BEHAVE B. Carpenter, Ed.
Internet-Draft Univ. of Auckland
Intended status: Standards Track M. Boucadair
Expires: November 12, 2009 France Telecom
S. Brim
Cisco
J. Halpern
Ericsson
S. Jiang
Huawei Technologies Co., Ltd
K. Moore
Network Heretics
May 11, 2009
A Generic Referral Object for Internet Entities
draft-carpenter-behave-referral-object-00
Status of this Memo
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Copyright (c) 2009 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 in effect on the date of
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Abstract
The purpose of a referral is to enable a given entity in a multiparty
application to pass information to another party. This memo
specifies a Generic Referral Object (GRO) to be used in the context
of referrals. The proposed object is compact and is application-
independent. Both IPv4 and IPv6 schemes are supported, as well as
upper layer identifiers. Additional information to characterise an
enclosed reference is also described. To allow proper interpretation
of referrals, a new notion of scope identifiers is introduced.
Table of Contents
1. Introduction and Motivation . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Normative Notation . . . . . . . . . . . . . . . . . . . . 5
2. Summary of Requirements . . . . . . . . . . . . . . . . . . . 5
3. Referral Semantics and Scope Identifiers . . . . . . . . . . . 6
4. Generic Referral Object Format . . . . . . . . . . . . . . . . 9
4.1. End of Qualifiers (EOQ) . . . . . . . . . . . . . . . . . 10
4.2. IPv4 and IPv6 Addresses (references) . . . . . . . . . . . 10
4.3. FQDN (reference) . . . . . . . . . . . . . . . . . . . . . 11
4.4. HIT (reference) . . . . . . . . . . . . . . . . . . . . . 11
4.5. HI (reference) . . . . . . . . . . . . . . . . . . . . . . 11
4.6. IPv4 and IPv6 Masks (qualifiers) . . . . . . . . . . . . . 11
4.7. Ref_lifetime (qualifier) . . . . . . . . . . . . . . . . . 11
4.8. Ref_source (qualifier) . . . . . . . . . . . . . . . . . . 12
4.9. Ref_scope (qualifier) . . . . . . . . . . . . . . . . . . 12
4.10. ScopeID (qualifier) . . . . . . . . . . . . . . . . . . . 13
4.11. Port_number (qualifier) . . . . . . . . . . . . . . . . . 13
4.12. Transport_protocol (qualifier) . . . . . . . . . . . . . . 13
4.13. Port_source (qualifier) . . . . . . . . . . . . . . . . . 14
4.14. Extensibility . . . . . . . . . . . . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
8. Change log . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1. Normative References . . . . . . . . . . . . . . . . . . . 16
9.2. Informative References . . . . . . . . . . . . . . . . . . 16
Appendix A. Example Use Cases . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction and Motivation
A frequently occurring situation is that one entity A connected to
the Internet (or to some private network using the Internet protocol
suite) needs to inform another entity B how to reach either A itself
or some third-party entity C. This is known as a referral.
In the original design of the Internet, IP addresses were global,
unique, and quasi-permanent. Also any differentiation beyond that
provided by an IP address was done by protocol and port numbers.
Referrals were therefore performed simply by passing an IP address
and possibly protocol and port numbers. In fact simple referrals
(the first case above, sometimes called first-party referrals) were
never needed since B could simply use A's address. Third-party
referrals were trivial: A would tell B about C's address. Thus, it
became common practice to pass raw addresses between entities. A
classical example is the FTP PORT command [RFC0959].
Unfortunately, this simple approach to referrals often fails in
today's Internet. As has been known for some time [RFC2101],
addresses no longer all have global scope, and may have limited
lifetime. Both addresses and port numbers may be different on either
side of a NAT or some other middlebox [RFC3234], and firewalls may
block them. Also, the Internet now has two coexisting address
formats for IPv4 and IPv6. Sending an out-of-scope or expired
address, or one of the wrong format, as a referral will fail.
