3Com CoreBuilder 3500, Руководство по внедрению, Страница: 238 / 592

238 C
HAPTER
10: P
ACKET
F
ILTERING
Type Filter This filter operates on the type field of a frame. It allows packets to be
forwarded that are IP frames. To customize this filter to another type
value, change the literal value loaded in the pushLiteral.w instruction.
Ethernet Type IPX and
Multicast Filter
This filter rejects frames that have either a Novell IPX Ethernet type field
(8134 hex) or a multicast destination address.
Multiple Destination
Address Filter
This filter operates on the destination address field of a frame. It allows
packets to be forwarded that are destined for one of four different
stations. To tailor this filter to other destinations, change the literal values.
name “Forward IP frames”
pushField.w 12 # Get type field.
pushLiteral.w 0x0800 # Load IP type value.
eq # Check for match.
name “Type > 900 or Multicast”
pushField.w 12 # Get type field.
pushLiteral.w 0x900 # Push type value to test
# against.
gt # Is type field > 900 (hex)?
reject # If yes: reject frame (done).
pushLiteral.b 0x01 # Multicast bit is low-order
pushField.b 0 # bit
and # Get 1 st byte of destination
not # Isolate multicast bit
# Top of stack 1 to accept,
# 0 to reject
name “Forward to four stations”
pushField.a 0 # Get destination address.
pushTop # Make 3 copies of address.
pushTop #
pushTop #
pushLiteral.a 0x367002010203 # Load allowed destination
# address.
eq # Check for match.
accept # Forward if valid address.
pushLiteral.a 0x468462236526 # Load allowed destination
# address.
eq # Check for match.
accept # Forward if valid address.
pushLiteral.a 0x347872927352 # Load allowed destination
# address.
eq # Check for match.
accept # Forward if valid address.
pushLiteral.a 0x080239572897 # Load allowed destination
# address.
eq # Check for match.