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Appendix E: Understanding IP and IP addressing 159
DMS-100 Family EIU User Guide TELECOM12
Figure 38 Simple network numbering
The Corporate Networking group assigns a class A address to each of its
departments. The three Ethernet networks on 20.0, 21.0, and 20.0.22.0 are
sufficient to interconnect most of the organization. The Corporate Networking
group reserves network 20.0.0.0 for its own use to interconnect the corporate
computers. Each of these departments has more than 16 million IP addresses
available for its personal computers, workstations, and hosts.
A fourth Ethernet goes to the Engineering group, which is assigned network
number 23. Since this group has multiple networks, they use subnetworking to
allocate their own Ethernet networks. They use the entire second octet in the
IP address to designate the subnetwork. They use subnetworks 23.1.0.0
through 23.4.0.0. This requires a subnet mask of 255.255.0.0.
The Ethernet linking the two routers (23.1.0.0) is a backbone between the two
group routers. Other addresses are used for individual workstations.
In this case, the administrators of both routers have to be aware of the
subnetworking strategy chosen by the Engineering group. The Corporate
Networking group router has to be aware that anything for 23.1.x should be
forwarded on its Ethernet, and that 23.2.x, 23.3.x, and 23.4.x addresses should
be directed to the other router for distribution and forwarding using 23.1.0.0.
Firewalls and network security
An important consideration when planning a network is security. There are
many ways security can be compromised, the most important being access
across an internetwork, from beyond the network borders.
Nortel recommends that the operating company, as a minimal precaution,
integrate intermediate security servers with encryption to avoid unauthorized
access to the switch. For alternative approaches, contact a Nortel
20.0.0.0
21.0.0.0
22.0.0.0
Corporate
router
23.4.0.0
23.3.0.0
23.2.0.0
Engineering
router
23.1.0.0