| IPv6 Operations (V6OPS) | J. Korhonen, Ed. |
| Internet-Draft | Renesas Mobile |
| Obsoletes: 3316 (if approved) | J. Arkko, Ed. |
| Intended status: Informational | Ericsson |
| Expires: March 18, 2014 | T. Savolainen |
| Nokia | |
| S.K. Krishnan | |
| Ericsson | |
| September 14, 2013 |
IPv6 for 3GPP Cellular Hosts
draft-ietf-v6ops-rfc3316bis-05.txt
As the deployment of third and fourth generation cellular networks progresses, a large number of cellular hosts are being connected to the Internet. Standardization organizations have made Internet Protocol version 6 (IPv6) mandatory in their specifications. However, the concept of IPv6 covers many aspects and numerous specifications. In addition, the characteristics of cellular links in terms of bandwidth, cost and delay put special requirements on how IPv6 is used. This document considers IPv6 for cellular hosts that attach to the General Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), or Evolved Packet System (EPS) networks (Hereafter collectively referred to as 3GPP networks). This document also lists out specific IPv6 functionalities that need to be implemented in addition what is already prescribed in the IPv6 Node Requirements document. It also discusses some issues related to the use of these components when operating in these networks. This document obsoletes RFC 3316.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 18, 2014.
Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
Technologies such as GPRS (General Packet Radio Service), UMTS (Universal Mobile Telecommunications System), Evolved Packet System (EPS), CDMA2000 (Code Division Multiple Access 2000) and eHRPD (Enhanced High Rate Packet Data) are making it possible for cellular hosts to have an always-on connection to the Internet. IPv6 [RFC2460] has become essential to such networks as the number of cellular hosts is increasing rapidly. Standardization organizations working with cellular technologies have recognized this and made IPv6 mandatory in their specifications.
Support for IPv6 and the introduction of UMTS started with 3GPP Release-99 networks and hosts. For the detailed description of IPv6 in 3GPP networks including the Evolved Packet System, see [RFC6459].
For the purpose of this document, a cellular interface is considered to be the interface to a cellular access network based on the following standards: 3GPP GPRS and UMTS Release-99, Release-4 to Release-11, and EPS Release-8 to Release-11 as well as future UMTS or EPS releases. A cellular host is considered to be a host with such a cellular interface.
This document complements the IPv6 node requirements [RFC6434] in places where clarifications are needed with discussion on the use of these selected IPv6 specifications when operating over a cellular interface. Such a specification is necessary in order to enable the optimal use of IPv6 in a cellular network environment. The description is made from a cellular host point of view. Complementary access technologies may be supported by the cellular host, but those are not discussed in detail. Important considerations are given in order to eliminate unnecessary user confusion over configuration options, ensure interoperability and to provide an easy reference for those who are implementing IPv6 in a cellular host. It is necessary to ensure that cellular hosts are good citizens of the Internet.
This document is informational in its nature, and it is not intended to replace, update, or contradict any IPv6 standards documents or the IPv6 node requirements [RFC6434].
This document is primarily targeted to the implementers of cellular hosts that will be used with the cellular networks listed in the scope. The document provides guidance on which IPv6 related specifications are to be implemented in such cellular hosts. Parts of this document may also apply to other cellular link types, but this document does not provide any detailed analysis on other link types. This document should not be used as a definitive list of IPv6 functionalies for cellular links other than those listed above. Future changes in 3GPP networks that impact host implementations may result in updates to this document.
There are different ways to implement cellular hosts:
If a cellular host has additional IP capable interfaces, (such as Ethernet, WLAN, Bluetooth, etc.) then there may be additional requirements for the device, beyond what is discussed in this document. Additionally, this document does not make any recommendations on the functionality required on laptop computers having a cellular interface such as an embedded modem or a USB modem stick, other than recommending link specific behavior on the cellular link.
This document discusses IPv6 functionality as of the time when this document has been written. Ongoing work on IPv6 may affect what is required of future hosts.
Transition mechanisms used by cellular hosts are not in the scope of this document and are left for further study. The primary transition mechanism supported by the 3GPP is dual-stack [RFC4213]. Dual-stack capable bearer support has been added to GPRS starting from the 3GPP Release-9 and to EPS starting from the Release-8 [RFC6459], whereas the earlier 3GPP releases required multiple single IP version bearers to support dual-stack.
This document lists IPv6 features for cellular hosts that are split into three groups.
For most parts refer to the IPv6 Node Requirements document [RFC6434].