In some cases, this problem may be readily solved by passing a Fully
Qualified Domain Name (FQDN) instead of an address. Indeed, that is
an architecturally preferred solution [RFC1958]. However, it is not
sufficient in many cases of dynamic referrals. Experience shows that
an application cannot use a domain name in order to reliably find the
address(es) of an arbitrary peer. Domain names work fairly well to
find the addresses of servers, as in web servers or SMTP servers,
because operators of public servers take pains to make sure that
their domain names work. But DNS records are not as reliably
maintained for arbitrary hosts such as might need to be contacted in
peer-to-peer applications. Many small networks do not even maintain
DNS entries for their hosts, and for some networks that do list local
hosts in DNS, the listings may well be unusable from a remote
location (say because of two-faced DNS, or because the A record
contains a private address). Furthermore, an FQDN may not be
sufficient to establish successful communications involving
heterogeneous peers (i.e. IPv4 and IPv6) since A and AAAA records
may not be correctly provisioned.
Another problem is that an application does not have a reliable way
of knowing its own domain name - or to be more precise, a way of
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knowing a domain name that will allow the application to be reached
from another environment.
For these reasons, the problem of address referrals cannot be solved
just by recommending the use of FQDNs instead.
The first motivation for this draft is the observation that unless
the parties involved have reached an understanding about the scope,
lifetime, and format of the elements in a referral through some other
means, that information must be passed with the referral. This is
required so that the receiving entity can determine whether or not
the referral is useful.
When a referral fails, good design suggests that the receiving entity
should attempt to correct the situation. For example, if
communication fails to be established using an IP address, it would
often be appropriate to attempt a DNS lookup. The second motivation
for this draft is that it may be helpful to the entity receiving a
referral to also receive information about the source of the
referral, such as an FQDN, if that is known to the sender of the
referral. The receiving entity can then attempt to recover a valid
address (and possibly port number) for the referred entity.
It should be noted that partial or application-specific solutions to
this problem abound. A non-normative Appendix gives examples, in the
form of use cases. The objective of this specification is to define
a generic and extensible solution, to allow more robust application
design. It is an open question whether existing applications will
benefit from retro-fitting GROs, or whether they will mainly be of
use for new applications.
1.1. Terminology
This document makes use of the following terms:
o "Generic Referral Object (GRO)": the data object defined by this
specification.
o "Entity": we use this rather than "application" to describe any
software component embedded in a host, not just a specific
application, that sends, receives or makes use of GROs. Also, in
case of dynamic load sharing or failover, an entity might even
migrate between hosts.
o "Referral": the act of one entity informing another entity how to
contact a specific entity.
o "Reference": the actual data (name, address, identitifier,
locator, pointer, etc.) that is the basis of a referral.
o "Scope Identifier (ScopeID): an identifier for the scope of
validity of a reference.
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o "Qualifier": a data item that gives additional information about a
Reference.
o "Referring entity": the entity that sends a referral.
o "Receiving entity": the entity that receives a referral.
o "Referenced entity": the entity described in a GRO.
1.2. Normative Notation
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 [RFC2119].
2. Summary of Requirements
A GRO should be self-describing; that is to say, even if it is
forwarded several times across the network, the ultimate receiving
entity should be able to extract and interpret all the information
inserted by the original referring entity.
A GRO should be compact (i.e., binary encoded) and designed for
efficient processing.
The GRO format must not be specific to a given IP version and must
not be application-specific.
A GRO should contain information that the referring entity can
provide about the scope, lifetime, format and source of the referral,
encoded in a universal format.
The GRO format should be extensible with well-defined backwards
compatibility.
A damaged GRO would be useless. However, to maintain efficiency,
intrinsic error detection or correction for GROs should not be
mandatory. Therefore, GROs SHOULD be sent over a channel supporting
error detection or correction.
A forged GRO would be at least as dangerous as a forged IP address.
However, to maintain efficiency, intrinsic cryptographic
authentication of GROs should not be mandatory. The use of an
authenticated channel to transmit GROs is RECOMMENDED.
