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Versions: 00 01 02 03 04 05 06 07                                       
   PANA Working Group
   Internet Draft                                      M. Parthasarathy
   Document: draft-ietf-pana-ipsec-04.txt                         Nokia
   Expires: March 2005                                   September 2004


                 PANA enabling IPsec based Access Control

Status of this Memo

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,
   and any of which I become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on December 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   The PANA (Protocol for carrying Authentication for Network Access)
   working group is developing a protocol for authenticating clients to
   the access network using IP based protocols.  The PANA protocol
   authenticates the client and also establishes a PANA security
   association between the PANA client and PANA authentication agent at
   the end of a successful authentication. This document discusses the
   details for establishing an IPsec security association using the PANA
   security association for enabling IPsec based access control.

Table of Contents



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               PANA enabling IPsec based Access Control September 2004

   1.0 Introduction..................................................2
   2.0 Keywords......................................................3
   3.0 Pre-requisites for IPsec SA establisment......................4
   4.0 IP Address Configuration......................................4
   5.0 IKE Pre-shared key derivation.................................5
   6.0 IKE and IPsec details.........................................6
   7.0 Packet Formats................................................6
   8.0 IPsec SPD entries.............................................7
   9.0 Dual Stack Operation.........................................11
   10.0 Security considerations.....................................11
   11.0 Normative References........................................12
   12.0 Informative References......................................12
   13.0 Acknowledgments.............................................13
   14.0 Revision log................................................13
   15.0 Appendix A..................................................14
   16.0 Author's Addresses..........................................15
   17.0 Full Copyright Statement..........Error! Bookmark not defined.


1.0 Introduction

   The PANA (Protocol for carrying Authentication for Network Access)
   working group is developing a protocol for authenticating clients to
   the access network using IP based protocols.  The PANA protocol
   authenticates the client and also establishes a PANA security
   association between the PANA client and PANA authentication agent at
   the end of successful authentication. The PANA authentication agent
   (PAA) indicates the results of the authentication using the PANA-
   Bind-Request message wherein it can indicate the access control
   method enforced by the access network. The PANA protocol [PANA-PROT]
   does not discuss any details of IPsec [RFC2401] security association
   (SA) establishment, when IPsec is used for access control. This
   document discusses the details of establishing an IPsec security
   association between PANA client and the enforcement point. The IPsec
   SA is established using IKE, which in turn uses the pre-shared key
   derived from the PANA SA for authentication. The IPsec SA used to
   protect the packet provides the assurance that the packet comes from
   the client that authenticated to the network.  Thus, the IPsec can be
   used for access control and specifically used to prevent the service
   theft mentioned in [PANA-THREATS]. The term "access control" in this
   document refers to the per-packet authentication provided by IPsec.

   Please refer to [PANAREQ] for terminology and definitions of terms
   used in this document. The following picture illustrates what is
   being protected with IPsec. The different scenarios of PANA usage are
   described in the [PANAREQ]. When IPsec is used, scenario 3 and 5 are
   supported as shown below. As shown in Figure 1, Enforcement Point
   (EP), Access Router (AR) and the PANA authentication agent are co-
   located which is described as scenario 3 in [PANAREQ].


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                      PaC ----------------------+
                      [D1]                      |
                                                +------EP/AR/PAA
                                                |
                      PaC ----------------------+
                      [D2]
                      |-----------IPsec----------|

                          Figure 1: PAA/EP/AR are co-located

   As show in Figure 2, only AR and EP are co-located. PAA is a separate
   node though located on the same link as AR and EP. All of them are
   one IP hop away from the PaC. This is the same as scenario 5
   described in [PANAREQ].

                                        +------PAA
                                        |
                      PaC ----------------------+
                      [D1]                      |
                                                +------EP/AR
                                                |
                      PaC ----------------------+
                      [D2]

                      |-----------IPsec----------|

                          Figure 2: EP and AR are co-located


   The IPsec security association protects the traffic between PaC and
   EP. In IPsec terms, EP is a security gateway (therefore a router) and
   forwards packets coming from the PaC to other nodes.

