Network Working Group A. Zinin
Internet-Draft Alcatel
Intended status: Standards Track A. Roy
Expires: August 15, 2008 L. Nguyen
Cisco Systems
B. Friedman
Redback Networks
D. Young
February 12, 2008
OSPF Link-local Signaling
draft-ietf-ospf-lls-04.txt
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Copyright (C) The IETF Trust (2008).
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Abstract
OSPF is a link-state intra-domain routing protocol. OSPF routers
exchange information on a link using packets that follow a well-
defined fixed format. The format is not flexible enough to enable
new features which need to exchange arbitrary data. This document
describes a backward-compatible technique to perform link-local
signaling, i.e., exchange arbitrary data on a link.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3
2. Proposed solution . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Options Field . . . . . . . . . . . . . . . . . . . . . . 5
2.2. LLS Data Block . . . . . . . . . . . . . . . . . . . . . . 5
2.3. LLS TLVs . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Extended Options TLV . . . . . . . . . . . . . . . . . . . 6
2.5. Cryptographic Authentication TLV (OSPFv2 ONLY) . . . . . . 7
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
4. Compatibility Issues . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Normative References . . . . . . . . . . . . . . . . . . . 12
6.2. Informative References . . . . . . . . . . . . . . . . . . 12
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
This document describes an extension to OSPFv2 [OSPFV2] and OSPFv3
[OSPFV3] allowing additional information to be exchanged between
routers on the same link. OSPFv2 and OSPFv3 packet formats are fixed
and do not allow for extension. This document proposes appending an
optional data block composed of Type/Length/Value (TLV) triplets to
existing OSPFv2 and OSPFv3 packets to carry this additional
information. Throughout this document, OSPF will be used when the
specification is applicable to both OSPFv2 and OSPFv3. Similarly,
OSPFv2 or OSPFv3 will be used when the text is protocol specific.
One potential way of solving this task could be introducing a new
packet type. However, that would mean introducing extra packets on
the network which may not be desirable and may cause backward
compatibility issues. This document describes how to exchange data
using standard OSPF packet types.
1.1. Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [KEY].
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2. Proposed solution
To perform link-local signaling (LLS), OSPF routers add a special
data block to the end of OSPF packets or right after the
authentication data block when cryptographic authentication is used.
The length of the LLS block is not included into the length of OSPF
packet, but is included in the IPv4/IPv6 packet length. Figure 1
illustrates how the LLS data block is attached.
+---------------------+ -- -- +---------------------+
| IP Header | ^ ^ | IPv6 Header |
| Length = HL+X+Y+Z | | Header Length | | Length = HL+X+Y |
| | v v | |
+---------------------+ -- -- +---------------------+
| OSPF Header | ^ ^ | OSPFv3 Header |
| Length = X | | | | Length = X |
|.....................| | X | X |.....................|
| | | | | |
| OSPFv2 Data | | | | OSPFv3 Data |
| | v v | |
+---------------------+ -- -- +---------------------+
| | ^ ^ | |
| Authentication Data | | Y | Y | LLS Data |
| | v v | |
+---------------------+ -- -- +---------------------+
| | ^
| LLS Data | | Z
| | v
+---------------------+ --
Figure 1: LLS Data Block in OSPFv2 and OSPFv3
The LLS data block MAY be attached to OSPF Hello and DD packets. The
data included in LLS block attached to a Hello packet MAY be used for
dynamic signaling since Hello packets may be sent at any time in
time. However, delivery of LLS data in Hello packets is not
guaranteed. The data sent with DD packets is guaranteed to be
delivered as part of the adjacency forming process.
This document does not specify how the data transmitted by the LLS
mechanism should be interpreted by OSPF routers. The interface
between the OSPF LLS component and its clients is implementation
specific.
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2.1. Options Field
A new L bit (L stands for LLS) is introduced to OSPF Options field
(see Figure 2a/2b). Routers set the L bit in Hello and DD packets to
indicate that the packet contains LLS data block. In other words,
LLS data block is only examined if the L bit is set.
+---+---+---+---+---+---+---+---+
| * | O | DC| L |N/P| MC| E | * |
+---+---+---+---+---+---+---+-+-+
Figure 2a: OSPFv2 Options field
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+--+--+--+--+--+
| | | | | | | | | | | | | | |L|AF|*|*|DC| R| N|MC| E|V6|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+--+--+--+--+--+--+
Figure 2b: OSPFv3 Options field
The L bit is only set in Hello and DD packets.
2.2. LLS Data Block
The data block used for link-local signaling is formatted as
described below (see Figure 3 for illustration).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum | LLS Data Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| LLS TLVs |
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Format of LLS Data Block
The Checksum field contains the standard IP checksum for the entire
contents of the LLS block.
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The 16-bit LLS Data Length field contains the length (in 32-bit
words) of the LLS block including the header and payload.
Implementations MUST NOT use the Length field in the IP packet header
to determine the length of the LLS data block.
Note that if the OSPF packet is cryptographically authenticated, the
LLS data block MUST also be cryptographically authenticated. In this
case, the regular LLS checksum is not calculated and the LLS block
will contain a cryptographic authentication TLV (see Section 2.5).
The rest of the block contains a set of Type/Length/Value (TLV)
triplets as described in Section 2.3. All TLVs MUST be 32-bit
aligned (with padding if necessary).
2.3. LLS TLVs
The contents of LLS data block is constructed using TLVs. See Figure
4 for the TLV format.
