Internet Engineering Task Force (IETF) J. Korhonen, Ed.

Internet Engineering Task Force (IETF) J. Korhonen, Ed.
Request for Comments: 6463 Nokia Siemens Networks
Category: Standards Track S. Gundavelli
ISSN: 2070-1721 Cisco
H. Yokota
KDDI Lab
X. Cui
Huawei Technologies
February 2012

Runtime Local Mobility Anchor (LMA) Assignment Support
for Proxy Mobile IPv6

Abstract

This document describes a runtime local mobility anchor assignment
functionality and corresponding mobility options for Proxy Mobile
IPv6. The runtime local mobility anchor assignment takes place
during a Proxy Binding Update and a Proxy Binding Acknowledgement
message exchange between a mobile access gateway and a local mobility
anchor. The runtime local mobility anchor assignment functionality
defined in this specification can be used, for example, for load-
balancing purposes.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6463.

Korhonen, et al. Standards Track [Page 1]

RFC 6463 Runtime LMA Assignment February 2012

Copyright Notice

Copyright (c) 2012 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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements and Terminology . . . . . . . . . . . . . . . . . 4
2.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. Proxy Mobile IPv6 Domain Assumptions . . . . . . . . . . . . . 5
4. Mobility Options . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Redirect-Capability Mobility Option . . . . . . . . . . . 5
4.2. Redirect Mobility Option . . . . . . . . . . . . . . . . . 6
4.3. Load Information Mobility Option . . . . . . . . . . . . . 7
4.4. Alternate IPv4 Care-of Address Mobility Option . . . . . . 9
5. Runtime LMA Assignment . . . . . . . . . . . . . . . . . . . . 9
5.1. General Operation . . . . . . . . . . . . . . . . . . . . 9
5.2. Mobile Access Gateway Operation . . . . . . . . . . . . . 10
5.3. Local Mobility Anchor Operation . . . . . . . . . . . . . 12
5.3.1. Co-Located rfLMA and r2LMA Functions . . . . . . . . . 13
5.3.2. Separate rfLMA and r2LMA Functions (Proxy-MAG) . . . . 14
6. Handoff and Multi-Homing Considerations . . . . . . . . . . . 18
7. Protocol Configuration Variables . . . . . . . . . . . . . . . 18
8. Security Considerations . . . . . . . . . . . . . . . . . . . 19
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
11.1. Normative References . . . . . . . . . . . . . . . . . . . 20
11.2. Informative References . . . . . . . . . . . . . . . . . . 20

Korhonen, et al. Standards Track [Page 2]

RFC 6463 Runtime LMA Assignment February 2012

1. Introduction

This specification describes a runtime assignment of a local mobility
anchor (LMA) for the Proxy Mobile IPv6 (PMIPv6) [RFC5213] protocol.
The runtime LMA assignment takes place during a Proxy Binding Update
(PBU) and a Proxy Binding Acknowledgement (PBA) message exchange
between a mobile access gateway (MAG) and a LMA. The runtime LMA
assignment functionality defined in this specification can be used,
for example, for load-balancing purposes. MAGs and LMAs can also
implement other load-balancing mechanisms that are completely
transparent at the PMIPv6 protocol level and do not depend on the
functionality defined in this specification.

The runtime LMA assignment functionality does not depend on the
Domain Name System (DNS) or the Authentication, Authorization, and
Accounting (AAA) infrastructure for the assignment of the LMA to
which the mobile node (MN) is anchored. All MAGs and LMAs (either
rfLMAs or r2LMAs; see Section 2.2) have to belong to the same PMIPv6
domain.

There are a number of reasons why the runtime LMA assignment is a
useful addition to the PMIPv6 protocol. A few are identified below:

o LMAs with multiple IP addresses: a cluster of LMAs or a blade
architecture LMA may appear to the routing system as multiple LMAs
with separate unicast IP addresses. A MAG can initially select
any of the LMAs as the serving LMA using, for example, DNS- and
AAA-based solutions. However, MAG's initial selection may be
suboptimal from the LMA point of view and immediate runtime
assignment to a "proper LMA" would be needed. The LMA could use a
[RFC5142]-based approach, but that would imply unnecessary setting
up of a mobility session in a "wrong LMA" with associated back-end
support system interactions, additional signaling between the MAG
and the LMA, and re-establishing a mobility session to the new LMA
again with associated signaling.

o Bypassing a load-balancer: a cluster of LMAs or a blade
architecture LMA may have a load-balancer in front of them or
integrated in one of the LMAs. The load-balancer would represent
multiple LMAs during the LMA discovery phase and only its IP
address would be exposed to the MAG thus hiding possible
individual LMA or LMA blade IP addresses from the MAG. However,
if all traffic must always go through the load-balancer, it
quickly becomes a bottleneck. Therefore, a PMIPv6 protocol-level
support for bypassing the load-balancer after the initial PBU/PBA
exchange would greatly help scalability. Also, bypassing the
load-balancer as soon as possible allows implementing load-
balancers that do not maintain any MN-specific state information.