   First, this document discusses some of the pre-requisites for IPsec
   SA establishment. Next, it gives details on what should be
   communicated between PAA and EP. Then, it gives the details of IKE
   exchange with IPsec packet formats and SPD entries. Finally, it
   discusses the dual stack operation.

2.0 Keywords





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   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 [RFC2118].


3.0 Pre-requisites for IPsec SA establisment

   This document assumes that the following have already happened before
   the IKE exchange starts.

     1) PANA client (PaC) and PAA mutually authenticate each other using
        EAP methods that derive AAA-key [EAP-KEY].

     2) PaC learns the IP address of the Enforcement point (EP) during
        the PANA exchange.

     3) PaC learns that the network uses IPsec [RFC2401] for securing
        the link between PaC and EP during the PANA exchange.

4.0 IP Address Configuration

   The IP address configuration is explained in [PANA-FRAME]. Some of
   the details relevant to IPsec are briefly repeated here for clarity.
   PaC configures an IP address before the PANA protocol exchange
   begins. This address is called a pre-PANA address (PRPA). After a
   successful authentication, the client may have to configure a post-
   PANA address (POPA) for communication with other nodes, if PRPA is a
   local-use (e.g., link-local or private address) or a temporarily
   allocated IP address.

   The PRPA of the PaC may be a link-local address [IPV4-LINK] or a
   private address [RFC1918] or a routable address or an IPv6 link-local
   address [RFC2462]. Please refer to [PANA-FRAME] for more details on
   how these addresses may be configured. PaC would use the PRPA as the
   outer address of IPsec tunnel mode SA (IPsec-TOA). PaC also needs to
   configure an inner address (IPsec-TIA). There are different ways to
   configure IPsec-TIA.

     1) Some IPv4 IPsec implementations are known to work properly when
        the same address is configured as both the IPsec-TIA and IPsec-
        TOA. When PRPA is a routable address, PRPA may be used as both
        IPsec-TIA and IPsec-TOA and POPA may not be configured.

     2) In IPv4, an IPsec-TIA can be obtained via the configuration
        method available using DHCP over IPsec tunnels [RFC3456]. The
        minor difference from the original usage of [RFC3456] is that
        the IPsec-TOA does not need to be a routable address when
        [RFC3456] is used between PaC and EP.



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     3) When IKEv2 [IKEV2] is used for security association negotiation,
        the address configuration method available in [IKEV2] can be
        used for configuring the IPsec-TIA for both IPv4 and IPv6.

   There are other address configuration methods possible. They have
   some implementation issues, which are described in the Appendix A.

5.0 IKE Pre-shared key derivation

   If the network chooses IPsec to secure the link between PaC and EP,
   PAA should communicate the IKE pre-shared key, Key-Id, PRPA of the
   PaC, and the session-Id to EP before the IKE exchange begins.
   Whenever the IKE pre-shared key changes due to re-authentication as
   described below, the new value is computed by the PAA and
   communicated to the EP with all the other parameters.

   The IKE exchange between PaC and PAA is equivalent to the 4-way
   handshake in [IEEE80211i] following the EAP exchange. The IKE
   exchange establishes the IPsec SA similar to the pair-wise transient
   keys (PTK) established in [IEEE80211i]. The IKE exchange provides
   both key confirmation and protected cipher-suite negotiation.

   IKE pre-shared key is derived as follows.

   IKE Pre-shared Key = HMAC-SHA-1 (AAA-key, "IKE-preshared key" |
                           Session ID | Key-ID | EP-address)

   The values have the following meaning:

   AAA-key: A key derived by the peer and EAP server and transported to
   the authenticator [EAP-KEY].

   Session ID: The value as defined in the PANA protocol [PANA-PROT],
   identifies a particular session of a client.

