Network Working Group A. Yegin, Ed. Internet-Draft Samsung AIT Expires:
January 9,April 27, 2006 July 8,October 24, 2005 Link-layer Event Notifications for Detecting Network Attachments draft-ietf-dna-link-information-02.txtdraft-ietf-dna-link-information-03.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 19,April 27, 2006. Copyright Notice Copyright (C) The Internet Society (2005). 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 document 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 . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 cdma2000/3GPP2 . . . . . . . . . . . . . . . . . . . . . . 8 2.3 IEEE 802.11/WiFi . . . . . . . . . . . . . . . . . . . . . 9 2.4 IEEE 802.3 CSMA/CD . . . . . . . . . . . . . . . . . . . . 10 2.4.1 Link Integrity Tests in 802.3 Networks . . . . . . . . 11 2.4.2 IEEE 802.1D Bridging and Its Effects on Link-layer Event Notifications . . . . . . . . . . . . . . . . . 12 2.4.3 802.1AB Link-Layer Discovery Protocol . . . . . . . . 14 2.4.4 Summary . . . . . . . . . . . . . . . . . . . . . . . 14 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 4. Security Considerations . . . . . . . . . . . . . . . . . . . 16 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 17 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19 7.1 Normative References . . . . . . . . . . . . . . . . . . . 19 7.2 Informative References . . . . . . . . . . . . . . . . . . 20 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 21 A. Change History . . . . . . . . . . . . . . . . . . . . . . . . 22 Intellectual Property and Copyright Statements . . . . . . . . 23 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 onto 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 (e.g., IEEE 802.11 BSSID and SSID), or network-layer configuration parameters obtained via the link-layer attachment process if available. 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 MAY 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 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 (e.g., signal strenght,strength, packet loss, etc.) may be used for other problem spaces, such as anticipation-based Mobile IP fast handovers [I-D.ietf-mobileip-lowlatency-handoffs-v4] [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]. 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. "Link" is a communication facility or medium over which network nodes can communicate. Each link is associated with a minimum of two endpoints. An "attachment point" is the link endpoint on the link to which the node is currently connected, such as an access point, a base station, or a wired switch. "Link up" is an event provided by the link-layer that signifies a state change associated with the interface becoming capable of communicating data packets. This event is associated with a link- layer connection between the node and an attachment point. 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. There is a non-deterministic usage of link up notification to accomodate implementations that desire to indicate the link is up but the data transmission may be blocked in the network (see IEEE 802.3 discussion). A link up notification MAY be generated with an appropriate attribute (e.g., "risk" indicated by R-flag) to convey the event. Alternatively, the link-layer implementation MAY choose to delay the link up notification until the risk conditions cease to exist. If a link up with the R-flag set was generated, another link up MUST follow up as soon as the link-layer is capable of generating a deterministic notification. The event attributes MUST indicate whether the packets transmitted since the previous notification were presumed to be blocked (B-flag) or allowed (A-flag) by the network if the link-layer could determine the exact conditions. If the link- layer cannot make a determination about the faith of these packets, it MUST generate a link up without any additional indications (no flags set). "Link down" is an event provided by the link-layer that signifies a state change associated with the interface no longer being capable of communicating data packets. A link down event is only generated once the link-layer considers the link unusable; transient periods of high frame loss are not sufficient. When the link-layer connection is physically or logically torn down and it can no longer carry data 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 interface is disabled, this MUST generate a link down event. Each one of these events MUST generate a notification in the 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 exist 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 four link-layer technologies and describe when a link-layer notification must be generated and what information must be included in it. 