Internet DRAFT - draft-hopps-ipsecme-iptfs
draft-hopps-ipsecme-iptfs
Network Working Group C. Hopps
Internet-Draft LabN Consulting, L.L.C.
Intended status: Standards Track June 5, 2019
Expires: December 7, 2019
IP Traffic Flow Security
draft-hopps-ipsecme-iptfs-01
Abstract
This document describes a mechanism to enhance IPsec traffic flow
security by adding traffic flow confidentiality to encrypted IP
encapsulated traffic. Traffic flow confidentiality is provided by
obscuring the size and frequency of IP traffic using a fixed-sized,
constant-send-rate IPsec tunnel. The solution allows for congestion
control as well.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 7, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology & Concepts . . . . . . . . . . . . . . . . . 3
2. The IP-TFS Tunnel . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Tunnel Content . . . . . . . . . . . . . . . . . . . . . 4
2.2. IPTFS_PROTOCOL Payload Content . . . . . . . . . . . . . 4
2.2.1. Data Blocks . . . . . . . . . . . . . . . . . . . . . 5
2.2.2. No Implicit Padding Required . . . . . . . . . . . . 6
2.2.3. Empty Payload . . . . . . . . . . . . . . . . . . . . 6
2.2.4. IP Header Value Mapping . . . . . . . . . . . . . . . 6
2.3. Exclusive SA Use . . . . . . . . . . . . . . . . . . . . 7
2.4. Initiating IP-TFS Operation On The SA. . . . . . . . . . 7
2.5. Modes of Operation . . . . . . . . . . . . . . . . . . . 7
2.5.1. Non-Congestion Controlled Mode . . . . . . . . . . . 7
2.5.2. Congestion Controlled Mode . . . . . . . . . . . . . 8
3. Congestion Information . . . . . . . . . . . . . . . . . . . 9
3.1. ECN Support . . . . . . . . . . . . . . . . . . . . . . . 10
4. Configuration . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Fixed Packet Size . . . . . . . . . . . . . . . . . . . . 10
4.3. Congestion Control . . . . . . . . . . . . . . . . . . . 11
5. IKEv2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. TFS Type Transform Type . . . . . . . . . . . . . . . . . 11
5.2. IPTFS_REQUIREMENTS Status Notification . . . . . . . . . 11
6. Packet and Data Formats . . . . . . . . . . . . . . . . . . . 12
6.1. ESP IP-TFS Payload . . . . . . . . . . . . . . . . . . . 12
6.1.1. Non-Congestion Control IPTFS_PROTOCOL Payload Format 12
6.1.2. Congestion Control IPTFS_PROTOCOL Payload Format . . 13
6.1.3. Data Blocks . . . . . . . . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7.1. IPTFS_PROTOCOL Type . . . . . . . . . . . . . . . . . . . 16
7.2. IKEv2 Transform Type TFS Type . . . . . . . . . . . . . . 16
7.3. TFS Type Transform IDs Registry . . . . . . . . . . . . . 17
7.4. IPTFS_REQUIREMENTS Notify Message Status Type . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Example Of An Encapsulated IP Packet Flow . . . . . 19
Appendix B. A Send and Loss Event Rate Calculation . . . . . . . 20
Appendix C. Comparisons of IP-TFS . . . . . . . . . . . . . . . 21
C.1. Comparing Overhead . . . . . . . . . . . . . . . . . . . 21
C.1.1. IP-TFS Overhead . . . . . . . . . . . . . . . . . . . 21
C.1.2. ESP with Padding Overhead . . . . . . . . . . . . . . 21
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C.2. Overhead Comparison . . . . . . . . . . . . . . . . . . . 22
C.3. Comparing Available Bandwidth . . . . . . . . . . . . . . 23
C.3.1. Ethernet . . . . . . . . . . . . . . . . . . . . . . 23
Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 25
Appendix E. Contributors . . . . . . . . . . . . . . . . . . . . 25
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
Traffic Analysis ([RFC4301], [AppCrypt]) is the act of extracting
information about data being sent through a network. While one may
directly obscure the data through the use of encryption [RFC4303],
the traffic pattern itself exposes information due to variations in
it's shape and timing ([I-D.iab-wire-image], [AppCrypt]). Hiding the
size and frequency of traffic is referred to as Traffic Flow
Confidentiality (TFC) per [RFC4303].
[RFC4303] provides for TFC by allowing padding to be added to
encrypted IP packets and allowing for transmission of all-pad packets
(indicated using protocol 59). This method has the major limitation
that it can significantly under-utilize the available bandwidth.
The IP-TFS solution provides for full TFC without the aforementioned
bandwidth limitation. To do this, we use a constant-send-rate IPsec
[RFC4303] tunnel with fixed-sized encapsulating packets; however,
these fixed-sized packets can contain partial, whole or multiple IP
packets to maximize the bandwidth of the tunnel.
For a comparison of the overhead of IP-TFS with the RFC4303
prescribed TFC solution see Appendix C.
Additionally, IP-TFS provides for dealing with network congestion
[RFC2914]. This is important for when the IP-TFS user is not in full
control of the domain through which the IP-TFS tunnel path flows.
1.1. Terminology & Concepts
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119] [RFC8174] when, and only when, they appear in all capitals,
as shown here.
