One document matched: draft-bournelle-pana-ctp-01.txt
Differences from draft-bournelle-pana-ctp-00.txt
Network Working Group J. Bournelle (Ed.)
Internet-Draft M. Laurent-Maknavicius
Expires: april 1, 2005 GET/INT
H. Tschofenig
Siemens
Y. El Mghazli
Alcatel
G. Giaretta
TILab
October 2004
Use of Context Transfer Protocol (CTP) for PANA
draft-bournelle-pana-ctp-01
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2004).
Abstract
The PANA protocol offers a way to authenticate clients in IP based
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access networks. It carries EAP over UDP which permits ISPs to use
multiple authentication methods. However, in roaming environments IP
clients might change of gateways and new EAP authentication from
scratch may occur. This can considerably degrade performance.
To enhance IP handover in mobile environments, the Context Transfer
Protocol (CTP) could be used. This protocol could recover from
previous PANA Authentication Agent the PANA security context
previously established. However the interaction between CTP and PANA
raises some questions and issues. It appears that it is difficult to
apply CTP for PANA.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 PANA overview . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1 IPsec based access control . . . . . . . . . . . . . . 5
3.1.2 Limitations . . . . . . . . . . . . . . . . . . . . . 6
3.2 CTP overview . . . . . . . . . . . . . . . . . . . . . . . 6
4. General considerations in the use of CTP for PANA . . . . . . 8
4.1 Conditions to Perform the Transfer . . . . . . . . . . . . 8
4.2 Transfer of AAA-Key . . . . . . . . . . . . . . . . . . . 8
4.3 Interaction with the AAA infrastructure . . . . . . . . . 9
4.4 The PANA Context . . . . . . . . . . . . . . . . . . . . . 11
5. Possible approaches to perform the transfer . . . . . . . . . 14
5.1 PANA solution . . . . . . . . . . . . . . . . . . . . . . 14
5.2 CTP friendly approach . . . . . . . . . . . . . . . . . . 15
5.2.1 Operations in non-predictive mode . . . . . . . . . . 15
5.2.2 Operations in predictive mode . . . . . . . . . . . . 17
5.3 Optimized approach . . . . . . . . . . . . . . . . . . . . 18
5.3.1 Operations in the Non-predictive mode . . . . . . . . 18
5.3.2 Operations in the Predictive mode . . . . . . . . . . 20
6. PANA CTP interactions . . . . . . . . . . . . . . . . . . . . 21
7. Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8. Security considerations . . . . . . . . . . . . . . . . . . . 23
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 24
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 25
Intellectual Property and Copyright Statements . . . . . . . . 27
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1. Introduction
In IP based access network, PANA [I-D.ietf-pana-pana] may be used as
a front-end to a AAA architecture in order to authenticate users
before granting them access to the resources. For this purpose, it
uses EAP which offers a variety of authentication methods. In a
shared medium this is typically accomplished with the help of
cryptographic mechanisms. Note that this type of cryptographic
mechanism prevents a malicious node from sending packet to the
network and thereby authenticating each data packet. In addition,
encryption is often enabled to prevent eavesdropping.
While roaming, the PANA client might change its access router.
Without extensions to PANA the PaC has to restart a new PANA protocol
exchange to authenticate itself to the network. In some cases it is
necessary to execute the EAP exchange from scratch whereas in other
cases it might be possible to benefit from state stored at the
visited networks AAA server. This procedure is known as fast resume.
In this document, we analyse the interaction between the framework
defined in [I-D.ietf-seamoby-ctp] and PANA. In particular, we define
what should be transferred (i.e. the PANA context) and the
interactions with the AAA infrastructure.
Three possible solutions are also given. The first one is the
solution given in the PANA specification [I-D.ietf-pana-pana]. In
the second approach, we try to strictly apply CTP. Finally, the last
approach proposed an optimized version of the previous one.
