IPng Working Group Matt Crawford
Internet Draft Fermilab
Bob Hinden
Ipsilon Networks
November 21, 1997
Router Renumbering for IPv6
<draft-ietf-ipngwg-router-renum-02.txt>
Status of this Memo
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Distribution of this memo is unlimited.
1. Abstract
IPv6 Neighbor Discovery [ND] and Address Autoconfiguration [SAA]
conveniently make initial assignments of address prefixes to hosts.
Aside from the problem of connection survival across a renumbering
event, these two mechanisms also simplify the reconfiguration of
hosts when the set of valid prefixes changes.
This document defines a mechanism called Router Renumbering (''RR'')
which allows address prefixes on routers to be configured and
reconfigured almost as easily as the combination of Neighbor
Discovery and Address Autoconfiguration works for hosts. It
provides a means for a network manager to make updates to the
prefixes used by and advertised by IPv6 routers throughout a site.
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2. Functional Overview
Router Renumbering Command packets contain a sequence of Prefix
Control Operations (PCOs). Each PCO specifies an operation, a
Match-Prefix, and zero or more Use-Prefixes. A router processes
each PCO in sequence, checking each of its interfaces for an address
or prefix which matches the Match-Prefix. For every interface on
which a match is found, the operation is applied. The operation is
one of ADD, CHANGE, or SET-GLOBAL to instruct the router to
respectively add the Use-Prefixes to the set of configured prefixes,
remove the prefix which matched the Match-Prefix and replace it with
the Use-Prefixes, or replace all global-scope prefixes with the
Use-Prefixes. If the set of Use-Prefixes in the PCO is empty, the
ADD operation does nothing and the other two reduce to deletions.
Additional information for each Use-Prefix is included in the Prefix
Control Operation: the valid and preferred lifetimes to be included
in Router Advertisement Prefix Information Options [ND], and either
the L and A flags for the same option, or an indication that they
are to be copied from the prefix that matched the Match-Prefix.
It is possible to instruct routers to create new prefixes by
combining the Use-Prefixes in a PCO with some portion of the
existing prefix which matched the Match-Prefix. This simplifies
certain operations which are expected to be among the most common.
For every Use-Prefix, the PCO specifies a number of bits which
should be copied from the existing address or prefix which matched
the Match-Prefix and appended to the use-prefix prior to configuring
the new prefix on the interface. The copied bits are zero or more
bits from the positions immediately after the length of the use-
prefix. If subnetting information is in the same portion of of the
old and new prefixes, this synthesis allows a single Prefix Control
Operation to define a new global prefix on every router in a site,
while preserving the subnetting structure.
Because of the power of the Router Renumbering mechanism, each RR
message includes a sequence number and an authenticator to guard
against replays. Each elementary RR operation is idempotent and so
could be retransmitted for improved reliability, as long as the
sequence number is current, without concern about multiple
processing. However, non-idempotent combinations of elementary RR
operations can easily be constructed and messages containing such
combinations could not be safely reprocessed. Therefore, all
routers are required to guard against processing an RR message more
than once.
Possibly a network manager will want to perform more renumbering, or
exercise more detailed control, than can be expressed in a single
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Router Renumbering packet on the available media. The RR mechanism
is most powerful when RR packets are multicast, so IP fragmentation
is undesirable. For these reasons, each RR packet contains a
"Segment Number". All RR packets which have a Sequence Number equal
to the highest value seen (for each valid key), and which pass the
authentication check, are equally valid and must be processed.
However, a router must keep track of the Segment Numbers of RR
messages already processed and avoid reprocessing a message whose
Sequence Number and Segment Number match a previously processed
message.
There is a "Dry Run" flag which indicates that all routers should
simulate processing of the RR message and not perform any actual
reconfiguration. A separate "Report" flag instructs routers to send
a Router Renumbering Result message back to the source of the RR
Command message indicating the actual or simulated result of the
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 this
document, regardless of the value of the "Report" flag.
3. Definitions
3.1. Requirements
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 [KWORD].
3.2. Terminology
Address
This term always refers to a 128-bit IPv6 address [AARCH]. When
referring to bits within an address, they are numbered from 0 to
127, with bit 0 being the first bit of the Format Prefix.
