Multiple Interfaces and Provisioning Domains Problem Statement
The information below is for an old version of the document that is already published as an RFC.
This is an older version of an Internet-Draft that was ultimately published as RFC 6418.
|Authors||Pierrick Seite , Marc Blanchet|
|Last updated||2015-10-14 (Latest revision 2011-05-09)|
|RFC stream||Internet Engineering Task Force (IETF)|
|Additional resources||Mailing list discussion|
|Stream||WG state||WG Document|
|IESG||IESG state||RFC 6418 (Informational)|
|Responsible AD||Jari Arkko|
|IESG note||The document shepherd is Hui Deng (firstname.lastname@example.org).|
|Send notices to||(None)|
Network Working Group M. Blanchet Internet-Draft Viagenie Intended status: Informational P. Seite Expires: November 10, 2011 France Telecom - Orange May 9, 2011 Multiple Interfaces and Provisioning Domains Problem Statement draft-ietf-mif-problem-statement-15.txt Abstract This document describes issues encountered by a node attached to multiple provisioning domains. This node receives configuration information from each of its provisioning domains where some configuration objects are global to the node, others are local to the interface. Issues such as selecting the wrong interface to send trafic happen when conflicting node-scoped configuration objects are received and inappropriately used. Moreover, other issues are the result of simulatenous attachment to multiple networks, such as domain selection or addressing and naming space overlaps, regardless of the provisioning mechanism. While multiple provisioning domains are typically seen on nodes with multiple interfaces, this document also discusses single interface nodes situation. Status of this Memo 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 November 10, 2011. Copyright Notice Copyright (c) 2011 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 Blanchet & Seite Expires November 10, 2011 [Page 1] Internet-Draft Multiple Interfaces Problem Statement May 2011 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Scope and Existing Work . . . . . . . . . . . . . . . . . . . 4 3.1. Below IP Interaction . . . . . . . . . . . . . . . . . . . 4 3.2. MIF node Characterization . . . . . . . . . . . . . . . . 4 3.3. Hosts Requirements . . . . . . . . . . . . . . . . . . . . 5 3.4. Mobility and other IP protocols . . . . . . . . . . . . . 6 3.5. Address Selection . . . . . . . . . . . . . . . . . . . . 6 3.6. Finding and Sharing IP Addresses with Peers . . . . . . . 6 3.7. Provisioning domain selection . . . . . . . . . . . . . . 7 3.8. Session management . . . . . . . . . . . . . . . . . . . . 7 3.9. Socket API . . . . . . . . . . . . . . . . . . . . . . . . 8 4. MIF Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 9 4.1. DNS resolution issues . . . . . . . . . . . . . . . . . . 9 4.2. Node Routing . . . . . . . . . . . . . . . . . . . . . . . 11 4.3. Policies conflict . . . . . . . . . . . . . . . . . . . . 12 4.4. Session management . . . . . . . . . . . . . . . . . . . . 12 4.5. Single Interface on Multiple Provisioning Domains . . . . 13 5. Underlying problems and causes . . . . . . . . . . . . . . . . 13 6. Security Considerations . . . . . . . . . . . . . . . . . . . 15 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 8. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 10. Informative References . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 Blanchet & Seite Expires November 10, 2011 [Page 2] Internet-Draft Multiple Interfaces Problem Statement May 2011 1. Introduction A multihomed node may have multiple provisioning domains (via physical and/or virtual interfaces). For example, a node may be simultaneously connected to a wired Ethernet LAN, a 802.11 LAN, a 3G cell network, one or multiple VPN connections or one or multiple tunnels(automatic or manual). Current laptops and smartphones typically have multiple access network interfaces and, thus, are often connected to different provisioning domains. A multihomed node receives configuration information from each of its attached networks, through various mechanisms such as DHCPv4 [RFC2131], DHCPv6 [RFC3315], PPP [RFC1661] and IPv6 Router Advertisements [RFC4861]. Some received configuration objects are specific to an interface such as the IP address and the link prefix. Others are typically considered by implementations as being global to the node, such as the routing information (e.g. default gateway), DNS servers IP addresses, and address selection policies, herein named "node-scoped". When the received node-scoped configuration objects have different values from each provisioning domains, such as different DNS servers IP addresses, different default gateways or different address selection policies, the node has to decide which one to use or how it will merge them. Other issues are the result of simulatenous attachment to multiple networks, such as addressing and naming space overlaps, regardless of the provisioning mechanism. The following sections define the multiple interfaces (MIF) node, the scope of this work, describe related work, list issues and then summarize the underlying problems. A companion document [I-D.ietf-mif-current-practices] discusses some current practices of various implementations dealing with MIF. 2. Terminology Administrative domain A group of hosts, routers, and networks operated and managed by a single organization [RFC1136]. Provisioning domain Blanchet & Seite Expires November 10, 2011 [Page 3] Internet-Draft Multiple Interfaces Problem Statement May 2011 A set of consistent configuration information (e.g. Default router, Network prefixes, DNS,...) and the corresponding interface. One administrative domain may have multiple provisioning domains. Successful attachment to the provisioning domain implies that the terminal attaches to the corresponding interface with appropriate configuration information. Reference to IP version When a protocol keyword such as IP, PPP, DHCP is used in this document without any reference to a specific IP version, then it implies both IPv4 and IPv6. A specific IP version keyword such as DHCPv4 or DHCPv6 is meant to be specific to that IP version. 