Subject: Protocol Action: A Link Layer Tunneling Mechanism for Unidirectional Links to Proposed Standard

From: The IESG <[email-masked]>
Date: Sat, 10 Feb 2001 17:27:09 -0500

The IESG has approved the Internet-Draft 'A Link Layer Tunneling
Mechanism for Unidirectional Links' <draft-ietf-udlr-lltunnel-06.txt>
as a Proposed Standard.  This document is the product of the
UniDirectional Link Routing Working Group.  The IESG contact persons
are David Oran and Rob Coltun.

Technical Summary

This document describes a link layer tunneling mechanism that allows
nodes which are directly connected by a unidirectional link (feeds
and receivers, see Section 2 for terminology) to send datagrams as if
they were connected to a bidirectional link. We present a generic
topology with a tunneling mechanism that supports multiple feeds and
receivers.

The tunneling mechanism requires that all nodes have an additional
interface to an IP interconnected infrastructure.

The tunneling mechanism is implemented at the link layer of the
interface of every node connected to the unidirectional link. The aim
is to hide from higher layers, i.e. the network layer and above, the
unidirectional nature of the link. The tunneling mechanism also
includes an automatic tunnel configuration protocol that allows nodes
to come up/down at any time.

Generic Routing Encapsulation [rfc2784] is suggested as the tunneling
mechanism as it provides a means for carrying IP, ARP datagrams, and
any other layer-3 protocol between nodes.

The tunneling mechanism described in this document was discussed and
agreed upon by the UDLR working group.

Working Group Summary

The UDLR work group first proposed to modify routing protocols
in order to support routing in the presence of unidirectional
links in the Internet. This proposal was not adopted as a
short term solution because it required to bring modification
to most routing protocols.

Then, the UDLR work proposed the Link Layer Tunneling Mechanism
that emulates a bidirectional connectivity between nodes connected
to a unidirectional link. This mechanism is implemented at link
layer level and is transparent to the IP layer. No more modifications
are required to routing protocols because IP layers see the link as
bidirectional.

This mechanism can be implemented either in hosts or routers in
order to provide full IP connectivity via a unidirectional link.

The first last call was issued in April 99. From that date on,
a security consideration section was added, an editorial and a
technical review were initiated on the mailing list. The current
document represents the consensus of the WG. See the udlr archive
for the discussions
(http://www-sop.inria.fr/rodeo/udlr/archive/threads.html)

Protocol Quality

Thie specification was reviewed for the IESG by Dave Oran.

There are four known different implementations. These
implementations come from Inria in France, the Wide project
in Japan, Sony and Hitachi.
They were all implemented independently by separate teams and
interoperability tests were led successfully.

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