Neighbor Unreachability Detection Is Too Impatient
RFC 7048
Document | Type |
RFC - Proposed Standard
(January 2014; No errata)
Updates RFC 4861
|
|
---|---|---|---|
Authors | Erik Nordmark , Igor Gashinsky | ||
Last updated | 2015-10-14 | ||
Replaces | draft-nordmark-6man-impatient-nud | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized bibtex | ||
Reviews | |||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Ole Trøan | ||
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 IANA Actions |
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 packets to send, the lack of an NCE will result in multicast Neighbor Solicitations being sent (to the solicited-node multicast address) every second instead of the unicast Neighbor Solicitations that NUDShow full document text