IP Parcels
draft-templin-intarea-parcels-09
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| Document | Type | Active Internet-Draft (individual) | |
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| Author | Fred Templin | ||
| Last updated | 2022-02-10 (Latest revision 2022-02-09) | ||
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draft-templin-intarea-parcels-09
Network Working Group F. L. Templin, Ed.
Internet-Draft Boeing Research & Technology
Updates: RFC2675 (if approved) 10 February 2022
Intended status: Standards Track
Expires: 14 August 2022
IP Parcels
draft-templin-intarea-parcels-09
Abstract
IP packets (both IPv4 and IPv6) are understood to contain a unit of
data which becomes the retransmission unit in case of loss. Upper
layer protocols such as the Transmission Control Protocol (TCP)
prepare data units known as "segments", with traditional arrangements
including a single segment per packet. This document presents a new
construct known as the "IP Parcel" which permits a single packet to
carry multiple segments, essentially creating a "packet-of-packets".
IP parcels provide an essential building block for accommodating
larger Maximum Transmission Units (MTUs) in the Internet as discussed
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
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 14 August 2022.
Copyright Notice
Copyright (c) 2022 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 (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
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Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Background and Motivation . . . . . . . . . . . . . . . . . . 4
4. IP Parcel Formation . . . . . . . . . . . . . . . . . . . . . 5
5. Transmission of IP Parcels . . . . . . . . . . . . . . . . . 8
6. Parcel Path Qualification . . . . . . . . . . . . . . . . . . 10
7. Integrity . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8. RFC2675 Updates . . . . . . . . . . . . . . . . . . . . . . . 14
9. IPv4 Jumbograms . . . . . . . . . . . . . . . . . . . . . . . 14
10. Implementation Status . . . . . . . . . . . . . . . . . . . . 14
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
12. Security Considerations . . . . . . . . . . . . . . . . . . . 15
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
14.1. Normative References . . . . . . . . . . . . . . . . . . 15
14.2. Informative References . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
IP packets (both IPv4 [RFC0791] and IPv6 [RFC8200]) are understood to
contain a unit of data which becomes the retransmission unit in case
of loss. Upper layer protocols such as the Transmission Control
Protocol (TCP) [RFC0793], QUIC [RFC9000], LTP [RFC5326] and others
prepare data units known as "segments", with traditional arrangements
including a single segment per packet. This document presents a new
construct known as the "IP Parcel" which permits a single packet to
carry multiple segments. This essentially creates a "packet-of-
packets" with the IP layer headers appearing only once but with
possibly multiple upper layer protocol segments.
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Parcels are formed when an upper layer protocol entity (identified by
the "5-tuple" source IP address/port number, destination IP address/
port number and protocol number) prepares a buffer of data with the
concatenation of up to 64 properly-formed segments that can be broken
out into smaller parcels using a copy of the IP header. All segments
except the final segment must be equal in size and no larger than
65535 octets (minus headers), while the final segment must be no
larger than the others but may be smaller. The upper layer protocol
entity then delivers the buffer and non-final segment size to the IP
layer, which appends the necessary IP headers to identify this as a
parcel and not an ordinary packet.
Each original parcel can traverse arbitrarily many parcel-capable IP
links in the path until arriving at a parcel-capable ingress
middlebox at the edge of a wide area Internetwork. The ingress
middlebox may break the parcel out into smaller (sub-)parcels and
encapsulate them in headers suitable for traversing the Internetwork.
These smaller parcels may then be rejoined into one or more larger
parcels at an egress middlebox which forwards them further over
parcel-capable IP links toward the final destination. Repackaging of
parcels is therefore commonplace, while reordering of segments within
a parcel or even loss of individual segments is possible but not
desirable. But, what matters is that the number of parcels delivered
to the final destination should be kept to a minimum, and that loss
or receipt of individual segments (and not parcel size) determines
the retransmission unit.