Korhonen, et al. Standards Track [Page 3]

RFC 6463 Runtime LMA Assignment February 2012

o Independence from DNS: DNS-based load-balancing is a common
practice. However, keeping MAGs up to date with LMA load status
using DNS is hard, e.g., due to caching and unpredictable zone
update delays [RFC6097]. Generally, LMAs constantly updating the
[RFC2136] zone's master DNS server might not feasible in a large
PMIPv6 domain due to increased load on the master DNS server and
additional background signaling. Furthermore, MAGs may perform
(LMA) destination address selection decisions that are not in line
with what the DNS administrator actually wanted [RFC3484].

o Independence from AAA: AAA-based solutions have basically the same
arguments as DNS-based solutions above. It is also typical that
AAA-based solutions offload the initial LMA selection to the DNS
infrastructure [RFC5779]. The AAA infrastructure does not return
an IP address or a Fully Qualified domain Name (FQDN) to a single
LMA; rather, it returns a FQDN representing a group of LMAs.

o Support for IPv6 anycast addressing [RFC4291]: the current PMIPv6
specification does not specify how the PMIPv6 protocol should
treat anycast addresses assigned to mobility agents. For example,
a blade architecture LMA may have a unique unicast IP address for
each blade and a single anycast address for all blades. A MAG
could then initially send a PBU to an anycast LMA address and
receive a PBA from an anycast LMA address. Once the MAG receives
the unicast address of the runtime-assigned LMA blade through the
initial PBU/PBA exchange, the subsequent communication continues
using the unicast address.

As a summary, the DNS/AAA-based approaches cannot be used to select
an "appropriate" LMA at runtime. Therefore, this specification
defines a solution that is applicable for LMA implementations where
the IP address known to the MAG is not the best LMA of choice at
runtime.

2. Requirements and Terminology

2.1. Requirements

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].

2.2. Terminology

In addition to the terminology defined in [RFC5213], the following
terminology is also used:

Korhonen, et al. Standards Track [Page 4]

RFC 6463 Runtime LMA Assignment February 2012

rfLMA

An LMA that receives a PBU from a MAG and decides to assign an IP
mobility session with a new target LMA (r2LMA).

r2LMA

The LMA assigned to a MAG as a result of the runtime LMA
assignment.

Runtime Assignment Domain

A group of LMAs that consists of at least one rfLMA and one or
more r2LMAs (all are part of the same PMIPv6 domain). A rfLMA is
allowed to assign MAGs only with r2LMAs that belong to the same
runtime assignment domain. The rfLMA and one or more r2LMAs may
consist of multiple blades in a single network element, multiple
physical network elements, or multiple LMAs distributed
geographically.

3. Proxy Mobile IPv6 Domain Assumptions

The runtime LMA assignment functionality has few assumptions within
the PMIPv6 domain.

Each LMA in a runtime assignment domain MUST be reachable at a
unicast IP address. The rfLMA and the r2LMA MUST have a prior
agreement, adequate means to secure their inter-LMA communication,
and an established trust relationship to perform the runtime LMA
assignment.

Each LMA and MAG participating in the runtime LMA assignment is
assumed to have required Security Associations (SAs) pre-established.
Dynamic negotiation of the SAs using, e.g., IKEv2 [RFC5996], SHOULD
be supported but is out of scope of this specification.

4. Mobility Options

In the following sections, all presented values, bit fields, and
addresses are in network byte order.

4.1. Redirect-Capability Mobility Option

The Redirect-Capability mobility option has the alignment requirement
of 4n. There can be zero or one Redirect-Capability mobility option
in the PBU. The format of the Redirect-Capability mobility option is
shown below:

Korhonen, et al. Standards Track [Page 5]

RFC 6463 Runtime LMA Assignment February 2012

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Redirect-Capability Mobility Option

o Option Type: 8-bit identifier set to 46.

o Option Length: 8-bit unsigned integer, representing the length of
the Redirect-Capability mobility option in octets, excluding the
Option Type and Length fields. The Option Length MUST be set to
2.

o Reserved: This field is reserved for future use. This field MUST
be set to zero by the sender and ignored by the receiver.

The Redirect-Capability option is used by the MAG to inform the LMA
that it implements and has enabled the runtime LMA assignment
functionality.

4.2. Redirect Mobility Option

The Redirect mobility option in the PBA MUST contain an unicast
address of the r2LMA and the address family MUST be the same as the
currently used transport between the MAG and the rfLMA. There can be
zero or one Redirect mobility option in the PBA. The Redirect
mobility option has the alignment requirement of 4n. The format of
the Redirect mobility option is shown below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |K|N| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Optional IPv6 r2LMA Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Optional IPv4 r2LMA Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Redirect Mobility Option

o Option Type: 8-bit identifier set to 47.

