Enterasys Networks 6H3xx Betriebsanweisung

Example 3, Filtering Traffic According to a Layer 4 Classification Rule

13-32

VLAN Operation and Network Applications

13.14 EXAMPLE 3, FILTERING TRAFFIC ACCORDING TO A LAYER 4

CLASSIFICATION RULE

This example illustrates how to filter out broadcast transmissions at Layer 4 from other parts of a
network.

In this example, illustrated in

Figure 13-16

, switches S1 and S2 have already been configured and

operating. However, it was discovered that the Routing Information Protocol (RIP) broadcast
frames from routers R1 and R2 were flooding the subnetwork of Switches S1 and S2.

Figure 13-16

Example 5, Filtering Traffic According to a Classification

13.14.1 Solving the Problem

To prevent the RIP broadcasts from flooding the users’ terminals connected to S1 and S2, a new
VLAN will be added to each switch, but not assigned to any ports (creating a Null VLAN). Then
each switch will be configured with a Layer 4 classification rule that will classify each RIP
broadcast frame received on Port 25 of each switch to the Null VLAN. Since the Null VLAN is not
associated with any ports, the frame will be dropped and not transmitted out any port.

In this example, the switches have already been configured and operating. The following covers
only those steps needed to configure each switch to eliminate the problem.

Switches 1 and 2

Each switch is set as follows:

1. A VLAN is added to the list of VLANs in the Module/VLAN Configuration screen and assigned

to an FDB ID. In this example, the switch is set as follows:

•

VLAN ID 99, FDB ID 99, with a VLAN Name of Null VLAN

2599_27

Users

Port 25