The following sections discuss rationale for creating and shipping
parcels as well as the actual protocol constructs and procedures
involved. IP parcels provide an essential building block for
accommodating larger Maximum Transmission Units (MTUs) in the
Internet. It is further expected that the parcel concept may drive
future innovation in applications, operating systems, network
equipment and data links.
2. Terminology
A "parcel" is defined as "a thing or collection of things wrapped in
paper in order to be carried or sent by mail". Indeed, there are
many examples of parcel delivery services worldwide that provide an
essential transit backbone for efficient business and consumer
transactions.
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In this same spirit, an "IP parcel" is simply a collection of up to
64 upper layer protocol segments wrapped in an efficient package for
transmission and delivery (i.e., a "packet of packets") while a
"singleton IP parcel" is simply a parcel that contains a single
segment. IP parcels are distinguished from ordinary packets through
the special header constructions discussed in this document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Background and Motivation
Studies have shown that by sending and receiving larger packets
applications can realize greater performance due to reduced numbers
of system calls and interrupts as well as larger atomic data copies
between kernel and user space. Large packets in the network also
result in reduced numbers of device interrupts and better network
utilization in comparison with smaller packet sizes.
A first study [QUIC] involved performance enhancement of the QUIC
protocol [RFC9000] using the linux Generic Segment/Receive Offload
(GSO/GRO) facility. GSO/GRO provide a robust (but non-standard)
service very similar in nature to the IP parcel service described
here, and its application has shown significant performance increases
due to the increased transfer unit size between the operating system
kernel and QUIC application.
A second study [I-D.templin-dtn-ltpfrag] showed that GSO/GRO also
improved performance for the Licklider Transmission Protocol (LTP)
[RFC5326] for small- to medium-sized segments. Historically, the NFS
protocol also saw significant performance increases using larger
(single-segment) UDP datagrams even when IP fragmentation is invoked,
and LTP still follows this profile today. Moreover, LTP shows this
(single-segment) performance increase profile extending to the
largest possible segment size which suggests that additional
performance gains may be possible using (multi-segment) IP parcels
that exceed 65535 octets.
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TCP also benefits from larger packet sizes and efforts have
investigated TCP performance using jumbograms internally with changes
to the linux GSO/GRO facilities [BIG-TCP]. The idea is to use the
jumbo payload internally and to allow GSO and GRO to use buffer sizes
larger than 65535 octets, but with the understanding that links that
support jumbos natively are not yet widely available. Hence, IP
parcels provides a packaging that can be considered in the near term
under current deployment limitations.
The issue with sending large packets is that they are often lost at
links with smaller Maximum Transmission Units (MTUs), and the
resulting Packet Too Big (PTB) message may be lost somewhere in the
path back to the original source. This "Path MTU black hole"
condition can degrade performance unless robust path probing
techniques are used, however the best case performance always occurs
when no packets are lost due to size restrictions.
These considerations therefore motivate a design where the maximum
segment size should be no larger than 65535 octets (minus headers),
while parcels that carry the segments may themselves be significantly
larger. Then, even if a middlebox needs to sub-divide the parcels
into smaller sub-parcels to forward further toward the final
destination, an important performance optimization for both the
original source and final destination can be realized.
An analogy: when a consumer orders 50 small items from a major online
retailer, the retailer does not ship the order in 50 separate small
boxes. Instead, the retailer puts as many of the small boxes as
possible into one or a few larger boxes (or parcels) then places the
parcels on a semi-truck or airplane. The parcels arrive at a
regional distribution center where they may be further redistributed
into slightly smaller parcels that get delivered to the consumer.
But most often, the consumer will only find one or a few parcels at
his doorstep and not 50 individual boxes. This greatly reduces
handling overhead for both the retailer and consumer.
