NETLMM WG A. Muhanna
Internet-Draft M. Khalil
Intended status: Standards Track Nortel
Expires: January 9, 2009 S. Gundavelli
K. Leung
Cisco Systems
July 08, 2008
GRE Key Option for Proxy Mobile IPv6
draft-muhanna-netlmm-grekey-option-04.txt
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Copyright (C) The IETF Trust (2008).
Abstract
The Proxy Mobile IPv6 base specification and Proxy Mobile IPv6
support for IPv4 allow the mobile node's IPv4 and IPv6 traffic
between the local mobility anchor and the mobile access gateway to be
tunneled using IPv6 or IPv4 encapsulation headers. These
encapsulation modes do not offer the tunnel end-points the required
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semantics to expose a service identifier that can be used to identify
traffic for a certain classification, such as for supporting mobile
nodes that are using overlapping private IPv4 addressing. The
extension defined in this document allow the mobile access gateway
and the local mobility anchor to negotiate GRE encapsulation mode and
exchange the GRE keys for marking the flows, so that differential
processing can be applied by the tunnel peers over those flows.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions & Terminology . . . . . . . . . . . . . . . . . . 3
2.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. GRE Encapsulation and Keys Exchange . . . . . . . . . . . . . 4
3.1. GRE Encapsulation Overview . . . . . . . . . . . . . . . . 4
3.2. GRE Encapsulation Support . . . . . . . . . . . . . . . . 6
3.3. GRE Keys Exchange Mechanism . . . . . . . . . . . . . . . 6
3.3.1. Initial GRE Keys Exchange . . . . . . . . . . . . . . 6
3.3.2. GRE Keys De-registration . . . . . . . . . . . . . . . 6
4. Mobile Access Gateway Considerations . . . . . . . . . . . . . 7
4.1. Extensions to the Conceptual Data Structure . . . . . . . 7
4.2. Operational Summary . . . . . . . . . . . . . . . . . . . 7
5. Local Mobility Anchor Considerations . . . . . . . . . . . . . 8
5.1. Extensions to the Binding Cache Entry . . . . . . . . . . 8
5.2. Operational Summary . . . . . . . . . . . . . . . . . . . 9
6. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 10
6.1. GRE Encapsulation Option . . . . . . . . . . . . . . . . . 10
6.2. Status Codes . . . . . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
10. Normative References . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
The base Proxy Mobile IPv6 specification [ID-PMIP6] and Proxy Mobile
IPv6 support for IPv4 [ID-PMIP6-IPv4] allow the use of IPv6 and IPv4
encapsulation modes [RFC2473] , [RFC2003] for the tunneled traffic
between the local mobility anchor and the mobile access gateway.
There are scenarios where these encapsulation modes are not
sufficient to uniquely identify the destination of packets of a
specific flow. Thus, there is a need for an encapsulation mode with
richer semantics. The Generic Routing Encapsulation [RFC2784] and
the Key extension as defined in [RFC2890], has the required semantics
to allow such distinction for use in Proxy Mobile IPv6.
This document defines an extension to the base Proxy Mobile IPv6
specification, for allowing the mobile access gateway and the local
mobility anchor to negotiate GRE encapsulation mode and exchange the
downlink and uplink GRE keys that can be used for marking the
downlink and uplink traffic which belong to a specific mobile node
session or a specific flow.
2. Conventions & Terminology
2.1. Conventions
The keywords "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
All the general mobility related terminology and abbreviations are to
be interpreted as defined in Mobile IPv6 specification [RFC3775] and
Proxy Mobile IPv6 specification [ID-PMIP6]. The following terms are
used in this document.
Downlink Traffic
The traffic in the tunnel between the local mobility anchor and
the mobile access gateway, heading towards the mobile access
gateway and tunneled at the local mobility anchor. This traffic
is also referenced as forward direction traffic.
Uplink Traffic
The traffic in the tunnel between the mobile access gateway and
the local mobility anchor, heading towards the local mobility
anchor and tunneled at the mobile access gateway. This traffic is
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also referenced as reverse direction traffic.
Downlink GRE Key
The GRE key is assigned by the mobile access gateway and used by
the local mobility anchor to mark the downlink traffic which
belongs to a specific mobile node session or flow as described in
this document.
Uplink GRE Key
The GRE key is assigned by the local mobility anchor and used by
the mobile access gateway to mark the uplink traffic which belongs
to a specific mobile node session or flow as described in this
document.
3. GRE Encapsulation and Keys Exchange
3.1. GRE Encapsulation Overview
Using the extension defined in this specification, the mobile access
gateway and the local mobility anchor can negotiate GRE encapsulation
mode and the exchange of GRE keys for marking the downlink and uplink
traffic.