Prefix
A prefix can be understood as an address plus a length, the
latter being an integer in the range 0 to 128 indicating how many
leading bits are significant. When referring to bits within a
prefix, they are numbered in the same way as the bits of an
address. For example, the significant bits of a prefix whose
length is L are the bits numbered 0 through L-1, inclusive.
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Match
An address A "matches" a prefix P whose length is L if the first
L bits of A are identical with the first L bits of P. (Every
address matches a prefix of length 0.) A prefix P1 with length
L1 matches a prefix P2 of length L2 if L1 >= L2 and the first L2
bits of P1 and P2 are identical.
Prefix Control Operation, Match-Prefix, Use-Prefix
These are defined section 2.
Matched Prefix
The existing prefix or address which matched a Match-Prefix.
New Prefix
A prefix constructed from a Use-Prefix, possibly including some
of the Matched-Prefix.
Recorded Sequence Number
The highest sequence number found in a valid, authenticated
message with a given key MUST be recorded in non-volatile storage
along with that key.
Note that "matches" is a transitive relation but not reflexive. If
two prefixes match each other, they are identical.
3.3. Authentication Algorithms
All implementations MUST support HMAC-MD5 [HMAC] for authentication.
Additional algorithms MAY be supported.
4. Message Format
There are two types of Router Renumbering messages: Commands, which
are sent to routers, and Results, which are sent by routers. The
two types of messages are distinguished the ICMPv6 "Code" field and
differ in the contents of the "Message Body" field.
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/ /
| IPv6 header, extension headers |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
| ICMPv6 & RR Header (16 octets) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
| RR Message Body |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
| Authentication Data (16 octets for HMAC-MD5) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Router Renumbering Message Format
Router Renumbering messages are carried in ICMPv6 packets with Type
= TBA. The RR message consists of
An RR header, containing the sequence and segment numbers and
information about the authentication key and the location and
length of the authentication data within the packet.
The RR Message Body, of variable length;
The authentication data, with length dependent on the
authentication type. For HMAC-MD5, 16 octets.
All fields marked "reserved" or "res" MUST be set to zero on
generation of an RR message. During processing of the message they
MUST be included in the authentication check, but otherwise ignored.
All implementations which generate Router Renumbering Command
messages MUST support sending them to the All Routers multicast
address with Link Local and Site Local scopes, and to unicast
addresses of link local and site local formats. All routers MUST be
capable of receiving RR messages sent to those multicast addresses
and to any of their link local and site local unicast addresses.
Implementations SHOULD support sending and receiving RR messages
addressed to other unicast addresses.
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4.1. Router Renumbering Header
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SegmentNumber | Flags | KeyID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AuthLen | AuthOffset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SequenceNumber |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type TBA, the ICMPv6 type code assigned to Router Renumbering
Code 0 = Router Renumbering Command
1 = Router Renumbering Result
Checksum The ICMPv6 checksum, as specified in [ICMPV6]. The
checksum covers the IPv6 pseudo-header and all fields of
the RR message from the Type field through the
Authentication Data. (For purposes of calculating and
verifying the Authentication Data, the ICMPv6 checksum
field is considered to be zero.)
SegmentNumber
An unsigned 8-bit field which enumerates different valid
RR messages having the same SequenceNumber and KeyID.
Flags A combination of one-bit flags. Six are defined and two
bits are reserved.
+-+-+-+-+-+-+-+-+
|D|R|A|S|P|E|res|
+-+-+-+-+-+-+-+-+
The flags D, R, A and S have defined meanings in an RR
Command message. In a Result message they MUST be
copied from the corresponding Command. The flags P and
E are meaningful only in a Result message and MUST be
zero in a Command.
D 0 indicates that the router configuration is to be
modified;
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1 indicates a "Dry Run" message: processing is to be
simulated and no configuration changes are to be
made.
R 0 indicates that a Result message MUST NOT be sent
(but other forms of logging are not precluded);
1 indicates that the router MUST send a Result
message upon completion of processing the Command
message;
A 0 indicates that the Command MUST NOT be applied to
interfaces which are administratively shut down;
1 indicates that the Command MUST be applied to
interfaces regardless of administrative shutdown
status.