4. IP Parcel Formation
IP parcel formation is invoked by an upper layer protocol (identified
by the 5-tuple as above) when it emits a data buffer containing the
concatenation of up to 64 segments. All non-final segments MUST be
equal in length while the final segment MUST NOT be larger but MAY be
smaller. Each non-final segment MUST be no larger than 65535 octets
minus the length of the IP header plus extensions, minus the length
of an additional IPv6 header in case an encapsulation middlebox is
visited on the path (see: Section 5). The upper layer protocol then
presents the buffer and non-final segment size to the IP layer which
appends a single IP header (plus any extension headers) before
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presenting the parcel to either the adaptation layer or the outgoing
network interface itself (see: Section 5).
For IPv4, the IP layer prepares the parcel by appending an IPv4
header with a Jumbo Payload option formed as follows:
+--------+--------+--------+--------+--------+--------+
|00001011|00000110| Jumbo Payload Length |
+--------+--------+--------+--------+--------+--------+
where option type is set to '00001011' and option length is set to
'00000110' which distinguishes the option from its former
(deprecated) use as "IPv4 Probe MTU" by [RFC1063]). In this new
format, "Jumbo Payload Length" is a 32-bit unsigned integer value (in
network byte order) set to the lengths of the IPv4 header plus all
concatenated segments. The IP layer next sets the IPv4 header DF bit
to 1, then sets the IPv4 header Total Length field to the length of
the IPv4 header plus the length of the first segment only. Note that
the IP layer can form true IPv4 jumbograms (as opposed to parcels) by
instead setting the IPv4 header Total Length field to the length of
the IPv4 header plus options (see: Section 9).
For IPv6, the IP layer forms a parcel by appending an IPv6 header
with a Jumbo Payload option [RFC2675] the same as for IPv4 above with
option type set to '11000010' and option length set to '00000100'
where "Jumbo Payload Length" is set to the lengths of the IPv6 Hop-
by-Hop Options header and any other extension headers present plus
all concatenated segments. The IP layer next sets the IPv6 header
Payload Length field to the lengths of the IPv6 Hop-by-Hop Options
header and any other extension headers present plus the length of the
first segment only. As with IPv4 the IP layer can form true IPv6
jumbograms (as opposed to parcels) by instead setting the IPv6 header
Payload Length field to 0 (see: [RFC2675]).
An IP parcel therefore has the following structure:
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+--------+--------+--------+--------+
| |
~ Segment J (K octets) ~
| |
+--------+--------+--------+--------+
~ ~
~ ~
+--------+--------+--------+--------+
| |
~ Segment 3 (L octets) ~
| |
+--------+--------+--------+--------+
| |
~ Segment 2 (L octets) ~
| |
+--------+--------+--------+--------+
| |
~ Segment 1 (L octets) ~
| |
+--------+--------+--------+--------+
| IP Header Plus Extensions |
~ {Total, Payload} Length = M ~
| Jumbo Payload Length = N |
+--------+--------+--------+--------+
where J is the total number of segments (between 1 and 64), L is the
length of each non-final segment which MUST NOT be larger than 65535
octets (minus headers as above) and K is the length of the final
segment which MUST NOT be larger than L. The values M and N are then
set to the length of the IP header plus extensions for IPv4 or to the
length of the extensions only for IPv6, then further calculated as
follows:
M = M + ((J-1) ? L : K)
N = N + (((J-1) * L) + K)
Note: a "singleton" parcel is one that includes only the IP header
plus extensions with a single segment of length K, while a "null"
parcel is a singleton with K=0, i.e., a parcel consisting of only the
IP header plus extensions with no octets beyond.
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5. Transmission of IP Parcels
The IP layer next presents the parcel to the outgoing network
interface. For ordinary IP interfaces, the IP layer simply forwards
the parcel over the underlying link the same as for any IP packet
after which it may then be forwarded by any number of routers over
additional parcel-capable IP links. If any next hop IP link in the
path either does not support parcels or configures an MTU that is too
small to transit the parcel without fragmentation, the router instead
opens the parcel and forwards each enclosed segment as a separate IP
packet (i.e., by appending a copy of the parcel's IP header to each
segment but with the Jumbo Payload option removed according to the
standards [RFC0791][RFC8200]). Or, if the router does not recognize
parcels at all, it drops the parcel and (for IPv6) may return an ICMP
"Parameter Problem" message according to [RFC2675].
