Introduction

The exercise is part of convergence scenario in a large hierarchical network shown below:

Network has almost converged and Core-A has already selected Core-B as its successor, resulting in update packets sent to DR routers and poison update sent to Core-B.

Exercise

Compute the EIGRP metric that Core-A reports to DR routers for RO-11 and DR-1 LAN. Compute the EIGRP metric for these destinations on DR-2 and DR-3 and verify that they select the paths over primary PVCs.

Additional data

To compute the metrics, you need delay and bandwidth parameters of all (sub)interface in the network. These parameters are specified at the beginning of Case Study #2 in Chapter 5 and are summarized in the table below for your convenience.

Link	Bandwidth	Delay
RO to DR	64 kbps	20000 msec
Primary PVC DR to Core	512 kbps	10000 msec
Shadow PVC DR to Core	256 kbps	40000 msec
Server LAN (Token Ring)	16 Mbps	630 msec
all LAN interfaces	10 Mbps	1000 msec

Solution

Core-A has already selected Core-B as its successor. The distance of RO-11 LAN and DR-1 LAN on Core-A is thus

Destination	Minimum Bandwidth	Total Delay
RO-11 LAN	64 kbps	61630
DR-1 LAN	256 kbps	41630

Core-B has already reported its distance to the same destinations in Step #6 of the convergence scenario. The distance reported by Core-B is:

Destination	Minimum Bandwidth	Total Delay
RO-11 LAN	64 kbps	61000
DR-1 LAN	256 kbps	41000

DR-2 receives update from Core-A over shadow PVC and keeps its current successor (Core-B) which is reachable over primary PVC. DR-3 receives updates from Core-A over primary PVC resulting in the following EIGRP topology table on DR-3:

Destination	Reported by Core		Distance on DR-3
	Bandwidth	Delay	Bandwidth	Delay
RO-11 LAN over Core-A	64 kbps	61000	64 kbps	101000
DR-1 LAN over Core-A	256 kbps	41000	256 kbps	81000
RO-11 LAN over Core-B	64 kbps	61630	64 kbps	81630
DR-1 LAN over Core-B	256 kbps	41630	256 kbps	61630

Based on the contents of its EIGRP topology table, DR-3 selects Core-B (reachable over primary PVC) as its successor for all destinations under discussion.

LAN subnets on DR-1 and RO-11 are thus reachable over primary PVC from DR-2 and DR-3.