Korhonen, et al. Standards Track [Page 6]

RFC 6463 Runtime LMA Assignment February 2012

o Option Length: 8-bit unsigned integer, representing the length of
the Redirect mobility option in octets, excluding the Option Type
and Length fields. If the 'K' flag is set and 'N' is unset, then
the length MUST be 18. If the 'K' flag is unset and 'N' is set,
then the length MUST be 6. Both the 'K' and 'N' flags cannot be
set or unset simultaneously.

o 'K' flag: This bit is set (1) if the 'Optional IPv6 r2LMA Address'
is included in the mobility option. Otherwise, the bit is unset
(0).

o 'N' flag: This bit is set (1) if the 'Optional IPv4 r2LMA Address'
is included in the mobility option. Otherwise, the bit is unset
(0).

o Reserved: This field is reserved for future use. MUST be set to
zero by the sender and ignored by the receiver.

o Optional IPv6 r2LMA Address: the unicast IPv6 address of the
r2LMA. This value is present when the corresponding PBU was
sourced from an IPv6 address.

o Optional IPv4 r2LMA Address: the IPv4 address of the r2LMA. This
value is present when the corresponding PBU was sourced from an
IPv4 address (for IPv4 transport, see [RFC5844]).

The Redirect option is used by the LMA to inform the MAG that the
runtime LMA assignment took place and the MAG has to update its
Binding Update List Entry (BULE) for the mobility session.

4.3. Load Information Mobility Option

The Load Information mobility option can be included in any PBA and
is used to report priority and key load information of a LMA to a MAG
(or to a 'proxy-MAG'). The Load Information mobility option has the
alignment requirement of 4n. The format of the mobility option is
shown below:

Korhonen, et al. Standards Track [Page 7]

RFC 6463 Runtime LMA Assignment February 2012

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sessions in Use |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Sessions |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Used Capacity |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Maximum Capacity |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Load Information Mobility Option

o Option Type: 8-bit identifier set to 48.

o Option Length: 8-bit unsigned integer, representing the length of
the Load Information mobility option in octets, excluding the
Option Type and Length fields. The length is set to 18.

o Priority: 16-bit unsigned integer, representing the priority of an
LMA. The lower value, the higher the priority. The priority only
has meaning among a group of LMAs under the same administration,
for example, determined by a common LMA FQDN, a domain name, or a
realm.

o Sessions in Use: 32-bit unsigned integer, representing the number
of parallel mobility sessions the LMA has in use.

o Maximum Sessions: 32-bit unsigned integer, representing the
maximum number of parallel mobility sessions the LMA is willing to
accept.

o Used Capacity: 32-bit unsigned integer, representing the used
bandwidth/throughput capacity of the LMA in kilobytes per second.

o Maximum Capacity: 32-bit unsigned integer, representing the
maximum bandwidth/throughput capacity in kilobytes per second the
LMA is willing to accept.

The session and capacity information can easily be used to calculate
different load factors of the LMA. A MAG (or a 'proxy-MAG') MAY use
the priority and load information to internally maintain priority
ordering of LMAs.

Korhonen, et al. Standards Track [Page 8]

RFC 6463 Runtime LMA Assignment February 2012

4.4. Alternate IPv4 Care-of Address Mobility Option

The Alternate IPv4 Care-of Address (A4CoA) mobility option has the
alignment requirement of 4n+2. The format of the mobility option is
shown below:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Alternate IPv4 Care-of Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Alternate IPv4 Care-of Address Mobility Option

o Option Type: 8-bit identifier set to 49.

o Option Length: 8-bit unsigned integer, representing the length of
the Load Information mobility option in octets, excluding the
Option Type and Length fields. The length is set to 4.

o Alternate IPv4 Care-of Address: an IPv4 equivalent of the
[RFC6275] Alternate Care-of Address option for IPv6. In the
context of PMIPv6, its semantic is equivalent to the Alternate
Care-of Address option for IPv6.

A MAG MAY include the Alternate IPv4 Care-of Address option in a PBU.
An LMA that receives and implements the Alternate IPv4 Care-of
Address option MUST echo the option as such back to the MAG in a
reply PBA.

5. Runtime LMA Assignment

5.1. General Operation

During the runtime LMA assignment, the PBA is returned from the LMA
Address to which the PBU was sent, i.e., from the rfLMA address.
After the runtime LMA assignment, all PMIPv6 communication continues
directly between the MAG and the r2LMA bypassing the rfLMA. The
overall runtime LMA assignment flow sequence is shown in Figure 1.

