Network Working Group A. Yegin, Ed.
Internet-Draft Samsung AIT
Expires: March 24, 2005 E. Njedjou
France Telecom
S. Veerepalli
Qualcomm
N. Montavont
T. Noel
LSIIT - University Louis Pasteur
September 23, 2004
Link-layer Event Notifications for Detecting Network Attachments
draft-ietf-dna-link-information-00.txt
Status of this Memo
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and any of which I become aware will be disclosed, in accordance with
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This Internet-Draft will expire on March 24, 2005.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
Certain network access technologies are capable of providing various
link-layer status information to IP. Link-layer event notifications
can help IP expeditiously detect configuration changes. This draft
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provides a non-exhaustive catalogue of information available from
well-known access technologies.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Requirements notation . . . . . . . . . . . . . . . . . . 4
2. Link-Layer Event Notifications . . . . . . . . . . . . . . . . 5
2.1 GPRS/3GPP . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 cdma2000/3GPP2 . . . . . . . . . . . . . . . . . . . . . . 7
2.3 IEEE 802.11/WiFi . . . . . . . . . . . . . . . . . . . . . 8
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
4. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1 Normative References . . . . . . . . . . . . . . . . . . . . 13
6.2 Informative References . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . 17
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1. Introduction
It is not an uncommon occurrence for a node to change its point-of
attachment to the network. This can happen due to mobile usage
(e.g., a mobile phone moving among base stations) or nomadic usage
(e.g., road-warrior case).
A node changing its point-of attachment to the network may end up
changing its IP subnet and therefore require re-configuration of
IP-layer parameters, such as IP address, default gateway information,
and DNS server address. Detecting the subnet change can usually use
network-layer indications such as a change in the advertised prefixes
(i.e., appearance and disappearance of prefixes). But generally
reliance on such indications does not yield rapid detection, since
these indications are not readily available upon node changing its
point of attachment.
The changes on the underlying link-layer status can be relayed to IP
in the form of link-layer event notifications. Establishment and
tear down of a link-layer connection are two basic events types.
Additional information can be conveyed in addition to the event type,
such as the identifier of the network attachment point, or
network-layer configuration parameters obtained via the link-layer
attachment process. It is envisaged that such event notifications
can in certain circumstances be used to expedite the inter-subnet
movement detection and reconfiguration process. For example, the
notification indicating that the node has established a new
link-layer connection can be used for immediately probing the network
for a possible configuration change. In the absence of such a
notification from the link-layer, IP has to wait for indications that
are not immediately available, such as receipt of next scheduled
router advertisement, unreachability of the default gateway, etc.
It should be noted that a link-layer event notification does not
always translate into a subnet change. Even if the node has torn
down a link-layer connection with one attachment point and
established a new connection with another, it may still be attached
to the same IP subnet. For example, several IEEE 802.11 access
points can be attached to the same IP subnet. Moving among these
access points does not warrant any IP-layer configuration change.
In order to enable an enhanced scheme for detecting change of subnet,
we need to define link-layer event notifications that can be
realistically expected from various access technologies. The
objective of this draft is to provide a catalogue of link-layer
events and notifications in various architectures. While this
document mentions the utility of this information for detecting
change of subnet (or, detecting network attachment - DNA), the
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detailed usage is left to other documents, namely DNA solution
specifications.
The document limits itself to the minimum set of information that is
necessary for solving the DNA problem [I-D.ietf-dna-goals]. A
broader set of information may be used for other problem spaces
(e.g., anticipation-based Mobile IP fast handovers
[I-D.ietf-mobileip-lowlatency-handoff][I-D.ietf-mipshop-fast-mipv6]).
Separate documents that are backward-compatible with this one can be
generated to discuss further enhancements.
These event notifications are considered with hosts in mind, although
they may also be available on the network side (e.g., on the access
points and routers). An API or protocol-based standard interface may
be defined between the link-layer and IP for conveying this
information. That activity is beyond the scope of this document.
1.1 Requirements notation
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].
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2. Link-Layer Event Notifications
Link-layer event notifications are considered to be one of the inputs
to the DNA process. A DNA process is likely to take other inputs
(e.g., presence of advertised prefixes, reachability of default
gateways) before determining whether IP-layer configuration must be
updated. It is expected that the DNA process can take advantage of
link-layer notifications when they are made available to IP. While
by itself a link-layer notification may not constitute all the input
DNA needs, it can at least be useful for prompting the DNA process to
collect further information (i.e., other inputs to the process). For
example, the node may send a router solicitation as soon as it learns
that a new link-layer connection is established.
Two basic link-layer events are considered potentially useful to DNA
process: link up and link down. Both of these events are
deterministic, and their notifications are provided to IP-layer after
the events successfully conclude. These events and notifications are
associated with a network interface on the node. The IP module may
receive simultaneous independent notifications from each one of the
network interfaces on the node.
