Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Obsoletes: rfc5320 (if approved) June 12, 2013
Intended status: Informational
Expires: December 14, 2013
The Subnetwork Encapsulation and Adaptation Layer (SEAL)
draft-templin-intarea-seal-56.txt
Abstract
This document specifies a Subnetwork Encapsulation and Adaptation
Layer (SEAL). SEAL operates over virtual topologies configured over
connected IP network routing regions bounded by encapsulating border
nodes. These virtual topologies are manifested by tunnels that may
span multiple IP and/or sub-IP layer forwarding hops, where they may
incur packet duplication, packet reordering, source address spoofing
and traversal of links with diverse Maximum Transmission Units
(MTUs). SEAL addresses these issues through the encapsulation and
messaging mechanisms specified in this document.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on December 14, 2013.
Copyright Notice
Copyright (c) 2013 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Approach . . . . . . . . . . . . . . . . . . . . . . . . . 6
1.3. Differences with RFC5320 . . . . . . . . . . . . . . . . . 7
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 8
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Applicability Statement . . . . . . . . . . . . . . . . . . . 10
5. SEAL Specification . . . . . . . . . . . . . . . . . . . . . . 11
5.1. SEAL Tunnel Model . . . . . . . . . . . . . . . . . . . . 11
5.2. SEAL Model of Operation . . . . . . . . . . . . . . . . . 12
5.3. SEAL Header and Trailer Format . . . . . . . . . . . . . . 13
5.4. ITE Specification . . . . . . . . . . . . . . . . . . . . 15
5.4.1. Tunnel Interface MTU . . . . . . . . . . . . . . . . . 15
5.4.2. Tunnel Neighbor Soft State . . . . . . . . . . . . . . 16
5.4.3. SEAL Layer Pre-Processing . . . . . . . . . . . . . . 17
5.4.4. SEAL Encapsulation and Segmentation . . . . . . . . . 18
5.4.5. Outer Encapsulation . . . . . . . . . . . . . . . . . 20
5.4.6. Path Probing and ETE Reachability Verification . . . . 21
5.4.7. Processing ICMP Messages . . . . . . . . . . . . . . . 21
5.4.8. IPv4 Middlebox Reassembly Testing . . . . . . . . . . 22
5.4.9. Stateful MTU Determination . . . . . . . . . . . . . . 23
5.4.10. Detecting Path MTU Changes . . . . . . . . . . . . . . 24
5.5. ETE Specification . . . . . . . . . . . . . . . . . . . . 24
5.5.1. Reassembly Buffer Requirements . . . . . . . . . . . . 24
5.5.2. Tunnel Neighbor Soft State . . . . . . . . . . . . . . 25
5.5.3. IP-Layer Reassembly . . . . . . . . . . . . . . . . . 25
5.5.4. Decapsulation, SEAL-Layer Reassembly, and
Re-Encapsulation . . . . . . . . . . . . . . . . . . . 25
5.6. The SEAL Control Message Protocol (SCMP) . . . . . . . . . 27
5.6.1. Generating SCMP Error Messages . . . . . . . . . . . . 27
5.6.2. Processing SCMP Error Messages . . . . . . . . . . . . 30
6. Link Requirements . . . . . . . . . . . . . . . . . . . . . . 32
7. End System Requirements . . . . . . . . . . . . . . . . . . . 32
8. Router Requirements . . . . . . . . . . . . . . . . . . . . . 32
9. Nested Encapsulation Considerations . . . . . . . . . . . . . 32
10. Reliability Considerations . . . . . . . . . . . . . . . . . . 33
11. Integrity Considerations . . . . . . . . . . . . . . . . . . . 33
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
13. Security Considerations . . . . . . . . . . . . . . . . . . . 34
14. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 35
15. Implementation Status . . . . . . . . . . . . . . . . . . . . 35
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 35
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
17.1. Normative References . . . . . . . . . . . . . . . . . . . 36
17.2. Informative References . . . . . . . . . . . . . . . . . . 37
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 40
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1. Introduction
As Internet technology and communication has grown and matured, many
techniques have developed that use virtual topologies (manifested by
tunnels of one form or another) over an actual network that supports
the Internet Protocol (IP) [RFC0791][RFC2460]. Those virtual
topologies have elements that appear as one network layer hop, but
are actually multiple IP or sub-IP layer hops. These multiple hops
often have quite diverse properties that are often not even visible
to the endpoints of the virtual hop. This introduces failure modes
that are not dealt with well in current approaches.
The use of IP encapsulation (also known as "tunneling") has long been
considered as the means for creating such virtual topologies (e.g.,
see [RFC2003][RFC2473]). However, the encapsulation headers often
include insufficiently provisioned per-packet identification values.
IP encapsulation also allows an attacker to produce encapsulated
packets with spoofed source addresses even if the source address in
the encapsulating header cannot be spoofed. A denial-of-service
vector that is not possible in non-tunneled subnetworks is therefore
presented.
Additionally, the insertion of an outer IP header reduces the
effective path MTU visible to the inner network layer. When IPv6 is
used as the encapsulation protocol, original sources expect to be
informed of the MTU limitation through IPv6 Path MTU discovery
(PMTUD) [RFC1981]. When IPv4 is used, this reduced MTU can be
accommodated through the use of IPv4 fragmentation, but unmitigated
in-the-network fragmentation has been found to be harmful through
operational experience and studies conducted over the course of many
years [FRAG][FOLK][RFC4963]. Additionally, classical IPv4 PMTUD
[RFC1191] has known operational issues that are exacerbated by in-
the-network tunnels [RFC2923][RFC4459].
The following subsections present further details on the motivation
and approach for addressing these issues.
1.1. Motivation
Before discussing the approach, it is necessary to first understand
the problems. In both the Internet and private-use networks today,
IP is ubiquitously deployed as the Layer 3 protocol. The primary
functions of IP are to provide for routing, addressing, and a
fragmentation and reassembly capability used to accommodate links
with diverse MTUs. While it is well known that the IP address space
is rapidly becoming depleted, there is also a growing consensus that
other IP protocol limitations have already or may soon become
problematic.
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First, the Internet historically provided no means for discerning
whether the source addresses of IP packets are authentic. This
shortcoming is being addressed more and more through the deployment
of site border router ingress filters [RFC2827], however the use of
encapsulation provides a vector for an attacker to circumvent
filtering for the encapsulated packet even if filtering is correctly
applied to the encapsulation header. Secondly, the IP header does
not include a well-behaved identification value unless the source has
included a fragment header for IPv6 or unless the source permits
fragmentation for IPv4. These limitations preclude an efficient
means for routers to detect duplicate packets and packets that have
been re-ordered within the subnetwork. Additionally, recent studies
have shown that the arrival of fragments at high data rates can cause
denial-of-service (DoS) attacks on performance-sensitive networking
gear, prompting some administrators to configure their equipment to
drop fragments unconditionally [I-D.taylor-v6ops-fragdrop].
For IPv4 encapsulation, when fragmentation is permitted the header
includes a 16-bit Identification field, meaning that at most 2^16
unique packets with the same (source, destination, protocol)-tuple
can be active in the network at the same time [RFC6864]. (When
middleboxes such as Network Address Translators (NATs) re-write the
Identification field to random values, the number of unique packets
is even further reduced.) Due to the escalating deployment of high-
speed links, however, these numbers have become too small by several
orders of magnitude for high data rate packet sources such as tunnel
endpoints [RFC4963].
Furthermore, there are many well-known limitations pertaining to IPv4
fragmentation and reassembly - even to the point that it has been
deemed "harmful" in both classic and modern-day studies (see above).
In particular, IPv4 fragmentation raises issues ranging from minor
annoyances (e.g., in-the-network router fragmentation [RFC1981]) to
the potential for major integrity issues (e.g., mis-association of
the fragments of multiple IP packets during reassembly [RFC4963]).
As a result of these perceived limitations, a fragmentation-avoiding
technique for discovering the MTU of the forward path from a source
to a destination node was devised through the deliberations of the
Path MTU Discovery Working Group (PMTUDWG) during the late 1980's
through early 1990's which resulted in the publication of [RFC1191].
In this negative feedback-based method, the source node provides
explicit instructions to routers in the path to discard the packet
and return an ICMP error message if an MTU restriction is
encountered. However, this approach has several serious shortcomings
that lead to an overall "brittleness" [RFC2923].
In particular, site border routers in the Internet have been known to
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discard ICMP error messages coming from the outside world. This is
due in large part to the fact that malicious spoofing of error
messages in the Internet is trivial since there is no way to
authenticate the source of the messages [RFC5927]. Furthermore, when
a source node that requires ICMP error message feedback when a packet
is dropped due to an MTU restriction does not receive the messages, a
path MTU-related black hole occurs. This means that the source will
continue to send packets that are too large and never receive an
indication from the network that they are being discarded. This
behavior has been confirmed through documented studies showing clear
evidence of PMTUD failures for both IPv4 and IPv6 in the Internet
today [TBIT][WAND][SIGCOMM][RIPE].
The issues with both IP fragmentation and this "classical" PMTUD
method are exacerbated further when IP tunneling is used [RFC4459].
For example, an ingress tunnel endpoint (ITE) may be required to
forward encapsulated packets into the subnetwork on behalf of
hundreds, thousands, or even more original sources. If the ITE
allows IP fragmentation on the encapsulated packets, persistent
fragmentation could lead to undetected data corruption due to
Identification field wrapping and/or reassembly congestion at the
ETE. If the ITE instead uses classical IP PMTUD it must rely on ICMP
error messages coming from the subnetwork that may be suspect,
subject to loss due to filtering middleboxes, or insufficiently
provisioned for translation into error messages to be returned to the
original sources.
