3Com 4007, Руководство по внедрению, Страница: 335 / 684

Custom Packet Filter Examples 335
Source Address and
Type Filter
This filter operates on the source address and type fields of a frame. It
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. You must pad the OUI
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.
Accept XNS or IP
Filter
This filter operates on the type field of a frame. It allows packets to be
forwarded that are XNS or IP frame. The pushTop instruction makes a
copy of the type field.
XNS Routing Filter
This filter operates on the type and data fields of a frame. It discards all
XNS routing packets.
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.
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.
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.