Internet DRAFT - draft-herbert-transports-over-udp
draft-herbert-transports-over-udp
INTERNET-DRAFT T. Herbert
Intended Status: Informational Facebook
Expires: November 20, 2016
May 19, 2016
Transport layer protocols over UDP
draft-herbert-transports-over-udp-00
Abstract
This specification defines a mechanism to encapsulate layer four
transport protocols over UDP. Such encapsulation facilitates
deployment of alternate transport protocols or transport protocol
features on the Internet. DTLS can be employed to encrypt the
encapsulated transport header in a packet thus minimizing the
exposure of transport layer information to the network and so
promoting the end-to-end networking principle.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright and License Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
Herbert Expires November 20, 2016 [Page 1]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Related work . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
2 Basic encapsulation . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Encapsulation format . . . . . . . . . . . . . . . . . . . . 5
2.2 Direct transport protocol encapsulation . . . . . . . . . . 6
2.3 Encapsulated Extension headers . . . . . . . . . . . . . . . 8
2.4 Obfuscating transport layer protocol number . . . . . . . . 8
3 Disassociated location encapsulation . . . . . . . . . . . . . . 9
3.1 Packet format . . . . . . . . . . . . . . . . . . . . . . . 9
3.2 TOU Identity . . . . . . . . . . . . . . . . . . . . . . . . 10
3.3 Sessions . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.4 Communication roles . . . . . . . . . . . . . . . . . . . . 11
3.5 Session identifier format . . . . . . . . . . . . . . . . . 11
3.6 Connection tuple . . . . . . . . . . . . . . . . . . . . . . 12
3.7 Operation . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.7.1 Session lookup tables . . . . . . . . . . . . . . . . . 12
3.7.2 Transport connection lookup . . . . . . . . . . . . . . 13
3.7.3 Session identifier negotiation . . . . . . . . . . . . . 14
3.7.3 Established state . . . . . . . . . . . . . . . . . . . 16
3.7.4 Closing a sessions . . . . . . . . . . . . . . . . . . . 16
3.7.5 Session creation deferral . . . . . . . . . . . . . . . 16
3.8 TCP over UDP example . . . . . . . . . . . . . . . . . . . . 16
4 Security Considerations . . . . . . . . . . . . . . . . . . . . 17
5 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 18
6 References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6.1 Normative References . . . . . . . . . . . . . . . . . . . 19
6.2 Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
Herbert Expires November 20, 2016 [Page 2]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
1 Introduction
This specification defines Transport Layer Protocols over UDP (TOU)
as generic mechanism to encapsulate IP transport protocols over UDP
[RFC0768]. The purpose of TOU to facilitate the use of alternate
protocols and protocol mechanisms over the Internet.
The realities of protocol ossification in the Internet, particularly
the infeasibility of deploying IP protocol extensions and alternative
transport protocols (protocols other than UDP and TCP), have been
well documented. A direction to resolve protocol ossification is
suggested in RFC7663 [RFC7663]:
"... putting a transport protocol atop a cryptographic protocol
atop UDP resets the transport versus middlebox tussle by making
inspection and modification above the encryption and demux layer
impossible."
Accordingly, this specification provides a method to encapsulate
transport layer protocols in UDP and allows encrypting most of the
UDP payload including the encapsulated transport headers and
payloads. This solution espouses a model that only the minimal
necessary information about the packet is made visible to the
network. This exposed information is sufficient to route the packet
through the network and to demultiplex and decrypt the packet at the
receiving end host. In particular, the encapsulated protocol and
related connection state may be rendered invisible to the network.
Additionally, this solution allows encapsulation of IPv6 extension
headers, particularly destination options, which can then also be
hidden from inspection in the network.
1.1 Requirements
The requirements of TOU are:
- Allow encapsulation of any IP transport layer protocol (e.g.
TCP, SCTP, UDP, DCCP, etc.) over UDP.
- Work seamlessly with NAT including conditions where the ports
or addresses being used for an encapsulated connection change.
To provide for this we disassociate the layer 4 endpoint
identification from the IP addresses.
