One document matched: draft-ietf-ipngwg-scopedaddr-format-02.txt
Differences from draft-ietf-ipngwg-scopedaddr-format-01.txt
INTERNET-DRAFT T. Jinmei, Toshiba
June 28, 2000 A. Onoe, Sony
An Extension of Format for IPv6 Scoped Addresses
<draft-ietf-ipngwg-scopedaddr-format-02.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026 [STD-PROC].
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/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet Draft will expire on December 28, 2000.
Abstract
This document defines an extension of the format for IPv6 scoped
addresses. In the format, a zone identifier is attached to a scoped
address in order to supplement ambiguity of the semantics of the
address. Using the format with some library routines will make
scope-aware applications simpler.
1. Introduction
There are several types of scoped addresses defined in the "IPv6
Addressing Architecture" [ADDRARCH]. Since uniqueness of a scoped
address is guaranteed only within a corresponding zone [SCOPEARCH],
the semantics for a scoped address is ambiguous on a zone
boundary. For example, when a user specifies to send a packet from
a node to a link-local address of another node, the user must
specify the link of the destination as well, if the node is
attached to more than one link.
This characteristic of scoped addresses may introduce additional
cost to scope-aware applications; a scope-aware application may
have to provide a way to specify a scope zone for each scoped
address (e.g. a specific link for a link-local address) that the
application uses. Also, it is hard for a user to "cut and paste" a
scoped address due to the ambiguity of its scope.
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Applications that are supposed to be used in end hosts
like telnet, ftp, and ssh, are not usually aware of scoped
addresses, especially of link-local addresses. However, an expert
user (e.g. a network administrator) sometimes has to give even
link-local addresses to such applications.
Here is a concrete example. Consider a multi-linked router, called
"R1", that has at least two point-to-point interfaces. Each of the
interfaces is connected to another router, called "R2" and "R3".
Also assume that the point-to-point interfaces are "unnumbered",
that is, they have link-local addresses only.
Now suppose that the routing system on R2 hangs up and has to be
reinvoked. In this situation, we may not be able to use a global
address of R2, because this is a routing trouble and we cannot
expect that we have enough routes for global reachability to R2.
Hence, we have to login R1 first, and then try to login R2 using
link-local addresses. In such a case, we have to give the
link-local address of R2 to, for example, telnet. Here we assume
the address is fe80::2.
Note that we cannot just type like
% telnet fe80::2
here, since R1 has more than one interface (i.e. link) and hence
the telnet command cannot detect which link it should try to
connect.
Although R1 could spray neighbor solicitations for fe80::2 on all
links that R1 attaches in order to detect an appropriate link, we
cannot completely rely on the result. This is because R3 might also
assign fe80::2 to its point-to-point interface and might return a
neighbor advertisement faster than R2. There is currently no
mechanism to (automatically) resolve such conflict. Even if we had
one, the administrator of R3 might not accept to change the
link-local address especially when R3 belongs to a different
organization from R1's.
Another example is an EBGP peering. When two IPv6 ISPs establish an
EBGP peering, using a particular ISP's global addresses for the
peer would be unfair, and using their link-local addresses would be
better in a neutral IX. In such a case, link-local addresses should
be specified in a router's configuration file and the link for the
addresses should be disambiguated, since a router usually connects
to multiple links.
This document defines an extension of the format for scoped addresses
in order to overcome this inconvenience. Using the extended format
with some appropriate library routines will make scope-aware
applications simpler.
2. Assumptions and Definitions
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In this document we adopt the same assumption of characteristics of
scopes as described in the scoped routing document [SCOPEDROUTING].
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, if and where they appear
in this document, are to be interpreted as described in [KEYWORDS].
3. Proposal
The proposed format for scoped addresses is as follows:
<scoped_address>%<zone_id>
where
<scoped_address> is a literal IPv6 address,
<zone_id> is a string to identify the scope zone of the address, and
`%' is a delimiter character to distinguish between
<scoped_address> and <zone_id>.
The following subsections describe detail definitions and concrete
examples of the format.
