draft-ietf-6man-impatient-nud-01.txt   draft-ietf-6man-impatient-nud-02.txt 
6MAN WG E. Nordmark 6MAN WG E. Nordmark
Internet-Draft Cisco Systems, Inc. Internet-Draft Cisco Systems, Inc.
Updates: 4861 (if approved) I. Gashinsky Updates: 4861 (if approved) I. Gashinsky
Expires: September 13, 2012 Yahoo! Expires: January 2, 2013 Yahoo!
March 12, 2012 Jul 2012
Neighbor Unreachability Detection is too impatient Neighbor Unreachability Detection is too impatient
draft-ietf-6man-impatient-nud-01.txt draft-ietf-6man-impatient-nud-02.txt
Abstract Abstract
IPv6 Neighbor Discovery includes Neighbor Unreachability Detection. IPv6 Neighbor Discovery includes Neighbor Unreachability Detection.
That function is very useful when a host has an alternative, for That function is very useful when a host has an alternative, for
instance multiple default routers, since it allows the host to switch instance multiple default routers, since it allows the host to switch
to the alternative in short time. This time is 3 seconds after the to the alternative in short time. This time is 3 seconds after the
node starts probing by default. However, if there are no node starts probing by default. However, if there are no
alternatives, this is far too impatient. This document specifies alternatives, this is far too impatient. This document specifies
relaxed rules for Neighbor Discovery retransmissions that allows an relaxed rules for Neighbor Discovery retransmissions that allows an
skipping to change at page 1, line 39 skipping to change at page 1, line 39
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 13, 2012. This Internet-Draft will expire on January 2, 2013.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 3, line 34 skipping to change at page 3, line 34
However, when there is no alternative there are several benefits in However, when there is no alternative there are several benefits in
making NUD try probing for a longer time. One of those benefits is making NUD try probing for a longer time. One of those benefits is
to be more robust against transient failures, such as spanning tree to be more robust against transient failures, such as spanning tree
reconvergence and other layer 2 issues that can take many seconds to reconvergence and other layer 2 issues that can take many seconds to
resolve. Marking the NCE as unreachable in that case causes resolve. Marking the NCE as unreachable in that case causes
additional multicast on the network. Assuming there are IP packets additional multicast on the network. Assuming there are IP packets
to send, the lack of an NCE will result in multicast Neighbor to send, the lack of an NCE will result in multicast Neighbor
Solicitations every second instead of the unicast Neighbor Solicitations every second instead of the unicast Neighbor
Solicitations that NUD sends. Solicitations that NUD sends.
As a result IPv6 is operationally more brittle than IPv4. For IPv4 As a result IPv6 Neighbor Discovery is operationally more brittle
there is no mandatory time limit on the retransmission behavior for than IPv4 ARP. For IPv4 there is no mandatory time limit on the
ARP [RFC0826] which allows implementors to pick more robust schemes. retransmission behavior for ARP [RFC0826] which allows implementors
to pick more robust schemes.
The following constant values in [RFC4861] seem to have been made The following constant values in [RFC4861] seem to have been made
part of IPv6 conformance testing: MAX_MULTICAST_SOLICIT, part of IPv6 conformance testing: MAX_MULTICAST_SOLICIT,
MAX_UNICAST_SOLICIT, and RETRANS_TIMER. While such strict MAX_UNICAST_SOLICIT, and RETRANS_TIMER. While such strict
conformance testing seems consistent with [RFC4861], it means that we conformance testing seems consistent with [RFC4861], it means that we
need to update the standard if we want to allow IPv6 Neighbor need to update the standard if we want to allow IPv6 Neighbor
Discovery to be as operationally robust as ARP. Discovery to be as robust as ARP.
This document updates RFC 4861 to relax the retransmission rules. This document updates RFC 4861 to relax the retransmission rules.
Additional motivations for making IPv6 Neighbor Discovery as robust Additional motivations for making IPv6 Neighbor Discovery more robust
as ARP are covered in [I-D.gashinsky-v6nd-enhance]. in the face of degenerate conditions are covered in [RFC6583].
2. Definition Of Terms 2. Definition Of Terms
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Protocol Updates 3. Protocol Updates
Giving up after three packets spaced one second apart is only Giving up after three packets spaced one second apart is only
REQUIRED when there is an alternative, such as an additional default REQUIRED when there is an alternative, such as an additional default
route or a redirect. route or a redirect.
If implementations transmit more than MAX_*CAST_SOLICIT packets it If implementations transmit more than MAX_*CAST_SOLICIT packets it
SHOULD use (binary) exponential backoff of the retransmit timer. SHOULD use (binary) exponential backoff of the retransmit timer.
This is to avoid any significant load due to a steady background This is to avoid any significant load due to a steady background
level of retransmissions from implementations that try for a long level of retransmissions from implementations that try for a long
time. time.
However, even if there is no alternative, the protocol needs to be Even if there is no alternative, the protocol needs to be able to
able to handle the case when the link-layer address of the handle the case when the link-layer address of the destination has
destination has changed by switching to multicast Neighbor changed by switching to multicast Neighbor Solicitations at some
Solicitations at some point in time. point in time.
In order to capture all the cases above this document introduces a In order to capture all the cases above this document introduces a
new UNREACHABLE state in the conceptual model described in [RFC4861]. new UNREACHABLE state in the conceptual model described in [RFC4861].
