Internet Engineering Task Force (IETF) M. Boucadair Request for Comments: 7291 France Telecom Category: Standards Track R. Penno ISSN: 2070-1721 D. Wing Cisco July 2014
DHCP Options for the Port Control Protocol (PCP)
This 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.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
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This document defines DHCPv4 [RFC2131] and DHCPv6 [RFC3315] options that can be used to configure hosts with PCP server [RFC6887] 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 [PCP-DEPLOYMENT] for a discussion on PCP deployment scenarios.
For guidelines on how a PCP client can use multiple IP addresses and multiple PCP servers, see [PCP-SERVER].
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].
o "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 [RFC6887].
o "PCP client" denotes a PCP software instance responsible for issuing PCP requests to a PCP server. Refer to [RFC6887].
The fields of the option shown in Figure 1 are as follows:
o Option-code: OPTION_V6_PCP_SERVER (86; see Section 9.1)
o Option-length: Length of the "PCP Server IPv6 Address(es)" field in octets. MUST be a multiple of 16.
o PCP Server IPv6 Addresses: Includes one or more IPv6 addresses [RFC4291] of the PCP server to be used by the PCP client. Note, IPv4-mapped IPv6 addresses (Section 126.96.36.199 of [RFC4291]) 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 [RFC3315].
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 [RFC6052]. Representing IPv4 addresses as IPv4-mapped IPv6 addresses follows the same logic as in Section 5 of [RFC6887].
The DHCPv6 client MUST silently discard multicast and host loopback addresses [RFC6890] conveyed in OPTION_V6_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:
1. the same PCP server: the DHCP server returns multiple addresses in the same instance of the DHCP PCP server option.
Boucadair, et al. Standards Track [Page 6]
RFC 7291 PCP DHCP Options July 2014
2. 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 [RFC6333]).
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 [DHC-CONFIG].
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 [PCP-SERVER].
The security considerations in [RFC2131] and [RFC3315] are to be considered. PCP-related security considerations are discussed in [RFC6887].
The PCP server option defined here is applicable when operating under the simple threat model (Section 18.1 of [RFC6887]). Operation under the advanced threat model (Section 18.2 of [RFC6887]) may or may not be appropriate; analysis of this question is out of the scope of this document.
Option Name Tag Data Length Meaning -------------------- --- ----------- -------------------------------- OPTION_V4_PCP_SERVER 158 Variable; Includes one or multiple lists the minimum of PCP server IP addresses; each length is list is treated as a separate 5. PCP server.