Enhanced Duplicate Address Detection
draft-ietf-6man-enhanced-dad-07
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (6man WG) | |
|---|---|---|---|
| Authors | Rajiv Asati , Hemant Singh , Wes Beebee , Carlos Pignataro , Eli Dart , Wesley George | ||
| Last updated | 2014-10-23 | ||
| Replaces | draft-hsingh-6man-enhanced-dad | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text htmlized pdfized bibtex | ||
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| Stream | WG state | WG Consensus: Waiting for Write-Up | |
| Document shepherd | Ole Trøan | ||
| Shepherd write-up | Show Last changed 2014-10-07 | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-6man-enhanced-dad-07
Network Working Group R. Asati
Internet-Draft H. Singh
Updates: 4862, 4861, 3971 (if approved) W. Beebee
Intended status: Standards Track C. Pignataro
Expires: April 26, 2015 Cisco Systems, Inc.
E. Dart
Lawrence Berkeley National Laboratory
W. George
Time Warner Cable
October 23, 2014
Enhanced Duplicate Address Detection
draft-ietf-6man-enhanced-dad-07
Abstract
IPv6 Loopback Suppression and Duplicate Address Detection (DAD) are
discussed in Appendix A of [RFC4862]. That specification mentions a
hardware-assisted mechanism to detect looped back DAD messages. If
hardware cannot suppress looped back DAD messages, a software
solution is required. Several service provider communities have
expressed a need for automated detection of looped backed Neighbor
Discovery (ND) messages used by DAD. This document includes
mitigation techniques and outlines the Enhanced DAD algorithm to
automate the detection of looped back IPv6 ND messages used by DAD.
For network loopback tests, the Enhanced DAD algorithm allows IPv6 to
self-heal after a loopback is placed and removed. Further, for
certain access networks the document automates resolving a specific
duplicate address conflict.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 26, 2015.
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Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Two Deployment Problems . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. Operational Mitigation Options . . . . . . . . . . . . . . . 5
3.1. Disable DAD on an Interface . . . . . . . . . . . . . . . 5
3.2. Dynamic Disable/Enable of DAD Using Layer-2 Protocol . . 5
3.3. Operational Considerations . . . . . . . . . . . . . . . 6
4. The Enhanced DAD Algorithm . . . . . . . . . . . . . . . . . 6
4.1. General Rules . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Processing Rules for Senders . . . . . . . . . . . . . . 7
4.3. Processing Rules for Receivers . . . . . . . . . . . . . 7
4.4. Impact on SEND . . . . . . . . . . . . . . . . . . . . . 8
4.5. Changes to RFC 4862 . . . . . . . . . . . . . . . . . . . 8
4.6. Changes to RFC 4861 . . . . . . . . . . . . . . . . . . . 9
4.7. Changes to RFC 3971 . . . . . . . . . . . . . . . . . . . 9
5. Actions to Perform on Detecting a Genuine Duplicate . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. Normative References . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
IPv6 Loopback Suppression and Duplicate Address Detection (DAD) are
discussed in Appendix A of [RFC4862]. That specification mentions a
hardware-assisted mechanism to detect looped back DAD messages. If
hardware cannot suppress looped back DAD messages, a software
solution is required. One specific DAD message is the Neighbor
Solicitation (NS), specified in [RFC4861]. The NS is issued by the
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network interface of an IPv6 node for DAD. Another message involved
in DAD is the Neighbor Advertisement (NA). The Enhanced DAD
algorithm specified in this document focuses on detecting an NS
looped back to the transmitting interface during the DAD operation.
Detecting a looped back NA does not solve the looped back DAD
problem. Detection of any other looped back ND messages during the
DAD operation is outside the scope of this document. This document
also includes a section on Mitigation that discusses means already
available to mitigate the DAD loopback problem.
1.1. Two Deployment Problems
In each problem articulated below, the IPv6 link-local address DAD
operation fails due to a looped back DAD probe. However, the looped
back DAD probe exists for any IPv6 address type including global
addresses.
