Network Working Group S. Krishnan Internet-Draft Ericsson Intended status: Standards Track G. Daley Expires:
October 6, 2008January 3, 2009 NetStar Networks April 4,July 2, 2008 Simple procedures for Detecting Network Attachment in IPv6 draft-ietf-dna-simple-00draft-ietf-dna-simple-01 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 6, 2008. Copyright Notice Copyright (C) The IETF Trust (2008).January 3, 2009. Abstract Detecting Network Attachment allows hosts to assess if its existing addressing or routing configuration is valid for a newly connected network. This document provides simple procedures for detecting network attachment in IPv6 hosts, and procedures for routers to support such services. Table of Contents 1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. DNA Roles . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2. Applicability . . . . . . . . . . . . . . . . . . . . . . 4 3. Host OperationsTerminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1.4. Host data structuresOperations . . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Link-Layer Indication4.1. Host data structures . . . . . . . . . . . . . . . . . . . 5 3.3. Optimistic DAD4.2. Steps involved in detecting link change . . . . . . . . . 5 4.3. Link-Layer Indication . . . . . . . . . . . . . . . . . . 5 22.214.171.124. Sending RS and NS probes . . . . . . . . . . . . . . . . . 6 126.96.36.199. Response Gathering . . . . . . . . . . . . . . . . . . . . 6 188.8.131.52. Further Host Operations . . . . . . . . . . . . . . . . . 7 184.108.40.206. Recommended retransmission behavior . . . . . . . . . . . 7 4.8 5. Router Operations . . . . . . . . . . . . . . . . . . . . . . 8 5.6. Constants . . . . . . . . . . . . . . . . . . . . . . . . . . 8 6.9 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 8.10 9. Security Considerations . . . . . . . . . . . . . . . . . . . 9 9.10 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 10.11 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 10.1.11.1. Normative References . . . . . . . . . . . . . . . . . . . 11 10.2.11.2. Informative References . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 1112 Intellectual Property and Copyright Statements . . . . . . . . . . 13 1. Requirements notation 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]. 2. Introduction Hosts require procedures to simply and reliably identify if they have moved to a different IP network to the one which they have been recently connected. In order to detect change, router and neighbour discovery messages are used to collect reachability and configuration information. This information is used to detect whether the existing router and address prefixes are likely to be present. This document incorporates feedback from host and router operating systems implementors, which seeks to make implementation and adoption of IPv6 change detection procedures simple for general use. The goal of this document is to specify a simple procedure for detecting network attachment (Simple DNA) that has the following characteristics. o Routers do not have to be modified to support this scheme. o Handle only the simplest and most likely use cases. o Work at least as quickly as standard neighbor discovery. o False positives are not acceptable. A host should not conclude that there is no link change when there is one o False negatives are acceptable. A host can conclude that there is a link change when there is none 2.1. DNA Roles Detecting Network Attachment is performed by hosts by sending IPv6 neighbour discovery and router discovery messages to routers after connecting to a network. It is desirable that routers adopt procedures which allow for fast unicast Router Advertisement (RA) messages. Routers that follow the standard neighbor discovery procedure described in [RFC4861] will delay the router advertisement by a random period between 0 and MAX_RA_DELAY_TIME (defined to be 500ms) as described in Section 6.2.6 of .[RFC4861]. This delay can be significant and may result in service disruption. Please note that support for fast unicast RAs is not necessary since the simple dna procedure can continue to work using the NS/NA exchange, which will complete earlier than the RA arrives. The host detects that the link-layer may have changed, and then simultaneously probes the network with Router Solicitations (RSs) and Neighbour Solicitations (NSs). The host uses advertisements to determine if the routers it currently has configured are still available. 2.2. Applicability There are a series of assumptions about the network environment which underpin these procedures. o The combination of the link layer address and the link local IPv6 address of a router is unique across links. o Hosts receive indications when a link-layer comes up. Without this, they would not know when to commence the DNA procedure. If these assumptions do not hold, host change detection systems will not function optimally. In that case, they may occasionally detect change spuriously, or experience some delay in detecting network attachment. The delays so experienced will be no longer than those caused by following the standard neighbor discovery procedure described in .