3. Scope and Existing Work This section describes existing related work and defines the scope of the problem. 3.1. Below IP Interaction Some types of interfaces have link layer characteristics which may be used in determining how multiple provisioning domain issues will be dealt with. For instance, link layers may have authentication and encryption characteristics which could be used as criteria for interface selection. However, network discovery and selection on lower layers as defined by [RFC5113] is out of scope of this document. Moreover, interoperability with lower layer mechanisms such as services defined in IEEE 802.21, which aims at facilitating handover between heterogeneous networks [MIH], is also out of scope. Some mechanisms (e.g., based on a virtual IP interface) allow sharing a single IP address over multiple interfaces to networks with disparate access technologies. From the IP stack view on the node, there is only a single interface and single IP address. Therefore, this situation is out of scope of this current problem statement. Furthermore, link aggregation done under IP where a single interface is shown to the IP stack is also out of scope. 3.2. MIF node Characterization A MIF node has the following characteristics: o A [RFC1122] IPv4 and/or [RFC4294] IPv6 compliant node Blanchet & Seite Expires November 10, 2011 [Page 4] Internet-Draft Multiple Interfaces Problem Statement May 2011 o A MIF node is configured with more than one IP addresses (excluding loopback and link-local) o A MIF node can attach to more than one provisioning domains, as presented to the IP stack. o The interfaces may be virtual or physical. o Configuration objects come from one or more administrative domains. o The IP addresses may be from the same or from different address families, such as IPv4 and IPv6. o Communications using these IP addresses may happen simultaneously and independently. o Some communications using these IP addresses are possible on all the provisioning domains, while some are only possible on a smaller set of the provisioning domains. o While the MIF node may forward packets between its interfaces, forwarding packets is not taken into account in this definition and is out of scope for this document. 3.3. Hosts Requirements The requirements for Internet Hosts [RFC1122] describe the multihomed node as if it has multiple IP addresses, which may be associated with one or more physical interfaces connected to the same or different networks. The requirements states that The node maintains a route cache table where each entry contains the local IP address, the destination IP address, Differentiated Services Code Point and Next-hop gateway IP address. The route cache entry would have data about the properties of the path, such as the average round-trip delay measured by a transport protocol. Nowadays, implementations are not caching these informations. [RFC1122] defines two host models: o The "Strong" host model defines a multihomed host as a set of logical hosts within the same physical host. In this model a packet must be sent on an interface that corresponds to the source address of that packet. o The "Weak" host model describes a host that has some embedded gateway functionality. In the weak host model, the host can send and receive packets on any interface. The multihomed node computes routes for outgoing datagrams differently depending on the model. Under the strong model, the route is computed based on the source IP address, the destination IP address and the Differentiated Services Code Point. Under the weak model, the source IP address is not used, but only the destination IP address and the Differentiated Services Code Point. Blanchet & Seite Expires November 10, 2011 [Page 5] Internet-Draft Multiple Interfaces Problem Statement May 2011 3.4. Mobility and other IP protocols The scope of this document is only about nodes implementing [RFC1122] for IPv4 and [RFC4294] for IPv6 without additional features or special-purpose support for transport layers, mobility, multi-homing, or identifier-locator split mechanisms. Dealing with multiple interfaces with such mechanisms is related but considered as a separate problem and is under active study elsewhere in the IETF [RFC4960], [RFC5206], [RFC5533], [RFC5648], [I-D.ietf-mptcp-architecture]. When an application is using one interface while another interface with better characteristics becomes available, the ongoing application session could be transferred to the newly enabled interface. However, in some cases, the ongoing session shall be kept on the current interface while initiating the new sessions on the new interface. The problem of the interface selection is