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2. Terminology
This document uses the following terms or abbreviations:
PANA Protocol for Carrying Network Authentication for Network Access
PaC PANA Client. A mobile node (MN) using a PANA protocol
implementation to authenticate itself to the network.
nAR New Access Router. The router to which the PaC attaches after
the handover.
pAR Previous Access Router. The router to which the PaC was attached
before the handover.
nPAA New PANA Authentication Agent. The PAA in charge of the subnet
to which the PaC was attached before the handover.
pPAA Previous PANA Authentication Agent. The PaC's default PAA prior
to handover.
EP Enforcement Point.
CTP Context Transfer Protocol.
CTD Context Transfer Data.
CTAR Context Transfer Activate Request.
CTAA Context Transfer Activate Acknowledge.
FPT Feature Profile Type.
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3. Background
3.1 PANA overview
PANA is a protocol that carries EAP over IP/UDP to authenticate
users. The PANA Authentication Agent (PAA) is the endpoint of the
PANA protocol at the access network. The PAA itself might not be
able to authenticate the user by terminating the EAP protocol.
Instead the PAA might forward the EAP payloads to the backend AAA
infrastructure.
The Enforcement Point (EP) is an entity which enforces the result of
the PANA protocol exchange. The EP might be co-located with the PAA
or separated as a stand-alone device. In the latter case, the SNMPv3
protocol [I-D.ietf-pana-snmp] is used to communicate between PAA and
EP.
A successful EAP authentication exchange results in a PANA security
association (PANA SA) if the EAP method was able to derive session
keys. In this case, all further PANA messages between PaC and PAA
will be authenticated, replay and integrity protected thanks to the
MAC AVP.
3.1.1 IPsec based access control
[I-D.ietf-pana-ipsec] describes how PANA could enable IPsec between
PaC and the EP. An IKE pre-shared key is distributed to PaC and EP.
Then, IKE is used to setup an ESP tunnel. Figure 1 describes a
possible architecture, AR/EP is the default router of the PaC and all
its traffic is protected by the ESP tunnel.
+----- PAA
|
|
PaC ================= AR/EP
(ESP tunnel)
Figure 1: PANA IPsec based access control
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3.1.2 Limitations
PaC ------------ pEP ---- pPAA
| |
| |
| +------ pAR
(roaming) |
|
v
PaC ------------ nEP ---- nPAA
|
|
+------ nAR
Figure 2: Example Scenario
Figure 2 shows an example scenario with a roaming PaC which has been
previously authenticated. The PAA must be at one IP hop away from
PaC; this means that a specific PANA module on a PAA is in charge of
one IP network. After a PaC's IP handover, the PaC changes of IP
subnet and of PAA accordingly. The new PAA (nPAA) does not share any
context with the PaC. The new EP (nEP) will detect the PaC and will
trigger a new PANA authentication phase from scratch. A new
authentication phase involving the AAA infrastructure will then
occur. Such a signaling can seriously degrades handover performance
in term of latency.
For this reason, we propose to use the Context Transfer Protocol
(CTP) to transfer PANA context established with the PaC from pPAA to
the nPAA.
3.2 CTP overview
Context Transfer Protocol (CTP) [I-D.ietf-seamoby-ctp] enables
context transfers between access routers (ARs). The context transfer
can be either initiated by a request from the mobile node ("mobile
initiated") or at the initiative of either the new or the previous
access router ("network initiated"). Furthermore it can be performed
prior to handover ("predictive mode") or after the handover
("non-predictive mode").
In non-predictive mode, the MN sends a CT Activate Request (CTAR) to
the new AR (nAR). In this message the MN includes an authorization
token: this token is calculated based on a secret shared between the
MN and the previous AR (pAR) and it is used in order to authorize the
transfer. This means that the MN and the AR must share a secret.
The definition of this secret is out of scope of CTP. As soon as the
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nAR receives a CTAR message, it generates a CT-Request message which
includes the authorization token and the context to be transferred
(i.e. Feature Profile Types). This message is received by the pAR
that verifies the authorization token and sends a Context Transfer
Data (CTD) message including the context requested.
