Monthly Archives: July 2013

3.5.d Implement and troubleshoot operations

3.5     Dual Finite State Machine (FSM)
The DUAL finite state machine embodies the decision process for all
route computations. It tracks all routes advertised by all neighbors.
The distance information, known as a metric, is used by DUAL to select
efficient loop free paths. DUAL selects routes to be inserted into a
routing table based on feasible successors. A successor is a
neighboring router used for packet forwarding that has least cost path
to a destination that is guaranteed not to be part of a routing loop.
When there are no feasible successors but there are neighbors
advertising the destination, a recalculation must occur to determine a
new successor.

3.5.d Implement and troubleshoot operations


Enhanced Interior Gateway Routing Protocol.

Active state
A route that is currently in an unresolved or un-converged
state. The term active is used because the router is actively
attempting to compute an SDAG.

an sdag is a succesor directed acyclic graph…

A DAG is a directed graph with no directed cycles. That is, it is formed by a collection of vertices and directed edges, each edge connecting one vertex to another, such that there is no way to start at some vertex v and follow a sequence of edges that eventually loops back to v again


Successor Directed Acyclic Graph(SDAG)
When a route to a destination becomes unreachable, it is required
that a router computes a directed graph with respect to the
destination. This decision requires the router to select from the
neighbor topology table a feasible successor.

eigrp begins to open…

check it out… russ white and company prepare to open eigrp…

The DUAL Diffusing Update Algorithm
The Diffusing Update Algorithm (DUAL) provides a loop-free path through
a network made up of nodes and edges (routers and links) at every
instant throughout a route computation. This allows all routers
involved in a topology change to synchronize at the same time. Routers
that are not affected by topology changes are not involved in the
recalculation. The convergence time with DUAL rivals that of any other
existing routing protocol.

3.1     Algorithm Description

The Diffusing Update Algorithm (DUAL) is used by EIGRP to achieve fast
loop-free convergence with little cost in overhead, allowing EIGRP to
provide convergence rates comparable, and in some cases better than,
most common link state protocols[7]. In addition, only nodes that are
affected by a topology change take corrective action which allows DUAL
to have good scaling properties, reduced overhead, and lower complexity
than other IGP protocols, and requiring less information to be