within the MIF scope and may leverage specific node functions (Section 3.8). However, if transfer of IP session is required, IP mobility mechanisms, such as [RFC3775], shall be used. 3.5. Address Selection The Default Address Selection specification [RFC3484] defines algorithms for source and destination IP address selections. It is mandatory to be implemented in IPv6 nodes, which also means dual- stack nodes. A node-scoped policy table managed by the IP stack is defined. Mechanisms to update the policy table are being defined [I-D.ietf-6man-addr-select-sol] to update the policy table. Issues on using the Default Address Selection were found in [RFC5220] and [RFC5221] in the context of multiple prefixes on the same link. 3.6. Finding and Sharing IP Addresses with Peers Interactive Connectivity Establishment (ICE [RFC5245]) is a technique for NAT traversal for UDP-based (and TCP) media streams established by the offer/answer model. The multiplicity of IP addresses, ports and transport in SDP offers are tested for connectivity by peer-to- peer connectivity checks. The result is candidate IP addresses and ports for establishing a connection with the other peer. However, ICE does not solve issues when incompatible configuration objects are received on different interfaces. Some application protocols do referrals of IP addresses, port numbers and transport for further exchanges. For instance, applications can provide reachability information to itself or to a third party. The general problem of referrals is related to the multiple interface Blanchet & Seite Expires November 10, 2011 [Page 6] Internet-Draft Multiple Interfaces Problem Statement May 2011 problem, since, in this context, referrals must provide consistent information depending on which provisioning domain is used. Referrals are discussed in [I-D.carpenter-referral-ps] and [I-D.ietf-shim6-app-refer]. 3.7. Provisioning domain selection In a MIF context, the node may handle simultaneously multiple domains with disparate characteristics, especially when supporting multiple access technologies. Selection is simple if the application is restricted to one specific provisioning domain: the application must start on the default provisioning domain if available, otherwise the application does not start. However, if the application can be run on several provisioning domains, the selection problem can be difficult. There is no standard method for selecting a provisioning domain but some recommendation exist while restricting the scope to the interface selection problem. For example, [TS23.234] proposes a default mechanism for the interface selection. This method uses the following information (non exhaustive list): o preferences provided by the user, o policies provided by network operator, o quality of the radio link, o network resource considerations (e.g. available QoS, IP connectivity check,...), o the application QoS requirements in order to map applications to the best interface However, [TS23.234] is designed for a specific multiple-interfaces use-case. A generic way to handle these characteristics is yet to be defined. 3.8. Session management Some implementations, specially in the mobile world, rely on higher- level session manager, also named connection manager, to deal with issues brought by simultaneous attachment to multiple provisioning domains. Typically, the session manager may deal with the selection of the interface, and/or the provisioning domain, on behalf to the applications, or tackle with complex issues such as policies conflict resolution (Section 4.3). As discussed previously in Section 3.7, the session manager may encounter difficulties because of multiple and diverse criteria. Session managers usually leverage the link-layer interface to gather information (e.g lower layer authentication and encryption methods, Blanchet & Seite Expires November 10, 2011 [Page 7] Internet-Draft Multiple Interfaces Problem Statement May 2011 see Section 3.1) and/or for control purpose. Such link-layer interface may not provide all required services to make a proper decision (e.g. interface selection). Some OS, or terminals, already implement session managers [I-D.ietf-mif-current-practices] and vendor-specific platforms sometimes provides specific socket API (Section 3.9) a session manager can use. However, the generic architecture of a session manager and its associated API are not currently standardized, so session management behavior may differ between OS and platforms. Multiple interfaces management sometimes relies on a virtual interface. For instance, virtual interface allows to support multi- homing, inter-technology handovers and IP flow mobility in a Proxy Mobile IPv6 network [I-D.ietf-netext-logical-interface-support]. This virtual interface allows a multiple-interfaces node sharing a set of IP addresses on multiple physical interfaces and can also add benefits to multi-access scenarios such as 3GPP Multi Access PDN Connectivity [TS23.402]. In most cases, the virtual interface will map several physical network interfaces and the session manager should control both, the configuration of each one of these virtual and physical interfaces, as well as the mapping between the virtual and the sub-interfaces. In multiple interfaces situation, active application sessions should survive to path failures. Here, the session manager may come into play but only relying on existing mechanisms to manage multipath (MPTCP [I-D.ietf-mptcp-architecture]) or failover (MIP6 [RFC3775], SHIM6 [RFC5533]). Description of interaction between these mechanisms and the session manager is out of the scope of this document. 