Korhonen, et al. Standards Track [Page 9]

RFC 6463 Runtime LMA Assignment February 2012

[MAG] [rfLMA] [r2LMA]
| | |
1) |--PBU-->| | LMA assignment takes place in rfLMA.
| | |
2) | | ~ ~ ~ >|\
| | | + BCE gets created in r2LMA.
3) | |<~ ~ ~ ~|/
| | |
4) |<--PBA--| | PBA contains r2LMA information.
| | |
|<=====data======>|
| | |
5) |-------PBU------>| Lifetime extension,
6) |<------PBA-------| de-registration, etc.
| | |

Figure 1: Runtime LMA Assignment from rfLMA to r2LMA and Setting Up a
Mobility Session in the r2LMA within a Runtime Assignment Domain

The assumption in the signaling flow step 1) shown in Figure 1 is
that the mobility session gets created in the r2LMA, although the
rfLMA is responsible for interfacing with the MAG. There are several
possible solutions for the rfLMA and the r2LMA interaction depending
on, e.g., the co-location properties of the rfLMA and the r2LMA.
This specification describes two:

o Co-located rfLMA and r2LMA functions, where the 'rfLMA side of the
LMA' is reachable via an anycast address or the loopback address
of the LMA. See Section 5.3.1 for further details.

o Separate rfLMA and r2LMA functions, where the rfLMA acts as a non-
transparent 'proxy-MAG' to a r2LMA. See Section 5.3.2 for further
details.

There are other possible implementations of the rfLMA and the r2LMA.
At the end, as long as the protocol between the MAG and the rfLMA
follows this specification , the co-location or inter-communication
properties of the rfLMA and the r2LMA do not matter.

5.2. Mobile Access Gateway Operation

In the base PMIPv6 protocol [RFC5213], a MAG sends a PBU to an LMA;
this results in creation of a Binding Cache Entry (BCE) at the LMA
and the LMA sending a PBA sent back to the MAG. The MAG in turn
creates a corresponding Binding Update List Entry (BULE). This
specification extends the base protocol with the runtime LMA
assignment functionality.

Korhonen, et al. Standards Track [Page 10]

RFC 6463 Runtime LMA Assignment February 2012

If the MAG supports the runtime LMA assignment and the functionality
is also enabled (see the EnableLMARedirectFunction configuration
variable in Section 7), then the MAG includes the Redirect-Capability
mobility option in a PBU that establishes a new mobility session
(i.e., Handoff Indicator Option in the PBU has the value of 1). The
Redirect-Capability mobility option in the PBU is also an indication
to an LMA that the MAG supports the runtime LMA assignment
functionality and is prepared to be assigned with a different LMA.
The runtime LMA assignment concerns always one mobility session at a
time.

If the MAG receives a PBA that contains the Redirect mobility option
without first including the Redirect-Capability mobility option in
the corresponding PBU, then the MAG MUST ignore the option and
process the PBA as described in RFC 5213.

If the MAG receives a PBA that contains the Redirect mobility option
and the MAG had included the Redirect-Capability mobility option in
the corresponding PBU, then the MAG MUST perform the following steps
in addition to the normal [RFC5213] PBA processing:

o The MAG updates its BULE to contain the r2LMA address included in
the received Redirect mobility option.

o If there is no SA between the MAG and the r2LMA, the MAG SHOULD
initiate a dynamic creation of the SA between the MAG and the
r2LMA as described in Section 4 of RFC 5213. If the dynamic SA
creation fails, the MAG SHOULD log the event. The MAG MAY retry
the dynamic creation of the SA, and if those also fail, the newly
created BULE (and also the BUL in the r2LMA) will eventually
timeout. If the failure is persistent, it can be regarded as a
system-level configuration error.

The MAG is not required to send a fresh PBU to the r2LMA after a
successful runtime assignment. The mobility session has already been
established in the r2LMA. The MAG MUST send all user traffic to the
r2LMA address. The MAG MUST send subsequent binding refresh PBUs
(e.g., lifetime extension, handoff, etc.) to the r2LMA address. If
there is no existing tunnel between the MAG and the r2LMA unicast
address, then the MAG creates one as described in Section 6.9.1.2 of
[RFC5213].

Korhonen, et al. Standards Track [Page 11]

RFC 6463 Runtime LMA Assignment February 2012

5.3. Local Mobility Anchor Operation

The text in the following sections refers to an 'LMA' when it means
the combination of the rfLMA and the r2LMA, i.e., the entity where
runtime LMA assignment is possible. When the text points to a
specific LMA role during the runtime assignment, it uses either the
'rfLMA' or the 'r2LMA'.