S This flag MUST be ignored unless the router treats
interfaces as belonging to different "sites".
0 indicates that the Command MUST be applied to
interfaces regardless of which site they belong
to;
1 indicates that the Command MUST be applied only to
interfaces which belong to the same site as the
interface to which the Command is addressed. If
the destination address is appropriate for
interfaces belonging to more than one site, then
the Command MUST be applied only to interfaces
belonging to the same site as the interface on
which the Command was received.
P 0 indicates that the Result message contains the
complete report of processing the Command;
1 indicates that the Command message was previously
processed (and is not a Dry Run) and the
responding router is not processing it again.
This Result message will have an empty body.
E 0 indicates that no error was encountered suring
processing of the Command;
1 indicates that an error was encoutered.
KeyID An unsigned 16-bit field that identifies the key used to
create and verify the Authentication Data for this RR
message. If multiple authentication algorithms are
supported by the implementation, the choice of algorithm
is implicit in the KeyID.
AuthLen An unsigned 16-bit field giving the length in octets of
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the Authentication Data.
AuthOffset An unsigned 16-bit offset, measured in octets, from the
beginning of the RR message (which is the beginning of
the ICMPv6 header) to the beginning of the
Authentication Data. The smallest valid value for
AuthOffset is 16.
SequenceNumber
An unsigned 32-bit sequence number. The sequence number
MUST be non-decreasing for all messages sent with the
same KeyID.
4.2. Message Body -- Command Message
The body of an RR Command message is a sequence of zero or more
Prefix Control Operations, each of variable length. The end of the
sequence MAY be located by the AuthOffset field in the RR header.
4.2.1. Prefix Control Operation
A Prefix Control Operation has one Match-Prefix Part of 24 octets,
followed by zero or more Use-Prefix Parts of 32 octets each.
4.2.1.1. Match-Prefix Part
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- -+
| |
+- MatchPrefix -+
| |
+- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
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OpCode An unsigned 8-bit field specifying the operation to be
performed when the associated MatchPrefix matches an
interface's prefix or address. Values are:
1 the ADD operation
2 the CHANGE operation
3 the SET-GLOBAL operation
OpLength The total length of this Prefix Control Operation, in
units of 8 octets. A valid OpLength will always be of
the form 4N+3, with N equal to the number of UsePrefix
parts (possibly zero).
Ordinal An 8-bit field which MUST have a different value in each
Prefix Control Operation contained in a given RR Command
message.
MatchLen An 8-bit unsigned integer between 0 and 128 inclusive
specifying the number of initial bits of MatchPrefix
which are significant in matching.
MatchPrefix The 128-bit prefix to be compared with each interface's
prefix or address.
4.2.1.2. Use-Prefix Part
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 | Mask | RAFlags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V|P| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- -+
| |
+- UsePrefix -+
| |
+- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Fields:
UseLen An 8-bit unsigned integer less than or equal to 128
specifying the number of initial bits of UsePrefix to
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 or
address which matched the associated Match-Prefix which
should be retained in the new prefix. The retained bits
are those at positions UseLen through (UseLen+KeepLen-1)
in the matched address or prefix, and they are copied to
the same positions in the New Prefix.
Mask An 8-bit mask. A 1 bit in any position means that the
corresponding flag bit in a Router Advertisement (RA)
Prefix Information Option for the New Prefix should be
set from the RAFlags field in this Use-Prefix Part. A 0
bit in the Mask means that the RA flag bit for the New
Prefix should be copied from the corresponding RA flag
bit of the Matched Prefix.
RAFlags An 8 bit field which, under control of the Mask field,
may be used to initialize the flags in Router
Advertisement Prefix Information Options [ND] which
advertise the New Prefix. Note that only two flags have
defined meanings to date: the L (on-link) and A
(autonomous configuration) flags. These flags occupy
the two leftmost bit positions in the RAFlags field,
corresponding to their position in the Prefix
Information Option.
