EAP Authentication Extensions for the
Dynamic Host Configuration Protocol for BroadbandCisco Systems80 Albert StreetBrisbane4000QueenslandAustralia+61 7 3238 8228+61 7 3211 3889ric@cisco.comNetwork Zen1310 East Thomas Street#306SeattleWashington98102USA+1 (206) 377-9035gwz@net-zen.net
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Dynamic Host Configuration WGDHCPEAPPPPCHAPAuthenticationDraftThis document defines Dynamic Host Configuration Protocol (DHCP)
extensions that provide for end-user authentication prior to
configuration of the host. The primary applicability is within a Digital
Subscriber Line (DSL) Broadband network environment in order to enable a
smooth migration from the Point to Point Protocol (PPP).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 RFC 2119.This document defines DHCP Options and procedures that allow for an
Extensible Authentication Protocol (EAP) authentication exchange to
occur in DHCP in order to enable smooth migration from Point-to-Point
Protocol (PPP) sessions to IP sessions in
a DSL Broadband network environment. Primary goals are integration of
authentication in such a way that it will operate seamlessly with
existing RADIUS-based Authentication, Authorization and Accounting (AAA)
infrastructure and Asynchronous Transfer Mode (ATM) or Ethernet based
DSL Networks. As such, only the termination points of PPP in the DSL
network are affected, both of which are devices that would logically
need to be updated in any transition from PPP to IP sessions.It should be noted that defines a
mechanism that provides authentication of individual DHCP messages.
While this mechanism does provide a method of authentication for a DHCP
Client based on a shared secret, it does not do so in a manner that can
be seamlessly integrated with existing RADIUS-based AAA
infrastructure.Digital Subscriber Line (DSL) broadband service providers are
witnessing a shift in the "last-mile" aggregation technologies and
protocols which have traditionally been relied upon. Two primary
transitions are from ATM to Ethernet in the access network, and from the
PPP for multi-protocol framing and dynamic endpoint configuration to
direct encapsulation of IP and DHCP for dynamic endpoint configuration
for some devices. The term used by the DSL Forum for the network state
associated with an authorized subscriber (that is using DHCP and IP
rather than PPP) is "IP session" . While
these trends can be readily witnessed, neither are occurring overnight.
In addition, they are not necessarily implemented in lock-step. Thus,
one may find ATM-based and Ethernet-based access networks running a
combination of PPP sessions and IP sessions at any given time,
particularly during transition periods. This coexistences will even
occur for the same service subscriber.Removing PPP, Point-to-Point Protocol over ATM (PPPoA) , and Point-to-Point Protocol over Ethernet
(PPPoE) from the subscriber access
network is relatively straightforward in that most of the properties
that DSL providers are interested in going forward are already present
in DHCP and IP sessions. Luckily, there are some capabilities of PPP
which the market does not continue to demand. For example, the Dynamic
configuration in PPP for IPX or NETBEUI, is no longer of concern.
Neither are the multi-link bonding capabilities of PPP commonly used on separate ISDN B-channels, and
the myriad of other features that PPP developed as the "dial-based"
access protocol of choice for framing, authentication, and dynamic
configuration for IP and other network layer protocols. Missing from IP
sessions and DHCP , however, are
isomorphic methods for user authentication and session liveness probing
(sometimes referred to as a session "keepalive"). For the latter,
existence of a client using a given IP address can be detected by a
number of means, including Address Resolution Protocol (ARP) , ICMP Echo/Echo Response , or Bidirectional Forwarding Detection (BFD)
. This leaves authentication as
an open issue needing resolution. Specifically, authentication based on
a username and secret password must be covered. This is something that
in PPP always occurs before dynamic configuration of an IP address and
associated parameters.While most DSL deployments utilize a username and password to
authenticate a subscriber and authorize access today, this is not the
only method for authentication that has been adopted when moving to DHCP
and IP sessions. "Option 82" is commonly
used with DHCP as a credential to authenticate a given subscriber line
and authorize service. In this model, the DSL Access Node, which always
sits between the DHCP Client and Server, snoops DHCP messages as they
pass, and inserts pre-configured information for a given line (e.g., an
ATM VPI/VCI, Ethernet VLAN, or other tag). That information, while
provided in clear text, traverses what is considered a physically
secured portion of the access network and is used to determine
(typically via a request to an AAA server) whether the DHCP exchange can
continue. This fits quite well with current DSL network architecture, as
long as the subscriber line itself is all that needs be authorized.