If the runtime assignment functionality is enabled (see the
EnableLMARedirectFunction configuration variable in Section 7) in the
rfLMA but the LMA assignment is not going to take place for some
reason, and the rfLMA is not willing to serve (or not capable of
serving) as a normal [RFC5213] LMA for the MAG, then the rfLMA MUST
reject the PBU and send back a PBA with Status Value set to 130
(Insufficient resources) error code. If the rfLMA is able to make
the assignment to an r2LMA, it returns a PBA with the Redirect
mobility option as defined below. Otherwise, the rfLMA MUST act as a
normal [RFC5213]- or [RFC5844]-defined LMA for the MAG.

The rfLMA MUST only assign the MAG to a new r2LMA with which it knows
the MAG has an SA or with which it knows the MAG can establish an SA
dynamically. The rfLMA MUST NOT assign the MAG with a r2LMA that the
rfLMA and the r2LMA do not have a prior agreement and an established
trust relationship for the runtime LMA assignment. These SA-related
knowledge issues and trust relationships are deployment specific in a
PMIPv6 domain and in a runtime assignment domain, and out of scope of
this specification. Possible context transfer and other coordination
management between the rfLMA and the r2LMA are again deployment
specific for LMAs in a runtime assignment domain. The rfLMA MUST NOT
change the used transport IP address family during the runtime LMA
assignment.

As a result of a successful runtime LMA assignment, the PBA MUST
contain the Redirect mobility option with a valid r2LMA unicast
address and the PBA Status Value indicating success.

Next, we describe two deployment and implementation models for the
runtime LMA assignment. In Section 5.3.1, we describe a model where
the rfLMA and r2LMA are co-located. In Section 5.3.2 we describe a
model where the rfLMA acts as a non-transparent 'proxy-MAG', and
where the rfLMA and the r2LMA are separate. There can be even more
implementation options depending on the rfLMA and the r2LMA
co-location properties, and how the inter-LMA communication is
arranged.

Korhonen, et al. Standards Track [Page 12]

RFC 6463 Runtime LMA Assignment February 2012

5.3.1. Co-Located rfLMA and r2LMA Functions

In this solution approach, the rfLMA and the r2LMA are part of the
same 'co-located LMA', and may even be using the same physical
network interface. The rfLMA is reachable via an anycast or a
loopback address of the LMA. Each r2LMA is reachable via its unicast
address. Figure 2 illustrates example signaling flows for the
solution.

The MAG-LMA SA is between the MAG and the rfLMA (i.e., the anycast or
the loopback address of the LMA). How this SA has been set up is out
of scope of this specification, but a manual SA configuration is one
possibility.

The rfLMA becomes active when the runtime LMA assignment
functionality is enabled (see the EnableLMARedirectFunction
configuration variable in Section 7). When the rfLMA receives a PBU
destined to it, and the PBU contains the Redirect-Capability mobility
option, then the 'co-located LMA' MUST create a mobility session in a
r2LMA role using the procedures described in [RFC5213]. If there is
no existing tunnel between the MAG and the r2LMA unicast address,
then the r2LMA creates one as described in Section 5.3 of [RFC5213].
The r2LMA used for accepting and anchoring the mobility session MUST
also have the runtime LMA assignment functionality enabled (see the
EnableLMARedirectAcceptFunction configuration variable in Section 7).

If the mobility session creation succeeded, then the 'co-located LMA'
in the rfLMA role sends a PBA to the MAG. The PBA is sourced using
the rfLMA (anycast or loopback) address. The PBA MUST contain the
r2LMA unicast address (IPv6 or IPv4) in the Redirect mobility option.

If the PBU is received on the r2LMA unicast address, then the PBU is
processed as described in RFC 5213 and the response PBA MUST NOT
contain the Redirect mobility option.

If the PBU is received on the rfLMA address and there is no Redirect-
Capability mobility option in the PBU, then the 'co-located LMA' MAY
choose to be a LMA for the MAG (assuming the rfLMA address is not an
anycast address). Otherwise, the rfLMA MUST reject the PBU and send
back a PBA in a rfLMA role with Status Value set to 130 (Insufficient
resources) error code (as mentioned in Section 5.3).

Korhonen, et al. Standards Track [Page 13]

RFC 6463 Runtime LMA Assignment February 2012

[MAG] [rfLMA /r2LMA_1/r2LMA_2/r2LMA_3]
| | | | |
MAG discovers rfLMA | | | |
BULE for rfLMA | | | |
| | | | |
|-- PBU --------------------->| | | |
| src=MAG_Proxy-CoA, | | | |
| dst=rfLMA, | | | |
| Redirect-Capability, .. | r2LMA gets selected |
| BCE is created in r2LMA_2
| |Tunnel setup in r2LMA_2|
| | | | |
|<- PBA ----------------------| | | |
| src=rfLMA, | | | |
| dst=MAG_Proxy-CoA, | | | |
| Redirect=r2LMA_2_address, | | | |
| Load Info, .. | | | |
| | | | |
BULE updated to r2LMA_2 | | | |
Tunnel setup | | | |
| | | | |
|<=========== MAG-r2LMA_2 tunnel ============>| |
| | | | |
Lifetime extension, etc. | | | |
| | | | |
|-- PBU ------------------------------------->| |
| src=MAG_Proxy-CoA, | | | |
| dst=r2LMA_2, .. | | | |
| | | | |
|<- PBA --------------------------------------| |
| src=r2LMA_2, | | | |
| dst=MAG_Proxy-CoA, | | | |
| Load Info, .. | | | |
| | | | |

