3Com 2200 manual To make a copy of the type field, Xns

Packet Filter Examples A-11

Source Address and This filter operates on the source address and type fields of a frame. It Type Filter allows XNS packets to be forwarded that are from stations with an OUI of

08-00-02. To customize this filter to another OUI value, change the literal value loaded in the last pushLiteral.l instruction. Note that the OUI must be padded with an additional 00 to fill out the literal to 4 bytes. To customize this filter to another type value, change the literal value loaded into the pushLiteral.w instruction.

name	“XNS from	08-00-02”
pushField.w	12	#	Get	type	field
pushLiteral.w	0x0600	#	Load	type	value
ne		# Check for mis-match
reject		#	Toss any non-XNS frames
pushLiteral.l	0xffffff00	# Set up mask to isolate first 3
		#	bytes
pushField.l	6	#	Get	first	4 bytes of source
		#	address
and		#	Top of stack now has OUI
pushLiteral.l	0x09000200	#	Load	OUI	value
eq		#	Check for		match

Accept XNS or IP This filter operates on the type field of a frame. It allows packets to be Filter forwarded that are XNS or IP frame. Note the use of the pushTop instruction

to make a copy of the type field.

name	“Forward	IP or	XNS”
pushField.w	12	#	Get type		field
pushTop		#	Push	copy	of	type
pushLiteral.w	0x0800	#	Load	IP type		value
eq		#	Check	for	match
pushLiteral.w	0x0600	#	Load	XNS	type	value
eq		#	Check	for	match

XNS Routing Filter This filter operates on the type and data fields of a frame. It discards all XNS Routing packets.

name	“Drop XNS	Routing”
pushField.w	12	#	Get	type	field
pushLiteral.w	0x0600	#	Load	XNS	type value
ne		#	Check for non-XNS packet
accept		#	Forward if non-XNS packet
pushLiteral.b	0x01	#	Load	XNS	routing type
pushField.b	19	#	Get	XNS	type
ne		#	Check for non-XNS routing
		#	packet