The type field contains the TLV ID which is unique for each type of
TLVs. The Length field contains the length of the Value field (in
bytes). The value field is variable and contains arbitrary data.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Value .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Format of LLS TLVs
Note that TLVs are always padded to 32-bit boundary, but padding
bytes are not included in TLV Length field (though they are included
in the LLS Data Length field in the LLS block header).
2.4. Extended Options TLV
This subsection describes a TLV called the Extended Options (EO) TLV.
The format of EO-TLV is shown in Figure 5.
Bits in the Value field do not have any semantics from the point of
view of the LLS mechanism. This field MAY be used to announce some
OSPF capabilities that are link-specific. Also, other OSPF
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extensions MAY allocate bits in the bit vector to perform boolean
link-local signaling.
The length of the Value field in the EO-TLV is 4 bytes.
The value of the type field in the EO-TLV is 1.
The EO-TLV MUST only appear once in the LLS data block.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Format of EO TLV
Currently, [OOB] and [RESTART] use bits in the Extended Options field
of the EO-TLV.
The Extended Options bits are defined in Section 3.
2.5. Cryptographic Authentication TLV (OSPFv2 ONLY)
This document defines a special TLV that is used for cryptographic
authentication (CA-TLV) of the LLS data block. This TLV MUST be
included in the LLS block when the cryptographic (MD5) authentication
is enabled on the corresponding interface. The message digest of the
LLS block MUST be calculated using the same key and authentication
algorithm as used for the OSPFv2 packet. The cryptographic sequence
number is included in the TLV and MUST be the same as the one in the
OSPFv2 authentication data for the LLS block to be considered
authentic.
The TLV is constructed as shown in Figure 6.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | AuthLen |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. AuthData .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Format of Cryptographic Authentication TLV
The value of the Type field for the CA-TLV is 2.
The Length field in the header contains the length of the data
portion of the TLV including 4 bytes for Sequence Number and the
length of the message digest (MD5) block for the whole LLS block in
bytes (this will always be 16 bytes for MD5). Hence, the AuthLen
field will be 20 for MD5 cryptographic authentication.
The Sequence Number field contains the cryptographic sequence number
that is used to prevent simple replay attacks. For the LLS block to
be considered authentic, the Sequence Number in the CA-TLV MUST match
the Sequence Number in the OSPFv2 packet header Authentication field.
In the event of Sequence Number mismatch or Authentication failure,
the whole LLS block MUST be ignored.
The AuthData contains the message digest calculated for the LLS data
block.
The CA-TLV MUST only appear once in the the LLS block. Also, when
present, this TLV SHOULD be the last TLV in the LLS block.
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3. IANA Considerations
LLS TLV types are maintained by the IANA. Extensions to OSPF which
require a new LLS TLV type MUST be reviewed by an designated expert
from the routing area.
Following the policies outlined in [IANA], LLS type values in the
range of 0-32767 are allocated through an IETF Consensus action and
LLS type values in the range of 32768-65536 are reserved for private
and experimental use.
This document assigns the following LLS TLV types in OSPFv2/OSPFv3.
TLV Type Name Reference
0 Reserved
1 Extended Options [RFCNNNN]*
2 Cryptographic Authentication+ [RFCNNNN]*
3-32767 Reserved for assignment by the IANA
32768-65535 Private Use
*[RFCNNNN] refers to the RFC number-to-be for this document.
+ Cryptographic Authentication TLV is only defined for OSPFv2
This document also assigns the following bits for the Extended
Options bits field in the EO-TLV outlined in Section 2.5:
Extended Options Bit Name Reference
0x00000001 LSDB Resynchronization (LR) [OOB]
0x00000002 Restart Signal (RS-bit) [RESTART]
Other Extended Options bits will be allocated through an IETF
consensus action.
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4. Compatibility Issues
The modifications to OSPF packet formats are compatible with standard
OSPF since OSPF router not supporting LLS will ignore the LLS data
block after the OSPF packet or cryptographic message digest.
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5. Security Considerations
The described technique provides the same level of security as OSPFv2
protocol by allowing LLS data to be authenticated using the same
cryptographic authentication that OSPFv2 uses (see Section 2.5 for
more details).
OSPFv3 utilizes IPSec for authentication and encryption [OSPFV3AUTH].
With IPsec, the AH (Authentication Header), ESP (Encapsulating
Security Payload), or both are applied to the entire OSPFv3 payload
including the LLS block.
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6. References
6.1. Normative References
[IANA] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 2334,
October 1998.
[KEY] Bradner, S., "Key words for use in RFC's to Indicate
Requirement Levels", RFC 2119, March 1997.
[OSPFV2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[OSPFV3] Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
RFC 2740, December 1999.
[OSPFV3AUTH]
Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, June 2006.
6.2. Informative References
[OOB] Zinin, A., Roy, A., and L. Nguyen, "OSPF Out-of-band LSDB
resynchronization", RFC 4811, March 2007.
[RESTART] Zinin, A., Roy, A., and L. Nguyen, "OSPF Restart
Signaling", RFC 4812, March 2007.
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Appendix A. Acknowledgements
The authors would like to acknowledge Russ White and Acee Lindem for
their thoughtful review of this document.
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Authors' Addresses
Alex Zinin
Alcatel
Sunnyvale
USA
Email: zinin@psg.com
Abhay Roy
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Email: akr@cisco.com
Liem Nguyen
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Email: lhnguyen@cisco.com
Barry Friedman
Redback Networks
100 Headquarters Drive
San Jose, CA 95134
USA
Email: friedman@redback.com
Derek Young
Email: derekmyeung@yahoo.com
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