As per Relevance of the word renumbering, we have this rfc below:
Network Working Group M.
Request for Comments: 2894
Category: Standards Track August 2000
Router Renumbering for IPv
Status of this
This document specifies an Internet standards track protocol for
Internet community, and requests discussion and suggestions
improvements. Please refer to the current edition of the "
Official Protocol Standards" (STD 1) for the standardization
and status of this protocol. Distribution of this memo is unlimited
Copyright
Copyright (C) The Internet Society (2000). All Rights Reserved
IESG Note
This document defines mechanisms for informing a set of routers
renumbering operations they are to perform, including a mode
operation in environments in which the exact number of routers
unknown. Reliably informing all routers when the actual number
routers is unknown is a difficult problem. Implementation
operational experience will be needed to fully understand
applicabilty and scalability aspects of the mechanisms defined
this document when the number of routers is unknown
IPv6 Neighbor Discovery and Address Autoconfiguration
make initial assignments of address prefixes to hosts. Aside
the problem of connection survival across a renumbering event,
two mechanisms also simplify the reconfiguration of hosts when
set of valid prefixes changes
This document defines a mechanism called Router Renumbering ("RR")
which allows address prefixes on routers to be configured
reconfigured almost as easily as the combination of
Discovery and Address Autoconfiguration works for hosts. It
a means for a network manager to make updates to the prefixes used
and advertised by IPv6 routers throughout a site
Crawford Standards Track [Page 1]
RFC 2894 Router Renumbering for IPv6 August 2000
Table of
1. Functional Overview ....................................... 2
2. Definitions ............................................... 4
2.1. Terminology ......................................... 4
2.2. Requirements ........................................ 5
3. Message Format ............................................ 5
3.1. Router Renumbering Header ........................... 7
3.2. Message Body -- Command Message ..................... 9
3.2.1. Prefix Control Operation ...................... 9
3.2.1.1. Match-Prefix Part ....................... 9
3.2.1.2. Use-Prefix Part ......................... 11
3.3. Message Body -- Result Message ...................... 12
4. Message Processing ........................................ 14
4.1. Header Check ........................................ 14
4.2. Bounds Check ........................................ 15
4.3. Execution ........................................... 16
4.4. Summary of Effects .................................. 17
5. Sequence Number Reset ..................................... 18
6. IANA Considerations ....................................... 19
7. Security Considerations ................................... 19
7.1. Security Policy and Association Database Entries .... 19
8. Implementation and Usage Advice for Reliability ........... 20
8.1. Outline and Definitions ............................. 21
8.2. Computations ........................................ 23
8.3. Additional Assurance Methods ........................ 24
9. Usage Examples ............................................ 25
9.1. Maintaining Global-Scope Prefixes ................... 25
9.2. Renumbering a Subnet ................................ 26
10. Acknowledgments .......................................... 27
11. References ............................................... 28
12. Author's Address ......................................... 29
Appendix -- Derivation of Reliability Estimates ............... 30
Full Copyright Statement ...................................... 32
1. Functional
Router Renumbering Command packets contain a sequence of
Control Operations (PCOs). Each PCO specifies an operation,
Match-Prefix, and zero or more Use-Prefixes. A router processes
PCO in sequence, checking each of its interfaces for an address
prefix which matches the Match-Prefix. For every interface on
a match is found, the operation is applied. The operation is one
ADD, CHANGE, or SET-GLOBAL to instruct the router to respectively
the Use-Prefixes to the set of configured prefixes, remove the
which matched the Match-Prefix and replace it with the Use-Prefixes
Crawford Standards Track [Page 2]
RFC 2894 Router Renumbering for IPv6 August 2000
or replace all global-scope prefixes with the Use-Prefixes. If
set of Use-Prefixes in the PCO is empty, the ADD operation
nothing and the other two reduce to deletions
Additional information for each Use-Prefix is included in the
Control Operation: the valid and preferred lifetimes to be
in Router Advertisement Prefix Information Options [ND], and
the L and A flags for the same option, or an indication that they
to be copied from the prefix that matched the Match-Prefix
It is possible to instruct routers to create new prefixes
combining the Use-Prefixes in a PCO with some portion of the
prefix which matched the Match-Prefix. This simplifies
operations which are expected to be among the most common. For
Use-Prefix, the PCO specifies a number of bits which should be
from the existing address or prefix which matched the Match-
and appended to the use-prefix prior to configuring the new prefix
the interface. The copied bits are zero or more bits from
positions immediately after the length of the Use- Prefix.
subnetting information is in the same portion of the old and
prefixes, this synthesis allows a single Prefix Control Operation
define a new global prefix on every router in a site,
preserving the subnetting structure
Because of the power of the Router Renumbering mechanism, each
message includes a sequence number to guard against replays, and
required to be authenticated and integrity-checked. Each
Prefix Control Operation is idempotent and so could be
for improved reliability, as long as the sequence number is current
without concern about multiple processing. However, non-
combinations of PCOs can easily be constructed and
containing such combinations could not be safely reprocessed
Therefore, all routers are required to guard against processing an
message more than once. To allow reliable verification that
have been received and processed by routers, a mechanism
duplicate-command notification to the management station is included
Possibly a network manager will want to perform more renumbering,
exercise more detailed control, than can be expressed in a
Router Renumbering packet on the available media. The RR
is most powerful when RR packets are multicast, so IP
is undesirable. For these reasons, each RR packet contains
"Segment Number". All RR packets which have a Sequence
greater than or equal to the highest value seen are valid and must
processed. However, a router must keep track of the Segment
of RR messages already processed and avoid reprocessing a
Crawford Standards Track [Page 3]
RFC 2894 Router Renumbering for IPv6 August 2000
whose Sequence Number and Segment Number match a previously
message. (This list of processed segment numbers is reset when a
highest Sequence Number is seen.)