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. - 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 GPRS MT that wants to establish IP-level connections MUST first perform a GPRS attach to the SGSN. This MUST be followed by a request to 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. It is only after the PDP Context has been established, address autoconfiguration and tunneling mechanism have taken place that the MT's IP packets can 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 link 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. An MT has the possibility to establish a secondary PDP Context while re-using the IP configuration acquired from a previously established and active PDP Context. Establishment of a secondary PDP Context does not provide additional information to IP-layer. Such a second PDP Context would basically have a different QoS profile so that a different type of application can be served. In that case, activation of the secondary PDP Context MUST NOT generate another link up event notification. However, a secondary PDP Context establishment that triggers a new IP configuration is to be treated from the IP layer as indicated above. With IPv4, the auxiliary information carried along with this notification MUST be the IPv4 address of the MT which is obtained as part of the PDP Context. With IPv6, the PDP Context activation response does not come along with a usable IPv6 address. Effectively, the IPv6 address received from the GGSN in the PDP address field of the message does not contain a valid prefix. The MN actually only uses the interface-identifier extracted from that field to form a link-local address, that it uses afterwards to obtain a valid prefix (e.g., by stateless [RFC2462][GPRS-CN] or stateful [RFC3315] [GPRS-GSSA] address configuration). Therefore no IPv6- related auxiliary information is provided to IP-layer. PDP Context deactivation is used to generate link down event notifications. Considering there may be multiple PDP Contexts with the same IP configuration parameters (e.g., primary and secondary contexts), the deactivation of the PDP Context that has the only instance of a given IP configuration MUST generate a link down event notification. For example, both the primary and the secondary PDP Contexts may be using the same configuration parameters. In that case, deactivation of the primary context would not generate a link down notification while the secondary context is active. If the primary context is deactivated first, and than the secondary is deactivated, only the latter action would generate the link down 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. - 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 (nevertheless it MAY be provided as auxiliary information for other uses). 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, either infrastructure mode or ad-hoc mode. In infrastructure mode, all link-layer frames are transmitted to an access point (AP) which then forwards them to the final receiver. A station (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 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, usually set to the MAC address of the wireless interface of the AP. 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 MUST 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 multiple 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,non-RSN-based, and de-authentication and disassociation events in non-RSN-basedRSN-based WiFi networks MUST translate to link down events, and generate the corresponding link-layer notifications. In ad-hoc mode, mobile stationstations (STA) in range may directly communicate with others,each other, i.e., without any infrastructure or intermediate hop. The set of communicating STAs is called IBSS for Independent Basic Service Set. In an IBSS, only STA services are available, i.e. authentication, deauthentication, privacy and MSDU delivery. STAs do not associate with each other, and therefore may exchange data frames in state 2 (authenticated and not associated) or even in state 1 (unauthenticated and unassociated) if the Distribution System is not used (i.e., "To DS" and "From DS" bits are clear). If authentication is performed, a link up indication can be generated upon authentication, and a link down indication can be generated upon deauthentication. Concerning the link layer identification, both the BSSID (which is a random MAC address chosen by a STA of the IBSS) and SSID may be used to identify a link, but not to make any assumptions on the IP network configuration. 2.4 IEEE 802.3 CSMA/CD IEEE 802.3 CSMA/CD (commonly referred to as Ethernet) is the most commonly deployed Local Area Network technology in use today. As deployed today, it is specified by botha physical layer/medium access control (MAC) layer specification [IEEE-802.3]. In order to provide connection of different LANs together into a larger network, 802.3 LANs are often bridged together [IEEE-802.1D]. In this section, the terms 802.3 and Ethernet are used interchangeably. This section describes some issues in providing link-layer indications on Ethernet networks, and shows how bridging affects these indications. In Ethernet networks, hosts are connected by wires or by optic fibre to a switch (bridge), a bus (e.g., co-axial cable), a repeater (hub), or directly to another Ethernet device. Interfaces are symmetric, in that while many different physical layers may be present, medium access control is uniform for all devices. In order to determine whether the physical medium is ready for frame transfer, IEEE 802.3 Ethernet specifies its own link monitoring mechanism, which is defined for some, but not all classes of media. Where available, this Link Integrity Test operation is used to identify when packets are able to be received on an Ethernet segment. It is applicable to both wired and optical physical layers, although details vary between technologies (link pulses in twisted pair copper, light levels in fibre). 