Network-based Localized Mobility J. Korhonen
Management (NetLMM) Nokia Siemens Networks
Internet-Draft V. Devarapalli
Intended status: Informational WiChorus
Expires: February 24, 2010 August 23, 2009
LMA Discovery for Proxy Mobile IPv6
draft-ietf-netlmm-lma-discovery-01.txt
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Abstract
Large Proxy Mobile IPv6 deployments would benefit from a
functionality, where a Mobile Access Gateway could dynamically
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discover a Local Mobility Anchor for a Mobile Node attaching to a
Proxy Mobile IPv6 domain. The purpose of the dynamic discovery
functionality is to reduce the amount of static configuration in the
Mobile Access Gateway. This specification describes a number of
possible dynamic Local Mobility Anchor discovery solutions.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. AAA-based Discovery Solutions . . . . . . . . . . . . . . . . . 3
2.1. Receiving LMA Address during the Network Access
Authentication . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Receiving LMA FQDN during the Network Access
Authentication . . . . . . . . . . . . . . . . . . . . . . 4
3. Lower Layers based Discovery Solutions . . . . . . . . . . . . 5
3.1. Constructing the LMA FQDN from a mobile node Identity . . . 5
3.2. Receiving LMA FQDN or IP Address from Lower Layers . . . . 6
3.3. Constructing the LMA FQDN from a Service Name . . . . . . . 6
4. Domain Name System Considerations . . . . . . . . . . . . . . . 6
5. Handover Considerations . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
9. Informative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
Large Proxy Mobile IPv6 (PMIPv6) [RFC5213] deployments would benefit
from a functionality, where a Mobile Access Gateway (MAG) could
dynamically discover a Local Mobility Anchor (LMA) for a Mobile Node
(MN) attaching to a PMIPv6 domain. The purpose of the dynamic
discovery functionality is to reduce the amount of static
configuration in the MAG. Other drivers for the dynamic discovery of
a LMA include LMA load balancing solutions and selecting LMA based on
desired services (i.e. allowing service-specific routing of traffic).
This document describes a number of possible dynamic LMA discovery
solutions.
There are a number of different ways for dynamically discovering the
LMA at the MAG. The following list briefly introduces solutions that
will be discussed in this specification:
o LMA Address from AAA during the network access authentication
procedure when the MN attaches to the MAG.
o LMA FQDN from AAA during the network access authentication,
followed by a Domain Name System (DNS) lookup.
o LMA FQDN derived from the MN identity received from the lower
layers during the network attachment, followed by a DNS lookup.
o LMA FQDN or IP address received from the lower layers during the
network attachment followed by an optional DNS lookup.
o LMA FQDN derived from the service selection indication received
from lower layers during the network attachment, followed by a DNS
lookup.
When a MN performs a handover from one MAG to another, the new MAG
must use the same LMA that the old MAG was using. This is required
for session continuity. The LMA discovery mechanism used by the new
MAG should be able to return the information about the same LMA that
was being used by the old MAG. This document also discusses
solutions for LMA discovery during a handover.
2. AAA-based Discovery Solutions
This section presents a LMA discovery solution that requires a MAG to
be connected to an AAA infrastructure. The AAA infrastructure is
also assumed to be aware of and support PMIPv6 functionality. A MN
attaching to a PMIPv6 domain is typically required to authenticate to
the network access and to be authorized for the mobility services
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before the MN is allowed to send or receive any IP packets or even
complete its IP level configuration.
The AAA-based LMA discovery solution hooks into the network access
authentication and authorization procedure. The MAG has also the
role of a Network Access Server (NAS) at this step. While the MN is
attaching to the network, the PMIPv6 related parameters are
bootstrapped at the same time the MN is authenticated for the network
access and authorized for the mobility services using the AAA
infrastructure. The PMIPv6 parameters bootstrapping involves the
Policy Profile download over the AAA infrastructure to the MAG. The
procedure for the Policy Profile download resembles largely the
client Mobile IPv6 Integrated Scenario bootstrapping [RFC5447].
2.1. Receiving LMA Address during the Network Access Authentication
After the MN has successfully authenticated for the network access
and authorized for the mobility service, the MAG receives the LMA IP
address(es) from the AAA server over the AAA infrastructure. The LMA
IP address information would be part of the AAA message(s) that ends
the successful authentication and authorization AAA exchange.
Once the MAG receives the LMA IP address(es), it sends Proxy Binding
Update (PBU) message for the newly authenticated and authorized MN.
The MAG trusts that the LMA returned by the AAA server is able to
provide mobility session continuity for the MN, i.e. after a handover
the LMA would be the same the MN already has a mobility session set
up with.
2.2. Receiving LMA FQDN during the Network Access Authentication
This solution is identical to the procedure described in Section 2.1.
The difference is that the MAG receives a Fully Qualified Domain Name
(FQDN) of the LMA instead of the IP address(es). The MAG has to
query the DNS infrastructure in order to resolve the FQDN to the LMA
IP address(es).