3.9. Socket API An Application Programming Interface (API) may expose objects that user applications, or session managers, use for dealing with multiple interfaces. For example, [RFC3542] defines how an application using the Advanced sockets API specifies the interface or the source IP address, through a simple bind() operation or with the IPV6_PKTINFO socket option. Other APIs have been defined to solve similar issues to MIF. For instance, [RFC5014] defines an API to influence the default address selection mechanism by specifying attributes of the source addresses it prefers. [I-D.ietf-shim6-multihome-shim-api] gives another example, in a multihoming context, by defining a socket API enabling interactions between applications and the multihoming shim layer for advanced locator management, and access to information about failure detection and path exploration. Blanchet & Seite Expires November 10, 2011 [Page 8] Internet-Draft Multiple Interfaces Problem Statement May 2011 4. MIF Issues This section describes the various issues when using a MIF node that has already received configuration objects from its various provisioning domains or when multiple interfaces are used and results in wrong domain selection, addressing or naming space overlaps. They occur, for example, when: 1. one interface is on the Internet and one is on a corporate private network. The latter may be through VPN. 2. one interface is on one access network (i.e. wifi) and the other one is on another access network (3G) with specific services. 4.1. DNS resolution issues A MIF node (M1) has an active interface(I1) connected to a network (N1) which has its DNS server (S1) and another active interface (I2) connected to a network (N2) which has its DNS server (S2). S1 serves with some private namespace "private.example.com". The user or the application uses a name "a.private.example.com" which is within the private namespace of S1 and only resolvable by S1. Any of the following situations may occur: 1. M1 stack, based on its routing table, uses I2 to reach S1 to resolve "a.private.example.com". M1 never reaches S1. The name is not resolved. 2. M1 keeps only one set of DNS server addresses from the received configuration objects and kept S2 address. M1 sends the forward DNS query for a.private.example.com to S2. S2 responds with an error for an non-existent domain (NXDOMAIN). The name is not resolved. This issue also arises when performing reverse DNS lookup. In the same situation, the reverse DNS query fails. 3. M1 keeps only one set of DNS server addresses from the received configuration objects and kept S2 address. M1 sends the DNS query for a.private.example.com to S2. S2 asks its upstream DNS and gets an IP address for a.private.example.com. However, the IP address is not the same one S1 would have given. Therefore, the application tries to connect to the wrong destination node, or to the wrong interface of the latter, which may imply security issues or result in lack of service. 4. S1 or S2 has been used to resolve "a.private.example.com" to an [RFC1918] address. Both N1 and N2 are [RFC1918] addressed networks. If addresses overlap, traffic may be sent using the wrong interface. This issue is not related to receiving multiple configuration objects, but to an address overlap between interfaces or attaching networks. Blanchet & Seite Expires November 10, 2011 [Page 9] Internet-Draft Multiple Interfaces Problem Statement May 2011 5. M1 has resolved an FQDN to locally valid IP address when connected to N1. If the node looses connection to N1, the node may try to connect, via N2, to the same IP address as earlier, but as the address was only locally valid, connection setup fails. Similarly, M1 may have received NXDOMAIN for an FQDN when connected to N1. After detachment from N1, the node should not assume the FQDN continues to be nonexistent on N2. 6. M1 requests AAAA record from a DNS server on a network that uses protocol translators and DNS64 [I-D.ietf-behave-dns64]. If the M1 receives synthesized AAAA record, it is guaranteed to be valid only on the network it was learned from. If the M1 uses synthesized AAAA on any other network interface, traffic may be lost, dropped or forwarded to the wrong network. Some networks requires the user to authenticate on a captive web portal before providing Internet connectivity. If this redirection is achieved by modifying the DNS reply, specific issues may occur. Consider a MIF node (M1) with an active interface(I1) connected to a network (N1), which has its DNS server (S1), and another active interface (I2) connected to a network (N2), which has its DNS server (S2). Until the user has not authenticated, S1 is configured to respond to any A or AAAA record query with the IP address of a captive portal, so as to redirect web browsers to an access control portal web page. This captive portal can be reached only via I1. When the user has authenticated to the captive portal, M1 can resolve an FQDN when connected to N1. However, if the address is only locally valid on N1, any of the issue described above may occur. When the user has not authenticated, any of the following situations may occur: 1. M1 keeps only one set of DNS server addresses from the received configuration objects and kept S2 address. M1 sends the forward DNS query for a.example.com to S2. S2 responds with the correct answer, R1. M1 attempts to contact R1 by way of I1. The connection fails. Or, the connection succeeds, bypassing the security policy on N1, possibly exposing the owner of M1 to prosecution. 