Network Working Group G. Tsirtsis Internet-Draft H. Soliman Intended status: Standards Track V. Park Expires: January 2, 2007 Qualcomm July 2006 Dual Stack Mobile IPv4 draft-ietf-mip4-dsmipv4-00.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 2, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Tsirtsis, et al. Expires January 2, 2007 [Page 1] Internet-Draft Dual Stack Mobile IPv4 July 2006 Abstract This specification provides IPv6 extensions to the Mobile IPv4 protocol. The extensions allow a dual stack node to use IPv4 and IPv6 home addresses as well as to move between IPv4 and dual stack network infrastructures. Table of Contents 1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Extension Formats . . . . . . . . . . . . . . . . . . . . . . 6 3.1. IPv6 Prefix Extension . . . . . . . . . . . . . . . . . . 6 3.2. IPv6 Code Extension . . . . . . . . . . . . . . . . . . . 7 3.3. IPv6 Tunneling Mode Extension . . . . . . . . . . . . . . 8 4. Mobile IP Registrations . . . . . . . . . . . . . . . . . . . 10 4.1. Registration Requests . . . . . . . . . . . . . . . . . . 10 4.2. Registration Reply . . . . . . . . . . . . . . . . . . . . 10 4.3. Home Agent Considerations . . . . . . . . . . . . . . . . 11 4.4. Foreign Agent Considerations . . . . . . . . . . . . . . . 12 4.5. Mobile Node Considerations . . . . . . . . . . . . . . . . 13 4.6. Dynamic IPv6 Prefix allocation . . . . . . . . . . . . . . 14 4.6.1. Mobile IP Style Address Allocation . . . . . . . . . . 14 4.6.2. Prefix Delegation . . . . . . . . . . . . . . . . . . 15 4.7. Deregistration of IPv6 Prefix . . . . . . . . . . . . . . 15 4.8. Registration with a private CoA . . . . . . . . . . . . . 15 5. Security Considerations . . . . . . . . . . . . . . . . . . . 16 6. Aknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 7. Normative References . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19 Intellectual Property and Copyright Statements . . . . . . . . . . 20 Tsirtsis, et al. Expires January 2, 2007 [Page 2] Internet-Draft Dual Stack Mobile IPv4 July 2006 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]. Tsirtsis, et al. Expires January 2, 2007 [Page 3] Internet-Draft Dual Stack Mobile IPv4 July 2006 2. Introduction Mobile IPv4 [RFC3344] allows a mobile node with an IPv4 address to maintain communications while moving in an IPv4 network. Extensions defined in this document allow a node that has IPv4 and IPv6 [RFC2460] addresses to maintain communications with either any of its addresses while moving in IPv4 or dual stack networks. Essentially, this specification separates the Mobile IPv4 signaling from the IP version of the traffic that it tunnels. Mobile IPv4 with the present extensions remains a signaling protocol that runs over IPv4, and yet can set-up any combination of IPv4 and/or IPv6 over IPv4 tunnels. The aim is two-fold: On one hand, Mobile IPv4 with the present extensions becomes a powerful transition mechanism, allowing automated but controlled tunneling of IPv6 traffic over IPv4 tunnels. Dual stack nodes in dual stack home networks can now roam to and from legacy IPv4 networks, while IPv4 mobile nodes and networks can migrate to IPv6 without changing mobility management, and without upgrading all network nodes to IPv6 at once. On the other hand, and more importantly, it allows dual stack mobile nodes and networks to utilize a single protocol for the movement of both IPv4 and IPv6 stacks in the network topology. Note that features like Mobile IPv6 [RFC3775] style route optimization will not be possible with this solution as it still relies on Mobile IPv4 signaling, which does not provide route optimization. 2.1. Goals a. The solution supports the registration of IPv6 address(es) and/or prefix(s) in addition to regular IPv4 home address registration b. The solution supports dynamic IPv6 address(s)/prefix(s) allocations c. The solution supports the above registrations with and without FA support Tsirtsis, et al. Expires January 2, 2007 [Page 4] Internet-Draft Dual Stack Mobile IPv4 July 2006 2.2. Non-Goals a. The solution does not provide support for IPv6 care-of address registration Tsirtsis, et al. Expires January 2, 2007 [Page 5] Internet-Draft Dual Stack Mobile IPv4 July 2006 3. Extension Formats The following extensions are defined according to this specification. 3.1. IPv6 Prefix Extension A new skippable extension to the Mobile IPv4 header in accordance to the short extension format of [RFC3344] is defined here. This extension contains a mobile IPv6 network prefix and its prefix length. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sub-Type | Prefix Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Mobile IPv6 Network Prefix + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: IPv6 Prefix Extension Type DSMIPv4 Extensions (skippable type range to be assigned by IANA) Length 20 Sub-Type 1 (IPv6 Prefix) Prefix Length Indicates the prefix length of the prefix included in the Mobile Network IPv6 Prefix Field Mobile IPv6 Network Prefix Tsirtsis, et al. Expires January 2, 2007 [Page 6] Internet-Draft Dual Stack Mobile IPv4 July 2006 A sixteen-byte field containing the Mobile IPv6 Network Prefix 3.2. IPv6 Code Extension A new skippable extension to the Mobile IPv4 header in accordance to the short extension format of [RFC3344] is defined here. This extension defines a mobile IPv6 network prefix and its prefix length, as well as a code. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sub-Type | Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Length | Reserved | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | | + + | | + Mobile IPv6 Network Prefix + | | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: IPv6 Code Extension Type DSMIPv4 Extensions (skippable type range to be assigned by IANA) Length 22 Sub-Type 2 (IPv6 Prefix Acknowledgment) Code A value indicating the result of the registration request with respect to the IPv6 home address registration Prefix Length Tsirtsis, et al. Expires January 2, 2007 [Page 7] Internet-Draft Dual Stack Mobile IPv4 July 2006 Indicates the prefix length of the prefix included in the Mobile Network IPv6 Prefix Field Reserved Set to 0 by the sender, ignored by the receiver Mobile IPv6 Network Prefix A sixteen-byte field containing the Mobile IPv6 Network Prefix The following values are defined for use as a Code value in the above extension 0 registration accepted, IPv6 to be tunneled to HoA 1 registration accepted, IPv6 to be tunneled to CoA 8 reason unspecified 9 administratively prohibited Note that a registration reply that does not include an IPv6 code extension indicates that the home agent does not support IPv6 extensions and thus has ignored such extensions in the registration reply. 3.3. IPv6 Tunneling Mode Extension A new skippable extension to the Mobile IPv4 header in accordance to the short extension format of [RFC3344] is defined here. This presence of this extension in a registration request message indicates that the sender supports the IPv6 extensions specified in this document. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Sub-Type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: IPv6 Tunneling Mode Extension Type Tsirtsis, et al. Expires January 2, 2007 [Page 8] Internet-Draft Dual Stack Mobile IPv4 July 2006 DSMIPv4 Extensions (skippable type range to be assigned by IANA) Length 4 Sub-Type 3 (IPv6 Tunneling Mode Extension) Reserved Set to 0 by the sender, ignored by the receiver Tsirtsis, et al. Expires January 2, 2007 [Page 9] Internet-Draft Dual Stack Mobile IPv4 July 2006 4. Mobile IP Registrations 4.1. Registration Requests A mobile IP client MAY include one or more IPv6 prefix extensions defined in this specification in a registration request. A mobile IP client MAY include exactly one IPv6 tunneling mode extension when it uses the collocated care-of address mode. When IPv6 prefix and/or IPv6 tunneling mode extension are used by the mobile client, they MUST be placed after the registration request header and before the mobile - home authentication extension so they MUST be included in the computation of any authentication extension. A foreign agent MAY include an IPv6 tunneling mode extension defined in the specification in a registration request when the care-of address mode of operation is used. When IPv6 tunneling mode extension are used they MUST be placed after the mobile - home authentication extensions and before the foreign - home authentication extension so they MUST be included in the computation of the foreign - home authentication extension when one exists. 