This document assumes familiarity with IP security concepts described
in [RFC4301].
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2. The IP-TFS Tunnel
As mentioned in Section 1 IP-TFS utilizes an IPsec [RFC4303] tunnel
(SA) as it's transport. To provide for full TFC we send fixed-sized
encapsulating packets at a constant rate on the tunnel.
The primary input to the tunnel algorithm is the requested bandwidth
of the tunnel. Two values are then required to provide for this
bandwidth, the fixed size of the encapsulating packets, and rate at
which to send them.
The fixed packet size may either be specified manually or can be
determined through the use of Path MTU discovery [RFC1191] and
[RFC8201].
Given the encapsulating packet size and the requested tunnel
bandwidth, the corresponding packet send rate can be calculated. The
packet send rate is the requested bandwidth divided by the payload
size of the encapsulating packet.
The egress of the IP-TFS tunnel MUST allow for, and expect the
ingress (sending) side of the IP-TFS tunnel to vary the size and rate
of sent encapsulating packets, unless constrained by other policy.
2.1. Tunnel Content
As previously mentioned, one issue with the TFC padding solution in
[RFC4303] is the large amount of wasted bandwidth as only one IP
packet can be sent per encapsulating packet. In order to maximize
bandwidth IP-TFS breaks this one-to-one association.
With IP-TFS we aggregate as well as fragment the inner IP traffic
flow into fixed-sized encapsulating IPsec tunnel packets. We only
pad the tunnel packets if there is no data available to be sent at
the time of tunnel packet transmission, or if fragmentation has been
disabled by the receiver.
In order to do this we use a new Encapsulating Security Payload (ESP,
[RFC4303]) payload type which is the new IP protocol number
IPTFS_PROTOCOL (TBD1).
2.2. IPTFS_PROTOCOL Payload Content
The IPTFS_PROTOCOL ESP payload is comprised a 4 or 16 octet header
followed by either a partial, a full or multiple partial or full data
blocks. The following diagram illustrates the IPTFS_PROTOCOL ESP
payload within the ESP packet. See Section 6.1 for the exact formats
of the IPTFS_PROTOCOL payload.
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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. Outer Encapsulating Header ... .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. ESP Header... .
+---------------------------------------------------------------+
| ... : BlockOffset |
+---------------------------------------------------------------+
: [Optional Congestion Info] :
+---------------------------------------------------------------+
| DataBlocks ... ~
~ ~
~ |
+---------------------------------------------------------------|
. ESP Trailer... .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Figure 1: Layout of an IP-TFS IPsec Packet
The "BlockOffset" value is either zero or some offset into or past
the end of the "DataBlocks" data.
If the "BlockOffset" value is zero it means that the "DataBlocks"
data begins with a new data block.
Conversely, if the "BlockOffset" value is non-zero it points to the
start of the new data block, and the initial "DataBlocks" data
belongs to a previous data block that is still being re-assembled.
The "BlockOffset" can point past the end of the "DataBlocks" data
which indicates that the next data block occurs in a subsequent
encapsulating packet.
Having the "BlockOffset" always point at the next available data
block allows for quick recovery with minimal inner packet loss in the
presence of outer encapsulating packet loss.
An example IP-TFS packet flow can be found in Appendix A.
2.2.1. Data Blocks
+---------------------------------------------------------------+
| Type | rest of IPv4, IPv6 or pad.
+--------
Figure 2: Layout of IP-TFS data block
A data block is defined by a 4-bit type code followed by the data
block data. The type values have been carefully chosen to coincide
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with the IPv4/IPv6 version field values so that no per-data block
type overhead is required to encapsulate an IP packet. Likewise, the
length of the data block is extracted from the encapsulated IPv4 or
IPv6 packet's length field.
2.2.2. No Implicit Padding Required
It's worth noting that there is never a need for an implicit pad at
the end of an encapsulating packet. Even when the start of a data
block occurs near the end of a encapsulating packet such that there
is no room for the length field of the encapsulated header to be
included in the current encapsulating packet, the fact that the
length comes at a known location and is guaranteed to be present is
enough to fetch the length field from the subsequent encapsulating
packet payload. Only when there is no data to encapsulate is padding
required, and then an explicit "Pad Data Block" would be used to
identify the padding.
2.2.3. Empty Payload
In order to support reporting of congestion control information
(described later) on a non-IP-TFS enabled SA, IP-TFS allows for the
sending of an IP-TFS payload with no data blocks (i.e., the ESP
payload length is equal to the IP-TFS header length). This special
payload is called an empty payload.
2.2.4. IP Header Value Mapping
[RFC4301] provides some direction on when and how to map various
values from an inner IP header to the outer encapsulating header,
namely the Don't-Fragment (DF) bit ([RFC0791] and [RFC8200]), the
Differentiated Services (DS) field [RFC2474] and the Explicit
Congestion Notification (ECN) field [RFC3168]. Unlike [RFC4301] with
IP-TFS we may and often will be encapsulating more than 1 IP packet
per ESP packet. To deal with this we further restrict these
mappings. In particular we never map the inner DF bit as it is
unrelated to the IP-TFS tunnel functionality; we never IP fragment
the inner packets and the inner packets will not affect the
fragmentation of the outer encapsulation packets. Likewise, the ECN
value need not be mapped as any congestion related to the constant-
send-rate IP-TFS tunnel is unrelated (by design!) to the inner
traffic flow. Finally, by default the DS field SHOULD NOT be copied
although an implementation MAY choose to allow for configuration to
override this behavior. An implementation SHOULD also allow the DS
value to be set by configuration.
