Network Working Group M. Blanchet Ed.
Internet-Draft Viagenie
Intended status: Informational P. Seite
Expires: April 29, 2010 France Telecom
October 26, 2009
Multiple Interfaces Problem Statement
draft-ietf-mif-problem-statement-01.txt
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Abstract
A multihomed host receives node configuration information from each
of its provisioning domain. Some configuration objects are global to
the node, some are local to the interface. Various issues arise when
multiple conflicting node-scoped configuration objects are received
on multiple interfaces. Similar situations also happen with single
interface host connected to multiple networks. This document
describes these issues.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Scope and Existing Work . . . . . . . . . . . . . . . . . . . 4
3.1. Below IP Interaction . . . . . . . . . . . . . . . . . . . 4
3.2. Hosts Requirements . . . . . . . . . . . . . . . . . . . . 4
3.3. Mobility and other IP protocols . . . . . . . . . . . . . 5
3.4. Address Selection . . . . . . . . . . . . . . . . . . . . 5
3.5. Interactive Connectivity Establishment (ICE) . . . . . . . 5
3.6. Socket API . . . . . . . . . . . . . . . . . . . . . . . . 6
3.7. Above IP Layers . . . . . . . . . . . . . . . . . . . . . 6
4. Symptoms . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. DNS resolution issues . . . . . . . . . . . . . . . . . . 6
4.2. Routing . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.3. Address Selection Policy . . . . . . . . . . . . . . . . . 8
4.4. Single Interface on Multiple Networks . . . . . . . . . . 9
5. Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Authors . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
11. Discussion home for this draft . . . . . . . . . . . . . . . . 10
12. Informative References . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
A multihomed host 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
automatic or manual tunnels. Current laptops and smartphones
typically have multiple access network interfaces and, thus, may be
simultaneously connected to different provisioning domains.
A multihomed host receives node configuration information from each
of its access networks, through various mechanims 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.
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 it will use or how
it will merge them.
Several issues regarding how the node-scoped configuration objects
are used in a multihomed node environment have been raised. The
following sections define the MIF host and the scope of this
document, describe related work, list the symptoms and then the
underlying problems.
A companion document [I-D.mrw-mif-current-practices] discusses
current practices.
2. Terminology
A MIF host is defined as:
o A [RFC1122] IPv4 and/or [RFC4294] IPv6 compliant host
o Configured with more than one IP addresses (excluding loopback,
link-local)
o On one or more provisioning domains, as presented to the IP stack.
o The interfaces may be logical, virtual or physical.
o The IP addresses come from more than one administrative domains.
o The IP addresses may be from the same or from different address
families, such as IPv4 and IPv6.
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o Communications using these IP addresses may happen simultaneously
and independently.
o Communications using these IP addresses may be tied on all the
possible provisioning domains, or, at least, on a limited number
of provisioning domains.
o While the MIF host may forward packets between its interfaces,
forwarding packets is not taken into account in this definition.
When a protocol keyword such as IP, PPP, DHCP is used 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
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
Network discovery and selection on lower layers as defined by
[RFC5113] is out of scope of this document. Moreover, lower layer
interaction such as IEEE 802.21 is also out of scope.
Proxy MIP allows sharing a single IP address across multiple interfac
es (e.g., WiMAX and CDMA, LTE and HSPA, etc) to disparate networks.
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.
Furthermore, link aggregation done under IP where a single interace
is shown to the IP stack is also out of scope.
3.2. Hosts Requirements
The requirements for Internet Hosts [RFC1122] describe the multihomed
host 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 host maintains a route cache table where each entry contains the
local IP address, the destination IP address, Type-of-Service 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.
As per [RFC1122], two models are defined:
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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 host 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 Type-of-Service. Under the weak model, the source IP
address is not used, but only the destination IP address and the
Type-of-Service.
3.3. Mobility and other IP protocols
This document assumes hosts only implementing [RFC1122] for IPv4 and
[RFC4294] for IPv6, and not using any kind of new transport
protocols. It is not required for the host to support additional IP
mobility or multihoming protocols, such as SHIM6, SCTP, Mobile IP,
HIP, RRG, LISP or else. Moreover, the peer of the connection is also
not required to use these mechanisms.
