User's Manual

Teklogix 9150 Wireless Gateway User Manual 83
Chapter 4: Access Point Configuration
Protocol Filters
4.4.3 Protocol Filters
When the 9150 receives frames, it can forward or discard the messages by filtering
the protocol Type fields encapsulated in the frame. The filtering is done on three
types of Ethernet headers: Ethernet II, LLC and SNAP.
Figure 4.7 on page 84 illustrates the Ethernet header formats. The parameters to
configure these filters are described in the sections which follow.
Note: Throughout these menus, the values for all the protocol types are, by con-
vention, entered in hexadecimal, preceded by “0x”.
The fields for a basic IEEE 802.3 Ethernet frame consist of a six-byte destination
MAC address, followed by a six-byte source MAC address, and a two-byte protocol
Type. The final fields in a frame are the Data field and the FCS field (Frame Check
Sequence, or CRC). If the Type field contains a value that is greater than or equal to
“0x0600”, it is assumed to be the protocol identifier for an Ethernet II header. This
field is used to determine which protocol is being used in the frame, and this is what
can be filtered (see “Ethernet II Filters” on page 86).
If the protocol Type is less than “0x05DC”, then the value is interpreted as a Length
field instead. It is assumed that an IEEE 802.2 Logical Link Control (LLC) header is
to follow the Length. This header consists of the Destination Service/Source Service
Access Point (DSAP/SSAP) and Control fields (see “LLC Filters” on page 87).