An intercepted GRO would be at least as revelatory as an intercepted
IP address. However, to maintain efficiency, intrinsic encryption of
GROs should not be mandatory. The use of an encrypted channel to
transmit GROs is RECOMMENDED.
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3. Referral Semantics and Scope Identifiers
The principal purpose of a referral is to enable one entity in a
multi-party application to pass information to another party involved
in the same application. This specification makes no assumptions
about whether the entities are acting as clients, servers, peers,
super-nodes, relays, proxies, etc., as far as the application is
concerned. Neither does it take a position as to how the various
entities become aware of the need to send a referral; this depends
entirely on the structure of the application.
It is the responsibility of the referring entity to construct a GRO
on the basis of information in its possession. It is the
responsibility of the receiving entity to interpret and check this
information. Due to the fluidity of connectivity in today's
Internet, the referring entity cannot guarantee that the referenced
entity can be reached. This can only be checked by the receiving
entity. In the event of a reachability problem, information in the
GRO may assist the receiving entity to find an alternative path.
Since the most fundamental quantity likely to be conveyed in a GRO is
an IP address, (and possibly a port number) its scope is a key
question. Address scope is not a simple concept, as shown by the
discussion in [RFC4007] and the practical difficulties caused by
[RFC3484]. Even the concept of link-local scope is complicated by
the existence of multi-link subnets [RFC4903]. For the purpose of
referrals, it seems that previous formalisations of the concept of
scope are inadequate. Assuming that a GRO is trustworthy, one
question that a receiving entity must answer is: can the address in
this GRO be reached from here? That question is not answered by
knowing only the scope (in the sense of RFC4007) as defined at the
location of the referring entity. For that reason, scope is
represented in a new way in GROs. Firstly, the scope is qualified
(to the best of the referring entity's knowledge) as follows:
o Null. The address is known not to be applicable outside the
referring host (e.g., a loopback address). This option is
provided mainly for completeness. There is no value in such a
GRO, and for privacy reasons it should not be communicated anyway.
o Link. Apart from the standard Ethernet-like view of link
locality, this scope would also apply to point-to-point links and
to fragments of a multi-link subnet. Although on-link referrals
should be trivial, this case is included to allow for uniform
design of applications utilising GROs, so that link-local does not
become a special case.
o Limited. The address has applicability beyond the link, but it is
known not to have global applicability. Examples include IPv4
private addresses [RFC1918] and IPv6 Unique Local Addresses
[RFC4193]. Other cases include addresses on subnets which the
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referring entity knows to be obstructed by firewalls, network
address translators, or other barriers to transparency [RFC2775].
o Global. The address has applicability beyond the link, and is
believed to have global applicability within its address family.
However, particularly in the case of limited scope, this is
insufficient for the receiving entity to decide whether the address
is applicable in the receiving entity's context. The scopes above
are described as if they were a set of concentric circles, but
reality is more complex, and limited scopes might overlap each other
in an arbitrary way, for example when multiple VPNs are formed.
Indeed, a referring entity may or may not be aware that the receiving
entity and the referenced entity are within a link scope or limited
scope that does not contain the referring entity. Therefore, a GRO
may also include a scope identifier (ScopeID), which is an arbitrary
label for a region of the network within which certain link or
limited scope addresses are applicable.
There needs to be a high level of assurance that ScopeIDs are unique,
or at least that a GRO will never be forwarded outside a region in
which ScopeIDs are unique. Also, all referring and receiving
entities need to be aware of the ScopeID(s) that apply to them.
However, it is clearly undesirable to create a new global
registration scheme for ScopeIDs.
The delimiter of a limited scope will in many cases be the device
(firewall or NAT) that obstructs transparency. A tempting solution
would be to use some unique identifier of that device as the unique
ScopeID. Unfortunately, this cannot be an IP address of the device,
since in the case of nested NATs, all its addresses may be ambiguous.
Neither can we rely on such a device having its own FQDN, or on that
FQDN being known to all entities within the scope concerned.
