1. Richard Ogier Presented by Tom Henderson March 23, 2006
IETF Meeting - OSPF WG
MANET Extension of OSPF Using CDS Flooding draft-ogier-manet-ospf-extension-07.txt
Richard Ogier
Presented by Tom Henderson
March 23, 2006

2. Changes from Version 06 to Version 07
Dependent Neighbors are now advertised in Hellos via a new LLS TLV, to allow each router to correctly update its Dependent Selectors.
The set of Dependent Neighbors has been narrowed to include only (Backup) MDR neighbors that should become adjacent. (The set therefore now depends on AdjConnectivity.)
The procedure for deciding whether to become adjacent with a neighbor has been simplified, and no longer depends on AdjConnectivity.
The parent selection algorithm has been simplified. The (Backup) Parent is now selected to be an adjacent (Backup) MDR neighbor whenever such a neighbor exists, to avoid forming a new adjacency when possible.
The min-cost LSA algorithm has been extended to support multiple interfaces, including non-MANET interfaces.

3. Reason for adding Dependent Neighbor List (DNL) TLV in Hellos
Previously, when a router received a Database Description packet from a (Backup) MDR, it set the Dependent Selector bit to 1 for the neighbor, which indicated the neighbor should be adjacent.
However, if the router temporarily loses the neighbor (due to inactivity timer) but the neighbor never loses the router, the Dependent Selector bit is reset to 0 and the adjacency is not reestablished.
With the modification, the router will see itself in the DNL sent by the neighbor, and will know that it should reestablish the adjacency.

4. Simplified Rule for Deciding Whether to Become Adjacent
The set of Dependent Neighbors has been narrowed to include only (Backup) MDR neighbors that should become adjacent. (The set therefore now depends on AdjConnectivity.)
As a result, a router becomes adjacent with a neighbor if and only if any of the following conditions is true:
Both the router and neighbor are (Backup) MDR and the neighbor is either a Dependent Neighbor or a Dependent Selector.
The router is a (Backup) MDR and the neighbor is a child.
The neighbor is a (Backup) MDR and is the router's (Backup) Parent.

5. Simplified Rule for Selecting Parents
Parent is selected to be an existing adjacent neighbor that is an MDR, if such a neighbor exists.
Otherwise, the neighbor with the largest value of (MDR Level, RtrPri, RID) is selected as parent.
Similarly, Backup Parent is selected to be an existing adjacent neighbor that is an MDR/BMDR if such a neighbor exists (if AdjConnectivity = 2).
By giving preference to neighbors that are already adjacent, the formation of a new adjacency is avoided when possible.

6. Future Work
Experiment with link quality conditions (hysteresis) for accepting new neighbors and declaring neighbors to be routable.
When selecting MDRs and Dependent Neighbors:
Give preference to more stable links to increase adjacency lifetime.
Give preference to existing adjacencies, to avoid forming new adjacencies when possible.