Internet DRAFT - draft-madanapalli-ipv6-periodic-rtr-advts
draft-madanapalli-ipv6-periodic-rtr-advts
Network Working Group S. Madanapalli
Internet-Draft LogicaCMG
Intended status: Standards Track B. Patil
Expires: February 5, 2007 Nokia
August 4, 2006
Recommendation to make periodic Router Advertisements in IPv6 optional
draft-madanapalli-ipv6-periodic-rtr-advts-00.txt
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Copyright (C) The Internet Society (2006).
Abstract
Periodic IPv6 router advertisements are a concern in mobile and
cellular networks in which the hosts are attached to the network and
access router but switch state to dormant mode in order to conserve
battery power. In addition the air interface is a resource that
should be used optimally and hence periodic router advertisements
that an access router would send should be limited. Transmission of
Periodic router advertisements to hosts on a link by a router should
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be optional. At the very least the interval between such router
advertisements should be configurable to a value that is
significantly higher than currently specified. This document
provides a recommendation for the periodic router advertisement
interval (MaxRtrAdvInterval) and router lifetime.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Adverse effects of frequent Periodic RAs . . . . . . . . . . . 3
3. Recommendations . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 7
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1. Introduction
[1] defines neighbor discovery procedures for IPv6 for router
discovery, prefix discovery, address resolution, neighbor
Unreachability detection and parameter discovery. [1] defines Router
Advertisements, which are sent either periodically or in response to
Router solicitations from a host. [1] recommends the interval between
periodic Router advertisements to be small enough such that the hosts
will be able to discover all routers on a link within the span of a
few minutes.
[1] also defines parameter values for various parameters. Two
specific parameters are considered within the scope of this document:
1. Router Lifetime during which a router acts as the default router
for a host. The current maximum recommended value for this
parameter is 150 minutes (9000 seconds).
2. MaxRtrAdvInterval: The maximum possible delay between two
consecutive periodic router advertisements. The current
recommended value is 30 minutes (1800 seconds).
Routers that implement the current recommendations would send the
periodic multicast router advertisements every 30 minutes, which can
be a significant problem in mobile/cellular network environments.
This document looks at the adverse effects of the current [1]
specification on mobile and cellular networks, resulting from
periodic multicast router advertisements and recommends that the
sending of such router advertisements be optional, i.e. it should be
possible to configure a router in specific environments or deployment
scenarios with periodic router advertisements switched off.
2. Adverse effects of frequent Periodic RAs
Mobile/cellular Networks like GPRS, 3G and WiMAX typically assign
long lived prefixes, and the default access routers (GGSN, PDSN, ASN
GW etc) for the hosts would typically be available for a long time on
a given link (possibly infinite). Generally there exists only one
default router at any given time on a given link for a host. The
host devices in these networks, i.e. the mobile nodes, have
constraints on battery power. To conserve battery life, mobile nodes
frequently enter idle or dormant mode. Typically a mobile node will
be in idle/dormant mode most of the time.
IPv6 capable mobile nodes that are attached to an access router and
are in idle/dormant mode will have to be awakened to deliver the
router advertisement. This incurs significant costs and has a
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negative impact on the battery lifetime of such devices. The mobile
node has to be paged and switched to a state, which allows it to
receive the router advertisement. Additionally bandwidth over the
air interface is used for transmission of such packets. From an
operational perspective, the periodic router advertisement in mobile
networks is detrimental to optimal use of the radio resources as well
as impacting battery power in mobile devices. The transmission and
delivery of periodic router advertisements to a mobile node which is
in dormant/idle mode at the expense of paging, allocating radio
resources and establishing a connection to the host is unnecessary.
Router advertisement is useful at the MN if it relied on it as the
means to detect movement. However in many of the cellular networks,
movement detection is not done at the IP layer. If an MN needs a
router advertisement for any reason, it can always solicit for it.
And if the network needs to deliver a router advertisement to a host
to convey changes, it can do so as well without having to depend on
periodic RAs.
3. Recommendations
In order to optimize IPv6 behavior for deployment in mobile/cellular
environments this document recommends the following changes to the ND
[1] specification:
o The transmission of periodic router advertisements should be
optional. Access routers in mobile/cellular environments should
have the option of switching off the sending of periodic RAs to
hosts that are currently attached to the AR. The host served by
such an AR should not expect to receive unsolicited RAs.
o The maximum router lifetime be increased beyond the current max
value of 9000 seconds.
o The maximum value of the parameter MaxRtrAdvInterval be greater
than 1800 seconds.
The changes recommended to be made for ND are as follows:
1. Router Life Time: Allow the setting of this parameter in the
router advertisement to 65535. This would imply that the router
is available as the default router for infinity. This value can
be updated by the subsequent router advertisements with a
specific value.
2. MaxRtrAdvInterval: Allow the parameter to be configurable with a
value set to 0 (zero). This indicates that the periodic
multicast router advertisements are switched off on this
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interface. In case no value is specified for this parameter,
then the MaxRtrAdvInterval should be computed as indicated below:
MaxRtrAdvInterval = 0.33 * min of {Router Lifetime, Prefix
lifetime}
This allows a host to receive three router advertisements
before either Router Lifetime, or Prefix lifetime expires so
that if there is any pocket loss in transmission it can be
alleviated.
3. Recommend that mobile nodes proactively solicit router
advertisements in any of the following cases:
The threshold of the router lifetime is 0.75 *
AdvDefaultLifetime and is triggered.
The threshold of the prefix lifetime is 0.75 *
AdvValidLifetime and is triggered.
4. Security Considerations
This document specifies a few amendments to the [1] and does not
introduce any new security threats. To reduce the threats associated
with ND it is recommended that deployments use SeND [2] to secure
neighbor discovery messages.
5. IANA Considerations
This document has no actions for IANA.
6. Acknowledgements
TBD
7. References
[1] "Neighbor Discovery for IP version 6 (IPv6),
draft-ietf-ipv6-2461bis-07.txt(work in progress)", May 2006.
[2] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
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Authors' Addresses
Syam Madanapalli
LogicaCMG
125 Yemlur Main Road
Off Airport Road
Bangalore 560037
India
Email: smadanapalli at gmail dot com
Basavaraj Patil
Nokia
6000 Connection Drive
Irving, TX 75039
USA
Email: basavaraj.patil@nokia.com
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