- Allow encryption/authentication of the encapsulated transport
packet including transport headers. The encryption algorithm
should be flexible to allow different methods. Any layer 4
information that is exposed in cleartext (such as session
identifier defined below) should be authenticated.
Herbert Expires November 20, 2016 [Page 3]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
- Information needed for TOU is sent with along with encapsulated
transport packets, there are no standalone TOU messages. Any
negotiation to set up state for TOU should not require any
additional round trips apart from those needed by the
encapsulated transport protocol.
- The solution must not be biased towards any particular
implementation method. Specifically, TOU should allow for
transport protocol implementations in userspace, kernel,
hardware, etc.
- Minimize changes to transport protocols and implementation. TOU
should not require any changes to the transport protocol
proper, however TOU will extend the concept of transport
endpoints beyond the canonical 5-tuple.
- Minimize changes to applications. TOU should be enabled with
existing applications, APIs, and transport protocols without
needing major rework. The desire to use transport layer
protocols over UDP should not require applications to adopt
completely new transport protocols.
1.2 Related work
Several transport and encapsulation protocols have been defined to be
encapsulated within UDP [RFC0768]. In this model, the payload of a
UDP packet contains a protocol header and payload for an encapsulated
protocol.
TCP-over-UDP [I-D.chesire-tcp-over-udp] specifies a method to
encapsulate TCP in UDP. That solution essentially casts UDP header
into a modified TCP header so that the port numbers simultaneously
refer to both the UDP and TCP flows. In TOU, the TCP header
(generally transport header) is encapsulated in UDP without changing
the header format.
SCTP-over-UDP [RFC6951] describes a straightforward encapsulation of
SCTP in UDP. This work should be leverage-able for use with SCTP in
TOU. One potential benefit of TOU is that disassociated location
encapsulation (described below) could be used to maintain SCTP
connections when UDP NAT flow mappings change.
QUIC [QUIC] implements a new transport protocol that is intended to
run over UDP. QUIC defines a connection identifier that is used to
identify connections at the endpoints independent of IP addresses or
UDP ports. A similar concept is adopted for TOU in the session
abstraction.
Herbert Expires November 20, 2016 [Page 4]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
SPUD [I-D.hildebrand-spud-prototype] defines an architecture for
group grouping UDP packets together in a "tube", also allowing
network devices on the path between endpoints to participate
explicitly in the tube outside the end-to-end context. TOU implements
a subset of the the SPUD architecture but expressly does not require
or include provisions to leak end-to-end information for consumption
in the network. The encapsulation protocol used in TOU (GUE) is
extensible to optionally allow information exposure if this proves to
be warranted.
1.3 Terminology
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 RFC 2119 [RFC2119].
2 Basic encapsulation
Generic UDP Encapsulation (GUE) [I-D.ietf-nvo3-gue] is the
encapsulation protocol for encapsulating transport layer protocols
over UDP. TOU can encapsulate both stateless transport protocols
(such as UDP, DCCP, UDP-lite) and stateful protocols (like TCP and
SCTP). Additionally, TOU may encapsulate IPv6 Destination Options
extension headers.
2.1 Encapsulation format
The general format of TOU encapsulation using GUE (UDP) is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source port | Destination port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0x0|C| Hlen | Proto/ctype | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ GUE Fields (optional) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Transport layer packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Proto/ctype contains the IP protocol number of the GUE payload, in
Herbert Expires November 20, 2016 [Page 5]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
the case of TOU this contains the protocol number of a transport
protocol (e.g. for TCP over UDP the value is 6). The C bit (control)
is not used with TOU indicating that GUE is carrying a data packet.
The flags and fields may be set for TOU as described below. Certain
general GUE flags-fields, such as remote checksum offload or
fragmentation, may be useful for TOU but not required for its
operation. The example packet formats in the remainder of the this
document do not indicate use of any flags or fields other than those
required for TOU operation.
The Hlen contains the GUE header length in 32-bit words, including
optional fields but not the first four bytes of the header. Computed
as (header_len - 4) / 4. All GUE headers are a multiple of four bytes
in length. Maximum header length is 128 bytes.
