Internet DRAFT - draft-ietf-isis-extended-sequence-no-tlv
draft-ietf-isis-extended-sequence-no-tlv
Working Group U. Chunduri
Internet-Draft W. Lu
Intended status: Standards Track A. Tian
Expires: October 24, 2015 Ericsson Inc.
N. Shen
Cisco Systems, Inc.
April 22, 2015
IS-IS Extended Sequence number TLV
draft-ietf-isis-extended-sequence-no-tlv-06
Abstract
This document defines Extended Sequence number TLV to protect
Intermediate System to Intermediate System (IS-IS) PDUs from replay
attacks.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Replay attacks and Impact on IS-IS networks . . . . . . . . . 4
2.1. IIHs . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. LSPs . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. SNPs . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Extended Sequence Number TLV . . . . . . . . . . . . . . . . 4
3.1. Sequence Number Wrap . . . . . . . . . . . . . . . . . . 5
4. Mechanism and Packet Encoding . . . . . . . . . . . . . . . . 6
4.1. IIHs . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. SNPs . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Backward Compatibility and Deployment . . . . . . . . . . . . 6
5.1. IIH and SNPs . . . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. ESSN Encoding Mechanisms . . . . . . . . . . . . . . 9
A.1. Using Timestamp . . . . . . . . . . . . . . . . . . . . . 9
A.2. Using Non-Volatile Storage . . . . . . . . . . . . . . . 10
Appendix B. Operational/Implementation consideration . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
With the rapid development of new data center infrastructures, due to
its flexibility and scalability attributes, Intermediate System to
Intermediate System (IS-IS, [ISO10589]) has been adopted widely
in various L2/L3 routing and switching deployment of the data centers
and for critical business operations. Also, while technologies such
as Software Defined Networks (SDN) may improve network management and
enable new applications, their use also has an effect on the security
requirements of the routing infrastructure.
A replayed IS-IS PDU can potentially cause many problems in the IS-IS
networks ranging from bouncing adjacencies to black hole or even some
form of Denial of Service (DoS) attacks as explained in Section 2.
This problem is also discussed in security consideration section, in
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the context of cryptographic authentication work as described in
[RFC5304] and in [RFC5310].
Currently, there is no mechanism to protect IS-IS HELLO PDUs (IIHs)
and Sequence number PDUs (SNPs) from the replay attacks. However,
Link State PDUs (LSPs) have sequence number in the LSP header as
defined in [ISO10589], with which it can effectively mitigate
the intra-session replay attacks. But, LSPs are still susceptible to
inter-session replay attacks.
This document defines Extended Sequence number (ESN) TLV to protect
Intermediate System to Intermediate System (IS-IS) PDUs from replay
attacks.
The new ESN TLV defined here thwart these threats and can be deployed
with authentication mechanism as specified in [RFC5304] and in
[RFC5310] for a more secure network.
Replay attacks can be effectively mitigated by deploying a group key
management protocol (being developed as defined in [I-D.yeung-
g-ikev2] and [I-D.hartman-karp-mrkmp]) with a frequent key change
policy. Currently, there is no such mechanism defined for IS-IS.
Even if such a mechanism is defined, usage of this TLV can be helpful
to avoid replays before the keys are changed.
Also, it is believed, even when such a key management system is
deployed, there always will be some manual key based systems that co-
exist with KMP (Key Management Protocol) based systems. The ESN TLV
defined in this document is more helpful for such deployments.
1.1. Requirements Language
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 RFC 2119 [RFC2119].
1.2. Acronyms
CSNP - Complete Sequence Number PDU
ESN - Extended Sequence Number
IIH - IS-IS Hello PDU
IS - Intermediate System
KMP - Key Management Protocol (auto key management)
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LSP - IS-IS Link State PDU
MKM - Manual Key management Protocols
PDU - Protocol Data Unit
PSNP - Partial Sequence Number PDU
SNP - Sequence Number PDU
2. Replay attacks and Impact on IS-IS networks
Replaying a captured protocol packet to cause damage is a common
threat for any protocol. Securing the packet with cryptographic
authentication information alone cannot mitigate this threat
completely. This section explains the replay attacks and the
applicability of the same for each IS-IS PDU.