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2.3. Exclusive SA Use
It is not the intention of this specification to allow for mixed use
of an IP-TFS enabled SA. In other words, an SA that has IP-TFS
enabled is exclusively for IP-TFS use and MUST NOT have non-IP-TFS
payloads such as IP (IP protocol 4), TCP transport (IP protocol 6),
or ESP pad packets (protocol 59) intermixed with non-empty IP-TFS (IP
protocol TBD1) payloads. While it's possible to envision making the
algorithm work in the presence of sequence number skips in the IP-TFS
payload stream, the added complexity is not deemed worthwhile. Other
IPsec uses can configure and use their own SAs.
2.4. Initiating IP-TFS Operation On The SA.
While a user will normally configure their IPsec tunnel (SA) to
operate using IP-TFS to start, we also allow IP-TFS operation to be
enabled post-SA creation and use. This late-enabling may be useful
for debugging or other purposes. To support this late-enabled
operation the receiver switches to IP-TFS operation on receipt of the
first ESP payload with the IPTFS_PROTOCOL indicated as the payload
type which also contains a data block (i.e., a non-empty IP-TFS
payload). The the receipt of an empty IPTFS_PROTOCOL payload (i.e.,
one without any data blocks) is used to communicate congestion
control information from the receiver back to the sender on a non-IP-
TFS enabled SA, and MUST NOT cause IP-TFS to be enabled on that SA.
2.5. Modes of Operation
Just as with normal IPsec/ESP tunnels, IP-TFS tunnels are
unidirectional. Bidirectional IP-TFS functionality is achieved by
setting up 2 IP-TFS tunnels, one in either direction.
An IP-TFS tunnel can operate in 2 modes, a non-congestion controlled
mode and congestion controlled mode.
2.5.1. Non-Congestion Controlled Mode
In the non-congestion controlled mode IP-TFS sends fixed-sized
packets at a constant rate. The packet send rate is constant and is
not automatically adjusted regardless of any network congestion
(e.g., packet loss).
For similar reasons as given in [RFC7510] the non-congestion
controlled mode should only be used where the user has full
administrative control over the path the tunnel will take. This is
required so the user can guarantee the bandwidth and also be sure as
to not be negatively affecting network congestion [RFC2914]. In this
case packet loss should be reported to the administrator (e.g., via
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syslog, YANG notification, SNMP traps, etc) so that any failures due
to a lack of bandwidth can be corrected.
2.5.2. Congestion Controlled Mode
With the congestion controlled mode, IP-TFS adapts to network
congestion by lowering the packet send rate to accommodate the
congestion, as well as raising the rate when congestion subsides.
Since overhead is per packet, by allowing for maximal fixed-size
packets and varying the send rate we minimize transport overhead.
The output of the congestion control algorithm will adjust the rate
at which the ingress sends packets. While this document does not
require a specific congestion control algorithm, best current
practice RECOMMENDS that the algorithm conform to [RFC5348].
Congestion control principles are documented in [RFC2914] as well.
An example of an implementation of the [RFC5348] algorithm which
matches the requirements of IP-TFS (i.e., designed for fixed-size
packet and send rate varied based on congestion) is documented in
[RFC4342].
The required inputs for the TCP friendly rate control algorithm
described in [RFC5348] are the receivers loss event rate and the
senders estimated round-trip time (RTT). These values are provided
by IP-TFS using the congestion information header fields described in
Section 3. In particular these values are sufficient to implement
the algorithm described in [RFC5348].
At a minimum, the congestion information must be sent, from the
receiver as well as from the sender, at least once per RTT. Prior to
establishing an RTT the information SHOULD be sent constantly from
the sender and the receiver so that an RTT estimate can be
established. The lack of receiving this information over multiple
consecutive RTT intervals should be considered a congestion event
that causes the sender to adjust it's sending rate lower. For
example, [RFC4342] calls this the "no feedback timeout" and it is
equal to 4 RTT intervals. When a "no feedback timeout" has occurred
[RFC4342] halves the sending rate.
An implementation could choose to always include the congestion
information in it's IP-TFS payload header if sending on an IP-TFS
enabled SA. Since IP-TFS normally will operate with a large packet
size, the congestion information should represent a small portion of
the available tunnel bandwidth.
When an implementation is choosing a congestion control algorithm (or
a selection of algorithms) one should remember that IP-TFS is not
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providing for reliable delivery of IP traffic, and so per packet ACKs
are not required and are not provided.
It's worth noting that the variable send-rate of a congestion
controlled IP-TFS tunnel, is not private; however, this send-rate is
being driven by network congestion, and as long as the encapsulated
(inner) traffic flow shape and timing are not directly affecting the
(outer) network congestion, the variations in the tunnel rate will
not weaken the provided inner traffic flow confidentiality.
