DHCP Options for Protocol for Carrying Authentication for Network Access (PANA) Authentication Agents
Two DHCP options that hand a network client the addresses of its PANA authentication agents.
Morand, L., Yegin, A., Kumar, S., and S. Madanapalli, "DHCP Options for Protocol for Carrying Authentication for Network Access (PANA) Authentication Agents", RFC 5192, DOI 10.17487/RFC5192, May 2008, <https://www.rfc-editor.org/info/rfc5192>.
@misc{rfc5192,
series = {Request for Comments},
number = 5192,
howpublished = {RFC 5192},
publisher = {RFC Editor},
doi = {10.17487/RFC5192},
url = {https://www.rfc-editor.org/info/rfc5192},
author = {L. Morand and A. Yegin and S. Kumar and S. Madanapalli},
title = {{DHCP Options for Protocol for Carrying Authentication for Network Access (PANA) Authentication Agents}},
pagetotal = 8,
year = 2008,
month = may,
} RFC text
Contents
Network Working Group L. Morand
Request for Comments: 5192 France Telecom R&D
Category: Standards Track A. Yegin
Samsung
S. Kumar
Tech Mahindra Ltd
S. Madanapalli
Samsung
May 2008
DHCP Options for Protocol for Carrying Authentication for
Network Access (PANA) Authentication Agents
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document defines new DHCPv4 and DHCPv6 options that contain a
list of IP addresses to locate one or more PANA (Protocol for
carrying Authentication for Network Access) Authentication Agents
(PAAs). This is one of the methods that a PANA Client (PaC) can use
to locate PAAs.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . . 2
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. PANA Authentication Agent DHCPv4 Option . . . . . . . . . . . . 3
5. PANA Authentication Agent DHCPv6 Option . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Protocol for carrying Authentication for Network Access (PANA)
[RFC5191] defines a new Extensible Authentication Protocol (EAP)
[RFC3748] lower layer that uses IP between the protocol end-points.
The PANA protocol is run between a PANA Client (PaC) and a PANA
Authentication Agent (PAA) in order to perform authentication and
authorization for the network access service.
This document specifies DHCPv4 [RFC2131] and DHCPv6 [RFC3315] options
that allow PANA clients (PaCs) to discover PANA Authentication Agents
(PAAs). This is one of the methods for locating PAAs.
The DHCP options defined in this document are used only as a PAA
discovery mechanism. These DHCP options MUST NOT be used to perform
any negotiation of the use of PANA between the PaC and a PAA.
2. Specification of Requirements
In this document, several words are used to signify the requirements
of the specification. These words are often capitalized. The key
words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document
are to be interpreted as described in [RFC2119].
3. Terminology
This document uses the DHCP terminology defined in [RFC2131],
[RFC2132], and [RFC3315].
This document uses the PANA terminology defined in [RFC5191]. In
particular, the following terms are defined:
PANA Client (PaC):
The client side of the protocol that resides in the access
device (e.g., laptop, PDA, etc.). It is responsible for
providing the credentials in order to prove its identity
(authentication) for network access authorization. The PaC and
the EAP peer are co-located in the same access device.
PANA Authentication Agent (PAA):
The protocol entity in the access network whose responsibility
it is to verify the credentials provided by a PANA client (PaC)
and authorize network access to the access device. The PAA and
the EAP authenticator (and optionally the EAP server) are
colocated in the same node.
4. PANA Authentication Agent DHCPv4 Option
This DHCPv4 option carries a list of 32-bit (binary) IPv4 addresses
indicating PANA Authentication Agents (PAAs) available to the PANA
client (PaC).
The DHCPv4 option for PANA Authentication Agent has the format shown
in Figure 1.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ PAA IPv4 Address +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: PAA DHCPv4 option
option-code: OPTION_PANA_AGENT (136).
option-length: Length of the 'options' field in octets;
MUST be a multiple of four (4).
PAA IPv4 Address: IPv4 address of a PAA for the client to use.
The PAAs are listed in the order of preference
for use by the client.
A PaC (DHCPv4 client) SHOULD request the PAA DHCPv4 Option in a
Parameter Request List, as described in [RFC2131] and [RFC2132].
If configured with a (list of) PAA address(es), a DHCPv4 server
SHOULD send a client the PAA DHCPv4 option, even if this option is
not explicitly requested by the client.
A PaC (DHCPv4 client) receiving the PAA DHCPv4 option SHOULD use the
(list of) IP address(es) to locate PAA(s).
The PaC (DHCPv4 client) MUST try the records in the order listed in
the PAA DHCPv4 option received from the DHCPv4 server.
5. PANA Authentication Agent DHCPv6 Option
This DHCPv6 option carries a list of 128-bit (binary) IPv6 addresses
indicating PANA Authentication Agents (PAAs) available to the PANA
client (PaC).
The DHCPv6 option for PANA Authentication Agent has the format shown
in Figure 2.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ PAA IPv6 Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: PAA DHCPv6 option
option-code: OPTION_PANA_AGENT (40).
option-length: Length of the 'options' field in octets;
MUST be a multiple of sixteen (16).
PAA IPv6 Address: IPv6 address of a PAA for the client to use.
The PAAs are listed in the order of preference
for use by the client.
A PaC DHCPv6 client SHOULD request the PAA DHCPv6 option in an
Options Request Option (ORO) as described in the DHCPv6 specification
[RFC3315].
If configured with a (list of) PAA address(es), a DHCPv6 server
SHOULD send a client the PAA DHCPv6 option, even if this option is
not explicitly requested by the client.
A PaC (DHCPv6 client) receiving the PAA DHCPv6 option SHOULD use the
(list of) IP address(es) to locate PAA(s).
