378 Chapter 10: X.25/Frame Relay Topologies
Scenario Answers
Answer to Scenario 1
Figure 10-28 shows one solution. There are other ways of meeting the company's requirements.
This is only a recommended solution that meets the requirements placed on the CCDP.
Figure 10-28
Suggested Solution for Scenario 1
1
The IP address assigned to the central site is 1.1.1.1. Meeting the requirement would
require a 30-bit subnet mask, or 255.255.255.252, which leaves you with two valid IP
addresses, 1.1.1.1 and 1.1.1.2. (1.1.1.0 and 1.1.1.3 are unusable with this 30-bit mask.)
The 1.1.1.2 address must be the ISP's address because 1.1.1.1 is being used at the local
company router. It often happens that a customer knows only their IP address (1.1.1.1) and
not the ISP's address. The engineer needs to determine by the network mask what the IP
address is at the ISP.
-- Central site: Notice in Figure 10-28 that the IP address range used for the
central site is 199.198.197.0-64.
That has been determined because a 26-bit mask or 255.255.255.192 is being used. This
effectively leaves about 61 addresses for devices, more than meeting the customer's
requirement.
Central site
Number this interface 1.1.1.1 from Internet
Ethernet interface -
199.198.197.65/26
199.198.197.178/29
Ethernet interface -
199.198.197.129/28
199.198.197.179/29
Ethernet interface -
199.198.197.145/28
199.198.197.180/29
Ethernet interface -
199.198.197.161/28
199.198.197.181/29
199.198.197.177/29
Ethernet interface -
199.198.197.1/26
Interface Serial0
encapsulation frame-relay
Remote Site 1
50 users
Remote Site 2
10 users
Remote Site 3
10 users
Remote Site 4
10 users
87200333.book Page 378 Wednesday, August 22, 2001 2:53 PM