A NCE in the UNREACHABLE state retains the link-layer address, and A NCE in the UNREACHABLE state retains the link-layer address, and
IPv6 packets continue to be sent to that link-layer address. But in IPv6 packets continue to be sent to that link-layer address. But in
the UNREACHABLE state the NUD Neighbor Solicitations are multicast, the UNREACHABLE state the NUD Neighbor Solicitations are multicast,
using a timeout that follows a (binary) exponential backoff. using a timeout that follows a (binary) exponential backoff.
In the places where RFC4861 says to to discard/delete the NCE after N In the places where RFC4861 says to to discard/delete the NCE after N
probes (Section 7.3, 7.3.3 and Appendix C) we will instead transition probes (Section 7.3, 7.3.3 and Appendix C) we will instead transition
skipping to change at page 5, line 46 skipping to change at page 5, line 46
That needs to be replaced by: That needs to be replaced by:
PROBE Retransmit timeout, Double timeout UNREACHABLE PROBE Retransmit timeout, Double timeout UNREACHABLE
N or more Send multicast NS N or more Send multicast NS
retransmissions. retransmissions.
UNREACHABLE Retransmit timeout Double timeout UNREACHABLE UNREACHABLE Retransmit timeout Double timeout UNREACHABLE
Send multicast NS Send multicast NS
The binary exponential backoff SHOULD be clamped at some reasonable The binary exponential backoff SHOULD be clamped at some reasonable
maximum retransmit timeout, such as 60 seconds. And if there is no maximum retransmit timeout, such as 60 seconds. If there is no IPv6
IPv6 packets sent using the UNREACHABLE NCE, then it makes sense to packets sent using the UNREACHABLE NCE, then it makes sense to stop
stop the retransmits of the multicast NS until either the NCE is the retransmits of the multicast NS until either the NCE is garbage
garbage collected, or there are IPv6 packets sent using the NCE. In collected or there are IPv6 packets sent using the NCE. The
essence the multicast NS and associated binary exponential backoff multicast NS and associated binary exponential backoff can be applied
can be conditioned on the continued use of the NCE to send IPv6 on the condition of the continued use of the NCE to send IPv6 packets
packets to the recorded link-layer address. to the recorded link-layer address.
A node MAY unicast the first few Neighbor Solicitation messages while A node MAY unicast the first few Neighbor Solicitation messages while
in UNREACHABLE state, but it MUST switch to multicast Neighbor in UNREACHABLE state, but it MUST switch to multicast Neighbor
Solicitations. Otherwise it would not detect a link-layer address Solicitations. Otherwise it would not detect a link-layer address
change for the target. change for the target.
4. Example Algorithm 4. Example Algorithm
This section is NOT normative, but specifies a simple implementation This section is NOT normative, but specifies a simple implementation
which conforms with this document. The implementation is described which conforms with this document. The implementation is described
skipping to change at page 7, line 21 skipping to change at page 7, line 21
configure are BACKOFF_MULTIPLE, MAX_UNICAST_SOLICIT and configure are BACKOFF_MULTIPLE, MAX_UNICAST_SOLICIT and
MAX_MULTICAST_SOLICIT. MAX_MULTICAST_SOLICIT.
It would be useful to have a maximum value for It would be useful to have a maximum value for
($BACKOFF_MULTIPLE^$solicit_attempt_num)*$RetransTimer so that the ($BACKOFF_MULTIPLE^$solicit_attempt_num)*$RetransTimer so that the
retransmissions are not too far apart. A value 60 seconds is retransmissions are not too far apart. A value 60 seconds is
consistent with DHCP. consistent with DHCP.
5. Acknowledgements 5. Acknowledgements
The comments from Thomas Narten and Philip Homburg have helped The comments from Thomas Narten, Philip Homburg, and Joel Jaeggli
improve this draft. have helped improve this draft.
6. Security Considerations 6. Security Considerations
Relaxing the retransmission behavior for NUD has no impact on Relaxing the retransmission behavior for NUD is belived to have no
security. In particular, it doesn't impact applying Secure Neighbor impact on security. In particular, it doesn't impact the application
Discovery [RFC3971]. Secure Neighbor Discovery [RFC3971].
7. IANA Considerations 7. IANA Considerations
This are no IANA considerations for this document. This are no IANA considerations for this document.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
skipping to change at page 8, line 7 skipping to change at page 8, line 7
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005. Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007. September 2007.
8.2. Informative References 8.2. Informative References
[I-D.gashinsky-v6nd-enhance]
Kumari, W., "Operational Neighbor Discovery Problems and
Enhancements.", draft-gashinsky-v6nd-enhance-00 (work in
progress), June 2011.
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or [RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37, address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982. RFC 826, November 1982.
[RFC6583] Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational
Neighbor Discovery Problems", RFC 6583, March 2012.
Authors' Addresses Authors' Addresses
Erik Nordmark Erik Nordmark
Cisco Systems, Inc. Cisco Systems, Inc.
510 McCarthy Blvd. 510 McCarthy Blvd.
Milpitas, CA, 95035 Milpitas, CA, 95035
USA USA
Phone: +1 408 527 6625 Phone: +1 408 527 6625
Email: nordmark@cisco.com Email: nordmark@cisco.com
 End of changes. 12 change blocks. 
31 lines changed or deleted 30 lines changed or added

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/