2.2 Direct transport protocol encapsulation
Transport protocol packets can be encapsulated directly in GUE. The
simplest format of this is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source port | Destination port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0x0|0| 0 | Protocol | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Transport layer packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Herbert Expires November 20, 2016 [Page 6]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
For example, TCP over UDP could be encapsulated as:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source port | Destination port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0x0|0| 0 | 6 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Acknowledgment Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data | |U|A|P|R|S|F| |
| Offset| Reserved |R|C|S|S|Y|I| Window |
| | |G|K|H|T|N|N| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | Urgent Pointer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For TOU the flow identification of the encapsulated transport packet
includes the encapsulating UDP source and destination port. For a
transport protocol that uses the canonical ports for flow
identification, flows are identified by the 7-tuple:
<Protocol, SrcIP, DstIP, SrcPort, DstPort, SrcUport, DstUport>
Where protocol refers to the encapsulated protocol (taken from the
Proto/ctype field in the GUE header), SrcIP and DstIP refer to the
source and destination IP addresses, SrcPort and DstPort refer to the
respective ports in the encapsulated transport header, SrcUport and
DstUport refer to the source and destination ports in the
encapsulating (outer) UDP header.
To reply to a transport layer packet encapsulated in TOU, a
corresponding TOU packet is sent where the source and destination
addresses, source and destination UDP ports, and source and
destination transport ports are swapped. The outer addresses and
ports may have undergone NAT so that the return path must also go
through NAT. To ensure reachabilty, a host MUST reply to a TOU
Herbert Expires November 20, 2016 [Page 7]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
encapsulated with a corresponding TOU packet.
Stateful protocol connections are identified by the 7-tuple as
defined above. Since the UDP ports are included in the connection
tuples, the typical transport layer 5-tuple (<Protocol, SrcIP, DstIP,
Sport, Dport>) of a TOU connection does not need to be unique with
those of non-TOU connections.
The inner and outer ports have no correlation. The lengths and
checksums must also be set correctly in each header layer. In the
case of UDP over UDP for IPv6 that both the inner and outer checksum
must be set.
For encapsulated transport packets that define a checksum that
includes a pseudo header (e.g. TCP) the checksum pseudo header
remains the same. The pseudo header includes the IP addresses and
transport layer ports. In particular the UDP ports are not included
in that pseudo header and the UDP checksum covers the UDP ports.
2.3 Encapsulated Extension headers
For IPv6, encapsulation of IPv6 Fragment and Destination Options
extension headers is permitted. These options are processed at a
destination after processing the UDP and GUE encapsulation headers.
Logically, the encapsulation headers are treated as though they are
themselves extension headers, so processing an encapsulated extension
header is done in the context of being an extension header within the
corresponding IP layer packet.
Since encapsulated extension headers are contained within the UDP
payload (and the payload may often be encrypted) there is no
allowance that intermediate devices parse these headers. Extension
headers that require visibility to intermediate nodes, such as hop by
hop option or routing header, cannot be encapsulated in TOU.
2.4 Obfuscating transport layer protocol number
The GUE header indicates the IP protocol of the encapsulated packet.
This is either contained in the Proto/ctype field of the primary GUE
header, or is contained in the Payload Type field of a GUE Transform
Field (used to encrypt the payload with DTLS). If the protocol must
be obfuscated, that is the transport protocol in use must be hidden
from the network, then a trivial destination options can be used.
The PadN destination option can be used to encode the transport
protocol as a next header of an extension header (and maintain
alignment of encapsulated transport headers). The Proto/ctype field
or Payload Type field of the GUE Transform field is set to 60 to
Herbert Expires November 20, 2016 [Page 8]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
indicate that the first encapsulated header is a Destination Options
extension header.
The format of the extension header is below:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | 2 | 1 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
For IPv4, it is permitted in TOU to used this precise destination
option to contain the obfuscated protocol number. In this case next
header must refer to a valid IP protocol for IPv4. No other extension
headers or destination options are permitted with IPv4.
3 Disassociated location encapsulation
TOU allows transport protocol encapsulation where the location is
disassociated from flow identification. That is a connection can
remain functional even if the addresses or encapsulation ports
change. A common use case will be when NAT state mappings for UDP
flows change. TOU includes a facility to negotiate a shared session
identifier for a transport connection which is sent as part of the
encapsulation of packets for the connection. The session identifier
is used in connection lookup instead of the IP addresses and
encapsulation ports.