In the predictive case, the pAR receives a CTAR message from the MN
whose feature contexts are to be transferred. This message provides
the IP address of the nAR and an authorization token. The pAR
predictively transmits to the nAR a Context Transfer Data (CTD) that
contains feature contexts. This message contains also parameters for
the nAR to compute an authorization token in order to verify the MN's
token. Regardless the MN sent the CTAR to the pAR, it sends another
CTAR message to the nAR in order to ascertain that the context
transfer reliably took place. Furthermore in this CTAR the MN
includes the authorization token so that the nAR verifies it.
CTP messages use Feature Profile Types (FPTs) to identify the way
data is organized for a particular feature context. The FPTs are
registered in a number space that allows a node to unambiguously
determine the type of context and the context parameters present in
the protocol messages.
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4. General considerations in the use of CTP for PANA
A PaC connected to an access network shares a context with its access
router like e.g. compression type, Quality of service parameters and
security state. As motivated in the previous sections, the goal of
this document is to reduce the overhead of establishing state between
the PaC and the nPAA. CTP [I-D.ietf-seamoby-ctp] permits to avoid
signaling overhead during roaming by enabling authorized context
transfer between access routers
However, CTP only offers a framework and does not define a particular
context. In particular, it appears that PANA is likely to use this
protocol to enhance mobility handling.
The aim of this section is to give general considerations on the use
of CTP for PANA.
4.1 Conditions to Perform the Transfer
In this section, we list conditions and recommandations to perform a
PANA context transfer between two PAAs. This list is mostly
inherited from [I-D.aboba-802-context]
o Homogeneous PAA's device deployment within a single administrative
domain.
o Trust between devices engaged in the context transfer. CTP
indicates that IPsec ESP must be used.
o The nPAA should not obtain keys used to encrypt traffic between
PaC and pEP.
4.2 Transfer of AAA-Key
According to EAP [I-D.ietf-eap-keying], the figure below illustrates
the keys hierarchy in the PANA case:
PaC pPAA AAA/EAP
--- ---- -------
MSK MSK MSK
EMSK EMSK
AAA-Key AAA-Key <---------- AAA-Key
PANA_MAC_Key PANA_MAC_Key
MSK and EMSK are derived from the EAP method used between the PaC and
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the AAA/EAP server. Those keys must not be exported from the EAP
module. The AAA-Key is computed from MSK and EMSK. This key is
exported to the pPAA. The PANA_MAC_KEY, used to protect PANA
messages, is derived from the AAA-Key using the following way:
PANA_MAC_KEY = The first N bits of
HMAC_SHA1(AAA-Key, PaC_nonce | PAA_nonce | Session-ID)
For security reasons, after the IP handover, the PaC and nPAA should
derive a new PANA_MAC_Key cryptographically separated from the
previous one. This can be accomplished by deriving a new AAA-Key
cryptographically separated from the previous AAA-Key.
The only solution to have a new PANA_MAC_Key cryptographically
separated from the old one should be to obtain a new one from the
AAA/EAP server.
We propose to use the same solutions as proposed in
[I-D.ietf-pana-pana]. For this, the pPAA provides to nPAA an
intermediate AAA-Key:
AAA-Key-int = The first N bits of
HMAC-SHA1(AAA-Key, DiameterIdentity | Session-ID)
DiameterIdentity is the identifier of the pPAA and Session-ID is the
identifier of the Session between the pPAA and PaC.
If there are two AAA-Keys generated by a NAP/ISP authentication.
pPAA provides the following key:
AAA-Key-int = The first N bits of
HMAC-SHA1(AAA-Key1 | AAA-Key2, DiameterIdentity |
Session-ID)
During the PSR/PSA exchange, PaC and nPAA must provide nonces that
are used to derive a new AAA-Key:
AAA-Key-new = The first N bits of
HMAC-SHA1(AAA-Key-int, PaC_nonce | PAA_nonce)
The new PANA_MAC_Key used to compute AVP MAC will be calculated from
this key.