2.4.1 Link Integrity Tests in 802.3 Networks Link Integrity Tests in 802.3 networks typically occur at initial physical connection time (for example, at the auto-negotiation stage), and periodically afterwards. It makes use of physical-layer specific operations to determine if a medium is able to support link- layer frames [IEEE-802.3]. The status of the link as determined by the Link Integrity Test is stored in the variable 'link_status'. Changes to the value of link_status (for example due to Link Integrity Test failure) will generate link indications if the technology dependent interface is implemented on an Ethernet device [IEEE-802.3]. The link_status has possible values of FAIL, READY and OK. When an interface is in FAIL state, Link Integrity Tests have failed. Where status is READY, the link segment has passed integrity tests, but autonegotiation has not completed. OK state indicates that the medium is able to send and receive packets. Upon transition to a particular state the Physical Medium Attachment subsystems generates a PMA_LINK.indicate(link_status). Indications of OK state MAY be used to generate a link up event notification. This indication do not definitively ensure that packets will be able to be received through the bridge domain, though [see the next section]. Such operations are governed by bridging. PMA_LINK.indicate(FAIL) MUST be used to generate a link down notification. 2.4.2 IEEE 802.1D Bridging and Its Effects on Link-layer Event Notifications Ethernet networks commonly consist of LANs joined together by transparent bridges (usually implemented as switches). TranparentTransparent bridges require the active topology to be loop free. The Spanning Tree Protocol (STP) achieves this by the exchange of Bridge Protocol Data Unit (BPDU), as defined in [IEEE-802.1D], which leads to, where required, the blocking of ports (i.e., not forwarding). By default, the spanning tree protocol does not know whether a particular newly connected piece of Ethernet will cause a loop. Therefore it will block all traffic from and to newly connected ports with the exception of some unbridged management frames. The STP will determine if the port can be connected to the network in a loop-free manner. For these technologies, even though the link-layer appears available, no data packet forwarding will occur until it is determined that the port can be connected to the network in a loop-free environment. For hosts which are providing indications to upper layer protocols, even if the host itself does not implement bridging or STP, packet delivery across the network can be affected by the presence of bridges. Where the host is not running STP itself, no explicit indication that forwarding has begun is sent from a bridge. Therefore, a host may not know when STP operations have completed, and when it is safe to inform upper layers to transmit packets. Where it is not known that forwarding operations are available, a host needs to assume that STP is being performed, and may indicate full connectivity only based on timeouts or reception of BPDUs. Most hosts today do not listen to BPDU frames. For these hosts, connectivity to the a port which is potentially bridged (any Ethernet port) carries the potential of frame loss if transmissions occur before any bridges' ForwardDelay timers have expired twice. This timeout defaults to 30 seconds (2 * 15 seconds), but may be as high as 60s [IEEE-802.1D]. When sending indications to upper layers, the period where frame forwarding is potentially unavailable should be indicated to upper-layer protocols. Alternatively, a host can listen for BPDUs and use them to determine the length of port blockage which will occur in their particular circumstances. In either case, as soon as link_status becomes OK a link up notification with the attribute (R-flag) that indicates the risk of packet loss MAY be sent. Upon learning that an adjacent port is running STP or RSTP, the host MUST send a link up notification upon expiry of calculated delays to indicate that general packet transfer is available across the LAN. If no bridge configuration messages are received within the Bridge_Max_Age interval (default 20s), then it is likely that there is no visible bridge whose port is enabled for bridging (S8.4.5 of [IEEE-802.1D]), since at least two BPDU hello messages would have been lost. Upon this timeout, a link up notification MUST be generated. It is not easy for a non-STP host to distinguish between Disabled bridge ports and non-bridge ports with no IP nodes on them, as Disabled ports will have no traffic on them, and incur 100% sender loss. Upon this Bridge_Max_Age timeout, a link up notification must be generated. If an earlier link up was generated with the R-flag set, this new one MUST set the A-flag showing that packets sent within the prior interval were likely to have traversed the forwarding path (unless the port is disabled). If a BPDU is received, and the adjacent bridge is running the original Spanning Tree Protocol, then a host cannot successfully send packets until at least twice the ForwardDelay value in the received BPDU has elapsed. After this time, a link up notification MUST be generated. If the previous link up notification had the R-flag set, then the B-flag) MUST be set in this notification. The B-flag signifies that the packets sent within the prior interval were lost. If the bridge is identified as performing Rapid Spanning Tree Protocol (RSTP), it instead waits Bridge_Max_Age after packet reception (advertised in the BPDU's Max Age field), before forwarding. For ports which are known to be point-to-point through autonegotiation, this delay is abbreviated to 3 seconds after autonegotiation completes [IEEE-802.1D]. 