Recently, service providers have reported a problem with DAD that is
caused by looped back NS messages. The following is a description of
the circumstances under which the problem arises. Loopback testing
for troubleshooting purposes is underway on a circuit connected to an
interface on a router. The interface on the router is enabled for
IPv6. The interface issues a NS for the IPv6 link-local address DAD.
The NS is reflected back to the router interface due to the loopback
condition of the circuit, and the router interface enters a DAD-
failed state. After the circuit troubleshooting has concluded and
the loopback condition is removed, IPv4 will return to operation
without further manual intervention. However, IPv6 will remain in
DAD-failed state until manual intervention on the router restores
IPv6 to operation.
There are other conditions which will also trigger similar problems
with DAD Loopback. While the following example is not a common
configuration, it has occurred in a large service provider network.
It is necessary to address it in the proposed solution because the
trigger scenario has the potential to cause significant IPv6 service
outages when it does occur. Two broadband modems in the same home
are served by the same service provider and both modems are served by
one access concentrator and one layer-3 interface on the access
concentrator. The two modems have the Ethernet ports of each modem
connected to a network hub. The access concentrator serving the
modems is the first-hop IPv6 router for the modems. The network
interface of the access concentrator serving the two broadband modems
is enabled for IPv6 and the interface issues a NS(DAD) message for
the IPv6 link-local address. The NS message reaches one modem first
and this modem sends the message to the network hub which sends the
message to the second modem which forwards the message back to the
access concentrator. The looped back NS message causes the network
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interface on the access concentrator to be in a DAD-failed state.
Such a network interface typically serves up to a hundred thousand
broadband modems causing all the modems (and hosts behind the modems)
to fail to get IPv6 online on the access network. Additionally, it
may be tedious for the access concentrator to find out which of the
hundred thousand or more homes looped back the DAD message. Clearly
there is a need for automated detection of looped back NS messages
during DAD operations by a node.
2. Terminology
o DAD-failed state - Duplication Address Detection failure as
specified in [RFC4862]. Note even Optimistic DAD as specified in
[RFC4429] can fail due to a looped back DAD probe. This document
covers looped back detection for Optimistic DAD as well.
o Looped back message - also referred to as a reflected message.
The message sent by the sender is received by the sender due to
the network or an Upper Layer Protocol on the sender looping the
message back.
o Loopback - A function in which the router's layer-3 interface (or
the circuit to which the router's interface is connected) is
looped back or connected to itself. Loopback causes packets sent
by the interface to be received by the interface and results in
interface unavailability for regular data traffic forwarding. See
more details in section 9.1 of [RFC1583]. The Loopback function
is commonly used in an interface context to gain information on
the quality of the interface, by employing mechanisms such as
ICMPv6 pings and bit-error tests. In a circuit context, this
function is used in wide area environments including optical Dense
Wave Division Multiplexing (DWDM) and SONET/SDH for fault
isolation (e.g. by placing a loopback at different geographic
locations along the path of a wide area circuit to help locate a
circuit fault). The Loopback function may be employed locally or
remotely.
o NS(DAD) - shorthand notation to denote an Neighbor Solicitation
(NS) (as specified in [RFC4861]) with unspecified IPv6 source-
address issued during DAD.
2.1. 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 [RFC2119].
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3. Operational Mitigation Options
Two mitigation options are described below. The mechanisms do not
require any change to existing implementations.
3.1. Disable DAD on an Interface
One can disable DAD on an interface so that there is no NS(DAD)
issued to be looped back. DAD is disabled by setting the interface's
DupAddrDetectTransmits variable to zero. While this mitigation may
be the simplest, the mitigation has three drawbacks.
This mitigation would likely require careful analysis of
configuration on such point-to-point interfaces, a one-time manual
configuration on each of such interfaces, and more importantly,
genuine duplicates in the link will not be detected.
A Service Provider router, such as an access concentrator, or network
core router, SHOULD support this mitigation strategy.
