--- 1/draft-ietf-dhc-vpn-option-09.txt 2009-03-03 18:12:07.000000000 +0100 +++ 2/draft-ietf-dhc-vpn-option-10.txt 2009-03-03 18:12:07.000000000 +0100 @@ -1,49 +1,54 @@ DHC Working Group Kim Kinnear Internet Draft Richard Johnson Intended Status: Standards Track Mark Stapp -Expires: January 8, 2009 Jay Kumarasamy +Expires: September 3, 2009 Jay Kumarasamy Cisco Systems - July 8, 2008 + March 3, 2009 Virtual Subnet Selection Options for DHCPv4 and DHCPv6 - + 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. + This Internet-Draft is submitted to IETF in full conformance with the + provisions of BCP 78 and 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 8, 2009 + This Internet-Draft will expire on September 3, 2009 Copyright Notice - Copyright (C) The IETF Trust (2008). + Copyright (c) 2009 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents in effect on the date of + publication of this document (http://trustee.ietf.org/license-info). + Please review these documents carefully, as they describe your rights + and restrictions with respect to this document. Abstract This memo defines a Virtual Subnet Selection (VSS) option for DHCPv4 and DHCPv6, and a DHCPv4 relay-agent-information sub-option. These are intended for use by DHCP clients, relay agents, and proxy clients in situations where VSS information needs to be passed to the DHCP server for proper address or prefix allocation to take place. For the DHCPv4 option and relay-agent-information sub-option, this @@ -53,36 +58,34 @@ 1. Introduction................................................. 2 2. Terminology.................................................. 3 3. Virtual Subnet Selection Option and Sub-Option Definitions... 5 3.1. DHCPv4 Virtual Subnet Selection Option..................... 5 3.2. DHCPv4 Virtual Subnet Selection Sub-Option................. 5 3.3. DHCPv6 Virtual Subnet Selection Option..................... 6 3.4. Virtual Subnet Selection Type and Information.............. 6 4. Overview of Virtual Subnet Selection Usage................... 7 5. Relay Agent Behavior......................................... 10 - 5.1. VPN assignment by the DHCP server.......................... 11 + 5.1. VPN assignment by the DHCP server.......................... 12 5.2. DHCP Leasequery............................................ 12 6. Client Behavior.............................................. 12 7. Server Behavior.............................................. 13 7.1. Returning the DHCPv4 or DHCPv6 Option...................... 14 - 7.2. Returning the DHCPv4 Sub-Option............................ 14 + 7.2. Returning the DHCPv4 Sub-Option............................ 15 7.3. Making sense of conflicting VSS information................ 15 - 8. Security..................................................... 15 - 9. IANA Considerations.......................................... 16 + 8. Security..................................................... 16 + 9. IANA Considerations.......................................... 17 10. Acknowledgments............................................. 17 - 11. Normative References........................................ 17 - 12. Informative References...................................... 18 - 13. Authors' Addresses.......................................... 18 - 14. Full Copyright Statement.................................... 19 - 15. Intellectual Property....................................... 20 - 16. Acknowledgment.............................................. 20 + 11. References.................................................. 18 + 11.1. Normative References...................................... 18 + 11.2. Informative References.................................... 18 + 12. Authors' Addresses.......................................... 19 1. Introduction There is a growing use of Virtual Private Network (VPN) configurations. The growth comes from many areas; individual client systems needing to appear to be on the home corporate network even when traveling, ISPs providing extranet connectivity for customer companies, etc. In some of these cases there is a need for the DHCP server to know the VPN (hereafter called a "Virtual Subnet Selector" or "VSS") from which an address, and other resources, should be @@ -101,24 +104,24 @@ If the allocation is being done through a DHCPv4 relay, then the relay sub-option defined here should be included. In some cases, however an IP address is being sought by a DHCPv4 proxy on behalf of a client (which may be assigned the address via a different protocol). In this case, there is a need to include VSS information relating to the client as a DHCPv4 option. If the allocation is being done through a DHCPv6 relay, then the DHCPv6 VSS option defined in this document should be included in the Relay-forward and Relay-reply message going between the DHCPv6 relay - and server. In some cases, addresses or prefixes are being sought - for by a DHCPv6 proxy on behalf of a client. In this case, there is - a need for the client itself to supply the VSS information using the - DHCPv6 VSS option in the messages that it sends to the DHCPv6 server. + and server. In some cases, addresses or prefixes are being sought by + a DHCPv6 proxy on behalf of a client. In this