However, in some service models it is still necessary for the subscriber
to provide credentials directly.From the perspective of the Network Access Server (NAS) where the
DHCP Server resides, the extensions defined in this document are
analogous to the commonly available "Option 82" method. The primary
difference between using Option 82 line configuration and a username and
password is that the authentication credentials are provided by the
subscriber rather than inserted by intervening network equipment.
Providing credentials from the subscriber rather than intervening
network equipment is particularly important for cases where subscriber
line information is unavailable, untrusted, or due to the terms of the
service changing at any time. Further, different devices in the home may
have different policies and require different credentials. Migration
scenarios where PPPoE and DHCP operate on the same network for a period
of time lend well to models which utilize identical authentication and
authorization credentials across the different data plane
encapsulations.The DSL Forum defines its ATM-based network architecture in and Ethernet-based network architecture in . The extensions for DHCP defined in this
document are designed to work identically on Ethernet or ATM
architectures. The diagram in and following
terminology will be used throughout: Access Node (AN): Network device, usually located at a service
provider central office or street cabinet, that terminates Access
Loop connections from Subscribers. In case the Access Loop is a
Digital Subscriber Line (DSL), this is often referred to as a DSL
Access Multiplexer (DSLAM). The AN may support one or more Access
Loop technologies and allow them to inter-work with a common
aggregation network technology.Network Access Server (NAS): Network device that aggregates
multiplexed Subscriber traffic from a number of Access Nodes. The
NAS plays a central role in per-subscriber policy enforcement and
QoS. Often referred to as a Broadband Network Gateway (BNG) or
Broadband Remote Access Server (BRAS). A detailed definition of the
NAS is given in .The Home Gateway (HGW) connects the different Customer Premises
Equipment (CPE) to the Access Node and the access network. In case
of DSL, the HGW is a DSL Network Termination (NT) that could either
operate as a layer 2 bridge or as a layer 3 router. In the latter
case, such a device is also referred to as a Routing Gateway
(RG).Referring to the DSL network architecture depicted in , PPP (via PPPoA
or PPPoE ) operates over the DSL
Access Network between the NAS and a device behind the HGW, or
between the NAS and the HGW itself. The DHCP Client resides either
on a home network device or the HGW, and the DHCP Server protocol
state machine may reside fully on the NAS. The NAS obtains
per-subscriber client configuration information either locally,
relayed from a DHCP server or from the AAA infrastructure (which
itself may consult external DHCP servers if necessary) after
authentication is successfully completed.The primary target for this extension is for DSL service provider
networks where PPP is being phased out to be replaced by native IP and
DHCP, or where new devices are being added which will not utilize PPP.
Very specific assumptions have been made with respect to the security
model, operational methods, and integration requirements for existing
AAA mechanisms during the design. It is understood that this mechanism
may not be generally applicable in this form for all network
environments where DHCP is deployed, though perhaps elements of it may
be used to develop a more generic approach while still meeting the
specific requirements set out by the DSL network architecture. Earlier
revisions of this document included a method to embed PPP CHAP authentication as Options in existing DHCP
messages. This method has been abandoned due to security vulnerabilities
in CHAP, as well as a lack of extensibility. This document bases its
authentication on EAP which can be used
with a large number of different authentication methods, including one
backwards compatible with existing PPP CHAP.This section describes the protocol operation for EAP within DHCPv4
and DHCPv6 . Options and message specifications used in
these operation descriptions are detailed in later sections.If multiple DHCP exchanges are occurring with multiple servers, both
IPv4 and IPv6 each needs to authenticate separately.It is essential that the user/node authentication occurs before the
assignment of an IP address and, further, that the assignment of the
address depends upon the details of the successful authentication. .
DHCP is widely used as an address
assignment method (among other things); EAP has been widely adapted for authentication
purposes, especially in those types of networks where DHCP is also
used. This section describes how to combine the two in order to
provide both strong authentication and authenticated address
assignment in an efficient manner.A (using the DHCP
Vendor-specific Message ) is used in the
DHCP message flow to support the new EAP phase which occurs before a
DHCPOFFER is sent by the Server. This message is used to integrate
authentication methods supported by EAP, including CHAP and any other
"in the clear" password mechanisms (for example, to support One-Time
Password mechanisms), or to carry other EAP methods. EAP is widely
used in other environments, outside of DSL Broadband, including 802.11
"Wi-Fi" access networks and 3GPP to name a few.To request the assignment of an IPv4 address with authentication, a
client first locates a DHCP server, then authenticates using EAP and
then requests the assignment of an address and other configuration
information from the server. The client sends a DHCPDISCOVER message
with an option specifying that the client understands the DHCP User
Authentication protocol using EAP, to find an available DHCP server.
