# An Example Network and Description

## Example Network Map and General Notes

The below network map is a fictional network. This network should provide examples of several of the common functions of a linux box in networking situations. The hostnames used in the documentation are taken from this network map. Where practical, I have tried to simulate real-world situations throughout the documentation, to ease the practical application of the concepts.

Because this guide focusses on linux networking, I have omitted discussion of the ISDN routers and unless relevant, the layer 2 devices (hubs and switches). The remaining hosts on the example network can be broken into three main categories: single-homed hosts (servers and workstations), masquerading (cf. NAT) routers, and public routers. For those viewing the above netmap from a security perspective, &wan-gw; and &masq-gw; would both run packet filters (at least), which turns the network into a traditional screened-subnet firewall.

The LAN shown above is a common leaf-network scenario for business offices. Frequently, there are one or two machines on a public network segment, a masquerading firewall, and one or more networks behind the masquerading firewall. Please do not consider this example network the only way to interconnect devices. The above is one method of designing a network--there are many practical issues to weigh in network design. I am deliberately skirting the issue of network design here and proposing an example network similar to or a superset of a commonly found network design.

It is rare for a business which is not an ISP to own a class C sized network today, but I have nonetheless chosen a class C sized public network as our fictitious company's network.

## Example Network Addressing Charts

In addition to the network map above, you may find the following network address and host address information handy as you read through the various examples and documentation based on this fictional network.

### Example Network; Network Addressing

network address | function
--- | ---
205.254.211.0/24 | public ISP-allocated network
192.168.100.0/24 | internal server network
192.168.99.0/24 | main office desktop network
192.168.98.0/24 | branch office desktop network

Host addressing information is summarized in this table. follows.

### Example Network; Host Addressing

hostname | interface | IP address | MAC address
--- | --- | --- | ---
&isolde; | eth0 | 192.168.100.17/24 | 00:80:c8:e8:4b:8e
&tristan; | eth0 | 192.168.99.35/24 | 00:80:c8:f8:4a:51
&morgan; | eth0 | 192.168.98.82/24 | 00:80:c8:f8:4a:53
&masq-gw; | eth0 | 192.168.100.254/24 | 00:80:c8:f8:5c:71
&masq-gw; | eth1 | 205.254.211.179/24 | 00:80:c8:f8:5c:72
&masq-gw; | eth2 | 192.168.99.254/24 | 00:80:c8:f8:5c:73
&masq-gw; | eth3 | 192.168.100.2/30 | 00:80:c8:f8:5c:74
&wan-gw; | eth0 | 205.254.211.254/24 | [ unknown ]
&wan-gw; | wan0 | 205.254.209.73/30 | [ n/a ]
&isdn-router; | (Ethernet) | 192.168.99.1/24 | 00:c0:7b:45:6a:39
&branch-router; | (Ethernet) | 192.168.98.254/24 | 00:c0:7b:37:af:91
&service-router; | (Ethernet) | 192.168.100.1/24 | 00:c0:7b:7d:00:c8

I have referred liberally to this example network throughout this documentation. Any example commands in the documentation assume the network configuration as shown on this network map.

Additionally, hosts which are not part of this (fictional) network but appear in the documentation will appear under the names &real-server; and &real-client;. This convention exists simply to disambiguate real-world examples from the machines in the fictional network.