4.2. Registration Reply The mechanism described in the specification depends on skippable extensions. For that reason a registration reply that does not include an IPv6 code extension, in response to a registration request that included an IPv6 prefix extension, indicates that the home agent does not support IPv6 extensions and has ignored the request. If an IPv6 code extension is included in a registration reply then, said extension indicates the success or failure of the IPv6 prefix registration. The IPv6 code extension does NOT affect in any way, the code value in the registration reply header. Note that a negative IPv6 code extension has the same effect with not including such extension at all in the sense that in both cases the mobile client and foreign agent must act as if the corresponding request of Ipv6 prefix registration was rejected. Of course negative IPv6 code extension allows the home agent to indicate why a given request was rejected. Tsirtsis, et al. Expires January 2, 2007 [Page 10] Internet-Draft Dual Stack Mobile IPv4 July 2006 4.3. Home Agent Considerations A dual stack home agent that supports the IPv6 extensions defined in this specification, MUST keep track of the following IPv6 related state for the mobile IP clients it supports, in addition to what state is defined in [RFC3344]. - Registered IPv6 prefix(es) and prefix length(s) - Tunneling mode for IPv6 traffic: - Tunnel to IPv4 HoA and accept IPv6 tunneled from IPv4 HoA - Tunnel to CoA and accept IPv6 tunneled from CoA If the tunnel for IPv4 traffic terminates at a different point than the tunnel for IPv6 traffic (mobile client's CoA vs HoA), both tunnels MUST use the tunneling mechanism negotiated by the Mobile IP header as defined in [RFC3344]. A home agent that supports this specification MUST be able to intercept IPv4 and IPv6 packets destined to registered mobile nodes according to mechanisms described in [RFC3344] and [RFC3775] specifications. All intercepted traffic SHOULD be tunneled to the registered care-of address or home address of the mobile client in question according to the tunneling mode selected for IPv6 traffic. Tunneling mode selection for IPv6 traffic depends on the following parameters in a successful registration request: 1) Registration request is received with one or more IPv6 prefix extensions. An IPv6 tunneling mode extension is not included. All IPv6 packets destined to the registered IPv6 prefix(es) MUST be tunneled by the home agent to the registered IPv4 home address of the mobile. Additionally, the home agent MUST be prepared to accept reverse tunneled packets from the IPv4 home address of the mobile encapsulating IPv6 packets sent by that mobile. 2) Registration request is received with one or more IPv6 prefix extensions. An IPv6 tunneling mode extension is included. All IPv6 packets destined to the registered IPv6 home address(s) SHOULD be tunneled by the home agent to the registered care-of address of the mobile client. Additionally, the home agent SHOULD be prepared to accept reverse tunneled packets from the care-of address of the mobile encapsulating IPv6 packets sent by that mobile. The home agent MAY ignore the presence of the IPv6 Tsirtsis, et al. Expires January 2, 2007 [Page 11] Internet-Draft Dual Stack Mobile IPv4 July 2006 tunneling mode extension and act as in case (1) above. The home agent SHOULD check that all IPv6 packets received from the mobile client over a tunnel from the home address or the care-of address, include a source address that falls under the registered IPv6 prefix(es) for that mobile client. For each IPv6 prefix extensions included in a valid registration request, a home agent that supports this specification SHOULD include a corresponding IPv6 code extension. For each accepted IPv6 prefix the home agent MUST decide the tunneling mode used according to this section and set the Code field of the IPv6 code extension to the appropriate value. The omission of a given code extension is equivalent to the rejection of the corresponding IPv6 prefix extension. The IPv6 prefix field of each of the IPv6 code extensions included in the registration reply MUST match a corresponding IPv6 prefix field of the IPv6 prefix extension included in the corresponding registration request message. 