Once the GRE keys have been exchanged between the mobile access
gateway and the local mobility anchor, the mobile access gateway will
use the uplink GRE key that is assigned by the local mobility anchor
in the GRE encapsulation header of the uplink payload packet.
Similarly, the local mobility anchor will use the downlink GRE key as
negotiated with the mobile access gateway in the GRE encapsulation
header of the downlink payload packet.
The following illustration explains the use of GRE encapsulation mode
and the use of GRE keys for supporting the scenario where overlapping
IPv4 private address [RFC1918] allocation is in use.
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+------------+
| Operator-A |
| |
| 10.x.0.0/16|
+------------+
/
+------+ +------+ /
| | ========================== | | /
MN-1---| | / \ | | / Key-1
| M | / ---Flows with GRE Key-1 ---- \ | L | / Traffic
MN-2---| A |--| |--| M |-
| G | \ ---Flows with GRE Key-2 ---- / | A | \ Key-2
MN-3---| | \ / | | \Traffic
| | ========================== | | \
MN-4---| | Proxy Mobile IPv6 Tunnel | | \
+------+ +------+ \
\
Operator-C: Access Network +------------+
| Operator-B |
| |
| 10.x.0.0/16|
+------------+
Figure 1: Overlapping IPv4 Private Address Space
Figure 1 illustrates a local mobility anchor providing mobility
service to mobile nodes that are from different operators and are
assigned IPv4 addresses from overlapping private address space. In
this scenario, the mobile access gateway and the local mobility
anchor must be able distinguish the flows belonging to a given
operator from the flows belonging to some other operator.
The mobile nodes, MN-1 and MN-2 are visiting from Operator-A, and
mobile nodes, MN-3 and MN-4 are visiting from Operator-B. The mobile
access gateway and the local mobility anchor exchange a specific pair
of downlink and uplink GRE keys and save them as part of the mobile
node binding to be used for identifying the flows belonging to each
mobile node.
The local mobility anchor and the mobile access gateway will be able
to distinguish each mobile node flow(s) based on the GRE key present
in the GRE header of the tunneled packet, and route them accordingly.
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3.2. GRE Encapsulation Support
To request GRE encapsulation support without exchanging the GRE keys,
the mobile access gateway MUST include the GRE Encapsulation Option
in the Proxy Binding Update message sent to the local mobility
anchor. The mobile access gateway MUST set the length field of the
GRE encapsulation option to 2.
If the local mobility anchor supports GRE encapsulation and upon the
successful process of the Proxy Binding Update, the LMA sends a Proxy
Binding Acknowledgement and MUST include the GRE Encapsulation option
with the length field set to 2.
However, If the local mobility anchor does not support GRE
encapsulation, the LMA MUST reject the Proxy Binding Update by
sending a Proxy Binding Acknowledgement message with the status field
is set to TBA1 as defined in Section 6.2.
3.3. GRE Keys Exchange Mechanism
The following subsections describe how the mobile access gateway and
the local mobility anchor exchange downlink and uplink GRE keys using
proxy mobile IPv6 registration procedure. The mechanism for de-
registering the GRE keys pair(s) is also described.
3.3.1. Initial GRE Keys Exchange
When the mobile access gateway determines based on, e.g., private
IPv4 address overlapping [RFC1918] support, the MAG local policy, or
MAG-LMA peer agreement that GRE encapsulation is needed and a new
pair of GRE keys is required, the mobile access gateway MUST include
the GRE Encapsulation Option in the Proxy Binding Update message sent
to the local mobility anchor. The mobile access gateway MUST include
the downlink GRE key in the GRE Key Identifier field.
Upon the successful process of the PBU and accepting the downlink GRE
key, the LMA MUST include the uplink GRE key and echo the downlink
included in the GRE Key Identifier field of the option. In this
case, the first key is the downlink key while the second is the
uplink key.
3.3.2. GRE Keys De-registration
If the GRE key option is present in the initial PBU, it MUST always
be present in the re-registration or de-registration messages and
with the same GRE key value.
If the local mobility anchor successfully process a deregistration
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PBU message which contains a GRE Encapsulation option with a downlink
GRE key included, the LMA follows the same session deregistration
process as per the base Proxy Mobile IPv6 specification [ID-PMIP6] to
clean the binding cache entry and the associated resources including
the uplink GRE key. In the case that the deregistration PBU does not
include the GRE encapsulation option and the corresponding mobile
node session has been assigned downlink and uplink GRE keys, the LMA
will follow the same process in cleaning the associated resources
including the GRE keys. The mechanism that the LMA uses for
reassigning the uplink GRE keys for other sessions is implementation
specific and out of scope.
