>[оверквотинг удален]
>>> Он выставляет 2-way уже после установления соседства, когда получил свой RID от
>>> с-о-с-е-д-а R2.
>> Тогда может быть ситуация, если R1 добавил R2 в соседи; R1 отправил
>> hello который содержит R2 в соседях; R2 получил hello, после чего
>> установил 2-way отношения с R1, НО  R2 по какой-то причине
>> не добавил R1 в соседи.
>> И получится ситуация что R2 установил 2-way отношения с R1, а R1
>> не установил 2-way с R2 ???
> Да.
> Bidirectional Forwarding Detection for OSPF.

А не, затупил :)
http://tools.ietf.org/html/draft-ietf-ospf-unidirectional-li...
и потом прямиком в 1583 >>

The Hello Protocol is responsible for establishing and
        maintaining neighbor relationships.  It also ensures that
        communication between neighbors is bidirectional.  Hello packets
        are sent periodically out all router interfaces.  Bidirectional
        communication is indicated when the router sees itself listed in
        the neighbor's Hello Packet.

        On multi-access networks, the Hello Protocol elects a Designated
        Router for the network.  Among other things, the Designated

        Router controls what adjacencies will be formed over the network
        (see below).

        The Hello Protocol works differently on broadcast networks, as
        compared to non-broadcast networks.  On broadcast networks, each
        router advertises itself by periodically multicasting Hello
        Packets.  This allows neighbors to be discovered dynamically.
        These Hello Packets contain the router's view of the Designated
        Router's identity, and the list of routers whose Hello Packets
        have been seen recently.

        On non-broadcast networks some configuration information is
        necessary for the operation of the Hello Protocol.  Each router
        that may potentially become Designated Router has a list of all
        other routers attached to the network.  A router, having
        Designated Router potential, sends Hello Packets to all other
        potential Designated Routers when its interface to the non-
        broadcast network first becomes operational.  This is an attempt
        to find the Designated Router for the network.  If the router
        itself is elected Designated Router, it begins sending Hello
        Packets to all other routers attached to the network.

        After a neighbor has been discovered, bidirectional
        communication ensured, and (if on a multi-access network) a
        Designated Router elected, a decision is made regarding whether
        or not an adjacency should be formed with the neighbor (see
        Section 10.4).  An attempt is always made to establish
        adjacencies over point-to-point networks and virtual links.  The
        first step in bringing up an adjacency is to synchronize the
        neighbors' topological databases.  This is covered in the next
        section.