   Key-ID: This identifies the AAA-key within a given session [PANA-
   PROT]. During the lifetime of the PANA session, there could be
   multiple EAP re-authentications. As EAP re-authentication changes the
   AAA-key, key-ID is used to identify the right AAA-key. This is
   contained in the Key-Id AVP [PANA-PROT].

   EP-address: This is the address of the enforcement point with which
   the IKE exchange is being performed. When PAA is controlling multiple
   EPs, this provides a different pre-shared key for each of the EPs.

   The character "|" denotes concatenation as defined in [RFC2409].

   During EAP re-authentication, the AAA-key changes. Whenever the AAA-
   key changes, a new value of Key-ID is established between the PaC and


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   PAA/EP as defined in [PANA-PROT]. If there is already an IKE SA or
   IPsec SA established, it MUST continue to be used till it expires. A
   change in the value of AAA-key MUST NOT result in re-negotiating a
   new IKE SA or IPsec SA immediately. But any new negotiation of IKE SA
   or IPsec SA MUST use the new pre-shared key derived from the latest
   AAA-key and is indicated by the Key-ID in the above equation. In case
   where two EAP authentications are performed during a single PANA
   authentication phase, AAA-key is derived from both authentications as
   specified in the [PANA-PROT].


6.0 IKE and IPsec details

   IKE [RFC2409] MUST be used for establishing the IPsec SA. The details
   specified in this document works with IKE as well as IKEv2 [IKEV2]
   also. Any difference between them would be explicitly noted. PANA
   authenticates the client and derives the keys to protect the traffic.
   Hence, manual keying cannot be used. Aggressive mode with pre-shared
   key MUST be supported. PaC and EP SHOULD use the following value in
   the payload of the ID_KEY_ID to identify the pre-shared key.

           ID_KEY_ID data = (Session-Id | Key-Id)

   The Session-Id and Key-Id are the values contained in the data
   portion of the Session-Id and Key-Id AVP respectively [PANA-PROT].
   They are concatenated to form the content of ID_KEY_ID data. IP
   addresses cannot be used as identifier as the PaC may be re-
   authenticated multiple times and hence may not uniquely identify the
   pre-shared key. For the same reason, main mode of IKE cannot be used,
   as it requires addresses to be used as identifiers.

   After Phase I SA is established, quick mode exchange is performed to
   establish an ESP tunnel mode IPsec SA for protecting the traffic
   between PaC and EP. The identities used during Phase II are explained
   in the next section. As mentioned in section 4.0, an address (POPA)
   may also have to be configured. The address configuration method to
   be used by the PaC is indicated in the PANA-Bind-Request message at
   the end of the successful PANA authentication. The PaC chooses the
   appropriate method and replies back in PANA-Bind-Answer message.

7.0 Packet Formats

   Following acronyms are used throughout this document.

   PAC-TIA denotes the IPsec-TIA used by the PaC. PAC-TIA may be set to
   a PRPA when the same PRPA is used as IPsec-TIA and IPsec-TOA on the
   PaC. Otherwise, PAC-TIA is set to POPA.

   PAC-TOA denotes the IPsec-TOA used by the PaC.


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   EP-ADDR denotes the address of the EP.

   The node with which the PaC is communicating is denoted by END-ADDR.