Valid Lifetime
A 32-bit unsigned integer which is the number of seconds
for which the New Prefix will be valid [ND, SAA].
Preferred Lifetime
A 32-bit unsigned integer which is the number of seconds
for which the New Prefix will be preferred [ND, SAA].
V A 1-bit flag indicating that the valid lifetime of the
New Prefix MUST be effectively decremented in real time.
P A 1-bit flag indicating that the preferred lifetime of
the New Prefix MUST be effectively decremented in real
time.
UsePrefix The 128-bit Use-prefix which either becomes or is used
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in forming (if KeepLen is nonzero) the New Prefix. It
MUST NOT have the form of a multicast or link-local
address [AARCH].
4.3. Message Body -- Result Message
The body of an RR Result message is a sequence of zero or more Match
Reports of 24 octets. An RR Command message with the "R" flag set
will elicit an RR Result message containing one Match Report for
each Prefix Control Operation, for each different prefix it matches
on each interface. The Match Report has the following format.
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 | Ordinal | MatchedLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| InterfaceIndex |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+- -+
| |
+- MatchedPrefix -+
| |
+- -+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Ordinal Copied from the Prefix Control Operation whose
MatchPrefix matched the MatchedPrefix on the interface
indicated by InterfaceIndex.
MatchedLen The length of the existing prefix which was matched by
the MatchPrefix.
InterfaceIndex
The router's numeric designation of the interface on
which the MatchedPrefix was configured. This SHOULD be
the same designation as is used in the SNMP Interfaces
group.
It is possible for a Result message to be larger than the Command
message which elicited it. Such a Result message may have to be
fragmented for transmission.
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4.4. Authentication
The authentication covers the following fields, which are to be
treated as contiguous data for the purose of computing and verifying
the AuthData.
The IPv6 source address,
The IPv6 destination address,
The ICMPv6 and RR Header,
The RR Message Body (which may be empty).
4.4.1. HMAC-MD5
When the key and algorithm associated with the KeyID indicate that
HMAC-MD5 authentication is to be used, the AuthData is generated in
accordance with RFC 2104 [HMAC].
Before generating the AuthData, all fields of the RR header and all
the PCOs are filled in, except that the ICMPv6 checksum field is set
to zero. AuthLen will be 16 and AuthOffset will be equal to the
length in octets of the RR message, not including the IPv6 header or
any extension headers, but including the ICMPv6 header.
When checking the AuthData, the ICMPv6 checksum must be set to zero.
4.4.2. IPSEC
The KeyID value zero is reserved to indicate that no Authentication
is done on the Router Renumbering message itself. An RR message
with Key ID zero MUST have AuthLen equal to zero and AuthOffset
equal to the total length of the ICMPv6/RR header plus the RR
message body. Such a message MUST be authenticated at the IP level
[IPSEC].
5. Message Processing
Processing of received Router Renumbering messages consists of three
parts: header check, authentication check, and execution.
5.1. Header Check
First, the existence and validity of the key indicated by the KeyID
are checked. If there is no such valid key, or if the value of
AuthLen is not correct for that key, the message MUST be discarded,
and SHOULD be logged to network management.
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Next, the SequenceNumber is compared to the Recorded Sequence Number
for the specified key. (If no messages have been received using
this key, the Recorded Sequence Number is zero.) This comparison is
done with the two numbers considered as unsigned integers, not as
DNS-style serial numbers. If the SequenceNumber is less than the
Recorded Sequence Number for the key, the message MUST be discarded
and SHOULD be logged to network management.
If the SequenceNumber in the message is equal to the Recorded
Sequence Number, the SegmentNumber MUST be checked. If a correctly
authenticated message with the same KeyID, SequenceNumber and
SegmentNumber has already been processed, then an RR Result message
MUST be sent to the source address of the Command if and only if the
R flag is set in the Command. If a Result message is sent, it MUST
have the P flag set in the RR header and contain no Match Reports.
Then the current message MUST be discarded but SHOULD NOT be logged
to network management.
Finally, if the router is multi-sited, and the S flag is set and the
destination address of the Command is appropriate for interfaces
belonging to more than one site, but is not appropriate for the
interface on which the Command was received, this is an error. If
the R flag is set, return a Result message with the E flag set and
no Match Reports. The Command message MUST be discarded and SHOULD
be logged to network management.