2.5.2.1. Circuit Breakers
In additional to congestion control, implementations MAY choose to
define and implement circuit breakers [RFC8084] as a recovery method
of last resort. Enabling circuit breakers is also a reason a user
may wish to enable congestion information reports even when using the
non-congestion controlled mode of operation. The definition of
circuit breakers are outside the scope of this document.
3. Congestion Information
In order to support the congestion control mode, the sender needs to
know the loss event rate and also be able to approximate the RTT
([RFC5348]). In order to obtain these values the receiver sends
congestion control information on it's SA back to the sender. Thus,
in order to support congestion control the receiver must have a
paired SA back to the sender (this is always the case when the tunnel
was created using IKEv2). If the SA back to the sender is a non-IP-
TFS enabled SA then an IPTFS_PROTOCOL empty payload (i.e., header
only) is used to convey the information.
In order to calculate a loss event rate compatible with [RFC5348],
the receiver needs to have a round-trip time estimate. Thus the
sender communicates this estimate in the "RTT" header field. On
startup this value will be zero as no RTT estimate is yet known.
In order to allow the sender to calculate the "RTT" value, the
receiver communicates the last sequence number it has seen to the
sender in the "LastSeqNum" header field. In addition to the
"LastSeqNum" value, the receiver sends an estimate of the amount of
time between receiving the "LastSeqNum" packet and transmitting the
"LastSeqNum" value back to the sender in the congestion information.
It places this time estimate in the "Delay" header field along with
the "LastSeqNum".
The receiver also calculates, and communicates in the "LossEventRate"
header field, the loss event rate for use by the sender. This is
slightly different from [RFC4342] which periodically sends all the
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loss interval data back to the sender so that it can do the
calculation. See Appendix B for a suggested way to calculate the
loss event rate value. Initially this value will be zero (indicating
no loss) until enough data has been collected by the receiver to
update it.
3.1. ECN Support
In additional to normal packet loss information IP-TFS supports use
of the ECN bits in the encapsulating IP header [RFC3168] for
identifying congestion. If ECN use is enabled and a packet arrives
at the egress endpoint with the Congestion Experienced (CE) value
set, then the receiver considers that packet as being dropped,
although it does not drop it. The receiver MUST set the E bit in any
IPTFS_PROTOCOL payload header containing a "LossEventRate" value
derived from a CE value being considered.
As noted in [RFC3168] the ECN bits are not protected by IPsec and
thus may constitute a covert channel. For this reason ECN use SHOULD
NOT be enabled by default.
4. Configuration
IP-TFS is meant to be deployable with a minimal amount of
configuration. All IP-TFS specific configuration should be able to
be specified at the unidirectional tunnel ingress (sending) side. It
is intended that non-IKEv2 operation is supported, at least, with
local static configuration.
4.1. Bandwidth
Bandwidth is a local configuration option. For non-congestion
controlled mode the bandwidth SHOULD be configured. For congestion
controlled mode one can configure the bandwidth or have no
configuration and let congestion control discover the maximum
bandwidth available. No standardized configuration method is
required.
4.2. Fixed Packet Size
The fixed packet size to be used for the tunnel encapsulation packets
can be configured manually or can be automatically determined using
Path MTU discovery (see [RFC1191] and [RFC8201]). No standardized
configuration method is required.
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4.3. Congestion Control
Congestion control is a local configuration option. No standardized
configuration method is required.
5. IKEv2
5.1. TFS Type Transform Type
When IP-TFS is used with IKEv2 a new "TFS Type" Transform Type (TBD2)
is used to negotiate (as defined in [RFC7296]) the possible operation
of IP-TFS on a child SA pair. This document defines 3 "TFS Type"
Transform IDs for the new "TFS Type" Transform Type: None (0),
TFS_IPTFS_CC (1) for congestion-controlled IP-TFS mode or
TFS_IPTFS_NOCC (2) for non-congestion controlled IP-TFS mode. The
selection of a proposal with a "TFS Type" Transform ID TFS_IPTFS_CC
or TFS_IPTFS_NOCC does not mandate the use of IP-TFS, rather it
indicates a willingness or intent to use IP-TFS on the SA pair. In
addition, a new Notify Message Status Type IPTFS_REQUIREMENTS (TBD3)
MAY be used by the initiator as well as the responder to further
refine any operational requirements.
Additional "TFS Type" Transform IDs may be defined in the future, and
so readers are referred to [IKEV2IANA] for the most up to date list.
5.2. IPTFS_REQUIREMENTS Status Notification
As mentioned in the previous section, a new Notify Message Status
Type IPTFS_REQUIREMENTS (TBD3) MAY be sent by the initiator and/or
the responder to further refine what will be supported. This
notification is sent during IKE_AUTH and new CREATE_CHILD_SA
exchanges; however, it MUST NOT be sent, and MUST be ignored, during
a CREATE_CHILD_SA rekeying exchange as the requirements are not
allowed to change during rekeying.
The IPTFS_REQUIREMENTS notification contains a 1 octet payload of
flags that specify any extra requirements from the sender of the
message. The flag values (currently a single flag) are defined
below. If the IPTFS_REQUIREMENTS notification is not sent then it
implies that all the flag bits are clear.