3.2. Dynamic Disable/Enable of DAD Using Layer-2 Protocol
One or more layer-2 protocols MAY include provisions to detect the
existence of a loopback on an interface circuit, usually by comparing
protocol data sent and received. For example, PPP uses magic number
(section 6.4 of [RFC1661]) to detect a loopback on an interface.
When a layer-2 protocol detects that a loopback is present on an
interface circuit, the device MUST temporarily disable DAD on the
interface. When the protocol detects that a loopback is no longer
present (or the interface state has changed), the device MUST
(re-)enable DAD on that interface.
This solution requires no protocol changes. This solution SHOULD be
enabled by default, and MUST be a configurable option if the layer-2
technology provides means for detecting loopback messages on an
interface circuit.
This mitigation has several benefits. They are
1. It leverages layer-2 protocol's built-in loopback detection
capability, if available.
2. It scales better since it relies on an event-driven model which
requires no additional state or timer. This may be a significant
scaling consideration on devices with hundreds or thousands of
interfaces that may be in loopback for long periods of time (such
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as while awaiting turn-up or during long-duration intrusive bit
error rate tests).
3.3. Operational Considerations
The mitigation options discussed in the document do not require the
devices on both ends of the circuit to support the mitigation
functionality simultaneously, and do not propose any capability
negotiation. The mitigation options discussed in this document are
effective for unidirectional circuit or interface loopback (i.e. the
the loopback is placed in one direction on the circuit, rendering the
other direction non-operational).
The mitigation options may not be effective for the bidirectional
loopback (i.e. the loopback is placed in both directions of the
circuit interface, so as to identify the faulty segment) if only one
device followed a mitigation option specified in this document, since
the other device would follow current behavior and disable IPv6 on
that interface due to DAD until manual intervention restores it.
This is nothing different from what happens today (without the
solutions proposed by this document) in case of unidirectional
loopback. Hence, it is expected that an operator would resort to
manual intervention for the devices not compliant with this document,
as usual.
4. The Enhanced DAD Algorithm
The Enhanced DAD algorithm covers detection of a looped back NS(DAD)
message. The document proposes use of the Nonce Option specified in
the SEND document of [RFC3971]. The nonce is a random number as
specified in [RFC3971]. If SEND is enabled on the router and the
router also supports the Enhanced DAD algorithm (specified in this
document), there is integration with the Enhanced DAD algorithm and
SEND. (See more details in the Impact on SEND section section 4.4.)
Since a nonce is used only once, The NS(DAD) for each IPv6 address of
an interface uses a different nonce. Additional details of the
algorithm are included in section 4.2.
Six bytes of random nonce is sufficiently large to minimize
collisions. However, if there is a collision because two nodes that
are using the same Target Address in their NS(DAD) and generated the
same random nonce, then the algorithm will incorrectly detect a
looped back NS(DAD) when a genuine address collision has occurred.
Since each looped back NS(DAD) event is logged to system management,
the administrator of the network will have access to the information
necessary to intervene manually. Also, because the nodes will have
detected what appear to be looped back NS(DAD) messages, they will
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continue to probe, and it is unlikely that they will choose the same
nonce the second time (assuming quality random number generators).
The algorithm is capable of detecting any ND solicitation (NS and
Router Solicitation) or advertisement (NA and Router Advertisement)
that is looped back. However, saving a nonce and nonce related data
for all ND messages has impact on memory requirements of the node and
also adds the algorithm state to a substantially larger number of ND
messages. Therefore, this document does not recommend using the
algorithm outside of the DAD operation by an interface on a node.
4.1. General Rules
If an IPv6 node implements the Enhanced DAD algorithm, the node MUST
implement detection of looped back NS(DAD) messages during DAD for an
interface address.
4.2. Processing Rules for Senders
If a node has been configured to use the Enhanced DAD algorithm, when
sending an NS(DAD) for a tentative or optimistic interface address
the sender MUST generate a random nonce associated with the interface
address, MUST save the nonce, and MUST include the nonce in the Nonce
Option included in the NS(DAD). If the interface does not receive
any DAD failure indications within RetransTimer milliseconds (see
[RFC4861]) after having sent DupAddrDetectTransmits Neighbor
Solicitations, the interface moves the Target Address to the assigned
state.