If the outgoing network interface is an OMNI interface
[I-D.templin-6man-omni], the OMNI Adaptation Layer (OAL) of this
First Hop Segment (FHS) OAL node forwards the parcel to the next OAL
hop which may be either an OAL intermediate node or the Last Hop
Segment (LHS) OAL node (which may also be the final destination
itself). The OAL assigns a monotonically- incrementing (modulo 127)
"Parcel ID" and subdivides the parcel into sub-parcels no larger than
the maximum of the path MTU to the next hop or 65535 octets (minus
the length of encapsulation headers) by determining the number of
segments of length L that can fit into each sub-parcel under these
size constraints. For example, if the OAL determines that a sub-
parcel can contain 3 segments of length L, it creates sub-parcels
with the first containing segments 1-3, the second containing
segments 4-6, etc. and with the final containing any remaining
segments. The OAL then appends an identical IP header plus
extensions to each sub-parcel while resetting M and N in each
according to the above equations with J set to 3 and K set to L for
each non-final sub-parcel and with J set to the remaining number of
segments for the final sub-parcel.
The OAL next performs IP encapsulation on each sub-parcel with
destination set to the next hop IP address then inserts an IPv6
Fragment Header after the IP encapsulation header, i.e., even if the
encapsulation header is IPv4, even if no actual fragmentation is
needed and/or even if the Jumbo Payload option is present. The OAL
then assigns a randomly-initialized 32-bit Identification number that
is monotonically-incremented for each consecutive sub-parcel, then
performs IPv6 fragmentation over the sub-parcel if necessary to
create fragments small enough to traverse the path to the next OAL
hop while writing the Parcel ID and setting or clearing the "Parcel
(P)" and "(More) Sub-Parcels (S)" bits in the Fragment Header of the
first fragment (see: [I-D.templin-6man-fragrep]). (The OAL sets P to
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1 for a parcel or to 0 for a non-parcel. When P is 1, the OAL next
sets S to 1 for non-final sub-parcels or to 0 if the sub-parcel
contains the final segment.) The OAL then forwards each IP
encapsulated packet/fragment to the next OAL hop.
When the next OAL hop receives the encapsulated IP fragments or whole
packets, it reassembles if necessary. If the P flag in the first
fragment is 0, the next hop then processes the reassembled entity as
an ordinary IP packet; otherwise it continues processing as a sub-
parcel. If the next hop is an OAL intermediate node, it retains the
sub-parcels along with their Parcel ID and Identification values for
a brief time in hopes of re-combining with peer sub-parcels of the
same original parcel identified by the 4-tuple consisting of the IP
encapsulation source and destination, Identification and Parcel ID.
The combining entails the concatenation of the segments included in
sub-parcels with the same Parcel ID and with Identification values
within 64 of one another to create a larger sub-parcel possibly even
as large as the entire original parcel. Order of concatenation is
not important, with the exception that the final sub-parcel (i.e.,
the one with S set to 0) must occur as the final concatenation before
transmission. The OAL then appends a common IP header plus
extensions to each re-combined sub-parcel while resetting M and N in
each according to the above equations with J, K and L set
accordingly.
This OAL intermediate node next forwards the re-combined sub-
parcel(s) to the next hop toward the LHS OAL node using encapsulation
the same as specified above. (The intermediate node MUST ensure that
the S flag remains set to 0 in the sub-parcel that contains the final
segment.) When the parcel or sub-parcels arrive at the LHS OAL node,
the OAL re-combines them into the largest possible sub-parcels while
honoring the S flag. If the LHS OAL node is also the final
destination, it delivers the sub-parcels to upper layers which act on
the enclosed 5-tuple information supplied by the original source. If
the LHS OAL node is not the final destination, it instead forwards
each sub-parcel the same as for an ordinary IP packet the same as
discussed above.