4.4. Foreign Agent Considerations A dual stack foreign agent that supports the IPv6 extensions defined in this specification MUST keep track of the following IPv6 related state for the mobile nodes it supports in addition to what state is defined in [RFC3344]. - IPv6 Prefix(es) and Prefix Length(s) - Tunneling mode for IPv6 traffic: - accept IPv6 encapsulated in IPv4 and reverse tunnel IPv6 When a foreign agent receives a registration request with IPv6 prefix extension(s) it has the following choices: 1) Ignore the extension(s). The registration request is forwarded as is with no IPv6 tunneling mode extension to the home agent. The foreign agent SHOULD operate according to [RFC3344] 2) Attach an IPv6 tunneling mode extension to the registration request sent to the home agent. The foreign agent MUST be prepared to de-capsulate and deliver IPv6 packets, in addition to the IPv4 packets, sent to it in the home agent to foreign agent tunnel for that mobile client. The foreign agent MUST be prepared to receive IPv6 packets from the mobile client, in addition to IPv4 packets. All IPv6 traffic MUST Tsirtsis, et al. Expires January 2, 2007 [Page 12] Internet-Draft Dual Stack Mobile IPv4 July 2006 be reverse tunneled to the home agent by the foreign agent irrespectively from the reverse tunneling setting negotiated for IPv4 packets by mechanisms in [RFC3024] If the foreign agent sets the R flag included in the mobility agent advertisement [RFC3344] and a mobile client uses the collocated address model, the foreign agent MUST NOT include an IPv6 tunneling mode extension in the registration request messages sent from that mobile client. 4.5. Mobile Node Considerations A dual stack mobile node that supports the extensions described in this document MAY use these extensions to register its IPv6 home address(es) and/or prefix(es) while moving between access routers. The mobile client MAY include one or more IPv6 Prefix extension(s) in the registration request. The mobile client MAY include one or more IPv6 Prefix extension(s) in the registration request. In this case the mobile MUST take the following action depending on the extensions included in the registration reply it receives in response to the registration request: 1) The registration reply does not include any IPv6 code extensions. The mobile client SHOULD assume that the home agent does not support the extensions defined in this specification. The mobile client SHOULD continue to operate according to RFC3344. 2) The registration reply includes one or more IPv6 code extensions. The mobile client MUST match each IPv6 code extension with one of the IPv6 prefix extensions earlier included in the corresponding registration request message. If a matching IPv6 code extension is not included for one or more of corresponding IPv6 prefix extensions included in the registration request message, the mobile client SHOULD assume that these IPv6 prefixes are rejected. For each matching IPv6 code extensions the mobile client MUST inspect the Code field. If the field is set to a rejection code then the corresponding IPv6 prefix registration has been rejected. If the field is set to an acceptance code then the corresponding IPv6 prefix registration has been accepted. Tsirtsis, et al. Expires January 2, 2007 [Page 13] Internet-Draft Dual Stack Mobile IPv4 July 2006 If the Code field is set to "0" then the mobile client MUST be prepared to send/receive IPv6 packets encapsulated in the bidirectional tunnel between the home agent address and the registered IPv4 home address of the mobile client. If the Code field is set to "1" then the mobile client MUST act as follows: - If the care-of address mode is used, the mobile client MUST be prepared to send/receive IPv6 traffic on its interface natively, unless reverse tunnel has been negotiated in which case both IPv4 and IPv6 traffic MUST be reverse tunneled according to [RFC3024]. If the collocated care-of address mode is used, the mobile client MUST be prepared to send/receive IPv6 packets over the bidirectional tunnel between the home agent address and its collocated care-of address. The mobile client SHOULD include exactly one IPv6 tunneling mode extension if it uses the collocated care-of address model and if it wants to request that IPv6 packets are tunneled to its collocated care-of address. If the mobile client uses the collocated care-of address model but it does not include the IPv6 tunneling mode extension the home agent will tunnel IPv6 traffic to the mobile client's home address. 