Static Routing and Distance Vector Routing Protocols - CCIE Routing and Switching Exam Certification Guide - page 345

Example 7-24 EIGRP Neighbor Database

Router#show ip eigrp neighbor
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq Type
(sec) (ms) Cnt Num
1 172.17.1.1 Se0 11 00:11:27 16 200 0 2
0 172.17.2.1 Et0 12 00:16:11 22 200 0 3

Address Interface Hold Uptime

RTP

RTP manages EIGRP packets, ensures reliable delivery of route updates, and uses sequence
numbers to ensure ordered delivery. Update packets are sent using multicast address
(224.0.0.10). Updates are acknowledged using unicast hello packets with no data.

DUAL

DUAL selects paths and guarantees freedom from routing loops. DUAL was developed by
Dr. J.J. Garcia Luna-Aceves. DUAL was mathematically proven to result in a loop-free topology
that provides no need for periodic updates or route holddown mechanisms that make
convergence slower.

DUAL selects a best path and a second best path to reach a destination. The best path selected
by DUAL is called the successor , and the second best path (if available) is the feasible succes-
sor . The feasible distance is the lowest calculated metric of a path to reach the destination. The
feasible distance can be viewed in the topology table, as shown in Example 7-25. The example
also shows two paths (Ethernet 0 and Ethernet 1) to reach 172.16.4.0/30. Because the paths have
different metrics, only one successor is chosen.

Example 7-25 Feasible Distance as Shown in EIGRP Topology Table

Router8#show ip eigrp topology
IP-EIGRP Topology Table for AS(100)/ID(172.16.3.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status

P P 172.16.4.0/30, 1 successors, FD is 2195456

via 172.16.1.1 (2195456/2169856), Ethernet0
via 172.16.5.1 (2376193/2348271), Ethernet1
P 172.16.1.0/24, 1 successors, FD is 281600
via Connected, Ethernet0

2195456

P 281600