3.1 Scoped Addresses
The proposed format is applied to all kinds of unicast and
multicast scoped addresses, that is, all non-global unicast and
multicast addresses.
The format should not be used for global addresses. However, an
implementation which handles addresses (e.g. name to address
mapping functions) MAY allow users to use such a notation (see also
Appendix C).
3.2 Zone Identifiers
An implementation SHOULD support at least numerical identifiers as
<zone_id>, which are non-negative decimal numbers. Positive
identifiers MUST uniquely specify a single zone for a given scoped
address. An implementation MAY use zero to have a special meaning,
for example, a meaning that no scope zone is specified.
An implementation MAY support other kinds of non-null strings as
<zone_id> unless the strings conflict with the delimiter
character. The precise semantics of such additional strings is
implementation dependent.
One possible candidate of such strings would be interface names,
since interfaces uniquely disambiguate any type of scopes
[SCOPEDROUTING]. In particular, if an implementation can assume
that there is a one-to-one mapping between links and interfaces
(and the assumption is usually reasonable,) using interface names
as link identifiers would be natural.
An implementation could also use interface names as <zone_id> for
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larger scopes than links, but there might be some confusion in such
use. For example, when more than one interface belongs to a same
site, a user would be confused about which interface should be
used. Also, a mapping function from an address to a name would
encounter a same kind of problem when it prints a scoped address
with an interface name as a zone identifier. This document does
not specify how these cases should be treated and leaves it
implementation dependent.
It cannot be assumed that a same identifier is common to all nodes in
a zone. Hence, the proposed format MUST be used only within a node
and MUST NOT be sent on a wire.
3.3 Examples
Here are examples. The following addresses
fe80::1234 (whose link identifier is 1)
fec0::5678 (whose site identifier is 2)
ff02::9abc (whose link identifier is 5)
ff08::def0 (whose organization identifier is 10)
would be represented as follows:
fe80::1234%1
fec0::5678%2
ff02::9abc%5
ff08::def0%10
If we use interface names as <zone_id>, those addresses could also
be represented as follows:
fe80::1234%ne0
fec0::5678%ether2
ff02::9abc%pvc1.3
ff08::def0%interface10
where the interface "ne0" belongs to link 1, "ether2" belongs to
site 2, and so on.
3.4 Omitting Zone Identifiers
This document does not intend to invalidate the original format
for scoped addresses, that is, the format without the scope
identifier portion. An implementation SHOULD rather provide a user
with a "default" zone of each scope and allow the user to omit
zone identifiers.
Also, when an implementation can assume that there is no ambiguity
of any type of scopes on a node, it MAY even omit the whole
functionality to handle the proposed format. An end host with a
single interface would be an example of such a case.
4. Combinations of Delimiter Characters
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There are other kinds of delimiter characters defined for IPv6
addresses. In this section, we describe how they should be combined
with the proposed format for scoped addresses.
The IPv6 addressing architecture [ADDRARCH] also defines the syntax
of IPv6 prefixes. If the address portion of a prefix is scoped one
and the scope should be disambiguated, the address portion SHOULD
be in the proposed format. For example, the prefix fec0:0:0:1::/64
on a site whose identifier is 2 should be represented as follows:
fec0:0:0:1::%2/64
In this combination, it is important to place the zone identifier
portion before the prefix length, when we consider parsing the
format by a name-to-address library function (see Appendix A). That
is, we can first separate the address with the zone identifier from
the prefix length, and just pass the former to the library function.
The preferred format for literal IPv6 addresses in URL's are also
defined [URLFORMAT]. When a user types the preferred format for an
IPv6 scoped address whose zone should be explicitly specified, the
user could use the proposed format combined with the preferred
format.
However, the typed URL is often sent on a wire, and it would cause
confusion if an application did not strip the <zone_id> portion
before sending. Also, the proposed format might conflict with the
URI syntax [URI], since the syntax defines the delimiter chracter
(`%') as the escape character.
