero and uniflow states (as marked in Figure 1.)
In addition, true uniflows - protocols which are solely
unidirectional (e.g. some applications over UDP) - will also use only
the uniflow-only states. In either case, current devices generally
don't associate much state with observed uniflows, and an idle
timeout is generally sufficient to expire this state.
3.2. Biflow States
A uniflow transitions to the associating state when the device
observes an association signal, and further to the associated state
when the device observes a subsequent confirmation signal; see
Section 4.2 for details. If the flow has not transitioned to from
the associating to the associated state after TO_IDLE, the device
drops state for the flow.
After transitioning to the associated state, the device starts a
timer TO_ASSOCIATED. It resets this timer for any packet it forwards
in either direction. The associated state represents a fully
established bidirectional communication. When timer TO_ASSOCIATED
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expires, the device assumes that the flow has shut down without
signaling as such, and drops state for the flow, performing any
associated processing. When a bidirectional stop signal (see
Section 4.3) is confirmed, the flow transitions to the stopping
state.
When a flow enters the stopping state, it starts a timer TO_STOP.
While the stop signal should be the last packet on a flow, the
TO_STOP timer ensures that reordered packets after the stop signal
will be accounted to the flow. When this timer expires, the device
drops state for the flow, performing any associated processing.
3.3. Additional States and Actions
This document is concerned only with states and transitions common to
transport- and function- independent state maintenance. Devices may
augment the transitions in this state diagram depending on their
function. For example, a firewall that decides based on some
information beyond the signals used by this state machine to shut
down a flow may transition it directly to a blacklist state on
shutdown. Or, a firewall may fail to forward additional packets in
the uniflow state until an association signal is observed.
4. Abstract Signaling Mechanisms
The state machine in Section 3 requires four signals: a new flow
signal, the first packet observed in a flow in the zero state; an
association signal, allowing a device to verify that an endpoint
wishes a bidirectional communication to be established or to
continue; a confirmation signal, allowing a device to confirm that
the initiator of a flow is reachable at its purported source address;
and a stop signal, noting that an endpoint wishes to stop a
bidirectional communication. Additional related signals may also be
useful, depending on the function a device provides. There are a few
different ways to implement these signals; here, we explore the
properties of some potential implementations.
We assume the following general requirements for these signals;
parallel to those given in [draft-trammell-plus-abstract-mech]:
o At least the endpoints can verify the integrity of the signals
exposed, and shut down a transport association when that
verification fails, in order to reduce the incentive for on-path
devices to attempt to spoof these signals.
o Endpoints and devices on path can probabilistically verify that a
originator of a signal is on-path.
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4.1. Flow Identification
In order to keep per-flow state, each device using this state machine
must have a function it can apply to each packet to be able to
extract common properties to identify the flow it is associated with.
In general, the set of properties used for flow identification on
presently deployed devices includes the source and destination IP
address, the source and destination transport layer port number, the
transport protocol number. The differentiated services field
[RFC2474] may also be included in the set of properties defining a
flow, since it may indicate different forwarding treatment.
However, other protocols may use additional bits in their own headers
for flow identification. In any case, a protocol implementing
signaling for this state machine must specify the function used for
flow identification.
4.2. Association and Confirmation Signaling
An association signal indicates that the endpoint that received the
first packet seen by the device has indeed seen that packet, and is
interested in continuing conversation with the sending endpoint.
This signal is roughly an in-band analogue to consent signaling in
ICE [RFC7675] that is carried to every device along the path.
A confirmation signal indicates that the endpoint that sent the first
packet seen by the device is reachable at its purported source
address, and is necessary to prevent spoofed or reflected packets
from driving the state machine into the associated state. It is
roughly equivalent to the final ACK in the TCP three-way handshake.
These two signals are related to each other, in that association
requires the receiving endpoint of the first packet to prove it has
seen that packet (or a subsequent packet), and to acknowledge it
wants to continue the association; while confirmation requires the
sending endpoint to prove it has seen the association token.
Transport-independent, path-verifiable association and confirmation
signaling can be implemented using three values carried in the packet
headers: an association token, a confirmation nonce, and an echo
token.
The association token is a cryptographically random value generated
by the endpoint initiating a connection, and is carried on packets in
the uniflow state. When a receiving endpoint wishes to send an
association signal, it generates an echo token from the association
token using a well-known, defined function (e.g. a truncated SHA-256
hash), and generates a cryptographically random confirmation nonce.
