3Com 4007, Руководство по внедрению, Страница: 324 / 684

324 C
HAPTER
15: P
ACKET
F
ILTERING
pushLiteral.size
<value> 1 (.b)
2 (.w)
4 (.l)
6 (.a) bytes
depending on the
size of <value>
plus 1 byte for a
total of 2, 3, 5, or 7
bytes Pushes a literal constant <value> onto the stack. The
most significant byte of the <value> is the first byte of
the literal. Bytes are copied directly from the operand
onto the stack. The size field of the instruction
determines number of bytes pushed.
Specify the value as either an octal, decimal, or
hexadecimal number.
■
Precede an octal number by a “0”.
■
Precede a hexadecimal number by either “0x” or
“0X”.
■
Use either upper or lower case letters for the
hexadecimal digits “a” through “f”.
pushTop 1 byte Pushes the current top of the stack onto the stack (that
is, it reads the top of the stack and pushes the value
onto the stack, which effectively duplicates the item
currently on top of the stack). The size of the contents
of the stack determines the size of the push.
Use
pushTop
for each additional comparison you
intend to make with the current top of the stack. The
pushTop
instruction makes a copy of the field more
efficiently than if you use a second
pushField
instruction.
If you are writing a filter that is going to check the
same offset more than once, such as checking the
Ethernet type field to filter multiple protocols, use the
following guidelines. Assume that you want to filter
DEC LAT, IP, and ARP traffic on a port.
Table 66 Packet Filtering Opcodes (continued)
Opcode
Memory
Requirements
Description