   Following is the IPv4 packet format on the wire for packets sent from
   PaC to EP:

         IPv4 header      (source = PAC-TOA,
                           destination = EP-ADDR)
         ESP  header
         IPv4 header      (source = PAC-TIA,
                           destination = END-ADDR)

   Following is the IPv6 packet format on the wire for packets sent from
   PaC to EP:

         IPv6 header      (source = PAC-TOA,
                           destination = EP-ADDR)
         ESP  header
         IPv6 header      (source = PAC-TIA,
                           destination = END-ADDR)

   Following is the IPv4 packet format on the wire for packets sent from
   EP to PaC:

         IPv4 header      (source = EP-ADDR,
                           destination = PAC-TOA)
         ESP  header
         IPv4 header      (source = END-ADDR,
                           destination = PAC-TIA)

   Following is the IPv6 packet format on the wire for packets sent from
   EP to PaC:

         IPv6 header      (source = EP-ADDR,
                           destination = PAC-TOA)
         ESP  header
         IPv6 header      (source = END-ADDR,
                           destination = PAC-TIA)

8.0 IPsec SPD entries

   The SPD entries for IPv4 and IPv6 are specified separately as they
   are different. All the SPD entries are dynamically created. When the
   same address is used as IPsec-TIA and IPsec-TOA, EP can add the entry
   to the SPD before the IKE exchange starts, as it knows the address a
   priori. When IKEv2 [IKEV2] or [RFC3456] is used for address
   configuration, the SPD entry cannot be created until the IPsec SA is


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   successfully negotiated as the address is not known a priori. This is
   very similar to the road warrior case described in [IPSEC-BIS]. In
   this case, an SPD entry with a name selector is used to start with
   and later changed with the appropriate addresses. The name used here
   could be the contents of ID_KEY_ID payload. The entries shown below
   are the entries that are added after the successful IPsec SA
   negotiation.

   The SPD entries shown here affect the flow of data traffic, which
   includes neighbor discovery messages for IPv6. When PAA and EP are
   not co-located, any traffic destined to PAA is forwarded to PAA after
   decrementing the TTL in the IP header. PAA would drop the packet if
   the TTL is not 255. PaC also would drop the packets coming from PAA
   if the TTL is not 255. Hence, we need the following explicit SPD
   entry on PaC and EP for bypassing IPsec protection for PANA traffic.

      If source_port = PANA_PORT OR dest_port = PANA_PORT
          THEN BYPASS

   PANA_PORT is the IANA assigned (TBD) PANA protocol number [PANA-
   PROT]. There may be other protocols that expect the TTL to be 255
   whose SPD entries are not shown here. Also, when the PaC is using
   IPsec for remote access, there may be additional SPD entries and
   IPsec security associations, which are not discussed in this
   document.


8.1 IPv4 SPD entries

   PaC's SPD OUT:

             IF source_port = PANA_PORT OR dest_port = PANA_PORT
              THEN BYPASS

             IF source = PAC-TIA & destination = any
              THEN USE ESP TUNNEL MODE SA:
              outer source = PAC-TOA
              outer destination = EP-ADDR

   PaC's SPD IN:

            IF source_port = PANA_PORT OR dest_port = PANA_PORT
              THEN BYPASS

            IF source = any & destination = PAC-TIA
             THEN USE ESP TUNNEL MODE SA:
             outer source = EP-ADDR
             outer destination = PAC-TOA



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   EP's SPD OUT:

            IF source_port = PANA_PORT OR dest_port = PANA_PORT
              THEN BYPASS

            IF source = any & destination = PAC-TIA
             THEN USE ESP TUNEL MODE SA:
             outer source = EP-ADDR
             outer destination = PAC-TOA

   EP's SPD IN:

            IF source_port = PANA_PORT OR dest_port = PANA_PORT
              THEN BYPASS

            IF source = PAC-TIA & destination = any
             THEN USE ESP TUNNEL MODE SA:
              outer source = PAC-TOA
              outer destination = EP-ADDR

   During the IPsec SA setup, PaC uses PAC-TIA as its phase 2 identity
   (IDci) and EP uses ID_IPV4_ADDR_RANGE or ID_IPV4_ADDR_SUBNET as its
   phase 2 identity. The starting address is zero IP address and the end
   address is all ones for ID_IPV4_ADDR_RANGE. The starting address is
   zero IP address and the end address is all zeroes for
   ID_IPV4_ADDR_SUBNET.