Hence, this document does not specify how the proposed format
should be combined with the preferred format for literal IPv6
addresses. As for the conflict issue with the URI format, it would
be better to wait until the relationship between the preferred
format and the URI syntax is clarified. Actually, the preferred
format for IPv6 literal addresses itself has same kind of conflict.
In any case, it is recommended to use an FQDN instead of a literal
IPv6 address in a URL, whenever an FQDN is available.
5. Related Issues
In this document, it is assumed that a zone identifier is not
necessarily common in a single zone. However, it would be useful if
a common notation is introduced (e.g. an organization name for a
site). In such a case, the proposed format could be commonly used
to designate a single interface (or a set of interfaces for a
multicast address) in a scope zone.
When the network configuration of a node changes, the change may
affect <zone_id>. Suppose that the case where numerical
identifiers are sequentially used as <zone_id>. When a network
interface card is newly inserted in the node, some identifiers may
have to be renumbered accordingly. This would be inconvenient,
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especially when addresses with the numerical identifiers are stored
in non-volatile storage and reused after rebooting.
6. Security Considerations
Since the use of this approach to represent IPv6 scoped addresses
is restricted within a single node, it does not cause a security
atack from the outside of the node.
However, a malicious node might send a packet that contains a
textual IPv6 scoped address in the proposed format, intending to
deceive the receiving node about the zone of the scoped
address. Thus, an implementation should be careful when it
receives packets that contain IPv6 scoped addresses as data.
Appendix A. Interaction with API
The proposed format would be useful with some library functions
defined in the "Basic Socket API" [BASICAPI], the functions which
translate a nodename to an address, or vice versa.
For example, if getaddrinfo() parses a literal IPv6 address in the
proposed format and fills an identifier according to <zone_id> in
the sin6_scope_id field of a sockaddr_in6 structure, then an
application would be able to just call getaddrinfo() and would not
have to care about scopes.
Also, if getnameinfo() returns IPv6 scoped addresses in the proposed
format, a user or an application would be able to reuse the result by
a simple "cut and paste" method.
The kernel should interpret the sin6_scope_id field properly in
order to make these extensions feasible. For example, if an
application passes a sockaddr_in6 structure that has a non-zero
sin6_scope_id value to the sendto() system call, the kernel should
send the packet to the appropriate zone according to the
sin6_scope_id field. Similarly, when a packet arrives from a scoped
address, the kernel should detect the correct zone identifier based
on the address and the receiving interface, fill the identifier in
the sin6_scope_id field of a sockaddr_in6 structure, and then pass
the packet to an application via the recvfrom() system call, etc.
Note that the ipng working group is now revising the basic socket
API in order to support scoped addresses appropriately. When the
revised version is available, it should be preferred to the
description of this section.
Appendix B. Implementation Experiences
The WIDE KAME IPv6 stack implements the extension to the
getaddrinfo() and the getnameinfo() functions described in Appendix
A of this document. The source code is available as free software,
bundled in the KAME IPv6 stack kit.
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The current implementation assumes a one-to-one mapping between
links and interfaces, and hence it uses interface names as
<zone_id> for links.
For instance, the implementation shows its routing table as
follows:
Internet6:
Destination Gateway Flags Intface
default fe80::fe32:93d1%ef0 UG ef0
This means that the default router is fe80::fe32:93d1 on the link
identified by the interface "ef0". A user can "cut and paste" the
result in order to telnet to the default router like this:
% telnet fe80::fe32:93d1%ef0
even on a multi-linked node.
As another example, we show how the implementation can be used for
the problem described in Section 1.
We first confirm the link-local address assigned to the
point-to-point interface of R2:
(on R1)% ping ff02::1%pvc0
PING(56=40+8+8 bytes) fe80::1 --> ff02::1
16 bytes from fe80::1%lo0, icmp_seq=0 hlim=64 time=0.474 ms
16 bytes from fe80::2%pvc0, icmp_seq=0 hlim=64 time=0.374 ms(DUP!)
...
(we assume here that the name of the point-to-point interface
on R1 toward R2 is "pvc0" and that the link-local address on
the interface is "fe80::1".)