Node's establishment of a link-layer connection with an attachment
point that signifies the availability of IP service (i.e., being able
to send and receive IP packets) between the two is considered a link
up event. The attachment point is typically an access network
element, such as an access point, a base station, or a wired switch
[TO-DO: How about ad-hoc networks? Attached neighbors may be
considered attachment points].
The actual event is managed by the link-layer of the node through
execution of link-layer protocols and mechanisms. Once the event
successfully completes within the link-layer, its notification must
be delivered to the IP-layer. By the time the notification is
delivered, the link-layer of the node must be ready to accept IP
packets from the IP and the physical-layers.
Link down event signifies the discontinuation of the IP service
between the node and the attachment point. When the link-layer
connection is physically or logically torn down and it can no longer
carry IP packets, this is considered to be a link down event.
Among these two events the first one to take place after an interface
becomes enabled must be a link up event. During the time a network
interface is enabled, it may go through a series of link up and down
events. Each time the interface changes its point of attachment, a
link down event with the previous attachment point must be followed
by a link up event with the new one. Finally, when the network
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interface is disabled, this must generate a link down event. Each
one of these events must generate a notification in order they occur.
A node may have to change its IP-layer configuration even when the
link-layer connection stays the same. An example scenario is the
IPv6 subnet renumbering [RFC2461]. Therefore, there exists cases
where IP-layer configuration may have to change even without the
IP-layer receiving a link up notification. Therefore, a link-layer
notification is not a mandatory indication of a subnet change.
In addition to the type of the event (link up, link down), a
link-layer notification may also optionally deliver information
relating to the attachment point. Such auxiliary information may
include identity of the attachment point (e.g., base station
identifier), or the IP-layer configuration parameters associated with
the attached subnet (e.g., subnet prefix, default gateway address,
etc.). While merely knowing that a new link-layer connection is
established may prompt DNA process to immediately seek other clues
for detecting network configuration change, auxiliary information may
constitute further clues (and even the final answers sometimes). In
cases where there is a one-to-one mapping between the attachment
point identifiers and the IP-layer configurations, learning the
former can reveal the latter. Furthermore, IP-layer configuration
parameters obtained during link-layer connection may be exactly what
the DNA process is trying to discover (e.g., IP address configured
during PPP link establishment).
The link-layer process leading to a link up or link down event
depends on the link technology. While a link-layer notification must
always indicate the event type, the availability and types of
auxiliary information on the attachment point depends on the
link-layer technology as well. The following subsections examine
three link-layer technologies and describe when a link-layer
notification must be generated and what information must be included
in it. The coverage on the link types may be expanded in the future
[TO-DO: Add IEEE 802.3].
2.1 GPRS/3GPP
GPRS is an enhancement to the GSM data transmission architecture and
capabilities, designed to allow for packet switching in user data
transmission within the GPRS network as well as for higher quality of
service for the IP traffic of Mobile Terminals with external Packets
Data Networks such as the Internet or corporate LANs
[GPRS][GPRS-LINK].
The GPRS architecture consists of a Radio Access Network and a packet
domain Core Network.
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- The GPRS Radio Access Network is composed of Mobile Terminals (MT),
a Base Station Subsystem and Serving GPRS Support Nodes (SGSN).
- An IP Core Network that acts as the transport backbone of user
datagrams between SGSNs and Gateway GPRS Support Nodes (GGSN). The
GGSN ensures the GPRS IP core network connectivity with external
networks, such as Internet or Local Area Networks. GGSN acts as the
default IP gateway for the MT.
A MT that wants to establish IP-level connections should first
perform a GPRS attach to the SGSN. This should be followed by a
request the GPRS network to settle the necessary soft state mechanism
(GPRS tunneling protocol) between its serving SGSN and the GGSN. The
soft state maintained between the MT, the SGSN and the GGSN is called
a PDP Context. It is used for guaranteeing a negotiated quality of
service for the IP flows exchanged between the GPRS MT and an
external Packet Data Network such as Internet . Only after the PDP
Context is established and tunneling mechanism takes place can the
MT's IP packets be forwarded to and from its remote IP peers. The
aim of PDP Context establishment is also to provide IP-level
configuration on top of the GPRS link-layer attachment.
Successful establishment of a PDP Context on a GPRS signifies the
availability of IP service to the MT. Therefore, this link-layer
event must generate a link up event notification sent to IP-layer.
The auxiliary information carried along with this notification must
be the IP address of the MT which is obtained as part of the PDP
Context. In case of IPv6, IPv6 address of the MT may be obtained by
alternative methods, such as DHCPv6 [RFC3315][GPRS-GSSA] or stateless
address autoconfiguration [RFC2462][GPRS-CN]. In that case, the IP
address auxiliary information must be set to null.