8.2 IPv6 SPD entries

   The IPv6 SPD entries are slightly different from IPv4 to prevent the
   neighbor and router discovery [RFC2461] packets from being protected
   with IPsec. The first three entries of the following SPD entries
   bypass IPsec protection for neighbor and router discovery packets.
   The latest version of the IPsec [IPSEC-BIS] document allows traffic
   selectors to be based on ICMPv6 type and code values. In that case,
   the first three entries can be based on ICMPv6 type and code values.

   Pac's SPD OUT:

             IF source = ::/128  & destination = any
              THEN BYPASS

             IF source = fe80::/10 & destination = any
             THEN BYPASS

             IF source = any & destination = fe80::/10
              THEN BYPASS

             IF source_port = PANA_PORT OR dest_port = PANA_PORT


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              THEN BYPASS

             IF source = PAC-TIA & destination = any
              THEN USE ESP TUNNEL MODE SA:
                 outer source = PAC-TOA
                 outer destination = EP-ADDR

   PaC's SPD IN:

             IF source = ::/128 & destination = any
              THEN BYPASS

             IF source = fe80::/10 & destination = any
             THEN BYPASS

             IF source = any & destination = fe80::/10
              THEN BYPASS

             IF source_port = PANA_PORT OR dest_port = PANA_PORT
              THEN BYPASS

             IF source = any & destination = PAC-TIA
                 THEN USE ESP TUNNEL MODE SA:
                    outer source = EP-ADDR
                    outer destination = PAC-TOA

   EP's SPD OUT:

             IF source = ::/128 & destination = any
              THEN BYPASS

             IF source = fe80::/10 & destination = any
             THEN BYPASS

             IF source = any & destination = fe80::/10
              THEN BYPASS

              IF source_port = PANA_PORT OR dest_port = PANA_PORT
               THEN BYPASS

             IF source = any & destination = PAC-TIA
                 THEN USE ESP TUNNEL MODE SA:
                    outer source = EP-ADDR
                    outer destination = PAC-TOA

   EP's SPD IN:

             IF source = ::/128 & destination = any
              THEN BYPASS


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             IF source = fe80::/10 & destination = any
             THEN BYPASS

             IF source = any & destination = fe80::/10
              THEN BYPASS

             IF source_port = PANA_PORT OR dest_port = PANA_PORT
              THEN BYPASS

             IF source = PAC-TIA & destination = any
              THEN USE ESP TUNNEL MODE SA:
                 outer source = PAC-TOA
                 outer destination = EP-ADDR


   During the IPsec SA setup, PaC uses PAC-TIA as its phase 2 identity
   (IDci) and EP uses ID_IPV6_ADDR_RANGE or ID_IPV6_ADDR_SUBNET as its
   phase 2 identity. The starting address is zero IP address and the end
   address is all ones for ID_IPV6_ADDR_RANGE. The starting address is
   zero IP address and the end address is all zeroes for
   ID_IPV6_ADDR_SUBNET.

9.0 Dual Stack Operation

   IKEv2 [IKEV2] can enable configuration of IPsec-TIA for both IPv4 and
   IPv6 TIAs by sending both IPv4 and IPv6 configuration attributes in
   the configuration request (CFG-REQUEST). This enables use of single
   IPsec tunnel mode SA for sending both IPv4 and IPv6 traffic.
   Therefore, IKEv2 is recommended for handling dual-stack PaCs where
   single execution of IKE is desired.

10.0 Security considerations

   This document discusses the use of IPsec for access control when PANA
   is used for authenticating the clients to the access network.

   If the EP does not verify whether PaC is authorized to use an IP
   address, it is possible for the PaC to steal the traffic destined to
   some other PaC. When IKEv2 [IKEV2] and [RFC3456] are used for address
   configuration, the address is assigned by the EP and hence this
   attack is not present in such cases. When the same address is used as
   both IPsec-TIA and IPsec-TOA, EP creates the SPD entry with the
   appropriate address for the PaC and hence the address is verified
   implicitly by the virtue of successful IPsec SA negotiation.