Note: while the LHS OAL node may be tempted to re-combine the sub-
parcels of multiple different parcels with identical upper layer
protocol 5-tuples and with non-final segments of identical length,
this process could become complicated when the different parcels each
have final segments of diverse lengths. Since this might interfere
with any perceived performance advantages, the decision of whether
and how to perform inter-parcel concatenation is an implementation
matter.
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Note: some IPv6 fragmentation and reassembly implementations may
require a well-formed IPv6 header to perform their operations. When
the encapsulation is based on IPv4, such implementations translate
the encapsulation header into an IPv6 header with IPv4-Mapped IPv6
addresses before performing the fragmentation/reassembly operation,
then restore the original IPv4 header before further processing.
6. Parcel Path Qualification
To determine whether parcels are supported over at least a leading
portion of the forward path toward the final destination, the
original source can send a singleton IP parcel formatted as a "Parcel
Probe" that contains an upper layer protocol probe segment (e.g., a
data segment, an ICMP Echo Request message, etc.). The purpose of
the probe is to elicit a "Parcel Reply" and possibly also an ordinary
upper layer protocol probe reply from the final destination.
If the original source receives a positive Parcel Reply, it marks the
path as "parcels supported" and ignores any ICMP [RFC0792][RFC4443]
and/or Packet Too Big (PTB) messages [RFC1191][RFC8201] concerning
the probe. If the original source instead receives a negative Parcel
Reply or no reply, it marks the path as "parcels not supported" and
may regard any ICMP and/or PTB messages concerning the probe (or its
contents) as indications of a possible middlebox restriction.
The original source can therefore send Parcel Probes in parallel with
sending real data as ordinary IP packets. If the original source
receives a positive Parcel Reply, it can begin using IP parcels.
Parcel Probes use the IP parcel option type (see: Section 4) but set
a different option length and replace the option value with control
information plus a 4-octet "Path MTU" value into which conformant
middleboxes write the minimum link MTU observed the same as described
in [RFC1063][I-D.ietf-6man-mtu-option]. Parcel Probes can also
include an upper layer protocol probe segment the same as described
in [RFC4821][RFC8899].
The original source sends Parcel Probes unidirectionally in the
forward path toward the final destination to elicit a Parcel Reply,
since it will often be the case that IP parcels are supported only in
the forward path and not in the return path. Parcel Probes may be
dropped in the forward path by any node that does not recognize IP
parcels, but a Parcel Reply must be packaged such that it will not be
dropped even if IP parcels are not recognized in the return path.
Original sources send Parcel Probes using the following option
format:
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+--------+--------+
| Type | Length |
+--------+--------+--------+--------+
| Nonce-1 | Nonce-2 (0-1) |
+--------+--------+--------+--------+
| Nonce-2 (2-3) |Reserved| Check |
+--------+--------+--------+--------+
| PMTU |
+--------+--------+--------+--------+
For IPv4, the original source MUST set Type to '00001011' and Length
to '00001110' - this is the same Type as for an ordinary IPv4 parcel
(see: Section 4) but with a different Length. The original source
then MUST set Nonce-1 to 0xffff, set Nonce-2 to a (pseudo)-random
32-bit value and set Reserved to 0. The original source finally MUST
set Check to the same value that will appear in the TTL of the
outgoing IPv4 header and MUST set PMTU to the MTU of the outgoing
IPv4 interface. The original source finally sends the Parcel Probe
over the outgoing IPv4 interface. According to [RFC7126],
middleboxes (i.e., routers, security gateways, firewalls, etc.) that
do not observe this specification SHOULD drop IP packets that contain
option type '00001011' ("IPv4 Probe MTU") but some might instead
either implement [RFC1063] or ignore the option altogether. IPv4
middleboxes that observe this specification instead MUST process the
option as a Parcel Probe as specified below.
