One document matched: draft-ietf-pana-ipsec-05.txt
Differences from draft-ietf-pana-ipsec-04.txt
PANA Working Group
Internet Draft M. Parthasarathy
Document: draft-ietf-pana-ipsec-05.txt Nokia
Expires: June 2005 December 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.
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This Internet-Draft will expire on June 2005.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
PANA (Protocol for carrying Authentication for Network Access) is 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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1.0 Introduction..................................................2
2.0 Keywords......................................................4
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................................................7
8.0 IPsec SPD entries.............................................8
9.0 Dual Stack Operation.........................................12
10.0 Security considerations.....................................12
11.0 Normative References........................................12
12.0 Informative References......................................13
13.0 Acknowledgments.............................................14
14.0 Revision log................................................14
15.0 Appendix A..................................................15
16.0 Author's Addresses..........................................16
Intellectual Property Statement..................................16
Disclaimer of Validity...........................................17
Copyright Statement..............................................17
Acknowledgment...................................................17
1.0 Introduction
PANA (Protocol for carrying Authentication for Network Access) is a
protocol [PANA-PROT] 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 (PaC) and PANA authentication agent (PAA) at the end of
successful authentication. The 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 the PANA client
and the enforcement point. The IPsec SA is established using IKE
[RFC2409], which in turn uses the pre-shared key derived from the EAP
authentication (AAA-Key). 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 SA 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.
IPsec is used to protect packets flowing between PaC and EP in both
directions.
Please refer to [PANAREQ] for terminology and definitions of terms
used in this document. The PANA framework document [PANA-FRAME]
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describes the deployment scenarios for IPsec. 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, scenarios 3 and 5 are supported as shown below. As shown in
Figure 1, the Enforcement Point (EP), Access Router (AR) and the PANA
authentication agent are co-located which is described as scenario 3
in [PANAREQ].
PaC ------------------+
|
+---EP/AR/PAA----Intranet/Internet
|
PaC ------------------+
<-----------IPsec-------->
Figure 1: PAA/EP/AR are co-located
As show in Figure 2, only the AR and EP are co-located. The PAA is a
separate node though located on the same link as the AR and EP. All
of them are one IP hop away from the PaC. This is the same as
scenario 5 described in [PANAREQ].
PaC ------------------+
|
+---PAA
|
+---EP/AR-----Intranet/Internet
|
PaC ------------------+
<-----------IPsec-------->
Figure 2: EP and AR are co-located
The IPsec security association protects the traffic between the PaC
and EP. In IPsec terms, the 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
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communicated between the 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
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) The PaC) and PAA mutually authenticate each other using an EAP
method that is able to derive a AAA-key [EAP-KEY].
2) The PaC learns the IP address of the Enforcement point (EP)
during the PANA exchange.
3) The PaC learns that the network uses IPsec [RFC2401] for
securing the link between the 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.
The 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. The PaC would use the PRPA as
the outer address of IPsec tunnel mode SA (IPsec-TOA). The 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, the PRPA may be used as
both the IPsec-TIA and IPsec-TOA and POPA may not be configured.
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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 the PaC and EP.
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 the PaC and
EP, the PAA should communicate the IKE pre-shared key (Pac-EP Master
Key), Key-Id, PRPA of the PaC, and the session-Id to the 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 the 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
key (PTK) established in [IEEE80211i]. The IKE exchange provides both
key confirmation and protected cipher-suite negotiation.
The 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 runs of 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].
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EP-address: This is the address of the enforcement point with which
the IKE exchange is being performed. When the 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
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. The IKE PSK continues to exist
even after the AAA-Key from which it is derived expires. When the
IPsec SA expires, a new IPsec SA is negotiated without negotiating a
new IKE SA. When the IKE SA expires, a new IKE PSK is derived from
the latest AAA-key and used in negotiating the IKE SA and IPsec SA.
In case where two runs of EAP authentication (NAP/ISP) are performed
during a single PANA authentication phase, a 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 IKEv2 [IKEV2] as well as IKE.