2. M1 keeps only one set of DNS server addresses from the received configuration objects and kept S1 address. M1 sends the DNS query for a.example.com to S1. S1 provides the address of its captive portal. M1 attempts to contact this IP address using I1. The application fails to connect, resulting in lack of service. Or, the application succeeds in connecting, but connects to the captive portal rather than the intended destination, resulting in lack of service (i.e. IP connectivity check issue described in Section 4.4). Blanchet & Seite Expires November 10, 2011 [Page 10] Internet-Draft Multiple Interfaces Problem Statement May 2011 4.2. Node Routing A MIF node (M1) has an active interface(I1) connected to a network (N1) and another active interface (I2) connected to a network (N2). The user or the application is trying to reach an IP address (IP1). Any of the following situations may occur: 1. For IP1, M1 has one default route (R1) via network (N1). To reach IP1, M1 stack uses R1 and sends through I1. If IP1 is only reachable by N2, IP1 is never reached or is not the right target. 2. For the IP1 address family, M1 has one default route (R1, R2) per network (N1, N2). IP1 is reachable by both networks, but N2 path has better characteristics, such as better round-trip time, least cost, better bandwidth, etc.... These preferences could be defined by user, provisioned by the network operator, or else. M1 stack uses R1 and tries to send through I1. IP1 is reached but the service would be better by I2. 3. For the IP1 address family, M1 has a default route (R1), a specific X.0.0.0/8 route R1B (for example but not restricted to RFC1918 prefix) to N1 and a default route (R2) to N2. IP1 is reachable by N2 only, but the prefix (X.0.0.0/8) is used in both networks. Because of the most specific route R1B, M1 stack sends through I2 and never reach the target. A MIF node may have multiple routes to a destination. However, by default, it does not have any hint concerning which interface would be the best to use for that destination. The first-hop selection may leverage on local routing policy, allowing some actors (e.g. network operator or service provider) to influence the routing table, i.e. make decision regarding which interface to use. For instance, a user on such multihomed node might want a local policy to influence which interface will be used based on various conditions. Some SDOs have defined policy-based routing selection mechanisms. For instance, the Access Network Discovery and Selection Function (ANDSF) [TS23.402] provides inter-systems routing policies to terminals with both a 3GPP and non-3GPP interfaces. However, the routing selection may still be difficult, due to disjoint criteria as discussed in Section 3.8. Moreover, information required to make the right decision may not be available. For instance, interfaces to lower layer may not provide all required hints to the selection (e.g. information on interface quality). A node usually has a node-scoped routing table. However, a MIF node is connected to multiple provisioning domains; if each of these domains pushes routing policies to the node, then conflicts between policies may happen and the node has no easy way to merge or reconciliate them. Blanchet & Seite Expires November 10, 2011 [Page 11] Internet-Draft Multiple Interfaces Problem Statement May 2011 On a MIF node, some source addresses are not valid if used on some interfaces. For example, an RFC1918 source address might be appropriate on the VPN interface but not on the public interface of the MIF node. If the source address is not chosen appropriately, then packets may be filtered in the path if source address filtering is in place ([RFC2827], [RFC3704]) and reply packets may never come back to the source. 4.3. Policies conflict The distribution of configuration policies (e.g. address selection, routing, DNS selection...) to end nodes is being discussed (e.g. ANDSF in [TS23.402], [I-D.ietf-mif-dhcpv6-route-option]). If implemented in multiple provisioning domains, such mechanisms may conflict and bring issues to the multihomed node. Considering a MIF node (M1) with an active interface(I1) connected to a network (N1) and another active interface (I2) connected to a network (N2), the following conflicts may occur: 1. M1 receives from both networks (N1 and N2) an update of its default address selection policy. However, the policies are specific to each network. The policies are merged by M1 stack. Based on the merged policy, the chosen source address is from N1 but packets are sent to N2. The source address is not reachable from N2, therefore the return packet is lost. Merging address selection policies may have important impacts on routing. 2. A node usually has a node-scoped routing table. However, each of the connected provisioning domains (N1 and N2) may push routing policies to the node, then conflicts between policies may happen and the node has no easy way to merge or reconciliate them. 3. M1 receives from one of the network an update of its access selection policy, e.g. via the 3GPP/ANDSF [TS23.402]. However, the policy is in conflict with the local policy (e.g. user defined, or default OS policy). Assuming that the network provides list of overloaded access network, if the policy sent by the network is ignored, packet may be sent to an access network with poor quality of communication. 