AERO Minimal
EncapsulationBoeing Research & TechnologyP.O. Box 3707SeattleWA98124USAfltemplin@acm.orgI-DInternet-DraftAsymmetric Extended Route Optimization (AERO) specifies both a
control messaging and data packet forwarding facility for managing
tunnels over an enterprise network or other Internetwork. Although AERO
can operate with any tunnel encapsulation format, the base document
considers Generic UDP Encapsulation (GUE) as the default. This document
presents minimal encapsulation formats for AERO using other
encapsulation types.Asymmetric Extended Route Optimization (AERO) specifies both a control messaging and
data packet forwarding facility for forwarding Internet Protocol (IP)
packets 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 between the inner and
outer IP headers per the Generic UDP Encapsulation (GUE) specification. This document presents
minimal encapsulation formats for AERO using other encapsulation
types.AERO can use common minimal encapsulations such as IP-in-IP ,
Generic Routing Encapsulation (GRE) and others. The encapsulation is therefore only
differentiated from non-AERO tunnels through the application of AERO
control messaging.In certain use cases, AERO minimal encapsulation formats may require
encapsulation layer fragmentation in the same manner as for GUE
fragmentation . For
simple IP-in-IP encapsulation, an 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. For
GRE encapsulation, a GRE fragment header is inserted within the GRE
header . shows the AERO IP-in-IP minimal encapsulation
format before any fragmentation is applied:GRE encapsulation can be used instead of simple IP-in-IP
encapsulation when GRE facilities such as keys and checksums are
desired. In that case, AERO can include a GRE fragment header in the
encapsulation as shown in
:An encapsulation fragment header is inserted when the AERO tunnel
ingress needs to apply fragmentation to accommodate packets that must be
delivered without loss due to a size restriction. Fragmentation is
performed on the inner packet while encapsulating each inner packet
fragment in identical outer IP and encapsulation layer headers.The 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, network nodes 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. The Identification value within each packet could further
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.In some use cases, there may be operational assurance that no
fragmentation of any kind will be necessary, or that only occasional
large control messages will require fragmentation. In that case, the
encapsulation fragment header can be omitted and ordinary fragmentation
of the outer IP protocol version can be applied when necessary.Minimal encapsulation is preferred in environments where GUE
encapsulation would add unnecessary overhead. For example, certain
low-bandwidth wireless data links may benefit from a reduced
encapsulation overhead. This is not likely to be a prime consideration
for many modern wireless data links nor for most modern wired-line data
links.GUE 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 determine
the potential for middlebox filtering before enabling minimal
encapsulation in a given environment.AERO can also operate over native links using no encapsulation at
all. In that case, AERO Clients can identify AERO Servers on the link
through their link-layer addresses, and the AERO prefix delegation,
mobility management, fault tolerance and route optimization facilities
operate on the native link the same as over an NBMA tunnel overlay.This document introduces no IANA considerations.Security considerations are discussed in the base AERO specification
.TBD