4.3 Interaction with the AAA infrastructure
PAAs use AAA infrastructure to authenticate PaC. This means that the
PAA contacts a (local) AAA server and relay the EAP messages in order
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to authenticate a PaC.
We have two possible situations depending on roaming situation. We
only consider use of RADIUS [RFC2865] or Diameter EAP application
[I-D.ietf-aaa-eap].
+-----+ +-----+ +-----+
| PaC |<------->| PAA |<----->| AAA |
+-----+ +-----+ +-----+
Figure 4: Local authentication
In Figure 4, the PaC is authenticated in its home domain. The PAA
contacts its local AAA server.
+-----+ +-----+ +------+
| PaC |<------->| PAA |<----->| AAAL |
+-----+ +-----+ +--+---+
^
|
v
+--+---+
| AAAH |
+------+
Figure 5: PaC in a visited domain
In Figure 5, the PaC is in a visited domain. It can not be
authenticated by the local AAA server (AAAL). In this case, the PAA
contacts a local AAA entity.
In the first situation, the PAA shares a session with only one AAA
server. This server keeps information on the PaC authenticated such
as session-lifetime, PAA's identity, authorized services...In some
cases, the AAA server may have to contact the PaC and thus if the PaC
changes of PAAs, it seems necessary to contact the AAA server to
inform it of the new PAA in charge of the PaC.
The second situation is a little bit more complex since the PAA does
not know the AAAH's identity. We can however state that it is
necessary for the PAA to inform its local AAA entity of PaC's new
location. Depending on policy, the AAAL server should inform the
AAAH server.
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+----------+
| AAA(L/H) |
+----------+
^
| nPAA's identity
|
|
+---+--+ +------+
| pPAA |----------------->| nPAA |
+------+ +------+
AAA's identity
Figure 6: The pPAA contacts the AAA infrastructure
To inform the AAA server of PaC's new location, we have two
solutions. In the first one (cf. Figure 6), the pPAA is in charge
of contacting the AAA server to inform it of the nPAA.
+----------+
| AAA(L/H) +<-----------------+
+----------+ |
I'm in |
charge of PaC |
|
|
+------+ +--+---+
| pPAA |----------------->| nPAA |
+------+ +------+
AAA's identity
Figure 7: The nPAA contacts AAA infrastructure
In the second one (cf. Figure 7), the nPAA informs the AAA server.
It also seems necessary to inform the nPAA of the AAA server's
identity.
4.4 The PANA Context
The PANA Context is what should be transferred between the two PAAs
to avoid re-authentication from scratch. The attributes described in
[I-D.ietf-pana-pana] list elements that could constitute the PANA
context at PAA. However some of these data are PAA specific and as
such does not need to be transferred.
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Figure 8 summarizes the PANA Context.
+------------------+------------+----------------------------+
| Data | Type | Length |
+------------------+------------+----------------------------+
| Session-Lifetime | Unsigned32 | Fixed |
| Elapsed | | |
+------------------+------------+----------------------------+
| AAA-Key-int | UTF8String | Fixed (64 octets) |
+------------------+------------+----------------------------+
| AAA server | UTF8String | Variable |
| Identity | | |
+------------------+------------+----------------------------+
| ISP-Identifier | Unsigned32 | Fixed |
+------------------+------------+----------------------------+
| ISP-Name | UTF8String | Variable |
+------------------+------------+----------------------------+
| NAP/ISP Separate | Unsigned32 | Fixed |
| Authentication | | |
+------------------+------------+----------------------------+
Figure 8: The PANA Context
Data have the following meanings:
Session-Lifetime: The authentication phase also determines the PANA
session lifetime when authorization succeeds. This value is
included in Session-Lifetime AVP. In Diameter [RFC3588], this AVP
(Session-Timeout) is of type Unsigned32 and contains the maximum
number of seconds of service to be provided to the user before
session termination. Note that the value forwarded to the new PAA
needs to reflect the already 'consumed' session lifetime. This
helps to avoid problems where roaming is used to reset the
lifetime when re-attaching at a new PAA. It must be assured that
the sum of the individual session lifetimes is never greater than
the initially communicated lifetime(type: Unsigned32, length: 4)
AAA-Key-int: cf. above.