   When IPv6 is used, the SPD entries bypass all link-local traffic
   without applying IPsec. This should not be a limitation as the link-
   local address is used only by link-local services e.g. neighbor and


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   router discovery, which could use [SEND] to protect their traffic.
   Moreover, this limitation may not be there in the future if IPsec
   extends the SPD selectors to specify ICMP types.

11.0 Normative References

   Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9,
      RFC 2026, October 1996.

   [RFC2401] S. Kent et al., "Security Architecture for the Internet
      Protocol", RFC 2401, November 1998

   [PANA-PROT] D. Fosberg et al., "Protocol for Carrying Authentication
      for Network Access", draft-ietf-pana-05.txt

   [PANA-THREATS] M. Parthasarathy, "PANA Threat analysis and security
      requirements", draft-ietf-pana-threats-eval-04.txt

12.0 Informative References

   [PANAREQ] A. Yegin et al., "Protocol for Carrying Authentication for
      Network Access (PANA) Requirements and Terminology", draft-ietf-
      pana-requirements-09.txt

   [PANA-FRAME] P. Jayaraman et al., "PANA Framework", draft-ietf-pana-
      framework-01.txt

   [RFC2119] S. Bradner, "Key words for use in RFCS to indicate
      requirement levels", RFC 2119, March 1997

   [RFC2409] D. Harkins et al., "Internet Key Exchange", RFC 2409,
      November 1998

   [IKEV2] C. Kauffman et al., "Internet Key Exchange(IKEv2) Protocol",
      draft-ietf-ipsec-ikev2-15.txt

   [IPSEC-BIS] S. Kent, "Security Architecture for the Internet
      Protocol", draft-ietf-ipsec-rfc2401bis-00.txt

   [RFC2131] R. Droms, "Dynamic Host Configuration Protocol", RFC 2131,
      March 1997

   [RFC3456] B. Patel et al., "Dynamic Host Configuration Protocol
      (DHCPv4) Configuration of IPsec Tunnel Mode", RFC 3456, January
      2003

   [RFC3315] R. Droms et. al, "Dynamic Host Configuration Protocol for
      IPv6", RFC 3315, July 2003



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   [RFC2461] T. Narten et al., "Neighbor Discovery for IP version 6
      (IPv6) ", RFC 2461, December 1998

   [RFC2462] S. Thomson et. al, "IPv6 Stateless Address
      Autoconfiguration", RFC 2462, December 1998

   [RFC3041] T. Narten et al., "Privacy Extensions for Stateless Address
      Autoconfiguration in IPv6", RFC 3041, January 2001

   [EAP-KEY] D. Simon et al., "EAP Key Management Framework", draft-
      ietf-eap-keying-02.txt

   [SEND] J. Arkko et al., "Secure Neighbor Discovery", draft-ietf-send-
      ndopt-06.txt

   [IPV4-LINK] B. Aboba et al., "Dynamic configuration of Link-local
      IPv4 addresses", draft-ietf-zeroconf-ipv4-linklocal-12.txt

   [RFC1918] Y. Rekhter et al., "Address Allocation for Private
      Internets", BCP 5, RFC 1918, February 1996

   [IEEE80211i] IEEE Draft 802.11I/D5.0, "Draft Supplement to STANDARD
      FOR Telecommunications and Information Exchange between Systems û
      LAN/MAN Specific Requirements - Part 11: Wireless Medium Access
      Control (MAC) and physical layer specifications: Specification for
      Enhanced Security", August 2003.

13.0 Acknowledgments

   The author would like to thank Francis Dupont, Pasi Eronen, Yoshihiro
   Ohba, Jari Arkko, Hannes Tschofenig, Alper Yegin, Erik Nordmark and
   other PANA WG members for their valuable comments and discussions.

