Behavior Engineering for Hindrance Avoidance (behave)

Last Modified: 2008-12-16

Additional information is available at tools.ietf.org/wg/behave

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Description of Working Group:

The behavior of NATs varies from one implementation to
another. As a result it is very difficult for applications to predict
or discover the behavior of these devices. Predicting and/or
discovering the behavior of NATs is important for designing
application protocols and NAT traversal techniques that work reliably
in existing networks. This situation is especially problematic for end-
to-end applications where one or both end-points are behind a NAT, such
as multiuser games, interactive multimedia and P2P download.

The working group documents best current practices to enable NATs to
function in as deterministic a fashion as possible. The NAT
behavior practices will be application independent. This has already
completed for UDP, TCP, DCCP, Multicast and ICMP. It continues with SCTP
and any additional protocol deemed necessary to handle. The WG has
documented approaches for characterizing and testing NAT devices.

BEHAVE will develop protocol-independent toolkits usable by application
protocols for NAT traversal. The WG has already produced an update of
the binding discovery protocol STUN. It will now produce a relay
protocol that focuses on security that is usable with both IPv4 and
IPv6, and capable of relaying between the two IP versions.

The goal of this work is to encourage migration to IPv6. To support
deployments where communicating hosts require using different address
families (IPv4 or IPv6), address family translation is needed to
establish communication. In BEHAVE's specification work on this topic
it will coordinate with the V6ops WG on requirements and operational
considerations.

"An IPv4 network" or "an IPv6 network" in the descriptions below refer
to a network with a clearly identifiable administrative domain (e.g., an
enterprise campus network, a mobile operator's cellular network, a
residential subscriber network, etc.). It will also be that network that
deploys the necessary equipment for translation.

The BEHAVE WG will design solutions for the following four translation
scenarios; other scenarios are out of scope:

1. An IPv6 network to IPv4 Internet, i.e. perform translation between
IPv4 and IPv6 for packets in uni- or bi-directional flows that are
initiated from an IPv6 host towards an IPv4 host. The translator
function is intended to service a specific IPv6 network of arbitary
size. Port translation is necessary on the IPv4 side for efficient
IPv4 address usage.

2. IPv6 Internet to an IPv4 network, i.e. perform translation between
IPv4 and IPv6 for packets in uni- or bi-directional flows that are
initiated from an IPv6 host towards an IPv4 host. The translator
function services is intended to service a specific IPv4 network
using either private or public IPv4 addresses. Because this scenario
has different constraints compared to (1), e.g. the IPv4 hosts that
are to be reachable over IPv6 can be enumerated. The WG should
attempt to design a simpler solution with less impact on
applications.

3. An IPv4 network to IPv6 Internet, i.e. perform translation between
IPv4 and IPv6 for packets in uni- or bi-directional flows that are
initiated from an IPv4 host towards an IPv6 host. The translator
function is intended to service a specific IPv4 network using either
public or private IPv4 address space.

4. IPv4 Internet to an IPv6 network, i.e. perform translation between
IPv4 and IPv6 for packets in uni- or bi-directional flows that are
initiated from an IPv4 host towards an IPv6 host. The translator
function is intended to service a specific IPv6 network where
selected IPv6 hosts and services are to be reachable.

All translation solutions shall be capable of handling flows using TCP,
UDP, DCCP, and SCTP, unless they prevent a timely completion of the work
item. The fundamental parts of ICMP are also required to work.
Additional protocols directly on top of IP may be supported. Translation
mechanisms must handle IP fragmentation.

The translators should support multicast traffic and its control traffic
(IGMP and MLD) across them, both Single Source Multicast (SSM) and Any
Source Multicast (ASM). However, the WG may determine that it becomes
too complex or too difficult to realize with maintained functionality,
for some or all cases of multicast functionality.

Translation mechanisms cannot transparently support protocols that embed
network addresses within their protocol messages without application
level gateways (ALGs). Because ALGs have security issues (like blocking
usage of TLS), are error prone and brittle, and hinder application
development, the usage of ALGs in the defined translators should be
avoided. Instead application developers will need to be aware and use
mechanisms that handle the address family translation. ALGs may be
considered only for the most crucial of legacy applications.

DNS is a crucial part in making a large number of applications work
across a translator. Thus the solution to the above translation cases
shall include recommendations for DNS. If additional DNS functionality
is needed, it may be developed. Any DNS extensions must be developed
together with the DNSEXT WG, including issuing a joint WG last call for
any documents.

The WG needs to determine the best method for providing address space to
a translator in the different deployment cases and documenting the pros
and cons of the suggested approaches. The WG is to seek input from the
Routing, Operations and Internet areas.

Solutions may solve more than one of the cases, however timely delivery
is more important than a unified solution.

Goals and Milestones:

Done  Submit BCP that defines unicast UDP behavioral requirements for NATs to IESG
Done  Submit a BCP that defines TCP behavioral requireents for NATs to IESG
Done  Submit a BCP that defines ICMP behavioral requirements for NATs to IESG
Done  Submit informational that discusses current NAT traversal techniques used by applications
Done  Submit BCP that defines multicast UDP
Done  Submit revision of RFC 3489 to IESG behavioral requirements for NATs to IESG
Done  Submit informational document for rfc3489bis test vectors
Done  Submit experimental document that describes how an application can determine the type of NAT it is behind
Done  Submit BCP document for DCCP NAT behavior
Dec 2008  Submit BCP document for SCTP NAT behavior
Dec 2008  Submit standards-track relay protocol
Jan 2009  Determine relative prioritization of the four translation cases.
Mar 2009  Submit standards-track document for relaying of a TCP bytestream
Mar 2009  Submit standard-track document of an IPv6 relay protocol to IESG
Mar 2009  Determine what solutions(s) and components are needed to solve each of the four cases. Create new milestones for the solution(s) and the components.
Sep 2009  Target for first solution to be submitted to IESG for publication as standards track RFC.

Internet-Drafts:

Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN) (202268 bytes)
Traversal Using Relays around NAT (TURN) Extension for IPv6 (23919 bytes)
NAT Behavior Discovery Using STUN (82888 bytes)
Traversal Using Relays around NAT (TURN) Extensions for TCP Allocations (26810 bytes)
Test vectors for STUN (16697 bytes)
Network Address Translation (NAT) Behavioral Requirements for the Datagram Congestion Control Protocol (21697 bytes)
Traversal Using Relays around NAT (TURN) Uniform Resource Identifiers (25982 bytes)
IP/ICMP Translation Algorithm (53002 bytes)
DNS64: DNS extensions for Network Address Translation from IPv6 Clients to IPv4 Servers (60470 bytes)
NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers (80136 bytes)
Framework for IPv4/IPv6 Translation (73641 bytes)
IPv6 Addressing of IPv4/IPv6 Translators (52293 bytes)

Request For Comments:

Network Address Translation (NAT) Behavioral Requirements for Unicast UDP (RFC 4787) (68693 bytes)
IP Multicast Requirements for a Network Address Translator (NAT) and a Network Address Port Translator (NAPT) (RFC 5135) (36528 bytes)
State of Peer-to-Peer(P2P) Communication Across Network Address Translators(NATs) (RFC 5128) (81008 bytes)
NAT Behavioral Requirements for TCP (RFC 5382) (50306 bytes)
Session Traversal Utilities for NAT (STUN) (RFC 5389) (125650 bytes) obsoletes RFC 3489
NAT Behavioral Requirements for ICMP (RFC 5508) (67985 bytes)

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