Multiple Interfaces

Document Charter Multiple Interfaces WG (mif)
Title Multiple Interfaces
Last updated 2015-10-14
State Approved
WG State Concluded
IESG Responsible AD Terry Manderson
Charter Edit AD Ted Lemon
Send notices to (None)


Nodes attached to multiple networks may encounter problems due to conflict
of network configuration information and/or simultaneous use of the multiple
available networks. This can happen over multiple physical network interfaces,
a combination of physical and virtual interfaces (VPNs or tunnels), or even
indirectly through multiple default routers being on the same link. For
instance, current laptops and smartphones typically have multiple access
network interfaces.

The MIF problem statement document [RFC6418] enumerates the problems into 3
categories: 1. Lack of consistent and distinctive management of configuration
elements, associated with different networks. 2. Inappropriate mixed use of
configuration elements, associated with different networks, in the course of a
particular network activity / connection. 3. Use of a particular network, not
consistent with the intent of the scenario / involved parties, leading to
connectivity failure and / or other undesired consequences.

The purpose of the MIF working group is to describe the architecture detailing
how devices attach to and operate in multiple networks. The group shall also
analyze how applications can be influenced by these existing mechanisms. The WG
shall employ and refer to existing IETF work in this area, including, for
instance, strong/weak models (RFC 1122), default address selection (RFC 6724),
ICE and other mechanisms higher layers can use for address selection, DHCP
mechanisms, Router Advertisement mechanisms, and DNS recommendations. The focus
of the working group should be on documenting the system level effects to host
IP stacks and identification of gaps between the existing IETF recommendations
and existing practice. Having completed some of its initial goals the group is
also developing the following:

1. An incrementally deployable architecture, defining a consistent approach and
recommended practices for handling sets of network configuration objects by
hosts, attached to multiple networks, which enable hosts to improve network
connectivity for the host's applications and users.   Each of these sets of
network configuration objects is referred to collectively as a provisioning
domain (PVD).

2. A set of requirements for changes  to or the uses of protocols, that provide
network configuration  information, to enable improved handling of multiple
sets of network configuration in networks and hosts. For example, requirements
for DHCPv6 options, Neighbor Discovery options etc. to communicate association
of the configuration information with particular networks.

3. In cooperation with other working groups, uses of existing protocols in
accordance with the requirements produced under item 2. Any changes of function
of protocols are out of scope.

4. A MIF API: While no changes are required for applications to run on multiple
interface hosts, a new API could provide additional services to applications
running on hosts attached to multiple networks. For instance, these services
could assist advanced applications in having greater control over first-hop,
source address and/or DNS resolver, interface and other network configuration
element selection. This API will be defined as an abstract interface
specification.   That is, specific details about mapping to operating system
primitives or programming languages will be left out, and the API will not be
specified in terms of familiar APIs (e.g., "BSD sockets API").   In
addition to the new API, the behavior of existing APIs may be changed to
improve the behavior of unmodified applications.

5. Guidelines to applications, to provide an improved connectivity experience
when the host is attached to multiple networks or there is a change in the set
of networks the host is attached to, e.g., via MIF API usage.

6.  The MIF working group will document either as part of the MIF API
specification, as part of the MIF architecture document, or in a separate
document, the issues and requirements for a high-level MIF user interface that
would allow the user to exert control over how individual applications or
application roles make use of different provisioning domains and network

7. A specification for the format, generation and usage of PVD IDs.

Network discovery and selection on lower layers as defined by RFC 5113 is out
of scope. With the exception of identifying requirements for additional DHCPv6
and/or ND options, as well as requirements for possible related changes in
these protocols, the group shall not assume any software beyond basic IP
protocol support on its peers or in network hosts. No work will be done to
enable traffic flows to move from one interface to another. The group
recognizes existing work on mechanisms that require peer or network support for
moving traffic flows such as RFC 5206, RFC 4980 and the use of multiple care-of
addresses in Mobile IPv6. This group does not work on or impact such
mechanisms.  Future work in this area requires rechartering the working group
or asking other, specialized working groups (such as DHC or 6MAN) to deal with
specific issues.