Although recent works have led to the development of a positive
feedback-based end-to-end MTU determination scheme [RFC4821], they do
not excuse tunnels from accounting for the encapsulation overhead
they add to packets. Moreover, in current practice existing
tunneling protocols mask the MTU issues by selecting a "lowest common
denominator" MTU that may be much smaller than necessary for most
paths and difficult to change at a later date. Therefore, a new
approach to accommodate tunnels over links with diverse MTUs is
necessary.
1.2. Approach
This document concerns subnetworks manifested through a virtual
topology configured over a connected network routing region and
bounded by encapsulating border nodes. Example connected network
routing regions include Mobile Ad hoc Networks (MANETs), enterprise
networks and the global public Internet itself. Subnetwork border
nodes forward unicast and multicast packets over the virtual topology
across multiple IP and/or sub-IP layer forwarding hops that may
introduce packet duplication and/or traverse links with diverse
Maximum Transmission Units (MTUs).
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This document introduces a Subnetwork Encapsulation and Adaptation
Layer (SEAL) for tunneling inner network layer protocol packets over
IP subnetworks that connect Ingress and Egress Tunnel Endpoints
(ITEs/ETEs) of border nodes. It provides a modular specification
designed to be tailored to specific associated tunneling protocols.
(A transport-mode of operation is also possible, but out of scope for
this document.)
SEAL provides a mid-layer encapsulation that accommodates links with
diverse MTUs, and allows routers in the subnetwork to perform
efficient duplicate packet and packet reordering detection. The
encapsulation further ensures message origin authentication, packet
header integrity and anti-replay in environments in which these
functions are necessary.
SEAL treats tunnels that traverse the subnetwork as ordinary links
that must support network layer services. Moreover, SEAL provides
dynamic mechanisms (including limited segmentation and reassembly) to
ensure a maximal path MTU over the tunnel. This is in contrast to
static approaches which avoid MTU issues by selecting a lowest common
denominator MTU value that may be overly conservative for the vast
majority of tunnel paths and difficult to change even when larger
MTUs become available.
1.3. Differences with RFC5320
This specification of SEAL is descended from an experimental
independent RFC publication of the same name [RFC5320]. However,
this specification introduces a number of important differences from
the earlier publication.
First, this specification includes a protocol version field in the
SEAL header whereas [RFC5320] does not, and therefore cannot be
updated by future revisions. This specification therefore obsoletes
(i.e., and does not update) [RFC5320].
Secondly, [RFC5320] forms a 32-bit Identification value by
concatenating the 16-bit IPv4 Identification field with a 16-bit
Identification "extension" field in the SEAL header. This means that
[RFC5320] can only operate over IPv4 networks (since IPv6 headers do
not include a 16-bit version number) and that the SEAL Identification
value can be corrupted if the Identification in the outer IPv4 header
is rewritten. In contrast, this specification includes a 32-bit
Identification value that is independent of any identification fields
found in the inner or outer IP headers, and is therefore compatible
with any inner and outer IP protocol version combinations.
Additionally, the SEAL segmentation and reassembly procedures defined
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in [RFC5320] differ significantly from those found in this
specification. In particular, this specification defines a 6-bit
Offset field that allows for smaller segment sizes when SEAL
segmentation is necessary (e.g., in order to observe the IPv4 minimum
MTU of 68 bytes). In contrast, [RFC5320] includes a 3-bit Segment
field and performs reassembly through concatenation of consecutive
segments.
The SEAL header in this specification also includes an optional
Integrity Check Vector (ICV) that can be used to digitally sign the
SEAL header and the leading portion of the encapsulated inner packet.
This allows for a lightweight integrity check and a loose message
origin authentication capability. The header further includes new
control bits as well as a link identification and encapsulation level
field for additional control capabilities.
Finally, this version of SEAL includes a new messaging protocol known
as the SEAL Control Message Protocol (SCMP), whereas [RFC5320]
performs signalling through the use of SEAL-encapsulated ICMP
messages. The use of SCMP allows SEAL-specific departures from ICMP,
as well as a control messaging capability that extends to other
specifications, including Virtual Enterprise Traversal (VET)
[I-D.templin-intarea-vet].
2. Terminology
The following terms are defined within the scope of this document:
subnetwork
a virtual topology configured over a connected network routing
region and bounded by encapsulating border nodes.
IP
used to generically refer to either Internet Protocol (IP)
version, i.e., IPv4 or IPv6.
Ingress Tunnel Endpoint (ITE)
a virtual interface over which an encapsulating border node (host
or router) sends encapsulated packets into the subnetwork.
Egress Tunnel Endpoint (ETE)
a virtual interface over which an encapsulating border node (host
or router) receives encapsulated packets from the subnetwork.
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SEAL Path
a subnetwork path from an ITE to an ETE beginning with an
underlying link of the ITE as the first hop. Note that, if the
ITE's interface connection to the underlying link assigns multiple
IP addresses, each address represents a separate SEAL path.
inner packet
an unencapsulated network layer protocol packet (e.g., IPv4
[RFC0791], OSI/CLNP [RFC0994], IPv6 [RFC2460], etc.) before any
outer encapsulations are added. Internet protocol numbers that
identify inner packets are found in the IANA Internet Protocol
registry [RFC3232]. SEAL protocol packets that incur an
additional layer of SEAL encapsulation are also considered inner
packets.
outer IP packet
a packet resulting from adding an outer IP header (and possibly
other outer headers) to a SEAL-encapsulated inner packet.
packet-in-error
the leading portion of an invoking data packet encapsulated in the
body of an error control message (e.g., an ICMPv4 [RFC0792] error
message, an ICMPv6 [RFC4443] error message, etc.).
Packet Too Big (PTB) message
a control plane message indicating an MTU restriction (e.g., an
ICMPv6 "Packet Too Big" message [RFC4443], an ICMPv4
"Fragmentation Needed" message [RFC0792], etc.).
Don't Fragment (DF) bit
a bit that indicates whether the packet may be fragmented by the
network. The DF bit is explicitly included in the IPv4 header
[RFC0791] and may be set to '0' to allow fragmentation or '1' to
disallow further in-network fragmentation. The bit is absent from
the IPv6 header [RFC2460], but implicitly set to '1' becauuse
fragmentation can occur only at IPv6 sources.
The following abbreviations correspond to terms used within this
document and/or elsewhere in common Internetworking nomenclature:
HLEN - the length of the SEAL header plus outer headers
ICV - Integrity Check Vector
MAC - Message Authentication Code
MTU - Maximum Transmission Unit
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SCMP - the SEAL Control Message Protocol
SDU - SCMP Destination Unreachable message
SPP - SCMP Parameter Problem message
SPTB - SCMP Packet Too Big message
SEAL - Subnetwork Encapsulation and Adaptation Layer
TE - Tunnel Endpoint (i.e., either ingress or egress)
VET - Virtual Enterprise Traversal
3. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. When used
in lower case (e.g., must, must not, etc.), these words MUST NOT be
interpreted as described in [RFC2119], but are rather interpreted as
they would be in common English.
4. Applicability Statement
SEAL was originally motivated by the specific case of subnetwork
abstraction for Mobile Ad hoc Networks (MANETs), however the domain
of applicability also extends to subnetwork abstractions over
enterprise networks, ISP networks, SO/HO networks, the global public
Internet itself, and any other connected network routing region.
SEAL provides a network sublayer for encapsulation of an inner
network layer packet within outer encapsulating headers. SEAL can
also be used as a sublayer within a transport layer protocol data
payload, where transport layer encapsulation is typically used for
Network Address Translator (NAT) traversal as well as operation over
subnetworks that give preferential treatment to certain "core"
Internet protocols, e.g., TCP, UDP, etc.. (However, note that TCP
encapsulation may not be appropriate for all use cases; particularly
those that require low delay and/or delay variance.) The SEAL header
is processed in a similar manner as for IPv6 extension headers, i.e.,
it is not part of the outer IP header but rather allows for the
creation of an arbitrarily extensible chain of headers in the same
way that IPv6 does.
To accommodate MTU diversity, the Ingress Tunnel Endpoint (ITE) may
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need to perform limited segmentation which the Egress Tunnel Endpoint
(ETE) reassembles. The ETE further acts as a passive observer that
informs the ITE of any packet size limitations. This allows the ITE
to return appropriate PMTUD feedback even if the network path between
the ITE and ETE filters ICMP messages.
SEAL further provides mechanisms to ensure message origin
authentication, packet header integrity, and anti-replay. The SEAL
framework is therefore similar to the IP Security (IPsec)
Authentication Header (AH) [RFC4301][RFC4302], however it provides
only minimal hop-by-hop authenticating services while leaving full
data integrity, authentication and confidentiality services as an
end-to-end consideration.
In many aspects, SEAL also very closely resembles the Generic Routing
Encapsulation (GRE) framework [RFC1701]. SEAL can therefore be
applied in the same use cases that are traditionally addressed by
GRE, but goes beyond GRE to also provide additional capabilities
(e.,g., path MTU accommodation, message origin authentication, etc.)
as described in this document.
