Avocent Cyclades-PR2000 Exterior Router, Let Mail out, Let Telnet Connections Out

Cyclades-PR2000

Exterior Router

The exterior router is the network’s first defense against attacks. For this reason, it is reasonable to prohibit all packets except for those explicitly allowed. This is done by choosing the Default Scope to be Deny. Thus, ALL desired traffic must be expressly allowed by the rules in the rule list.

DENY

Let

e-mail out

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DENY

Let Telnet

Connections Out

FIGURE 12.3 DENY AS DEFAULT SCOPE

In Figure 12.3, a conceptual equivalent of the interface is shown. All packets except those which fall into the holes in the ball will be denied entry in to or out of the network.

Chapter 12 - Filters and Rules 99