case, there is a need + for the client itself to supply the VSS information using the DHCPv6 + VSS option in the messages that it sends to the DHCPv6 server. In the remaining text of this document, when a DHCPv6 address is indicated the same information applies to DHCPv6 Prefix Delegation [RFC3633] as well. 2. Terminology 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 [RFC2119]. @@ -136,35 +139,35 @@ and DHCP messages between clients and servers residing on different subnets, per [RFC951] and [RFC1542]. o "DHCP server" A DHCP server is a host that returns configuration parameters to DHCP clients. o "DHCPv4 option" - An option or used to implement a capability defined by the - DHCPv4 RFCs [RFC2131][RFC2132]. These options have one octet - code and size bytes. + An option used to implement a capability defined by the DHCPv4 + RFCs [RFC2131][RFC2132]. These options have one-octet code and + size fields. o "DHCPv4 sub-option" As used in this document, a DHCPv4 sub-option refers to a sub- option of the relay-agent-information option [RFC3046]. These - sub-options have one octet code and size bytes. + sub-options have one-octet code and size fields. o "DHCPv6 option" An option used to implement a capability defined by the DHCPv6 - RFC [RFC3315]. These options have two octet code and size - bytes. + RFC [RFC3315]. These options have two-octet code and size + fields. o "downstream" Downstream is the direction from the access concentrator towards the subscriber. o "upstream" Upstream is the direction from the subscriber towards the access concentrator. @@ -174,26 +177,25 @@ Information about a VPN necessary to allocate an address to a DHCP client on that VPN and necessary to forward a DHCP reply packet to a DHCP client on that VPN. o "VPN" Virtual private network. A network which appears to the client to be a private network. o "VPN Identifier" - The VPN-ID is defined by [RFC2685] to be a sequence of 7 octets. 3. Virtual Subnet Selection Option and Sub-Option Definitions - The Virtual Subnet Selection options and sub-option contains a + The Virtual Subnet Selection options and sub-option contain a generalized way to specify the VSS information about a VPN. There are two options and one sub-option defined in this section. The actual VSS information is identical in each. 3.1. DHCPv4 Virtual Subnet Selection Option The format of the option is: 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 @@ -251,38 +253,38 @@ Type VSS Information format: 0 NVT ASCII VPN identifier 1 RFC2685 VPN-ID 2-254 Not Allowed 255 Global, default VPN. o Type 0 -- NVT ASCII VPN identifier - Indicates that the VSS information consists of a NVT ASCII string. - It MUST NOT be terminated with a zero byte. + Indicates that the VSS information consists of a NVT ASCII + string. It MUST NOT be terminated with a zero byte. o Type 1 -- RFC2685 VPN-ID Indicates that the VSS information consists of an RFC2685 VPN-ID [RFC2685], which is defined to be 7 octets in length. o Type 255 -- Global, default VPN Indicates that there is no explicit, non-default VSS information - but rather that this option references the normal, global, default - address space. In this case, there MUST NOT be any VSS Information - and the length of the VSS option MUST be 1. + but rather that this option references the normal, global, + default address space. In this case, there MUST NOT be any VSS + Information and the length of the VSS option MUST be 1. - All other values of the Type field are invalid as of this memo and a - VSS option with a Type field containing any value other than zero - (0), one (1), or 255 SHOULD be ignored. + All other values of the Type field are invalid as of this memo and + a VSS option with a Type field containing any value other than + zero (0), one (1), or 255 SHOULD be ignored. 4. Overview of Virtual Subnet Selection Usage At the highest level, the VSS option or sub-option determines the VPN on which a DHCP client is supposed to receive an IP address. How the option or sub-option is entered and processed is discussed below, but the point of all of the discussion is to determine the VPN on which the DHCP client resides. This will affect a relay agent, in that it will have to ensure that the packets sent to and received from the DHCP client flow over the correct VPN. This will affect the DHCP @@ -322,52 +324,63 @@ request or response, this situation is neither typical nor useful. There are two known paradigms for use of the VSS option or sub- option, which are discussed below. The typical use of the VSS option or sub-option is for the relay agent to know the VPN on which the DHCP client is operating. The DHCP client itself does not, in this scenario, know the VPN on which it resides. The relay agent is responsible for mediating the access between the VPN on which the DHCP client resides and the DHCP server. In this situation, the relay agent will insert a VSS sub-option into - the relay-agent-information option (for DHCPv4) or a VSS option the - Relay-forward message (for DHCPv6) of every request it forwards from - the DHCP client. The server will use the VSS option or sub-option to - determine the VPN on which the client resides, and use that VPN - information to select the address space within its