+-+-+-+-+-+-+-+-+
|0|0|0|0|0|0|0|D|
+-+-+-+-+-+-+-+-+
0:
MUST be zero on send and MUST be ignored on receive.
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D:
Don't Fragment bit, if set indicates the sender of the notify
message does not support receiving packet fragments (i.e., inner
packets MUST be sent using a single "Data Block"). This value
only applies to what the sender is capable of receiving; the
sender MAY still send packet fragments unless similarly restricted
by the receiver in it's IPTFS_REQUIREMENTS notification.
6. Packet and Data Formats
6.1. ESP IP-TFS Payload
An ESP IP-TFS payload is identified by the IP protocol number
IPTFS_PROTOCOL (TBD1). This payload begins with a fixed 4 or 16
octet header followed by a variable amount of "DataBlocks" data. The
exact payload format and fields are defined in the following
sections.
6.1.1. Non-Congestion Control IPTFS_PROTOCOL Payload Format
The non-congestion control IPTFS_PROTOCOL payload is comprised of a 4
octet header followed by a variable amount of "DataBlocks" data as
shown below.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V|C| Reserved | BlockOffset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DataBlocks ...
+-+-+-+-+-+-+-+-+-+-+-
V:
A 1 bit version field that MUST be set to zero. If received as
one the packet MUST be dropped.
C:
A 1 bit value that MUST be set to 0 to indicate no congestion
control information is present.
Reserved:
A 14 bit field set to 0 and ignored on receipt.
BlockOffset:
A 16 bit unsigned integer counting the number of octets of
"DataBlocks" data before the start of a new data block.
"BlockOffset" can count past the end of the "DataBlocks" data in
which case all the "DataBlocks" data belongs to the previous data
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block being re-assembled. If the "BlockOffset" extends into
subsequent packets it continues to only count subsequent
"DataBlocks" data (i.e., it does not count subsequent packets
non-"DataBlocks" octets).
DataBlocks:
Variable number of octets that begins with the start of a data
block, or the continuation of a previous data block, followed by
zero or more additional data blocks.
6.1.2. Congestion Control IPTFS_PROTOCOL Payload Format
The congestion control IPTFS_PROTOCOL payload is comprised of a 16
octet header followed by a variable amount of "DataBlocks" data as
shown below.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V|C|E| Reserved | BlockOffset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RTT | Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LossEventRate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LastSeqNum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DataBlocks ...
+-+-+-+-+-+-+-+-+-+-+-
V:
A 1 bit version field that MUST be set to zero. If received as
one the packet MUST be dropped.
C:
A 1 bit value that MUST be set to 1 which indicates the presence
of the congestion information header fields "RTT", "Delay",
"LossEventRate" and "LastSeqNum".
E:
A 1 bit value if set indicates that Congestion Experienced (CE)
ECN bits were received and used in deriving the reported
"LossEventRate".
Reserved:
A 13 bit field set to 0 and ignored on receipt.
BlockOffset:
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The same value as the non-congestion controlled payload format
value.
RTT:
A 16 bit value specifying the sender's current round-trip time
estimate in milliseconds. The value MAY be zero prior to the
sender having calculated a round-trip time estimate. The value
SHOULD be set to zero on non-IP-TFS enabled SAs.
Delay:
A 16 bit value specifying the delay in milliseconds incurred
between the receiver receiving the "LastSeqNum" packet and the
sending of this acknowledgement of it.
LossEventRate:
A 32 bit value specifying the inverse of the current loss event
rate as calculated by the receiver. A value of zero indicates no
loss. Otherwise the loss event rate is "1/LossEventRate".
LastSeqNum:
A 32 bit value containing the lower 32 bits of the largest
sequence number last received. This is the latest in the sequence
not necessarily the most recent (in the case of re-ordering of
packets it may be less recent). When determining largest and 64
bit extended sequence numbers are in use, the upper 32 bits should
be used during the comparison.
DataBlocks:
Variable number of octets that begins with the start of a data
block, or the continuation of a previous data block, followed by
zero or more additional data blocks. For the special case of
sending congestion control information on an non-IP-TFS enabled SA
this value MUST be empty (i.e., be zero octets long).
6.1.3. Data Blocks
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | IPv4, IPv6 or pad...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
Type:
A 4 bit field where 0x0 identifies a pad data block, 0x4 indicates
an IPv4 data block, and 0x6 indicates an IPv6 data block.
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6.1.3.1. IPv4 Data Block
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x4 | IHL | TypeOfService | TotalLength |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Rest of the inner packet ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
These values are the actual values within the encapsulated IPv4
header. In other words, the start of this data block is the start of
the encapsulated IP packet.
Type:
A 4 bit value of 0x4 indicating IPv4 (i.e., first nibble of the
IPv4 packet).
TotalLength:
The 16 bit unsigned integer length field of the IPv4 inner packet.
6.1.3.2. IPv6 Data Block
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x6 | TrafficClass | FlowLabel |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TotalLength | Rest of the inner packet ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
These values are the actual values within the encapsulated IPv6
header. In other words, the start of this data block is the start of
the encapsulated IP packet.
Type:
A 4 bit value of 0x6 indicating IPv6 (i.e., first nibble of the
IPv6 packet).
TotalLength:
The 16 bit unsigned integer length field of the inner IPv6 inner
packet.