AAA server identify: Identity of the AAA server used to authenticate
the PaC.
ISP-Identifier IANA assigned "SMI Network Management Private
Enterprise Codes" of the provider.
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ISP-Name UTF8-encoded name of the provider.
Separate NAP/ISP authentication This variable indicates if a separate
NAP/ISP authentication has been performed at pPAA.
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5. Possible approaches to perform the transfer
The transfer may occur either after or before the handover. From
this standpoint, we define two operating transfer modes:
Non-predictive mode: the PaC has already performed the handover. We
assume that it has already acquired an address.
Predictive mode: the transfer occurs before the handover.
Different approaches exist to perform PANA context transfer using
CTP. The aim of this section is to describe three of them and to
discuss interaction between CTP specification and PANA.
In each of those 3 solutions, the transfer occurs between PAAs and
they use a CTD message containing the PANA context.
The CTD message is described in the following figure (ABNF notation):
CTD-PANA ::= < CTD-Header>
< Context Data Block, Ctx-Type: PANA-Context-Transfer, FPT>
{ Session-Lifetime-Elapsed }
{ AAA-Key-int }
{ AAA server's identity }
{ ISP-Identifier }
{ ISP-Name }
{ Double Authentication NAP/ISP information }
Figure 9: CTD-PANA message
where FPT (Feature Profile Type) identifies the way the particular
feature context is organized.
5.1 PANA solution
In the solution proposed by PANA [I-D.ietf-pana-pana], the PaC does
not use CTAR message to request and activate the context. Instead,
it replies to PSR message with a PSA message containing the unexpired
previous PANA session identifier and a MAC AVP (cf. Figure 10).
This AVP is computed using the PANA_MAC_KEY shared between the PaC
and its pPAA.
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PaC nPAA pPAA
--- ---- ----
PSR[PAA_Nonce]
<------------
PSA[oSession-ID][PaC_Nonce][MAC]
-------------->
CT-Request [PSA]
---------------->
CTD-PANA
<----------------
PBR[nSession-Id][MAC]
<--------------
PBA [MAC]
--------------->
Figure 10: The PANA approach
The nPAA receives this PSA message and it deduces that it must
perform CTP (because of the Session-Id AVP). It determines the
identity of pPAA by looking at the DiameterIdentity part of the PANA
session identifier. It sends a CT-Request to the pPAA containing the
PSA message. The pPAA checks the validity of the PSA message and
transfers the PANA context in the CTD message. Then the PANA session
continues with a PANA-Bind exchange.
This procedure has the following issues:
o It does not support predictive mode since we do not have a CTAR
message.
o CTP does not define a way to carry PSA message in CT-Request.
o The CTP module can not validate the transfer since the CT-Request
does not provide any authorization token.
5.2 CTP friendly approach
5.2.1 Operations in non-predictive mode
As described in the previous paragraph, in order to handle PaC
mobility in the reactive case, the approach based on
[I-D.ietf-pana-pana] has some unsolved issues: these issues concern
the usage of CTP to perform the context transfer between PAAs. A
possible alternative approach is to perform the context transfer
relying completely on CTP as specified in [I-D.ietf-seamoby-ctp].
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Figure 11 shows the message flow if this CTP-friendly approach is
used.