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The initiating endpoint sends a confirmation signal on the next
packet it sends after receiving the confirmation nonce, by applying a
function to the echo token and the confirmation nonce, and sending
the result as a new association token.
Devices on path verify that the echo token corresponds to a
previously seen association token to recognize an association signal,
and recognize that an association token corresponds to a previously
seen echo token and confirmation nonce to recognize an association
signal.
If the association token and confirmation nonce are predictable, off-
path devices can spoof association and confirmation signals. In
choosing the number of bits for an association token, there is a
tradeoff between per-packet overhead and state overhead at on-path
devices, and assurance that an association token is hard to guess.
This tradeoff must be evaluated at protocol design time.
There are a few considerations in choosing a function (or functions)
to generate the echo token from the association token, to verify an
echo token given an association token, and to derive a next
association token from the echo token and confirmation nonce. The
functions could be extremely simple (e.g., identity for the echo
token and addition for the nonce) for ease of implementation even in
extremely constrained environments. Using one-way functions (e.g.,
truncated SHA-256 hash to derive echo token from association token;
XOR followed by truncated SHA-256 hash to derive association token
from echo token and confirmation nonce) requires slightly more work
from on-path devices, but the primitives will be available at any
endpoint using an encrypted transport protocol. In any case, a
concrete implementation of association and confirmation signaling
must choose a set of functions, or mechanism for unambiguously
choosing one, at both endpoints as well as along the path.
4.2.1. Start-of-flow versus continual signaling
There are two possible points in the design space here: these signals
could be continually exposed throughout the flow, or could be exposed
only on the first few packets of a connection (those corresponding to
the cryptographic and/or transport state handshakes in the overlying
protocols).
In the former case, an on-path device could re-establish state in the
middle of a flow; e.g. due to a reboot of the device, due to a NAT
association change without the endpoints' knowledge, or due to idle
periods longer than the TO_ESTABLISHED timeout value. The on-path
device would receive no special information about which packets were
associated with the start of association. In this case, the series
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of exposed association tokens, echo tokens, and confirmation nonces
can also be observed to derive a running round-trip time estimate for
the flow.
In the latter case, an on-path device would need to observe the start
of the flow to establish state, and would be able to distinguish
connection-start packets from other packets.
4.3. Bidirectional Stop Signaling
The transport-independent state machine uses bidirectional stop
signaling to tear down state. This requires a stop signal to be
observed in one direction, and a stop confirmation signal to be
observed in the other, to complete tearing down an association.
A stop signal is directly carried or otherwise encoded in the
protocol header to indicate that a flow is ending, whether normally
or abnormally, and that state associated with the flow should be torn
down. Upon decoding a stop signal, a device on path should move the
flow from uniflow state to zero, or from associated state to stop-
wait state, to wait for a confirmation signal in the other direction.
While in stop-wait state, state will be maintained until a timer set
to TO_ASSOCIATED expires, with any packet forwarded in either
direction reseting the timer.
A stop confirmation signal is directly carried or otherwise encoded
in the protocol header to indicate that the endpoint receiving the
stop signal confirms that the stop signal is valid. The stop
confirmation signal contains some assurance that the far endpoint has
seen the stop signal. When a stop confirmation signal is observed in
the opposite direction from the stop signal, a device on path should
move the flow from stop-wait state to stopping state. The flow will
then remain in stopping state until a timer set to TO_STOP has
expired, after which state for the flow will be dropped. The
stopping timeout TO_STOP is intended to ensure that any packets
reordered in delivery are accounted to the flow before state for it
is dropped.
We assume the encoding of stop and stop confirmation signals into a
packet header, as with all other signals, is integrity protected end-
to-end. Stop signals, as association signals, could be forged by a
single on-path device. However, unless a stop confirmation signal
that can be associated with the stop signal is observed in the other
direction, the flow remains in stop-wait state, during which state is
maintained and packets continue to be forwarded in both directions.
So this attack is of limited utility; an attacker wishing to inject
state teardown would need to control at least one on-path device on
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each side of a target device to spoof both stop and corresponding
stop confirmation signals.
