Packet Filtering Overview; What Can You Filter - 3Com corebuilder 3500 Implementation Manual

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Packet Filtering

The packet filtering feature allows a switch to make a permit-or-deny

decision for each packet based on the packet contents. Use packet filters

to control traffic on your network segments to:

Improve LAN performance.

Implement LAN security controls.

Shape traffic flow to emulate virtual LAN (VLAN) behavior. See

Before you create a packet filter, you must decide which part of the

packet you want to use for your filtering decisions. You can filter on any

data in the first 64 bytes of the frame. You can filter Ethernet, Fast

Ethernet, Fiber Distributed Data Interface (FDDI), or Gigabit Ethernet

frames by the destination address, source address, type, length, or any

attribute within the first 64 bytes. Keep in mind that the offsets may

differ between FDDI and Ethernet, so the same filter may not work on all

interfaces. Ethernet and FDDI packet fields are shown in Figure 35.

Figure 35 Ethernet and FDDI Packet Fields

(Ethernet Type field if > 1500;

802.3 Length field if - 1500)

Source Address

Internal Packet Data

Filter First 64 Bytes of Frame

Internal Packet Data

Filter First 64 Bytes of Frame

Ethernet Packet