[RFC4861]. If systems do not meet these assumptions or if systems seek deterministic change detection operations they are directed to follow the complete dna procedure as defined in .[I-D.ietf-dna-protocol]. 3. Terminology +---------------------+---------------------------------------------+ | Term | Definition | +---------------------+---------------------------------------------+ | Valid IPv6 address | An IPv6 address configured on the node that | | | has a valid lifetime greater than zero. | | | | | Operable IPv6 | An IPv6 address configured on the node that | | address | can be used safely on the current link. | +---------------------+---------------------------------------------+ Table 1: Simple DNA Terminology 4. Host Operations When a host has an existing configuration for IP address prefixes and next hop routing, it may be disconnected from its link-layer, and then subsequently reconnect the link-layer on the same interface. When the link-layer becomes available again, it is important to determine whether the existing addressing and routing configuration are still valid. In order to determine this, the host performs the detecting network attachment procedure. 220.127.116.11. Host data structures In order to correctly perform the procedure described in this document the host needs to maintain a data structure called the Simple DNA address table (SDAT). Each entry in the SDAT table consists of at least the following parametersparameters. o IPv6 address and its related parameters like valid lifetime o Prefix from which the address was formed o Link local IPv6 address of the router that advertised the prefix o Link layer (MAC) address of the router that advertised the prefix o DHCP Unique IDentifier (DUID) in case DHCPv6 was used to acquire the address 4.2. Steps involved in detecting link change The steps involved in basic detection of network attachment are: o Link-Layer Indication o Optimistic DAD oSending RS and NS probes o Response gathering and assessment These steps are described below. 18.104.22.168. Link-Layer Indication In order to start Detection of network attachment procedures, a host typically requires a link-layer indication that the medium has become available . When[RFC4957]. After the indication is received, the host marksconsiders all currently configured (non-tentative) IP addresses to Optimistic state . 3.3. Optimistic DAD All Router Solicitations and unicast Neighbour Solicitations sent for DNA purposes while addresses are in optimistic state SHOULD include the Tentative Option . This allows for DAD-safe transmission of unicast response to solicitation, even if the router has no existing Neighbour Cache entry foras deprecated until the solicitor. 3.4.change detection process completes. 4.4. Sending RS and NS probes When a host receives a link-layer "up" indication, it SHOULD immediately send both a Router Solicitation and if it retains at least one valid IPv6 address, one or more unicast Neighbor Solicitations. The Router Solicitation is sent to the All-routers multicast address containing one ofusing a link-local address as the host's optimistic unicastsource address . If[RFC4861]. Even if the host is in possession of more than one valid IPv6 address, it MUST send only one router solicitation using any one of itsa valid IPv6 addresseslink-local address as the source address..address. For the purpose of sending neighbor solicitations to previous routers, the host first needs to pick a subset of operable IPv6 addresses (candidate set) that it wishes to use. How this subset of addresses is picked is based on host configuration. e.g. The host may select configured addresses from each of zero, one or two previously connected links. If the addresses obtained from a previous router are no longer valid, the host does include these addresses in the candidate set for NS based probing. For each of the addresses in the candidate set, the host looks up the SDAT to find out the link local and MAC addresses of the router that advertised the prefix used to form the address. It then sends an unicast Neighbor Solicitations to each router's link local address it obtained from the lookup on the SDAT. The host SHOULD NOT send unicast Neighbor Solicitations to a test node corresponding to an IPv6 address that is no longer valid. Please note that the Neighbour Solicitations SHOULD be sent in parallel with the Router Solicitations. Since sending NSs is just an optimization, doing the NSs and RSs in parallel ensures that the procedure does not run slower than it would if it only used an RS. Be aware that each unicast solicitation which is not successful may cause packet flooding in bridged networks, if the networks are not properly configured. This is further described in Section 6.7. Where flooding may cause performance issues within the LAN, host SHOULD limit the number of unicast solicitations. 