Figure 2: Co-Located rfLMA and r2LMA Example

5.3.2. Separate rfLMA and r2LMA Functions (Proxy-MAG)

In this solution approach, the rfLMA and the r2LMA are two isolated
functions, and may even be physically separate networking nodes. The
r2LMA can be any [RFC5213]- or [RFC5844]-compliant LMA that doesn't
have any knowledge of this specification when IPv6 transport is used.
In case of IPv4 transport, the [RFC5844]-compliant LMA MUST also
implement the Alternate IPv4 Care-of Address option (see
Section 4.4). Figure 3 illustrates example signaling flows for the
solution.

Korhonen, et al. Standards Track [Page 14]

RFC 6463 Runtime LMA Assignment February 2012

The rfLMA is actually a non-transparent 'proxy-MAG' that shows up as
an LMA implementing this specification towards the MAG, and as a base
[RFC5213]-compliant MAG to the r2LMA. (See [RFC2616] for a generic
definition of a non-transparent proxy; although it's for HTTP, the
idea also applies here.) This type of operation is also referred to
as 'chaining' in other contexts. The protocol between the 'proxy-
MAG' and the r2LMA is the base [RFC5213] PMIPv6 protocol.

The MAG-LMA SA is between the MAG and the rfLMA, and [RFC5213] SA
considerations apply fully. The MAG has no knowledge of the 'proxy-
MAG'-r2LMA SA. [RFC5213] considerations regarding the SA between the
'proxy-MAG' and the r2LMA apply fully. It is also possible that
'proxy-MAG'-r2LMA security is arranged using other means than IPsec,
for example, using layer-2 VPNs.

When the rfLMA receives a PBU, and the PBU contains the Redirect-
Capability mobility option, then the rfLMA in a 'proxy-MAG' role:

o Processes the PBU using the procedures described in RFC 5213
except that no mobility session gets created. Instead, the rfLMA
creates a proxy state based on the received PBU.

o Assigns a r2LMA to the MAG.

o Creates a new PBU', which includes all non-security related
mobility options from the original PBU and an Alternate Care-of
Address (ACoA) option containing the Proxy Care-of Address of the
original MAG. If the original PBU already included an ACoA
option, then the content of the ACoA option in the PBU' MUST be
the same as in the original PBU.

Note, in case of IPv4 transport [RFC5844], the Alternate IPv4
Care-of Address (A4CoA) option MUST be used and contain the IPv4
Proxy Care-of Address of the original MAG.

o Sends the new PBU' sourced from its 'proxy-MAG' IPv6 or IPv4 Proxy
Care-of Address and destined to the r2LMA address using the
procedures described in RFC 5213 (or RFC 5844 in case of IPv4
transport).

The r2LMA processes the received PBU' using the procedures described
in RFC 5213 or RFC 5844. In case of IPv4 transport, the r2LMA uses
the IPv4 Proxy Care-of Address from the Alternate IPv4 Care-of
Address option for the tunnel setup and the creation of the BCE. The
reply PBA' MUST be destined to the source address of the received
PBU', i.e., the Care-of Address the 'proxy-MAG'.

Korhonen, et al. Standards Track [Page 15]

RFC 6463 Runtime LMA Assignment February 2012

Once the rfLMA in a 'proxy-MAG' role receives a reply PBA' from the
r2LMA and the mobility session creation succeeded in the r2LMA, the
rfLMA sends a PBA to the original MAG. The PBA is sourced from the
rfLMA address and destined to the MAG (IPv6 or IPv4) Proxy Care-of
Address. The PBA MUST contain the r2LMA (IPv6 or IPv4) unicast
address in the Redirect mobility option. Other non-security-related
mobility options (including the Load Information option) are copied
from the PBA' to the PBA as such.

