Internet DRAFT - draft-ietf-6man-resilient-rs
draft-ietf-6man-resilient-rs
6man Working Group S. Krishnan
Internet-Draft Ericsson
Updates: 4861 (if approved) D. Anipko
Intended status: Standards Track Unaffiliated
Expires: October 11, 2015 D. Thaler
Microsoft
April 9, 2015
Packet loss resiliency for Router Solicitations
draft-ietf-6man-resilient-rs-06
Abstract
When an interface on a host is initialized, the host transmits Router
Solicitations in order to minimize the amount of time it needs to
wait until the next unsolicited multicast Router Advertisement is
received. In certain scenarios, these router solicitations
transmitted by the host might be lost. This document specifies a
mechanism for hosts to cope with the loss of the initial Router
Solicitations.
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 of the Internet Engineering
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This Internet-Draft will expire on October 11, 2015.
Copyright Notice
Copyright (c) 2015 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
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 2
2. Proposed algorithm . . . . . . . . . . . . . . . . . . . . . 4
2.1. Stopping the retransmissions . . . . . . . . . . . . . . 4
3. Configuring the use of retransmissions . . . . . . . . . . . 5
4. Known Limitations . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
As specified in [RFC4861], when an interface on a host is
initialized, in order to obtain Router Advertisements quickly, a host
transmits up to MAX_RTR_SOLICITATIONS (3) Router Solicitation
messages, each separated by at least RTR_SOLICITATION_INTERVAL (4)
seconds. In certain scenarios, these router solicitations
transmitted by the host might be lost. e.g. The host is connected to
a bridged residential gateway over Ethernet or WiFi. LAN
connectivity is achieved at interface initialization, but the
upstream WAN connectivity is not active yet. In this case, the host
just gives up after the initial RS retransmits.
Once the initial RSs are lost, the host gives up and assumes that
there are no routers on the link as specified in Section 6.3.7 of
[RFC4861]. The host will not have any form of Internet connectivity
until the next unsolicited multicast Router Advertisement is
received. These Router Advertisements are transmitted at most
MaxRtrAdvInterval seconds apart (maximum value 1800 seconds). Thus
in the worst case scenario a host would be without any connectivity
for 30 minutes. This delay may be unacceptable in some scenarios.
1.1. Conventions used in this document
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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].
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2. Proposed algorithm
To achieve resiliency to packet loss, the host needs to continue
retransmitting the Router Solicitations until it receives a Router
Advertisement, or until it is willing to accept that no router
exists. If the host continues retransmitting the RSs at
RTR_SOLICITATION_INTERVAL second intervals, it may cause excessive
network traffic if a large number of such hosts exists. To achieve
resiliency while keeping the aggregate network traffic low, the host
can use some form of exponential backoff algorithm to retransmit the
RSs.
Hosts complying to this specification MUST use the exponential
backoff algorithm for retransmits that is described in Section 14 of
[RFC3315] in order to continuously retransmit the Router
Solicitations until a Router Advertisement is received. The hosts
SHOULD use the following variables as input to the retransmission
algorithm:
IRT 4 seconds
MRT 3600 seconds
MRC 0
MRD 0
The initial value IRT was chosen to be in line with the current
retransmission interval (RTR_SOLICITATION_INTERVAL) that is specified
by [RFC4861] and the maximum retransmission time MRT was chosen to be
in line with the new value of SOL_MAX_RT as specified by [RFC7083].
This is to ensure that the short term behavior of the RSs is similar
to what is experienced in current networks, and longer term
persistent retransmission behavior trends towards being similar to
that of DHCPv6 [RFC3315] [RFC7083].
2.1. Stopping the retransmissions
On multicast-capable links, the hosts following this specification
SHOULD stop retransmitting the RSs when Router Discovery is
successful (i.e. an RA with a non-zero Router Lifetime that results
in a default route is received). If an RA is recieved from a router
and it does not result in a default route (i.e. Router Lifetime is
zero) the host MUST continue retransmitting the RSs.
On non-multicast links, the hosts following this specification MUST
continue retransmitting the RSs even after an RA that results in a
default route is received. This is required because, in such links,
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sending an RA can only be triggered by an RS. Please note that such
links have special mechanisms for sending RSes as well. e.g. The
mechanism specified in Section 8.3.4. of ISATAP [RFC5214] unicasts
the RSes to specific routers.
3. Configuring the use of retransmissions
Implementations of this specification are encouraged to provide a
configuration option to enable or disable potentially infinite RS
retransmissions. If a configuration option is provided, it MUST
enable RS retransmissions by default. Providing an option to enable/
disable retransmissions on a per-interface basis allows network
operators to configure RS behavior most applicable to each connected
link.
4. Known Limitations
When an IPv6-capable host attaches to a network that does not have
IPv6 enabled, it transmits 3 (MAX_RTR_SOLICITATIONS) Router
Solicitations as specified in [RFC4861]. If it receives no Router
Advertisements, it assumes that there are no routers present on the
link and it ceases to send further RSs. With the mechanism specified
in this document, the host will continue to retransmit RSs
indefinitely at the rate of approximately 1 RS per hour. It is
unclear how to differentiate between such a network with no IPv6
routers and a link where an IPv6 router is temporarily unreachable
but could become reachable in the future.
5. IANA Considerations
This document does not require any IANA actions.
6. Security Considerations
This document does not present any additional security issues beyond
those discussed in [RFC4861] and those RFCs that update [RFC4861].
7. Acknowledgements
The authors would like to thank Steve Baillargeon, Erik Kline, Andrew
Yourtchenko, Ole Troan, Erik Nordmark, Lorenzo Colitti, Thomas
Narten, Ran Atkinson, Allison Mankin, Les Ginsberg, Brian Carpenter,
Barry Leiba, Brian Haberman, Spencer Dawkins, Alia Atlas, Stephen
Farrell and Mehmet Ersue for their reviews and suggestions that made
this document better.
8. References
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8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC7083] Droms, R., "Modification to Default Values of SOL_MAX_RT
and INF_MAX_RT", RFC 7083, November 2013.
8.2. Informative References
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
Authors' Addresses
Suresh Krishnan
Ericsson
8400 Decarie Blvd.
Town of Mount Royal, QC
Canada
Phone: +1 514 345 7900 x42871
Email: suresh.krishnan@ericsson.com
Dmitry Anipko
Unaffiliated
Phone: +1 425 442 6356
Email: dmitry.anipko@gmail.com
Dave Thaler
Microsoft
One Microsoft Way
Redmond, WA
USA
Email: dthaler@microsoft.com
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