The Internet Protocol Version 6 (IPv6) is specified in [RFC2460]. This specification is a mandatory part of IPv6. A cellular host must conform to the generic IPv6 Host Requirements [RFC6434], unless specifically pointed out otherwise in this document.
A cellular host must support Neighbor Solicitation and Neighbor Advertisement messages [RFC4861]. Some further notes on how these are applied in the particular type of an interface can be useful, however:
In 3GPP networks, some Neighbor Discovery messages can be unnecessary in certain cases. GPRS, UMTS and EPS links resemble a point-to-point link; hence, the cellular host's only neighbor on the cellular link is the default router that is already known through Router Discovery. The cellular host always solicits for routers when the cellular interface is brought up (as described in [RFC4861], Section 6.3.7).
There are no link layer addresses on the 3GPP cellular link technology. Therefore, address resolution and next-hop determination are not needed. If the cellular host still attempts to do the address resolution e.g., for the default router, it must be understood that the GGSN/PGW may not even answer the address resolution Neighbor Solicitations. And even if it does, the Neighbor Advertisement is unlikely to contain the Target link-layer address option as there are no link-layer addresses on the 3GPP cellular link technology.
The cellular host must support Neighbor Unreachability Detection (NUD) as specified in [RFC4861]. Note that the link-layer address considerations above also apply to the NUD. The NUD triggered Neighbor Advertisement is also unlikely to contain the Target link-layer address option as there are no link-layer addresses. The cellular host should also be prepared for a router (i.e., GGSN/PGW) initiated NUD. However, it is unlikely a router to host NUD should ever take place on a GPRS, UMTS and EPS links. See Appendix A for more discussion on the router to host NUD.
In 3GPP networks, it is desirable to reduce any additional periodic signaling. Therefore, the cellular host should include a mechanism in upper layer protocols to provide reachability confirmations when two-way IP layer reachability can be confirmed (see [RFC4861], Section 7.3.1). These confirmations would allow the suppression of NUD-related messages in most cases.
Host TCP implementation should provide reachability confirmation in the manner explained in [RFC4861], Section 7.3.1.
The widespread use of UDP in 3GPP networks poses a problem for providing reachability confirmation. As UDP itself is unable to provide such confirmation, applications running on top of UDP should provide the confirmation where possible. In particular, when UDP is used for transporting DNS, the DNS response should be used as a basis for reachability confirmation. Similarly, when UDP is used to transport RTP [RFC3550], the RTCP protocol [RFC3550] feedback should be used as a basis for the reachability confirmation. If an RTCP packet is received with a reception report block indicating some packets have gone through, then packets are reaching the peer. If they have reached the peer, they have also reached the neighbor.
When UDP is used for transporting SIP [RFC3261], responses to SIP requests should be used as the confirmation that packets sent to the peer are reaching it. When the cellular host is acting as the server side SIP node, no such confirmation is generally available. However, a host may interpret the receipt of a SIP ACK request as confirmation that the previously sent response to a SIP INVITE request has reached the peer.
IPv6 Stateless Address Autoconfiguration is defined in [RFC4862]. This specification is a mandatory part of IPv6 and also the only mandatory method to configure an IPv6 address in a 3GPP cellular host.
A cellular host in a 3GPP network must process a Router Advertisement as stated in [RFC4862]. The Router Advertisement contains a maximum of one prefix information option with lifetimes set to infinite (both valid and preferred lifetimes). The advertised prefix cannot ever be used for on-link determination (see [RFC6459], Section 5.2) and the lifetime of the advertised prefix is tied to the PDP Context/PDN Connection lifetime. Keeping the forward compatibility in mind there is no reason for the 3GPP cellular host to have 3GPP specific handling of the prefix information option(s) although 3GPP specifications state that the Router Advertisement may contain a maximum of one prefix information option and the lifetimes are set to infinite.
Hosts in 3GPP networks can set DupAddrDetectTransmits equal to zero, as each assigned prefix is unique within its scope when advertised using the 3GPP IPv6 Stateless Address Autoconfiguration. In addition, the default router (GGSN/PGW) will not configure any addresses on its interfaces based on prefixes advertised to IPv6 cellular hosts on those interfaces. Thus, the host is not required to perform Duplicate Address Detection on the cellular interface.
Furthermore, the GGSN/PGW will provide the cellular host with an interface identifier that must be used for link-local address configuration. The link-local address configured from this interface identifier is guaranteed not to collide with the link-local address that the GGSN/PGW uses. Thus, the cellular host is not required to perform Duplicate Address Detection for the link-local address on the cellular interface.