4. Mobile Access Gateway Considerations
4.1. Extensions to the Conceptual Data Structure
Every mobile access gateway maintains a Binding Update List entry for
each currently attached mobile node, as explained in Section 6.1 of
the base Proxy Mobile IPv6 specification [ID-PMIP6]. To support this
specification, the conceptual Binding Update List entry data
structure must be extended with the following three new additional
fields.
o A flag indicating whether GRE encapsulation is enabled for the
mobile node's traffic flows.
o The Downlink GRE Key used in the GRE encapsulation header of the
tunneled packet from the local mobility anchor to the mobile
access gateway that is destined to the mobile node. This GRE Key
is generated by the MAG and communicated to the LMA in the GRE
Encapsulation option in the PBU message.
o The Uplink GRE Key used in the GRE encapsulation header of the
tunneled packet from the mobile access gateway to the local
mobility anchor that is originating from the mobile node. This
GRE Key is obtained from the GRE Key Identifier field of the GRE
Encapsulation option present in the received PBA message sent by
the LMA as specified in this document.
4.2. Operational Summary
o If IPv4 Home Address support is enabled for the mobile node and if
the IPv4 Home Address Option is included in the Proxy Binding
Update message that is sent by the mobile access gateway to the
mobile node's local mobility anchor, the GRE Encapsulation Option
MAY be included in the Proxy Binding Update message. In order to
exchange GRE keys, the MAG MUST include the downlink GRE key in
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the GRE Key Identifier field.
o After receiving a Proxy Binding Acknowledgment message with the
status code indicating the acceptance of the Proxy Binding Update
message and with the GRE Encapsulation Option with both the
downlink and uplink GRE keys, the mobile access gateway MUST
update the related three fields in the mobile node Binding Update
List entry described in Section 4.1. Additionally, the MAG MUST
use the assigned uplink GRE Key for tunneling all the traffic
originating from the mobile node.
o For a given mobile node, if the local mobility anchor rejects the
Proxy Binding Update by sending the Proxy Binding Acknowledgement
with the status code TBA1 (GRE Encapsulation not supported), the
mobile access gateway MUST NOT include the GRE Encapsulation
Option in the subsequent Proxy Binding Update messages that are
sent to that LMA.
o If the mobile access gateway has sent a Proxy Binding Update
message without the GRE Encapsulation Option, but the received
Proxy Binding Acknowledgement has the Status Code TBA2, indicating
that the GRE encapsulation is required, the mobile access gateway
SHOULD resend the Proxy Binding Update message with the GRE
Encapsulation Option.
o On receiving a packet from the tunnel with the GRE encapsulation
header, the mobile access gateway MUST use the GRE Key to
determine the necessary special processing for the data packet,
e.g., lookup the mobile node's layer-2 address, determine any
special processing or treatment for the data packet flow, before
forwarding the packet after removing the encapsulation headers.
5. Local Mobility Anchor Considerations
5.1. Extensions to the Binding Cache Entry
When the local mobility anchor and the mobile access gateway
successfully negotiates GRE encapsulation and exchange downlink and
uplink GRE keys, the local mobility anchor MUST maintain the downlink
and uplink GRE keys as part of the mobile node BCE. This requires
that the BCE described in section 5.1 of the Proxy Mobile IPv6 base
specification [ID-PMIP6] is extended. To support this specification,
the BCE must be extended with the following three additional fields.
o A flag indicating whether GRE encapsulation is enabled for the
mobile node's traffic flows.
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o The Downlink GRE Key, assigned by the MAG and used in the GRE
encapsulation header of the tunneled packet from the local
mobility anchor to the mobile access gateway.
o The Uplink GRE Key, assigned by the LMA and used in the GRE
encapsulation header of the tunneled packet from the mobile access
gateway to the local mobility anchor.
5.2. Operational Summary
o Upon receiving a Proxy Binding Update message with the GRE
Encapsulation Option, the local mobility anchor, if it does not
support GRE encapsulation mode, MUST send the Proxy Binding
Acknowledgement message to the mobile access gateway with the
status code TBA1 as defined in Section 6.2.
o Upon the successful process of a Proxy Binding Update message with
the GRE Encapsulation Option with the downlink GRE key included in
the GRE Key Identifier field, the local mobility anchor MUST
include the GRE Encapsulation option with the downlink and uplink
GRE keys in the GRE Key Identifier field when responding with a
successful PBA message. When GRE Key Identifier field carries the
downlink and uplink GRE keys, the first key is always set to the
downlink GRE key.
o If the GRE tunneling is negotiated and the downlink and uplink GRE
keys have been exchanged between the local mobility anchor and the
mobile access gateway, every packet that is destined to the mobile
node through the local mobility anchor MUST be encapsulated with a
GRE header using the negotiated downlink GRE key.
o If the received Proxy Binding Update message does not contain the
GRE Encapsulation Option, and if the local mobility anchor
determines that GRE encapsulation is required, e.g., overlapping
IPv4 private addressing is in use, LMA local policy, the local
mobility anchor MUST reject the request, and MUST send the Proxy
Binding Acknowledgement message to the mobile access gateway with
the status code TBA2, indicating that GRE encapsulation is
required.
o On receiving a packet from the tunnel with the GRE encapsulation
header, the local mobility anchor MUST use the GRE Key present in
the GRE extension header to determine the necessary special
processing for the data packet, e.g., lookup the mobile node's
home gateway address, determine any special processing or
treatment for the data packet flow, before forwarding the packet
after removing the encapsulation headers.
