--- 1/draft-ietf-dhc-subnet-option-00.txt 2006-02-04 23:05:58.000000000 +0100 +++ 2/draft-ietf-dhc-subnet-option-01.txt 2006-02-04 23:05:58.000000000 +0100 @@ -1,19 +1,19 @@ Network Working Group G. Waters INTERNET-DRAFT Nortel Networks - February 1999 + March 1999 The Subnet Selection Option for DHCP - - Friday, February 19, 1999, 3:01 PM + + Tuesday, March 23, 1999, 4:35 PM Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. @@ -35,25 +35,25 @@ This memo defines a new DHCP option for selecting the subnet on which to allocate an address. This option would override a DHCP server's normal methods of selecting which subnet on which to allocate an address for a client. Table of Contents 1. Introduction......................................................2 2. Subnet Selection Option...........................................3 - 3. Intellectual Property.............................................3 + 3. Intellectual Property.............................................4 4. Acknowledgements..................................................4 5. Security Considerations...........................................4 6. References........................................................4 - 7. Editor's Addresses................................................4 + 7. Editor's Addresses................................................5 8. Full Copyright Statement..........................................5 1. Introduction This memo was produced by the DHCP Working Group and defines a new DHCP option that specifies the subnet on which a DHCP server should use when selecting an address. This option takes precedence over other methods that the DHCP server may use to determine the subnet on which to select an address. Two existing methods of determining the subnet on which to select an address are: @@ -81,59 +81,68 @@ there is a requirement to allocate addresses for devices connected to those networks. Since there is no network connectivity between the DHCP server and the packet-handling plane, the control plane must allocate addresses using the DHCP on behalf of the packet-handling plane. Because the control plane is requesting the addresses, the DHCP server would normally have the undesired result of allocating the address on the subnet on which the control plane is connected. - If the option specified by this memo is included in the DHCPDISCOVER - then the server should allocate addresses on the subnet specified by - this option. The option would specify an address of one of the packet- + If the option specified by this memo is included in the + DHCPDISCOVER/DHCPREQUEST message then the server should allocate an + address on the subnet or network segment that is specified by this + option. The option would specify an address of one of the packet- handling plane's subnets. 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. Subnet Selection Option The subnet selection option is a DHCP option. The option contains a single IP address that is the address of a subnet. The value for the subnet address is determined by taking any IP address on the subnet and ANDing that address with the subnet mask (i.e.: the network and subnet bits are left alone and the remaining (address) bits are set to - zero). When this option is present the DHCP server MUST use the subnet - specified on which to allocate an address. + zero). When this option is present, the DHCP server MUST use either + the: + + o The subnet specified in the option, or; + o A subnet on the same network segment as the subnet specified in the + option; + + on which to allocate an address. The format of the option is: Code Len IP Address +-----+-----+-----+-----+-----+-----+ | TBD | 4 | A1 | A2 | A3 | A4 | +-----+-----+-----+-----+-----+-----+ In order to ensure backwards compatibility of clients that do support this option when communicating with DHCP servers that do not support this option, the DHCP client SHOULD check that an allocated address in - on the requested subnet. The client SHOULD NOT respond to an DHCPOFFER - of an address which is not on the requested subnet. + on the requested subnet or network segment. The client SHOULD NOT + respond to a DHCPOFFER or DHCPACK of an address that is not on the + requested subnet or network segment. This option does not require any change to other operations or features of the DHCP server other than to select the subnet on which to allocate an address. For example, the handling of DHCPDISCOVER for an unknown subnet may continue to operate unchanged. - A server that supports this option MUST NOT offer an address that is - not on the requested subnet when this option is present. + When this option is present and the server supports this option, the + server MUST NOT offer an address that is not on the requested subnet + or network segment. Existing methods for determining where to send a reply to a DHCP client are not changed when this option is present in a request. 3. Intellectual Property The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or