PaC nPAA pPAA
--- ---- ----
PSR [PAA_Nonce] (handoff)
<--------------
CTAR
--------------->
CT-Request
--------------->
CTD-PANA
<----------------
CTAA
<---------------
PSA[(old Session-ID,) PaC_Nonce]
--------------->
PBR[nSession-Id]
<-------------
PBA
------------->
Figure 11: CTP friendly approach: non predictive mode
When the PaC performs a change of the point of attachment to the
network, it receives a trigger indicating that a handoff has occured
and consequently a context transfer should be performed. This
trigger might be a PSR message sent by the nPAA (as depicted in
Figure 11) or an internal DNA trigger (e.g. L2 "link-up" trigger).
Based on this event notification, the PaC begins the CTP procedure
sending to the nPAA a CTAR message to trigger the context transfer.
Based on [I-D.ietf-seamoby-ctp] this message MUST include the
previous address of the PaC, the address of the pPAA and an
authorization token needed to authorize the transfer. This
authorization token is computed using a key that we called
PANA_CTP_KEY. The nPAA sends a CT-Request to the pPAA including the
previous address of the PaC and the authorization token. These data
are needed to the pPAA in order to identify the PaC and to retrieve
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the associated PANA state. If the authorization token is verified
successfully, the pPAA sends to the nPAA the PANA context of the PaC
through a CTD-PANA message. Finally the nPAA sends a CTAA message to
the PaC as a confirm that the context transfer has been accomplished.
Upon the receipt of the CTAA, the PaC sends to the nPAA a PSA
message: the protocol operation continues as specified in section
4.11 of [I-D.ietf-pana-pana].
Even if it is compliant to CTP specification, this approach has
several open issues:
o [I-D.ietf-seamoby-ctp] specifies that the context transfer is
performed between Access Routers, while in this scenario it is
performed between PAAs;
o in CTP the transfer is authorized through the authorization token:
it should be defined the key (called PANA_CTP_KEY in this
document) needed to calculate this authorization token;
o if CTP operations are triggered by a PSR message (i.e. it is not
provided by layer 2 or by a DNA solution), the nPAA keeps on
sending PSR messages waiting to receive a PSA message; indeed the
PaC sends the PSA message only once the context transfer is
accomplished. This implies an inefficiency in PANA protocol
operations.
o in order to send a CTAR message, the PaC must know the nPAA IP
address. This could be an issue if CTP is triggered by DNA, since
a DNA solution might not provide the IP address of the nPAA. For
this reason, the PaC might be forced to perform a new discovery
phase to get the nPAA's address.
5.2.2 Operations in predictive mode
To trigger the transfer, PaC/MN sends a CTAR message to pPAA. In
this message, it includes data which permit the pPAA to recover the
nPAA's address. The nAR's address should be this value. An
authorization token is also computed using PANA-CTP-Key.
The pPAA sends the CTD message to the nPAA/AR indicated in the CTAR
message. In this case, it is a predictive CTD message and thus it
must also contain:
o Algorithm, Key length and PANA-CTP-Key: allows the nPAA to compute
a token locally and verify against the token present in the CTAR
message.
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o The PANA context as described above in Section 4.4
o The (previous) IP address of PaC.
pPAA may set the A flag (see [I-D.ietf-seamoby-ctp]) in order to have
an acknowledgment of this message.
The nPAA creates an entry for this PaC. PaC performs the handover
and sends CTAR message (after receiving a PSR message). nPAA
recovers the context using PaC's address indicated in the CTAR
message. It verifies the authorization token and if it is correct it
activates the context. Then they perform a PBR/PBA exchange. Thus
the nPAA can allocate a new session-id.
This predictive mode raises the following issue:
o After receiving the CTD message from pPAA, the nPAA creates an
entry for the PaC. But in which state is it for this PaC ? Do we
need to introduce a new state ?
5.3 Optimized approach
In this approach, we embed the CTAR message in the PSA message.
Thus, we reduce the number of messages.