4.4. Session management Consider that a node has selected an interface and managed to configure it (i.e. the node obtained a valid IP address from the network). However, the Internet connectivity is not available. The problem could be due to the following reasons: 1. The network requires a web-based authentication (e.g. the access network is a WiFi Hot Spot). In this case the user can only access to a captive portal. For instance, the network may perform HTTP redirection or modify DNS behaviour (Section 4.1) until the user has not authenticated. Blanchet & Seite Expires November 10, 2011 [Page 12] Internet-Draft Multiple Interfaces Problem Statement May 2011 2. IP interface is configured active but layer 2 is so poor (e.g. poor radio condition) that no layer 3 traffic can succeed. In this situation, the session management should be able to perform IP connectivity checks before selecting an interface. Session issues may also arise when the node discovers a new provisioning domain. Consider a MIF node (M1) has an active interface(I1) connected to a network (N1) where an application is running a TCP session. A new network (N2) becomes available. If N2 is selected (e.g. because of better quality of communication), M1 gets IP connectivity to N2 and updates the routing table priority. So, if no specific route to the correspondent node and if the node implements the weak host model [RFC1122], the TCP connection breaks as next hop changes. In order to continue communicating with the correspondent node, M1 should try to re-connect the server via N2. In some situation, it could be preferable to maintain current sessions on N1 while new sessions start on N2. 4.5. Single Interface on Multiple Provisioning Domains When a node using a single interface is connected to multiple networks, such as different default routers, similar issues as described above happen. Even with a single interface, a node may wish to connect to more than one provisioning domain: that node may use more than one IP source address and may have more than one default router. The node may want to access services that can only be reached using one of the provisioning domain. In this case, it needs to use the right outgoing source address and default gateway to reach that service. In this situation, that node may also need to use different DNS servers to get domain names in those different provisioning domains. 5. Underlying problems and causes This section lists the underlying problems, and their causes, which lead to the issues discussed in the previous section. The problems can be divided into five categories: 1) Configuration 2) DNS resolution 3) Routing 4) Address selection and 5) session management and API. They are shown as below: 1. Configuration. In a MIF context, configuration information specific to a provisioning domain may be ignored because: 1. Configuration objects (e.g. DNS servers, NTP servers, ...) are node-scoped. So the IP stack is not able to maintain the mapping between information and corresponding provisioning domain. Blanchet & Seite Expires November 10, 2011 [Page 13] Internet-Draft Multiple Interfaces Problem Statement May 2011 2. Same configuration objects (e.g. DNS server addresses, NTP server addresses, ..) received from multiple provisioning domains may be overwritten. 3. Host implementations usually do not keep separate network configuration (such as DNS server addresses) per provisioning domain. 2. DNS resolution 1. Some FQDN can be resolvable only by sending queries to the right server (e.g. intranet services). However, DNS query could be sent to the wrong interface because DNS server addresses may be node-scoped. 2. A DNS answer may be only valid on a specific provisioning domain but applications may not be aware of that mapping because DNS answers may not be kept with the provisioning from which the answer comes from. 3. Routing 1. In the MIF context, routing information could be specific to each interface. This could lead to routing issue because, in current node implementations, routing tables are node-scoped. 2. Current node implementations do not take into account the Differentiated Services Code Point or path characteristics in the routing table. 3. Even if implementations take into account path characteristics, the node has no way to properly merge or reconciliate the provisioning domain preferences. 4. a node attached to multiple provisioning domain could be provided with incompatible selection policies. If the different actors (e.g. user and network operator) are allowed to provide their own policies, the node has no way to properly merge or reconciliate multiple selection policies. 5. The problem of first hop selection could not be solved via configuration (Section 3.7), and may leverage on sophisticated and specific mechanisms (Section 3.8). 4. Address selection 1. Default Address Selection policies may be specific to their corresponding provisioning domain. However, a MIF node may not be able to manage per-provisioning domain address selection policies because default Address Selection policy is node-scoped. 