3Com 4007, Implementation Manual, Page: 310 / 684

310 C
HAPTER
15: P
ACKET
F
ILTERING
Placing a filter on the receive path confines the packet to the segment
that it originated from if it does not meet the forwarding criteria. Placing
a filter on the
transmit path prohibits a packet from accessing certain
segments unless it meets the forwarding criteria. The module discards any
packet that does not meet the forwarding criteria on the
transmit path.
If you want to filter packets destined for the switch itself (for example,
ping packets or Telnet packets), you must use the
receive internal path.
They are not filtered on the receive all path.
Custom Packet Filters You create custom packet filters by writing a packet filter definition .
Software implements custom filters. Consequently, use custom filters only
on ports and paths that need them. Processing too many frames in
software can affect performance on the ports where custom filters are
assigned.
If you are trying to filter a certain type of broadcast or multicast packet
assign the filter to either the TxM or the RxM paths, allowing only unicast
traffic to bypass the filter.
Each packet-processing path on a port may have a unique custom packet
filter definition or may share a definition with other ports on the module.
Custom packet filter definitions are written in the
packet filter language,
which allows you to construct complex logical expressions.
After you write a packet filter definition, you load it onto a module; the
corresponding port assignments are preserved in the nonvolatile memory
(NVRAM) of the module, thus ensuring that the packet filter
configuration for each module is saved across system or module reboots
and power failures.