4.3.1. Authenticated Stop Signaling
Additionally, the stop and stop confirmation signals could be
designed to authenticate themselves. Each endpoint could reveal a
stop hash during the initial association, which is the result of a
chosen cryptographic hash function applied to a stop token which that
endpoint keeps secret. An endpoint wishing to end the association
then reveals the stop token, which can be verified both by the far
endpoint and devices on path which have cached the stop hash to be
authentic. A stop confirmation signal additionally contains
information derived from the initiating stop signal's stop token, as
further assurance that the stop token was observed by the far
endpoint.
4.4. Separate Utility
Although all of these signals are required to drive the state machine
described by this document, note that association/confirmation and
bidirectional stop signaling have separate utility. A transport
protocol may expose the end of a flow without any proof of
association or confirmation of return routability of the initiator.
Alternately, the transport protocol could rely on short timeouts to
clean up stale state on path, while exposing continuous association
and confirmation signals to quickly reestablish state.
5. Deployment Considerations
The state machine defined in this document is most useful when
implemented in a single instantiation (wire format for signals, and
selection of functions for deriving values to be exposed and
verified) by multiple transport protocols. It is intended for use
with protocols that encrypt their transport- layer headers, and that
are encapsulated within UDP, as is the case with QUIC
[I-D.ietf-quic-transport]. Definition of that instantiation is out
of scope for the present revision of this document.
The following subsections discuss incentives for deployment of this
state machine both at middleboxes and at endpoints.
5.1. Middlebox Deployment
The state machine defined herein is designed to replace TCP state-
tracking for firewalls and NAT devices. When encrypted transport
protocols encapsulated in UDP adopt a set of signals and a wire
format for those signals to drive this state machine, these
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middleboxes could continue using TCP-like logic to handle those UDP
flows. Recognizing the wire format used by those signals would allow
these middleboxes to distinguish "UDP with an encrypted transport"
from undifferentiated UDP, and to treat the former case more like
TCP, providing longer timeouts for established flows, as well as
stateful defense against spoofed or reflected garbage traffic.
5.2. Endpoint Deployment
An encrypted, UDP-encapsulated transport protocol has two primary
incentives to expose these signals. First, allowing firewalls on
networks that generally block UDP (about 3-5% of Internet-connected
networks, depending on the study) to distinguish "UDP with an
encrypted transport" traffic from other UDP traffic may result in
less blocking of that traffic. Second, the difference between the
timeouts TO_IDLE and TO_ASSOCIATED, as well as the continuous state
establishment possible with some instantiations of the association
and confirmation signals, would allow these transport protocols to
send less unproductive keepalive traffic for long-lived, sparse
flows.
While both of these advantages require middleboxes on path to
recognize and use the signals driving this state machine, we note
that content providers driving the deployment of this protocols are
also operators of their own content provision networks, and that many
of the benefits of encrypted- encapsulated transport firewalls will
accrue to them, giving these content providers incentives to deploy
both endpoints and middleboxes.
6. Signal mappings for transport protocols
We now show how this state machine can be driven by signals available
in TCP and QUIC.
6.1. Signal mapping for TCP
A mapping of TCP flags to transitions in to the state machine in
Section 3 shows how devices currently using a model of the TCP state
machine can be converted to use this state machine.
TCP [RFC0793] provides start-of-flow association only. A packet with
the SYN and ACK flags set in the absence of the FIN or RST flags, and
an in-window acknowledgment number, is synonymous with the
association signal. A packet with the ACK flag set in the absence of
the FIN or RST flags after an initial SYN, and an in-window
acknowledgment number, is synonymous with the confirmation signal.
For a typical TCP flow:
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1. The initial SYN places the flow into uniflow state,
2. The SYN-ACK sent in reply acts as a association signal and places
the flow into associating state,
3. The ACK sent in reply acts as a confirmation signal and places
the flow into associated state,
4. The final FIN is a stop signal, and
5. the ACK of the final FIN is a stop confirmation signal, moving
the flow into stopping state.
Note that abormally closed flows (with RST) do not provide stop
confirmation, and are therefore not provided for by this state
machine. Due to TCP's support for half-closed flows, additional
state modeling is necessary to extract a stop signal from the final
FIN.
Note also that the association and stop signals derived from the TCP
header are not integrity protected, and association and confirmation
signals based on in-window ACK are not particularly resistant to off-
path attacks [IMC-TCP]. The state machine is therefore more
susceptible to manipulation when used with vanilla TCP as when with a
transport protocol providing full integrity protection for its
headers end-to-end.