6.1.3.3. Pad Data Block
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1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x0 | Padding ...
+-+-+-+-+-+-+-+-+-+-+-
Type:
A 4 bit value of 0x0 indicating a padding data block.
Padding:
extends to end of the encapsulating packet.
7. IANA Considerations
7.1. IPTFS_PROTOCOL Type
This document requests a protocol number IPTFS_PROTOCOL be allocated
by IANA from "Assigned Internet Protocol Numbers" registry for
identifying the IP-TFS ESP payload format.
Type:
TBD1
Description:
IP-TFS ESP payload format.
Reference:
This document
7.2. IKEv2 Transform Type TFS Type
This document requests an IKEv2 Transform Type "TFS Type" be
allocated by IANA from the "Transform Type Values" registry.
Type:
TBD2
Description:
TFS Type
Used In:
(optional in ESP)
Reference:
This document
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7.3. TFS Type Transform IDs Registry
This document requests a "Transform Type TBD3 - TFS Type Transform
IDs" registry be created. The registration procedure is Expert
Review. The initial values are as follows:
Number Name Reference
----------------------------------------
0 NONE This document
1 TFS_IPTFS_CC This document
2 TFS_IPTFS_NOCC This document
3-65535 Reserved This document
7.4. IPTFS_REQUIREMENTS Notify Message Status Type
This document requests a status type IPTFS_REQUIREMENTS be allocated
from the "IKEv2 Notify Message Types - Status Types" registry.
Value:
TBD3
Name:
IPTFS_REQUIREMENTS
Reference:
This document
8. Security Considerations
This document describes a mechanism to add Traffic Flow
Confidentiality to IP traffic. Use of this mechanism is expected to
increase the security of the traffic being transported. Other than
the additional security afforded by using this mechanism, IP-TFS
utilizes the security protocols [RFC4303] and [RFC7296] and so their
security considerations apply to IP-TFS as well.
As noted previously in Section 2.5.2, for TFC to be fully maintained
the encapsulated traffic flow should not be affecting network
congestion in a predictable way, and if it would be then non-
congestion controlled mode use should be considered instead.
9. References
9.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References
[AppCrypt]
Schneier, B., "Applied Cryptography: Protocols,
Algorithms, and Source Code in C", 11 2017.
[I-D.iab-wire-image]
Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", draft-iab-wire-image-01 (work in
progress), November 2018.
[IKEV2IANA]
IANA, "Internet Key Exchange Version 2 (IKEv2)
Parameters",
<http://www.iana.org/assignments/ikev2-parameters/>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.
[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>.
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[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000,
<https://www.rfc-editor.org/info/rfc2914>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4342] Floyd, S., Kohler, E., and J. Padhye, "Profile for
Datagram Congestion Control Protocol (DCCP) Congestion
Control ID 3: TCP-Friendly Rate Control (TFRC)", RFC 4342,
DOI 10.17487/RFC4342, March 2006,
<https://www.rfc-editor.org/info/rfc4342>.
[RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP
Friendly Rate Control (TFRC): Protocol Specification",
RFC 5348, DOI 10.17487/RFC5348, September 2008,
<https://www.rfc-editor.org/info/rfc5348>.
[RFC7510] Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
"Encapsulating MPLS in UDP", RFC 7510,
DOI 10.17487/RFC7510, April 2015,
<https://www.rfc-editor.org/info/rfc7510>.
[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers",
BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017,
<https://www.rfc-editor.org/info/rfc8084>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
Appendix A. Example Of An Encapsulated IP Packet Flow
Below we show an example inner IP packet flow within the
encapsulating tunnel packet stream. Notice how encapsulated IP
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packets can start and end anywhere, and more than one or less than 1
may occur in a single encapsulating packet.
Offset: 0 Offset: 100 Offset: 2900 Offset: 1400
[ ESP1 (1500) ][ ESP2 (1500) ][ ESP3 (1500) ][ ESP4 (1500) ]
[--800--][--800--][60][-240-][--4000----------------------][pad]
Figure 3: Inner and Outer Packet Flow
The encapsulated IP packet flow (lengths include IP header and
payload) is as follows: an 800 octet packet, an 800 octet packet, a
60 octet packet, a 240 octet packet, a 4000 octet packet.
The "BlockOffset" values in the 4 IP-TFS payload headers for this
packet flow would thus be: 0, 100, 2900, 1400 respectively. The
first encapsulating packet ESP1 has a zero "BlockOffset" which points
at the IP data block immediately following the IP-TFS header. The
following packet ESP2s "BlockOffset" points inward 100 octets to the
start of the 60 octet data block. The third encapsulating packet
ESP3 contains the middle portion of the 4000 octet data block so the
offset points past its end and into the forth encapsulating packet.
The fourth packet ESP4s offset is 1400 pointing at the padding which
follows the completion of the continued 4000 octet packet.
Appendix B. A Send and Loss Event Rate Calculation
The current best practice indicates that congestion control should be
done in a TCP friendly way. A TCP friendly congestion control
algorithm is described in [RFC5348]. For our use case (as with
[RFC4342]) we consider our (fixed) packet size the segment size for
the algorithm. The formula for the send rate is then as follows:
1
X_Pps = -----------------------------------------------
R * (sqrt(2*p/3) + 12*sqrt(3*p/8)*p*(1+32*p^2))
Where "X_Pps" is the send rate in packets per second, "R" is the
round trip time estimate and "p" is the loss event rate (the inverse
of which is provided by the receiver).