Similarly, PDP Context deactivation must generate a link down event
notification.
2.2 cdma2000/3GPP2
cdma2000-based 3GPP2 packet data services provide mobile users wide
area high-speed access to packet switched networks [CDMA2K]. Some of
the major components of the 3GPP2 packet network architecture consist
of:
- Mobile Station (MS), which allows mobile access to packet-switched
networks over a wireless connection.
- Radio Access Network, which consists of the Base Station
Transceivers, Base Station Controllers, and the Packet Control
Function.
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- Network Access Server known as the Packet Data Switching Node
(PDSN). The PDSN also serves as default IP gateway for the IP MS.
3GPP2 networks use the Point-to-Point Protocol (PPP [RFC1661]) as the
link-layer protocol between the MS and the PDSN. Before any IP
packets may be sent or received, PPP must reach the Network-Layer
Protocol phase, and the IP Control Protocol (IPCP [RFC1332], IPV6CP
[RFC2472]) reach the Opened state. When these states are reached in
PPP, a link up event notification must be delivered to the IP-layer.
When the PPP is used for 3GPP2 Simple (i.e., non-Mobile) IPv4
Service, IPCP enables configuration of IPv4 address on the MS. This
IPv4 address must be provided as the auxiliary information along with
the link up notification. IPV6CP used for Simple IPv6 service does
not provide an IPv6 address, but the interface-identifiers for local
and remote end-points of the PPP link. Since there is no
standards-mandated correlation between the interface-identifier and
other IP-layer configuration parameters, this information is deemed
not useful for DNA (hence it is not provided as auxiliary
information).
IPCP/IPV6CP termination, or the underlying LCP or NCP reaching Closed
State signify the end of corresponding IP service on the PPP link.
This event must generate a link down notification delivered to the
IP-layer.
2.3 IEEE 802.11/WiFi
IEEE 802.11-based WiFi networks are the wireless extension of the
Local Area Networks. Currently available standards are IEEE 802.11b
[IEEE-802.11b], IEEE 802.11g [IEEE-802.11g], and IEEE 802.11a
[IEEE-802.11a]. The specifications define both the MAC-layer and the
physical-layer. The MAC layer is the same for all these
technologies.
Two operating modes are available in the IEEE 802.11 series. In
ad-hoc mode, mobile station (STA) in range may directly communicate
with other, i.e., without any infrastructure or intermediate hop. In
infrastructure mode, all link-layer frames are transmitted to an
access point (AP) which then forwards them to the final receiver.
This document only considers infrastructure mode [for now... TO-DO:
consider ad-hoc too].
A STA must establish a IEEE 802.11 link with an AP in order to send
and receive IP packets. In a WiFi network that supports Robust
Secure Network (RSN [IEEE-802.11i]), successful completion of 4-way
handshake between the STA and AP commences the availability of IP
service. The link up event notification must be generated upon this
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event. In non-RSN-based networks, successful association or
re-association events on the link-layer must cause a link up
notification sent to the IP-layer.
As part of the link establishment, Basic Service Set Identification
(BSSID) and Service Set Identifier (SSID) associated with the AP is
learned by the STA. BSSID is a unique identifier of the AP. Its
value is set to the MAC address of the AP in infrastructure mode.
SSID carries the identifier of the Extended Service Set (ESS) - the
set composed of APs and associated STAs that share a common
distribution system. BSSID and SSID should be provided as auxiliary
information along with the link up notification. Unfortunately this
information does not provide a deterministic indication of whether
the IP-layer configuration must be changed upon movement. There is
no standards-mandated one-to-one relation between the BSSID/SSID
pairs and IP subnets. An AP with a given BSSID can connect a STA to
any one of more than one IP subnets. Similarly, an ESS with the
given SSID may span multiple IP subnets. And finally, the SSIDs are
not globally unique. The same SSID may be used by multiple
independent ESSs. See Appendix A of [DNA4] for a detailed
discussion. Nevertheless, BSSID/SSID information may be used in a
probabilistic way by the DNA process, hence it is provided with the
link up event notification.
Disassociation event in RSN-based, and de-authentication and
disassociation events in non-RSN-based WiFi networks must translate
to link down events, and generate the corresponding link-layer
notifications.
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3. IANA Considerations
This document has no actions for IANA.
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4. Security Considerations
A faked link-layer event notification can be used to launch a
denial-of service attack on the node and the associated network.
Secure generation and delivery of these notifications must be
ensured. This is a subject for link-layer and network stack designs
and therefore it is outside the scope of this document.
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5. Acknowledgements
The authors would like to acknowledge Bernard Aboba, Sanjeev Athalye,
JinHyeock Choi, Greg Daley, Pekka Nikander, and Muhammad Mukarram bin
Tariq for their useful comments and suggestions.