5. SEAL Specification
The following sections specify the operation of SEAL:
5.1. SEAL Tunnel Model
SEAL is an encapsulation sublayer used within point-to-point, point-
to-multipoint, and non-broadcast, multiple access (NBMA) tunnels.
Each SEAL path is configured over one or more underlying interfaces
attached to subnetwork links. The SEAL tunnel connects an ITE to one
or more ETE "neighbors" via encapsulation across an underlying
subnetwork, where the tunnel neighbor relationship may be either
unidirectional or bidirectional.
A unidirectional tunnel neighbor relationship allows the near end ITE
to send data packets forward to the far end ETE, while the ETE only
returns control messages when necessary. A bidirectional tunnel
neighbor relationship is one over which both TEs can exchange both
data and control messages.
Implications of the SEAL unidirectional and bidirectional models are
the same as discussed in [I-D.templin-intarea-vet].
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5.2. SEAL Model of Operation
SEAL-enabled ITEs encapsulate each inner packet in a SEAL header and
any outer header encapsulations as shown in Figure 1:
+--------------------+
~ outer IP header ~
+--------------------+
~ other outer hdrs ~
+--------------------+
~ SEAL Header ~
+--------------------+ +--------------------+
| | --> | |
~ Inner ~ --> ~ Inner ~
~ Packet ~ --> ~ Packet ~
| | --> | |
+--------------------+ +----------+---------+
Figure 1: SEAL Encapsulation
The ITE inserts the SEAL header according to the specific tunneling
protocol. For simple encapsulation of an inner network layer packet
within an outer IP header, the ITE inserts the SEAL header following
the outer IP header and before the inner packet as: IP/SEAL/{inner
packet}.
For encapsulations over transports such as UDP, the ITE inserts the
SEAL header following the outer transport layer header and before the
inner packet, e.g., as IP/UDP/SEAL/{inner packet}. In that case, the
UDP header is seen as an "other outer header" as depicted in Figure 1
and the outer IP and transport layer headers are together seen as the
outer encapsulation headers.
SEAL supports both "nested" tunneling and "re-encapsulating"
tunneling. Nested tunneling occurs when a first tunnel is
encapsulated within a second tunnel, which may then further be
encapsulated within additional tunnels. Nested tunneling can be
useful, and stands in contrast to "recursive" tunneling which is an
anomalous condition incurred due to misconfiguration or a routing
loop. Considerations for nested tunneling and avoiding recursive
tunneling are discussed in Section 4 of [RFC2473].
Re-encapsulating tunneling occurs when a packet arrives at a first
ETE, which then acts as an ITE to re-encapsulate and forward the
packet to a second ETE connected to the same subnetwork. In that
case each ITE/ETE transition represents a segment of a bridged path
between the ITE nearest the source and the ETE nearest the
destination. Considerations for re-encapsulating tunneling are
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discussed in[I-D.templin-ironbis]. Combinations of nested and re-
encapsulating tunneling are also naturally supported by SEAL.
The SEAL ITE considers each underlying interface as the ingress
attachment point to a SEAL path to the ETE. The ITE therefore may
experience different path MTUs on different SEAL paths.
Finally, the SEAL ITE ensures that the inner network layer protocol
will see a minimum MTU of 1500 bytes over each SEAL path regardless
of the outer network layer protocol version, i.e., even if a small
amount of fragmentation and reassembly are necessary. This is
necessary to avoid path MTU "black holes" for the minimum MTU
configured by the vast majority of links in the Internet.
5.3. SEAL Header and Trailer Format
The SEAL header is formatted as follows:
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|VER|C|A|I|V|R|RES|M| Offset | NEXTHDR | LINK_ID |LEVEL|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Integrity Check Vector (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 2: SEAL Header Format
VER (2)
a 2-bit version field. This document specifies Version 0 of the
SEAL protocol, i.e., the VER field encodes the value 0.
C (1)
the "Control/Data" bit. Set to 1 by the ITE in SEAL Control
Message Protocol (SCMP) control messages, and set to 0 in ordinary
data packets.
A (1)
the "Acknowledgement Requested" bit. Set to 1 by the ITE in SEAL
data packets for which it wishes to receive an explicit
acknowledgement from the ETE. Also used as a message-dependent
bit indication in SCMP messages, e.g., A==1 in SCMP Packet Too Big
(SPTB) messages indicates that the ETE supports limited
reassembly.
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I (1)
the "Identification Included" bit.
V (1)
the "Integrity Check Vector included" bit.
R (1)
the "Redirects Permitted" bit (reserved for use by VET:
[I-D.templin-intarea-vet]).
RES (2) a 2-bit reserved field.
M (1) the "More Segments" bit. Set to 1 in a non-final segment and
set to 0 in the final segment of the SEAL packet.
Offset (6) a 6-bit Offset field. Set to 0 in the first segment of a
segmented SEAL packet. Set to an integral number of 32 byte
blocks in subsequent segments (e.g., an Offset of 10 indicates a
block that begins at the 320th byte in the packet).
NEXTHDR (8) an 8-bit field that encodes the next header Internet
Protocol number the same as for the IPv4 protocol and IPv6 next
header fields.
LINK_ID (5)
a 5-bit link identification value, set to a unique value by the
ITE for each SEAL path over which it will send encapsulated
packets to the ETE (up to 32 SEAL paths per ETE are therefore
supported). Note that, if the ITE's interface connection to the
underlying link assigns multiple IP addresses, each address
represents a separate SEAL path that must be assigned a separate
LINK_ID.
LEVEL (3)
a 3-bit nesting level; use to limit the number of tunnel nesting
levels. Set to an integer value up to 7 in the innermost SEAL
encapsulation, and decremented by 1 for each successive additional
SEAL encapsulation nesting level. Up to 8 levels of nesting are
therefore supported.
Identification (32)
an optional 32-bit per-packet identification field; present when
I==1. Set to a 32-bit value (beginning with 0) that is
monotonically-incremented for each SEAL packet transmitted to this
ETE.
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Integrity Check Vector (ICV) (variable)
an optional variable-length integrity check vector field; present
when V==1.
5.4. ITE Specification
5.4.1. Tunnel Interface MTU
The tunnel interface must present a constant MTU value to the inner
network layer as the size for admission of inner packets into the
interface. Since NBMA tunnel virtual interfaces may support a large
set of SEAL paths that accept widely varying maximum packet sizes,
however, a number of factors should be taken into consideration when
selecting a tunnel interface MTU.
Due to the ubiquitous deployment of standard Ethernet and similar
networking gear, the nominal Internet cell size has become 1500
bytes; this is the de facto size that end systems have come to expect
will either be delivered by the network without loss due to an MTU
restriction on the path or a suitable ICMP Packet Too Big (PTB)
message returned. When large packets sent by end systems incur
additional encapsulation at an ITE, however, they may be dropped
silently within the tunnel since the network may not always deliver
the necessary PTBs [RFC2923]. The ITE SHOULD therefore set a tunnel
interface MTU of at least 1500 bytes.
The inner network layer protocol consults the tunnel interface MTU
when admitting a packet into the interface. For non-SEAL inner IPv4
packets with the IPv4 Don't Fragment (DF) bit cleared (i.e, DF==0),
if the packet is larger than the tunnel interface MTU the inner IPv4
layer uses IPv4 fragmentation to break the packet into fragments no
larger than the tunnel interface MTU. The ITE then admits each
fragment into the interface as an independent packet.
For all other inner packets, the inner network layer admits the
packet if it is no larger than the tunnel interface MTU; otherwise,
it drops the packet and sends a PTB error message to the source with
the MTU value set to the tunnel interface MTU. The message contains
as much of the invoking packet as possible without the entire message
exceeding the network layer minimum MTU size.
The ITE can alternatively set an indefinite MTU on the tunnel
interface such that all inner packets are admitted into the interface
regardless of their size. For ITEs that host applications that use
the tunnel interface directly, this option must be carefully
coordinated with protocol stack upper layers since some upper layer
protocols (e.g., TCP) derive their packet sizing parameters from the
MTU of the outgoing interface and as such may select too large an
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initial size. This is not a problem for upper layers that use
conservative initial maximum segment size estimates and/or when the
tunnel interface can reduce the upper layer's maximum segment size,
e.g., by reducing the size advertised in the MSS option of outgoing
TCP messages (sometimes known as "MSS clamping").
In light of the above considerations, the ITE SHOULD configure an
indefinite MTU on tunnel *router* interfaces so that SEAL performs
all subnetwork adaptation from within the interface as specified in
Section 5.4.3. The ITE can instead set a smaller MTU on tunnel
*host* interfaces, e.g., the maximum of 1500 bytes and the smallest
MTU among all of the underlying links minus the size of the
encapsulation headers.
5.4.2. Tunnel Neighbor Soft State
The tunnel virtual interface maintains a number of soft state
variables for each ETE and for each SEAL path.
When per-packet identification is required, the ITE maintains a per
ETE window of Identification values for the packets it has recently
sent to this ETE. The ITE then sets a variable "USE_ID" to TRUE, and
includes an Identification in each packet it sends to this ETE;
otherwise, it sets USE_ID to FALSE.
When message origin authentication and integrity checking is
required, the ITE also includes an ICV in the packets it sends to the
ETE. The ICV format is shown in Figure 3:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|Key|Algorithm| Message Authentication Code (MAC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ...