The IP-TFS receiver, having the RTT estimate from the sender MAY use
the same method as described in [RFC4342] to collect the loss
intervals and calculate the loss event rate value using the weighted
average as indicated. The receiver communicates the inverse of this
value back to the sender in the IPTFS_PROTOCOL payload header field
"LossEventRate".
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The IP-TFS sender now has both the "R" and "p" values and can
calculate the correct sending rate ("X_Pps"). If following [RFC5348]
the sender SHOULD also use the slow start mechanism described therein
when the IP-TFS SA is first established.
Appendix C. Comparisons of IP-TFS
C.1. Comparing Overhead
C.1.1. IP-TFS Overhead
The overhead of IP-TFS is 40 bytes per outer packet. Therefore the
octet overhead per inner packet is 40 divided by the number of outer
packets required (fractional allowed). The overhead as a percentage
of inner packet size is a constant based on the Outer MTU size.
OH = 40 / Outer Payload Size / Inner Packet Size
OH % of Inner Packet Size = 100 * OH / Inner Packet Size
OH % of Inner Packet Size = 4000 / Outer Payload Size
Type IP-TFS IP-TFS IP-TFS
MTU 576 1500 9000
PSize 536 1460 8960
-------------------------------
40 7.46% 2.74% 0.45%
576 7.46% 2.74% 0.45%
1500 7.46% 2.74% 0.45%
9000 7.46% 2.74% 0.45%
Figure 4: IP-TFS Overhead as Percentage of Inner Packet Size
C.1.2. ESP with Padding Overhead
The overhead per inner packet for constant-send-rate padded ESP
(i.e., traditional IPsec TFC) is 36 octets plus any padding, unless
fragmentation is required.
When fragmentation of the inner packet is required to fit in the
outer IPsec packet, overhead is the number of outer packets required
to carry the fragmented inner packet times both the inner IP overhead
(20) and the outer packet overhead (36) minus the initial inner IP
overhead plus any required tail padding in the last encapsulation
packet. The required tail padding is the number of required packets
times the difference of the Outer Payload Size and the IP Overhead
minus the Inner Payload Size. So:
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Inner Paylaod Size = IP Packet Size - IP Overhead
Outer Payload Size = MTU - IPsec Overhead
Inner Payload Size
NF0 = ----------------------------------
Outer Payload Size - IP Overhead
NF = CEILING(NF0)
OH = NF * (IP Overhead + IPsec Overhead)
- IP Overhead
+ NF * (Outer Payload Size - IP Overhead)
- Inner Payload Size
OH = NF * (IPsec Overhead + Outer Payload Size)
- (IP Overhead + Inner Payload Size)
OH = NF * (IPsec Overhead + Outer Payload Size)
- Inner Packet Size
C.2. Overhead Comparison
The following tables collect the overhead values for some common L3
MTU sizes in order to compare them. The first table is the number of
octets of overhead for a given L3 MTU sized packet. The second table
is the percentage of overhead in the same MTU sized packet.
Type ESP+Pad ESP+Pad ESP+Pad IP-TFS IP-TFS IP-TFS
L3 MTU 576 1500 9000 576 1500 9000
PSize 540 1464 8964 536 1460 8960
-----------------------------------------------------------
40 500 1424 8924 3.0 1.1 0.2
128 412 1336 8836 9.6 3.5 0.6
256 284 1208 8708 19.1 7.0 1.1
536 4 928 8428 40.0 14.7 2.4
576 576 888 8388 43.0 15.8 2.6
1460 268 4 7504 109.0 40.0 6.5
1500 228 1500 7464 111.9 41.1 6.7
8960 1408 1540 4 668.7 245.5 40.0
9000 1368 1500 9000 671.6 246.6 40.2
Figure 5: Overhead comparison in octets
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Type ESP+Pad ESP+Pad ESP+Pad IP-TFS IP-TFS IP-TFS
MTU 576 1500 9000 576 1500 9000
PSize 540 1464 8964 536 1460 8960
-----------------------------------------------------------
40 1250.0% 3560.0% 22310.0% 7.46% 2.74% 0.45%
128 321.9% 1043.8% 6903.1% 7.46% 2.74% 0.45%
256 110.9% 471.9% 3401.6% 7.46% 2.74% 0.45%
536 0.7% 173.1% 1572.4% 7.46% 2.74% 0.45%
576 100.0% 154.2% 1456.2% 7.46% 2.74% 0.45%
1460 18.4% 0.3% 514.0% 7.46% 2.74% 0.45%
1500 15.2% 100.0% 497.6% 7.46% 2.74% 0.45%
8960 15.7% 17.2% 0.0% 7.46% 2.74% 0.45%
9000 15.2% 16.7% 100.0% 7.46% 2.74% 0.45%
Figure 6: Overhead as Percentage of Inner Packet Size
C.3. Comparing Available Bandwidth
Another way to compare the two solutions is to look at the amount of
available bandwidth each solution provides. The following sections
consider and compare the percentage of available bandwidth. For the
sake of providing a well understood baseline we will also include
normal (unencrypted) Ethernet as well as normal ESP values.