3.4. Address Selection
The Default Address Selection [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.
Provisions are made to change or update the policy table, however, no
mechanism is defined.
Issues on using the Default Address Selection were found [RFC5112] in
the context of multiple prefixes on the same link. New work
[I-D.chown-addr-select-considerations] discusses the multiple
attached networks scenarios and how to update the policy table.
3.5. Interactive Connectivity Establishment (ICE)
Interactive Connectivity Establishment (ICE [I-D.ietf-mmusic-ice]) is
a technique for NAT traversal for UDP-based (and TCP) media streams
established by the offer/answer model. The multiplicity of IP
addresses and ports 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.
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ICE does not solve the MIF issues, such as the incompatible
configuration objects received on different interfaces. However, ICE
may be of use for address selection if the application is ICE-
enabled.
3.6. Socket API
Application Programming Interface (API) may expose objects that user
applications may use for the MIF purpose. For example, [RFC3542]
shows how an application using the Advanced sockets API can specify
the interface or the source IP address, through simple bind()
operation or IPV6_PKTINFO socket option.
An API is also defined [RFC5014] to influence the default address
selection mechanism by specifying attributes of the source addresses
it prefers.
3.7. Above IP Layers
The MIF issues discussed in this document assume no changes in
transport protocols or applications. However, fixing the issues
might involve these layers.
4. Symptoms
This section describes the various symptoms found using a MIF host
that has already received configuration objects from its various
provisioning domains.
These situations are also described in
[I-D.savolainen-6man-fqdn-based-if-selection], [I-D.yang-mif-req] and
[RFC4477]. 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 host (H1) 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:
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1. H1 stack, based on its routing table, uses I2 to reach S1 to
resolve "a.private.example.com". H1 never reaches S1. The name
is not resolved.
2. H1 keeps only one set of DNS server addresses from the received
configuration objects and kept S2 address. H1 sends the DNS A
query for a.private.example.com to S2. S2 responds with an error
for an non-existant domain (NXDOMAIN). The name is not resolved.
3. H1 keeps only one set of DNS server addresses from the received
configuration objects and kept S2 address. H1 sends the DNS A
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 right one S1 would have given. Therefore,
the application tries to connect to the wrong destination host,
which may imply security issues.
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. IPv4 source address selection may face challenges, as
due address overlapping the source/destination IP addresses do
not necessarily provide enough information for making proper
address selection decisions.
5. H1 has resolved an FQDN to locally valid IP address when
connected to N1. After movement from N1 to N2, the host tries to
connect to the same IP address as earlier, but as the address was
only locally valid, connection setup fails.
6. H1 requests AAAA record from a DNS server on a network that uses
protocol translators and DNS64 [I-D.ietf-behave-dns64]. If the
H1 receives synthesized AAAA record, it is quaranteed to be valid
only on the network it was learned from. If the H1 uses
synthesized AAAA on an network interface it is not valid on, the
packets will be dropped by the network.
4.2. Routing
A MIF host (H1) 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 the IP1 address family, H1 has one default route (R1, R2) per
network (N1, N2). IP1 is only reachable by N2. H1 stack uses R1
and tries to send through I1. IP1 is never reached or is not the
right target.
2. For the IP1 address family, H1 has one default route (R1, R2) per
network (N1, N2). IP1 is reachable by both networks, but N2 path
has better characterictics, such as better round-trip time, least
cost, better bandwidth, etc.... These preferences could be
defined by user, by the provider, by discovery or else. H1 stack
uses R1 and tries to send through I1. IP1 is reached but the
service would be better by I2.
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3. For the IP1 address family, H1 has a default route (R1), a
specific X.0.0.0/8 route R1B (eg. 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, H1 stack sends through I2 and never reach the
target.
A MIF host 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. For example, as discussed
in [I-D.savolainen-6man-fqdn-based-if-selection],
[I-D.hui-ip-multiple-connections-ps] and [I-D.yang-mif-req], a
service provider might want to influence the routing table of the
host connecting to its network.
A host usually has a node-scoped routing table. Therefore, when a
MIF host is connected to multiple provisioning domains where each
service provider wants to influence the routing table of the host,
then conflicts might arise from the multiple routing information
being pushed to the host.
A user on such multihomed host might want a local policy to influence
which interface will be used based on various conditions.
