wdiff rfc7527.original rfc7527.txt

Network Working Group
Internet Engineering Task Force (IETF) R. Asati
Internet-Draft
Request for Comments: 7527 H. Singh
Updates: 4862, 4429, 4861, 4429 (if approved) 4862 W. Beebee
Intended status:
Category: Standards Track C. Pignataro
Expires: September 6, 2015
ISSN: 2070-1721 Cisco Systems, Inc.
E. Dart
Lawrence Berkeley National Laboratory
W. George
Time Warner Cable
March 5,
April 2015

Enhanced Duplicate Address Detection
draft-ietf-6man-enhanced-dad-15

Abstract

IPv6 Loopback Suppression and Duplicate Address Detection (DAD) are
discussed in Appendix A of RFC4862. RFC 4862. 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 back 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 networks, this document automates resolving a specific
duplicate address conflict. This document updates RFC4861, RFC4862, RFCs 4429, 4861,
and RFC4429. 4862.

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 an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of six months RFC 5741.

Information about the current status of this document, any errata,
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This Internet-Draft will expire on September 6, 2015.
http://www.rfc-editor.org/info/rfc7527.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3. Operational Mitigation Options . . . . . . . . . . . . . . . 4
3.1. Disable DAD on an Interface . . . . . . . . . . . . . . . 4
3.2. Dynamic Disable/Enable of DAD Using Layer-2 Layer 2 Protocol . . 5
3.3. Operational Considerations . . . . . . . . . . . . . . . 5
4. The Enhanced DAD Algorithm . . . . . . . . . . . . . . . . . 6
4.1. Processing Rules for Senders . . . . . . . . . . . . . . 6
4.2. Processing Rules for Receivers . . . . . . . . . . . . . 7
4.3. Changes to RFC 4861 . . . . . . . . . . . . . . . . . . . 7
5. Action to Perform on Detecting a Genuine Duplicate . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . Normative References . . . . . . . . . . . . . . . . . . . . 8
8.
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . 8 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 10

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
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 mitigation that discusses means already
available to mitigate the DAD loopback problem. This document
updates RFC4861, RFC4862, RFCs 4429, 4861, and RFC4429. 4862. It updates RFC 4862 and RFC RFCs 4429 and 4862 to
use the enhanced-dad Enhanced DAD algorithm to detect looped back DAD probes, and RFC4861
it updates RFC 4861 as described in Section 4.3 below.

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 [RFC2119].

1.2. 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 upper-layer protocol on the sender looping the
message back.

o Loopback - A function in which the router's layer-3 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 Section 9.1 of [RFC2328]. 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 wide-area environments including optical Dense
Wave
Wavelength Division Multiplexing (DWDM) and SONET/SDH Synchronous Optical
Network / Synchronous Digital Hierarchy (SONET/SDH) for fault
isolation (e.g. (e.g., by placing a loopback at different geographic
locations along the path of a wide area 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 a Neighbor Solicitation
(NS) (as specified in [RFC4861]) with that has an unspecified IPv6 source-
source address and was issued during DAD.

2. Problem Statement

Service providers have reported a problem with DAD that arises in a
few scenarios. In the first scenario, loopback testing for
troubleshooting purposes is underway on a circuit connected to an
IPv6-enabled interface on a router. The interface issues a an 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 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.

In the second scenario, two broadband modems are served by the same
service provider and terminate to the same layer-3 Layer 3 interface on an
IPv6-enabled access concentrator. In this case, the two modems'
Ethernet interfaces are also connected to a common local network
(collision domain). The access concentrator serving the modems is
the first-hop IPv6 router for the modems and issues a NS(DAD) message
for the IPv6 link-local address of its layer-3 Layer 3 interface. The NS
message reaches one modem first first, and this modem sends the message to
the local network, where the second modem receives the message and
then forwards it back to the access concentrator. The looped back NS
message causes the network interface on the access concentrator to be
in a DAD-failed state. Such a network interface typically serves
thousands of broadband modems, and all would have their IPv6
connectivity affected until the DAD-failed state is cleared.
Additionally, it may be difficult for the user of the access
concentrator to determine the source of the looped back DAD message.
Thus
Thus, in order to avoid IPv6 outages that can potentially affect
multiple users, there is a need for automated detection of looped
back NS messages during DAD operations by a node.

Note: In both examples above, the IPv6 link-local address DAD
operation fails due to a looped back DAD probe. However, the problem
of a looped back DAD probe exists for any IPv6 address type including
global addresses.

3. Operational Mitigation Options

Two mitigation options are described below that 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 are no NS(DAD)
messages issued. While this mitigation may be the simplest, the
mitigation has three drawbacks: 1) care is needed when making such
configuration changes on point-to-point interfaces, 2) this is a one-
time manual configuration on each interface, and 3) genuine
duplicates on the link will not be detected.

A Service Provider service provider router, such as an access concentrator, or network
core router, SHOULD support the DAD deactivation per interface.

3.2. Dynamic Disable/Enable of DAD Using Layer-2 Layer 2 Protocol

Some layer-2 Layer 2 protocols include provisions to detect the existence of
a loopback on an interface circuit, usually by comparing protocol
data sent and received. For example, the Point-to-Point Protocol
(PPP) uses a magic number (section (Section 6.4 of [RFC1661]) to detect a
loopback on an interface.

When a layer-2 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 mitigation has several benefits. It leverages the layer-2 Layer 2
protocol's built-in hardware loopback detection capability, if
available. It Being a hardware solution, it scales better than the
software solution proposed in this document. This mitigation also
scales better since it relies on an event-driven model which that requires
no additional state or timer. This may be significant on devices
with hundreds or thousands of interfaces that may be in loopback for
long periods of time (e.g., awaiting turn-up).