Finally, some limited scopes may not be hidden behind a single such
device; for example, a limited scope might consist of a company's
network and selected VPN connections to subsets of several business
partners' networks. Alternatively, multiple limited scopes might be
hidden behind the same device. Device addresses are therefore not
suitable as ScopeIDs.
Therefore, a limited scope can best be defined as whatever set of
referring and receiving entities have been configured (statically or
dynamically) to accept a given ScopeID in some unambiguous namespace
(see Section 4.10).
Methods for configuring, advertising and discovering ScopeIDs are not
defined in this document. However, in their absence, it is extremely
hard for receiving entities to interpret and use information about
limited scopes. To the extent possible, all entities involved in
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referrals should determine what scope is shared between the referred
entity and the receiving entity, by any means. Those means are not
covered in this document, but may include use of external services,
agreement on scope identifiers, or direct negotiation.
o If shared scope (or set of scopes) is determined, a referral
should ideally only include information useful in that scope or
set of scopes.
o If shared scope is uncertain, a referral should include all
information that might be useful, taking privacy considerations
into account.
In general, the referring entity cannot know the scope in which the
GRO will be interpreted. For example, the initial receiving entity
may itself be behind a NAT, unknown to the referring entity, or the
receiving entity may send the GRO onwards to another host in yet
another scope. In practice, we have to leave the receiver to decide
whether certain information is useful or not. In the case of a
ScopeID in particular, the referring entity is not required to know
which ScopeIDs apply to the receiving entity.
Discovery or negotiation of ScopeIDs between referring, referenced
and receiving entities is certainly a possibility, but may be
expensive, and is not assumed by this specification.
A referring entity may obtain the address and port number for the
referenced entity in various ways, and knowledge about this may help
the receiving entity when combined with scope information. For
example, if the receiving entity is aware that the address has been
translated, and that it has global scope, it may choose to use it
without further checks. If it is not marked as translated, and has
limited scope, the receiving entity may then verify whether it has a
suitable ScopeID.
To enable such logic, a GRO may describe the source of an address or
port number. How knowledge of this source is obtained is outside the
scope of the present specification, but ICE [I-D.ietf-mmusic-ice] is
an example method. It is also out of scope here to describe exactly
how the receiving entity uses the information; for example GRO
semantics do not include or imply preferences or priorities when
multiple addresses are provided. The receiving entity may choose to
use a predefined policy, apply general logic as sketched in the
previous paragraph, or follow application-specific logic, all based
on the data provided in a GRO.
Obviously, a GRO is no use unless it contains at least one item that
can be used to find a path to the referred entry. One option would
be to make the presence of at least one IP address mandatory.
However, there are alternatives, the most obvious one being an FQDN.
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Any form of identifier-locator separation, with HIP [RFC5201] as an
example, may also offer an alternative. Therefore, we do not require
a GRO to include an IP address, even though its inclusion is a very
likely case.
4. Generic Referral Object Format
A GRO is composed of a sequence of binary-encoded type-length-value
fields (TLVs) transmitted in network byte order. The TLV format is
as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+..
| GRType |Q| GRLength | GRValue ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+..
A GRO MUST include at least one reference that allows a receiving
entity to attempt to establish a path to the referred entity. A
typical case is an IPv4_address or IPv6_address TLV. Multiple
references may be present, and their order is not significant.
Apart from this, all TLVs are OPTIONAL.
[[ Discusssion invited: At the moment, there is no total length field
or end flag for the whole GRO, assuming that GROs will be sent in
some kind of container. Opinions among the authors vary about
whether this is OK. ]]
GRType: Specifies the type of the current TLV. GRType is encoded in
7 bits. The initially specified types are, in decimal:
0: EOQ.
1: IPv4_address.
2: IPv6_address.
3: FQDN.
4: HIT.
5: HI.
65: IPv4_mask.
66: IPv6_mask.
67: Ref_lifetime.
68: Ref_source.
69: Ref_scope.
70: ScopeID.
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71: Port_number.
72: Transport_protocol.
73: Port_source.
127: reserved.
A receiving entity MUST silently ignore any TLV with an unknown or
reserved GRType.