Figure 3: Integrity Check Vector (ICV) Format
As shown in the figure, the ICV begins with a 1-octet control field
with a 1-bit (F)lag, a 2-bit Key identifier and a 5-bit Algorithm
identifier. The control octet is followed by a variable-length
Message Authentication Code (MAC). The ITE maintains a per ETE
algorithm and secret key to calculate the MAC in each packet it will
send to this ETE. (By default, the ITE sets the F bit and Algorithm
fields to 0 to indicate use of the HMAC-SHA-1 algorithm with a 160
bit shared secret key to calculate an 80 bit MAC per [RFC2104] over
the leading 128 bytes of the packet. Other values for F and
Algorithm are out of scope.) The ITE then sets a variable "USE_ICV"
to TRUE, and includes an ICV in each packet it sends to this ETE;
otherwise, it sets USE_ICV to FALSE.
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For each SEAL path, the ITE must also account for encapsulation
header lengths. The ITE therefore maintains the per SEAL path
constant values "SHLEN" set to the length of the SEAL header, "THLEN"
set to the length of the outer encapsulating transport layer headers
(or 0 if outer transport layer encapsulation is not used), "IHLEN"
set to the length of the outer IP layer header, and "HLEN" set to
(SHLEN+THLEN+IHLEN). (The ITE must include the length of the
uncompressed headers even if header compression is enabled when
calculating these lengths.) In addition, the ITE maintains a per
SEAL path variable "MAXMTU" initialized to the maximum of 1500 bytes
and the MTU of the underlying link minus HLEN.
The ITE further sets a variable 'MINMTU' to the minimum MTU for the
SEAL path over which encapsulated packets will travel. For IPv6
paths the ITE sets MINMTU=1280 (see: [RFC2460]) and for IPv4 paths
the ITE sets MINMTU=576 even though the true MINMTU for IPv4 is only
68 bytes (see: [RFC0791]).
The ITE can also set MINMTU to a larger value if there is reason to
believe that the minimum path MTU is larger, or to a smaller value if
there is reason to believe the MTU is smaller, e.g., if there may be
additional encapsulations on the path. If this value proves too
large, the ITE will receive PTB message feedback either from the ETE
or from a router on the path and will be able to reduce its MINMTU to
a smaller value.
The ITE may instead maintain the packet sizing variables and
constants as per ETE (rather than per SEAL path) values. In that
case, the values reflect the lowest-common-denominator size across
all of the SEAL paths associated with this ETE.
5.4.3. SEAL Layer Pre-Processing
The SEAL layer is logically positioned between the inner and outer
network protocol layers, where the inner layer is seen as the (true)
network layer and the outer layer is seen as the (virtual) data link
layer. Each packet to be processed by the SEAL layer is either
admitted into the tunnel interface by the inner network layer
protocol as described in Section 5.4.1 or is undergoing re-
encapsulation from within the tunnel interface. The SEAL layer sees
the former class of packets as inner packets that include inner
network and transport layer headers, and sees the latter class of
packets as transitional SEAL packets that include the outer and SEAL
layer headers that were inserted by the previous hop SEAL ITE. For
these transitional packets, the SEAL layer re-encapsulates the packet
with new outer and SEAL layer headers when it forwards the packet to
the next hop SEAL ITE.
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We now discuss the SEAL layer pre-processing actions for these two
classes of packets.
5.4.3.1. Inner Packet Pre-Processing
For each inner packet admitted into the tunnel interface, if the
packet is itself a SEAL packet (i.e., one with the port number for
SEAL in the transport layer header or one with the protocol number
for SEAL in the IP layer header) and the LEVEL field of the SEAL
header contains the value 0, the ITE silently discards the packet.
Otherwise, for non-SEAL IPv4 inner packets with DF==0 in the IP
header and IPv6 inner packets with a fragment header and with (MF=0;
Offset=0), if the packet is larger than (MINMTU-HLEN) the ITE uses IP
fragmentation to fragment the packet into N roughly equal-length
pieces, where N is minimized and each fragment is significantly
smaller than (MINMTU-HLEN) to allow for additional encapsulations in
the path. The ITE then submits each fragment for SEAL encapsulation
as specified in Section 5.4.4.
For all other inner packets, if the packet is no larger than MAXMTU
for the corresponding SEAL path the ITE submits it for SEAL
encapsulation as specified in Section 5.4.4. Otherwise, the ITE
drops the packet and sends an ordinary PTB message appropriate to the
inner protocol version (subject to rate limiting) with the MTU field
set to MAXMTU. (For IPv4 SEAL packets with DF==0, the ITE should set
DF=1 and re-calculate the IPv4 header checksum before generating the
PTB message in order to avoid bogon filters.) After sending the PTB
message, the ITE discards the inner packet.
5.4.3.2. Transitional SEAL Packet Pre-Processing
For each transitional packet that is to be processed by the SEAL
layer from within the tunnel interface, the ITE sets aside the SEAL
encapsulation headers that were received from the previous hop.
Next, if the packet is no larger than MAXMTU for the next hop SEAL
path the ITE submits it for SEAL encapsulation as specified in
Section 5.4.4. Otherwise, the ITE drops the packet and sends an SCMP
Packet Too Big (SPTB) message to the previous hop subject to rate
limiting (see: Section 5.6.1.1) with the MTU field set to MAXMTU.
After sending the SPTB message, the ITE discards the packet.
5.4.4. SEAL Encapsulation and Segmentation
For each inner packet/fragment submitted for SEAL encapsulation, the
ITE next encapsulates the packet in a SEAL header formatted as
specified in Section 5.3. The SEAL header includes an Identification
field when USE_ID is TRUE, followed by an ICV field when USE_ICV is
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TRUE.
The ITE next sets C=0 and RES=0 in the SEAL header. The ITE also
sets A=1 if ETE reachability determination is necessary (see: Section
5.4.6) or for stateful MTU determination (see Section 5.4.9).
Otherwise, the ITE sets A=0.
The ITE then sets LINK_ID to the value assigned to the underlying
SEAL path, and sets NEXTHDR to the protocol number corresponding to
the address family of the encapsulated inner packet. For example,
the ITE sets NEXTHDR to the value '4' for encapsulated IPv4 packets
[RFC2003], '41' for encapsulated IPv6 packets [RFC2473][RFC4213],
'80' for encapsulated OSI/CLNP packets [RFC1070], etc.
Next, if the inner packet is not itself a SEAL packet the ITE sets
LEVEL to an integer value between 0 and 7 as a specification of the
number of additional layers of nested SEAL encapsulations permitted.
If the inner packet is a SEAL packet that is undergoing nested
encapsulation, the ITE instead sets LEVEL to the value that appears
in the inner packet's SEAL header minus 1. If the inner packet is
undergoing SEAL re-encapsulation, the ITE instead copies the LEVEL
value from the SEAL header of the packet to be re-encapsulated.
Next, if the inner packet is no larger than (MINMTU-HLEN) or larger
than 1500, the ITE sets (M=0; Offset=0). Otherwise, the ITE breaks
the inner packet into a N roughly equal-length non-overlapping
segments (where N is minimized and each fragment is significantly
smaller than (MINMTU-HLEN) to allow for additional encapsulations in
the path) then appends a clone of the SEAL header from the first
segment onto the head of each additional segment. The ITE MUST also
include an Identification field and set USE_ID=TRUE for each segment.
The ITE then sets (M=1; Offset=0) in the first segment, sets (M=0/1;
Offset=O(1)) in the second segment, sets (M=0/1; Offset=O(2)) in the
third segment (if needed), etc., then finally sets (M=0; Offset=O(n))
in the final segment (where O(i) is the number of 32 byte blocks that
preceded this segment). Note that in some instances the ETE may be
incapable of reassembling segmented SEAL packets prepared in this
fashion. In that case, the ITE will receive SPTB messages as
described in Section 5.6 and should refrain from performing SEAL
segmentation for future packets destined to this ETE.
When USE_ID is FALSE, the ITE next sets I=0. Otherwise, the ITE sets
I=1 and writes a monotonically-incrementing integer value for this
ETE in the Identification field beginning with 0 in the first packet
transmitted. (For SEAL packets that have been split into multiple
pieces, the ITE writes the same Identification value in each piece.)
The monotonically-incrementing requirement is to satisfy ETEs that
use this value for anti-replay purposes. The value is incremented
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modulo 2^32, i.e., it wraps back to 0 when the previous value was
(2^32 - 1).
When USE_ICV is FALSE, the ITE next sets V=0. Otherwise, the ITE
sets V=1, includes an ICV and calculates the MAC using HMAC-SHA-1
with a 160 bit secret key and 80 bit MAC field. Beginning with the
SEAL header, the ITE sets the ICV field to 0, calculates the MAC over
the leading 128 bytes of the packet (or up to the end of the packet
if there are fewer than 128 bytes) and places the result in the MAC
field. (For SEAL packets that have been split into multiple pieces,
each piece calculates its own MAC.) The ITE then writes the value 0
in the F flag and 0x00 in the Algorithm field of the ICV control
octet (other values for these fields, and other MAC calculation
disciplines, are outside the scope of this document and may be
specified in future documents.)
The ITE then adds the outer encapsulating headers as specified in
Section 5.4.5.
5.4.5. Outer Encapsulation
Following SEAL encapsulation, the ITE next encapsulates each segment
in the requisite outer transport (when necessary) and IP layer
headers. When a transport layer header such as UDP or TCP is
included, the ITE writes the port number for SEAL in the transport
destination service port field.