The Segment Number does not impose an ordering on packet processing
If a specific sequence of operations is desired, it may be
by ordering the PCOs in a single RR Command message or through
Sequence Number field
There is a "Test" flag which indicates that all routers
simulate processing of the RR message and not perform any
reconfiguration. A separate "Report" flag instructs routers to
a Router Renumbering Result message back to the source of the
Command message indicating the actual or simulated result of
operations in the RR Command message
The effect or simulated effect of an RR Command message may also
reported to network management by means outside the scope of
document, regardless of the value of the "Report" flag
2.
2.1.
This term always refers to a 128-bit IPv6 address [AARCH].
referring to bits within an address, they are numbered from 0
127, with bit 0 being the first bit of the Format Prefix
A prefix can be understood as an address plus a length, the
being an integer in the range 0 to 128 indicating how many
bits are significant. When referring to bits within a prefix
they are numbered in the same way as the bits of an address.
example, the significant bits of a prefix whose length is L
the bits numbered 0 through L-1, inclusive
An address A "matches" a prefix P whose length is L if the first
bits of A are identical with the first L bits of P. (
address matches a prefix of length 0.) A prefix P1 with length L
matches a prefix P2 of length L2 if L1 >= L2 and the first L2
of P1 and P2 are identical
Crawford Standards Track [Page 4]
RFC 2894 Router Renumbering for IPv6 August 2000
Prefix Control
This is the smallest individual unit of Router
operation. A Router Renumbering Command packet includes zero
more of these, each comprising one matching condition, called
Match-Prefix Part, and zero or more substitution specifications
called Use-Prefix Parts
Match-
This is a Prefix against which a router compares the addresses
prefixes configured on its interfaces
Use-
The prefix and associated information which is to be configured
a router interface when certain conditions are met
Matched
The existing prefix or address which matched a Match-Prefix
New
A prefix constructed from a Use-Prefix, possibly including some
the Matched Prefix
Recorded Sequence
The highest sequence number found in a valid message MUST
recorded in non-volatile storage
Note that "matches" is a transitive relation but not symmetric
If two prefixes match each other, they are identical
2.2.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
document are to be interpreted as described in [KWORD].
3. Message
There are two types of Router Renumbering messages: Commands,
are sent to routers, and Results, which are sent by routers. A
message type is used to synchronize a reset of the Recorded
Number with the cancellation of cryptographic keys. The three
of messages are distinguished the ICMPv6 "Code" field and differ
the contents of the "Message Body" field
Crawford Standards Track [Page 5]
RFC 2894 Router Renumbering for IPv6 August 2000
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ IPv6 header, extension headers /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ ICMPv6 & RR Header (16 octets) /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ RR Message Body /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Router Renumbering Message
Router Renumbering messages are carried in ICMPv6 packets with Type =
138. The RR message comprises an RR Header, containing the ICMPv
header, the sequence and segment numbers and other information,
the RR Message Body, of variable length
All fields marked "reserved" or "res" MUST be set to zero
generation of an RR message, and ignored on receipt
All implementations which generate Router Renumbering
messages MUST support sending them to the All Routers
address with link and site scopes, and to unicast addresses of link
local and site-local formats. All routers MUST be capable
receiving RR Commands sent to those multicast addresses and to any
their link local and site local unicast addresses.
SHOULD support sending and receiving RR messages addressed to
unicast addresses. An implementation which is both a sender
receiver of RR commands SHOULD support use of the All
multicast address with node scope
Data authentication and message integrity MUST be provided for
Router Renumbering Command messages by appropriate IP
[IPSEC] means. The integrity assurance must include the IPv
destination address and the RR Header and Message Body. See
7, "Security Considerations".
The use of authentication for Router Renumbering Result messages
RECOMMENDED
Crawford Standards Track [Page 6]
RFC 2894 Router Renumbering for IPv6 August 2000
3.1. Router Renumbering
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SequenceNumber |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SegmentNumber | Flags | MaxDelay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields
Type 138 (decimal), the ICMPv6 type value assigned to
Code 0 for a Router Renumbering
1 for a Router Renumbering
255 for a Sequence Number Reset
The Sequence Number Reset is described in section 5.
Checksum The ICMPv6 checksum, as specified in [ICMPV6].
checksum covers the IPv6 pseudo-header and all fields
the RR message from the Type field onward
An unsigned 32-bit sequence number. The sequence
MUST be non-decreasing between Sequence Number Resets
An unsigned 8-bit field which enumerates different
RR messages having the same SequenceNumber. No
among RR messages is imposed by the SegmentNumber
Flags A combination of one-bit flags. Five are defined
three bits are reserved
+-+-+-+-+-+-+-+-+
|T|R|A|S|P| res |
+-+-+-+-+-+-+-+-+
Crawford Standards Track [Page 7]
RFC 2894 Router Renumbering for IPv6 August 2000
The flags T, R, A and S have defined meanings in an
Command message. In a Result message they MUST
copied from the corresponding Command. The P flag
meaningful only in a Result message and MUST be zero
a transmitted Command and ignored in a received Command
T Test command --
0 indicates that the router configuration is to
modified
1 indicates a "Test" message: processing is to
simulated and no configuration changes are to
made
R Result requested --
0 indicates that a Result message MUST NOT be
(but other forms of logging are not precluded);
1 indicates that the router MUST send a
message upon completion of processing the
message
A All interfaces --
0 indicates that the Command MUST NOT be applied
interfaces which are administratively shut down
1 indicates that the Command MUST be applied to
interfaces regardless of administrative
status
S Site-specific -- This flag MUST be ignored
the router treats interfaces as belonging
different "sites".