5.2. Authentication Check
The authentication check is performed over the RR message, without
any IPv6 or extension headers. In the case of HMAC-MD5 it proceeds
as described in [HMAC] and [MD5]. If the computed authentication
value is not equal to the AuthData in the received packet, the
authentication check fails.
If the authentication check fails, the message MUST be discarded and
SHOULD be logged to network management.
If the authentication check passes, and the SequenceNumber is
greater than the Recorded Sequence Number for the key, then the list
of processed SegmentNumbers, if any, MUST be cleared and the
Recorded Sequence Number MUST be updated to the value used in the
current message, regardless of subsequent processing errors.
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5.3. Execution
For each applicable router interface, as determined by the A and S
flags, the Prefix Control Operations in an RR Command message must
be carried out in order of appearance. The order of PCO processing
on different interfaces is not specified.
If the R flag is set in the RR header, begin constructing an RR
Result message. The RR header is completely determined at this time
except for the Checksum and AuthOffset.
For each interface and for each Prefix Control Operation, each
prefix configured on that interface is tested to determine whether
it matches (as defined in section 3.2.) the MatchPrefix of the PCO.
The prefixes are tested in an arbitrary order. Any new prefix
configured on an interface by the effect of a given PCO MUST NOT be
tested against that PCO, but MUST be tested against any subsequent
PCOs in the same RR Command message.
Under a certain condition the addresses on an interface are also
tested to see whether any of them matches the MatchPrefix. If and
only if a prefix "P" does not match the MatchPrefix "M" but M does
match P (this can happen only if M is longer than P), then those
addresses on that interface which match P MUST be tested to
determine 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, when KeepLen is non-zero, bits are copied from the
address.
If P does not match M, processing is finished for this combination
of PCO, interface and prefix. Continue with another prefix on the
same interface if there are any more prefixes which have not been
tested against this PCO and were not created by the action of this
PCO. If no such prefixes remain on the current interface, continue
processing with the next PCO on the same interface, or with another
interface.
If P does match M, either directly or because a configured address
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
the Result message being constructed. If the D flag is
set, processing is now complete for this combination of
PCO, interface and prefix. Otherwise, continue with the
remaining steps.
If the OpCode is CHANGE, mark P for deletion from the
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current interface.
If the OpCode is SET-GLOBAL, mark all global-scope
prefixes on the current interface for deletion.
If there are any Use-Prefix parts in the current PCO, form
the New Prefixes. For each New Prefix which is already
configured on the current interface, unmark that prefix
for deletion and update the lifetimes and RA flags. For
each New Prefix which is not already configured, add the
prefix and, if appropriate, configure an address on that
prefix.
Delete any prefixes which are still marked for deletion,
together with any addresses which match those prefixes but
do not match any prefix which is not marked for deletion.
After succesful processing of all the Prefix Control Operations on
all the interfaces, an implementation MUST record the SegmentNumber
of the packet in a list associated with the KeyID and
SequenceNumber.
If the Command has the R flag set, compute the AuthData and append
it to the Result message, fill in the AuthOffset and Checksum and
send the Result message.
6. Key Management
As with all security methods using keys, it is necessary to change
the RR Authentication Key on a regular basis. To provide RR
functionality during key changes, implementations MUST be able to
store and use more than one Authentication Key at the same time.
The Authentication Keys SHOULD NOT be stored or transmitted using
algorithms or protocols that have known flaws. Implementations MUST
support the storage of more than one key at the same time, MUST
associate a specific lifetime (start and end times) and a key
identifier with each key, and MUST support manual key distribution
(e.g., manual entry of the key, key lifetime, and key identifier on
the router console).
An infinite key lifetime SHOULD NOT be allowed. If infinite
lifetimes are allowed, manual deletion of valid keys MUST be
supported; otherwise manual deletion SHOULD be supported. The
implementation MAY automatically delete expired keys.