C.3.1. Ethernet
In order to calculate the available bandwidth we first calculate the
per packet overhead in bits. The total overhead of Ethernet is 14+4
octets of header and CRC plus and additional 20 octets of framing
(preamble, start, and inter-packet gap) for a total of 48 octets.
Additionally the minimum payload is 46 octets.
Size E + P E + P E + P IPTFS IPTFS IPTFS Enet ESP
MTU 590 1514 9014 590 1514 9014 any any
OH 74 74 74 78 78 78 38 74
------------------------------------------------------------
40 614 1538 9038 45 42 40 84 114
128 614 1538 9038 146 134 129 166 202
256 614 1538 9038 293 269 258 294 330
536 614 1538 9038 614 564 540 574 610
576 1228 1538 9038 659 606 581 614 650
1460 1842 1538 9038 1672 1538 1472 1498 1534
1500 1842 3076 9038 1718 1580 1513 1538 1574
8960 11052 10766 9038 10263 9438 9038 8998 9034
9000 11052 10766 18076 10309 9480 9078 9038 9074
Figure 7: L2 Octets Per Packet
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Size E + P E + P E + P IPTFS IPTFS IPTFS Enet ESP
MTU 590 1514 9014 590 1514 9014 any any
OH 74 74 74 78 78 78 38 74
--------------------------------------------------------------
40 2.0M 0.8M 0.1M 27.3M 29.7M 31.0M 14.9M 11.0M
128 2.0M 0.8M 0.1M 8.5M 9.3M 9.7M 7.5M 6.2M
256 2.0M 0.8M 0.1M 4.3M 4.6M 4.8M 4.3M 3.8M
536 2.0M 0.8M 0.1M 2.0M 2.2M 2.3M 2.2M 2.0M
576 1.0M 0.8M 0.1M 1.9M 2.1M 2.2M 2.0M 1.9M
1460 678K 812K 138K 747K 812K 848K 834K 814K
1500 678K 406K 138K 727K 791K 826K 812K 794K
8960 113K 116K 138K 121K 132K 138K 138K 138K
9000 113K 116K 69K 121K 131K 137K 138K 137K
Figure 8: Packets Per Second on 10G Ethernet
Size E + P E + P E + P IPTFS IPTFS IPTFS Enet ESP
590 1514 9014 590 1514 9014 any any
74 74 74 78 78 78 38 74
----------------------------------------------------------------------
40 6.51% 2.60% 0.44% 87.30% 94.93% 99.14% 47.62% 35.09%
128 20.85% 8.32% 1.42% 87.30% 94.93% 99.14% 77.11% 63.37%
256 41.69% 16.64% 2.83% 87.30% 94.93% 99.14% 87.07% 77.58%
536 87.30% 34.85% 5.93% 87.30% 94.93% 99.14% 93.38% 87.87%
576 46.91% 37.45% 6.37% 87.30% 94.93% 99.14% 93.81% 88.62%
1460 79.26% 94.93% 16.15% 87.30% 94.93% 99.14% 97.46% 95.18%
1500 81.43% 48.76% 16.60% 87.30% 94.93% 99.14% 97.53% 95.30%
8960 81.07% 83.22% 99.14% 87.30% 94.93% 99.14% 99.58% 99.18%
9000 81.43% 83.60% 49.79% 87.30% 94.93% 99.14% 99.58% 99.18%
Figure 9: Percentage of Bandwidth on 10G Ethernet
A sometimes unexpected result of using IP-TFS (or any packet
aggregating tunnel) is that, for small to medium sized packets, the
available bandwidth is actually greater than native Ethernet. This
is due to the reduction in Ethernet framing overhead. This increased
bandwidth is paid for with an increase in latency. This latency is
the time to send the unrelated octets in the outer tunnel frame. The
following table illustrates the latency for some common values on a
10G Ethernet link. The table also includes latency introduced by
padding if using ESP with padding.
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ESP+Pad ESP+Pad IP-TFS IP-TFS
1500 9000 1500 9000
------------------------------------------
40 1.14 us 7.14 us 1.17 us 7.17 us
128 1.07 us 7.07 us 1.10 us 7.10 us
256 0.97 us 6.97 us 1.00 us 7.00 us
536 0.74 us 6.74 us 0.77 us 6.77 us
576 0.71 us 6.71 us 0.74 us 6.74 us
1460 0.00 us 6.00 us 0.04 us 6.04 us
1500 1.20 us 5.97 us 0.00 us 6.00 us
Figure 10: Added Latency
Notice that the latency values are very similar between the two
solutions; however, whereas IP-TFS provides for constant high
bandwidth, in some cases even exceeding native Ethernet, ESP with
padding often greatly reduces available bandwidth.
Appendix D. Acknowledgements
We would like to thank Don Fedyk for help in reviewing this work.
Appendix E. Contributors
The following people made significant contributions to this document.
Lou Berger
LabN Consulting, L.L.C.
Email: lberger@labn.net
Author's Address
Christian Hopps
LabN Consulting, L.L.C.
Email: chopps@chopps.org
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