2.1. IIHs
When an adjacency is brought up an IS sends an IIH packet with an
empty neighbor list (TLV 6), which can be sent with or without
authentication information. Packets can be replayed later on the
broadcast network which may cause all ISes to bounce the adjacency,
thus churning the network. Note that mitigating replay is only
possible when authentication information is present.
2.2. LSPs
Normal operation of the IS-IS update Process as specified in
[ISO10589] provides timely recovery from all LSP replay
attacks. Therefore the use of the extensions defined in this
document are prohibited in LSPs. Further discussion of the
vulnerability of LSPs to replay attacks can be found in [I-D.ietf-
karp-isis-analysis].
2.3. SNPs
A replayed CSNP can result in the sending of unnecessary PSNPs on a
given link. A replayed CSNP or PSNP can result in unnecessary LSP
flooding on the link.
3. Extended Sequence Number TLV
The Extended Sequence Number (ESN) TLV is composed of 1 octet for the
Type, 1 octet that specifies the number of bytes in the Value field
and a 12 byte Value field. This TLV is defined only for IIH and SNP
PDUs.
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x CODE - 11.
x LENGTH - total length of the value field, which is 12 bytes.
x Value - 64-bit Extended Session Sequence Number (ESSN), which is
followed by a 32 bit monotonically increasing per Packet Sequence
Number (PSN).
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Session Sequence Number (High Order 32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extended Session Sequence Number (Low Order 32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet Sequence Number (32 Bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended Sequence Number (ESN) TLV
The ESN TLV defined here is optional. Though this is an optional
TLV, this can be mandatory on a link when 'verify' mode is enabled as
specified in Section 5.1. The ESN TLV MAY be present only in any IIH
and SNP PDUs. A PDU with multiple ESN TLVs is invalid and MUST be
discarded on receipt.
The 64 bit ESSN MUST be non-zero and MUST contain ever increasing
number whenever it is changed due any situation as specified in
Section 3.1. Encoding the 64-bit unsigned integer ESSN value is a
local matter and implementations MAY use one of the alternatives
provided in Appendix A. Effectively, for each PDU which contains the
ESN TLV the 96 bit unsigned integer value consisting of the 64 bit
ESSN and 32 bit Packet Sequence Number (PSN) - where ESSN is the
higher order 64 bits - MUST be greater than the most recently
received value in a PDU of the same type originated by the same IS.
3.1. Sequence Number Wrap
If the 32-bit Packet Sequence Number in ESN TLV wraps or for the cold
restart of the router, the 64-bit ESSN value MUST be set higher than
the previous value. IS-IS implementations MAY use guidelines
provided in Appendix A for accomplishing this.
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4. Mechanism and Packet Encoding
The encoding of ESN TLV in each applicable IS-IS PDU is detailed
below. Please refer to Section 5 for appropriate operations on how
to inter-op with legacy node(s) that do not support the extensions
defined in this document. If the received PDU with ESN TLV is
accepted then the stored value for the corresponding originator and
PDU type MUST be updated with the latest value received. Please note
that level information is included in the PDU type.
4.1. IIHs
ESN TLV information is maintained for each type of IIH PDU being sent
on a given circuit. The procedures for encoding, verification and
sequence number wrap scenarios are explained in Section 3.
4.2. SNPs
A separate CSNP/PSNP ESN TLV information is maintained per PDU type,
per originator and per link. The procedures for encoding,
verification and sequence number wrap scenarios are explained in
Section 3.
5. Backward Compatibility and Deployment
The implementation and deployment of the ESN TLV can be done to
support backward compatibility and gradual deployment in the network
without requiring a flag day. This feature can also be deployed for
the links in a certain area of the network where the maximum security
mechanism is needed, or it can be deployed for the entire network.