Each TLV is classified semantically as a reference or as a qualifier.
A qualifier provides extra information about a reference or another
qualifier..
[[ Discusssion invited: Do we need a syntactic method of
distinguishing references from qualifiers? Since unknown TLVs are
always discarded, why would that be needed? ]]
Q bit: If this bit is set to 1, the current TLV is followed by one or
more TLVs that qualify it.
GRLength: The length in bytes of the GRValue field. Thus, the total
length of the TLV is GRLength+2 bytes.
GRValue: The content and encoding depend on GRType. Any padding
required to fill an integral number of bytes MUST consist of a
sequence of zero bits at the end of the content.
4.1. End of Qualifiers (EOQ)
This TLV follows the last TLV that qualifies a TLV whose Q bit is set
to 1. Its GRLength must be set to 0.
The Q bit and EOQ MAY be used recursively, so that qualifiers may
themselves be qualified if that proves to be useful.
Example (GT=GRType):
GT Q|GT Q|GT Q|GT Q|GT Q|GT Q|GT Q|GT Q
A 1|xx 0|xx 0|B 1|xx 0|xx 0|EOQ 0|EOQ 0
<-------> Qualifiers of B
<----------------------------> Qualifiers of A
The Q bit MUST NOT be set in an EOQ TLV.
4.2. IPv4 and IPv6 Addresses (references)
IPv4 and IPv6 addresses are encoded in their normal binary form, with
GRLength being 4 and 16 respectively.
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When multiple addresses are provided, their order does not imply an
order of preference. The receiving entity SHOULD apply a local
policy and mechanism to choose between alternative addresses, using
other information included in the GRO appropriately. This document
does not describe such policies and mechanisms, which could be
application specific.
4.3. FQDN (reference)
The Fully Qualified Domain Name of the referenced entity in ASCII
format according to [RFC1035].
The GRLength is variable (maximum 63).
[[ Discussion invited: Is there also value in a generic URI item?
See section on Extensibility below for a related discussion point. ]]
4.4. HIT (reference)
The Host Identity Tag of the referenced entity [RFC5201].
The GRLength must be set to 16.
4.5. HI (reference)
The Host Identifier of the referenced entity [RFC5201].
The GRLength is variable.
[[ Discussion invited: Is this necessary in order to run the HIP base
exchange? The HI is a large object to include in a GRO. Also, do we
need a more precise definition of what the HI is (see section 5.2.8
of RFC5201)? ]]
4.6. IPv4 and IPv6 Masks (qualifiers)
IPv4 and IPv6 masks are encoded in their normal binary form, with
GRLength being 4 and 16 respectively.
4.7. Ref_lifetime (qualifier)
Remaining lifetime in seconds of the reference that it qualifies,
encoded as a 32 bit binary number in the format of an IPv6 Valid
Lifetime [RFC4861]. GRLength must be set to 4.
If the lifetime is absent, or if it indicates an infinite lifetime
[RFC4861], the receiving entity MUST assign a lifetime of one day to
the corresponding reference.
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The receiving entity MUST count down a received lifetime
appropriately. If the GRO is forwarded to an additional receiving
entity, the lifetime MUST be updated appropriately.
[[ Discussion invited: would it be better to specify an expiry
timestamp? ]]
[[ Discussion invited: is the default of one day reasonable? ]]
4.8. Ref_source (qualifier)
This is a single byte indicating the source of the reference that it
qualifies. GRLength must be set to 1. The following values may be
used:
0: source was static configuration
1: source was DNS lookup
2: source was DHCP or DHCPv6
3: source was SLAAC
4: relayed address (e.g. from TURN [I-D.ietf-behave-turn] or
SOCKS)
5: translated address. ("server reflexive" in ICE
[I-D.ietf-mmusic-ice] terminology.)
A receiving entity MUST silently ignore unknown values.
4.9. Ref_scope (qualifier)
This is a single byte indicating the scope of the reference that it
qualifies. GRLength must be set to 1. The scopes are explained in
Section 3. The currently defined values are as follows:
0: Null
1: Link
2: Limited
7: Global. Note that some unused values precede this value, in
case of future changes.