See Appendix A for more details on 3GPP IPv6 Stateless Address Autoconfiguration.
A cellular host in a 3GPP network that supports PPP [RFC1661] on the interface between the MT and the TE, must support the IPv6CP [RFC5072] interface identifier option. This option is needed to be able to connect other devices to the Internet using a PPP link between the cellular device (MT, e.g., a USB dongle) and other devices (TE, e.g., a laptop). The MT performs the PDP Context activation based on a request from the TE. This results in an interface identifier being suggested by the MT to the TE, using the IPv6CP option. To avoid any duplication in link-local addresses between the TE and the GGSN/PGW, the MT must always reject other suggested interface identifiers by the TE. This results in the TE always using the interface identifier suggested by the GGSN/PGW for its link-local address.
The rejection of interface identifiers suggested by the TE is only done for creation of link-local addresses, according to 3GPP specifications. The use of privacy addresses [RFC4941] or similar technologies for unique local IPv6 unicast addresses (ULA) [RFC4193] and global addresses is not affected by the above procedure.
Within 3GPP networks, hosts connect to their default routers (GGSN/PGW) via point-to-point links. Moreover, there are exactly two IP devices connected to the point-to-point link, and no attempt is made (at the link-layer) to suppress the forwarding of multicast traffic. Consequently, sending MLD reports for link-local addresses in a 3GPP environment is not necessary, although sending those cause no harm or interoperability issues. Refer Section 5.10 of [RFC6434] for MLD usage for multicast group knowledge that is not link-local.
Privacy Extensions for Stateless Address Autoconfiguration [RFC4941] or other similar technologies may be supported by a cellular host. Privacy in general, is important for the Internet. In 3GPP networks the lifetime of an address assignment depends on many factors such as radio coverage, device status and user preferences. As a result also the prefix the cellular host uses is a subject to frequent changes.
Refer to Section 7 for a discussion of the benefits of privacy extensions in a 3GPP network.
As of 3GPP Release-11 The Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315] is neither required nor supported for address autoconfiguration. The IPv6 stateless autoconfiguration still remains the only mandatory address configuration method. However, DHCPv6 may be useful for other configuration needs on a cellular host. e.g. Stateless DHCPv6 [RFC3736] may be used to configure DNS and SIP server addresses, and DHCPv6 prefix delegation [RFC3633] may be used to delegate a prefix to the cellular host for use on its downstream non-cellular links.
Starting from Release-10 DHCPv6 Prefix Delegation was added as an optional feature to the 3GPP system architecture [RFC3633]. The prefix delegation model defined for Release-10 requires that the /64 IPv6 prefix assigned to the cellular host on the 3GPP link must aggregate with the shorter delegated IPv6 prefix. The cellular host should implement the Prefix Exclude Option for DHCPv6 Prefix Delegation [RFC6603] (see [RFC6459], Section 5.3 for further discussion).
The cellular host should implement the Default Router Preferences and More-Specific Routes extension to Router Advertisement messages [RFC4191]. These options may be useful for cellular hosts that also have additional interfaces on which IPv6 is used.
The DNS server configuration is learned from the 3GPP link layer signaling. However, the cellular host should also implement the IPv6 Router Advertisement Options for DNS Configuration [RFC6106]. DHCPv6 is still optional for cellular hosts, and learning the DNS server addresses from the link layer signaling can be cumbersome when the MT and the TE are separated using other techniques than PPP interface.
The cellular host should also honor the MTU option in the Router Advertisement (see [RFC4861], Section 4.6.4). 3GPP system architecture uses extensive tunneling in its packet core network below the 3GPP link and this may lead to packet fragmentation issues. Therefore, the GGSN/PGW may propose a MTU to the cellular host that takes the additional tunneling overhead into account.
IPsec [RFC4301] is a fundamental but not mandatory part of IPv6. Refer to the IPv6 Node Requirements Section 11 of [RFC6434] for the security requirements that also apply to cellular hosts.
The support for the Routing Header Type 0 (RH0) has been deprecated [RFC5095]. Therefore, the cellular host should as a default setting follow the RH0 processing described in Section 3 of [RFC5095].
IPv6 packet fragmentation has known security concerns. The cellular host must follow the handling of overlapping fragments as described in [RFC5722] and the cellular host must not fragment any neighbor discovery messages as described in [RFC6980].
