| Network Working Group | M. Boucadair |
| Internet-Draft | C. Jacquenet |
| Intended status: Standards Track | France Telecom |
| Expires: January 4, 2016 | T. Reddy |
| Cisco | |
| July 3, 2015 |
DHCP Options for Network-Assisted Multipath TCP (MPTCP)
draft-boucadair-mptcp-dhc-01
One of the promising deployment scenarios for Multipath TCP (MPTCP) is to enable a Customer Premises Equipment (CPE) that is connected to multiple networks (e.g., DSL, LTE, WLAN) to optimize the usage of its network attachments. Because of the lack of MPTCP support at the server side, some service providers now consider a “network-assisted mode” that relies upon the activation of a dedicated function called: MPTCP Concentrator. This document focuses on the explicit deployment scheme where the identity of the MPTCP Concentrator(s) is explicitly configured on connected hosts.
This document specifies DHCP (IPv4 and IPv6) options to configure hosts with Multipath TCP (MPTCP) parameters.
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].
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One of the promising deployment scenarios for Multipath TCP (MPTCP, [RFC6824]) is to enable a Customer Premises Equipment (CPE) that is connected to multiple networks (e.g., DSL, LTE, WLAN) to optimize the usage of such resources, see for example [I-D.deng-mptcp-proxy] or [RFC4908]. This deployment scenario relies on MPTCP Proxy on both the CPE and the network sides (Figure 1). The latter plays the role of traffic concentrator. A concentrator terminates the MPTCP sessions, from a CPE, before redirecting traffic into a legacy TCP session.
IP Network #1
+------------+ _--------_ +------------+
| | (e.g., LTE ) | |
| CPE +======================+ |
| (MPTCP | (_ _) |Concentrator|
| Proxy) | (_______) | (MPTCP |
| | | Proxy) |------> Internet
| | | |
| | IP Network #2 | |
| | _--------_ | |
| | ( e.g., DSL ) | |
| +======================+ |
| | (_ _) | |
+-----+------+ (_______) +------------+
|
----CPE network----
|
end-nodes
Figure 1: “Network-Assisted” MPTCP Design
Both implicit and explicit modes are considered to steer traffic towards an MPTCP Concentrator. This document focuses on the explicit mode that consists in configuring explicitly the reachability information of the MPTCP concentrator on a host.
This document defines DHCPv4 [RFC2131] and DHCPv6 [RFC3315] options that can be used to configure hosts with MPTCP Concentrator IP addresses.
This specification assumes an MPTCP Concentrator is reachable through one or multiple IP addresses. As such, a list of IP addresses can be returned in the DHCP MPTCP option. Also, it assumes the various network attachments provided to an MPTCP-enabled CPE are managed by the same administrative entity.
This document makes use of the following terms:
The DHCPv6 MPTCP option can be used to configure a list of IPv6 addresses of an MPTCP Concentrator.
The format of this option is shown in Figure 2.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | OPTION_V6_MPTCP | Option-length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | ipv6-address | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | ipv6-address | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: DHCPv6 MPTCP option
To discover one or more MPTCP Concentrators, the DHCPv6 client requests MPTCP Concentrator IP addresses by including OPTION_V6_MPTCP 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_MPTCP; each instance is to be treated separately as it corresponds to a given MPTCP Concentrator: there are as many concentrators as instances of the OPTION_V6_MPTCP option.
If an IPv4-mapped IPv6 address is received in OPTION_V6_MPTCP, it indicates that the MPTCP Concentrator has the corresponding IPv4 address.
The DHCPv6 client MUST silently discard multicast and host loopback addresses [RFC6890] conveyed in OPTION_V6_MPTCP.
The DHCPv4 MPTCP option can be used to configure a list of IPv4 addresses of an MPTCP Concentrator. The format of this option is illustrated in Figure 3.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | List-Length | List of | +-+-+-+-+-+-+-+-+ MPTCP | / Concentrator IPv4 Addresses / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- | List-Length | List of | | +-+-+-+-+-+-+-+-+ MPTCP | | / Concentrator IPv4 Addresses / | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | . ... . optional +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | List-Length | List of | | +-+-+-+-+-+-+-+-+ MPTCP | | / Concentrator IPv4 Addresses / | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
Figure 3: DHCPv4 MPTCP option
0 8 16 24 32 40 48
+-----+-----+-----+-----+-----+-----+--
| a1 | a2 | a3 | a4 | a1 | a2 | ...