Any server that can that can authenticate and address it responds with
a DHCPEAP message containing the first packet of the EAP protocol.Servers which support DHCP User Authentication will respond with a
DHCPEAP message. The client may receive one or more DHCPEAP messages
from one or more DHCP Servers or DHCP relays. The Client may also
receive one or more DHCPOFFER messages from other DHCP Servers which
may not understand, or choose not to employ the DHCP User
Authentication protocol. The Client chooses one server to reply to. If
the selected server has sent a DHCPEAP message, then the Client will
send a DHCPEAP message in reply. The DHCPEAP message contains EAP
packets which facilitate the EAP authentication exchange. The exchange
may occur between the DHCP Client and DHCP Server embedded within a
NAS, or be carried transparently to the AAA Server. Upon successful
completion of the authentication phase, the DHCP server sends a
DHCPOFFER with the appropriate IP configuration for the authenticated
user. The client then follows the normal DHCP procedures of a
successful DHCP exchange by sending a DHCPREQUEST, followed by a
DHCPACK from the Server.If the authentication phase fails the DHCP server may choose to
either terminate all communication with a client or offer some default
address possibly with some limited access policy. (Configuration
policy for this is outside of the scope of this document).The final EAP-Success or EAP-Failure message is always communicated
using the DHCPEAP message type. If the Server will be sending a
DHCPOFFER message, this message is sent immediately after the final
DHCPEAP message.A typical message flow proceeds as shown in : The retransmission is handled by EAP as per
Section 4.1 in .The message exchange presented in is an
example of simple one-way user authentication, e.g. the Server
verifies the credentials of the HGW Client. The client indicates the
ability to have an EAP exchange and the NAS (which takes on the EAP
authenticator role) initiates the first EAP request to the DHCP Client
(which takes on the EAP peer role).When the NAS is acting as a DHCP Relay the BRAS may split the EAP
Messages from DHCP and perform the AAA authentication with an AAA
server. This allows use of existing DHCP servers and existing AAA
servers.An example message flow for DHCP Relay proceeds as shown in : When the DHCP relay agent in the NAS receives a DHCP message from
the client, it MAY append a DHCP Relay Agent Information option
containing the RADIUS Attributes suboption, along with any other
suboptions it is configured to supply. The RADIUS Attributes suboption
is defined in .DHCP Authentication uses one suboption inside the
Vendor-identifying vendor-specific message option and makes use of the
Vendor-specific Message option: in the
DHCPDISCOVER to specify the type of authentication exchange and
makes use of a new DHCP Vendor-specific Message type to carry
the EAP data in the DHCPEAP messages.This section describes the protocol operation for extending Dynamic
Host Configuration Protocol for IPv6
for an EAP phase.The same as the previous section on extending DHCP in IPv4 a new
DHCP message, is used to
support EAP authentication before host configuration occurs. The
mechanisms described here follow a similar methodology as that for
DHCPv4 described in Section 5.1.The client sends a Solicit message with an Option specifying the
session authentication protocol as EAP to the
All_DHCP_Relay_Agents_and_Servers address to find available DHCP
servers. Any server that can authenticate and address it responds with
a DHCPEAP message.The client may receive one or more DHCPEAP messages from one or
more DHCP Servers. The Client chooses one to reply to, and sends a
DHCPEAP message, silently discarding DHCPEAP messages from other
Servers (?? As per the question above, is there some type of EAP
message which can be sent to the other servers to stop EAP there?).