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7. Usage Guidelines
7.1. Updating Global-Scope Prefixes
A simple use of the Router Renumbering mechanism, and one which is
expected to to be common, is the maintenance of a set of global
prefixes with a subnet structure that matches that of the site's
site-local address assignments.
7.2. Key Changes
Using a new authentication key while a previously used key is still
valid can open the possibility of a replay attack. The processing
rules as given in section 5. specify that routers keep track of the
highest sequence number seen for each key, and that messages with
that key and seuence number remain valid until either a higher
sequence number is seen or the key expires. The difficulty arises
when a new key is used to send a message which supersedes the last
message sent with another still-valid key. That older message can
still be replayed.
This vulnerability can be avoided in practice by sending a "NO-OP"
message with the old key and a valid new sequence number before
using a newer key. This mesage will then become the only one which
can be replayed with the old key. An example of a NO-OP message
would be one which contains no Prefix Control Operations.
Cearly a management station must keep track of the highest sequence
number it has used for each authentication key, at least to the
extent of being able to generate a larger value when needed. A
timestamp may make a good sequence number.
8. Points for Discussion
Is there a less colloquial (more nearly i18n-freindly)
term for Dry Run, which isn't too wordy and which doesn't
start with R, A, or S?
The "reserved" field of the Match-Prefix Part could be
used to specify another condition in addition to matching
a prefix. For example, one of the prefix lifetime timers
could be tested against a value.
If the messages of several different protocols use the
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same authentication mechanism then it's possible for one
authenticated message body to be grafted onto a different
set of headers and cause at least some confusion, and
possibly worse. This can be prevented by placing magic
numbers or other fixed data in the packets so that a
packet for one protocol is never valid for another.
Another solution is never to use the same set of keys for
two different protocols.
Since RR messages will presumably be generated only by a
set network management stations which is disjoint from the
set of routers to which they are directed, an asymmetric
authentication scheme would be desirable.
Do we need to specify when it's appropriate for the router
to configure an address on a new prefix? And if so, how?
(Stateless Auto vs. DHCPv6.)
9. Security Considerations
The Router Renumbering mechanism proposed here is very powerful and
prevention of spoofing it is important. Replay of old messages must
be prevented, except in the narrow case of idempotent messages which
are still valid at the time of replay. We believe the
authentication mechanisms included in this specification achieve the
necessary protections, so long as authentication keys are not
compromised.
Authentication keys must be as well protected as is any other access
method that allows reconfiguration of a site's routers.
Distribution of keys must not expose them or permit alteration, and
key lifetimes must be limited.
NOTE: The auth. processing must be changed to include the
destination address. May as well include the source address for
lagniappe.
10. Acknowledgments
Some of the key management text was borrowed from "RIP-II MD5
Authentication." (And the loan was repaid in kind.)
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11. References
[AARCH] R. Hinden, S. Deering, "IP Version 6 Addressing
Architecture", draft-ietf-ipngwg-addr-arch-v2-05.txt.
[HMAC] H. Krawczyk, M. Bellare, R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104.
[ICMPV6]A. Conta, S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)",
currently draft-ietf-ipngwg-icmp-v2-00.txt.
[IPSEC] S. Kent, R. Atkinson, "Security Architecture for the
Internet Protocol", currently draft-ietf-ipsec-arch-sec-
02.txt.
[KWORD] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels," RFC 2119.
[MD5] R. Rivest, "The MD5 Message-Digest Algorithm", RFC 1321.
[ND] T. Narten, E. Nordmark, W. Simpson, "Neighbor Discovery for
IP Version 6 (IPv6)", currently draft-ietf-ipngwg-
discovery-v2-00.txt.
[SAA] S. Thomson, T. Narten, "IPv6 Stateless Address
Autoconfiguration", draft-ietf-ipngwg-addrconf-v2-00.txt.
12. Authors' Addresses
Matt Crawford Robert M. Hinden
Fermilab MS 368 Ipsilon Networks, Inc.
PO Box 500 232 Java Drive
Batavia, IL 60510 Sunnyvale, CA 94089
USA USA
Phone: +1 630 840 3461 Phone: +1 408 990 2004
Email: crawdad@fnal.gov Email: hinden@ipsilon.com
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