If one of these errors occurs:

o the PBA' Status Value indicates that the mobility session creation
failed in the r2LMA. For example, the Status Value in the PBA' is
set to 130 (Insufficient resources), or

o there was no PBA' response from the r2LMA, or

o the PBA' did not include the Alternate IPv4 Care-of Address option
although it was included in the corresponding PBU' (when using
IPv4 transport),

then the rfLMA SHOULD assign the MAG to a new r2LMA and rerun the
procedure for sending the PBU' described earlier for the new r2LMA.
The number and order of r2LMA reassignment attempts is controlled by
the local policy and the amount of known r2LMAs in the rfLMA. When
the rfLMA in a 'proxy-MAG' role concludes the mobility session
creation failed with r2LMA(s), the rfLMA MUST set the Status Value in
the PBA as received from the latest contacted PBA' Status Value or to
130 (Insufficient resources) in case of no responses from rfLMAs, and
send the reply PBA to the MAG. The PBA is sourced from the rfLMA
address and destined to the MAG Proxy Care-of Address. Other
possible non-security-related mobility options (including the Load
Information option) are copied from the PBA' to the PBA as such.

Once the rfLMA has sent the reply PBA to the MAG, it can remove the
proxy state. Subsequent traffic between the MAG and the r2LMA will
bypass the rfLMA (assuming the mobility session creation succeeded in
the r2LMA).

If the rfLMA receives a PBU with no Redirect-Capability mobility
option in the PBU, then the PBU is processed as described in
Section 5.3, i.e., the rfLMA may or may not act as an [RFC5213] or
[RFC5844] LMA to the MAG.

Korhonen, et al. Standards Track [Page 16]

RFC 6463 Runtime LMA Assignment February 2012

[MAG] [rfLMA] [r2LMA]
| | |
MAG discovers rfLMA | |
BULE for rfLMA | |
| | |
|-- PBU --------------------->| rfLMA assigns a r2LMA and |
| src=MAG_Proxy-CoA, | creates a proxy state |
| dst=rfLMA, | |
| Redirect-Capability, .. | |
| |-- PBU' -------------------->|
| | src=proxy-MAG_Proxy-CoA, |
| | dst=r2LMA, |
| | ACoA/A4CoA=MAG_Proxy-CoA, |
| | .. |
| | BCE created in r2LMA
| | Tunnel setup
| | Proxy-CoA is MAG's address
| | |
| rfLMA removes the |<- PBA' ---------------------|
| proxy state | src=r2LMA, |
| | dst=proxy-MAG_Proxy-CoA, |
| | Load Info, .. |
|<- PBA ----------------------| |
| src=rfLMA, | |
| dst=MAG_Proxy-CoA, | |
| Redirect=r2LMA_address, | |
| Load Info, .. | |
| | |
BULE updated to r2LMA | |
Tunnel setup | |
| | |
|<===================== MAG-r2LMA tunnel ==================>|
| | |
Lifetime extension, etc. | |
| | |
|-- PBU --------------------------------------------------->|
| src=MAG_Proxy-CoA, dst=r2LMA, .. |
| | |
|<- PBA ----------------------------------------------------|
| src=r2LMA, dst=MAG_Proxy-CoA, Load Info, .. |
| | |

Figure 3: Separate rfLMA and r2LMA ('proxy-MAG') Example

Korhonen, et al. Standards Track [Page 17]

RFC 6463 Runtime LMA Assignment February 2012

6. Handoff and Multi-Homing Considerations

A MN can be multi-homed, i.e., have network connectivity over
multiple interfaces connected to one or more accesses. If PMIPv6-
based handovers between multiple interfaces or accesses are desired,
then a single LMA should have a control over all possible multi-homed
mobility sessions the MN has. Once the MN has established one
mobility session with one LMA, the subsequent mobility sessions of
the same MN would be anchored to the LMA that was initially assigned.
If each mobility session over a different interface (and possibly a
MAG) has no requirements for PMIPv6-based handovers between accesses
or interfaces, then the rest of the considerations in this section do
not apply.

One possible solution already supported by this specification is
applying the runtime LMA assignment only for the very first initial
attach a multi-homed MN does towards a PMIPv6 domain. After the
initial attach, the assigned r2LMA address has been stored in the
policy profile. For the subsequent mobility sessions of the multi-
homed MN, the same assigned r2LMA address would be used and there is
no need to contact the rfLMA. Ensuring the discovery of the same
r2LMA each time relies on the MN having an identity that can always
point to the same policy profile, independent of the access that is
used.

MAGs have a control over selectively enabling and disabling the
runtime assignment of the LMA. If the multi-homed MN is attached to
a PMIPv6 domain via multiple MAGs, the assigned r2LMA address should
be stored in the remote policy store and downloaded as a part of the
policy profile download to a MAG. Alternatively, MAGs can share
policy profile information using other means. In both cases, the
actual implementation of the policy profile information sharing is
specific to a PMIPv6 deployment and out of scope of this
specification.

7. Protocol Configuration Variables

This specification defines two configuration variables that control
the runtime LMA assignment functionality within a PMIPv6 domain.

EnableLMARedirectFunction

This configuration variable is available in both a MAG and in a
rfLMA. When set to TRUE (i.e., enabled), the PMIPv6 node enables
the runtime LMA assignment functionality. The default value is
FALSE (i.e., disabled).

