DHCP Options for the Port Control
Protocol (PCP)France TelecomRennes35000Francemohamed.boucadair@orange.comCiscoUSArepenno@cisco.comCisco Systems, Inc.170 West Tasman DriveSan JoseCalifornia95134USAdwing@cisco.comPCP Working GroupPCP Server discoveryPort MappingShared AddressThis document specifies DHCP (IPv4 and IPv6) options to configure
hosts with Port Control Protocol (PCP) server IP addresses. The use of
DHCPv4 or DHCPv6 depends on the PCP deployment scenarios.
The set of deployment scenarios to which DHCPv4 or DHCPv6
can be applied is outside the scope of this document.
This document defines DHCPv4 and
DHCPv6 options that can be used to
configure hosts with PCP server IP
addresses.This specification assumes a PCP server is reachable with one or
multiple IP addresses. As such, a list of IP addresses can be returned
in the DHCP PCP server option.This specification allows returning one or multiple lists of PCP
server IP addresses. This is used as a hint to guide the PCP client when
determining whether to send PCP requests to one or multiple PCP servers.
Concretely, the PCP client needs an indication to decide whether entries
need to be instantiated in all PCP servers (e.g., multi-homing, multiple
PCP-controlled devices providing distinct services, etc.) or use one
IP address from the list (e.g., redundancy group scenario, proxy-based
model, etc.). Refer to for a discussion on
PCP deployment scenarios.For guidelines on how a PCP client can use multiple IP addresses and
multiple PCP servers, see .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.This document makes use of the following terms:"PCP server" denotes a functional element that receives and
processes PCP requests from a PCP client. A PCP server can be
co-located with or be separated from the function (e.g., NAT,
Firewall) it controls. Refer to ."PCP client" denotes a PCP software instance responsible for
issuing PCP requests to a PCP server. Refer to ."DHCP" refers to both DHCPv4 and
DHCPv6 ."DHCP client" denotes a node that initiates requests to obtain
configuration parameters from one or more DHCP servers."DHCP server" refers to a node that responds to requests from DHCP
clients.The DHCPv6 PCP server option can be used to configure a list of
IPv6 addresses of a PCP server.The format of this option is shown in .The fields of the option shown in are as follows:Option-code: OPTION_V6_PCP_SERVER (86; see )Option-length: Length of the "PCP Server IPv6 Address(es)" field
in octets. MUST be a multiple of 16.PCP Server IPv6 Addresses: Includes one or more IPv6 addresses
of the PCP server to be used by the
PCP client. Note, IPv4-mapped IPv6 addresses (Section 2.5.5.2 of
) are allowed to be included in this
option.To return more than one PCP server to the
DHCPv6 client (as opposed to more than one address for a single PCP
server), the DHCPv6 server returns multiple instances of
OPTION_V6_PCP_SERVER.To discover one or more PCP servers, the DHCPv6 client requests PCP
server IP addresses by including OPTION_V6_PCP_SERVER in an Option
Request Option (ORO), as described in Section 22.7 of .The DHCPv6 client MUST be prepared to receive multiple instances of
OPTION_V6_PCP_SERVER; each instance is to be treated as a separate PCP
server.If an IPv4-mapped IPv6 address is received in OPTION_V6_PCP_SERVER,
it indicates that the PCP server has the corresponding IPv4
address.Note: When presented with the IPv4-mapped prefix, current
versions of Windows and Mac OS generate IPv4 packets but will not
send IPv6 packets . Representing
IPv4 addresses as IPv4-mapped IPv6 addresses follows the same
logic as in Section 5 of .The DHCPv6 client MUST silently discard multicast and host loopback
addresses conveyed in
OPTION_V6_PCP_SERVER.The DHCPv4 PCP server option can be used to configure a list of
IPv4 addresses of a PCP server. The format of this option is
illustrated in .The descriptions of the fields are as follows:Code: OPTION_V4_PCP_SERVER (158; see );Length: Length of all included data in octets. The minimum
length is 5.List-Length: Length of the "List of PCP Server IPv4 Addresses"
field in octets. MUST be a multiple of 4.List of PCP Server IPv4 Addresses: Contains one or more IPv4
addresses of the PCP server to be used by the PCP client. The
format of this field is shown in .OPTION_V4_PCP_SERVER can include multiple lists of PCP server
IPv4 addresses; each list is treated as a separate PCP server.