When UDP encapsulation is used, the ITE sets the UDP checksum field
to zero for IPv4 packets and also sets the UDP checksum field to zero
for IPv6 packets even though IPv6 generally requires UDP checksums.
Further considerations for setting the UDP checksum field for IPv6
packets are discussed in [RFC6935][RFC6936].
The ITE then sets the outer IP layer headers the same as specified
for ordinary IP encapsulation (e.g., [RFC1070][RFC2003], [RFC2473],
[RFC4213], etc.) except that for ordinary SEAL packets the ITE copies
the "TTL/Hop Limit", "Type of Service/Traffic Class" and "Congestion
Experienced" values in the inner network layer header into the
corresponding fields in the outer IP header. For transitional SEAL
packets undergoing re-encapsulation, the ITE instead copies the "TTL/
Hop Limit", "Type of Service/Traffic Class" and "Congestion
Experienced" values in the outer IP header of the received packet
into the corresponding fields in the outer IP header of the packet to
be forwarded (i.e., the values are transferred between outer headers
and *not* copied from the inner network layer header).
The ITE also sets the IP protocol number to the appropriate value for
the first protocol layer within the encapsulation (e.g., UDP, TCP,
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SEAL, etc.). When IPv6 is used as the outer IP protocol, the ITE
then sets the flow label value in the outer IPv6 header the same as
described in [RFC6438]. When IPv4 is used as the outer IP protocol,
the ITE instead sets DF=0 in the IPv4 header to allow the packet to
be fragmented if it encounters a restricting link (for IPv6 SEAL
paths, the DF bit is implicitly set to 1).
The ITE finally sends each outer packet via the underlying link
corresponding to LINK_ID.
5.4.6. Path Probing and ETE Reachability Verification
All SEAL data packets sent by the ITE are considered implicit probes.
SEAL data packets will elicit an SCMP message from the ETE if it
needs to acknowledge a probe and/or report an error condition. SEAL
data packets may also be dropped by either the ETE or a router on the
path, which may or may not result in an ICMP message being returned
to the ITE.
The ITE processes ICMP messages as specified in Section 5.4.7.
The ITE processes SCMP messages as specified in Section 5.6.2.
5.4.7. Processing ICMP Messages
When the ITE sends SEAL packets, it may receive ICMP error messages
[RFC0792][RFC4443] from an ordinary router within the subnetwork.
Each ICMP message includes an outer IP header, followed by an ICMP
header, followed by a portion of the SEAL data packet that generated
the error (also known as the "packet-in-error") beginning with the
outer IP header.
The ITE should process ICMPv4 Protocol Unreachable messages and
ICMPv6 Parameter Problem messages with Code "Unrecognized Next Header
type encountered" as a hint that the IP destination address does not
implement SEAL. The ITE can optionally ignore ICMP messages that do
not include sufficient information in the packet-in-error, or process
them as a hint that the SEAL path may be failing.
For other ICMP messages, the ITE should use any outer header
information available as a first-pass authentication filter (e.g., to
determine if the source of the message is within the same
administrative domain as the ITE) and discards the message if first
pass filtering fails.
Next, the ITE examines the packet-in-error beginning with the SEAL
header. If the value in the Identification field (if present) is not
within the window of packets the ITE has recently sent to this ETE,
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or if the MAC value in the SEAL header ICV field (if present) is
incorrect, the ITE discards the message.
Next, if the received ICMP message is a PTB the ITE sets the
temporary variable "PMTU" for this SEAL path to the MTU value in the
PTB message. If PMTU==0, the ITE consults a plateau table (e.g., as
described in [RFC1191]) to determine PMTU based on the length field
in the outer IP header of the packet-in-error. For example, if the
ITE receives a PTB message with MTU==0 and length 4KB, it can set
PMTU=2KB. If the ITE subsequently receives a PTB message with MTU==0
and length 2KB, it can set PMTU=1792, etc. to a minimum value of
PMTU=(1500+HLEN). If the ITE is performing stateful MTU
determination for this SEAL path (see Section 5.4.9), the ITE next
sets MAXMTU=MAX((PMTU-HLEN), 1500). (Note however that the ITE may
need to set a smaller MAXMTU size if the ETE is not configured to
perform reassembly.)
If the ICMP message was not discarded, the ITE then transcribes it
into a message to return to the previous hop. If the inner packet
was a SEAL data packet, the ITE transcribes the ICMP message into an
SCMP message. Otherwise, the ITE transcribes the ICMP message into a
message appropriate for the inner protocol version.
To transcribe the message, the ITE extracts the inner packet from
within the ICMP message packet-in-error field and uses it to generate
a new message corresponding to the type of the received ICMP message.
For SCMP messages, the ITE generates the message the same as
described for ETE generation of SCMP messages in Section 5.6.1. For
(S)PTB messages, the ITE writes (PMTU-HLEN) in the MTU field.
The ITE finally forwards the transcribed message to the previous hop
toward the inner source address.
5.4.8. IPv4 Middlebox Reassembly Testing
The ITE can perform a qualification exchange to ensure that the
subnetwork correctly delivers fragments to the ETE. This procedure
can be used, e.g., to determine whether there are middleboxes on the
path that violate the [RFC1812], Section 5.2.6 requirement that: "A
router MUST NOT reassemble any datagram before forwarding it".
The ITE should use knowledge of its topological arrangement as an aid
in determining when middlebox reassembly testing is necessary. For
example, if the ITE is aware that the ETE is located somewhere in the
public Internet, middlebox reassembly testing should not be
necessary. If the ITE is aware that the ETE is located behind a NAT
or a firewall, however, then reassembly testing can be used to detect
middleboxes that do not conform to specifications.
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The ITE can perform a middlebox reassembly test by selecting a data
packet to be used as a probe. While performing the test with real
data packets, the ITE should select only inner packets that are no
larger than (1500-HLEN) bytes for testing purposes. The ITE can also
construct an explicit probe packet instead of using ordinary SEAL
data packets.
To generate an explicit probe packet, the ITE creates a packet buffer
beginning with the same outer headers, SEAL header and inner network
layer header that would appear in an ordinary data packet, then pads
the packet with random data to a length that is at least 128 bytes
but no longer than (1500-HLEN) bytes. The ITE then writes the value
'0' in the inner network layer TTL (for IPv4) or Hop Limit (for IPv6)
field.
The ITE then sets C=0 in the SEAL header of the probe packet and sets
the NEXTHDR field to the inner network layer protocol type. (The ITE
may also set A=1 if it requires a positive acknowledgement;
otherwise, it sets A=0.) Next, the ITE sets LINK_ID and LEVEL to the
appropriate values for this SEAL path, sets Identification and I=1
(when USE_ID is TRUE), then finally calculates the ICV and sets V=1
(when USE_ICV is TRUE).
The ITE then encapsulates the probe packet in the appropriate outer
headers, splits it into two outer IPv4 fragments, then sends both
fragments over the same SEAL path.
The ITE should send a series of probe packets (e.g., 3-5 probes with
1sec intervals between tests) instead of a single isolated probe in
case of packet loss. If the ETE returns an SCMP PTB message with MTU
!= 0, then the SEAL path correctly supports fragmentation; otherwise,
the ITE enables stateful MTU determination for this SEAL path as
specified in Section 5.4.9.
(Examples of middleboxes that may perform reassembly include stateful
NATs and firewalls. Such devices could still allow for stateless MTU
determination if they gather the fragments of a fragmented IPv4 SEAL
data packet for packet analysis purposes but then forward the
fragments on to the final destination rather than forwarding the
reassembled packet.)
5.4.9. Stateful MTU Determination
SEAL supports a stateless MTU determination capability, however the
ITE may in some instances wish to impose a stateful MTU limit on a
particular SEAL path. For example, when the ETE is situated behind a
middlebox that performs IPv4 reassembly (see: Section 5.4.8) it is
imperative that fragmentation be avoided. In other instances (e.g.,
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when the SEAL path includes performance-constrained links), the ITE
may deem it necessary to cache a conservative static MTU in order to
avoid sending large packets that would only be dropped due to an MTU
restriction somewhere on the path.
To determine a static MTU value, the ITE sends a series of probe
packets of various sizes to the ETE with A=1 in the SEAL header and
DF=1 in the outer IP header. The ITE then caches the size 'S' of the
largest packet for which it receives a probe reply from the ETE by
setting MAXMTU=MAX((S-HLEN), 1500) for this SEAL path. (Note however
that the ITE may need to set a smaller MAXMTU size if the ETE is not
configured to perform reassembly.)
For example, the ITE could send probe packets of 4KB, followed by
2KB, followed by 1792 bytes, etc. While probing, the ITE processes
any ICMP PTB message it receives as a potential indication of probe
failure then discards the message.
5.4.10. Detecting Path MTU Changes
When stateful MTU determination is used, the ITE SHOULD periodically
reset MAXMTU and/or re-probe the path to determine whether MAXMTU has
increased. If the path still has a too-small MTU, the ITE will
receive a PTB message that reports a smaller size.
5.5. ETE Specification
5.5.1. Reassembly Buffer Requirements
For IPv6, the ETE configures a reassembly buffer size of (1500 +
HLEN) bytes for the reassembly of outer IPv6 packets, i.e., even
though the true minimum reassembly size for IPv6 is only 1500 bytes
[RFC2460]. For IPv4, the ETE also configures a reassembly buffer
size of (1500 + HLEN) bytes for the reassembly of outer IPv4 packets,
i.e., even though the true minimum reassembly size for IPv4 is only
576 bytes [RFC1122].