So the address should be fe80::2. Then we can login R2 using the
address by the telnet command without ambiguity:
% telnet fe80::2%pvc0
Though the implementation supports the extended format for all type
of scoped addresses, our current experience is limited to link-local
addresses. For other type of scopes, we need more experience.
The implementation also supports the notion of "default" scope zone
as described in Section 3.4. If a user specified "pvc0" as the
default link in the above example, the user can just type
% telnet fe80::2
then the kernel will automatically use the link identified by
"pvc0" as the link of the address fe80::2.
Appendix C. A Comprehensive Description of KAME's getXXXinfo Functions
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The following tables describe the behavior of the KAME's
implementation we mentioned in Appendix B using concrete
examples. Note that those tables are not intended to be standard
specifications of the extensions but are references for other
implementors.
Those tables summarize what value the getXXXinfo functions return
against various arguments. For each of two functions we first
explain typical cases and then show non-typical ones.
The tables for getaddrinfo() have four columns. The first two are
arguments for the function, and the last two are the results. The
tables for getnameinfo() also have four columns. The first three
are arguments, and the last one is the results.
Columns "Hostname" contain strings that are numeric or non-numeric
IPv6 hostnames.
Columns "NI_NUMERICHOST" or "NHOST" show if the NI_NUMERICHOST is
set to flags for the corresponding getXXXinfo function. Columns
"NSCOPE" show if the NI_NUMERICSCOPE is set to flags for the
corresponding getnameinfo function. The value "1" means the flag
is set, and "0" means the flag is clear. "-" means that the field
does not affect the result.
Columns "sin6_addr" contain IPv6 binary addresses in the textual
format, which mean the values of the sin6_addr field of the
corresponding sockaddr_in6 structure.
Columns "sin6_scope_id" contain numeric numbers, which mean the
values of the sin6_scope_id field of the corresponding sockaddr_in6
structure.
If necessary, we use an additional column titled "N/B" to note
something special.
If an entry of a result column has the value "Error", it means the
corresponding function fails.
In the examples, we assume the followings:
- The hostname "foo.kame.net" has a AAAA DNS record
"3ffe:501::1". We also assume the reverse map is configured
correctly.
- There is no FQDN representation for scoped addresses.
- The numeric link identifier for the interface "ne0" is 5.
- We have an interface belonging to a site whose numeric identifier
is 10.
- The numeric identifier "20" is invalid for any type of scopes.
- We use the string "none" as an invalid non-numeric zone identifier.
Typical cases for getaddrinfo():
Hostname NI_NUMERICHOST sin6_addr sin6_scope_id
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"foo.kame.net" 0 3ffe:501::1 0
"3ffe:501::1" - 3ffe:501::1 0
"fec0::1%10" - fec0::1 10
"fe80::1%ne0" - fe80::1 5
"fe80::1%5" - fe80::1 5
Typical cases for getnameinfo():
sin6_addr sin6_scope_id NHOST NSCOPE Hostname
3ffe:501::1 0 0 - "foo.kame.net"
3ffe:501::1 0 1 - "3ffe:501::1"
fec0::1 10 - - "fec0::1%10"
fe80::1 5 - 0 "fe80::1%ne0"
fe80::1 5 - 1 "fe80::1%5"
Non-typical cases for getaddrinfo():
Hostname NI_NUMERICHOST sin6_addr sin6_scope_id N/B
"foo.kame.net" 1 Error
"foo.kame.net%20" - Error (*1)
"foo.kame.net%none" - Error (*1)
"3ffe:501::1%none" - Error
"3ffe:501::1%0" - 3ffe:501::1 0 (*2)
"3ffe:501::1%20" - 3ffe:501::1 20 (*2)
"fec0::1%none" - Error
"fec0::1" - fec0::1 0 (*3)
"fec0::1%0" - fec0::1 0 (*4)
"fec0::1%20" - fec0::1 20 (*5)
"fe80::1%none" - Error
"fe80::1" - fe80::1 0 (*3)
"fe80::1%0" - fe80::1 0 (*4)
"fe80::1%20" - fe80::1 20 (*5)
(*1) <zone_id> against an FQDN is invalid.
