Detecting Network Attachment
Detecting Network Attachment WG
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When an IPv6 node detects or suspects that its
underlying link layer (L2) connectivity has or
may have undergone a change, it needs to check
whether its IP layer (L3) addressing and routing
configurations are still valid or have changed.
In the case that the L3 connectivity has changed,
the node needs to reconfigure and may need to
initiate mobility procedures, such as sending
Mobile IP binding updates. Changes in an L2
connection do not necessarily mean that
there has been change in L3 connectivity.
For the purposes of detecting network attachment,
an L3 link is defined as the topological range
within which IP packets may be sent without resorting to
forwarding. In other words, a link is the
range where a given IP configuration is valid.
In IPv6, the IP layer configuration information
includes the set of valid unicast addresses[RFC 2462,
RFC 3315], the Duplicate Address Detection (DAD)
status of the addresses[RFC 2462], valid routing
prefixes[RFC 2461], set of default routers[RFC 2461],
neighbor and destination caches[RFC 2461], multicast
listener (MLD) state[RFC 2710]. The current IPv6
stateless and stateful autoconfiguration procedures
may take a fairly long time due to delays associated
with Router Discovery and Duplicate Address Detection.
The main goal of this WG is to develop mechanisms that
reduce or avoid such delays, in cases where they are
not necessary. For example if an interface comes back
up after having been down momentarily, it can be
quicker to verify that one is still attached to the
same link than rerunning the full reconfiguration as
if one were connecting to a new L3 link and had no
previous configuration information cached.
In some wireless technologies, the link layer state
and events may not give an accurate indication of
whether or not the IP addressing configuration and
routability have changed. For example, a host may
be able to see a base station but still be unable to
deliver or receive IP packets within the L3 link.
Moreover, a hardware indication that a radio link
is up does not necessarily mean that all link layer
configuration, such as authentication or virtual
LAN connectivity has been completed. Therefore
detecting network attachment requires not only
change detection but IP layer connectivity testing.
The purpose of the DNA working group is to define
standards track and BCP documents that allow hosts
to detect their IP layer configuration and
connectivity status quickly, proposing some
optimization to the current specifications that
would allow a host to reconfigure its IPv6 layer
faster than today.
The group will define a set of goals for detecting
network attachment, describing existing issues
and important properties of potential solutions.
The working group will describe best current practice
for nodes making use of existing information
for detecting network attachment.
The working group will define a set of extensions to the
current IPv6 configuration protocols [RFC 2461, 2462,
possibly RFC 3315] that allow the nodes to
discover whether L3 configuration or connectivity
may have changed more reliably and easily than today.
Initiation of L3 link change detection procedures can
be achieved either through reception (or lack of
reception) of messages at the IP layer or through
indications from other layers. The working group
will produce an informational document that
contains a catalogue of the indications currently
available from a subset of wireless link layer
The DNA WG will not define new procedures or APIs
related to link layers.
* Define goals for detecting network attachment in IPv6
* Specify recommendations for detecting network
attachment and L3 link change in IPv6 networks (BCP).
* Define a protocol extension for detecting network
attachment and L3 link change in IPv6 networks
more reliably and easily (Standards Track).
* Document existing link layer (L2) information which is
useful to start detecting network attachment