0 indicates that the Command MUST be applied
interfaces regardless of which site they
to
1 indicates that the Command MUST be applied only
interfaces which belong to the same site as
interface to which the Command is addressed.
the destination address is appropriate
interfaces belonging to more than one site,
the Command MUST be applied only to
belonging to the same site as the interface
which the Command was received
P Processed previously --
0 indicates that the Result message contains
complete report of processing the Command
Crawford Standards Track [Page 8]
RFC 2894 Router Renumbering for IPv6 August 2000
1 indicates that the Command message was
processed (and is not a Test) and the
router is not processing it again. This
message MAY have an empty body
MaxDelay An unsigned 16-bit field specifying the maximum time,
milliseconds, by which a router MUST delay sending
reply to this Command. Implementations MAY generate
random delay between 0 and MaxDelay milliseconds with
finer granularity than 1ms
3.2. Message Body -- Command
The body of an RR Command message is a sequence of zero or
Prefix Control Operations, each of variable length. The end of
sequence MAY be inferred from the IPv6 length and the lengths
extension headers which precede the ICMPv6 header
3.2.1. Prefix Control
A Prefix Control Operation has one Match-Prefix Part of 24 octets
followed by zero or more Use-Prefix Parts of 32 octets each
3.2.1.1. Match-Prefix
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OpCode | OpLength | Ordinal | MatchLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MinLen | MaxLen | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- -+
| |
+- MatchPrefix -+
| |
+- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields
OpCode An unsigned 8-bit field specifying the operation to
performed when the associated MatchPrefix matches
interface's prefix or address. Values are
1 the ADD
Crawford Standards Track [Page 9]
RFC 2894 Router Renumbering for IPv6 August 2000
2 the CHANGE
3 the SET-GLOBAL
OpLength The total length of this Prefix Control Operation,
units of 8 octets. A valid OpLength will always be
the form 4N+3, with N equal to the number of
parts (possibly zero).
Ordinal An 8-bit field which MUST have a different value in
Prefix Control Operation contained in a given RR
message. The value is otherwise unconstrained
MatchLen An 8-bit unsigned integer between 0 and 128
specifying the number of initial bits of
which are significant in matching
MinLen An 8-bit unsigned integer specifying the minimum
which any configured prefix must have in order to
eligible for testing against the MatchPrefix
MaxLen An 8-bit unsigned integer specifying the maximum
which any configured prefix may have in order to
eligible for testing against the MatchPrefix
MatchPrefix The 128-bit prefix to be compared with each interface'
prefix or address
Crawford Standards Track [Page 10]
RFC 2894 Router Renumbering for IPv6 August 2000
3.2.1.2. Use-Prefix
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UseLen | KeepLen | FlagMask | RAFlags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V|P| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- -+
| |
+- UsePrefix -+
| |
+- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields
UseLen An 8-bit unsigned integer less than or equal to 128
specifying the number of initial bits of UsePrefix
use in creating a new prefix for an interface
KeepLen An 8-bit unsigned integer less than or equal to (128-
UseLen) specifying the number of bits of the prefix
address which matched the associated Match-Prefix
should be retained in the new prefix. The retained
are those at positions UseLen through (UseLen+KeepLen-1)
in the matched address or prefix, and they are copied
the same positions in the New Prefix
FlagMask An 8-bit mask. A 1 bit in any position means that
corresponding flag bit in a Router Advertisement (RA
Prefix Information Option for the New Prefix should
set from the RAFlags field in this Use-Prefix Part. A 0
bit in the FlagMask means that the RA flag bit for
New Prefix should be copied from the corresponding
flag bit of the Matched Prefix
RAFlags An 8 bit field which, under control of the
field, may be used to initialize the flags in
Advertisement Prefix Information Options [ND]
advertise the New Prefix. Note that only two flags
Crawford Standards Track [Page 11]
RFC 2894 Router Renumbering for IPv6 August 2000
defined meanings to date: the L (on-link) and
(autonomous configuration) flags. These flags
the two leftmost bit positions in the RAFlags field
corresponding to their position in the
Information Option
Valid
A 32-bit unsigned integer which is the number of
for which the New Prefix will be valid [ND, SAA].
Preferred
A 32-bit unsigned integer which is the number of
for which the New Prefix will be preferred [ND, SAA].
V A 1-bit flag indicating that the valid lifetime of
New Prefix MUST be effectively decremented in real time
P A 1-bit flag indicating that the preferred lifetime
the New Prefix MUST be effectively decremented in
time
UsePrefix The 128-bit Use-prefix which either becomes or is
in forming (if KeepLen is nonzero) the New Prefix.
MUST NOT have the form of a multicast or link-
address [AARCH].
3.3. Message Body -- Result
The body of an RR Result message is a sequence of zero or more
Reports of 24 octets. An RR Command message with the "R" flag
will elicit an RR Result message containing one Match Report for
Prefix Control Operation, for each different prefix it matches
each interface. The Match Report has the following format
Crawford Standards Track [Page 12]
RFC 2894 Router Renumbering for IPv6 August 2000
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved |B|F| Ordinal | MatchedLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| InterfaceIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- -+
| |
+- MatchedPrefix -+
| |
+- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields
B A one-bit flag which, when set, indicates that one
more fields in the associated PCO were out of bounds
The bounds check is described in section 4.2.