The implementation SHOULD allow the configuration of ESN TLV feature
on each IS-IS link level. The implementation SHOULD also allow
operators to control the configuration of the 'send' and/or 'verify'
feature of IS-IS PDUs for the links and for the node. In this
document, the 'send' operation is to include the ESN TLV in its own
IS-IS PDUs; and the 'verify' operation is to process the ESN TLV in
the receiving IS-IS PDUs from neighbors.
In the face of an adversary doing an active attack, it is possible to
have inconsistent data view in the network, if there is a
considerable delay in enabling ESN TLV 'verify' operation from first
node to the last node in the network or all nodes of a particular LAN
segment, where 'send' mode is configured. This can happen primarily
because, replay PDUs can potentially be accepted by the nodes where
'verify' operation is still not provisioned at the time of the
attack. To minimize such a window it is recommended that
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provisioning of 'verify' SHOULD be done in a timely fashion by the
network operators.
5.1. IIH and SNPs
On the link level, ESN TLV involves the IIH PDUs and SNPs (both CSNP
and PSNP). The "send" and "verify" modes described above can be set
independently on each link and in the case of a broadcast network
independently for each level.
To introduce ESN support without disrupting operations, ISs on a
given interface are first configured to operate in 'send' mode. Once
all routers operating on an interface are operating in 'send' mode
'verify' mode can be enabled on each IS. Once 'verify' mode is set
for an interface all the IIH and SNP PDUs being sent on that
interface MUST contain the ESN TLV. Any such PDU received without an
ESN TLV MUST be discarded when 'verify' mode is enabled. Similarly,
to safely disable ESN support on a link, 'verify' mode is disabled on
all ISs on the link. Once all routers operating on an interface are
disabled from 'verify' mode 'send' mode can be disabled on each IS.
Please refer Section 5 for considerations on enabling or disabling
'verify' mode on all ISs on a link.
6. IANA Considerations
A new TLV code point is assigned by IANA from the IS-IS TLV
Codepoints Registry as defined in this document, referred to as the
"Extended Sequence Number" TLV, with the following attributes:
Type Description IIH LSP SNP Purge
---- --------------------- --- --- --- -----
11 ESN TLV Y N Y N
Figure 2: IS-IS Codepoints Registry Entry
7. Security Considerations
This document describes a mechanism to the replay attack threat as
discussed in the Security Considerations section of [RFC5304] and in
[RFC5310]. If an adversary either does not forward the packets or
delay the same as specified in Section 3.3 of [RFC6862], the
mechanism specified in this document cannot mitigate those threats.
Also some of the threats as specified in Section 2.3 of [I-D.ietf-
karp-isis-analysis] are not addressable with ESN TLV as specified in
this document. This document does not introduce any new security
concerns to IS-IS or any other specifications referenced in this
document.
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8. Contributors
Authors would like to thank Les Ginsberg for his significant
contribution in detailed reviews and suggestions.
9. Acknowledgements
As some sort of sequence number mechanism to thwart protocol replays
is a old mechanism, authors of this document do not make any claims
on the originality of the overall protection idea described. Authors
are thankful for the review and the valuable feedback provided by
Acee Lindem and Joel Halpern. Thanks to Alia Atlas, Chris Hopps,
Nevil Brownlee and Adam W. Montville for their reviews and
suggestions during IESG directorate review. Authors would also thank
Christer Holmberg, Ben Campbell, Barry Leiba, Stephen Farrell and
Alvaro Retana for their reviews on this document.
10. References
10.1. Normative References
[ISO10589]
International Organization for Standardization,
"Intermediate system to intermediate system intra-domain-
routing routine information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473)", ISO/
IEC 10589:2002, Second Edition, Nov. 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
10.2. Informative References
[I-D.hartman-karp-mrkmp]
Hartman, S., Zhang, D., and G. Lebovitz, "Multicast Router
Key Management Protocol (MaRK)", draft-hartman-karp-
mrkmp-05 (work in progress), September 2012.