This section describes the protocol formats and operational aspects
of TOU for disassociated location transport protocol encapsulation.
3.1 Packet format
Transport layer packets are encapsulated using Generic UDP
Encapsulation (GUE). Two GUE flags and one field are defined for TOU.
The format of this encapsulation is illustrated below:
Herbert Expires November 20, 2016 [Page 9]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source port | Destination port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0x0|0| 2 | Protocol | 0 |S|I| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Session identifier +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Transport layer packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
S: Session identifier bit. This indicates the presence of the
session identifier field.
I: Initiator bit. When set indicates that the packet is sent from
the initiator side of the session, when not set indicates the
packet is sent from the target.
Session identifier: 64-bit field that holds the session
identifier.
3.2 TOU Identity
TOU disassociates the IP address of a peer from the abstraction of
transport protocol endpoint. A peer's identity is implicit in a
session identifier that is established between the two nodes of a
communications session (corresponding to one transport connection).
All packets sent in the session contain a session identifier. The
session identifier is unique among all other communications for a
node, so the node can use it to distinguish between different
communicating peers. A session identifier is meaningful only to the
nodes that share it in a communication, externally to those nodes it
has no defined meaning. Since session identifiers are disassociated
with IP addresses, no relevant information can consistently be
inferred in the network. Two packets containing the same session
identifier but use different addresses may in fact refer to the same
session. Two packets with the same session identifier and same
addresses (and UDP ports) that are temporally observed probably, but
not definitely, refer to the same session.
Transport layer communications occurs between two nodes in a network.
Herbert Expires November 20, 2016 [Page 10]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
Nodes in this context is not restricted to hosts, any application or
process can be considered a node. A node is unambiguously reachable
and distinguishable from other nodes, that is if a packet is received
it must be deterministic as to which node on the host the packet
belongs. For a server application that listens on one or more UDP
ports for TOU packets, each listener port instance can be considered
a node. For a client application, each peer destination (IP address,
TOU port) might be considered to belong to a different node, however
for simplicity the whole client application could considered as one
node.
3.3 Sessions
TOU uses sessions to enable communications between two nodes using an
encapsulated transport layer protocol. A session is represented by a
session identifier. The session identifier has two uses:
1) An location independent representation of the identities in the
communication.
2) Security context for encryption or authentication of the
encapsulated packet.
Each node defines a namespace over its communications. Session
identifiers must be unique in the name space of each node in the
communication. Each side of a communication contributes to the
session identifier so that the identifier is unique relative to each
node.
3.4 Communication roles
At the start of a communications the session identifier must be
negotiated between two nodes. The node that initiates a communication
is the "initiator" and its peer is the "target". The roles are
persistent for the lifetime of the session, each packet in the
session is marked to indicate whether it was sent by the initiator or
the target.
3.5 Session identifier format
A session identifier is a 64-bit value that is sent in each packet of
a session. To ensure relative uniqueness within both nodes of a
communication, each side contributes part of the session identifier.
A session identifier negotiation is defined to create the shared
session identifier.
The session identifier is split into a 32-bit initiator component and
a 32-bit target component as illustrated below:
Herbert Expires November 20, 2016 [Page 11]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initiator component |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Target component |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Initiator and Target components of the Session Identifier are
always non-zero except in the case that session identifier
negotiation is in progress in which case an initiator sends a session
identifier with a Target component that is zero.
3.6 Connection tuple
The session identifier, instead of IP addresses, provides the
endpoint identity of a transport layer connection. As mentioned this
allows the IP addresses associated with the endpoint addresses to
change without breaking the connection. The transport layer tuple
that identifies a specific connection thus changes accordingly to use
the session identifier instead of addresses.
For a transport protocol that uses canonical ports for flow
identification, a flow in TOU is identified by the 4-tuple:
<protocol, session, source port, destination port>
Where the source and destination ports refer to the encapsulated
transport layer ports in a TOU packet.
