DUAL EIGRP Terminology

DUAL EIGRP Terminology

·  Selects lowest-cost, loop-free paths to each destination

· AD = cost between the next-hop router and the destination

· FD = cost from local router = AD of next-hop router + cost between the local router and the next-hop router

· Lowest-cost = lowest FD

· (Current) successor = next-hop router with lowest-cost, loop free path

· Feasible successor = backup router with loop-free path (AD of feasible successor must be less than FD of current successor route)

 

R1#sho ip eigrp topology

IP-EIGRP Topology Table for AS(100)/ID(10.1.1.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,

       r - reply Status, s - sia Status

P 10.3.3.0/24, 1 successors, FD is 332800

          FD= cost b/w r1 & r3      AD= cost b/w r2 & r3

 via 10.1.1.2 (332800/307200), FastEthernet0/0

P 10.2.2.0/24, 1 successors, FD is 307200

via 10.1.1.2 (307200/281600), FastEthernet0/0

P 10.1.1.0/24, 1 successors, FD is 281600

via Connected, FastEthernet0/0

A successor  is a neighboring router that has a least-cost path to

a destination (the lowest FD)

 

DUAL also keeps backup paths to each destination in case the successor is no longer available and its called feasible successor. To qualify as a feasible successor, a next-hop router must have an AD less than the FD of the current successor route