In addition to this outer reassembly buffer requirement, the ETE
further configures a SEAL reassembly buffer size of (1500 + HLEN)
bytes for the reassembly of segmented SEAL packets (see: Section
5.5.4).
In some deployments, it may not be practical for the ETE to perform
reassembly. In those cases, the ETE can omit these reassembly
requirements and return SPTB messages for any packets that arrive as
fragments as specified in section 5.6.
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5.5.2. Tunnel Neighbor Soft State
When message origin authentication and integrity checking is
required, the ETE maintains a per-ITE MAC calculation algorithm and a
symmetric secret key to verify the MAC. When per-packet
identification is required, the ETE also maintains a window of
Identification values for the packets it has recently received from
this ITE.
When the tunnel neighbor relationship is bidirectional, the ETE
further maintains a per SEAL path mapping of outer IP and transport
layer addresses to the LINK_ID that appears in packets received from
the ITE.
5.5.3. IP-Layer Reassembly
The ETE reassembles fragmented IP packets that are explcitly
addressed to itself if it is configured to do so. For IP fragments
that are received via a SEAL tunnel, the ETE SHOULD maintain
conservative reassembly cache high- and low-water marks. When the
size of the reassembly cache exceeds this high-water mark, the ETE
SHOULD actively discard stale incomplete reassemblies (e.g., using an
Active Queue Management (AQM) strategy) until the size falls below
the low-water mark. The ETE SHOULD also actively discard any pending
reassemblies that clearly have no opportunity for completion, e.g.,
when a considerable number of new fragments have arrived before a
fragment that completes a pending reassembly arrives.
The ETE processes non-SEAL IP packets as specified in the normative
references, i.e., it performs any necessary IP reassembly then
discards the packet if it is larger than the reassembly buffer size
or delivers the (fully-reassembled) packet to the appropriate upper
layer protocol module.
For SEAL packets, the ETE performs any necessary IP reassembly then
submits the packet for SEAL decapsulation as specified in Section
5.5.4. (Note that if the packet is larger than the reassembly buffer
size, the ETE still examines the leading portion of the (partially)
reassembled packet during decapsulation.)
5.5.4. Decapsulation, SEAL-Layer Reassembly, and Re-Encapsulation
For each SEAL packet accepted for decapsulation, when I==1 the ETE
first examines the Identification field. If the Identification is
not within the window of acceptable values for this ITE, the ETE
silently discards the packet.
Next, if V==1 the ETE SHOULD verify the MAC value (with the MAC field
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itself reset to 0) and silently discard the packet if the value is
incorrect.
Next, if the packet arrived as multiple IP fragments, the ETE sends
an SPTB message back to the ITE with MTU set to the size of the
largest fragment received minus HLEN (see: Section 5.6.1.1).
Next, if the packet arrived as multiple IP fragments and the inner
packet is larger than 1500 bytes, the ETE silently discards the
packet; otherwise, it continues to process the packet.
Next, if there is an incorrect value in a SEAL header field (e.g., an
incorrect "VER" field value), the ETE discards the packet. If the
SEAL header has C==0, the ETE also returns an SCMP "Parameter
Problem" (SPP) message (see Section 5.6.1.2).
Next, if the SEAL header has C==1, the ETE processes the packet as an
SCMP packet as specified in Section 5.6.2. Otherwise, the ETE
continues to process the packet as a SEAL data packet.
Next, if the SEAL header has (M==1 || Offset!=0) the ETE caches the
segment for reassembly if it is configured to do so. (Otherwise, it
discards the packet and (if M==1 && Offset==0) sends an SPTB message
back to the ITE as specified in Section 5.6). To perform reassembly,
the ETE checks to see if the other segments of this already-segmented
SEAL packet have arrived, i.e., by looking for additional segments
that have the same outer IP source address, destination address,
source transport port number (if present) and SEAL Identification
value. If the other segments have already arrived, the ETE discards
the SEAL header and other outer headers from the non-initial segments
and appends them onto the end of the first segment according to their
offset value. Otherwise, the ETE caches the segment for at most 60
seconds while awaiting the arrival of its partners. During this
process, the ETE discards any segments that are overlapping with
respect to segments that have already been received. The ETE further
SHOULD manage the SEAL reassembly cache the same as described for the
IP-Layer Reassembly cache in Section 5.5.3, i.e., it SHOULD perform
an early discard for any pending reassemblies that have low
probability of completion.
Next, if the SEAL header in the (reassembled) packet has A==1, the
ETE sends an SPTB message back to the ITE with MTU=0 (see: Section
5.6.1.1).
Finally, the ETE discards the outer headers and processes the inner
packet according to the header type indicated in the SEAL NEXTHDR
field. If the inner (TTL / Hop Limit) field encodes the value 0, the
ETE silently discards the packet. Otherwise, if the next hop toward
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the inner destination address is via a different interface than the
SEAL packet arrived on, the ETE discards the SEAL header and delivers
the inner packet either to the local host or to the next hop
interface if the packet is not destined to the local host.
If the next hop is on the same interface the SEAL packet arrived on,
however, the ETE submits the packet for SEAL re-encapsulation
beginning with the specification in Section 5.4.3 above and without
decrementing the value in the inner (TTL / Hop Limit) field. In this
process, the packet remains within the tunnel (i.e., it does not exit
and then re-enter the tunnel); hence, the packet is not discarded if
the LEVEL field in the SEAL header contains the value 0.
5.6. The SEAL Control Message Protocol (SCMP)
SEAL provides a companion SEAL Control Message Protocol (SCMP) that
uses the same message types and formats as for the Internet Control
Message Protocol for IPv6 (ICMPv6) [RFC4443]. As for ICMPv6, each
SCMP message includes a 32-bit header and a variable-length body.
The ITE encapsulates the SCMP message in a SEAL header and outer
headers as shown in Figure 4:
+--------------------+
~ outer IP header ~
+--------------------+
~ other outer hdrs ~
+--------------------+
~ SEAL Header ~
+--------------------+ +--------------------+
| SCMP message header| --> | SCMP message header|
+--------------------+ +--------------------+
| | --> | |
~ SCMP message body ~ --> ~ SCMP message body ~
| | --> | |
+--------------------+ +--------------------+
SCMP Message SCMP Packet
before encapsulation after encapsulation
Figure 4: SCMP Message Encapsulation
The following sections specify the generation, processing and
relaying of SCMP messages.
5.6.1. Generating SCMP Error Messages
ETEs generate SCMP error messages in response to receiving certain
SEAL data packets using the format shown in Figure 5:
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0 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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type-Specific Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As much of the invoking SEAL data packet as possible |
~ (beginning with the SEAL header) without the SCMP ~
| packet exceeding MINMTU bytes (*) |
(*) also known as the "packet-in-error"
Figure 5: SCMP Error Message Format
The error message includes the 32-bit SCMP message header, followed
by a 32-bit Type-Specific Data field, followed by the leading portion
of the invoking SEAL data packet beginning with the SEAL header as
the "packet-in-error". The packet-in-error includes as much of the
invoking packet as possible extending to a length that would not
cause the entire SCMP packet following outer encapsulation to exceed
MINMTU bytes.
When the ETE processes a SEAL data packet for which the
Identification and ICV values are correct but an error must be
returned, it prepares an SCMP error message as shown in Figure 5.
The ETE sets the Type and Code fields to the same values that would
appear in the corresponding ICMPv6 message [RFC4443], but calculates
the Checksum beginning with the SCMP message header using the
algorithm specified for ICMPv4 in [RFC0792].
The ETE next encapsulates the SCMP message in the requisite SEAL and
outer headers as shown in Figure 4. During encapsulation, the ETE
sets the outer destination address/port numbers of the SCMP packet to
the values associated with the ITE and sets the outer source address/
port numbers to its own outer address/port numbers.
The ETE then sets (C=1; RES=0; M=0; Offset=0) in the SEAL header (by
default, the ETE also sets A=0 in the SEAL header except as otherwise
noted for specific SCMP messages). The ETE then sets I, V, NEXTHDR
and LEVEL to the same values that appeared in the SEAL header of the
data packet. If the neighbor relationship between the ITE and ETE is
unidirectional, the ETE next sets the LINK_ID field to the same value
that appeared in the SEAL header of the data packet. Otherwise, the
ETE sets the LINK_ID field to the value it would use in sending a
SEAL packet to this ITE.
When I==1, the ETE next sets the Identification field to an
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appropriate value for the ITE. If the neighbor relationship between
the ITE and ETE is unidirectional, the ETE sets the Identification
field to the same value that appeared in the SEAL header of the data
packet. Otherwise, the ETE sets the Identification field to the
value it would use in sending the next SEAL packet to this ITE.
When V==1, the ETE then prepares the ICV field the same as specified
for SEAL data packet encapsulation in Section 5.4.4.
Finally, the ETE sends the resulting SCMP packet to the ITE the same
as specified for SEAL data packets in Section 5.4.5.
The following sections describe additional considerations for various
SCMP error messages:
5.6.1.1. Generating SCMP Packet Too Big (SPTB) Messages
An ETE generates an SPTB message when it receives a SEAL data packet
that arrived as multiple outer IP fragments. The ETE prepares the
SPTB message the same as for the corresponding ICMPv6 PTB message,
and writes the length of the largest outer IP fragment received minus
HLEN in the MTU field of the message.