A session is created for each transport layer connection, there is no
concept of multiplexing different transport connections over a single
sessions. If such semantics are needed the transport layer protocol
can provide that (SCTP sub-streams for instance).
3.7 Operation
This section describes the operation of TOU using disassociated
location encapsulation. TOU state, such as session, is created and
destroyed in conjunction with corresponding state changes in the
connection of an encapsulated transport protocol.
3.7.1 Session lookup tables
TOU logically uses two different tables to perform session lookup.:
- Session negotiation table
The tuple used to match in this table is:
Herbert Expires November 20, 2016 [Page 12]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
<srcIP, dstIP, udp_sport, udp_dport, ISID>
Where ISID refers to the initiator component of the session
identifier, the target component is not considered for lookup
in the session negotiation table.
- Established sessions table
Lookups in the established sessions table are performed on the
session identifier of a received packet. The lookup tuple in
established sessions table is trivially:
<Session identifier>
Before session negotiation completes connection lookup is always
performed on the session negotiation table using fixed location mode
(that is the addresses, ports, and initiator component of the session
identifier are matched).
The target must consult the session negotiation table when the Target
session identifier component of a received packet is zero. It
consults the established sessions table when the Target component of
session identifier is non-zero.
The initiator first consults the established sessions table for every
packet. If an entry is not found for the session identifier then the
session negotiation table is consulted. Note that if the ISID is
unique for all connections in the node then the two tables can be
consolidated into a single one which is keyed solely by ISID. So in
this method the session lookup process is:
1) Initiator performs a lookup based on ISID. If no entry is found
then the session does not exist in the node's namespace.
2) If the entry contains a non-zero TSID and the TSID matches that
received in the packet then this entry is a match. If the TSID
doesn't match then the session is not matched.
3) Otherwise the the entry contains a zero value for the transport
component of the session ID so session negotiation is in
progress. Perform fixed location verification by matching the
received address and port numbers to the recorded values. If
they all match, then the session is matched. The recorded TSID
is set to the non-zero value received in the packet which
implicitly moves the entry to the established sessions table.
3.7.2 Transport connection lookup
Herbert Expires November 20, 2016 [Page 13]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
A connected transport protocol typically maintains one or more tables
of connections (i.e. multiple tables may be used for different
connection states). In lieu of using IP addresses, connection lookup
is performed in TOU using the session (specifically a reference to
the session).
For a transport protocol using the canonical definition of ports, the
tuple for matching connections in TOU becomes:
<Protocol, Session, Source-port, Destination-port>
This implies that connection lookup for a received packet involves
two lookups:
1) A lookup is performed to find the session.
2) A connection lookup is performed using the session found in #1
in the lookup tuple.
Note that TOU requires that a separate session is created for each
encapsulated transport layer connection. This allows consolidating
session and connection lookup by including a reference to the
transport connection in the session state.
3.7.3 Session identifier negotiation
A session must be negotiated between two nodes to create a unique
session identifier within the namespace of each node. Session
negotiation is initiated by one node which assumes the role of
"initiator", and its peer node has the role of "target". Typically,
initiators would be clients and targets are servers. Initiating a
session identifier negotiation coincides with the start of connection
establishment in the encapsulated transport protocol.
During session identifier negotiation session lookup is be done in
fixed location mode (IP address, UDP ports, ISID must be matched) for
either the initiator or the target.
The steps for session negotiation are:
1) Initiator creates initial packet for sending to a target with
an encapsulated transport packet. The transport packet must
contain an initial packet for establishing a transport layer
connection (e.g. a TCP-SYN). The initiator component of the
session identifier is set to a random value that makes it
unique with other existing sessions in the node; the target
component is set to zero.
Herbert Expires November 20, 2016 [Page 14]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
2) Target receives packet. Since the target portion of the session
identifier is zero this indicates a session identifier
negotiation. Target performs a lookup in the session identifier
negotiation table in fixed location mode. The session
identifier negotiation table records session negotiations that
are in progress.
- If an entry is not found in the session negotiation table
then this is a new negotiation. The target creates the target
portion of the session identifier such that whole session
identifier is unique in the target node's name space. Next
the target creates a corresponding entry in the session
negotiation table.