2. On a MIF node, some source addresses are not valid if used on some interfaces or even on some default routers on the same interface. In this situation, the source address should be taken into account in the routing table; but current node implementations do not support such a feature. 3. Source address or address selection policies could be specified by applications. However, there is no advanced APIs to allow applications realizing such operations. Blanchet & Seite Expires November 10, 2011 [Page 14] Internet-Draft Multiple Interfaces Problem Statement May 2011 5. Session management and API 1. Some implementations, specially in the mobile world, have higher-level API and/or session manager (aka connection manager) to address MIF issues. These mechanisms are not standardized and do not necessarily behave the same way across different OS, and/or platforms, in the presence of the MIF problems. This lack of consistency is an issue for user and operator who could experience different session manager behaviors depending on the terminal. 2. Session managers usually leverage on interface to link layer to gather information (e.g lower layer authentication and encryption methods) and/or for control purpose. However, such link layer interface may not provide all required services (e.g. may not provide all information allowing to make a proper interface selection). 3. A MIF node can support different session managers, which may have contradictory ways to solve the MIF issues. For instance, because of different selection algorithms, two different session managers could select different domains in a same context. Or, when dealing with different domain selection policies, a session manager may give precedence to user policy while another could favor mobile operator policy. 4. When host routing is updated and if weak host model is supported, ongoing TCP sessions may break if routes changes for these sessions. When TCP sessions should be bound to the interface, the strong host model should be used. 5. When provided by different actors (e.g. user, network, default-OS), policies may conflict and, thus, need to be reconciliated at the host level. Policy conflict resolution may impact other functions (e.g. naming, routing). 6. Even if the node has managed to configure an interface, Internet connectivity could be not available. It could be due to an access control function coming into play above the layer 3, or because of poor layer 2 conditions. IP connectivity check should be performed before selecting an interface. 6. Security Considerations The problems discussed in this document have security implications, such as when the packets sent on the wrong interface might be leaking some confidential information. Configuration parameters from one provisioning domain could cause a denial of service on another provisioning domain (e.g. DNS issues). Moreover, the undetermined behavior of IP stacks in the multihomed context bring additional threats where an interface on a multihomed node might be used to conduct attacks targeted to the networks connected by the other Blanchet & Seite Expires November 10, 2011 [Page 15] Internet-Draft Multiple Interfaces Problem Statement May 2011 interfaces.corrupted provisioning domain selection policy may induce a node to make decisions causing certain traffic to be forwarded to the attacker. Additional security concerns are raised by possible future mechanisms that provide additional information to the node so that it can make a more intelligent decision with regards to the issues discussed in this document. Such future mechanisms may themselves be vulnerable and may not be easy to protect in the general case. 7. IANA Considerations This document has no actions for IANA. 8. Authors This document is a joint effort with authors of the MIF requirements draft [I-D.yang-mif-req]. The authors of this document, in alphabetical order, include: Marc Blanchet, Jacqni Qin, Pierrick Seite, Carl Williams and Peny Yang. 9. Acknowledgements The initial Internet-Drafts prior to the MIF working group and the discussions during the MIF BOF meeting and on the mailing list around the MIF charter scope on the mailing list brought very good input to the problem statement. This draft steals a lot of text from these discussions and initial drafts (e.g. [I-D.yang-mif-req], [I-D.hui-ip-multiple-connections-ps], [I-D.ietf-mif-dns-server-selection]). Therefore, the editor would like to acknowledge the following people (in no specific order), from which some text has been taken from: Jari Arkko, Keith Moore, Sam Hartman, George Tsirtsis, Scott Brim, Ted Lemon, Bernie Volz, Giyeong Son, Gabriel Montenegro, Julien Laganier, Teemu Savolainen, Christian Vogt, Lars Eggert, Margaret Wasserman, Hui Deng, Ralph Droms, Ted Hardie, Christian Huitema, Remi Denis-Courmont, Alexandru Petrescu, Zhen Cao, Gaetan Feige, Telemaco Melia and Juan-Carlos Zuniga. Sorry if some contributors have not been named. 