F A one-bit flag which, when set, indicates that one
more Use-Prefix parts from the associated PCO were
honored by the router because of attempted formation
a forbidden prefix format, such as a multicast
loopback address
Ordinal Copied from the Prefix Control Operation
MatchPrefix matched the MatchedPrefix on the
indicated by InterfaceIndex
MatchedLen The length of the Matched Prefix
The router's numeric designation of the interface
which the MatchedPrefix was configured. This MUST
the same as the value of ipv6IfIndex which
that index in the SNMP IPv6 MIB General Group [IPV6MIB].
It is possible for a Result message to be larger than the
message which elicited it. Such a Result message may have to
fragmented for transmission. If so, it SHOULD be fragmented to
IPv6 minimum required MTU [IPV6].
Crawford Standards Track [Page 13]
RFC 2894 Router Renumbering for IPv6 August 2000
4. Message
Processing of received Router Renumbering Result messages is
implementation-defined. Implementation of Command message
may vary in detail from the procedure set forth below, so long as
result is not affected
Processing of received Router Renumbering Command messages
of three conceptual parts: header check, bounds check, and execution
4.1. Header
The ICMPv6 checksum and type are presumed to have been checked
a Router Renumbering module receives a Command to process. In
implementation environment where this may not be the case,
checks MUST be made at this point in the processing
If the ICMPv6 length derived from the IPv6 length is less than 16
octets, the message MUST be discarded and SHOULD be logged to
management
If the ICMPv6 Code field indicates a Result message, a router
is not a source of RR Command messages MUST discard the message
SHOULD NOT log it to network management
If the IPv6 destination address is neither an All Routers
address [AARCH] nor one of the receiving router's unicast addresses
the message MUST be discarded and SHOULD be logged to
management
Next, the SequenceNumber is compared to the Recorded Sequence Number
(If no RR messages have been received and accepted since
initialization, the Recorded Sequence Number is zero.)
comparison is done with the two numbers considered as
integers, not as DNS-style serial numbers. If the SequenceNumber
less than the Recorded Sequence Number, the message MUST be
and SHOULD be logged to network management
Finally, if the SequenceNumber in the message is greater than
Recorded Sequence Number or the T flag is set, skip to the
check. Otherwise the SegmentNumber MUST now be checked. If
correctly authenticated message with the same SequenceNumber
SegmentNumber has not already been processed, skip to the
check. Otherwise, this Command is a duplicate and not a
Command. If the R flag is not set, the duplicate message MUST
discarded and SHOULD NOT be logged to network management. If R
set, an RR Result message with the P flag set MUST be scheduled
transmission to the source address of the Command after a random
Crawford Standards Track [Page 14]
RFC 2894 Router Renumbering for IPv6 August 2000
uniformly distributed between 0 and MaxDelay milliseconds. The
of that Result message MUST either be empty or be a saved copy of
Result message body generated by processing of the previous
with the same SequenceNumber and SegmentNumber. After scheduling
Result message, the Command MUST be discarded without
processing
4.2. Bounds
If the SequenceNumber is greater than the Recorded Sequence Number
then the list of processed SegmentNumbers and the set of saved
messages, if any, MUST be cleared and the Recorded Sequence
MUST be updated to the value used in the current message,
of subsequent processing errors
Next, if the ICMPv6 Code field indicates a Sequence Number Reset
skip to section 5.
At this point, if T is set in the RR header and R is not set,
message MAY be discarded without further processing
If the R flag is set, begin constructing an RR Result message.
RR header of the Result message is completely determined at this
except for the Checksum
The values of the following fields of a PCO MUST be checked to
that they are within the appropriate bounds
OpCode must be a defined value
OpLength must be of the form 4N+3 and consistent the the
of the Command packet and the PCO's offset within
packet
MatchLen must be between 0 and 128
UseLen,
in each Use-Prefix Part must be between 0 and 128
inclusive, as must the sum of the two
If any of these fields are out of range in a PCO, the entire PCO
NOT be performed on any interface. If the R flag is set in the
header then add to the RR Result message a Match Report with the
flag set, the F flag clear, the Ordinal copied from the PCO, and
other fields zero. This Match Report MUST be included only once,
once per interface
Crawford Standards Track [Page 15]
RFC 2894 Router Renumbering for IPv6 August 2000
Note that MinLen and MaxLen need not be explicitly bounds checked
even though certain combinations of values will make any
impossible
4.3.
For each applicable router interface, as determined by the A and
flags, the Prefix Control Operations in an RR Command message must
carried out in order of appearance. The relative order of
processing among different interfaces is not specified
If the T flag is set, create a copy of each interface's
on which to operate, because the results of processing a PCO
affect the processing of subsequent PCOs. Note that if
operations are performed on one interface before proceeding
another interface, only one interface-configuration copy will
required at a time
For each interface and for each Prefix Control Operation, each
configured on that interface with a length between the MinLen
MaxLen values in the PCO is tested to determine whether it
(as defined in section 2.1) the MatchPrefix of the PCO.
configured prefixes are tested in an arbitrary order. Any new
configured on an interface by the effect of a given PCO MUST NOT
tested against that PCO, but MUST be tested against all
PCOs in the same RR Command message
Under a certain condition the addresses on an interface are
tested to see whether any of them matches the MatchPrefix. If
only if a configured prefix "P" does have a length between MinLen
MaxLen inclusive, does not match the MatchPrefix "M", but M
match P (this can happen only if M is longer than P), then
addresses on that interface which match P MUST be tested to
whether any of them matches M. If any such address does match M
process the PCO as if P matched M, but when forming New Prefixes,
KeepLen is non-zero, bits are copied from the address. This
case allows a PCO to be easily targeted to a single
interface in a network
If P does not match M, processing is finished for this combination
PCO, interface and prefix. Continue with another prefix on the
interface if there are any more prefixes which have not been
against this PCO and were not created by the action of this PCO.
