Neighbor Unreachability Detection Is Too Impatient
RFC 7048
| Document | Type |
RFC - Proposed Standard
(January 2014; No errata)
Updates RFC 4861
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Replaces | draft-nordmark-6man-impatient-nud | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Reviews | |||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Ole Troan | ||
| Shepherd write-up | Show (last changed 2013-02-18) | ||
| IESG | IESG state | RFC 7048 (Proposed Standard) | |
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Brian Haberman | ||
| IESG note | Ole Troan is the document shepherd. | ||
| Send notices to | (None) | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | No IC | ||
Internet Engineering Task Force (IETF) E. Nordmark
Request for Comments: 7048 Arista Networks
Updates: 4861 I. Gashinsky
Category: Standards Track Yahoo!
ISSN: 2070-1721 January 2014
Neighbor Unreachability Detection Is Too Impatient
Abstract
IPv6 Neighbor Discovery includes Neighbor Unreachability Detection.
That function is very useful when a host has an alternative neighbor
-- for instance, when there are multiple default routers -- since it
allows the host to switch to the alternative neighbor in a short
time. By default, this time is 3 seconds after the node starts
probing. However, if there are no alternative neighbors, this
timeout behavior is far too impatient. This document specifies
relaxed rules for Neighbor Discovery retransmissions that allow an
implementation to choose different timeout behavior based on whether
or not there are alternative neighbors. This document updates RFC
4861.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7048.
Nordmark & Gashinsky Standards Track [Page 1]
RFC 7048 NUD Is Too Impatient January 2014
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
2. Definition of Terms .............................................3
3. Protocol Updates ................................................3
4. Example Algorithm ...............................................6
5. Acknowledgements ................................................7
6. Security Considerations .........................................8
7. References ......................................................8
7.1. Normative References .......................................8
7.2. Informative References .....................................8
1. Introduction
IPv6 Neighbor Discovery [RFC4861] includes Neighbor Unreachability
Detection (NUD), which detects when a neighbor is no longer
reachable. The timeouts specified for NUD are very short (by
default, three transmissions spaced one second apart). These short
timeouts can be appropriate when there are alternative neighbors to
which the packets can be sent -- for example, if a host has multiple
default routers in its Default Router List or if the host has a
Neighbor Cache Entry (NCE) created by a Redirect message. In those
cases, when NUD fails, the host will try the alternative neighbor by
redoing the next-hop selection. That implies picking the next router
in the Default Router List or discarding the NCE created by a
Redirect message, respectively.
The timeouts specified in [RFC4861] were chosen to be short in order
to optimize scenarios where alternative neighbors are available.
However, when there is no alternative neighbor, there are several
benefits to making NUD probe for a longer time. One benefit is to
make NUD more robust against transient failures, such as spanning
Nordmark & Gashinsky Standards Track [Page 2]
RFC 7048 NUD Is Too Impatient January 2014
tree reconvergence and other layer 2 issues that can take many
seconds to resolve. Marking the NCE as unreachable, in that case,
causes additional multicast on the network. Assuming there are IP
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