Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Intended status: Informational November 10, 2014
Expires: May 14, 2015
AERO Minimal Encapsulation
draft-templin-aeromin-00.txt
Abstract
Asymmetric Extended Route Optimization (AERO) specifies both a
control messaging facility and an encapsulation format for managing
tunnels over an enterprise network or other Internetwork. Although
AERO can operate with any tunnel encapsulation format, the base
document considers IP-in-UDP-in-IP encapsulation as the default.
This document presents a minimal encapsulation format for AERO for
use when a UDP header is not needed.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Minimal Encapsulation Format . . . . . . . . . . . . . . . . 3
3. When to Insert the IPv6 Fragment Header . . . . . . . . . . . 3
4. Considerations for Using Minimal Encapsulation . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
8.1. Normative References . . . . . . . . . . . . . . . . . . 4
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Asymmetric Extended Route Optimization (AERO) [I-D.templin-aerolink]
specifies both a control messaging facility and an encapsulation
format for forwarding Internet Protocol (IP) packets [RFC0791]
[RFC2460] over an enterprise network or other Internetwork through a
process known as tunneling. Although AERO can operate with any
tunnel encapsulation format, the base document specifies the
insertion of a User Datagram Protocol (UDP) header [RFC0768] with
port 8060 between the inner and outer IP headers, i.e., as IP-in-UDP-
in-IP. This document presents a minimal encapsulation format for
AERO for use when a UDP header is not needed.
In its minimal form, AERO can use direct IP-in-IP encapsulation
[RFC2003][RFC2473][RFC4213] with no intermediate layer between the
inner and outer IP headers for interior routing and addressing
services. The encapsulation is therefore only differentiated from
other IP-in-IP tunnel types through the application of AERO control
messaging facilities.
However, the tunnel fragmentation required by AERO to support a
guaranteed minimum 1500 bytes cannot be accomplished by inserting an
IPv6 Fragment Header immediately following the UDP header, since the
UDP header is not included for minimal encapsulation. Instead, the
IPv6 fragment header is inserted directly between the inner and outer
IP headers when needed, i.e., even if the outer header is IPv4. The
IPv6 Fragment Header is identified to the outer IP layer by its IP
protocol number, and the Next Header field in the IPv6 Fragment
Header identifies the inner IP header version.
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2. Minimal Encapsulation Format
Figure 1 shows the AERO minimal encapsulation format before any
fragmentation is applied:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer IPv4 Header | | Outer IPv6 Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|IPv6 Fragment Header (optional)| |IPv6 Fragment Header (optional)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner IP Header | | Inner IP Header | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
~ Inner Packet Body ~ ~ Inner Packet Body ~
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6
Figure 1: Minimal Encapsulation Format
3. When to Insert the IPv6 Fragment Header
The IPv6 Fragment Header is inserted whenever the AERO tunnel ingress
needs to apply fragmentation to accommodate packets no larger than
1500 bytes. Fragmentation is performed on the inner packet while
encapsulating each inner packet fragment in identical outer IP and
IPv6 Fragment Headers. Fragmentation therefore follows the same
procedure as for the case when a UDP header is included, which
follows the same procedure as for standard IPv6 fragmentation.
The IPv6 Fragment Header can also be inserted in order to include a
coherent Identification value with each packet, e.g., to aid in
Duplicate Packet Detection (DPD). In this way, networking devices
can cache the Identification values of recently-seen packets and use
the cached values to determine whether a newly-arrived packet is in
fact a duplicate.
Finally, the Identification value within each packet could provide a
rough indicator of packet reordering, e.g., in cases when the tunnel
egress wishes to discard packets that are grossly out of order.
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4. Considerations for Using Minimal Encapsulation
Minimal encapsulation is preferred in environments where UDP
encapsulation would add unnecessary overhead. For example, certain
low-bandwidth wireless data links may benefit from an 8-byte-per-
packet overhead reduction. This is not likely to be a prime
consideration for many modern wireless data links nor for most modern
wired-line data links.
UDP encapsulation can traverse network paths that are inaccessible to
minimal encapsulation, e.g., for crossing Network Address Translators
(NATs). More and more, network middleboxes are also being configured
to discard packets that include anything other than a well-known IP
protocol such as UDP and TCP. It may therefore be necessary to
consider the potential for middlebox filtering before enabling
minimal encapsulation in a given environment.
Evidence seems to suggest that IPv6 fragmentation does not work along
all paths, since well-meaning network middleboxes may consider it as
an attack.
5. IANA Considerations
This document introduces no IANA considerations.
6. Security Considerations
Security considerations are discussed in the base AERO specification
[I-D.templin-aerolink].
7. Acknowledgements
TBD
8. References
8.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
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[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
8.2. Informative References
[I-D.templin-aerolink]
Templin, F., "Transmission of IP Packets over AERO Links",
draft-templin-aerolink-46 (work in progress), October
2014.
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
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