no such prefixes remain on the current interface, continue
with the next PCO on the same interface, or with another interface
Crawford Standards Track [Page 16]
RFC 2894 Router Renumbering for IPv6 August 2000
If P does match M, either directly or because a configured
which matches P also matches M, then P is the Matched Prefix
Perform the following steps
If the Command has the R flag set, add a Match Report to
Result message being constructed
If the OpCode is CHANGE, mark P for deletion from the
interface
If the OpCode is SET-GLOBAL, mark all global-scope prefixes on
current interface for deletion
If there are any Use-Prefix parts in the current PCO, form the
Prefixes. Discard any New Prefix which has a forbidden format
and if the R flag is set in the command, set the F flag in
Match Report for this PCO and interface. Forbidden prefix
include, at a minimum, multicast, unspecified and
addresses. [AARCH] Any implementation MAY forbid, or allow
network manager to forbid other formats as well
For each New Prefix which is already configured on the
interface, unmark that prefix for deletion and update
lifetimes and RA flags. For each New Prefix which is not
configured, add the prefix and, if appropriate, configure
address with that prefix
Delete any prefixes which are still marked for deletion,
with any addresses which match those prefixes but do not match
prefix which is not marked for deletion
After processing all the Prefix Control Operations on all
interfaces, an implementation MUST record the SegmentNumber of
packet in a list associated with the SequenceNumber
If the Command has the R flag set, compute the Checksum
schedule the Result message for transmission after a random
interval uniformly distributed between 0 and
milliseconds. This interval SHOULD begin at the conclusion
processing, not the beginning. A copy of the Result message
be saved to be retransmitted in response to a duplicate Command
4.4. Summary of
The only Neighbor Discovery [ND] parameters which can be affected
Router Renumbering are the following
Crawford Standards Track [Page 17]
RFC 2894 Router Renumbering for IPv6 August 2000
A router's addresses and advertised prefixes, including the
lengths
The flag bits (L and A, and any which may be defined in
future) and the valid and preferred lifetimes which appear in
Router Advertisement Prefix Information Option
That unnamed property of the lifetimes which specifies
they are fixed values or decrementing in real time
Other internal router information, such as the time until the
unsolicited Router Advertisement or MIB variables MAY be affected
needed
All configuration changes resulting from Router Renumbering SHOULD
saved to non-volatile storage where this facility exists.
problem of properly restoring prefix lifetimes from non-
storage exists independently of Router Renumbering and
careful attention, but is outside the scope of this document
5. Sequence Number
It may prove necessary in practice to reset a router's
Sequence Number. This is a safe operation only when
cryptographic keys previously used to authenticate RR Commands
expired or been revoked. For this reason, the Sequence Number
message is defined to accomplish both functions
When a Sequence Number Reset (SNR) has been authenticated and
passed the header check, the router MUST invalidate all keys
have been used to authenticate previous RR Commands, including
key which authenticated the SNR itself. Then it MUST discard
saved RR Result messages, clear the list of recorded
and reset the Recorded Sequence Number to zero
If the router has no other, unused authentication keys
available for Router Renumbering use it SHOULD establish one or
new valid keys. The details of this process will depend on
manual keying or a key management protocol is used. In either case
if no keys are available, no new Commands can be processed
A SNR message SHOULD contain no PCOs, since they will be ignored.
and only if the R flag is set in the SNR message, a router
respond with a Result Message containing no Match Reports.
header and transmission of the Result are as described in section 3.
The invalidation of authentication keys caused by a valid SNR
will cause retransmitted copies of that message to be ignored
Crawford Standards Track [Page 18]
RFC 2894 Router Renumbering for IPv6 August 2000
6. IANA
Following the policies outlined in [IANACON], new values of the
field in the Router Renumbering Header (section 3.1) and the
field of the Match-Prefix Part (section 3.2.1.1) are to be
by IETF consensus only
7. Security
The Router Renumbering mechanism proposed here is very powerful
prevention of spoofing it is important. Replay of old messages must
in general, be prevented (even though a narrow class of
exists for which replay would be harmless). What constitutes
sufficiently strong authentication algorithm may change from time
time, but algorithms should be chosen which are strong
current key-recovery and forgery attacks
Authentication keys must be as well protected as any other
method that allows reconfiguration of a site's routers.
of keys must not expose them or permit alteration, and key
must be limited in terms of time and number of
authenticated
Note that although a reset of the Recorded Sequence Number
the cancellation of previously-used authentication keys,
of new keys and expiration of old keys does not require resetting
Recorded Sequence Number
7.1. Security Policy and Association Database
The Security Policy Database (SPD) [IPSEC] of a router
this specification MUST cause incoming Router Renumbering
packets to either be discarded or have IPsec applied. (
determination of "discard" or "apply" MAY be based on the
address.) The resulting Security Association Database (SAD)
MUST ensure authentication and integrity of the destination
and the RR Header and Message Body, and the body length implied
the IPv6 length and intervening extension headers.
requirements are met by the use of the Authentication Header [AH]
transport or tunnel mode, or the Encapsulating Security Payload [ESP
in tunnel mode with non-NULL authentication. The mandatory-to
implement IPsec authentication algorithms (other than NULL)
strong enough for Router Renumbering at the time of this writing
Note that for the SPD to distinguish Router Renumbering from
ICMP packets requires the use of the ICMP Type field as a selector
This is consistent with, although not mentioned by, the
Architecture specification [IPSEC].