10. Informative References [I-D.carpenter-referral-ps] Carpenter, B., Jiang, S., and Z. Cao, "Problem Statement for Referral", draft-carpenter-referral-ps-02 (work in Blanchet & Seite Expires November 10, 2011 [Page 16] Internet-Draft Multiple Interfaces Problem Statement May 2011 progress), February 2011. [I-D.hui-ip-multiple-connections-ps] Hui, M. and H. Deng, "Problem Statement and Requirement of Simple IP Multi-homing of the Host", draft-hui-ip-multiple-connections-ps-02 (work in progress), March 2009. [I-D.ietf-6man-addr-select-sol] Matsumoto, A., Fujisaki, T., and R. Hiromi, "Solution approaches for address-selection problems", draft-ietf-6man-addr-select-sol-03 (work in progress), March 2010. [I-D.ietf-behave-dns64] Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum, "DNS64: DNS extensions for Network Address Translation from IPv6 Clients to IPv4 Servers", draft-ietf-behave-dns64-11 (work in progress), October 2010. [I-D.ietf-mif-current-practices] Wasserman, M. and P. Seite, "Current Practices for Multiple Interface Hosts", draft-ietf-mif-current-practices-11 (work in progress), April 2011. [I-D.ietf-mif-dhcpv6-route-option] Dec, W., Mrugalski, T., Sun, T., and B. Sarikaya, "DHCPv6 Route Option", draft-ietf-mif-dhcpv6-route-option-01 (work in progress), March 2011. [I-D.ietf-mif-dns-server-selection] Savolainen, T., Kato, J., and T. Lemon, "Improved DNS Server Selection for Multi-Homed Nodes", draft-ietf-mif-dns-server-selection-02 (work in progress), April 2011. [I-D.ietf-mptcp-architecture] Ford, A., Raiciu, C., Handley, M., Barre, S., and J. Iyengar, "Architectural Guidelines for Multipath TCP Development", draft-ietf-mptcp-architecture-05 (work in progress), January 2011. [I-D.ietf-netext-logical-interface-support] Melia, T. and S. Gundavelli, "Logical Interface Support for multi-mode IP Hosts", draft-ietf-netext-logical-interface-support-02 (work in Blanchet & Seite Expires November 10, 2011 [Page 17] Internet-Draft Multiple Interfaces Problem Statement May 2011 progress), March 2011. [I-D.ietf-shim6-app-refer] Nordmark, E., "Shim6 Application Referral Issues", draft-ietf-shim6-app-refer-00 (work in progress), July 2005. [I-D.ietf-shim6-multihome-shim-api] Komu, M., Bagnulo, M., Slavov, K., and S. Sugimoto, "Socket Application Program Interface (API) for Multihoming Shim", draft-ietf-shim6-multihome-shim-api-17 (work in progress), April 2011. [I-D.yang-mif-req] Yang, P., Seite, P., Williams, C., and J. Qin, "Requirements on multiple Interface (MIF) of simple IP", draft-yang-mif-req-00 (work in progress), March 2009. [MIH] IEEE, "IEEE Standard for Local and Metropolitan Area Networks - Part 21: Media Independent Handover Services, IEEE LAN/MAN Std 802.21-2008, January 2009.", 2010. [RFC1122] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, October 1989. [RFC1136] Hares, S. and D. Katz, "Administrative Domains and Routing Domains: A model for routing in the Internet", RFC 1136, December 1989. [RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, July 1994. [RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and E. Lear, "Address Allocation for Private Internets", BCP 5, RFC 1918, February 1996. [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000. [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. [RFC3484] Draves, R., "Default Address Selection for Internet Blanchet & Seite Expires November 10, 2011 [Page 18] Internet-Draft Multiple Interfaces Problem Statement May 2011 Protocol version 6 (IPv6)", RFC 3484, February 2003. [RFC3542] Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei, "Advanced Sockets Application Program Interface (API) for IPv6", RFC 3542, May 2003. [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed Networks", BCP 84, RFC 3704, March 2004. [RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in IPv6", RFC 3775, June 2004. [RFC4294] Loughney, J., "IPv6 Node Requirements", RFC 4294, April 2006. [RFC4477] Chown, T., Venaas, S., and C. Strauf, "Dynamic Host Configuration Protocol (DHCP): IPv4 and IPv6 Dual-Stack Issues", RFC 4477, May 2006. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September 2007. [RFC4960] Stewart, R., "Stream Control Transmission Protocol", RFC 4960, September 2007. [RFC5014] Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6 Socket API for Source Address Selection", RFC 5014, September 2007. [RFC5113] Arkko, J., Aboba, B., Korhonen, J., and F. Bari, "Network Discovery and Selection Problem", RFC 5113, January 2008. [RFC5206] Nikander, P., Henderson, T., Vogt, C., and J. Arkko, "End- Host Mobility and Multihoming with the Host Identity Protocol", RFC 5206, April 2008. [RFC5220] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama, "Problem Statement for Default Address Selection in Multi- Prefix Environments: Operational Issues of RFC 3484 Default Rules", RFC 5220, July 2008. [RFC5221] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama, "Requirements for Address Selection Mechanisms", RFC 5221, July 2008. [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Blanchet & Seite Expires November 10, 2011 [Page 19] Internet-Draft Multiple Interfaces Problem Statement May 2011 Traversal for Offer/Answer Protocols", RFC 5245, April 2010. [RFC5533] Nordmark, E. and M. Bagnulo, "Shim6: Level 3 Multihoming Shim Protocol for IPv6", RFC 5533, June 2009. [RFC5648] Wakikawa, R., Devarapalli, V., Tsirtsis, G., Ernst, T., and K. Nagami, "Multiple Care-of Addresses Registration", RFC 5648, October 2009. [TS23.234] 3GPP, "3GPP system to Wireless Local Area Network (WLAN) interworking; TS 23.234", 2009. [TS23.402] 3GPP, "Architecture enhancements for non- 3GPP accesses; TS 23.402", 2010. Authors' Addresses Marc Blanchet Viagenie 2875 boul. Laurier, suite D2-630 Quebec, QC G1V 2M2 Canada Email: Marc.Blanchet@viagenie.ca URI: http://viagenie.ca Pierrick Seite France Telecom - Orange 4, rue du Clos Courtel, BP 91226 Cesson-Sevigne 35512 France Email: email@example.com Blanchet & Seite Expires November 10, 2011 [Page 20]