[I-D.ietf-karp-isis-analysis]
Chunduri, U., Tian, A., and W. Lu, "KARP IS-IS security
analysis", draft-ietf-karp-isis-analysis-04 (work in
progress), March 2015.
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[I-D.weis-gdoi-mac-tek]
Weis, B. and S. Rowles, "GDOI Generic Message
Authentication Code Policy", draft-weis-gdoi-mac-tek-03
(work in progress), September 2011.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, February 2009.
[RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Design Guidelines", RFC 6518,
February 2012.
[RFC6862] Lebovitz, G., Bhatia, M., and B. Weis, "Keying and
Authentication for Routing Protocols (KARP) Overview,
Threats, and Requirements", RFC 6862, March 2013.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, April 2015.
Appendix A. ESSN Encoding Mechanisms
IS-IS nodes implementing this specification SHOULD use available
mechanisms to preserve the 64-bit Extended Session Sequence Number's
strictly increasing property, whenever it is changed for the deployed
life of the IS-IS node (including cold restarts).
This Appendix provides only guidelines for achieving the same and
implementations can resort to any similar method as far as strictly
increasing property of the 64-bit ESSN in ESN TLV is maintained.
A.1. Using Timestamp
One mechanism for accomplishing this is by encoding 64-bit ESSN as
system time represented in 64-bit unsigned integer value. This MAY
be similar to the system timestamp encoding for NTP long format as
defined in Appendix A.4 of [RFC5905]. New current time MAY be used
when the IS-IS node loses its sequence number state including in
Packet Sequence Number wrap scenarios.
Implementations MUST make sure while encoding the 64-bit ESN value
with current system time, it should not default to any previous value
or some default node time of the system; especially after cold
restarts or any other similar events. In general system time must be
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preserved across cold restarts in order for this mechanism to be
feasible. One example of such implementation is to use a battery
backed real-time clock (RTC).
A.2. Using Non-Volatile Storage
One other mechanism for accomplishing this would be similar to the
one as specified in [RFC7474], to use the 64-bit ESSN as a wrap/boot
count stored in non-volatile storage. This value is incremented
anytime the IS-IS node loses its sequence number state including in
Packet Sequence Number wrap scenarios.
The drawback of this approach per Section 8 of [RFC7474], if used is
applicable here. It requires the IS-IS implementation to be able to
save its boot count in non-volatile storage. If the non-volatile
storage is ever repaired or router hardware is upgraded such that the
contents are lost, keys MUST be changed to prevent replay attacks.
Appendix B. Operational/Implementation consideration
Since the ESN is maintained per interface, per level and per PDU
type, this scheme can be useful for monitoring the health of the IS-
IS adjacency. A Packet Sequence Number skip on IIH can be recorded
by the neighbors which can be used later to correlate with adjacency
state changes over the interface. For instance in a multi-access
media, all the neighbors have the skips from the same IIH sender or
only one neighbor has the Packet Sequence Number skips can indicate
completely different issues on the network. Effective usage of the
TLV defined in this document for operational issues MAY also need
more system information before making concrete conclusions and
defining all that information is beyond the scope of this document.
Authors' Addresses
Uma Chunduri
Ericsson Inc.
300 Holger Way,
San Jose, California 95134
USA
Phone: 408 750-5678
Email: uma.chunduri@ericsson.com
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Wenhu Lu
Ericsson Inc.
300 Holger Way,
San Jose, California 95134
USA
Email: wenhu.lu@ericsson.com
Albert Tian
Ericsson Inc.
300 Holger Way,
San Jose, California 95134
USA
Phone: 408 750-5210
Email: albert.tian@ericsson.com
Naiming Shen
Cisco Systems, Inc.
225 West Tasman Drive,
San Jose, California 95134
USA
Email: naiming@cisco.com
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