A receiving entity MUST silently ignore unknown values.
References qualified with the Null value SHOULD NOT be sent and MUST
be silently ignored by a receiving entity.
When a receiving entity receives a reference qualified with a Link or
Limited Ref_scope, and without a ScopeID, it should take locally
defined steps to check whether the reference is in fact within a
reachable scope.
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4.10. ScopeID (qualifier)
A ScopeID, if present, is a label for the scope of the reference that
it qualifies.
When a receiving entity receives a reference qualified with a
Ref_scope and a ScopeID, it should verify the ScopeID against a list
of ScopeIDs known to be reachable and if not, take other locally
defined steps to check whether the reference is in fact within a
reachable scope.
ScopeIDs should be reasonably certain to be unique, yet require no
new system for central administration.
[[ Discusssion invited: It isn't clear to the authors that a single
syntax for ScopeID is sufficient. Should we allow for subtypes, so
that (e.g.) ULA format and FQDN format would both be possible? The
following proposal is tentative. ]]
The proposed method is that each organisation that needs to define a
ScopeID will first generate a ULA prefix as defined in [RFC4193], and
then form a specific IPv6 address using that ULA prefix. It is
RECOMMENDED to form an address using a valid universal EUI-64
interface identifier according to [RFC4291], and this EUI-64
identifier MAY be the same one as used in the RFC4193 procedure.
The GRLength must be set to 16. The GRValue is the ScopeID in the
format of an IPv6 address, although it will be treated entirely as an
opaque binary value in the GRO referring and receiving entities.
4.11. Port_number (qualifier)
The inbound TCP/UDP/SCTP/DCCP port number associated with the
reference that it qualifies. The port number may be bound to a
specific transport protocol (see next item).
The GRLength must be set to 2.
This TLV MAY be qualified by Transport_protocol or Port_source TLVs.
An IP address may be qualified by zero, one or several Port_number
TLVs.
4.12. Transport_protocol (qualifier)
This is a single byte indicating the IPv4 protocol number or IPv6
Next Header value used with the reference or Port_number that it
qualifies. GRLength must be set to 1.
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A receiving entity MUST silently ignore unknown values.
4.13. Port_source (qualifier)
This is a single byte indicating the source of the Port_number that
it qualifies. GRLength must be set to 1. Accepted values are:
0: direct (i.e. known to be the original port number used by the
referenced entity)
4: relayed port (e.g. from TURN [I-D.ietf-behave-turn] or SOCKS)
5: translated port. ("server reflexive" in ICE
[I-D.ietf-mmusic-ice] terminology.)
[[ Discussion invited: Is this distinction usfeul? ]]
The assigned values were chosen to align with those for Ref_source.
A receiving entity MUST silently ignore unknown values.
4.14. Extensibility
Additional GRTypes may be assigned in the range up to 126 by IANA
action as defined in Section 6. The documentation of a new GRType
must specify its name, define its GRLength, and describe the contents
and meaning of its GRValue, including whether it is a reference or a
qualifier.
This extensibility is not intended to allow a GRO to grow enough to
contain every possible kind of application-layer identifier that
could ever be used in a referral, because then it would be too hard
to write a generic "please connect me to the peer at this GRO"
function. Thus, additional GRTypes SHOULD NOT be assigned except for
generic purposes that will apply to multiple applications.
Similarly, additional sub-types for Address_source, Address_scope,
Transport_protocol, and Port_source SHOULD NOT be assigned except for
generic purposes.
[[ Discussion invited: Sheng Jiang suggested that there should be a
generic 'Application-specific ID' GRType, for example in URI format.
A problem with this is that it might end up as a catch-all like a DNS
TXT record, and threaten interoperability as a result. ]]
The reserved GRType value 127 is intended to be used to define an
extended range of GRTypes in the highly unlikely event that this
becomes necessary.
5. Security Considerations
Forged or intercepted GROs would enable a wide variety of attacks.