Detecting looped back DAD messages using a layer-2 Layer 2 protocol SHOULD be
enabled by default, and it MUST be a configurable option if the layer-2 Layer
2 technology provides means for detecting loopback messages on an
interface circuit.

3.3. Operational Considerations

The mitigation options discussed above do not require the devices on
both ends of the circuit to support the mitigation functionality
simultaneously,
simultaneously and do not propose any capability negotiation. They
are effective for unidirectional circuit or interface loopback (i.e.
the loopback is placed in one direction on the circuit, rendering the
other direction non-operational), nonoperational), but they may not be effective for a
bidirectional loopback (i.e. (i.e., the loopback is placed in both
directions of the circuit interface, so as to identify the faulty
segment). This is because because, unless both ends followed a mitigation
option specified in this document, the non-compliant noncompliant device would
follow current behavior and disable IPv6 on that interface due to DAD
until manual intervention restores it.

4. The Enhanced DAD Algorithm

The Enhanced DAD algorithm covers detection of a looped back NS(DAD)
message. The This document proposes use of a random number in the Nonce
Option specified in SEND SEcure Neighbor Discovery (SEND) [RFC3971]. Note
[RFC3971] does not provide a recommendation for pseudo-random pseudorandom
functions. Pseudo-random Pseudorandom functions are covered in [RFC4086]. 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. Section 4.1.

If there is a collision because two nodes used 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 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, there may be increased implementation
complexity and memory usage for the sender node to store a nonce and
nonce related
nonce-related state for all ND messages. Therefore, this document
does not recommend using the algorithm outside of the DAD operation
by an interface on a node.

4.1. 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 address,
the sender MUST generate a random nonce associated with the interface
address, MUST store the nonce internally, and MUST include the nonce
in the Nonce Option 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 milliseconds apart. Section 2 of
[RFC3971] defines a single-use nonce, so each Enhanced DAD probe uses
a different nonce. 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.

4.2. 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 stored 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. If the received NS(DAD) message includes a nonce and no
match is found with any stored nonce, the node SHOULD log a system
management message for a DAD-failed state, state and SHOULD update any
statistics counter.

4.3. 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
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.

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.

5. Action 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 Section 5.4.5 of
[RFC4862]. However, in certain cases, if the genuine duplicate
matches the tentative or optimistic IPv6 address of a network
interface of the access concentrator, additional automated action is
recommended.

Some networks follow a trust model where a trusted router serves un-
trusted
untrusted 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. One
example of a type of access network is cable broadband deployment
where the access concentrator is the first-hop IPv6 router to
multiple broadband modems and 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 SHOULD log a system management message, drop the
received ND message, and block the modem on whose layer-2 Layer 2 service
identifier the duplicate NS(DAD) or NA message was received on. received. Any
other network that follows the same trust model MAY use the automated
action proposed in this section.

6. Security Considerations

This document does not improve nor or reduce the security posture of
[RFC4862]. 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. Source Address Validation Improvement (SAVI) [RFC6620] also
protects against various attacks by on-link rogues.

7. IANA Considerations

None.

8. Acknowledgements

Thanks (in alphabetical order by first name) to Adrian Farrel, Benoit
Claise, Bernie Volz, Brian Haberman, Dmitry Anipko, Eric Levy-
Abegnoli, Eric Vyncke, Erik Nordmark, Fred Templin, Hilarie Orman,
Jouni Korhonen, Michael Sinatra, Ole Troan, Pascal Thubert, Ray
Hunter, Suresh Krishnan, Tassos Chatzithomaoglou, and Tim Chown 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 some of the use cases.

9. Normative References

[RFC1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", STD
51, RFC 1661, July 1994. 1994,
<http://www.rfc-editor.org/info/rfc1661>.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. 1998,
<http://www.rfc-editor.org/info/rfc2328>.

[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. 2005,
<http://www.rfc-editor.org/info/rfc3971>.

[RFC4086] Eastlake, Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086,
June 2005. 2005, <http://www.rfc-editor.org/info/rfc4086>.

[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, April 2006. 2006,
<http://www.rfc-editor.org/info/rfc4429>.

[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007. 2007, <http://www.rfc-editor.org/info/rfc4861>.

[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007. 2007,
<http://www.rfc-editor.org/info/rfc4862>.

[RFC6620] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS
SAVI: First-Come, First-Served Source Address Validation
Improvement for Locally Assigned IPv6 Addresses", RFC
6620, May 2012. 2012, <http://www.rfc-editor.org/info/rfc6620>.

Acknowledgements

Authors' Addresses

Rajiv Asati
Cisco Systems, Inc.
7025 Kit Creek road
Research Triangle Park, NC 27709-4987
USA

Email:
United States

EMail: rajiva@cisco.com
URI: http://www.cisco.com/

Hemant Singh
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
United States

Phone: +1 978 936 1622
Email:
EMail: shemant@cisco.com
URI: http://www.cisco.com/

Wes Beebee
Cisco Systems, Inc.
1414 Massachusetts Ave.
Boxborough, MA 01719
USA
United States

Phone: +1 978 936 2030
Email:
EMail: wbeebee@cisco.com
URI: http://www.cisco.com/
Carlos Pignataro
Cisco Systems, Inc.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
USA

Email:
United States

EMail: cpignata@cisco.com
URI: http://www.cisco.com/

Eli Dart
Lawrence Berkeley National Laboratory
1 Cyclotron Road, Berkeley, CA 94720
USA

Email:
United States

EMail: dart@es.net
URI: http://www.es.net/

Wesley George
Time Warner Cable
13820 Sunrise Valley Drive
Herndon, VA 20171
USA

Email:
United States

EMail: wesley.george@twcable.com