Crawford Standards Track [Page 19]
RFC 2894 Router Renumbering for IPv6 August 2000
At the time of this writing, there exists no multicast key
protocol for IPsec and none is on the horizon. Manually
Security Associations will therefore be common. The occurrence
"from traffic" in the table below would therefore more
be a wildcard or a fixed range. Use of a small set of shared
per management station suffices, so long as key distribution
storage are sufficiently safeguarded
A sufficient set of SPD entries for incoming traffic could
Field SPD Entry SAD
------- --------- ---------
Source wildcard from
Destination wildcard from
Transport ICMPv6 from
ICMP Type Rtr. Renum. from
Action Apply
SA Spec AH/Transport
or there might be an entry for each management station and/or
each of the router's unicast addresses and for each of the
All-Routers multicast addresses, and a final wildcard entry
discard all other incoming RR messages
The SPD and SAD are conceptually per-interface databases. This
may be exploited to permit shared management of a border router,
example, or to discard all Router Renumbering traffic arriving
tunnels
8. Implementation and Usage Advice for
Users of Router Renumbering will want to be sure that every non
trivial message reaches every intended router. Well-
exploitation of Router Renumbering's retransmission and response
directing features should make that goal achievable with
confidence even in a minimally reliable network
In one set of cases, probably the majority, the network
station will know the complete set of routers under its control
Commands can be retransmitted, with the "R" (Reply-requested)
set in the RR header, until Results have been collected from
routers. If unicast Security Associations (or the means for
them) are available, the management station may switch from
to unicast transmission when the number of routers still unheard-
is suitably small
Crawford Standards Track [Page 20]
RFC 2894 Router Renumbering for IPv6 August 2000
To maintain a list of managed routers, the management station
employ any of several automatic methods which may be more
than manual entry in a large network. Multicast RR "Test"
can be sent periodically and the results archived, or the
station can use SNMP to "peek" into a link-state routing
such as OSPF [OSPFMIB]. (In the case of OSPF, roughly one router
area would need to be examined to build a complete list of routers.)
In a large dynamic network where the set of managed routers is
known but reliable execution is desired, a scalable method
achieving confidence in delivery is described here. Nothing in
section affects the format or content of Router Renumbering messages
nor their processing by routers
A management station implementing these reliability mechanisms
alert an operator who attempts to commence a set of
Renumbering Commands when retransmission of a previous set is not
completed, but SHOULD allow the operator to override the warning
8.1. Outline and
The set of routers being managed with Router Renumbering
considered as a set of populations, each population having
characteristic probability of successful round-trip delivery of
Command/Result pair. The goal is to estimate a lower bound, P,
the round-trip probability for the whole set. With this estimate
other data about the responses to retransmissions of the Command,
confidence level can be computed for hypothesis that all routers
been heard from
If the true probability of successful round-trip communication with
managed router were a constant, p, for all managed routers then
estimate P of p could be derived from either of these statistics
The expected ratio of the number of routers first heard from
transmission (N + 1) to the number first heard from after N
(1 - p).
When N different routers have been heard from after
transmissions of a Command, the expected total number of
messages received is pNM. If R is the number of Results
received, then P = R/MN
The two methods are not equivalent. The first suffers
problems when the number of routers still to be heard from
small, so the P = R/MN estimate should be used
Crawford Standards Track [Page 21]
RFC 2894 Router Renumbering for IPv6 August 2000
Since the round-trip probability is not expected to be uniform in
real world, and the less-reliable units are more important to
lower-bound estimate but more likely to be missed in sampling,
sample from which P is computed is biased toward the less-
routers. After the Nth transmission interval, N > 2, neglect
routers heard from in intervals 1 through F from the
estimate, where F is the greatest integer less than one-half of N
For example, after five intervals, only routers first heard from
the third through fifth intervals will be counted
A management station implementing the methods of this section
allow the user to specify the following parameters, and default
to the indicated values
Ct The target delivery confidence, default 0.999.
Pp A presumptive, pessimistic initial estimate of the
bound of the round-trip probability, P, to prevent
termination. (See below.) Default 0.75.
Ti The initial time between Command retransmissions. Default 4
seconds. MaxDelay milliseconds (see section 3.1) must
added to the retransmission timer. Knowledge of
routers' processing time for RR Commands may influence
setting of Ti. Ti+MaxDelay is also the minimum time
management station must wait for Results after
transmission before computing a new confidence level.
phrase "end of the Nth interval" means a time Ti+
after the Nth transmission of a Command
Tu The upper bound on the period between
retransmissions. Default 512 seconds
The following variables, some a function of the
counter N, are used in the next section
T(N) The time between Command transmissions N and N+1 is V*T(N) +
MaxDelay, where V is random and roughly uniform in the
[0.75, 1.0]. T(1) = Ti and for N > 1, T(N) = min(2*T(N-1),
Tu).
M(N) The cumulative number of distinct routers from which
have been received to any of the first N transmissions
the Command
Crawford Standards Track [Page 22]
RFC 2894 Router Renumbering for IPv6 August 2000
F=F(N) FLOOR((N-1)/2). All routers from which responses
received in the first F intervals will be
omitted from the estimate of the round-trip
computed at the Nth interval
R(N,F) The total number of RR Result messages,
duplicates, received by the end of the Nth interval
those routers which were NOT heard from in any of the
F intervals
p(N) The estimate of the worst-case round-trip
probability
c(N) The computed confidence level
An asterisk (*) is used to denote multiplication and a caret (^)
denotes exponentiation
If the difference in reliability between the "good" and "bad"
of a managed network is very great, early c(N) values will be
high. Retransmissions should continue for at least Nmin = log(1-
Ct)/log(1-Pp) intervals, regardless of the current
estimate. (In fact, there's no need to compute p(N) and c(N)
after Nmin intervals.)