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6. Message Formats
This section defines an extension to the Mobile IPv6 [RFC3775]
protocol messages for supporting the GRE tunneling and GRE Keys
exchange for Proxy Mobile IPv6.
6.1. GRE Encapsulation Option
A new option, the GRE Encapsulation Option, is defined for use in the
Proxy Binding Update and Proxy Binding Acknowledgment messages
exchanged between the mobile access gateway and the local mobility
anchor. This option can be used for negotiating GRE encapsulation
and exchanging the GRE keys to be applied by the peer on all GRE
encapsulated packets for the specified mobile node session or flow.
The alignment requirement for this option is 4n.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Key Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: GRE Encapsulation Option
Type
<IANA>
Length
8-bit unsigned integer indicating the length in octets of the
option, excluding the type and length fields. If the Length field
is set to 2, it indicates that the GRE keys are not being carried
in the option. If the length field is set to a value of 6 or 10,
it means that down link GRE key or downlink and uplink GRE keys
are carried, respectively.
Reserved
These fields are unused. They MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
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GRE Key Identifier
32-bit field containing the Downlink GRE Key, or 64-bit field
containing the Downlink and Uplink GRE keys. This field is
present in the mobility option only if the GRE keys are being
exchanged using the PBU and PBA messages.
6.2. Status Codes
The following status code values are defined for using them in the
Binding Acknowledgment message when using Proxy Mobile IPv6 protocol.
The value allocation for this usage needs to be approved by the IANA
and must be updated in the IANA registry.
TBA1: GRE Encapsulation not required.
TBA2: GRE Encapsulation and GRE Key Identifier option required.
7. IANA Considerations
This document defines a new Option, the GRE Encapsulation Option,
described in Section 6.1. This option is carried in the Mobility
Header. The type value for this option needs to be assigned from the
same numbering space as allocated for the other mobility options
defined in the Mobile IPv6 specification [RFC3775].
This document also defines two new Binding Acknowledgement status
codes TBA1 and TBA2 as described in Section 6.2. This document
requests that these two codes be allocated from the "Status Codes"
registry of the Mobility IPv6 Parameters located at
http://www.iana.org/assignments/mobility-parameters and that the
numeric value of these codes be greater than 128.
8. Security Considerations
The GRE Encapsulation Option, defined in this document, that can be
carried in Proxy Binding Update and Proxy Binding Acknowledgement
messages, reveals the group affiliation of a mobile node identified
by its NAI or an IP address. It may help an attacker in targeting
flows belonging to a specific group. This vulnerability can be
prevented, by enabling confidentiality protection on the Proxy
Binding Update and Acknowledgement messages where the presence of the
NAI and GRE Encapsulation Options establish a mobile node's relation
to a specific group. This vulnerability can also be avoided by
enabling confidentiality protection on all the tunneled data packets
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between the mobile access gateway and the local mobility anchor, for
hiding all the markings.
9. Acknowledgements
The authors would like to thank Allesio Casati, Barney Barnowski,
Mark Grayson and Parviz Yegani for their input on the need for this
option. The authors would like to thank Curtis Provost, Irfan Ali,
Julien Langanier, Jouni Korhonen, Suresh Krishnan, Kuntal Chowdhury,
and Vijay Devarapalli for their review and comments.
10. Normative References
[ID-PMIP6]
Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6",
draft-ietf-netlmm-proxymip6-18 (work in progress),
May 2008.
[ID-PMIP6-IPv4]
Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
Mobile IPv6", draft-ietf-netlmm-pmip6-ipv4-support-03
(work in progress), May 2008.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, September 2000.
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004.
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Authors' Addresses
Ahmad Muhanna
Nortel
2221 Lakeside Blvd.
Richardson, TX 75082
USA
Email: amuhanna@nortel.com
Mohamed Khalil
Nortel
2221 Lakeside Blvd.
Richardson, TX 75082
USA
Email: mkhalil@nortel.com
Sri Gundavelli
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Email: sgundave@cisco.com
Kent Leung
Cisco Systems
170 West Tasman Drive
San Jose, CA 95134
USA
Email: kleung@cisco.com
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