For the purposes of this document, IP mobility is not relevant. The movement of cellular hosts within 3GPP networks is handled by link layer mechanisms in majority of cases. 3GPP Release-8 introduced the dual-stack Mobile IPv6 (DSMIPv6) for a client based mobility [RFC5555]. Client based IP mobility is optional in 3GPP architecture.
This document has no IANA actions.
The authors would like to thank the original authors for their grounding work on this documents: Gerben Kuijpers, John Loughney, Hesham Soliman and Juha Wiljakka.
The original [RFC3316] document was based on the results of a team that included Peter Hedman and Pertti Suomela in addition to the authors. Peter and Pertti have contributed both text and their IPv6 experience to this document.
The authors would like to thank Jim Bound, Brian Carpenter, Steve Deering, Bob Hinden, Keith Moore, Thomas Narten, Erik Nordmark, Michael Thomas, Margaret Wasserman and others at the IPv6 WG mailing list for their comments and input.
We would also like to thank David DeCamp, Karim El Malki, Markus Isomaki, Petter Johnsen, Janne Rinne, Jonne Soininen, Vlad Stirbu and Shabnam Sultana for their comments and input in preparation of this document.
For the revised version of the [RFC3316] the authors would like thank Dave Thaler, Ales Vizdal, Gang Chen, Ray Hunter, Charlie Kaufman, Owen DeLong and Alexey Melnikov for their comments, reviews and inputs.
This document does not specify any new protocols or functionalities, and as such, it does not introduce any new security vulnerabilities. However, specific profiles of IPv6 functionality are proposed for different situations, and vulnerabilities may open or close depending on which functionality is included and what is not. There are also aspects of the cellular environment that make certain types of vulnerabilities more severe. The following issues are discussed:
The appendix aims to very briefly describe the 3GPP IPv6 addressing model for 2G (GPRS), 3G (UMTS) and 4G (EPS) cellular networks from Release-99 onwards. More information for 2G and 3G can be found from 3GPP Technical Specifications [TS.23060] and [TS.29061]. The equivalent documentation for 4G can be found from 3GPP Technical Specifications [TS.23401], [TS.23402] and [TS.29061].
There are two possibilities to allocate the address for an IPv6 node: stateless and stateful autoconfiguration. The stateful address allocation mechanism needs a DHCP server to allocate the address for the IPv6 node. On the other hand, the stateless autoconfiguration procedure does not need any external entity involved in the address autoconfiguration (apart from the GGSN/PGW). At the time of writing this document, the IPv6 stateless address autoconfiguration mechanism is still the only mandatory and supported address configuration method for the cellular 3GPP link.
In order to support the standard IPv6 stateless address autoconfiguration mechanism as recommended by the IETF, the GGSN/PGW shall assign a single /64 IPv6 prefix that is unique within its scope to each primary PDP Context or PDN Connection that uses IPv6 stateless address autoconfiguration. This avoids the necessity to perform Duplicate Address Detection (DAD) at the network level for any address built by the mobile host. The GGSN/PGW always provides an interface identifier to the mobile host. The Mobile host uses the interface identifier provided by the GGSN/PGW to generate its link-local address. The GGSN/PGW provides the cellular host with the interface identifier, usually in a random manner. It must ensure the uniqueness of such identifier on the link (i.e., no collisions between its own link-local address and the cellular host's).
In addition, the GGSN/PGW will not use any of the prefixes assigned to cellular hosts to generate any of its own addresses. This use of the interface identifier, combined with the fact that each PDP Context or PDN Connection is allocated a unique prefix, will eliminate the need for DAD messages over the air interface, and consequently reduces inefficient use of radio resources. Furthermore, the allocation of a prefix to each PDP Context or PDN Connection will allow hosts to implement the Privacy Extensions in [RFC4941] without the need for further DAD messages.
In practice, the GGSN/PGW only needs to route all traffic destined to the cellular host that falls under the prefix assigned to it. This implies the GGSN/PGW may implement a minimal neighbor discovery protocol subset; since, due the point-to-point link model and the absence of link-layer addressing the address resolution can be entirely statically configured per PDP Context or PDN Connection, and there is no need to defend any other address than the link-local address for very unlikely duplicates. This has also an additional effect on a router to host NUD. There is really no need for it, since from the GGSN/PGW point of view it does not need to care for a single address, just routes the whole prefix to the cellular host. However, the cellular host must be prepared for the unlikely event of receiving a NUD against its link-local address. It should be noted that the 3GPP specifications at the time of writing this document are silent what should happen if the router to host NUD fails.
See Sections 5 of [RFC6459] for further discussion on 3GPP address allocation and link model.