8.2.
Letting A = N*(M(N)-M(F))/R(N,F) for brevity, the estimate of
round-trip delivery probability is p(N) = 1-Q, where Q is that
of the
Q^N - A*Q + (A-1) = 0
which lies between 0 and 1. (Q = 1 is always a root. If N is
there is also a negative root.) This may be solved numerically,
example with Newton's method (see any standard text, for
[ANM]). The first-order
Q1 = 1 - 1/
may be used as a starting point for iteration. But Q1 should NOT
used as an approximate solution as it always underestimates Q,
hence overestimates p(N), which would cause an overestimate of
confidence level
If necessary, the spurious root Q = 1 can be divided out,
Q^(N-1) + Q^(N-2) + ... + Q - (A-1) = 0
Crawford Standards Track [Page 23]
RFC 2894 Router Renumbering for IPv6 August 2000
as the equation to solve. Depending on the numerical method used
this could be desirable as it's just possible (but very unlikely
that A=N and so Q=1 was a double root of the earlier equation
After N > 2 (or N >= Nmin) intervals have been completed, Compute
lower-bound reliability
p(N) = R(N,F)/((N-F)*(M(N) - M(F))).
Compute the confidence
c(N) = (1 - (1-p(N))^N)^(M(N) - M(F) + 1).
which is the Bayesian probability that M(N) is the number of
present given the number of responses which were collected,
opposed to M(N)+1 or any greater number. It is assumed that the
priori probability of there being K routers was no greater than
of K-1 routers, for all K > M(N).
When c(N) >= Ct and N >= Nmin, retransmissions of the Command
cease. Otherwise another transmission should be scheduled at a
V*T(N) + MaxDelay after the previous (Nth) transmission, or V*T(N
after the conclusion of processing responses to the Nth transmission
whichever is later
One corner case needs consideration. Divide-by-zero may occur
computing p. This can happen only when no new routers have
heard from in the last N-F intervals. Generally, the
estimate c(N) will be close to unity by then, but in a
case such as a large number of routers with reliable
and a much smaller number with very poor communication,
confidence estimate may still be less than Ct when p's
vanishes. The implementation may continue, and should continue
the minimum number of transmissions given in the previous
have not yet been made. If new routers are heard from, p(N)
again be non-singular
Of course no limited retransmission scheme can fully address
possibility of long-term problems, such as a partitioned network
The network manager is expected to be aware of such conditions
they exist
8.3. Additional Assurance
As a final means to detect routers which become reachable
missing renumbering commands during an extended network split,
management station MAY adopt the following strategy. When
each new operation, increment the SequenceNumber by more than one
Crawford Standards Track [Page 24]
RFC 2894 Router Renumbering for IPv6 August 2000
After the operation is believed complete, periodically send
"no-op" RR Command with the R (Result Requested) flag set and
SequenceNumber one less than the highest used. Any responses to
a command can only come from router that missed the last operation
An example of a suitable "no-op" command would be an ADD
with MatchLen = 0, MinLen = 0, MaxLen = 128, and no Use-Prefix Parts
If old authentication keys are saved by the management station,
the reappearance of routers which missed a Sequence Number Reset
be detected by the transmission of no-op commands with the
key and a SequenceNumber higher than any used before the key
invalidated. Since there is no other way for a management station
distinguish a router's failure to receive an entire sequence
repeated SNR messages from the loss of that router's single
Result Message, this is the RECOMMENDED way to test for
reception of a SNR Command
9. Usage
This section sketches some sample applications of Router Renumbering
Extension headers, including required IPsec headers, between the IPv
header and the ICMPv6 header are not shown in the examples
9.1. Maintaining Global-Scope
A simple use of the Router Renumbering mechanism, and one which
expected to to be common, is the maintenance of a set of
prefixes with a subnet structure that matches that of the site'
site-local address assignments. In the steady state this would
to keep the Preferred and Valid lifetimes set to their
values. During a renumbering transition, similar Command
can add new prefixes and/or delete old ones. An outline of
suitable Command message follows. Fields not listed are presumed
to suitable values. This Command assumes all router interfaces to
maintained already have site-local [AARCH] addresses
IPv6
Next Header = 58 (ICMPv6)
Source Address = (Management Station
Destination Address = FF05::2 (All Routers, site-local scope
ICMPv6/RR
Type = 138 (Router Renumbering), Code = 0 (Command
Flags = 60 hex (R, A
Crawford Standards Track [Page 25]
RFC 2894 Router Renumbering for IPv6 August 2000
First (and only) PCO
Match-Prefix
OpCode = 3 (SET-GLOBAL
OpLength = 4 N + 3 (assuming N global prefixes
Ordinal = 0 (arbitrary
MatchLen = 10
MatchPrefix = FEC0::0
First Use-Prefix
UseLen = 48 (Length of TLA ID + RES + NLA ID [AARCH])
KeepLen = 16 (Length of SLA (subnet) ID [AARCH])
FlagMask, RAFlags, Lifetimes, V & P flags -- as
UsePrefix = First global /48
. . .