The DHCPEAP messages contain EAP packets which facilitate the EAP
authentication exchange. The exchange may occur between the DHCP
Client and DHCP Server embedded within a NAS, or be carried
transparently to the AAA Server. Upon successful completion of the
authentication phase, the DHCP server sends a ADVERTISE with the
appropriate configuration for the authenticated user. The client then
follows the normal DHCP procedures of a successful DHCP exchange by
sending a REQUEST, followed by an ACK from the Server.If the authentication phase fails (e.g., the user does not provide
appropriate credentials), then according to configured policy the DHCP
Client is either denied any IP configuration with the DHCP Server
sending a NAK accordingly, or the DHCP Client is given a "limited
access" configuration profile and the DHCP exchange continues as if
the authentication was successful.A typical message flow proceeds as shown in :The retransmission is handled by EAP as per Section 4.1 in .When the NAS is acting as a DHCPv6 Relay the BRAS may split the EAP
Messages from DHCP and perform the AAA authentication with an AAA
server. This allows use of existing DHCPv6 servers and existing AAA
servers.The message following this exchange is an ADVERTISE, sent unchanged
by the Server. A typical message flow proceeds as shown in :When the DHCP relay agent in the NAS receives a DHCP message from
the client, it MAY append a DHCP Relay option or DHCP relay
information suboption containing the RADIUS Attributes information,
along with any other relay options or relay information suboptions it
is configured to supply. The RADIUS Attributes suboption for DHCPv4 is
defined in One DHCP Vendor-specific suboption is defined in this section. The
is included
into the client's DHCPDISCOVER or SOLICIT message to specify that the
client understand DHCPEAP messages, as defined below (see).The DHCPv4 DHCPEAP-Capability Vendor-identifying Vendor-specific
suboption is sent from the DHCPv4 Client to the DHCPv4 Server to
indicate that the client is capable of understanding DHCPv4 DHCPEAP
Messages. This suboption is defined using the DHCPv4
Vendor-identifying Vendor-specific option:Opt-code: 125Length: 7Enterprise-ID: 9 (Cisco Systems)Data-length: 2Suboption: 14 (DHCPEAP Capability suboption)Subopt-length: 0The DHCPv6 DHCPEAP-Capability Vendor-specific suboption is sent
from the DHCPv6 Client to the DHCPv6 Server to indicate that the
client is capable of understanding DHCPv6 DHCPEAP Messages. This
suboption is defined using the DHCPv6 Vendor-specific option:OPTION_VENDOR_OPTS: 17Length: 6Enterprise-ID: 9 (Cisco Systems)Suboption: 14 (DHCPEAP Capability suboption)Subopt-length: 0One new DHCPv4 message type and one new DHCPv6 message type are
defined in order to carry the EAP messages between the client and the
server. These messages make use of the Vendor-specific Message type and
are defined using the Enterprise-ID for Cisco Systems.The format of the DHCPEAP Message type for DHCPv4 follows the
current draft , and is defined as
follows:Vendor-msg: TBDEnterprise-ID: 9 (Cisco Systems)Msg-type: 1 (DHCPEAP)Suboption: 1 (DHCPEAP-Message)EAP-length: (length of the EAP message)Note that according to the current DHCPv4 Vendor-specific Message
draft, a "vendor-msg-type" field is the first octet after the
enterprise-ID, and after this octet all data should be in
"code/length/value" fields "identical to the DHCP options field".
Thus, the "vendor-msg-type" field ("Msg-type" in the figure above) is
set to "1" and the next field is the suboption value, which is also
set to "1", followed one octet specifying the length of the EAP
message, followed by the EAP message itself.The maximum size of a DHCP option is 255 octets. While in some
cases (e.g., EAP MD5-Challenge ) a
complete EAP message may fit in a single DHCP option, in general this
is not the case. If an EAP message is too large to fit into a single
DHCP Vendor-specific Message option, the method defined in MUST be used to split the EAP message into
separate options for transmission. Similarly, EAP assumes a minimum
MTU of 1020 octets while the minimum DHCP packet size is 576 octets,
including 312 octets reserved for options. A DHCP client including the
EAP-Message option SHOULD also include the 'maximum DHCP message size'
option to set a suitable DHCP message
size.If a DHCP message is received containing more than one DHCPEAP
Message type option, the method defined in MUST be used to reassemble the separate
options into the original EAP message. A DHCP server receiving an EAP
message MAY forward it via a AAA protocol (such as RADIUS or Diameter
] ).The format of the DHCPEAP Message type for DHCPv6 follows the
current draft , and is defined as
follows:Note that according to the current DHCPv6 Vendor-specific Message
draft, a "vendor-msg-type" field is the first octet after the
enterprise-ID, and after this octet all data should be in
"code/length/value" fields "identical to the DHCPv6 options field".