The LMA FQDN might be a generic to a PMIPv6 domain resolving to one
or more LMAs in the said domain. Alternatively the LMA FQDN might
resolve to exactly one LMA within the PMIPv6 domain. The latter
approach would obviously be useful if a new target MAG after a
handover should resolve the LMA FQDN to the LMA IP address where the
MN mobility session is already located.
The procedures described in this section and in Section 2.1 may also
be used together. For example, the AAA server might return a generic
LMA FQDN during the MN initial attach and once the LMA gets selected,
return the LMA IP address during the subsequent attachments to other
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MAGs in the PMIPv6 domain. In order for this to work, the resolved
and selected LMA IP address must be updated to the remote Policy
Store. For example, the LMA could perform the update once it
receives the initial PBU from the MAG for the new mobility session.
3. Lower Layers based Discovery Solutions
The following section discusses solutions, where the MAG receives
information from lower layers below the IP layer when the MN attaches
to the MAG. Based on this information, the MAG is then able to
determine which LMA to contact. These solution could essentially
allow large PMIPv6 deployments without the AAA infrastructure. The
lower layers discussed here are not explicitly defined but could
include different radio access technologies and tunneling solutions
such as IKEv2 [RFC4306] IPsec tunnel [RFC4303].
3.1. Constructing the LMA FQDN from a mobile node Identity
Depending on the actual network access technology, the MAG may be
able to receive a MN identity (or actually the subscription identity
but from now on we assume that the MN identity equals to the
subscription identity, which is a rather broad simplification) as a
result of the network access attachment procedure. The MN may signal
its identity as part of the attachment signaling or alternatively the
MAG receives the MN identity from a remote policy store.
Once the MAG has acquired the MN identity, the MAG can use the
information embedded in the identity to construct a generic LMA FQDN
(based on some pre-configured formatting rules) and then proceed to
resolve the LMA IP address(es) using the DNS. Obviously, the MN
identity must embed information elements that can be extracted and at
minimum used to determine the entity hosting and operating the LMA
for the MN. Thus the MN identity in this solution cannot be a "flat"
identity without any structure and "clear text" parts containing the
hosting entity information. Examples of such identities are the
International Mobile Subscriber Identity (IMSI) or Globally Unique
Temporary User Equipment Identity (GUTI) [3GPP.23.003] that both
contain information of the operator owning the given subscription.
The solution discussed in this section has issues if MN's identity
does not embed enough information. In a case the MN identity does
not embed any LMA hosting entity information, the MAG might use a
local database to map MN identities to corresponding LMAs. However,
this solution is unlikely to scale outside a limited PMIPv6 domain.
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3.2. Receiving LMA FQDN or IP Address from Lower Layers
The solution described in this section is similar to the solution
discussed in Section 3.1. Instead of deriving the LMA FQDN from the
MN identity, the MAG receives explicit LMA FQDN or IP address
information from lower layers. This usually means the MN is the
originator of the LMA information and explicitly participates to the
mobility management signaling (even if that only means providing LMA
discovery assisting information).
3.3. Constructing the LMA FQDN from a Service Name
Some network access technologies (including tunneling solutions)
allow the MN to signal the service name that identifies a particular
service or the external network it wants to access. If the MN
originated service name also embeds the information of the entity
hosting the service or the external network, then the MAG can
construct a generic LMA FQDN (e.g., based on some pre-configured
formatting rules) providing an access to the service or the external
network. Once the MAG has the FQDN it can proceed to resolve the LMA
IP address(es) using the DNS. Example of such service or external
network name is the Access Point Name (APN) [3GPP.23.003] that
contain information of the operator providing the access to the given
service or the external network.
4. Domain Name System Considerations
A number of LMA discovery solutions described in Section 2 and
Section 3 eventually depend on the DNS. This section discusses
impacts of the DNS response caching and issues related to the Dynamic
DNS [RFC2136] updates.
The caching (positive or negative) properties of the DNS [RFC2308]
and the fact that updates to the DNS take time to propagate globally,
need to be considered when applying DNS-based solutions to the PMIPv6
domain. First, the caching of DNS responses effectively delay the
propagation of up to date FQDN to IP address mappings (after both
addition and deletion). Hosts in the PMIPv6 domain keep using the
stale cached DNS response (positive or negative) until they give up
or the caching times out. The delay can be in order of hours in the
worst case. On the other hand, DNS administrators can lower the
resource record caching time (the Time To Live (TTL) value).
Obviously, too low TTL values increase the number of DNS queries
considerably. Second, the secondary DNS servers do not get
immediately updated when the masters do. These updates are also
periodic, usually in order of several hours, and may cause
considerable delay on global propagation of the updated naming
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information. Third, some DNS resolvers ignore low TTLs, replacing
them with a higher default value. This could lead to outdated LMA
information being around for longer than desired.