4.6. Dynamic IPv6 Prefix allocation 4.6.1. Mobile IP Style Address Allocation A mobile client MAY include one or more IPv6 prefix extensions with the IPv6 prefix field set to zero. Such IPv6 prefix extensions indicate that the mobile client requests IPv6 prefix(es) to be assigned to it by the home agent. The mobile client MAY set the prefix length field of such extensions to zero or to a length of its choice as a hint to the home agent. A home agent receiving an IPv6 prefix extension with the IPv6 prefix field set to zero MAY return an IPv6 Code extension with the IPv6 prefix field set to the IPv6 prefix allocated to the mobile client. The length of that prefix is at the discretion of the home agent. The home agent MAY take into account the prefix length hint if one is included in the IPv6 prefix extension. For stateless auto-configuration of addresses [RFC2462], a mobile client MAY include one or more IPv6 prefix extensions with the IPv6 Prefix field set to ::interface_identifier. Such IPv6 prefix extensions indicate that the mobile client requests IPv6 address(es) Tsirtsis, et al. Expires January 2, 2007 [Page 14] Internet-Draft Dual Stack Mobile IPv4 July 2006 to be assigned to it by the home agent. The prefix length field in such an extension SHOULD be set to 64 or 128. The home agent MAY in this case return an IPv6 Code extension with: - the IPv6 prefix field set to PREFIX:: and the prefix length field set to 64. - the IPv6 prefix field set to PREFIX::interface_identifier and the prefix length field set to 128. The HA SHOULD perform Duplicate Address Detection (DAD) according to [RFC2462] before it returns an IPv6 home address in an IPv6 Code extension. If a prefix is returned DAD is not applicable. The HA MUST send a Neighbor Advertisement, as defined in [RFC2461] for every IPv6 address it allocates with this mechanism so that all traffic to this address is directed to itself. 4.6.2. Prefix Delegation A dual stack mobile node MAY also use Prefix Delegation as defined in [draft-ietf-nemo-dhcpv6-pd-01.txt] to get a prefix. In that case the mobile MUST first register its IPv4 home address as per [RFC3344]. When that is done the mobile can generate a link local IPv6 address and use it to send DHCP messages according to [draft-ietf-nemo-dhcpv6-pd-01.txt]. All IPv6 messages required for Prefix Delegation MUST be tunneled over the IPv4 tunnel between the mobile and the home agent. 4.7. Deregistration of IPv6 Prefix The mobile IP registration lifetime included in the registration request header is valid for all binding created by the registration request, which may include bindings for an IPv6 Prefix(es). A registration request with a zero lifetime can be used to remove all bindings from the home agent. A re-registration request with non-zero lifetime can be used to deregister some of the registered IPv6 prefixes by not including corresponding IPv6 prefix extensions in the registration request message. 4.8. Registration with a private CoA If the care-of address is a private address then Mobile IP NAT Traversal as described in [RFC3519] MAY be used in combination with the extensions described in this specification. Tsirtsis, et al. Expires January 2, 2007 [Page 15] Internet-Draft Dual Stack Mobile IPv4 July 2006 5. Security Considerations This specification operates in the security constraints and requirements of [RFC3344]. It extends the operations defined in [RFC3344] for IPv4 home addresses to cover IPv6 prefixes and provides the same level of security for both IP versions. Tsirtsis, et al. Expires January 2, 2007 [Page 16] Internet-Draft Dual Stack Mobile IPv4 July 2006 6. Aknowledgements Thanks to Pat Calhoun, Paal Engelstad, Tom Hiller and Pete McCann for earlier work on this subject. Thanks also to Alex Petrescu for suggesting the use of prefix delegation for dynamic IPv6 address allocation. Tsirtsis, et al. Expires January 2, 2007 [Page 17] Internet-Draft Dual Stack Mobile IPv4 July 2006 7. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998. [RFC2462] Thomson, S. and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 2462, December 1998. [RFC2794] Calhoun, P. and C. Perkins, "Mobile IP Network Access Identifier Extension for IPv4", RFC 2794, March 2000. [RFC3024] Montenegro, G., "Reverse Tunneling for Mobile IP, revised", RFC 3024, January 2001. [RFC3344] Perkins, C., "IP Mobility Support for IPv4", RFC 3344, August 2002. [RFC3519] Levkowetz, H. and S. Vaarala, "Mobile IP Traversal of Network Address Translation (NAT) Devices", RFC 3519, May 2003. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. Tsirtsis, et al. Expires January 2, 2007 [Page 18] Internet-Draft Dual Stack Mobile IPv4 July 2006 Authors' Addresses George Tsirtsis Qualcomm Phone: +908-947-7059 Email: tsirtsis@qualcomm.com Hesham Soliman Qualcomm Phone: +614-111-410-445 Email: hesham@qualcomm.com Vincent Park Qualcomm Phone: +908-947-7084 Email: vpark@qualcomm.com Tsirtsis, et al. Expires January 2, 2007 [Page 19] Internet-Draft Dual Stack Mobile IPv4 July 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Tsirtsis, et al. Expires January 2, 2007 [Page 20]