2.4.3 802.1AB Link-Layer Discovery Protocol The recently defined 802.1AB Link-Layer Discovery Protocol (LLDP) provides information to devices which are directly adjacent to them on the local LAN [IEEE-802.1ab]. LLDP sends information periodically, and at link status change time to indicate the configuration parameters of the device. Devices may either send or receive these messages, or both. The LLDP message may contain a System Capabilities TLV, which describes the MAC and IP layer functions which a device is currently using. Where a host receives the Systems Capabilities TLV which indicate that no Bridging or Repeating is occurring on the LLDP transmitter, then no delays for STP calculation will be applied to packets sent through this transmitter, if the host does not perform STP itself. This would allow the generation of a link up notification. Additionally, if a host receives a Systems Capabilities TLV which indicates that the LLDP transmitter is a bridge, the host's advertisement that it is an (end-host) Station-Only, may tell the bridge not to run STP, and immediately allow forwarding. Proprietary extensions may also indicate that data forwarding is already available on such a port. Discussion of such optimizations is out-of-scope for this document. Due to the protocol's newness and lack of deployment, it is unclear how this protocol will eventually affect DNA in IPv4 or IPv6 networks. 2.4.4 Summary Link-Layer indications in Ethernet-like networks are complicated by additional unadvertised delays due to Spanning Tree calculations. This may cause re-indication (link up with A-flag) or retraction (link up with B-flag) of indications previously sent to upper layer protocols. 3. IANA Considerations This document has no actions for IANA. 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. 5. Contributors Text for the specific link-layer technologies covered by this document are contributed by Eric Njedjou (GPRS), Siva Veerepalli (cdma2000), Nicolas Montavont (IEEE 802.11b), Thomas Noel (IEEE 802.11b), and Greg Daley (IEEE 802.3). 6. Acknowledgements The authors would like to acknowledge Bernard Aboba, Sanjeev Athalye, JinHyeock Choi, John Loughney, Pekka Nikander, Brett Pentland, Tom Petch, Dan Romascanu, Pekka Savola, and Muhammad Mukarram bin Tariq for their useful comments and suggestions. 7. References 7.1 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., "Goals of Detecting Network Attachment in IPv6", draft-ietf-dna-goals-04 (work in progress), December 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, "Supplement to STANDARD FOR Telecommunications and Information Exchange between Systems - LAN/MAN Specific Requirements - Part 11: Wireless Medium Access Control (MAC) and physical layer (PHY) specifications: Specification for Enhanced Security", IEEE IEEE 802.11i, December 2004. [IEEE-802.1D] Institute of Electrical and Electronics Engineers, "IEEE standard for local and metropolitan area networks - common specific ations - Media access control (MAC) Bridges", ISO/IEC IEEE Std 802.1D, 2004. [IEEE-802.1ab] Institute of Electrical and Electronics Engineers, "Draft Standard for Local and Metropolitan Networks: Station and Media Access Control Connectivity Discovery (Draft 13)", IEEE draft Std 802.1AB, 2004. [IEEE-802.3] Institute of Electrical and Electronics Engineers, "IEEE standard for local and metropolitan area networks - Specific Require ments, Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications", ISO/IEC IEEE Std 802.3, 2002. [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. 7.2 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-mipv6-03 (work in progress), October 2004. [I-D.ietf-mobileip-lowlatency-handoffs-v4] Malki, K., "Low latencyLatency Handoffs in Mobile IPv4", draft-ietf-mobileip-lowlatency-handoffs-v4-09draft-ietf-mobileip-lowlatency-handoffs-v4-11 (work in progress), June 2004.October 2005. [RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. Author's Address Alper E. Yegin (editor) Samsung Advanced Institute of Technology 75 West Plumeria Drive San Jose, CA 95134 USA Phone: +1 408 544 5656 Email: email@example.com Appendix A. Change History The following changes were made on draft version 00: - IEEE 802.11 ad-hoc mode discussion added. - IPv6 address configuration over 3GPP networks clarified. The following changechanges were made on draft version 01: - Text for IEEE 802.3 added. - Multiple 3GPP PDP Contexts scenario clarified. The following change was made on draft version 02: - Editorial fixes as suggested by WG last call feedback. 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