3Com CoreBuilder 3500, Руководство по внедрению, Страница: 228 / 592

228 C
HAPTER
10: P
ACKET
F
ILTERING
Packet Filter Opcodes Opcodes are instructions used in packet filter definitions. The available
opcodes are described in Table 33.
Table 33 Packet Filtering Opcodes
Opcode
Memory
Requirements
Description
name “<name>” 2 + n bytes,
where n is the length
of the <name>
Assigns a user-defined <name> to the packet filter.
The name may be any sequence of ASCII characters
other than quotation marks. The name is limited to
32 characters. You can include only a single name
statement in each packet filter program.
pushField.size <offset> 3 bytes Pushes a field from the target packet onto the stack.
Packet data starting at <offset> is copied onto the
stack. The most significant byte of the field is the byte
at the specified offset. The size field of the instruction
determines the number of bytes pushed. The pushField
instruction provides direct access to any 1, 2, 4, or 6
byte (.b, .w, .l, or .a) field contained within the first
64 bytes of the target packet.
Specify the offset as 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”.
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”.