For IPv6, the original source MUST set Type to '11000010' and Length
to '00001100' - this is the same Type as for an ordinary IPv6 parcel
(see: Section 4) but with a different Length. The original source
then MUST set both Nonce-1 and Nonce-2 to a (pseudo)-random 48-bit
value and set Reserved to 0. The original source finally MUST set
Check to the same value that will appear in the Hop Limit of the
outgoing IPv6 header and MUST set PMTU to the MTU of the outgoing
IPv6 interface. The original source finally sends the Parcel Probe
over the outgoing IPv6 interface. According to [RFC2675],
middleboxes (i.e., routers, security gateways, firewalls, etc.) that
understand the IPv6 Jumbo Payload option are required to detect a
number of possible format errors and return an ICMPv6 Parameter
Problem message, but no guidance is given regarding forwarding. IPv6
middleboxes that observe this specification instead MUST process the
option as a Parcel Probe as specified below.
When a middlebox that observes this specification receives a Parcel
Probe it first compares the Check value with the IP header Hop Limit/
TTL; if the values differ, the middlebox MUST return a negative
Parcel Reply (see below) and drop the probe.
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Next, if the next hop IP link either does not support parcels or
configures an MTU that is too small to pass the parcel, the middlebox
compares the Parcel Probe PMTU value with the MTU of the inbound link
for the probe and MUST (re)set PMTU to the lower MTU. The middlebox
then MUST return a positive Parcel Reply (see below) and convert the
probe into an ordinary IP packet by removing the Parcel Probe option
according to the standards [RFC0791][RFC8200]. If the next hop IP
link configures a sufficiently large MTU, the middlebox then MUST
forward the ordinary IP packet to the next hop; otherwise, it MUST
drop the packet and should return a suitable PTB.
If the next hop IP link both supports parcels and configures an MTU
that is large enough to pass the parcel, the middlebox instead
compares the Parcel Probe PMTU value with the MTUs of both the
inbound and outbound links for the probe and MUST (re)set PMTU to the
lower MTU. The middlebox then MUST reset Check to the same value
that will appear in the TTL/Hop Limit of the outgoing IP header, and
MUST forward the Parcel Probe to the next hop.
The final destination may therefore receive either an ordinary IP
packet containing an upper layer protocol probe or a Parcel Probe.
If the final destination receives an ordinary IP packet, it performs
any necessary integrity checks then delivers the packet to upper
layers which will return an upper layer probe response. If the final
destination instead receives a Parcel Probe, it first compares the
Check value with the IP header Hop Limit/TTL; if the values differ,
the final destination MUST drop the probe and return a negative
Parcel Reply (see below). Otherwise, the final destination compares
the Parcel Probe PMTU value with the MTU of the inbound link for the
probe and MUST (re)set PMTU to the lower MTU. The final destination
then MUST return a positive Parcel Reply (see below) and convert the
probe into an ordinary IP packet by removing the Parcel Probe option
according to the standards [RFC0791][RFC8200].The final destination
then performs any necessary integrity checks and delivers the packet
to upper layers.
When the middlebox or final destination returns a Parcel Reply, it
prepares an IP header of the same protocol version that appeared in
the Parcel Probe with source and destination addresses reversed, with
{Protocol, Next Header} set to the value '60' (i.e., "IPv6
Destination Option") and with an IPv6 Destination Option header with
Next Header set to the value '59' (i.e., "IPv6 No Next Header")
[RFC8200]. The node next copies the body of the Parcel Probe option
as the sole Parcel Reply Destination Option (and for IPv4 resets Type
to '11000010' and Length to '00001100') and includes no other octets
beyond the end of the option. The node then MUST (re)set Check to 1
for a positive or to 0 for a negative Parcel Reply, then MUST finally
set the IP header {Total, Payload} Length field according to the
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length of the included Destination Option and return the Parcel Reply
to the source. (Since filtering middleboxes may drop IPv4 packets
with Protocol '60' the destination should wrap an IPv4 Parcel Reply
in UDP/IPv4 headers with the IPv4 source and destination addresses
copied from the Parcel Reply and with UDP port numbers set to the UDP
port number for OMNI [I-D.templin-6man-omni].)