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Although not fundamentally different from attacks based on forged or
observed IP addresses or FQDNs, no doubt GROs would allow such
attacks to be more ingenious, simply because they provide more
information than an address or FQDN alone. As noted in Section 2,
GROs SHOULD be transmitted through authenticated and encrypted
channels. Since this is a requirement of the channel and not of the
GRO, and the channel used depends on a specific use case, it is not
further elaborated here.
GROs are variable length objects with no defined maximum length. It
is possible that a malicious GRO could be constructed, with harmful
code masquerading as legitimate or unknown GRType items. All
implementations of receiving entities MUST guard against buffer
overflows, as well as obeying the rules about ignoring unknown values
in Section 4.
Unknown TLVs in GROs are to be ignored by the receiving entity.
However, GROs may be forwarded to additional receiving entities, in
which case the unknown TLVs will be forwarded too. A receiving
entity MAY remove unknown TLVs before forwarding a GRO, as a
precaution against malicious use.
GROs raise potential privacy issues, which are not explored in this
document. For example, in the SIP context, mechanisms such as
[RFC3323] and [I-D.ietf-sip-ua-privacy] are available to hide
information that might identify end-points. Usage scenarios for GROs
MUST ensure that they do not unintentionally defeat privacy
solutions.
6. IANA Considerations
IANA is requested to established a Generic Referral Object (GRO)
registry, containing sub-registries for GRType, Ref_source,
Ref_scope, and Port_source. The range and initial assignments are
defined in Section 4.
New values in this registry are to be assigned according to the
Specification Required policy defined in [RFC5226], which implies
review by a Designated Expert according to Section 4.14.
[[ Discussion invited: It has been suggested to define a (small)
registry for Global ScopeIDs, instead of assuming that "global" for
IPv4 and IPv6 is unambiguous. ]]
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7. Acknowledgements
This document originated from a Thai Lunch BOF (a variant of a Bar
BOF) at IETF74. Valuable comments and contributions were made by Dan
Wing, ...
This document was produced using the xml2rfc tool [RFC2629].
8. Change log
draft-carpenter-referral-object-00: original version, 2009-05-11
9. References
9.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
9.2. Informative References
[I-D.boucadair-sipping-ipv6-atypes]
Boucadair, M., Noisette, Y., and A. Allen, "The atypes
media feature tag for Session Initiation Protocol (SIP)",
draft-boucadair-sipping-ipv6-atypes-01 (work in progress),
March 2009.
[I-D.ietf-behave-turn]
Rosenberg, J., Mahy, R., and P. Matthews, "Traversal Using
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Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)",
draft-ietf-behave-turn-14 (work in progress), April 2009.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
[I-D.ietf-sip-ua-privacy]
Munakata, M., Schubert, S., and T. Ohba, "UA-Driven
Privacy Mechanism for SIP", draft-ietf-sip-ua-privacy-07
(work in progress), April 2009.
[RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC1958] Carpenter, B., "Architectural Principles of the Internet",
RFC 1958, June 1996.
[RFC2101] Carpenter, B., Crowcroft, J., and Y. Rekhter, "IPv4
Address Behaviour Today", RFC 2101, February 1997.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
June 1999.
[RFC2775] Carpenter, B., "Internet Transparency", RFC 2775,
February 2000.
[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, February 2002.
[RFC3323] Peterson, J., "A Privacy Mechanism for the Session
Initiation Protocol (SIP)", RFC 3323, November 2002.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC4007] Deering, S., Haberman, B., Jinmei, T., Nordmark, E., and
B. Zill, "IPv6 Scoped Address Architecture", RFC 4007,
March 2005.
[RFC4091] Camarillo, G. and J. Rosenberg, "The Alternative Network
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Address Types (ANAT) Semantics for the Session Description
Protocol (SDP) Grouping Framework", RFC 4091, June 2005.
[RFC4092] Camarillo, G. and J. Rosenberg, "Usage of the Session
Description Protocol (SDP) Alternative Network Address
Types (ANAT) Semantics in the Session Initiation Protocol
(SIP)", RFC 4092, June 2005.