5.3.1 Operations in the Non-predictive mode
PaC nPAA pPAA
--- ---- ----
PSR [PAA_Nonce]
<---------------
PSA [CTAR][PaC_Nonce]
--------------->
CT-Request
-------------->
CTD
<--------------
PBR[nSession-Id]
<-------------
PBA
------------->
While entering in the new network, the PaC will be detected and the
nPAA will send a PSR message. To trigger the transfer we propose to
answer by a PSA message containing a CTAR message in an AVP. The PSA
message should contain an AVP PaC_Nonce.
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This CTAR message should contain the following data:
o The previous PaC's address.
o The previous PAA's address.
o An authorization token computed over this message using a shared
key between PaC and pPAA (the PANA_CTP_KEY).
After receiving the PSA-CTAR message from the PaC, the PANA module
delivers the CTAR message to the PANA-CTP module. The PAA sends a
CT-Request to request the transfer. As noted in Section 4.1, this
message must be protected by ESP [I-D.ietf-ipsec-esp-v3] as specified
in [I-D.ietf-seamoby-ctp].
The pPAA verifies the authorization token before sending the CTD
message. The CTD message contains:
o The Elapsed Time in milliseconds. This value reflects the already
'consumed' session lifetime.
o The PaC's previous address.
o The PANA Context block.
This message must also be protected by ESP.
After receiving the CTD message, nPAA processes the following task:
o Parses the CTD message.
o (Changes state for this PaC ?)
o Generates the PAA_Nonce
o Computes the AAA-Key-new (from PaC_Nonce, AAA-Key-int and
PAA_Nonce)
o Derives the new PANA_MAC_Key
o Sends a PANA-Bind-Request containing:
* The newly allocated Session-ID in a Session-ID AVP.
* The PAA_Nonce.
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* An AVP MAC signed with the new PANA_MAC_Key.
o Waits a PANA-Bind-Answer from the PaC.
Issues:
o Do we need to introduce a new state to handle the period of time
where the nPAA is waiting the PaC's context from pPAA ?
o how do we generate the PANA-CTP-Key ?
o Piggyback of a CTP message in PANA.
5.3.2 Operations in the Predictive mode
The operations here are quite similar than in Section 5.2.2. The
difference is that the PaC embeds the CTAR message in the PSA after
the IP handover.
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6. PANA CTP interactions
The table below summarizes issues in using CTP to carry PANA context.
+----------+------------+-------------+
| PANA | CTP | Optimized |
+------------------+----------+------------+-------------+
| Transfer | no | no | no |
| between ARs | | | |
+------------------+----------+------------+-------------+
| CTAR message | no | yes | yes |
+------------------+----------+------------+-------------+
| predictive mode | no | yes | yes |
| supported | | | |
+------------------+----------+------------+-------------+
| Transfer | | | |
| authorized by | PANA | CTP | CTP |
+------------------+----------+------------+-------------+
| Trigger | PSR | PSR/DNA | PSR |
+------------------+----------+------------+-------------+
| State Machine | ? | yes | yes |
| Issue | | | |
+------------------+----------+------------+-------------+
Figure 13: PANA-CTP interactions
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7. Issues
This section lists the different issues raised in previous section.
o PAAs are not Access Routers. CTP states that context transfer
occurs between ARs.
o CT-request does not define a way to carry PSA message.
o Which protocol can be used to inform the AAA server of the nPAA in
charge of the PaC ? A AAA extension ?
o Who informs the local AAA entity of the new PAA in charge of the
PaC ? (pPAA or nPAA ?)
o How do we compute the PANA-CTP-Key ?
o If Session-Lifetime is near its expiration, is it necessary to
perform the transfer ? If yes, how do we manage this ?
o State machine modification in PaC and PAA ?
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8. Security considerations
This document deals with interaction between the Seamoby Context
Transfer Protocol and PANA. Therefore, all security considerations
described in [I-D.ietf-seamoby-ctp] and in [I-D.ietf-pana-pana] apply
also here.