The ETE also generates an SPTB message when it receves a SEAL data
packet with (M==1 && Offset==0) in the SEAL header but for which it
is unable to perform reassembly.
The ETE finally also generates an SPTB message when it accepts a SEAL
protocol data packet with A==1 in the SEAL header. The ETE prepares
the SPTB message the same as above, except that it writes the value 0
in the MTU field.
In each case, the ETE sets A=1 in the SEAL header of the SPTB message
if it supports reassembly; otherwise, it sets A=0.
5.6.1.2. Generating Other SCMP Error Messages
An ETE generates an SCMP "Destination Unreachable" (SDU) message
under the same circumstances that an IPv6 system would generate an
ICMPv6 Destination Unreachable message.
An ETE generates an SCMP "Parameter Problem" (SPP) message when it
receives a SEAL packet with an incorrect value in the SEAL header.
TEs generate other SCMP message types using methods and procedures
specified in other documents. For example, SCMP message types used
for tunnel neighbor coordinations are specified in VET
[I-D.templin-intarea-vet].
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5.6.2. Processing SCMP Error Messages
An ITE may receive SCMP messages with C==1 in the SEAL header after
sending packets to an ETE. The ITE first verifies that the outer
addresses of the SCMP packet are correct, and (when I==1) that the
Identification field contains an acceptable value. The ITE next
verifies that the SEAL header fields are set correctly as specified
in Section 5.6.1. When V==1, the ITE then verifies the ICV. The ITE
next verifies the Checksum value in the SCMP message header. If any
of these values are incorrect, the ITE silently discards the message;
otherwise, it processes the message as follows:
5.6.2.1. Processing SCMP PTB Messages
After an ITE sends a SEAL data packet to an ETE, it may receive an
SPTB message with a packet-in-error containing the leading portion of
the packet (see: Section 5.6.1.1). For SPTB messages with MTU==0,
the ITE processes the message as confirmation that the ETE received a
SEAL data packet with A==1 in the SEAL header. The ITE then discards
the message.
For SPTB messages with A==0, the ITE process the message as an
indication that the ETE cannot perform SEAL reassembly. In that
case, the ITE sends a suitable PTB message back to the original
source as described below. The ITE should thereafter disable SEAL
layer segmentation for this ETE and reduce its MTU estimate
accordingly.
For all other SPTB messages, the ITE processes the message as an
indication of a packet size limitation as follows. If the inner
packet is no larger than 1500 bytes, the ITE reduces its MINMTU value
for this ITE. If the inner packet length is larger than 1500 and the
MTU value is not substantially less than MINMTU bytes, the value is
likely to reflect the true MTU of the restricting link on the path to
the ETE; otherwise, a router on the path may be generating runt
fragments.
In that case, the ITE can consult a plateau table (e.g., as described
in [RFC1191]) to rewrite the MTU value to a reduced size. For
example, if the ITE receives an IPv4 SPTB message with MTU==256 and
inner packet length 4KB, it can rewrite the MTU to 2KB. If the ITE
subsequently receives an IPv4 SPTB message with MTU==256 and inner
packet length 2KB, it can rewrite the MTU to 1792, etc., to a minimum
of 1500 bytes. If the ITE is performing stateful MTU determination
for this SEAL path, it then writes the new MTU value minus HLEN in
MAXMTU.
The ITE then checks its forwarding tables to discover the previous
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hop toward the source address of the inner packet. If the previous
hop is reached via the same tunnel interface the SPTB message arrived
on, the ITE relays the message to the previous hop. In order to
relay the message, the first writes zero in the Identification and
ICV fields of the SEAL header within the packet-in-error. The ITE
next rewrites the outer SEAL header fields with values corresponding
to the previous hop and recalculates the MAC using the MAC
calculation parameters associated with the previous hop. Next, the
ITE replaces the SPTB's outer headers with headers of the appropriate
protocol version and fills in the header fields as specified in
Section 5.4.5, where the destination address/port correspond to the
previous hop and the source address/port correspond to the ITE. The
ITE then sends the message to the previous hop the same as if it were
issuing a new SPTB message. (Note that, in this process, the values
within the SEAL header of the packet-in-error are meaningless to the
previous hop and therefore cannot be used by the previous hop for
authentication purposes.)
If the previous hop is not reached via the same tunnel interface, the
ITE instead transcribes the message into a format appropriate for the
inner packet (i.e., the same as described for transcribing ICMP
messages in Section 5.4.7) and sends the resulting transcribed
message to the original source. (NB: if the inner packet within the
SPTB message is an IPv4 SEAL packet with DF==0, the ITE should set
DF=1 and re-calculate the IPv4 header checksum while transcribing the
message in order to avoid bogon filters.) The ITE then discards the
SPTB message.
Note that the ITE may receive an SPTB message from another ITE that
is at the head end of a nested level of encapsulation. The ITE has
no security associations with this nested ITE, hence it should
consider this SPTB message the same as if it had received an ICMP PTB
message from an ordinary router on the path to the ETE. That is, the
ITE should examine the packet-in-error field of the SPTB message and
only process the message if it is able to recognize the packet as one
it had previously sent.
5.6.2.2. Processing Other SCMP Error Messages
An ITE may receive an SDU message with an appropriate code under the
same circumstances that an IPv6 node would receive an ICMPv6
Destination Unreachable message. The ITE either transcribes or
relays the message toward the source address of the inner packet
within the packet-in-error the same as specified for SPTB messages in
Section 5.6.2.1.
An ITE may receive an SPP message when the ETE receives a SEAL packet
with an incorrect value in the SEAL header. The ITE should examine
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the SEAL header within the packet-in-error to determine whether a
different setting should be used in subsequent packets, but does not
relay the message further.
TEs process other SCMP message types using methods and procedures
specified in other documents. For example, SCMP message types used
for tunnel neighbor coordinations are specified in VET
[I-D.templin-intarea-vet].
6. Link Requirements
Subnetwork designers are expected to follow the recommendations in
Section 2 of [RFC3819] when configuring link MTUs.
7. End System Requirements
End systems are encouraged to implement end-to-end MTU assurance
(e.g., using Packetization Layer Path MTU Discovery (PLPMTUD) per
[RFC4821]) even if the subnetwork is using SEAL.
When end systems use PLPMTUD, SEAL will ensure that the tunnel
behaves as a link in the path that assures an MTU of at least 1500
bytes while not precluding discovery of larger MTUs. The PMPMTUD
mechanism will therefore be able to function as designed in order to
discover and utilize larger MTUs.
8. Router Requirements
Routers within the subnetwork are expected to observe the standard IP
router requirements, including the implementation of IP fragmentation
and reassembly as well as the generation of ICMP messages
[RFC0792][RFC1122][RFC1812][RFC2460][RFC4443][RFC6434].
Note that, even when routers support existing requirements for the
generation of ICMP messages, these messages are often filtered and
discarded by middleboxes on the path to the original source of the
message that triggered the ICMP. It is therefore not possible to
assume delivery of ICMP messages even when routers are correctly
implemented.
9. Nested Encapsulation Considerations
SEAL supports nested tunneling for up to 8 layers of encapsulation.
In this model, the SEAL ITE has a tunnel neighbor relationship only
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with ETEs at its own nesting level, i.e., it does not have a tunnel
neighbor relationship with other ITEs, nor with ETEs at other nesting
levels.
Therefore, when an ITE 'A' within an outer nesting level needs to
return an error message to an ITE 'B' within an inner nesting level,
it generates an ordinary ICMP error message the same as if it were an
ordinary router within the subnetwork. 'B' can then perform message
validation as specified in Section 5.4.7, but full message origin
authentication is not possible.
Since ordinary ICMP messages are used for coordinations between ITEs
at different nesting levels, nested SEAL encapsulations should only
be used when the ITEs are within a common administrative domain
and/or when there is no ICMP filtering middlebox such as a firewall
or NAT between them. An example would be a recursive nesting of
mobile networks, where the first network receives service from an
ISP, the second network receives service from the first network, the
third network receives service from the second network, etc.
NB: As an alternative, the SCMP protocol could be extended to allow
ITE 'A' to return an SCMP message to ITE 'B' rather than return an
ICMP message. This would conceptually allow the control messages to
pass through firewalls and NATs, however it would give no more
message origin authentication assurance than for ordinary ICMP
messages. It was therefore determined that the complexity of
extending the SCMP protocol was of little value within the context of
the anticipated use cases for nested encapsulations.
10. Reliability Considerations
Although a SEAL tunnel may span an arbitrarily-large subnetwork
expanse, the IP layer sees the tunnel as a simple link that supports
the IP service model. Links with high bit error rates (BERs) (e.g.,
IEEE 802.11) use Automatic Repeat-ReQuest (ARQ) mechanisms [RFC3366]
to increase packet delivery ratios, while links with much lower BERs
typically omit such mechanisms. Since SEAL tunnels may traverse
arbitrarily-long paths over links of various types that are already
either performing or omitting ARQ as appropriate, it would therefore
be inefficient to require the tunnel endpoints to also perform ARQ.
11. Integrity Considerations
The SEAL header includes an integrity check field that covers the
SEAL header and at least the inner packet headers. This provides for
header integrity verification on a segment-by-segment basis for a
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segmented re-encapsulating tunnel path.
Fragmentation and reassembly schemes must also consider packet-
splicing errors, e.g., when two fragments from the same packet are
concatenated incorrectly, when a fragment from packet X is
reassembled with fragments from packet Y, etc. The primary sources
of such errors include implementation bugs and wrapping IPv4 ID
fields.
