Internet DRAFT - draft-krishnan-6man-resilient-rs
draft-krishnan-6man-resilient-rs
6man Working Group S. Krishnan
Internet-Draft Ericsson
Intended status: Standards Track D. Anipko
Expires: January 17, 2013 D. Thaler
Microsoft
July 16, 2012
Packet loss resiliency for Router Solicitations
draft-krishnan-6man-resilient-rs-01
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. Furthermore, on some links, unsolicited multicast
Router Advertisements are never sent and the mechanism in this
document is intended to work even in such scenarios.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on January 17, 2013.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions used in this document . . . . . . . . . . . . . 3
2. Proposed algorithm . . . . . . . . . . . . . . . . . . . . . . 4
3. Open Issue . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5
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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.
The generic scenario is that the interface on the host comes up
before it gets access to a router. Examples include:
a. 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.
b. Access networks/links that turn off periodic RAs and only send
RAs in response to RSs. In this case, if the link between the AP
and the host comes up before the link between the AP and the
Controller/Router, the host will never be able to connect.
c. Links that are not multicast capable. In this case, sending an
RA can only be triggered by an RS (as is the case, for instance,
on ISATAP [RFC5214] links).
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. In general, the delay may be unacceptable in some
scenarios.
1.1. Conventions used in this document
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 [SOLMAXRT].
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] [SOLMAXRT].
3. Open Issue
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.
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4. IANA Considerations
This document does not require any IANA actions.
5. Security Considerations
This document does not present any additional security issues beyond
those discussed in [RFC4861].
6. Acknowledgements
The author would like to thank Steve Baillargeon, and Erik Kline for
their reviews and suggestions that made this document better.
7. References
7.1. 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.
[SOLMAXRT]
Droms, R., "Modification to Default Value of SOL_MAX_RT",
draft-droms-dhc-dhcpv6-solmaxrt-update-02 (work in
progress), January 2012.
7.2. Informative References
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
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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
Microsoft
One Microsoft Way
Redmond, WA
USA
Phone: +1 425 703 7070
Email: danipko@microsoft.com
Dave Thaler
Microsoft
One Microsoft Way
Redmond, WA
USA
Email: dthaler@microsoft.com
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