Any difference between them would be explicitly noted. PANA
authenticates the client and network, and derives the keys to protect
the traffic. Hence, manual keying cannot be used. If IKE is used,
aggressive mode with pre-shared key MUST be supported. The 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 same PaC or different
PaC may use the same IP address across a PANA session. For the same
reason, main mode of IKE cannot be used, as it requires addresses to
be used as identifiers.
After a Phase 1 SA is established, quick mode exchange is performed
to establish an ESP tunnel mode IPsec SA for protecting the traffic
between the PaC and EP. The identities (traffic selectors in IKEv2)
used during Phase 2 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
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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 the IPsec-TIA and IPsec-TOA on
the PaC. Otherwise, PAC-TIA is set to the POPA.
PAC-TOA denotes the IPsec-TOA used by the PaC.
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
the PaC to the 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
the PaC to the 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
the EP to the 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
the EP to the PaC:
IPv6 header (source = EP-ADDR,
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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 described below are dynamically
created. When the same address is used as IPsec-TIA and IPsec-TOA,
the 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 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
and when the IPsec SA is successfully negotiated, a new SPD entry is
created with the appropriate addresses. The name used here could be
the contents of ID_KEY_ID payload. The SPD entries shown below are
the entries that are added after the successful IPsec SA negotiation.
In environments where the PaC is a router, the IPsec-TIA can be a
range of addresses (prefix) instead of a single host address. The PaC
acts like a security gateway in this case establishing the IPsec SA
with another security gateway (EP). This scenario is supported by
[RFC2401] and [IPSEC-BIS]. It is assumed that the PaC obtains the
prefix through other mechanisms not defined in this document. When
the IPsec SA is negotiated, the prefix is carried in the traffic
selectors.
The SPD entries shown here affect the flow of data traffic, which
includes neighbor discovery messages for IPv6. The SPD entries in the
PaC protect all the traffic with source address set to IPsec-TIA.
When IPsec-TIA and IPsec-TOA are the same (as discussed in section
4.0), the PANA traffic also gets protected with IPsec. The PANA
traffic destined to the PAA from the PaC is forwarded to PAA after
decrementing the TTL in the IP header. The PAA would drop the packet
if the TTL is not 255. Hence, we need explicit entries to bypass
IPsec protection for PANA traffic on PaC. This may not be needed
always for traffic going from PAA to PaC. If PAA and EP are not co-
located, PAA would send traffic directly to PaC without going through
EP. Hence, EP does not need to have SPD entries to bypass IPsec in
this case. If PAA and EP are co-located, the PANA packets will be
protected with IPsec only if the IPsec-TIA and IPsec-TOA are same.
Hence, we need explicit entries to bypass IPsec protection when PAA
and EP are co-located.
If source_port = PANA_PORT OR dest_port = PANA_PORT
THEN BYPASS
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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
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
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outer destination = EP-ADDR
During the IPsec SA setup, the 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
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
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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
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, the PaC uses PAC-TIA as its phase 2
identity (IDci) and the EP uses ID_IPV6_ADDR_RANGE or
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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.
The aggressive mode in IKE [RFC2409] is considered bad due to its DoS
properties i.e., any attacker can bombard IKE aggressive mode packets
making the EP perform heavy diffie-hellman calculations. As the
ID_KEY_ID can be verified by the EP before doing the diffie-hellman
calculation, it prevents random attacks. The attacker now needs to
listen on the traffic between PaC and PAA to originate IKE requests
with valid ID_KEY_ID.
If the EP does not verify whether the 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, the 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
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.
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[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
[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
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[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,
Giaretta Gerardo, Rafa Marin Lopez, Tero Kivinen and other PANA WG
members for their valuable comments and discussions.
14.0 Revision log
Changes between revision 04 and 05
-working group last call comments (mostly editorial)
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
-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.
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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.,
the default router address) 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 the
IPsec-TIA on the IPsec tunnel interface. This may work without
problems when the 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 the 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 the IPsec-TIA
that is different from the 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 typically assigned
to the IPsec tunnel interface. The IPsec-TOA is assigned to the
physical interface. As there is only one address on each
interface, there are no address selection issues.
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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
a 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
Email: mohanp@sbcglobal.net
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