- If an entry is found, then this is a retransmission of a
session negotiation packet. The target value saved in the
entry indicates the value to set in session identifier for
reply packets.
3) Target responds with a transport protocol packet. In the case
of TCP connection establishment this will be a SYN-ACK. The
fully qualified session identifier is used in the TOU
encapsulation.
4) Initiator receives response packet (SYN-ACK). It performs a
session lookup using the session identifier.
- First the established sessions table is consulted. If an
entry for the session identifier is present in the table then
the session is matched.
- If no entry is found in the established sessions table, then
the session negotiation table is consulted. The initiator
component is used for lookup. If a matching entry is found,
the addresses and ports in the packet must be verified to
match the entry using fixed location mode.
5) Initiator sends an ACK (completing three-way handshake in the
transport protocol). The fully qualified session identifier is
used in the TOU encapsulation.
6) Target receives ACK. Target moves the session entry from the
session negotiation table to the established sessions table.
Note that after a session moves to the established sessions table in
a target, it is possible that an out of order retransmission of an
initial packet (e.g. SYN) may be received for the session. The TSID
of the packet is zero and the target will not find the session in the
Herbert Expires November 20, 2016 [Page 15]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
session identifier negotiation table. The target will treat this as
new connection and reply to the intiator with different session
identfier (TSID differs) than that for the established session. When
the initiator receives the reply packet it may match the ISID to the
established session, but the TSID in the received packet differs from
the recorded one so the packet is dropped. The spurious session in
session negotiation table of the target will be removed when the
underlying connection times out. Alternatively, the target may
maintain an entry in the session negotiation table for some period of
time to identify retransmitted session negotiation packets.
Since the initiator component is assumed to be unique for all created
sessions, the session negotiation table and established tables can be
consolodated into a single table keyed by the initiator component of
the session identifier.
3.7.3 Established state
After session establishment, which normally corresponds to transport
protocol connection being established, running operations commences.
Each packet sent on the underlying connection will be encapsulated
using TOU. The 64-bit session identifier is set by both sides of the
connection, and each side sets the Initiator bit (I bit in the GUE
header) accordingly-- the initiator sets I bit in all packets of the
connection, the target clears the bit. When either side receives a
packet a lookup is performed on the session identifier in the
established sessions table.
3.7.4 Closing a sessions
A session is closed when the underlying transport connection closes
(e.g. a TCP connection moves to closed state).
3.7.5 Session creation deferral
When a target receives an initial packet (e.g. a TCP SYN with a
session identifier whose target component is zero) creating a session
state may be deferred until until the transport layer creates its
state. If the transport layer does not create a state (e.g. the SYN
generated a reset) no TOU state is created. The reply packet is
returned with TOU using the same session identifier received in the
request (in this case target component of the session identifier is
zero).
3.8 TCP over UDP example
TCP over UDP implicitly allows nodes using TCP to be multihomed and
mobile.
Herbert Expires November 20, 2016 [Page 16]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
For SYN packets the target session identifier must be set to zero.
The initiator's session identifier is set to a value that is unique
among all connections in the client name space.
The initiator must set the I bit for all packet sent for a
connection. SYN packets (no ACK) MUST contain a zero value in the
Target session identifier field. If a SYN packet with a nonzero
Target Session Identifier is received from an initiator the packet
must be dropped. All other packets sent by the initiator must have
the Target Session Identifier set to nonzero, if a non-SYN packet is
received from an initiator (I bit is set) with a nonzero Target
session identifier then the packet must be dropped.
The target must clear the I bit for all packet sent for a connection.
All packet sent by a target (I bit not set) must have a nonzero
Target session identifier except in the case that the target is
rejecting a connection request (e.g. a TCP-RST is sent in reply to a
TCP-SYN).
Note that simultaneous opens cannot happen. A simultaneous connection
attempt between two nodes with same TCP ports will result in two
different sessions with two different identifiers.
Session state can be created in conjunction with creating TCP state
(TCP PCB for instance). If a TCP packet is received for which no
state exists, a rely to the packet is sent without creating session
state. For instance this would happen is a TCP stack sends a TCP-RST
in response to a SYN.
