User manual

8-2 Packet Filter

Filtering Overview

Packet filters are primarily used in networks that cross

organizational or corporate boundaries. They control inter-

network data transmission by accepting or rejecting the passage

of specific packets through network interfaces based on packet

header information.

When data packets are received by a network interface such as a

modem, the packet filter analyzes the packet header information

against its set of rules. Based on these rules that you define, the

filter permits the packet to pass through or discards it.

NETServer Filtering Capabilities

The NETServer supports the following filtering capabilities:

• Input and output filtering; packet filters can be created to

control either inbound or outbound data packets

• Source and destination address filtering; a packet filter can

accept or deny access based on the address of the source

and/or destination

• Protocol filtering; inbound or outbound network traffic can

be evaluated based on the protocol

• Source and destination port filtering; a packet filter can

control what services local or remote users can access

• Call filtering can control whether a packet can initiate an

outgoing call

• Route filtering can filter source and destination addresses in

packets (for example, RIP packets) that exchange routing

table information

• Established session filtering; a packet filter can permit users

to connect with a remote network without letting remote

users have access to the local network (or vice versa)