The above considerations are valid when, for example, the PMIPv6
domain LMA availability or load information is dynamically updated
into the DNS. There are incentives for doing so, however, the
concerns described above need to be understood clearly in that case.
5. Handover Considerations
Whenever a MN moves and attaches to a new MAG in a PMIPv6 domain, all
the MAGs that the MN attaches to, should use the same LMA. If there
is only one LMA per PMIPv6 domain, then there is no issue. If there
is a context transfer mechanism available between the MAGs, then the
new MAG knows the LMA information from the old MAG. Such a mechanism
is described in [I-D.ietf-mipshop-pfmipv6]. If the MN related
context is not transferred between the MAGs, then a mechanism to
deliver the current LMA information to the new MAG is required.
Relying on DNS during handovers is not generally a working solution
if the PMIPv6 domain has more than one LMA, unless the DNS
consistently assigns a specific LMA for each given MN. In most cases
described in Section 3, where the MAG derives the LMA FQDN, there is
no prior knowledge whether the LMA FQDN resolves to one or more LMA
IP address(es) in the PMIPv6 domain. However, depending on the
deployment and deployment related regulation (such as inter-operator
roaming consortium agreements) the situation might not be this
desperate. For example, a MAG might be able to synthesize a LMA
specific FQDN (e.g. out of MN identity or some other service specific
parameters). Another alternative could that MAG uses, for example, a
MN identity as an input to an algorithm that deterministically
assigns the same LMA out of a pool of LMAs (assuming the MAG has e.g.
learned a group of LMA FQDNs via SRV [RFC2782] query). These
approaches would guarantee that DNS returns always the same LMA
Address to the MAG.
Once the MN completes its initial attachment to a PMIPv6 domain, the
information about the LMA that is selected to serve the MN is stored
in the Policy Store (or the AAA server). The LMA information is
conveyed to the policy store by the LMA after the initial attachment
is completed [I-D.ietf-dime-pmip6]. Typically AAA infrastructure is
used for exchanging information between the LMA and the Policy Store.
When the MN moves and attaches to another MAG in the PMIPv6 domain,
then the AAA servers delivers the existing LMA information to the new
MAG as part of the authentication and authorization procedure as
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described in Section 2.1
6. Security Considerations
The use of DNS for obtaining the IP address of a mobility agent
carries certain security risks. These are explained in detail in
Section 9.1 of RFC 5026 [RFC5026]. However, the risks described in
RFC 5026 are mitigated to a large extent in this document, since the
MAG and the LMA belong belong to the same PMIPv6 domain. The DNS
server that the MAG queries is also part of the same PMIPv6 domain.
Even if the MAG obtains the IP address of a bogus LMA from a bogus
DNS server, further harm is prevented since the MAG and the LMA
should authenticate each other before exchanging PMIPv6 signaling
messages. RFC 5213 [RFC5213] specifies the use of IKEv2 [RFC4306]
between the MAG and the LMA to authenticate each other and setup
IPsec security associations for protecting the PMIPv6 signaling
messages.
The AAA infrastructure may be used to transport the LMA discovery
related information between the MAG and the AAA server via one or
more AAA brokers and/or AAA proxies. In this case the MAG to the AAA
server communication relies on the security properties of the
intermediate AAA brokers and AAA proxies.
7. IANA Considerations
This specification has no actions for IANA.
8. Acknowledgements
The authors would like to thank Julien Laganier, Christian Vogt,
Ryuji Wakikawa, Frank Xia and Behcet Sarikaya for their comments and
suggestions on this document.
9. Informative References
[3GPP.23.003]
3GPP, "Numbering, addressing and identification", 3GPP
TS 23.003 8.2.0, September 2008.
[I-D.ietf-dime-pmip6]
Korhonen, J., Bournelle, J., Chowdhury, K., Muhanna, A.,
and U. Meyer, "Diameter Proxy Mobile IPv6: Mobile Access
Gateway and Local Mobility Anchor Interaction with
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Diameter Server", draft-ietf-dime-pmip6-02 (work in
progress), April 2009.
[I-D.ietf-mipshop-pfmipv6]
Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F.
Xia, "Fast Handovers for Proxy Mobile IPv6",
draft-ietf-mipshop-pfmipv6-08 (work in progress),
July 2009.
[RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, April 1997.
[RFC2308] Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, March 1998.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4306] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
RFC 4306, December 2005.
[RFC5026] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6
Bootstrapping in Split Scenario", RFC 5026, October 2007.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
[RFC5447] Korhonen, J., Bournelle, J., Tschofenig, H., Perkins, C.,
and K. Chowdhury, "Diameter Mobile IPv6: Support for
Network Access Server to Diameter Server Interaction",
RFC 5447, February 2009.
Authors' Addresses
Jouni Korhonen
Nokia Siemens Networks
Linnoitustie 6
FIN-02600 Espoo
Finland
Email: jouni.nospam@gmail.com
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Vijay Devarapalli
WiChorus
3950 North First Street
San Jose, CA 95134
USA
Email: vijay@wichorus.com
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