Nth Use-Prefix
UseLen = 48
KeepLen = 16
FlagMask, RAFlags, Lifetimes, V & P flags -- as
UsePrefix = Last global /48
This will cause N global prefixes to be set (or updated) on
applicable interface. On each interface, the SLA ID (subnet)
of each global prefix will be copied from the existing site-
prefix
9.2. Renumbering a
A subnet can be gracefully renumbered by setting the valid
preferred timers on the old prefix to a short value and having
run down, while concurrently adding adding the new prefix. Later
the expired prefix is deleted. The first step is described by
following RR Command
IPv6
Next Header = 58 (ICMPv6)
Source Address = (Management Station
Destination Address = FF05::2 (All Routers, site-local scope
ICMPv6/RR
Type = 138 (Router Renumbering), Code = 0 (Command
Flags = 60 hex (R, A
Crawford Standards Track [Page 26]
RFC 2894 Router Renumbering for IPv6 August 2000
First (and only) PCO
Match-Prefix
OpCode = 2 (CHANGE
OpLength = 11 (reflects 2 Use-Prefix Parts
Ordinal = 0 (arbitrary
MatchLen = 64
MatchPrefix = Old /64
First Use-Prefix
UseLen = 0
KeepLen = 64 (this retains the old prefix value intact
FlagMask = 0, RAFlags = 0
Valid Lifetime = 28800 seconds (8 hours
Preferred Lifetime = 7200 seconds (2 hours
V flag = 1, P flag = 1
UsePrefix = 0::0
Second Use-Prefix
UseLen = 64
KeepLen = 0
FlagMask = 0, RAFlags = 0
Lifetimes, V & P flags -- as
UsePrefix = New /64
The second step, deletion of the old prefix, can be done by an
Command with the same Match-Prefix Part (except for an
reduced from 11 to 3) and no Use-Prefix Parts. Any temptation to
KeepLen = 64 in the second Use-Prefix Part above should be resisted
as it would instruct the router to sidestep address configuration
10.
This protocol was designed by Matt Crawford based on an idea
Robert Hinden and Geert Jan de Groot. Many members of the
Working Group contributed useful comments, in particular members
the DIGITAL UNIX IPv6 team. Bill Sommerfeld provided helpful
expertise. Relentless browbeating by various IESG members may
improved the final quality of this specification
Crawford Standards Track [Page 27]
RFC 2894 Router Renumbering for IPv6 August 2000
11.
[AARCH] Hinden, R. and S. Deering, "IP Version 6
Architecture", RFC 2373, July 1998.
[AH] Kent, S. and R. Atkinson, "IP Authentication Header",
2402, November 1998.
[ANM] Isaacson, E. and H. B. Keller, "Analysis of
Methods", John Wiley & Sons, New York, 1966.
[ESP] Kent, S. and R. Atkinson, "IP Encapsulating
Payload (ESP)", RFC 2406, November 1998.
[IANACON] Narten, T. and H. Alvestrand, "Guidelines for Writing
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[ICMPV6] Conta, A. and S. Deering, "Internet Control
Protocol (ICMPv6) for the Internet Protocol Version 6
(IPv6)", RFC 2463, December 1998.
[IPSEC] Kent, S. and R. Atkinson, "Security Architecture for
Internet Protocol", RFC 2401, November 1998.
[IPV6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[IPV6MIB] Haskin, D. and S. Onishi, "Management Information Base
IP Version 6: Textual Conventions and General Group",
2466, December 1998.
[KWORD] Bradner, S., "Key words for use in RFCs to
Requirement Levels", BCP 14, RFC 2119, March 1997.
[ND] Narten, T., Nordmark, E. and W. Simpson, "
Discovery for IP Version 6 (IPv6)", RFC 2461,
1998.
[OSPFMIB] Baker, F. and R. Coltun, "OSPF Version 2
Information Base", RFC 1850, November 1995.
Crawford Standards Track [Page 28]
RFC 2894 Router Renumbering for IPv6 August 2000
12. Author's
Matt
Fermilab MS 368
PO Box 500
Batavia, IL 60510
Phone: +1 630 840 3461
EMail: crawdad@fnal.
Crawford Standards Track [Page 29]
RFC 2894 Router Renumbering for IPv6 August 2000
Appendix -- Derivation of Reliability
If a population S of size k is repeatedly sampled with an
p, the expected number of members of S first discovered on the
sampling
m = [1 - (1-p)^n] *
The expected total number of members of S found in samples,
duplicates,
r = n * p *
Taking the ratio of m to r cancels the unknown factor k and yields
[1 - (1-p)^n] / p = nm/
which may be solved for p, which is then an estimator of the
efficiency. (The statistical properties of the estimator will not
examined here.) Under the substitution p = 1-q, this becomes
first equation of Section 8.2.
With the estimator p in hand, and a count m of members of
discovered after n samplings, we can compute the a
probability that the true size of S is m+j, for j >= 0. Let
denote the hypothesis that the true size of S is m+j, and let
denote the result that m members have been found in n samplings
P{R | Hj} = [(m+j)!/m!j!] * [1-(1-p)^n]^m * [(1-p)^n]^
We are interested in P{H0 | R}, but to find it we need to assign
priori values to P{Hj}. Let the size of S be
P{Hj} / P{H0} = h^(-j
for arbitrary h in (0, 1). The value of h will be eliminated
the result
The Bayesian method
P{Hj | R} / P{H0 | R} = [(m+j)!/m!j!] * [h*(1-p)^n]^
The reciprocal of the sum over j >= 0 of these ratios
P{H0 | R} = [1-h*(1-p)^n] ^ (m+1)
Crawford Standards Track [Page 30]
RFC 2894 Router Renumbering for IPv6 August 2000
and the confidence estimate of Section 8.2 is the h -> 1 limit
this expression
Crawford Standards Track [Page 31]
RFC 2894 Router Renumbering for IPv6 August 2000
Full Copyright
Copyright (C) The Internet Society (2000). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
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document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
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developing Internet standards in which case the procedures
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The limited permissions granted above are perpetual and will not
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
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Crawford Standards Track [Page 32]
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