If any probe is looped back within RetransTimer milliseconds after
having sent DupAddrDetectTransmits NS(DAD) messages, the interface
continues with another MAX_MULTICAST_SOLICIT number of NS(DAD)
messages transmitted RetransTimer millseconds apart. If no probe is
looped back within RetransTimer milliseconds after
MAX_MULTICAST_SOLICIT NS(DAD) messages are sent, the probing stops.
The probing MAY be stopped via manual intervention. When probing is
stopped, the interface moves the Target Address to the assigned
state.
4.3. Processing Rules for Receivers
If the node has been configured to use the Enhanced DAD algorithm and
an interface on the node receives any NS(DAD) message where the
Target Address matches the interface address (in tentative or
optimistic state), the receiver compares the nonce included in the
message, with any saved nonce on the receiving interface. If a match
is found, the node SHOULD log a system management message, SHOULD
update any statistics counter, and MUST drop the received message.
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If the received NS(DAD) message includes a nonce and no match is
found with any saved nonce, the node SHOULD log a system management
message for a DAD-failed state, and SHOULD update any statistics
counter. If the interface does not receive any DAD failure
indications within RetransTimer milliseconds after having sent
DupAddrDetectTransmits Neighbor Solicitations, the interface moves
the Target Address to the assigned state.
4.4. Impact on SEND
The SEND document uses the Nonce Option in the context of matching an
NA with an NS. However, no text in SEND has an explicit mention of
detecting looped back ND messages. As this document updates
[RFC4862], SEND should be updated to integrate with the Enhanced DAD
algorithm. A minor update to SEND would be to explicitly mention
that the nonce in SEND is also used by SEND to detect looped back
NS(DAD) messages during DAD operations by the node. In a mixed SEND
environment with SEND and unsecured nodes, the lengths of the nonce
used by SEND and unsecured nodes MUST be identical.
4.5. Changes to RFC 4862
The following text is added to the end of the Introduction section of
[RFC4862].
A network interface of an IPv6 node SHOULD implement the Enhanced DAD
algorithm. For example, if the interface on an IPv6 node is
connected to a circuit that supports loopback testing, then the node
SHOULD implement the Enhanced DAD algorithm that allows the IPv6
interface to self-heal after loopback testing is ended on the
circuit. Another example is when the IPv6 interface resides on an
access concentrator running DAD Proxy. The interface supports up to
a hundred thousand IPv6 clients (broadband modems) connected to the
interface. If the interface performs DAD for its IPv6 link-local
address and the DAD probe is reflected back to the interface, the
interface is stuck in DAD-failed state and IPv6 services to the
hundred thousand clients is denied. Disabling DAD for such an IPv6
interface on an access concentrator is less desirable than
implementing the algorithm because the network also needs to detect
genuine duplicates in the interface downstream network. The Enhanced
DAD algorithm also facilitates detecting a genuine duplicate for the
interface on the access concentrator. (See the Actions to Perform on
Detecting a Genuine Duplicate section of the Enhanced DAD document.)
The following text is added to the end of Appendix A of [RFC4862].
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The Enhanced DAD algorithm from draft-ietf-6man-enhanced-dad is
designed to detect looped back DAD probes. A network interface of an
IPv6 node SHOULD implement the Enhanced DAD algorithm.
4.6. Changes to RFC 4861
The following text is appended to the RetransTimer variable
description in section 6.3.2 of [RFC4861]:
The RetransTimer may be overridden by a link-specific document if a
node supports the Enhanced DAD algorithm.
The following text is appended to the Source Address definition in
section 4.3 of [RFC4861]:
If a node has been configured to use the Enhanced DAD algorithm, an
NS with an unspecified source address adds the Nonce option to the
message and implements the state machine of the Enhanced DAD
algorithm.