22.214.171.124. Response Gathering When a responding Neighbour Advertisement is received from a test node, the host MUST verify that both the IPv6 and link layer (MAC) addresses of the test node match the expected values before utilizing the configuration associated with the detected network (prefixes, MTU etc.). On reception of a Router Advertisement which contains prefixes which intersect with those previously advertised by a known router, the host utilizes the configuration associated with the detected network. When the host receives a router advertisement containing only prefixes which are disjoint from known advertised prefixes, the host MUST determine whether the solicited router advertisement corresponds to any of the routers probed via NS. If it does, then the host SHOULD conclude that the IPv6 addresses corresponding to that router are no longer valid. Since any NS probes to that router will no longer provide useful information, probing of that router SHOULD be aborted. Where the conclusions obtained from the Neighbor Solicitation/ Advertisement from a given router and the RS/RA exchange with the same router differ, the results obtained from the RS/RA will be considered definitive. 126.96.36.199. Further Host Operations Operations subsequent to detecting network attachment depend upon whether change was detected. After confirming the reachability of the associated router using an NS/NA pair, the host should assess whether it can use the existing configured addresses using Optimistic Duplicate Address Detection . Also,performs the following steps o The host SHOULD rejoin any solicited nodes' multicast groups for addresses it continues to use, anduse. o The host SHOULD select a default router .as described in [RFC4861]. If the host has determined that there has been no link change, it SHOULD NOT perform duplicate address detection on the addresses that have been confirmed to be operable. If the NS based probe with a router did not complete or if the RS based probe on the same router completed with different prefixes than the ones in the SDAT the host MUST unconfigure all the existing addresses received from the given router, and MUST begin address configuration techniques, as indicated in the received Router Advertisement . 3.7.[RFC4861][RFC4862]. 4.7. Recommended retransmission behavior In situations where Neighbor Solicitation probes and Router Solicitation probes are used on the same link, it is possible that the NS probe will complete successfully, and then the RS probe will complete later with a different result. If this happens, the implementation SHOULD abandon the results obtained from the NS probe of the router that responded to the RS and the implementation SHOULD behave as if the NS probe did not successfully complete. If the confirmed address was assigned manually, the implementation SHOULD NOT unconfigure the manually assigned address and SHOULD log an error about the mismatching prefix. Where the NS probe does not complete successfully, it usually implies that the host is not attached to the network whose configuration is being tested. In such circumstances, there is typically little value in aggressively retransmitting unicast neighbor solicitations that do not elicit a response. Where unicast Neighbor Solicitations and Router Solicitations are sent in parallel, one strategy is to forsake retransmission of Neighbor Solicitations and to allow retransmission only of Router Solicitations or DHCPv6. In order to reduce competition between unicast Neighbor Solicitations and Router Solicitations and DHCPv6 retransmissions, a DNAv6 implementation that retransmits may utilize the retransmission strategy described in the DHCPv6 specification [RFCDHCPv6], scheduling DNAv6 retransmissions between Router Solicitation or DHCPv6 retransmissions. If a response is received to any unicast Neighbor Solicitation, Router Solicitation or DHCPv6 message, pending retransmissions MUST be canceled. A Simple DNA implementation SHOULD NOT retransmit a Neighbor Solicitation more than twice. To provide damping in the case of spurious Link Up indications, the host SHOULD NOT perform the the Simple DNA procedure more than once a second. 4.5. Router Operations Hosts checking their network attachment are unsure of their address status, and may be using Tentative link-layer addressing information in their router or neighbour solicitations. A router which desires to support hosts' DNA operations MUST process Tentative Options from unicast source addressed Router and Neighbour Solicitations, as described in . 5.[I-D.ietf-dna-tentative]. 6. Constants These constants are described as in .