The approach described in this document considers only the
intra-domain scenario. This means that the PAAs involved in the
context transfer belong to the same administrative domain.
Therefore, at this stage the inter-domain scenario is out of scope.
As described in [I-D.ietf-seamoby-ctp] IPsec ESP must be used to
protect CTP messages between PAAs. In order to avoid the
introduction of additional latency due to the need for establishment
of a secure channel between the context transfer peers, the two PAAs
should establish such a secure channel in advance. The mechanism
used by the PAAs to establish such a channel is out of the scope of
this draft: for example, IKE [RFC2409] with pre-shared key
authentication might be used.
Furthermore, CTP requires that the PaC and the PAA possess a shared
secret to calculate the authorization token: for this purpose, this
document defines a new key PANA-CTP-Key probably derived from the
AAA-Key. The mechanism used by the nPAA to derive a new AAA-key and
consequently a new PANA-CTP-key is specified in [I-D.ietf-pana-pana].
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9. Acknowledgements
The authors would like to thank Rafael Marin Lopez, Yoshihiro Ohba,
Jean-Jacques Puig, Ren?? Soltwitsch and Alper Yegin for their
valuable comments.
10 References
[I-D.irtf-aaaarch-handoff]
Arbaugh, W. and B. Aboba, "Experimental Handoff Extension
to RADIUS", draft-irtf-aaaarch-handoff-04 (work in
progress), November 2003.
[I-D.ietf-pana-pana]
Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H. and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", draft-ietf-pana-pana-06 (work in
progress), October 2004.
[I-D.ietf-pana-ipsec]
Parthasarathy, M., "PANA enabling IPsec based Access
Control", draft-ietf-pana-ipsec-04 (work in progress),
September 2004.
[I-D.ietf-pana-snmp]
Mghazli, Y., Ohba, Y. and J. Bournelle, "SNMP usage for
PAA-2-EP interface", draft-ietf-pana-snmp-01 (work in
progress), July 2004.
[I-D.ietf-seamoby-ctp]
Loughney, J., "Context Transfer Protocol",
draft-ietf-seamoby-ctp-11 (work in progress), August 2004.
[I-D.ietf-ipsec-esp-v3]
Kent, S., "IP Encapsulating Security Payload (ESP)",
draft-ietf-ipsec-esp-v3-09 (work in progress), October
2004.
[I-D.aboba-802-context]
Aboba, B. and T. Moore, "A Model for Context Transfer in
IEEE 802", draft-aboba-802-context-02 (work in progress),
April 2002.
[RFC2988] Paxson, V. and M. Allman, "Computing TCP's Retransmission
Timer", RFC 2988, November 2000.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
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[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.
[I-D.ietf-eap-keying]
Aboba, B., "Extensible Authentication Protocol (EAP) Key
Management Framework", draft-ietf-eap-keying-03 (work in
progress), July 2004.
[I-D.ietf-aaa-eap]
Eronen, P., Hiller, T. and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application",
draft-ietf-aaa-eap-09 (work in progress), August 2004.
[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)", RFC
2865, June 2000.
Authors' Addresses
Julien Bournelle
GET/INT
9 rue Charles Fourier
Evry 91011
France
EMail: julien.bournelle@int-evry.fr
Maryline Laurent-Maknavicius
GET/INT
9 rue Charles Fourier
Evry 91011
France
EMail: maryline.maknavicius@int-evry.fr
Hannes Tschofenig
Siemens Corporate Technology
Otto-Hahn-Ring 6
81739 Munich
Germany
EMail: Hannes.Tschofenig@siemens.com
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Yacine El Mghzali
Alcatel
Route de Nozay
Marcoussis 91460
France
EMail: yacine.el_mghazli@alcatel.fr
Gerardo Giaretta
TILab
via G. Reiss Romoli, 274
TORINO 10148
Italy
EMail: gerardo.giaretta@telecomitalia.it
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