configuration from - which to allocate an IP address to the DHCP client. + the relay-agent-information option (for DHCPv4) or a VSS option into + the Relay-forward message (for DHCPv6) of every request it forwards + from the DHCP client. The server will use the VSS option or sub- + option to determine the VPN on which the client resides, and use that + VPN information to select the address space within its configuration + from which to allocate an IP address to the DHCP client. - In this scenario, the relay agent might also send in either a DHCPv4 - or DHCPv6 Leasequery request, but in this case, it would use the VSS - option in the Leasequery request to select the correct address space - for the Leasequery. In this scenario, the relay agent would be - acting as a DHCP client from a Leasequery standpoint, but it would - not be as if a DHCP client were sending in a VSS option in a standard - DHCP address allocation request, say a DHCPDISCOVER. + In this scenario, the relay agent might also send a VSS option or + sub-option in either a DHCPv4 or DHCPv6 Leasequery request, but in + this case, it would use the VSS option in the Leasequery request to + select the correct address space for the Leasequery. In this + scenario, the relay agent would be acting as a DHCP client from a + Leasequery standpoint, but it would not be as if a DHCP client were + sending in a VSS option in a standard DHCP address allocation + request, say a DHCPDISCOVER. In this scenario, only one relay agent would mediate the VPN access for the DHCP client to the DHCP server, and it would be the relay - agent which inserts the VSS information into the packet and would - remove it prior to forwarding the packet on. + agent which inserts the VSS information into the request packet and + would remove it prior to forwarding the response packet on. The DHCP server would know that it should respond to VPN information specified in a VSS option or sub-option, and it would be configured with appropriate VPN address spaces to service the projected client requirements. Thus, in this common scenario, the DHCP client knows nothing of any VPN access, the relay agent has been configured in some way that allows it to determine the VPN of the DHCP client and transmit that using a VSS option or sub-option to the DHCP server, and the DHCP server responds to the VPN specified by the relay agent. There is no conflict between different entities trying to specify different VSS information -- each entity knows its role through policy or configuration external to this document. + It is important to ensure that each entity in this scenario both + supports the VSS option and sub-option (for DHCPv4) or the VSS option + (for DHCPv6), and that it is configured correctly. Deploying relay + agents which support and emit VSS sub-options in concert with DHCPv4 + servers which do not support the VSS option or sub-option as defined + in this document SHOULD NOT be done, as such an ensemble will not + operate correctly together because all of the IP addresses will be + allocated from the global or default VPN regardless of the VPN on + which the client's reside. + In the second scenario, the DHCP server would be configured in some way to know the VPN on which a particular DHCP client should be given access. The DHCP server would in this case include the VSS sub- option in the relay-agent-information option for DHCPv4 or the VSS option in the Relay-reply message for DHCPv6. The relay agent responsible for mediating VPN access would use this information to select the correct VPN for the DHCP client. In the event that there were more than one relay agent involved in this transaction, some external configuration or policy would be needed to inform the DHCPv6 server into which Relay-reply message the VSS option should go. @@ -378,20 +391,26 @@ conflict with the DHCP server's idea of the proper VPN for the client, everything works correctly. In this second scenario, the DHCP client is again unaware of any VPN activity. In this case, however, the DHCP server knows the VPN for the client, and the relay agent responds to the VSS information specified by the DHCP server. Similar to the first scenario, each entity knows its role through a means external to this document and no two entities try to specify VSS information in conflict. + Again, in this scenario, it is important that both the relay agent as + well as the DHCP server both support the VSS option and sub-option + (for DHCPv4) and the VSS option (for DHCPv6). Deploying and + configuring VPN support in one element and not in the other is not a + practical approach. + There are many other scenarios which can be created with multiple relay agents each inserting VSS information into different Relay- forward messages, relay agent VSS information conflicting with client VSS information, or DHCP server VSS information conflicting with relay agent and client VSS information. Since these scenarios do not describe situations that are useful today, specifying precisely how to resolve all of these conflicts is unlikely to be valuable in the event that these scenarios actually become practical in the future. The current use of the VSS option and sub-option require that each @@ -422,49 +441,52 @@ A DHCPv4 relay agent SHOULD include a DHCPv4 VSS sub-option in a relay-agent-information option [RFC3046], while a DHCPv6 relay agent SHOULD include a DHCPv6 VSS option in the Relay-forward message. The value placed in the Virtual Subnet Selection sub-option or option SHOULD be sufficient for the relay agent to properly route any DHCP reply packet returned from the DHCP server to the DHCP client for which it is destined. + Anytime a relay agent places a VSS option or sub-option in a DHCP + request, it MUST send it only to a DHCP server which supports the VSS + option or sub-option. + Since this option or sub-option is placed in the packet in order to specify the VPN on which an IP address is allocated for a particular DHCP client, one presumes that an allocation on that VPN is necessary for correct operation. If this presumption is correct, then a relay agent which places this option in a packet and doesn't receive it (or receives a different value than that sent to the server) in the returning packet should drop the packet since the IP address that was allocated will not be in the correct VPN. If an IP address that is - not on the requested VPN is not required, then the relay agent is - free to accept the IP address that is not on the VPN that was - requested. + on the requested VPN is not required, then the relay agent is free to + accept the IP address that is not on the VPN that was requested. The converse, however, is more complicated. In the DHCPv6 case, the appearance of the option in the Relay-reply packet does indeed indicate that the DHCPv6 server understood and acted upon the contents of the VSS option in the Relay-forward packet. In the DHCPv4 case, however, the appearance of the sub-option in the relay- agent-information option received by the relay agent does not necessarily indicate that the DHCPv4 server even understood, let alone acted correctly upon, the VSS sub-option that it received. The reason is that [RFC3046] specifies that a DHCPv4 server which supports the relay-agent-information option SHALL copy all sub- options received in a relay-agent-information option into any outgoing relay-agent-information option. Because of these requirements, even a DHCPv4 server which doesn't implement support - for Virtual Subnet Selection sub-option will almost certainly copy it - into the outgoing relay-agent-information option. This means that - the appearance of the Virtual Subnet Selection sub-option in a + for the Virtual Subnet Selection sub-option will almost certainly + copy it into the outgoing relay-agent-information option. This means + that the appearance of the Virtual Subnet Selection sub-option in a relay-agent-information option doesn't indicate support for the Virtual Subnet Selection sub-option. There are only two pieces of information which can be determined from the appearance or lack of appearance of the DHCPv4 Virtual Subnet Selection sub-option in a relay-agent-information option received by a relay agent from a DHCPv4 server. First, if the Virtual Subnet Selection sub-option does not appear, then the server was able to support this sub-option but chose not to do so. Second, if the Virtual Subnet Selection sub-option appears and has a different value @@ -501,20 +523,24 @@ In some cases, a DHCP server may use the Virtual Subnet Selection sub-option or option to inform a relay agent that a particular DHCP client is associated with a particular VPN. It does this by sending the Virtual Subnet Selection sub-option or option with the appropriate information to the relay agent in the relay-agent- information option for DHCPv4 or the Relay-reply message in DHCPv6. If the relay agent is unable to honor the DHCP server's requirement to place the DHCP client into that VPN it MUST drop the packet and not send it to the DHCP client. + The DHCP server MUST NOT place VSS information in an outgoing packet + if the relay agent or DHCP client is unprepared to properly interpret + the VSS information. + In this situation, once the relay agent has placed the DHCP client into the VPN specified by the DHCP server, it will send in a VSS option or sub-option when forwarding packets from the client. The DHCP server in normal operation will echo this VSS information into the outgoing replies. 5.2. DHCP Leasequery Sometimes a relay-agent needs to submit a DHCP Leasequery [RFC4388] [RFC5007] packet to the DHCP server in order to recover information @@ -542,23 +568,23 @@ DHCPv6 address is indicated the same information applies to DHCPv6 Prefix Delegation [RFC3633] as well. Since this option is placed in the packet in order to change the VPN on which an IP address is allocated for a particular DHCP client, one presumes that an allocation on that VPN is necessary for correct operation. If this presumption is correct, then a client which places this option in a packet and doesn't receive it or receives a different value in the returning packet should drop the packet since the IP address that was allocated will not be in the correct VPN. If - an IP address that is not on the requested VPN is not required, then - the client is free to accept the IP address that is not on the VPN - that the was requested. + an IP address that is on the requested VPN is not required, then