The PaC (DHCPv6 client) MUST try the records in the order listed in
the PAA DHCPv6 option received from the DHCPv6 server.
6. IANA Considerations
The following DHCPv4 option code for PANA Authentication Agent
options has been assigned by IANA:
Option Name Value Described in
-----------------------------------------------
OPTION_PANA_AGENT 136 Section 4
The following DHCPv6 option code for PANA Authentication Agent
options has been assigned by IANA:
Option Name Value Described in
------------------------------------------------
OPTION_PANA_AGENT 40 Section 5
7. Security Considerations
The security considerations in [RFC2131], [RFC2132], and [RFC3315]
apply. If an adversary manages to modify the response from a DHCP
server or insert its own response, a PANA Client could be led to
contact a rogue PANA Authentication Agent, possibly one that then
intercepts authentication requests and/or denies network access to
the access device.
In most networks, the DHCP exchange that delivers the options prior
to network access authentication is neither integrity protected nor
origin authenticated. Therefore, the options defined in this
document MUST NOT be used to perform any negotiation on the use of
PANA between the PANA Client and a PANA Authentication Agent. Using
the presence (or absence) of these DHCP options as an indication of
network mandating PANA authentication (or not) is an example of such
a negotiation mechanism. This negotiation would allow bidding-down
attacks by making the clients choose to use a lower-grade security
mechanism (or even no security at all).
8. Acknowledgements
We would like to thank Ralph Droms, Stig Venaas, Ted Lemon, Andre
Kostur and Bernie Volz for their valuable comments. We would also
like to thank Jari Arkko, Thomas Narten and Bernard Aboba that
provided several reviews, as well as all members of the PANA and DHC
working groups that contribute to improve this document.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A.
Yegin, "Protocol for Carrying Authentication for Network
Access (PANA)", RFC 5191, May 2008.
9.2. Informative References
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H.
Levkowetz, "Extensible Authentication Protocol (EAP)",
RFC 3748, June 2004.
Authors' Addresses
Lionel Morand
France Telecom R&D
EMail: lionel.morand@orange-ftgroup.com
Alper E. Yegin
Samsung
EMail: a.yegin@partner.samsung.com
Suraj Kumar
Tech Mahindra Ltd
EMail: surajk@techmahindra.com
Syam Madanapalli
Samsung
EMail: syam@samsung.com
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AI ELI5
On this page
§1Finding the Authentication Agent
RFC 5191 defines PANA, a lower layer for the Extensible Authentication Protocol (EAP) that runs over IP between a PANA Client (PaC) and a PANA Authentication Agent (PAA). Before they can talk, the client has to find a PAA.
RFC 5192 specifies DHCPv4 and DHCPv6 options that let a PaC discover PAAs. This is one of the methods for locating PAAs, not the only one.
The options are used only for discovery. They MUST NOT be used to negotiate whether PANA is used between the PaC and a PAA.
Before you can show your pass you must know where the guard is standing. This document is a note the network gives you with the guard's address.
§3PaC and PAA
The PANA Client (PaC) is the client side of the protocol and lives in the access device, such as a laptop or PDA. It provides the credentials that prove its identity so network access can be authorized. The PaC and the EAP peer sit in the same device.
The PANA Authentication Agent (PAA) is the entity in the access network that verifies the credentials and authorizes network access. The PAA and the EAP authenticator, and optionally the EAP server, are colocated in the same node.
The PaC is you with your pass. The PAA is the guard at the door who checks it.
§4The DHCPv4 Option
The DHCPv4 option carries a list of 32-bit IPv4 addresses of PAAs available to the client. Its option-code is OPTION_PANA_AGENT (136). The option-length is the length of the address list in octets and MUST be a multiple of four.
The addresses are listed in order of preference. A client SHOULD ask for the option in a Parameter Request List. A server that is configured with PAA addresses SHOULD send the option even if the client did not ask for it.
A client that receives the option SHOULD use the addresses to locate PAAs, and MUST try them in the order listed.
The network gives you a list of guard addresses, best one first. You ask them in that order.
§5The DHCPv6 Option
The DHCPv6 option works the same way but carries 128-bit IPv6 addresses. Its option-code is OPTION_PANA_AGENT (40), and the option-length MUST be a multiple of sixteen.
A DHCPv6 client SHOULD request the option in an Options Request Option (ORO). A configured server SHOULD send it even if it was not requested. The client SHOULD use the addresses to locate PAAs and MUST try them in the listed order.
Same note, but written with the longer kind of address used by the newer network.
| Protocol | Option code | Address size | Length rule |
|---|---|---|---|
| DHCPv4 | 136 | 32-bit IPv4 | Multiple of 4 octets |
| DHCPv6 | 40 | 128-bit IPv6 | Multiple of 16 octets |
§6IANA Option Codes
IANA assigned the option name OPTION_PANA_AGENT the value 136 for DHCPv4 (described in Section 4) and the value 40 for DHCPv6 (described in Section 5). The same name is used in both protocols, but the numbers differ because each protocol has its own option number space.
Each kind of network keeps its own phone book of option numbers, so the same option has a different number in each.
§7Rogue Agents and Bidding Down
The security considerations of the DHCP RFCs apply. If an attacker modifies a DHCP response or inserts its own, a PaC could be led to contact a rogue PAA, which might intercept authentication requests or deny the device network access.
In most networks the DHCP exchange before network access authentication is neither integrity protected nor origin authenticated. For that reason the options MUST NOT be used to negotiate PANA. Treating the presence or absence of the option as a signal that the network requires PANA (or not) is an example of what is forbidden, since it would allow bidding-down attacks that push clients to a weaker security mechanism, or none.
A stranger could slip you a note pointing to a fake guard. So the note may say where guards are, but must never decide whether you need to show a pass.