In particular, the IPv4 16-bit ID field can wrap with only 64K
packets with the same (src, dst, protocol)-tuple alive in the system
at a given time [RFC4963]. When the IPv4 ID field is re-written by a
middlebox such as a NAT or Firewall, ID field wrapping can occur with
even fewer packets alive in the system. It is therefore essential
that IPv4 fragmentation and reassembly be avoided.
12. IANA Considerations
The IANA is requested to allocate a User Port number for "SEAL" in
the 'port-numbers' registry. The Service Name is "SEAL", and the
Transport Protocols are TCP and UDP. The Assignee is the IESG
(iesg@ietf.org) and the Contact is the IETF Chair (chair@ietf.org).
The Description is "Subnetwork Encapsulation and Adaptation Layer
(SEAL)", and the Reference is the RFC-to-be currently known as
'draft-templin-intarea.seal'.
13. Security Considerations
SEAL provides a segment-by-segment message origin authentication,
integrity and anti-replay service. The SEAL header is sent in-the-
clear the same as for the outer IP and other outer headers. In this
respect, the threat model is no different than for IPv6 extension
headers. Unlike IPv6 extension headers, however, the SEAL header can
be protected by an integrity check that also covers the inner packet
headers.
An amplification/reflection/buffer overflow attack is possible when
an attacker sends IP fragments with spoofed source addresses to an
ETE in an attempt to clog the ETE's reassembly buffer and/or cause
the ETE to generate a stream of SCMP messages returned to a victim
ITE. The SCMP message ICV, Identification, as well as the inner
headers of the packet-in-error, provide mitigation for the ETE to
detect and discard SEAL segments with spoofed source addresses.
Security issues that apply to tunneling in general are discussed in
[RFC6169].
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14. Related Work
Section 3.1.7 of [RFC2764] provides a high-level sketch for
supporting large tunnel MTUs via a tunnel-level segmentation and
reassembly capability to avoid IP level fragmentation.
Section 3 of [RFC4459] describes inner and outer fragmentation at the
tunnel endpoints as alternatives for accommodating the tunnel MTU.
Section 4 of [RFC2460] specifies a method for inserting and
processing extension headers between the base IPv6 header and
transport layer protocol data. The SEAL header is inserted and
processed in exactly the same manner.
IPsec/AH is [RFC4301][RFC4301] is used for full message integrity
verification between tunnel endpoints, whereas SEAL only ensures
integrity for the inner packet headers. The AYIYA proposal
[I-D.massar-v6ops-ayiya] uses similar means for providing message
authentication and integrity.
SEAL, along with the Virtual Enterprise Traversal (VET)
[I-D.templin-intarea-vet] tunnel virtual interface abstraction, are
the functional building blocks for the Interior Routing Overlay
Network (IRON) [I-D.templin-ironbis] and Routing and Addressing in
Networks with Global Enterprise Recursion (RANGER) [RFC5720][RFC6139]
architectures.
The concepts of path MTU determination through the report of
fragmentation and extending the IPv4 Identification field were first
proposed in deliberations of the TCP-IP mailing list and the Path MTU
Discovery Working Group (MTUDWG) during the late 1980's and early
1990's. An historical analysis of the evolution of these concepts,
as well as the development of the eventual PMTUD mechanism, appears
in [RFC5320].
15. Implementation Status
An early implementation of the first revision of SEAL [RFC5320] is
available at: http://isatap.com/seal.
16. Acknowledgments
The following individuals are acknowledged for helpful comments and
suggestions: Jari Arkko, Fred Baker, Iljitsch van Beijnum, Oliver
Bonaventure, Teco Boot, Bob Braden, Brian Carpenter, Steve Casner,
Ian Chakeres, Noel Chiappa, Remi Denis-Courmont, Remi Despres, Ralph
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Droms, Aurnaud Ebalard, Gorry Fairhurst, Washam Fan, Dino Farinacci,
Joel Halpern, Sam Hartman, John Heffner, Thomas Henderson, Bob
Hinden, Christian Huitema, Eliot Lear, Darrel Lewis, Joe Macker, Matt
Mathis, Erik Nordmark, Dan Romascanu, Dave Thaler, Joe Touch, Mark
Townsley, Ole Troan, Margaret Wasserman, Magnus Westerlund, Robin
Whittle, James Woodyatt, and members of the Boeing Research &
Technology NST DC&NT group.
Discussions with colleagues following the publication of [RFC5320]
have provided useful insights that have resulted in significant
improvements to this, the Second Edition of SEAL.
This document received substantial review input from the IESG and
IETF area directorates in the February 2013 timeframe. IESG members
and IETF area directorate representatives who contributed helpful
comments and suggestions are gratefully acknowledged.
Path MTU determination through the report of fragmentation was first
proposed by Charles Lynn on the TCP-IP mailing list in 1987.
Extending the IP identification field was first proposed by Steve
Deering on the MTUDWG mailing list in 1989.
17. References
17.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
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[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
17.2. Informative References
[FOLK] Shannon, C., Moore, D., and k. claffy, "Beyond Folklore:
Observations on Fragmented Traffic", December 2002.
[FRAG] Kent, C. and J. Mogul, "Fragmentation Considered Harmful",
October 1987.
[I-D.massar-v6ops-ayiya]
Massar, J., "AYIYA: Anything In Anything",
draft-massar-v6ops-ayiya-02 (work in progress), July 2004.
[I-D.taylor-v6ops-fragdrop]
Jaeggli, J., Colitti, L., Kumari, W., Vyncke, E., Kaeo,
M., and T. Taylor, "Why Operators Filter Fragments and
What It Implies", draft-taylor-v6ops-fragdrop-01 (work in
progress), June 2013.
[I-D.templin-intarea-vet]
Templin, F., "Virtual Enterprise Traversal (VET)",
draft-templin-intarea-vet-40 (work in progress), May 2013.
[I-D.templin-ironbis]
Templin, F., "The Interior Routing Overlay Network
(IRON)", draft-templin-ironbis-15 (work in progress),
May 2013.
[RFC0994] International Organization for Standardization (ISO) and
American National Standards Institute (ANSI), "Final text
of DIS 8473, Protocol for Providing the Connectionless-
mode Network Service", RFC 994, March 1986.
[RFC1063] Mogul, J., Kent, C., Partridge, C., and K. McCloghrie, "IP
MTU discovery options", RFC 1063, July 1988.
[RFC1070] Hagens, R., Hall, N., and M. Rose, "Use of the Internet as
a subnetwork for experimentation with the OSI network
layer", RFC 1070, February 1989.
[RFC1146] Zweig, J. and C. Partridge, "TCP alternate checksum
options", RFC 1146, March 1990.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
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[RFC1701] Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
Routing Encapsulation (GRE)", RFC 1701, October 1994.
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, August 1996.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, August 1999.
[RFC2764] Gleeson, B., Heinanen, J., Lin, A., Armitage, G., and A.
Malis, "A Framework for IP Based Virtual Private
Networks", RFC 2764, February 2000.
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers",
BCP 37, RFC 2780, March 2000.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
[RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery",
RFC 2923, September 2000.
[RFC3232] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by
an On-line Database", RFC 3232, January 2002.
[RFC3366] Fairhurst, G. and L. Wood, "Advice to link designers on
link Automatic Repeat reQuest (ARQ)", BCP 62, RFC 3366,
August 2002.
[RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, July 2004.
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[RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and
More-Specific Routes", RFC 4191, November 2005.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4459] Savola, P., "MTU and Fragmentation Issues with In-the-
Network Tunneling", RFC 4459, April 2006.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963, July 2007.
[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common
Mitigations", RFC 4987, August 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5320] Templin, F., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", RFC 5320, February 2010.
[RFC5445] Watson, M., "Basic Forward Error Correction (FEC)
Schemes", RFC 5445, March 2009.
[RFC5720] Templin, F., "Routing and Addressing in Networks with
Global Enterprise Recursion (RANGER)", RFC 5720,
February 2010.
[RFC5927] Gont, F., "ICMP Attacks against TCP", RFC 5927, July 2010.
[RFC6139] Russert, S., Fleischman, E., and F. Templin, "Routing and
Addressing in Networks with Global Enterprise Recursion
(RANGER) Scenarios", RFC 6139, February 2011.
[RFC6169] Krishnan, S., Thaler, D., and J. Hoagland, "Security
Templin Expires December 14, 2013 [Page 39]
Internet-Draft SEAL June 2013
Concerns with IP Tunneling", RFC 6169, April 2011.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, August 2011.
[RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
Requirements", RFC 6434, December 2011.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, November 2011.
[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",
RFC 6864, February 2013.
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935, April 2013.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, April 2013.
[RIPE] De Boer, M. and J. Bosma, "Discovering Path MTU Black
Holes on the Internet using RIPE Atlas", July 2012.
[SIGCOMM] Luckie, M. and B. Stasiewicz, "Measuring Path MTU
Discovery Behavior", November 2010.
[TBIT] Medina, A., Allman, M., and S. Floyd, "Measuring
Interactions Between Transport Protocols and Middleboxes",
October 2004.
[WAND] Luckie, M., Cho, K., and B. Owens, "Inferring and
Debugging Path MTU Discovery Failures", October 2005.
Templin Expires December 14, 2013 [Page 40]
Internet-Draft SEAL June 2013
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
Templin Expires December 14, 2013 [Page 41]