After sending a Parcel Probe the original source may therefore
receive a Parcel Reply (see above) and/or an upper layer protocol
probe reply. If the source receives a Parcel Reply, it first matches
Nonce-2 (and for IPv6 only also matches Nonce-1) with the values it
had included in the Parcel Probe. If the values do not match, the
source discards the Parcel Reply. Next, the source examines the
Check value and marks the path as "parcels supported" if the value is
1 or "parcels not supported" otherwise. If the source marks the path
as "parcels supported", it also records the PMTU value as the maximum
parcel size for the forward path to this destination.
After receiving a positive Parcel Reply, the original source can
begin sending IP parcels up to the size recorded in the PMTU to the
final destination. Any upper layer protocol probe replies will
determine the maximum segment size that can be included in the
parcel, but this is an upper layer consideration. The original
source should then periodically re-initiate Parcel Path Qualification
as long as its session with the final destination is sustained (i.e.,
in case the forward path fluctuates). If at any time performance
appears to degrade, the original source should immediately re-
initiate Parcel Path Qualification.
7. Integrity
Each segment of a (multi-segment) IP parcel includes its own upper
layer protocol integrity check. This allows for IP parcels to
support much stronger integrity for the same amount of upper layer
protocol data in comparison with an ordinary IP packet or Jumbogram
containing only a single segment. The integrity checks must then be
verified at the final destination, which accepts any segments with
correct integrity while discarding any corrupted segments and
counting them as a loss event.
IP parcels can range in length from as small as only the IP header
sizes to as large as the IP headers plus (64 * (65535 minus headers))
octets. Although link layer integrity checks provide sufficient
protection for contiguous data blocks up to approximately 9KB,
reliance on the presence of link-layer integrity checks may not be
possible over links such as tunnels. Moreover, the segment contents
of a received parcel may arrive in an incomplete and/or rearranged
order with respect to their original packaging.
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For these reasons, the OAL at each hop of an OMNI link includes an
integrity check when it performs IP fragmentation on a sub-parcel,
with the integrity verified during reassembly at the next hop.
8. RFC2675 Updates
Section 3 of [RFC2675] provides a list of certain conditions to be
considered as errors. In particular:
error: IPv6 Payload Length != 0 and Jumbo Payload option present
error: Jumbo Payload option present and Jumbo Payload Length <
65,536
Implementations that obey this specification ignore these conditions
and do not consider them as errors.
9. IPv4 Jumbograms
By defining a new IPv4 Jumbo Payload option, this document also
implicitly enables an IPv4 jumbogram service defined as an IPv4
packet with Total Length set to the length of the IPv4 header plus
extensions only, and with a Jumbo Payload option in the IPv4
extension headers. All other aspects of IPv4 jumbograms are the same
as for IPv6 jumbograms [RFC2675].
10. Implementation Status
Common widely-deployed implementations include services such as TCP
Segmentation Offload (TSO) and Generic Segmentation/Receive Offload
(GSO/GRO). These services support a robust (but not standardized)
service that has been shown to improve performance in many instances.
Implementation of the IP parcel service is a work in progress.
11. IANA Considerations
The IANA is instructed to change the "MTUP - MTU Probe" entry in the
'ip option numbers' registry to the "JUMBO - IPv4 Jumbo Payload"
option. The Copy and Class fields must both be set to 0, and the
Number and Value fields must both be set to 11'. The reference must
be changed to this document (RFCXXXX).