Thus, the "vendor-msg-type" field ("Msg-type" in the figure above) is
set to "1" and the next field is the suboption value, which is also
set to "1", followed two octets specifying the length of the EAP
message, followed by the EAP message itself.This section describes the overall DHCP message contents for all
messages which are used in implementing the DHCP EAP User Authentication
extensions.The authentication data in a DHCPv4 DHCPEAP message is carried in a
DHCPEAP-Messsage type .As shown in the DHCP
Client starts the process by sending the DISCOVER to the MAC
broadcast address. A client sending this EAP-Capability option in
the DHCPDISCOVER is expected to be able to handle EAP messaging and
the associated additional methods and fragmentation handling. The
NAS that handles this request could be a DHCP server or a relay
DHCP. As per the NAS can send the
initial EAP-Request to the client or the NAS can send an EAP-Start
to the server. The diagrams in this draft assume the NAS sends the
initial EAP-Reqest as reads as if
that is the recommended behaviour.The NAS responds to DHCP Client by sending an initial DHCPEAP to
the clients MAC address (unicast). Subsequent NAS DHCP messages
would look the same; unicast response for these messages to avoid
the EAP conversation being replicated to many downstream clients. As
noted in , if an EAP packet is lost in
transit between the authenticating peer and the NAS (or vice versa),
the NAS will retransmit.The DHCPEAP messages for DHCPv6 follow the format for DHCP messages
defined in RFC 2131 and is identified by
the presence of a vendor specific DHCP Message Type option as per
, which
encodes DHCPEAP message type.As shown in the DHCP
Client starts the process by sending the SOLICIT to the
All_DHCP_Relay_Agents_and_Servers multicast address. The NAS that
handles this request could be a DHCP server or a relay DHCP. A
client sending this EAP-Capability option in the DHCPDISCOVER is
expected to be able to handle EAP messaging and the associated
additional methods and fragmentation handling. As per the NAS can send the initial EAP-Request to
the client or the NAS can send an EAP-Start to the server. The
diagrams in this draft assume the NAS sends the initial EAP-Reqest
as reads as if that is the
recommended behaviour.The NAS responds to DHCP Client by sending an initial DHCPEAP to
the clients MAC address (unicast). Subsequent NAS DHCP messages
would look the same; unicast response for these messages to avoid
the EAP conversation being replicated to many downstream clients. As
noted in [], if an EAP packet is lost
in transit between the authenticating peer and the NAS (or vice
versa), the NAS will retransmit.Encapsulating EAP messages within DHCP raises the question of whether
there are potential difficulties with respect to the MTU sizes of the
EAP and DHCP messages, as well as the underlying link MTU.EAP as defined in Section 3.1
says:[4] Minimum MTU. EAP is capable of functioning on lower layers that
provide an EAP MTU size of 1020 octets or greater.DHCP as defined in Section 2 says:... This requirement implies that a DHCP client must be
prepared to receive a message of up to 576 octets, the minimum IP
datagram size an IP host must be prepared to accept [3]. DHCP clients
may negotiate the use of larger DHCP messages through the 'maximum DHCP
message size' option. The options field may be further extended into the
'file' and 'sname' fields.If we assume EAP MTU-sized packets, the overhead to pack an EAP
packet into DHCP options is 2*(1020/255), or 8 octets. Adding the DHCP
header (240 octets), UDP (8 octets), and the IP header (20 octets) gives
278 octets total overhead. Since the Ethernet effective MTU is 1500
octets, this 278 octet overhead leaves the DHCP protocol with 1222
octets to carry EAP. This space is over 200 octets more than the EAP MTU
of 1020 octets.If we add the SNAME and CHADDR fields to the option pool, then there
are nearly 400 octets available for DHCP options in an Ethernet
MTU-sized DHCP packet, encapsulating EAP.In short, when the 'maximum DHCP message size' option is used by the
client, there is no problem carrying in EAP over DHCP. i.e. clients
capable of performing EAP over DHCP should also advertise a maximum
message that is capable of carrying EAP over DHCP.This section is aimed at describing interoperability scenarios
involving HGW and NAS with or without DHCP Authentication mechanism
support in order to analyze compatibility issues that could be faced
between newer and older products during the introduction of the DHCP
Authentication functionally in current implemented network
environments.Scenario 1: Both HGW and NAS do not support DHCP AuthenticationIn this case the authentication process does not start,
thus traditional DHCP message flow applies.Scenario 2: HGW does not support DHCP Authentication and NAS supports
DHCP AuthenticationIn this case the DHCP client does not start DHCP
Authentication transaction, NAS MAY decide to respond to HGW without