6.2. Signal mapping for QUIC
QUIC [I-D.ietf-quic-transport] is a moving target; however, signals
for driving this state machine are fundamentally compatible with the
protocol's design and could easily be added to the protocol
specification.
Specifically, QUIC's handshake is visible to on-path devices, as it
begins with an unencrypted version negotiation which exposes a 64-bit
connection ID, which can serve as an association and echo token as in
Section 4.2. The function of the confirmation nonce is not fully
exposed to the path at this point, but could be implemented by
exposing information from the proof of source address ownership
(section 7.4 of [I-D.ietf-quic-transport]) or via echoing the random
initial packet number (as suggested by https://github.com/quicwg/
base-drafts/pull/391).
The addition of a public reset signal that would act as a stop signal
as in Section 4.3 is presently under discussion within the QUIC
working group; the proposal for self-authenticating public reset at
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https://github.com/quicwg/base-drafts/pull/20 inspired the addition
of Section 4.3.1 to this document.
7. IANA Considerations
This document has no actions for IANA.
8. Security Considerations
This document defines a state machine for transport-independent state
management on middleboxes, using in-band signaling, to replace the
commonly- implemented current practice of incomplete TCP state
modeling on these devices. It defines new signals for state
management. While these signals can be spoofed by any device on path
that observes traffic in both directions, we presume the presence of
end-to-end integrity protection of these signals provided by the
upper-layer transport driving them. This allows such spoofing to be
detected and countered by endpoints, reducing the threat from on-path
devices to connection disruption, which such devices are trivially
placed to perform in any case.
9. Acknowledgments
Thanks to Christian Huitema for discussions leading to this document,
and to Andrew Yourtchenko for the feedback. The mechanism for using
a revealed value to prove ownership of a stop token was inspired by
Eric Rescorla's suggestion to use a fundamentally identical mechanism
for the QUIC public reset.
This work is partially supported by the European Commission under
Horizon 2020 grant agreement no. 688421 Measurement and Architecture
for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
for Education, Research, and Innovation under contract no. 15.0268.
This support does not imply endorsement.
10. References
10.1. Normative References
[RFC5103] Trammell, B. and E. Boschi, "Bidirectional Flow Export
Using IP Flow Information Export (IPFIX)", RFC 5103,
DOI 10.17487/RFC5103, January 2008,
<https://www.rfc-editor.org/info/rfc5103>.
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[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[RFC7398] Bagnulo, M., Burbridge, T., Crawford, S., Eardley, P., and
A. Morton, "A Reference Path and Measurement Points for
Large-Scale Measurement of Broadband Performance",
RFC 7398, DOI 10.17487/RFC7398, February 2015,
<https://www.rfc-editor.org/info/rfc7398>.
10.2. Informative References
[draft-trammell-plus-abstract-mech]
Trammell, B., "Abstract Mechanisms for a Cooperative Path
Layer under Endpoint Control", September 2016.
[I-D.hardie-path-signals]
Hardie, T., "Path signals", draft-hardie-path-signals-01
(work in progress), May 2017.
[I-D.ietf-quic-tls]
Thomson, M. and S. Turner, "Using Transport Layer Security
(TLS) to Secure QUIC", draft-ietf-quic-tls-07 (work in
progress), October 2017.
[I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-07 (work
in progress), October 2017.
[IMC-GATEWAYS]
Hatonen, S., Nyrhinen, A., Eggert, L., Strowes, S.,
Sarolahti, P., and M. Kojo, "An experimental study of home
gateway characteristics (Proc. ACM IMC 2010)", October
2010.
[IMC-TCP] Luckie, M., Beverly, R., Wu, T., Allman, M., and k.
claffy, "Resilience of Deployed TCP to Blind Attacks.
(Proc. ACM IMC 2015)", October 2015.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
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[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,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC7675] Perumal, M., Wing, D., Ravindranath, R., Reddy, T., and M.
Thomson, "Session Traversal Utilities for NAT (STUN) Usage
for Consent Freshness", RFC 7675, DOI 10.17487/RFC7675,
October 2015, <https://www.rfc-editor.org/info/rfc7675>.
Authors' Addresses
Mirja Kuehlewind
ETH Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Email: mirja.kuehlewind@tik.ee.ethz.ch
Brian Trammell
ETH Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Email: ietf@trammell.ch
Joe Hildebrand
Email: hildjj@cursive.net
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