[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
June 2007.
[RFC5201] Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
"Host Identity Protocol", RFC 5201, April 2008.
Appendix A. Example Use Cases
[[ This appendix is incomplete and preliminary. ]]
Referrals may be used to add an entity to a multi-party conversation,
or they may be used (in applications such as telephony) as the first
step of transferring one end of a conversation from the referring
entity to the receiving entity. [[ Say more? ]]
TBD: FTP/PORT, HTTP referrals... text needed
BitTorrent is a distributed file sharing infrastructure. It is based
on P2P techniques for exchanging files between connected users.
Three parties are involved in a BitTorrent architecture: (1) The
server into which, has been uploaded the torrent file. (2) The
Tracker which maintains a list of clients which have the file or some
portions of that file. (3) Entities which are downloading and/or
uploading portions of the file. In order to download a given file, a
BitTorrent client needs to obtain the corresponding torrent file
(i.e. a file which includes the meta-data information of the file to
be shared: the file name, its length, a hash and the URL of the
tracker.). Then, it connects to the tracker to retrieve a list of
lechers (clients which are currently downloading the file but do not
yet detain all the portions of the file) and seeders (clients which
detain all the portions of the file and are uploading them to other
requesting clients). The client connects to those machines and
downloads the available portions of the requested file.
In a GRO for Skype purposes, if the address fails, you'd have to fall
back to the Skype ID instead of an FQDN. This is a case where
allowing an application-specific ID might be valuable. Another case
would be Lotus Domino databases - if both IP address and FQDN fail to
find the relevant server, the server name and the database name could
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be used as fallback identifiers.
In SIP environments, a SIP Proxy Server intervenes in the placement
of SIP sessions between two UAs. Particularly, the SDP part of
relayed SIP messages includes required information for establishment
of RTP sessions (particularly IP address and port number). A media
description may be unidirectional or symmetric. ICE and ANAT allow
listing several network types and addresses in the same SDP offer.
ANAT: ANAT [RFC4091],[RFC4092] is a procedure used by Dual Stack UAs
to provide both IPv4 and IPv6 addresses in the context of a single
logical media stream. This helps interworking as, whatever the
distant UA version is (IPv4/IPv6-only or Dual-Stack) provided that
this latter is able to understand at least one of the offers. ANAT
semantic does not allow to characterize the IP address(es) it
carries. For instance, no indication if the UA is behind a
translator or not is supported by ANAT (or even ICE). ICE deprecates
ANAT attribute.
Atypes [I-D.boucadair-sipping-ipv6-atypes]: atypes is a SIP media
feature tag which indicates the IP address type capabilities of the
UA (User Agent) and can aid the routing process and ease the
invocation of required functions (e.g. SIP-ALG, NAT64, NAT46) when
heterogeneous (i.e. IPv4 and IPv6) parties are involved in a given
SIP session. Atypes can be used jointly with GRO (also with ICE and
ANAT) to optimise the media path as experienced between involved
parties (especially when Dual-stacks UAs are involved).
Authors' Addresses
Brian Carpenter (editor)
Department of Computer Science
University of Auckland
PB 92019
Auckland, 1142
New Zealand
Email: brian.e.carpenter@gmail.com
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Mohamed Boucadair
France Telecom
3, Avenue Francois Chateaux
Rennes 35000
France
Email: mohamed.boucadair@orange-ftgroup.com
Scott Brim
Cisco
146 Honness Lane
Ithaca, NY 14850
US
Email: swb@employees.org
Joel M. Halpern
Ericsson
P. O. Box 6049
Leesburg, VA 20178
US
Email: jhalpern@redback.com
Sheng Jiang
Huawei Technologies Co., Ltd
KuiKe Building, No.9 Xinxi Rd.,
Shang-Di Information Industry Base, Hai-Dian District, Beijing
P.R. China
Email: shengjiang@huawei.com
Keith Moore
Network Heretics
Email: moore@network-heretics.com
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