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6. References
6.1 Normative References
[CDMA2K] "IS-835 - cdma2000 Wireless IP Network Standard", .
[GPRS] "Digital cellular telecommunications system (Phase 2+);
General Packet Radio Service (GPRS) Service description;
Stage 2", 3GPP 3GPP TS 03.60 version 7.9.0 Release 98.
[GPRS-LINK]
"Digital cellular telecommunications system (Phase 2+);
Radio subsystem link control", 3GPP GSM 03.05 version
7.0.0 Release 98.
[I-D.ietf-dna-goals]
Choi, J., "Detecting Network Attachment in IPv6 Goals",
draft-ietf-dna-goals-01 (work in progress), September
2004.
[IEEE-802.11a]
Institute of Electrical and Electronics Engineers, "IEEE
Std 802.11a-1999, supplement to IEEE Std 802.11-1999, Part
11: Wireless MAN Medium Access Control (MAC) and Physical
Layer (PHY) specifications: High-speed Physical Layer in
the 5 GHZ band", IEEE Standard 802.11a, September 1999.
[IEEE-802.11b]
Institute of Electrical and Electronics Engineers, "IEEE
Std 802 Part 11, Information technology -
Telecomunications and information exchange between systems
- Local and metropolitan area networks - Specific
requirements - Part 11: Wireless Lan Medium Access Control
(MAC) And Physical Layer (PHY) Specifications", IEEE
Standard 802.11b, August 1999.
[IEEE-802.11g]
Institute of Electrical and Electronics Engineers, "IEEE
Std 802.11g-2003, Amendment to IEEE Std 802.11, 1999
edition, Part 11: Wireless MAN Medium Access Control (MAC)
and Physical Layer (PHY) specifications. Amendment 4:
Further Higher Data Rate Extension in the 2.4 GHz Band",
IEEE Standard 802.11g, June 2003.
[IEEE-802.11i]
Institute of Electrical and Electronics Engineers, "Draft
Supplement to STANDARD FOR Telecommunications and
Information Exchange between Systems - LAN/MAN Specific
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Requirements - Part 11: Wireless Medium Access Control
(MAC) and physical layer (PHY) specifications:
Specification for Enhanced Security", IEEE Draft 802.11I/
D8, February 2004.
[RFC1332] McGregor, G., "The PPP Internet Protocol Control Protocol
(IPCP)", RFC 1332, May 1992.
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[RFC2472] Haskin, D. and E. Allen, "IP Version 6 over PPP", RFC
2472, December 1998.
[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.
6.2 Informative References
[GPRS-CN] "Technical Specification Group Core Network;
Internetworking between the Public Land Mobile Network
(PLMN) supporting packet based services and Packet Data
Networks (PDN) (Release 6)", 3GPP 3GPP TS 29.061 version
6.1.0 2004-06.
[GPRS-GSSA]
"Technical Specification Group Services and System Aspect;
General Packet Radio Service (GPRS) Service description;
Stage 2 (Release 6)", 3GPP 3GPP TS 23.060 version 6.5.0
2004-06.
[I-D.ietf-mipshop-fast-mipv6]
Koodli, R., "Fast Handovers for Mobile IPv6",
draft-ietf-mipshop-fast-mipv6-02 (work in progress), July
2004.
[I-D.ietf-mobileip-lowlatency-handoff]
Malki, K., "Low latency Handoffs in Mobile IPv4",
draft-ietf-mobileip-lowlatency-handoffs-v4-09 (work in
progress), June 2004.
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[RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
Authors' Addresses
Alper E. Yegin (editor)
Samsung Advanced Institute of Technology
75 West Plumeria Drive
San Jose, CA 95134
USA
Phone: +1 408 544 5656
EMail: alper.yegin@samsung.com
Eric Njedjou
France Telecom
4, Rue du Clos Courtel BP 91226
Cesson-SȨvignȨ, 35512
France
Phone: +33 299124202
EMail: eric.njedjou@france-telecom.com
Siva Veerepalli
Qualcomm
5775 Morehouse Drive
San Diego, CA 92131
USA
Phone: +1 858 658 4628
EMail: sivav@qualcomm.com
Nicolas Montavont
LSIIT - University Louis Pasteur
Pole API, bureau C428
Boulevard Sebastien Brant
Illkirch, 67400
France
Phone: +33 390 244 587
EMail: montavont@dpt-info.u-strasbg.fr
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Thomas Noel
LSIIT - University Louis Pasteur
Pole API, bureau C428
Boulevard Sebastien Brant
Illkirch, 67400
France
Phone: +33 390 244 592
EMail: noel@dpt-info.u-strasbg.fr
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