+-----+-----+-----+-----+-----+-----+--
IPv4 Address 1 IPv4 Address 2 ...
The description of the fields is as follows:
This format assumes that an IPv4 address is encoded as a1.a2.a3.a4.
Figure 4: Format of the List of MPTCP Concentrator IPv4 Addresses
[RFC3396] MUST be used if OPTION_V4_MPTCP exceeds the maximum DHCPv4 option size of 255 octets.
To discover one or more MPTCP Concentrators, the DHCPv4 client requests MPTCP Concentrator’s IP addresses by including OPTION_V4_MPTCP in a Parameter Request List Option [RFC2132].
The DHCPv4 client MUST be prepared to receive multiple lists of MPTCP Concentrator IPv4 addresses in the same OPTION_V4_MPTCP; each list is to be treated as a separate MPTCP Concentrator instance.
The DHCPv4 client MUST silently discard multicast and host loopback addresses [RFC6890] conveyed in OPTION_V4_MPTCP.
DHCP servers that support the DHCP MPTCP Concentrator option can be configured with a list of IP addresses of the MPTCP Concentrator(s). If multiple IP addresses are configured, the DHCP server MUST be explicitly configured whether all or some of these addresses refer to:
Precisely how DHCP servers are configured to separate lists of IP addresses according to which MPTCP Concentrator they refer to is out of scope for this document. However, DHCP servers MUST NOT combine the IP addresses of multiple MPTCP Concentrators and return them to the DHCP client as if they were belonging to a single MPTCP Concentrator, and DHCP servers MUST NOT separate the addresses of a single MPTCP Concentrator and return them as if they were belonging to distinct MPTCP Concentrators. For example, if an administrator configures the DHCP server by providing a Fully Qualified Domain Name (FQDN) for a MPTCP Concentrator, 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 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.
Since this option requires support for IPv4-mapped IPv6 addresses, a DHCPv6 server implementation will not be complete if it does not query A records and represent any that are returned as IPv4-mapped IPv6 addresses in DHCPv6 responses. 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 [I-D.ietf-dhc-topo-conf].
The security considerations in [RFC2131] and [RFC3315] are to be considered. MPTCP-related security considerations are discussed in [RFC6824].
IANA is requested to assign the following new DHCPv6 Option Code in the registry maintained in http://www.iana.org/assignments/dhcpv6-parameters:
| Option Name | Value |
|---|---|
| OPTION_V6_MPTCP | TBA |
IANA is requested to assign the following new DHCPv4 Option Code in the registry maintained in http://www.iana.org/assignments/bootp-dhcp-parameters/:
| Option Name | Value | Data length | Meaning |
|---|---|---|---|
| OPTION_V4_MPTCP | TBA | Variable; the minimum length is 5. | Includes one or multiple lists of MPTCP Concentrator IP addresses; each list is treated as a separate MPTCP Concentrator. |
TBC.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, 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. |
| [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. |
| [RFC3396] | Lemon, T. and S. Cheshire, "Encoding Long Options in the Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396, November 2002. |
| [RFC4291] | Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. |
| [RFC6824] | Ford, A., Raiciu, C., Handley, M. and O. Bonaventure, "TCP Extensions for Multipath Operation with Multiple Addresses", RFC 6824, January 2013. |
| [RFC6890] | Cotton, M., Vegoda, L., Bonica, R. and B. Haberman, "Special-Purpose IP Address Registries", BCP 153, RFC 6890, April 2013. |
| [I-D.deng-mptcp-proxy] | Lingli, D., Liu, D., Sun, T., Boucadair, M. and G. Cauchie, "Use-cases and Requirements for MPTCP Proxy in ISP Networks", Internet-Draft draft-deng-mptcp-proxy-01, October 2014. |
| [I-D.ietf-dhc-topo-conf] | Lemon, T. and T. Mrugalski, "Customizing DHCP Configuration on the Basis of Network Topology", Internet-Draft draft-ietf-dhc-topo-conf-04, January 2015. |
| [RFC0793] | Postel, J., "Transmission Control Protocol", STD 7, RFC 793, September 1981. |
| [RFC4908] | Nagami, K., Uda, S., Ogashiwa, N., Esaki, H., Wakikawa, R. and H. Ohnishi, "Multi-homing for small scale fixed network Using Mobile IP and NEMO", RFC 4908, June 2007. |
| [RFC6333] | Durand, A., Droms, R., Woodyatt, J. and Y. Lee, "Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion", RFC 6333, August 2011. |