4.7. Changes to RFC 3971
The following text is changed in section 5.3.2 of [RFC3971]:
The purpose of the Nonce option is to make sure that an advertisement
is a fresh response to a solicitation sent earlier by the node.
The new text is included below:
The purpose of the Nonce option is to make sure that an advertisement
is a fresh response to a solicitation sent earlier by the node. The
nonce is also used to detect looped back NS messages when the network
interface performs DAD [RFC4862]. Detecting looped back DAD messages
is covered by the Enhanced DAD algorithm as specified in draft-ietf-
6man-enhanced-dad. In a mixed SEND environment with SEND and
unsecured nodes, the lengths of the nonce used by SEND and unsecured
nodes MUST be identical.
5. Actions to Perform on Detecting a Genuine Duplicate
As described in the paragraphs above, the nonce can also serve to
detect genuine duplicates even when the network has potential for
looping back ND messages. When a genuine duplicate is detected, the
node follows the manual intervention specified in section 5.4.5 of
[RFC4862]. However, in certain networks such as an access network,
if the genuine duplicate matches the tentative or optimistic IPv6
address of a network interface of the access concentrator, automated
actions are recommended.
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One access network is a cable broadband deployment where the access
concentrator is the first-hop IPv6 router to several hundred thousand
broadband modems. The router also supports proxying of DAD messages.
The network interface on the access concentrator initiates DAD for an
IPv6 address and detects a genuine duplicate due to receiving an
NS(DAD) or an NA message. On detecting such a duplicate, the access
concentrator logs a system management message, drops the received ND
message, and blocks the modem on whose layer-2 service identifier the
NS(DAD) or NA message was received on.
The network described above follows a trust model where a trusted
router serves un-trusted IPv6 host nodes. Operators of such networks
have a desire to take automated action if a network interface of the
trusted router has a tentative or optimistic address duplicated by a
host. Any other network that follows the same trust model MAY use
the automated actions proposed in this section.
6. Security Considerations
The nonce can be exploited by a rogue deliberately changing the nonce
to fail the looped back detection specified by the Enhanced DAD
algorithm. SEND is recommended to circumvent this exploit.
Additionally, the nonce does not protect against the DoS caused by a
rogue node replying by a fake NA to all DAD probes. SEND is
recommended to circumvent this exploit also. Disabling DAD has an
obvious security issue before a remote node on the link can issue
reflected NS(DAD) messages. Again, SEND is recommended for this
exploit.
7. IANA Considerations
None.
8. Acknowledgements
Thanks (in alphabetical order by first name) to Bernie Volz, Dmitry
Anipko, Eric Levy-Abegnoli, Eric Vyncke, Erik Nordmark, Fred Templin,
Jouni Korhonen, Michael Sinatra, Ole Troan, Ray Hunter, Suresh
Krishnan, and Tassos Chatzithomaoglou for their guidance and review
of the document. Thanks to Thomas Narten for encouraging this work.
Thanks to Steinar Haug and Scott Beuker for describing the use cases.
9. Normative References
[RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994.
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, April 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
Authors' Addresses
Rajiv Asati
Cisco Systems, Inc.
7025 Kit Creek road
Research Triangle Park, NC 27709-4987
USA
Email: rajiva@cisco.com
URI: http://www.cisco.com/
Hemant Singh
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
Phone: +1 978 936 1622
Email: shemant@cisco.com
URI: http://www.cisco.com/
Wes Beebee
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
Phone: +1 978 936 2030
Email: wbeebee@cisco.com
URI: http://www.cisco.com/
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Carlos Pignataro
Cisco Systems, Inc.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
USA
Email: cpignata@cisco.com
URI: http://www.cisco.com/
Eli Dart
Lawrence Berkeley National Laboratory
1 Cyclotron Road, Berkeley, CA 94720
USA
Email: dart@es.net
URI: http://www.es.net/
Wes George
Time Warner Cable
13820 Sunrise Valley Drive
Herndon, VA 20171
USA
Email: wesley.george@twcable.com
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