On a MIF host, 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 host. If the source address is not chosen appropriately,
then sent packets might be filtered in the path if source address
filtering is in place ([RFC2827],[RFC3704]) and reply packets might
never come back to the source.
4.3. Address Selection Policy
A MIF host (H1) 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. H1 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 H1 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.
2. TBD: add more
Merging address selection policies may have important impacts on
routing.
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4.4. Single Interface on Multiple Networks
When a MIF host using a single interface is connected to multiple
networks with different default routers, similar issues as described
above happen.
5. Problems
This section tries to list the underlying problems corresponding to
the issues discussed in the previous section.
1. Routing tables are usually node-scoped.
2. DNS server addresses and other configuration objects (NTP
servers, ...) are usually node-scoped.
3. Same configuration objects (eg DNS server addresses, NTP server
addresses, ..) received from multiple provisioning domains are
usually overwritten.
4. Default Address Selection policies are usually node-scoped.
5. Default Address Selection policies may differ when received on
different provisioning domains.
6. Host implementations usually do not implement the [RFC1122]
strong model where the source address is in the routing table.
7. Host implementations usually do not implement the [RFC1122]
model where the Type-of-Service are in the routing table.
8. Host implementations usually do not keep path characteristics,
user or provider preferences in the routing table.
9. Applications usually do not use advanced APIs to specify the
source IP address or to set preferences on the address selection
policies.
10. DNS answers are usually not kept with the interface from which
the answer comes from.
11. Host implementations usually do not keep separate network
configuration (such as DNS server addresses) per provisioning
domain.
6. Summary
A MIF host receives node configuration information from each of its
provisioning domains. Some configuration objects are global to the
node, some are local to the interface. Various issues arise when
multiple conflicting node-scoped configuration objects are received
via multiple provisioning domains. Similar situations also happen
with single interface host connected to multiple networks.
Therefore, there is a need to define the appropriate behavior of an
IP stack and possibly define protocols to manage these cases.
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7. 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. Moreover, the undetermined behavior
of IP stacks in the multihomed context bring additional threats where
an interface on a multihomed host might be used to conduct attacks
targeted to the networks connected by the other interfaces.
8. IANA Considerations
This document has no actions for IANA.
9. 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.
10. 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 the initial drafts. 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, Teemu Savolainen, Christian Vogt, Lars
Eggert, Margaret Wasserman, Hui Deng, Ralph Droms, Ted Hardie,
Christian Huitema, Remi Denis-Courmont. Sorry if some contributors
have not been named.
11. Discussion home for this draft
This document is intended to define the problem space discussed in
the mif@ietf.org mailing list.
12. Informative References
[I-D.chown-addr-select-considerations]
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Chown, T., "Considerations for IPv6 Address Selection
Policy Changes", draft-chown-addr-select-considerations-03
(work in progress), July 2009.
[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-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-dns64-01 (work in progress),
October 2009.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
[I-D.mrw-mif-current-practices]
Wasserman, M., "Current Practices for Multiple Interface
Hosts", draft-mrw-mif-current-practices-02 (work in
progress), March 2009.
[I-D.savolainen-6man-fqdn-based-if-selection]
Savolainen, T., "Domain name based network interface
selection",
draft-savolainen-6man-fqdn-based-if-selection-00 (work in
progress), October 2008.
[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.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 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.
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[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
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.
[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.
[RFC5014] Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
Socket API for Source Address Selection", RFC 5014,
September 2007.
[RFC5112] Garcia-Martin, M., "The Presence-Specific Static
Dictionary for Signaling Compression (Sigcomp)", RFC 5112,
January 2008.
[RFC5113] Arkko, J., Aboba, B., Korhonen, J., and F. Bari, "Network
Discovery and Selection Problem", RFC 5113, January 2008.
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Authors' Addresses
Marc Blanchet
Viagenie
2600 boul. Laurier, suite 625
Quebec, QC G1V 4W1
Canada
Email: Marc.Blanchet@viagenie.ca
URI: http://www.viagenie.ca
Pierrick Seite
France Telecom
4, rue du Clos Courtel, BP 91226
Cesson-Sevigne 35512
France
Email: pierrick.seite@orange-ftgroup.com
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