AN Lesson-18

Configuring Packet Filters

Packet Filters

•  Packet filters are rules defined for a particular interface that allow or restrict traffic by source address, destination address, direction, or protocol type.
• You can think of packet filters as holes you create in a firewall to allow external clients access to specific internal services.

The packet filtering feature in Routing And Remote Access is based on exceptions. You can set packet filters per interface and configure them to do one of the following:

■ Pass through all traffic except packets prohibited by filters.

■ Discard all traffic except packets allowed by filters.

Types:

In Windows Server 2003, packet filters occur in two types: input filters and output filters.

• Input filters restrict traffic entering into an interface from the immediately attached network.
• Output filters restrict traffic being sent from an interface onto the immediately attached network.

 Figure below represents an example of an input filter denying all packets except those destined for TCP port 1723 and IP address 207.46.22.1.

Creating Packet Filters

You create packet filters in the Routing And Remote Access console through the IP Routing node. Within the IP Routing node, select either the General node or the NAT/Basic Firewall node. Packet filters are then configured through the properties dialog box of the appropriate interface, listed in the details pane.

Note that the NAT/Basic Firewall node allows you to create packet filters only for external interfaces, whereas the General node allows you to create packet filters for any interface.

To add a packet filter, complete the following steps:

1. Open the Routing And Remote Access console.

2. In the console tree, expand IP Routing, and click the General node.

3. In the details pane, right-click the interface on which you want to add a filter, and then click Properties.

The interface properties dialog box opens, shown in Figure below.

4. On the General tab, click either Inbound Filters or Outbound Filters.

5. In the Inbound Filters dialog box or the Outbound Filters dialog box, click New.

6. In the Add IP Filter dialog box, type the settings for the filter, and then click OK.

7. In Filter Action, select the appropriate filter action, and then click OK.