(*2) We do not expect that <zone_id> is specified for a global
address, but we don't regard it as invalid.
(*3) We usually expect that a scoped address is specified with
<zone_id>, but if no identifier is specified we just set 0 to
the sin6_scope_id field.
(*4) Explicitly specifying 0 as <zone_id> is not meaningful, but
we just treat the value as opaque.
(*5) The <zone_id> portion is opaque to getaddrinfo() even if it
is invalid. It is kernel's responsibility to raise errors, if
there is any connection attempt that the kernel cannot handle.
Non-typical cases for getnameinfo():
sin6_addr sin6_scope_id NHOST NSCOPE Hostname N/B
3ffe:501::1 20 1 - "3ffe:501::1%20" (*6)
3ffe:501::1 20 0 - "foo.kame.net" (*7)
fec0::1 20 - - "fec0::1%20"
fec0::1 0 - - "fec0::1" (*8)
fe80::1 20 - - "fe80::1%20"
fe80::1 0 - - "fe80::1" (*8)
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(*6) We do not expect that a global IPv6 address has a non-zero
zone identifier. But if it is the case, we just treat it as
opaque.
(*7) Despite the above, if the NI_NUMERICHOST is clear, we resolve
the address to a hostname and print the name without scope
zone information. We might have to reconsider this behavior.
(*8) We usually expect that a scoped address has a non-zero zone
identifier. But if the identifier is 0, we simply print the
address portion without scope zone information.
Acknowledgments
We authors are indebted to Brian Zill, Richard Draves, and Francis
Dupont for their careful comments and suggestions in a discussion
to define a unified format among early implementations.
Jim Bound also gave us valuable comments and clarifications through
discussions about API extensions for scoped addresses in the ipngwg
mailing list.
Hideaki YOSHIFUJI commented on relationship between the URI syntax
and the proposed format, and helped us improve the related section.
Jun-ichiro Hagino has been helping us through all the discussions
and his implementation efforts.
Authors' Addresses
Tatuya JINMEI
Research and Development Center, Toshiba Corporation
1 Komukai Toshiba-cho, Kawasaki-shi
Kanagawa 212-8582, JAPAN
Tel: +81-44-549-2230
Fax: +81-44-520-1841
Email: jinmei@isl.rdc.toshiba.co.jp
Atsushi Onoe
Internet Systems Laboratory, IN Laboratories, Sony Corporation
6-7-35 Kitashinagawa, Shinagawa-ku, Tokyo 141-0001, JAPAN
Tel: +81-3-5448-4620
Fax: +81-3-5448-4622
Email: onoe@sm.sony.co.jp
References
[ADDRARCH] Hinden, R., Deering, S., "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[BASICAPI] Gilligan, R. E., Thomson, S., Bound, J., Stevens, W.,
"Basic Socket Interface Extensions for IPv6", Internet-Draft,
May 2000, <draft-ietf-ipngwg-rfc2553bis-00.txt>.
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
draft-ietf-ipngwg-scopedaddr-format-02.txt [Page 10]
INTERNET-DRAFT Format for IPv6 Scoped Addresses June 2000
Requirement Levels", BCP 14, RFC 2119, March 1997.
[SCOPEARCH] S. Deering, B. Haberman, B. Zill, "IP Version 6 Scoped
Address Architecture", Internet-Draft, March 2000,
<draft-ietf-ipngwg-scoping-arch-00.txt>.
[SCOPEDROUTING] Haberman, B., "Routing of Scoped Addresses in the
Internet Protocol Version 6 (IPv6)", Internet-Draft,
March 2000, <draft-ietf-ipngwg-scoped-routing-03.txt>.
[STD-PROC] Bradner, S., The Internet Standards Process -- Revision 3,
RFC 2026, October 1996.
[URLFORMAT] Hinden, R., Carpenter, B., Masinter, L., "Preferred
Format for Literal IPv6 Addresses in URL's", RFC 2732,
December 1999.
[URI] T. Berners-Lee, R. Fielding, and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
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