[I-D.ietf-dna-protocol]. UNICAST_RA_INTERVAL Definition: The interval corresponding to the maximum average rate of Router Solicitations that the router is prepared to service with unicast responses. This is the interval at which the token bucket controlling the unicast responses is replenished. Value: 50 milliseconds MAX_UNICAST_RA_BURST Definition: The maximum size burst of Router Solicitations that the router is prepared to service with unicast responses. This is the maximum number of tokens allowed in the token bucket controlling the unicast responses. Value: 20 SEND_NA_GRACE_TIME Definition: An optional period to wait after Neighbour Solicitation before adopting a non-SEND RA's link change information. Value: 40 milliseconds 6.7. Open Issues This section documents issues that are still outstanding within the document, and the simple DNA solution in general. Rate limitation for solicitations. Hosts MAY implement hysteresis mechanisms to pace solicitations where necessary to prevent damage to a particular medium. Implementors should be aware that when such hysteresis is triggered, Detecting Network Attachment may be slowed, which may affect application traffic. 7.8. IANA Considerations There are no changes to IANA registries required in this document 8.9. Security Considerations When providing fast responses to router solicitations, it is possible to cause collisions with other signaling packets on contention based media. This can cause repeated packet loss or delay when multiple routers are present on the link. As such the fast router advertisement system is NOT RECOMMENDED in this form for media which are susceptible to collision loss. Such environments may be better served using the procedures defined in .[I-D.ietf-dna-protocol]. A host may receive Router Advertisements from non SEND devices, after receiving a link-layer indications. While it is necessary to assess quickly whether a host has moved to another network, it is important that the host's current secured SEND [RFC3971] router information is not replaced by an attacker which spoofs an RA and purports to change the link. As such, the host SHOULD send a Neighbour Solicitation to the existing SEND router upon link-up indication as described above in Section 188.8.131.52. The host SHOULD then ensure that unsecured router information does not cause deletion of existing SEND state, within MIN_DELAY_BETWEEN_RAS, in order to allow for a present SEND router to respond. The host MAY delay SEND_NA_GRACE_TIME after transmission before adopting a new default router, if it is operating on a network where there is significant threat of RA spoofing. Even if SEND signatures on RAs are used, it may not be immediately clear if the router is authorized to make such advertisements. As such, a host SHOULD NOT treat such devices as secure until and unless authorization delegation discovery is successful. It is easy for hosts soliciting without SEND to deplete a SEND router's fast advertisement token buckets, and consume additional bandwidth. As such, a router MAY choose to preserve a portion of their token bucket to serve solicitations with SEND signatures. 9.10. Acknowledgments This document is the product of a discussion between the authors had with Bernard Aboba, Thomas Narten, Erik Nordmark and Dave Thaler at IETF 69. The authors would like to thank them for clearly detailing the requirements of the solution and the goals it needed to meet and for helping to explore the solution space. The authors would like to thank the authors and editors of the complete DNA specification for detailing the overall problem space and solutions. The authors would like to thank Jari Arkko for driving the evolution of a simple and probabilistic DNA solution. The authors would like to thank Bernard Aboba, Thomas Narten, Sathya NarayanNarayan, Julien Laganier, Domagoj Premec, Jin Hyeock-Choi, Alfred Hoenes and Frederic Rossi for performing reviews on the document and providing valuable comments to drive the document forward. 10.11. References 10.1.11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4861] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 4861, December 1998. [RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005. [I-D.ietf-dna-tentative] Daley, G., Nordmark, E., and N. Moore, "Tentative Options for IPv6 Neighbour Discovery", draft-ietf-dna-tentative-01 (work in progress), July 2007.  Moore, N., "Optimistic Duplicate Address Detection for IPv6", RFC RFC4429, April 2006. [I-D.ietf-dna-protocol] Narayanan, S., "Detecting Network Attachment in IPv6 Networks (DNAv6)", draft-ietf-dna-protocol (work in progress), June 2007. 10.2.11.2. Informative References [RFC4957] Krishnan, S., Montavont, N., Njedjou, E., Veerepalli, S., and A. Yegin, "Link-Layer Event Notifications for Detecting Network Attachments", RFC 4957, August 2007. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, September 2007. Authors' Addresses Suresh Krishnan Ericsson 8400 Decarie Blvd. Town of Mount Royal, QC Canada Phone: +1 514 345 7900 x42871 Email: email@example.com Greg Daley NetStar Networks Level 9/636 St Kilda Rd Melbourne, Victoria 3004 Australia Phone: +61 405 494849 Email: firstname.lastname@example.org Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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