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12. Security Considerations
Original sources match the Jumbo Payload Length and Nonce values in
received Parcel Replies with the Parcel Probes they send. If the
values match, the Parcel Reply is likely an authentic response to the
Parcel Probe. In environments where stronger authentication is
necessary, the encapsulating authentication services of OMNI can be
used [I-D.templin-6man-omni].
Communications networking security is necessary to preserve
confidentiality, integrity and availability.
13. Acknowledgements
This work was inspired by ongoing AERO/OMNI/DTN investigations. The
concepts were further motivated through discussions on the intarea
and 6man lists.
A considerable body of work over recent years has produced useful
"segmentation offload" facilities available in widely-deployed
implementations.
.
14. References
14.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, DOI 10.17487/RFC2675, August 1999,
<https://www.rfc-editor.org/info/rfc2675>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
14.2. Informative References
[BIG-TCP] Dumazet, E., "BIG TCP, Netdev 0x15 Conference (virtual),
https://netdevconf.info/0x15/session.html?BIG-TCP", 31
August 2021.
[I-D.ietf-6man-mtu-option]
Hinden, R. M. and G. Fairhurst, "IPv6 Minimum Path MTU
Hop-by-Hop Option", Work in Progress, Internet-Draft,
draft-ietf-6man-mtu-option-12, 27 January 2022,
<https://www.ietf.org/archive/id/draft-ietf-6man-mtu-
option-12.txt>.
[I-D.ietf-tcpm-rfc793bis]
Eddy, W. M., "Transmission Control Protocol (TCP)
Specification", Work in Progress, Internet-Draft, draft-
ietf-tcpm-rfc793bis-26, 8 February 2022,
<https://www.ietf.org/archive/id/draft-ietf-tcpm-
rfc793bis-26.txt>.
[I-D.templin-6man-fragrep]
Templin, F. L., "IPv6 Fragment Retransmission and Path MTU
Discovery Soft Errors", Work in Progress, Internet-Draft,
draft-templin-6man-fragrep-05, 22 December 2021,
<https://www.ietf.org/archive/id/draft-templin-6man-
fragrep-05.txt>.
[I-D.templin-6man-omni]
Templin, F. L. and T. Whyman, "Transmission of IP Packets
over Overlay Multilink Network (OMNI) Interfaces", Work in
Progress, Internet-Draft, draft-templin-6man-omni-52, 31
December 2021, <https://www.ietf.org/archive/id/draft-
templin-6man-omni-52.txt>.
[I-D.templin-dtn-ltpfrag]
Templin, F. L., "LTP Fragmentation", Work in Progress,
Internet-Draft, draft-templin-dtn-ltpfrag-08, 1 February
2022, <https://www.ietf.org/archive/id/draft-templin-dtn-
ltpfrag-08.txt>.
[QUIC] Ghedini, A., "Accelerating UDP packet transmission for
QUIC, https://blog.cloudflare.com/accelerating-udp-packet-
transmission-for-quic/", 8 January 2020.
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[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC1063] Mogul, J., Kent, C., Partridge, C., and K. McCloghrie, "IP
MTU discovery options", RFC 1063, DOI 10.17487/RFC1063,
July 1988, <https://www.rfc-editor.org/info/rfc1063>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
<https://www.rfc-editor.org/info/rfc4821>.
[RFC5326] Ramadas, M., Burleigh, S., and S. Farrell, "Licklider
Transmission Protocol - Specification", RFC 5326,
DOI 10.17487/RFC5326, September 2008,
<https://www.rfc-editor.org/info/rfc5326>.
[RFC7126] Gont, F., Atkinson, R., and C. Pignataro, "Recommendations
on Filtering of IPv4 Packets Containing IPv4 Options",
BCP 186, RFC 7126, DOI 10.17487/RFC7126, February 2014,
<https://www.rfc-editor.org/info/rfc7126>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/info/rfc8899>.
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[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
United States of America
Email: fltemplin@acm.org
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