14.0 Revision log

   Changes between revision 03 and 04

   -Comments from Erik Nordmark (mostly editorial)

   Changes between revision 02 and 03

   -Clarified the use of key-Id in ID_KEY_ID payload
   -Clarified the address configuration issues.
   -Added an Appendix to clarify implementation issues.

   Changes between revision 01 and 02

   -Updated the draft with the fixes for all open issues
   -Added the IP configuration section


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   -Modified the IKE pre-shared key derivation to handle PAA controlling
   multiple EPs
   -Clarification regarding DHCP usage and RFC3456 usage.
   -Only aggressive mode to be supported. Main mode not needed anymore.

   Changes between revision 00 and 01

   -Specified the use of ESP tunnel mode SA instead of IP-IP transport
   mode SA after working group discussion.
   -Specified the IKE pre-shared key derivation.

15.0 Appendix A

   This section describes the alternate address configuration methods
   for Post-PANA address (POPA) and the issues associated with it. As
   mentioned in section 4, there are multiple ways by which the PaC may
   configure the POPA address. Only [IKEV2] and [RFC3456] address
   configuration methods were described in section 4. Other
   possibilities and the issues are as follows.

     1) Some IKEv1 implementations support IKEv1 MODECFG for configuring
        IP address. There is no RFC describing MODECFG feature of IKEv1.
        Also, there is not much information on its widespread support
        among the implementations. Hence, this document does not
        recommend it.

     2) The address may also be obtained using DHCP [RFC2131] [RFC3315]
        before the IKE exchange starts. Normally the implementations
        associate the address and other configuration information (e.g.
        default router) with the interface on which the DHCP is
        performed. This can cause problems with implementations if they
        attempt to use an IP address that is configured via [RFC2131]
        [RFC3315] on the physical interface and use it as IPsec-TIA on
        the IPsec tunnel interface. This may work without problems when
        IPsec-TIA and IPsec-TOA are same as the IPv4 PRPA that was
        obtained using DHCP, as the source address selection has to deal
        with just one address. But using an IPv4 IPsec-TOA different
        than IPsec-TIA on a single interface may cause source address
        selection problem, as there is more than one address to be dealt
        with. Similarly, an IPv6 address obtained and maintained through
        a physical link but used on a tunnel interface requires
        additional implementation considerations. Therefore, this
        document does not handle the case where DHCP is used to acquire
        an address for IPsec-TIA that is different from IPsec-TOA. Note
        that this case is different from the address configuration using
        [RFC3456], which also uses DHCP. When [RFC3456] is used, DHCP is
        run over the IPsec tunnel and the address (IPsec-TIA) is
        assigned to the IPsec tunnel interface. The link-local address
        (IPsec-TOA) is assigned to the physical interface. As there is


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               PANA enabling IPsec based Access Control September 2004

        only one address on each interface, there are no address
        selection issues.

     3) The address may also be obtained using auto-configuration
        [RFC2461] including the temporary addresses described in
        [RFC3041]. The problem described above for DHCP applies to this
        also. The implementations would associate the auto-configured
        addresses and the default router with the interface on which the
        router advertisement was received. As we configure the SPD to
        bypass IPsec for router discovery and neighbor discovery
        messages, the address would be associated with the physical
        interface and not with the IPsec interface. There is also an
        additional issue, as the address configured by the PaC is not
        known to the EP. It needs to trust whatever PaC provides in its
        traffic selector during the IPsec SA negotiation. This leads to
        DoS attack where the PaC can steal some other PaC's address,
        which cannot be prevented unless [SEND] is deployed.

16.0 Author's Addresses

   Mohan Parthasarathy
   313 Fairchild Drive
   Mountain View CA-94043

   Phone: 408-734-8820
   Email: mohanp@sbcglobal.net

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               PANA enabling IPsec based Access Control September 2004

   this standard.  Please address the information to the IETF at
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