Korhonen, et al. Standards Track [Page 18]

RFC 6463 Runtime LMA Assignment February 2012

EnableLMARedirectAcceptFunction

This configuration variable is available in a r2LMA. When set to
TRUE (i.e., enabled), the r2LMA is able to accept runtime LMA
assignment mobility sessions from a rfLMA. The default value is
FALSE (i.e., disabled).

Note that the MAG and LMA configuration variables from Sections 9.1
and 9.2 of [RFC5213] do not apply for an LMA when it is in an rfLMA
role.

8. Security Considerations

The security considerations of PMIPv6 signaling described in RFC 5213
apply to this document. An incorrectly configured LMA may cause
unwanted runtime LMA assignment attempts to non-existing LMAs or to
other LMAs that do not have and will not have an SA with the MAG.
Consequently, the MAG will experience failed binding updates or
unsuccessful creation of mobility sessions. An incorrectly
configured LMA may also cause biased load distribution within a
PMIPv6 domain. This document also assumes that the LMAs that
participate in runtime LMA assignment have adequate prior agreement
and trust relationships between each other.

If the SAs between MAGs and LMAs are manually keyed (as may be needed
by the scenario described in Section 5), then the anti-replay service
of ESP-protected PMIPv6 traffic cannot typically be provided. This
is, however, deployment specific to a PMIPv6 domain.

If a PMIPv6 domain deployment with a runtime LMA assignment requires
that a rfLMA has to modify a PBU/PBA in any way, e.g., by changing
the source and destination IP address or any other field of the
encapsulating IP packet, then the security mechanism (such as
possible authentication options) used to protect the PBU/PBA MUST NOT
cover the outer IP packet on those parts that might get modified.
Alternatively, the rfLMA can do all required security processing on
the PBU/PBA, and the communication between the rfLMA and the r2LMA
would be unprotected at the PMIPv6 protocol level. In this case, the
runtime assignment domain MUST implement an adequate level of
security using other means, such as layer-2 VPNs.

Korhonen, et al. Standards Track [Page 19]

RFC 6463 Runtime LMA Assignment February 2012

9. IANA Considerations

New mobility options for use with PMIPv6 are defined in the [RFC6275]
"Mobility Options" registry. The mobility options are defined in
Section 4:

Redirect-Capability Mobility Option 46
Redirect Mobility Option 47
Load Information Mobility Option 48
Alternate IPv4 Care-of Address 49

10. Acknowledgements

The author would like to thank Basavaraj Patil, Domagoj Premec, Ahmad
Muhanna, Vijay Devarapalli, Rajeev Koodli, Yungui Wang, Pete McCann,
and Qin Wu for their discussion of this document. A special thanks
to Qian Li for her detailed feedback on the protocol details.

11. References

11.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

[RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
in IPv6", RFC 6275, July 2011.

11.2. Informative References

[RFC2136] Vixie, P., Thomson, S., Rekhter, Y., and J. Bound,
"Dynamic Updates in the Domain Name System (DNS UPDATE)",
RFC 2136, April 1997.

[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.

[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.

Korhonen, et al. Standards Track [Page 20]

RFC 6463 Runtime LMA Assignment February 2012

[RFC5142] Haley, B., Devarapalli, V., Deng, H., and J. Kempf,
"Mobility Header Home Agent Switch Message", RFC 5142,
January 2008.

[RFC5779] Korhonen, J., Bournelle, J., Chowdhury, K., Muhanna, A.,
and U. Meyer, "Diameter Proxy Mobile IPv6: Mobile Access
Gateway and Local Mobility Anchor Interaction with
Diameter Server", RFC 5779, February 2010.

[RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
Mobile IPv6", RFC 5844, May 2010.

[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.

[RFC6097] Korhonen, J. and V. Devarapalli, "Local Mobility Anchor
(LMA) Discovery for Proxy Mobile IPv6", RFC 6097,
February 2011.

Korhonen, et al. Standards Track [Page 21]

RFC 6463 Runtime LMA Assignment February 2012

Authors' Addresses

Jouni Korhonen (editor)
Nokia Siemens Networks
Linnoitustie 6
FI-02600 Espoo
Finland

EMail: [email protected]

Sri Gundavelli
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA

EMail: [email protected]

Hidetoshi Yokota
KDDI Lab
2-1-15 Ohara, Fujimino
Saitama 356-8502
Japan

EMail: [email protected]

Xiangsong Cui
Huawei Technologies
Huawei Building, No. 156 Beiqing Rd.
Z-park, Shi-Chuang-Ke-Ji-Shi-Fan-Yuan
Hai-Dian District, Beijing 100095
P.R. China

EMail: [email protected]

Korhonen, et al. Standards Track [Page 22]