When several lists of PCP server IPv4 addresses are to be
included, the "List-Length" and "List of PCP Server IPv4
Addresses" fields are
repeated.OPTION_V4_PCP_SERVER is a
concatenation-requiring option. As such, the mechanism specified in
MUST be used if OPTION_V4_PCP_SERVER
exceeds the maximum DHCPv4 option size of 255 octets.To discover one or more PCP servers, the DHCPv4 client requests PCP
server IP addresses by including OPTION_V4_PCP_SERVER in a Parameter
Request List option .The DHCPv4 client MUST be prepared to receive multiple lists of PCP
server IPv4 addresses in the same DHCPv4 PCP server option; each list
is to be treated as a separate PCP server.The DHCPv4 client MUST silently discard multicast and host loopback
addresses conveyed in
OPTION_V4_PCP_SERVER.DHCP servers supporting the DHCP PCP server option can be configured
with a list of IP addresses of the PCP server(s). If multiple IP
addresses are configured, the DHCP server MUST be explicitly configured
whether all or some of these addresses refer to:the same PCP server: the DHCP server returns multiple addresses
in the same instance of the DHCP PCP server option.distinct PCP servers: the DHCP server returns multiple lists of
PCP server IP addresses to the requesting DHCP client (encoded as
multiple OPTION_V6_PCP_SERVERs or in the same OPTION_V4_PCP_SERVER);
each list is referring to a distinct PCP server. For example,
multiple PCP servers may be configured to a PCP client in some
deployment contexts such as multi-homing. It is out of the scope of this
document to enumerate all deployment scenarios that require multiple
PCP servers to be returned.Precisely how DHCP servers are configured to separate lists of IP
addresses according to which PCP server they address is out of the scope of
this document. However, DHCP servers MUST NOT combine the IP addresses
of multiple PCP servers and return them to the DHCP client as if they
belong to a single PCP server, and DHCP servers MUST NOT separate the
addresses of a single PCP server and return them as if they belong to
distinct PCP servers. For example, if an administrator configures the
DHCP server by providing a Fully Qualified Domain Name (FQDN) for a PCP
server, even if that FQDN resolves to multiple addresses, the DHCP
server MUST deliver them within a single server address block.DHCPv6 servers that implement this option and that can populate the
option by resolving FQDNs will need a mechanism for indicating whether
to query for A records or only AAAA records. When a query returns A
records, the IP addresses in those records are returned in the DHCPv6
response as IPv4-mapped IPv6 addresses. Discussion: The motivation for this design is to accommodate
deployment cases where an IPv4 connectivity service is provided
while only DHCPv6 is in use (e.g., an IPv4-only PCP server in a
Dual-Stack Lite (DS-Lite) context ).Since this option requires support for IPv4-mapped IPv6 addresses, a
DHCPv6 server implementation will not be complete if it does not query
for A records and represent any that are returned as IPv4-mapped IPv6
addresses in DHCPv6 responses. This behavior is neither required nor
suggested for DHCPv6 options in general: it is specific to
OPTION_V6_PCP_SERVER. The mechanism whereby DHCPv6 implementations
provide this functionality is beyond the scope of this document.For guidelines on providing context-specific configuration
information (e.g., returning a regional-based configuration) and
information on how a DHCP server might be configured with FQDNs that get
resolved on demand, see .A dual-stack host might receive a PCP server option via both DHCPv4 and
DHCPv6. For guidance on how a DHCP client can handle PCP server IP lists
for the same network but obtained via different mechanisms, see .A host may have multiple network interfaces (e.g., 3G, IEEE 802.11,
etc.), each configured differently. Each PCP server learned MUST be
associated with the interface via which it was learned.Refer to and
Section 8.4 of for more discussion on
multi-interface considerations.The security considerations in and
are to be considered. PCP-related
security considerations are discussed in .
The PCP server option defined here is applicable when operating
under the simple threat model (Section 18.1 of ). Operation
under the advanced threat model (Section 18.2 of ) may
or may not be appropriate; analysis of this question is out of the
scope of this document.
IANA has assigned the following new DHCPv6 Option Code in
the registry maintained in
<http://www.iana.org/assignments/dhcpv6-parameters>:Option NameValueOPTION_V6_PCP_SERVER86IANA has assigned the following new DHCPv4 Option Code in
the registry maintained in
<http://www.iana.org/assignments/bootp-dhcp-parameters>:Option NameTagData LengthMeaningOPTION_V4_PCP_SERVER158Variable; the minimum length is 5.Includes one or multiple lists of PCP server IP addresses; each
list is treated as a separate PCP server.Many thanks to C. Jacquenet, R. Maglione, D. Thaler, T. Mrugalski, T. Reddy, S. Cheshire, M. Wasserman, C. Holmberg, A. Farrel, S. Farrel,
B. Haberman, and P. Resnick for their review and comments.Special thanks to T. Lemon and B. Volz for their reviews and their
efforts to enhance this specification.Customizing DHCP Configuration on the Basis of Network TopologyPCP Server SelectionPort Control Protocol (PCP) Deployment Models