Network Working Group J. Korhonen
Internet-Draft Nokia Siemens Networks
Intended status: Informational February 9, 2009
Expires: August 13, 2009
Proxy Mobile IPv6 Mobility Session Redirection Problem Statement
draft-korhonen-netext-redirect-ps-00.txt
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Abstract
This document discusses a Proxy Mobile IPv6 mobility session
redirection functionality at the Proxy Mobile IPv6 base protocol
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level. The redirection functionality would allow a Local Mobility
Anchor to redirect the Mobile Access Gateway during the Proxy Binding
Update and Acknowledgement exchange to an alternative Local Mobility
Anchor. The benefit of redirection at the protocol level is that it
removes the dependence on having such functionality provided by the
Authentication, Authorization and, Accounting elements or the Domain
Name System in a Proxy Mobile IPv6 Domain. Furthermore, doing the
redirection at the base protocol level reduces the amount of
signaling, unnecessary costly setup of mobility sessions and
unnecessary costly interactions with backend systems.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Redirection Approaches . . . . . . . . . . . . . . . . . . . . 4
4. Redirection Scenarios . . . . . . . . . . . . . . . . . . . . . 4
4.1. Redirection During the Initial Attach . . . . . . . . . . . 4
4.2. Redirection of an Active IP Mobility Session . . . . . . . 5
5. Proxy Mobile IPv6 Domain Considerations . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
This document discusses a mobility session redirection functionality
for the Proxy Mobile IPv6 (PMIPv6) protocol. The redirection
functionality would allow a Local Mobility Anchor (LMA) to redirect
the Mobile Access Gateway (MAG) during the Proxy Binding Update (PBU)
and the Proxy Binding Acknowledgement (PBA) exchange to an
alternative LMA. The benefit of redirection at the protocol level is
that it removes the dependence on having such functionality provided
by the Authentication, Authorization and, Accounting (AAA) elements
or the Domain Name System (DNS) in a PMIPv6 Domain. Furthermore,
doing the redirection at the base protocol level reduces the amount
of signaling, unnecessary costly setup of mobility sessions and
unnecessary costly interactions with backend systems.
The redirection during the initial attach and the exchange of PBU/PBA
messages seems to be the most natural place for redirection, because
the mobility session setup is still in progress. Therefore, the
redirection during the initial attach is also the main problem
interest area of this document. The redirection of an active
mobility session can be seen as a handover between LMAs.
Accomplishing a handover between LMAs and maintaining the active
mobility session, which may even include moving the Home Network
Prefix (HNP) to a new topological location in the network, can be
really challenging. Therefore, the redirection of an active mobility
session is the secondary problem interest area of this document.
The following sections evaluate existing solutions for redirection
that may be used with PMIPv6. This document also briefly describes
few use cases where redirection would be useful, and finally
describes deployment consideration within a PMIPv6 Domain when
redirection is used.
2. Terminology
In addition to the terminology defined in RFC 5213 [RFC5213], the
following terminology is also used:
rfLMA
The LMA which receives the PBU from a MAG and decides to redirect
the IP mobility session, and forwards the PBU to the target LMA
(r2LMA).
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r2LMA
The LMA to which a MAG was redirected to. During the redirection,
the PBA is possibly sent to the MAG from this LMA.
3. Redirection Approaches
The dependency on DNS for redirection may not be deterministic enough
from the PMIPv6 Domain point of view, for example in cases where MAGs
cache DNS responses. DNS based approach is also applicable only
during the initial attach. Furthermore, globally deployed DNS has
unpredictable latencies on dynamic DNS updates that again make DNS
suboptimal tool for redirection. Using AAA for redirection is also
another possibility. However, relying on the AAA infrastructure
would mean, in most cases, unnecessary updates to a remote Policy
Store and subsequent Policy Profile downloads before and after
redirection. Compared to DNS based approach, the AAA infrastructure
would allow initiating the redirection of an active mobility session.
Another redirection approach would be utilizing Home Agent Switch
[RFC5142] type of solution, which appears to be suitable especially
initiating the redirection of an active mobility session. The
drawback of this approach during the initial attach is increased
signaling. One additional roundtrip is required to inform the MAG of
a LMA redirection, one roundtrip to remove the existing binding on
the old rfLMA, and one roundtrip to establish a new mobility session
at the target r2LMA. Also, there is no guarantee that the mobility
session continuity can be preserved. Furthermore, this approach
would mean unnecessary creation of a "temporary" state in the rfLMA
and unnecessary interactions with the backend systems.