using DHCP Authentication, falling back to traditional DHCP message flow
and assigning different network resources.Scenario 3: HGW supports the DHCP Authentication and NAS does not
support DHCP Authentication.In this case the DHCP client inserts in the DHCPDISCOVER
message sent to NAS, the DHCP Authentication Protocol Option described
in the draft in order to communicate the NAS that it is able to perform
authentication and for indicating the authentication algorithm preferred
by the client. NAS on receiving a DHCPDISCOVER with unknown option
silently discards unknown message. Alternatively NAS MAY ignore the
unknown option, but still process the message and then reply to the DHCP
client with traditional response. The HGW, that has upgraded software,
realizes that the NAS does not support DHCP Authentication and can
reverts back to normal DHCP message flow.Scenario 4 Both HGW and NAS support DHCP AuthenticationIn this case DHCP client inserts in the DHCPDISCOVER
message sent to NAS, the DHCP Authentication Protocol Option in order to
communicate the NAS that it is able to perform authentication and for
indicating the authentication algorithm preferred by the client, NAS
replies according to the message flow described in this draft.The following table summarizes the behavior in the 4 described
scenarios:RFC 3118 provides a mechanism to cryptographically protect DHCP
messages using a key, K, shared between a DHCP client and Server,
however no mechanism is defined to manage these keys. Authentication
exchanges based on EAP have been built into authentication portions of
network access protocols such as PPP, 802.1X, PANA, IKEv2, and now
DHCP. EAP methods may provide for the derivation of shared key
material, the MSK and the EMSK, on the EAP peer and EAP server. This
dynamic key generation enables
protection and allows modes of operation where messages are protected
from DHCP client to DHCP relay which previously would be difficult to
manage.A future document will look at how to derive the key, K, from the
EMSK resulting from an EAP exchange and at how this mechanism
interacts with the DHCP authentication or any EAP authentication prior
to DHCP.This specification requires three values to be assigned by IANA if
non-Vendor message and option space is not use. Currently the draft
needs no IANA specified number but this information is captured here
incase that needs to change in the future.The three numbers that could be assigned by IANA are:Two are "BOOTP Vendor Extensions and DHCP Options" (DHCPAUTH-Protocol)(DHCPAUTH-Data)Two DHCP Message Type 53 Values - per [RFC2132], for DHCPEAP
message type.Many thanks to Carlos Pignataro for help editing this document.Thanks to Roberta Maglione for setting many of the requirements and
network context for this work.Thanks to Richard Johnson, Alan DeKok, Wojciech Dec, Eric Voit, Mark
Townsley and Ralph Droms for help with this document.Thanks to Amy Zhao and Yizhou Li for their work on DHCP
Authentication and helping with laying the ground for this document.This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November 10,
2008. The person(s) controlling the copyright in some of this material
may not have granted the IETF Trust the right to allow modifications of
such material outside the IETF Standards Process. Without obtaining an
adequate license from the person(s) controlling the copyright in such
materials, this document may not be modified outside the IETF Standards
Process, and derivative works of it may not be created outside the IETF
Standards Process, except to format it for publication as an RFC or to
translate it into languages other than English.Bidirectional Forwarding DetectionJuniper NetworksCisco SystemsDSL Evolution - Architecture Requirements for the Support of
QoS-Enabled IP ServicesDSL ForumMigration to Ethernet Based DSL AggregationDSL ForumInternet Protocol (IP) SessionsDSL ForumNumerous members of the service provider community have
recently shown significant interest in migrating from a pure PPP
access environment towards one with IP subscriber sessions for
delivery of all IP services such as voice, video and high speed
Internet over a common data transport protocol. A number of
factors are driving the interest for such a transition. For one,
operators see a potential in simplifying their operational/user
support complexity, as well as harmonizing network element
functionality around the IP protocol. Operators running multiple
access networks also view IP service delivery as the key lowest
common denominator towards delivering common services in a
converged network, where the PPP would be specific only to PSTN
dial and DSL access segments. Given these motivations, the ability
to transition to an IP user service delivery model suggests the
adoption of a subscriber IP session construct in order to allow
the service provider to handle each subscriber according to their
individual service contract. This document provides the
description of the construct and relevant IP node
requirements.