6man Working Group Yu hua bing
Internet-Draft Ruijie Networks, China
Intended status: Standards Track
Expiration: August 28, 2011
February 28, 2011
IPv6 Stateless Address Autoconfiguration With Prefixes Longer Than 64
draft-yhb-6man-slaac-improvement-00
Abstract
IPv6 stateless address autoconfiguration described by RFC4862 only
supports 64-bit prefixes. This approach can't be deployed in the
sites with prefixes longer than 64. We have no right to require that
the sites MUST use 64-bit prefixes. This document tries to implement
stateless address autoconfiguration with prefixes longer than 64.
Status of this Memo
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Table of Contents
1. Introduction ....................................................2
2. Protocol Specification ..........................................2
2.1. Router Advertisement Processing ............................2
2.2. ISATAP Tunnel ..............................................4
2.3. Analysis of Duplicate Address Possiblity ...................4
3. References ......................................................5
3.1. Normative References .......................................5
3.2. Informative References .....................................5
1. Introduction
The IPv6 stateless address autoconfiguration described by RFC4862
requires no manual configuration of hosts and no additional servers,
so it is welcomed by a lot of users. But it has a detect that some
users complain about:
The sum of the prefix length and interface identifier length MUST
equal 128 bits. RFC4291 specifies that for all unicast addresses,
except those that start with the binary value 000, Interface IDs are
required to be 64 bits long. It means the prefix length MUST be 64,
and this approach can't be deployed in the sites with prefixes longer
than 64.
A 64-bit prefix can generate at most 2^64 IPv6 addresses. In fact,
any LAN can't run out of so many IPv6 addresses, and only a very
small part of IPv6 addresses are used, so it is a serious waste. Some
sites do not need 64-bit prefixes. We have no right to require
that the sites MUST use 64-bit prefixes.
If the prefix of the site is longer than 64, or if the prefix is 64
bits long, and the site is divided into several subnets, then the
stateless address autoconfiguration cannot be used and the
convenience it will bring cannot be shared.
So we scream for stateless address autoconfiguration with prefixes
longer than 64.
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [RFC2119].
2. Protocol Specification
2.1. Router Advertisement Processing
When a host receives a valid router advertisement, execute the
following steps for each Prefix-Information option in the router
advertisement:
(1) If the Autonomous flag is not set, silently ignore the Prefix
Information option.
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(2) If the prefix is a link-local prefix, silently ignore the
Prefix Information option.
(3) If the preferred lifetime is greater than the valid lifetime,
silently ignore the Prefix Information option. A node MAY wish to
log a system management error in this case.
(4) If the prefix length is less than (128 - length of interface ID)
or more than 126, the Prefix Information option MUST be ignored. An
implementation MAY wish to log a system management error in this
case.
(5) If the prefix advertised overlaps with the prefix of an
address configured by stateless autoconfiguration already in the
list of addresses associated with the interface, and the former is
not equal to the latter, the Prefix Information option MUST be
ignored. An implementation MAY wish to log a system management error
in this case.
(6) If the receiving interface is not ISATAP tunnel interface, the
Valid Lifetime is not 0, host ID is configured (the host ID greater
than 0 and less than 2 ^ (128 - prefix length) is valid), an address
is formed by combining the advertised prefix with the host ID as
follows:
| N bits | 128 - N bits |
+---------------------------------------+------------------------+
| link prefix | host ID |
+----------------------------------------------------------------+
A host MUST allow the host ID to be configured by system management.
If the host ID configured on the host is invalid, an address can't
be formed. A node MUST log a system management error in this case.
(7) If the receiving interface is Ethernet, and the Valid Lifetime
is not 0, do with the Prefix-Information option as follows:
(7.1) If the prefix length is 64, an address is formed by combining
the advertised prefix with the interface identifier.
(7.2)If the prefix length is greater than 64 and is not greater than
80, an address is formed by combining the advertised prefix with
the MAC address of the interface as follows:
| N bits | (80 - N) bits | 48 bits |
+------------------------------+---------------+-----------------+
| link prefix | reserved | MAC address |
+----------------------------------------------------------------+
The middle (80 - N) bits are reserved for future use, now it MUST be
zero.
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(7.3) If the prefix length is greater than 80, a random number
between 0 and 2 ^ (128 - prefix length) is generated, and an address
is formed by combining the advertised prefix with the random number
as follows:
| N bits | 128 - N bits |
+---------------------------------------+------------------------+
| link prefix | random number |
+----------------------------------------------------------------+
(8) If the receiving interface is not Ethernet, execute step d in
section 5.5.3 of RFC4862.
(9) If the advertised prefix is equal to the prefix of an address
configured by stateless autoconfiguration in the list, execute step
e in section 5.5.3 of RFC4862.
2.2. ISATAP Tunnel
Besides Ethernet, stateless address autoconfiguration is often used
on an ISATAP tunnel. But, it is a pity that the ISATAP tunnel can't
support stateless address autoconfiguration with prefixes longer
than 64 because of ISATAP interface identifier.
2.3. Analysis of Duplicate Address Possibility
On the Ethernet, if the prefix length is not less than 64 and not
greater than 80,use the MAC address to form the IPv6 address. The
possibility that the IPv6 address is duplicate is very low, because
the possibility that the MAC address is duplicate is very low.
If the prefix length is greater than 80, it is more convenient for
users to use the random number to form the IPv6 address, but the
IPv6 address is possibly duplicate. Suppose there are M hosts on the
link,the prefix length is N, if all hosts run stateless address
autoconfiguration almost at the same time, for each host, duplicate
address possibility P is (M-1)/(2^(128-N)-1). In order to ensure
each host runs stateless address autoconfiguration successfully, P
SHOULD be less than 1/1000. For example, there are 1000 hosts on the
link, if it is required that P should be less than 1/1000, N should
be less than 108.If stateless address autoconfiguration fails for
the first time, it is a good idea to try more times.
Another choice is that the network administrator assigns host IDs to
each host. The first benefit is that the IPv6 addresses can be fully
used, for example, on the link with 1000 hosts, the 118-bit prefix
is enough. The second benefit is that duplicate address possibility
is very low, almost zero.
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3. References
3.1. Normative References
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
3.2. Informative References
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4941] T. Narten,R. Draves and S. Krishnan, "Privacy Extensions
for Stateless Address Autoconfiguration in IPv6", RFC
4941, September 2007.
[RFC5214] F. Templin,T. Gleeson and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
Authors' Addresses
Yu hua bing
Ruijie Networks
Fuzhou
Fujian
China
Email: yhb@ruijie.com.cn
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