Based on the above observations, a more efficient redirection
mechanism can be justified that would be part of the PMIPv6 base
protocol and independent of external supporting infrastructures. The
details of how a LMA determines the redirection and possibly the
communication between LMAs in a PMIP6 Domain to maintain a list of
available LMAs is outside the scope of this document.
4. Redirection Scenarios
4.1. Redirection During the Initial Attach
This is the basic use case for the redirection functionality. A MAG
sends an initial PBU for establishing a mobility session to a known
LMA address within the PMIPv6 Domain. The MAG may find out the "well
known" IP address or addresses of the LMA through various PMIPv6
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bootstrapping mechanisms [I-D.ietf-dime-pmip6]
[I-D.korhonen-netlmm-lma-discovery]. The MAG receives the PBA from
the r2LMA and will send subsequent PBUs and user traffic to the
r2LMA. The MAG updates its Binding Cache and Policy Profile to
reflect the r2LMA to which PBUs associated with the MN need to be
sent.
4.2. Redirection of an Active IP Mobility Session
This use case would allow a redirection of an active mobility
session. The MAG would be redirected to a new r2LMA during a normal
Binding Lifetime Extension PBU/PBA exchange. Reasons for doing so
is, for example, moving Mobile Nodes (MS) anchored to a certain LMA
to another in order to allow graceful shutdown of the LMA for
maintenance purposes. Another reason could again be load balancing
in abrupt change of load condition on the LMA, and therefore redirect
some of the mobility sessions to another less loaded LMA.
If there is a need to maintain mobility session continuity during the
redirection, then additional functionality is required in LMAs and
possibly in the PMIPv6 Domain routing system. A context transfer
mechanism directly between LMAs, via a remote Policy Store or via
some other control function would be an obvious requirement.
However, context transfer specifics are outside the scope of this
document.
5. Proxy Mobile IPv6 Domain Considerations
The redirection problem discussed in this document is only possible
between MAGs and LMAs that have an existing SA set up. It is the
responsibility of the rfLMA that receives a PBU from a MAG to
redirect the MAG to a such r2LMA whom the MAG already has a SA set up
with. Furthermore, the rfLMA and the r2LMA must have a prior
agreement and an established trust relationship to perform
redirection. How a LMA learns and knows of other LMAs (where the
mobility session can be redirected), is not covered by this problem
statement. Dynamic establishment of a SA during redirection is not
covered in this problem statement.
6. Security Considerations
The security considerations of PMIPv6 signaling described in RFC 5213
[RFC5213] apply to this document. An incorrectly configured
redirection functionality may cause unwanted redirection attempts to
non-existing LMAs or to other LMAs that do not have and will not have
a SA with the redirected MAG. At the same time, a falsely redirected
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MAG will experience failing binding updates and failing creation of
mobility sessions. An incorrectly configured redirection
functionality may also cause biased load distribution within a PMIPv6
Domain. This document also assumes that the LMAs participating to
the redirection have adequate prior agreement and trust relationship
between each other.
7. IANA Considerations
This document has no IANA actions.
8. References
8.1. Normative References
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
8.2. Informative References
[I-D.ietf-dime-pmip6]
Korhonen, J., Bournelle, J., Muhanna, A., Chowdhury, K.,
and U. Meyer, "Diameter Proxy Mobile IPv6: Support For
Mobile Access Gateway and Local Mobility Anchor to
Diameter Server Interaction", draft-ietf-dime-pmip6-00
(work in progress), January 2009.
[I-D.korhonen-netlmm-lma-discovery]
Korhonen, J. and V. Devarapalli, "LMA Discovery for Proxy
Mobile IPv6", draft-korhonen-netlmm-lma-discovery-00 (work
in progress), October 2008.
[RFC5142] Haley, B., Devarapalli, V., Deng, H., and J. Kempf,
"Mobility Header Home Agent Switch Message", RFC 5142,
January 2008.
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Author's Address
Jouni Korhonen
Nokia Siemens Networks
Linnoitustie 6
FIN-02600 Espoo
FINLAND
Email: jouni.nospam@gmail.com
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