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The Problem-Solving Model

Divide-by-Half Troubleshooting

The third and final method is the

divide-by-half troubleshooting

method,

which is depicted in Figure 1.8. Divide-by-half indicates that a point between
two ends of a network problem is used as a troubleshooting reference point.
Either half may be investigated first. In this example, you start by trying to
FTP to any machine within Campus B. Depending on the results, you
can divide in half again and test. If the test results in a successful FTP to
any machine on the Campus B network, then the new point to test is another
machine on VLAN 3. If the test fails, the new testing point is to try to FTP
to a local machine. In this case, the divide-by-half method takes three steps,
just as the inside-out method does.

F I G U R E 1 . 8

Divide-by-half method

Campus A

Frame

relay

cloud

Campus B

FDDI

ring

Host B

Host C

Host D

Host F

Host G

Host E

Host H

Host J

Host K

Host I

Host L

Host X

Host Y

Host W

Host Z

Host A

VLAN 1

FTP OK

Locally (3)

(1)

(2)

VLAN 1

VLAN 3

VLAN 2

1. No FTP between
Host A and Host Z

2. No FTP between
Host A and any host
on Campus B

3. FTP works on local
network.

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