draft-ietf-dhc-subnet-option-00.txt   draft-ietf-dhc-subnet-option-01.txt 
Network Working Group G. Waters Network Working Group G. Waters
INTERNET-DRAFT Nortel Networks INTERNET-DRAFT Nortel Networks
February 1999 March 1999
The Subnet Selection Option for DHCP The Subnet Selection Option for DHCP
<draft-ietf-dhc-subnet-option-00.txt> <draft-ietf-dhc-subnet-option-01.txt>
Friday, February 19, 1999, 3:01 PM Tuesday, March 23, 1999, 4:35 PM
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with all This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026. provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts. groups may also distribute working documents as Internet-Drafts.
skipping to change at page 2, line 9 skipping to change at page 2, line 9
This memo defines a new DHCP option for selecting the subnet on which 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 to allocate an address. This option would override a DHCP server's
normal methods of selecting which subnet on which to allocate an normal methods of selecting which subnet on which to allocate an
address for a client. address for a client.
Table of Contents Table of Contents
1. Introduction......................................................2 1. Introduction......................................................2
2. Subnet Selection Option...........................................3 2. Subnet Selection Option...........................................3
3. Intellectual Property.............................................3 3. Intellectual Property.............................................4
4. Acknowledgements..................................................4 4. Acknowledgements..................................................4
5. Security Considerations...........................................4 5. Security Considerations...........................................4
6. References........................................................4 6. References........................................................4
7. Editor's Addresses................................................4 7. Editor's Addresses................................................5
8. Full Copyright Statement..........................................5 8. Full Copyright Statement..........................................5
1. Introduction 1. Introduction
This memo was produced by the DHCP Working Group and defines a new 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 DHCP option that specifies the subnet on which a DHCP server should
use when selecting an address. This option takes precedence over use when selecting an address. This option takes precedence over
other methods that the DHCP server may use to determine the subnet on other methods that the DHCP server may use to determine the subnet on
which to select an address. Two existing methods of determining the which to select an address. Two existing methods of determining the
subnet on which to select an address are: subnet on which to select an address are:
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there is a requirement to allocate addresses for devices connected to there is a requirement to allocate addresses for devices connected to
those networks. those networks.
Since there is no network connectivity between the DHCP server and the Since there is no network connectivity between the DHCP server and the
packet-handling plane, the control plane must allocate addresses using packet-handling plane, the control plane must allocate addresses using
the DHCP on behalf of the packet-handling plane. Because the control the DHCP on behalf of the packet-handling plane. Because the control
plane is requesting the addresses, the DHCP server would normally have plane is requesting the addresses, the DHCP server would normally have
the undesired result of allocating the address on the subnet on which the undesired result of allocating the address on the subnet on which
the control plane is connected. the control plane is connected.
If the option specified by this memo is included in the DHCPDISCOVER If the option specified by this memo is included in the
then the server should allocate addresses on the subnet specified by DHCPDISCOVER/DHCPREQUEST message then the server should allocate an
this option. The option would specify an address of one of the packet- 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. handling plane's subnets.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Subnet Selection Option 2. Subnet Selection Option
The subnet selection option is a DHCP option. The option contains a 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 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 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 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 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 zero). When this option is present, the DHCP server MUST use either
specified on which to allocate an address. 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: The format of the option is:
Code Len IP Address Code Len IP Address
+-----+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+
| TBD | 4 | A1 | A2 | A3 | A4 | | TBD | 4 | A1 | A2 | A3 | A4 |
+-----+-----+-----+-----+-----+-----+ +-----+-----+-----+-----+-----+-----+
In order to ensure backwards compatibility of clients that do support In order to ensure backwards compatibility of clients that do support
this option when communicating with DHCP servers that do not support this option when communicating with DHCP servers that do not support
this option, the DHCP client SHOULD check that an allocated address in this option, the DHCP client SHOULD check that an allocated address in
on the requested subnet. The client SHOULD NOT respond to an DHCPOFFER on the requested subnet or network segment. The client SHOULD NOT
of an address which is not on the requested subnet. 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 This option does not require any change to other operations or
features of the DHCP server other than to select the subnet on which features of the DHCP server other than to select the subnet on which
to allocate an address. For example, the handling of DHCPDISCOVER for to allocate an address. For example, the handling of DHCPDISCOVER for
an unknown subnet may continue to operate unchanged. an unknown subnet may continue to operate unchanged.
A server that supports this option MUST NOT offer an address that is When this option is present and the server supports this option, the
not on the requested subnet when this option is present. 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 Existing methods for determining where to send a reply to a DHCP
client are not changed when this option is present in a request. client are not changed when this option is present in a request.
3. Intellectual Property 3. Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to pertain intellectual property or other rights that might be claimed to pertain
to the implementation or use of the technology described in this to the implementation or use of the technology described in this
document or the extent to which any license under such rights might or document or the extent to which any license under such rights might or
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