In the cases of SYN cookies, a target may send a SYN-ACK without
creating a session state. A session identifier should be created so
that it is unique with other established sessions or any values used
in other SYN responses within last N minutes. When a client responds
to the SYN cookie ACK and the server verifies the SYN cookie is valid
(including the session identifier) the TCP connection state and
session state can then be created using the session identifier
provided in the received packet.
The session state is destroyed when the underlying TCP connection
moves to closed state. In the initiator this entails freeing session
identifier to be used with new connections. At the target, the full
session identifier is free to be reused.
4 Security Considerations
Using strong end to end security is recommended with TOU. In
disassociated location encapsulation security is extremely important
to prevent spoofing and connection hijacking (assuming that an
Herbert Expires November 20, 2016 [Page 17]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
attacker can deduce the session identifiers). In order to thwart this
end to end security should be established that authenticates the
nodes in a communication.
Security is provided using DTLS [RFC6347] and the GUE Payload
Transform Field [I-D.hy-gue-4-secure-transport]. The encapsulation
format of TOU with DTLS is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source port | Destination port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0x0|0| 3 | Protocol | 0 |T|S|I| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Transform Field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Session identifier (optional) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Encrypted transport layer packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The T flag bit in the GUE header indicates the presence of the
Payload Transform Field.
The Payload Transform field is defined as:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Payload Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: Payload transform codepoint. 0x1 indicates DTLS.
Payload type: IP protocol of the encrypted payload.
The Proto/type field in the GUE header is set to 59 "no next header"
to indicate that the GUE payload cannot be parsed as an IP protocol.
5 IANA Considerations
Two bits and one field in the GUE header are reserved for TOU use.
Herbert Expires November 20, 2016 [Page 18]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
Port 6080 has been reserved for GUE, however we will request another
port specficilly for TOU. GUE would be used on this TOU port, however
only TOU that encapsulates a transport protocol with TCP-frienly
congestion control is used. Thus traffic destined to the TOU port (as
well as traffic in the reverse direction of a flow) can be assumed to
be properly congestion controlled and not suject to reflection or
other attacks common to some uses of UDP.
6 References
6.1 Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980, <http://www.rfc-editor.org/info/rfc768>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012,
<http://www.rfc-editor.org/info/rfc6347>.
6.2 Informative References
[RFC7663] B. Trammell, Ed., M. Kuehlewind, Ed. "Report from the IAB
Workshop on Stack Evolution in a Middlebox Internet
(SEMI)}, October 2015.
[I-D.chesire-tcp-over-udp] Chesire, S., Graessley, J., and McGuire,
R., "Encapsulation of TCP and other Transport Protocols
over UDP", June 2013
[QUIC] Roskind, J., "QUIC: Multiplexed Stream Transport Over UDP",
http://www.ietf.org/proceedings/88/slides/slides-88-
tsvarea-10.pdf
[RFC6951] Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
Control Transmission Protocol (SCTP) Packets for End-Host
to End-Host Communication", RFC 6951, May 2013,
<http://www.rfc-editor.org/info/rfc6951>.
[I-D.hildebrand-spud-prototype] Hildebrand, J. and Trammell, B.
"Substrate Protocol for User Datagrams (SPUD) Prototype",
draft-hildebrand-spud-prototype-03 (work in preogress),
March 2015.
[I-D.ietf-nvo3-gue] Herbert, T., Yong, L., and Zia, O., "Generic UDP
Encapsulation", draft-ietf-nvo3-gue-01 (work in progress),
March 2016.
[I-D.hy-gue-4-secure-transport] Yong, L. and Herbert, T. Generic UDP
Herbert Expires November 20, 2016 [Page 19]
INTERNET DRAFT Transport layer protocols over UDP May 19, 2016
Encapsulation (GUE) for Secure Transport draft-hy-gue-4-
secure-transport-03 (work in progress), March 2016
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, January 2012,
<http://www.rfc-editor.org/info/rfc6347>.
Authors' Addresses
Tom Herbert
Facebook
1 Hacker Way
Menlo Park, CA
US
EMail: tom@herbertland.com
Herbert Expires November 20, 2016 [Page 20]