the + client is free to accept the IP address that is not on the VPN that + the was requested. Clients should be aware that some DHCP servers will return a VSS option with different values than that which was sent in. In addition, a client may receive a response from a DHCP server with a VSS option when none was sent in by the Client. Note that when sending a DHCP Leasequery request, a relay agent is acting as a DHCP client and so it should include the respective DHCPv4 or DHCPv6 VSS option in its DHCPv4 or DHCPv6 Leasequery packet if the DHCP Leasequery request is generated for other than the @@ -611,26 +637,32 @@ relay agent receiving a reply containing a VSS option will correctly understand the VSS option. Otherwise, the client or relay agent will end up using the address as though it were a global address. 7.1. Returning the DHCPv4 or DHCPv6 Option DHCPv4 or DHCPv6 servers receiving a VSS option (for sub-option processing, see below) MUST return an instance of this option in the reply packet or message if the server successfully uses this option to allocate an IP address, and it MUST NOT include an instance of - this option if the server was unable to or not configured to support - the requested VPN. + this option if the server is unable to support, is not configured to + support, or does not implement support for VSS information in general + or the requested VPN in particular. If they echo the option (based on the criteria above), servers SHOULD - return the an exact copy of the option unless they desire to change - the VPN on which a client was configured. + return an exact copy of the option unless they desire to change the + VPN on which a client was configured. + + The appearance of the DHCPv6 VSS option in the OPTION_ORO [RFC3315] + or the OPTION_ERO [RFC4994] should not change the processing or + decision to return (or not to return) the VSS option as specified in + this document. 7.2. Returning the DHCPv4 Sub-Option The case of the DHCPv4 sub-option is a bit more complicated. Note that [RFC3046] specifies that a DHCPv4 server which supports the relay-agent-information option SHALL copy all sub-options received in a relay-agent-information option into any outgoing relay-agent- information option. Thus, the default behavior for any DHCPv4 server is to return any VSS sub-option received to the relay agent whether or not the DHCPv4 server understand the VSS sub-option. A server @@ -761,23 +793,29 @@ type byte may only be defined by IETF Consensus, as described in [RFC5226]. Basically, this means that they are defined by RFCs approved by the IESG. 10. Acknowledgments Bernie Volz recommended consolidation of the DHCPv4 option and sub- option drafts after extensive review of the former drafts, and provided valuable assistance in structuring and reviewing this document. Alper Yegin expressed interest in the DHCPv6 VSS option, - resulting in this combined draft covering all three areas. + resulting in this combined draft covering all three areas. Alfred + Hoenes provided assistance with editorial review as well as raising + substantive protocol issues. David Hankins and Bernie Volz each + raised important protocol issues which resulted in a clarified + document. Josh Littlefield provided editorial assistance. -11. Normative References +11. References + +11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, March 1997. @@ -788,60 +826,61 @@ 3046, January 2001. [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. [RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic Host Configuration Protocol (DHCP) version 6", RFC 3633, December 2003. -12. Informative References + [RFC4994] Zeng, S., Volz, B., Kinnear, K. and J. Brzozowski, "DHCPv6 + Relay Agent Echo Request Option", RFC 4994, September 2007. + +11.2. Informative References [RFC951] Croft, B. and J. Gilmore, "Bootstrap Protocol", RFC 951, September 1985. [RFC1542] Wimer, W., "Clarifications and Extensions for the Bootstrap Protocol", RFC 1542, October 1993. - [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", RFC 2119, March 1997. - [RFC3118] Droms, R. and W. Arbaugh, "Authentication for DHCP Messages", RFC 3118, June 2001. [RFC3942] Volz, B., "Reclassifying Dynamic Host Configuration Protocol version 4 (DHCPv4) Options", RFC 3942, November 2004. [RFC4030] Stapp, M. and T. Lemon, "The Authentication Suboption for the Dynamic Host Configuration Protocol (DHCP) Relay Agent Option", RFC 4030, March 2005. [RFC4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration Protocol (DHCP) Leasequery", RFC 4388, February 2006. [RFC5007] Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng, "DHCPv6 Leasequery", RFC 5007, September 2007. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. -13. Authors' Addresses +12. Authors' Addresses Kim Kinnear Cisco Systems 1414 Massachusetts Ave. Boxborough, Massachusetts 01719 Phone: (978) 936-0000 EMail: kkinnear@cisco.com + Richard Johnson Cisco Systems 170 W. Tasman Dr. San Jose, CA 95134 Phone: (408) 526-4000 EMail: raj@cisco.com Mark Stapp @@ -854,55 +892,10 @@ EMail: mjs@cisco.com Jay Kumarasamy Cisco Systems 170 W. Tasman Dr. San Jose, CA 95134 Phone: (408) 526-4000 EMail: jayk@cisco.com - -14. 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