3Com corebuilder 3500 Implementation Manual page 232

232 C 10: P
HAPTER ACKET
Table 33 Packet Filtering Opcodes (continued)
Opcode
accept
reject
shiftl (shift left)
shiftr (shift right)
F
ILTERING
Memory
Requirements
1 byte
1 byte
1 byte
1 byte
Description
Conditionally accepts the packet that is being
examined. Pops a byte from the stack. If its value is
non-zero, the packet is accepted and evaluation of the
filter ends immediately; otherwise, filter evaluation
continues with the next instruction.
Use accept with and and or operators when you
have sequential tests and you would like the filter to
accept a packet before the entire expression has been
evaluated. Using accept can significantly improve the
performance of certain types of filters. See
"Implementing Sequential Tests in a Packet
elsewhere in the chapter for more information.
Conditionally rejects the packet being examined. Pops
a byte from the stack. If its value is non-zero, the
packet is rejected and filter evaluation ends
immediately; otherwise, the filter evaluation continues
with the next instruction.
Use reject with and and or operators when you
have sequential tests and you would like the filter to
reject a packet before the entire expression has been
evaluated. Using reject can significantly improve the
performance of certain types of filters. See
"Implementing Sequential Tests in a Packet
earlier in the chapter for more information.
Pops two values from the stack and shifts the first
operand left by the number of bits specified by the
second operand. Bits shifted out of the left side of the
operand are discarded, and zeros are shifted in from
the right. The resulting value is pushed back onto the
stack. The contents of the top of the stack determines
the size of the first operand and the size of the result.
The second operand is always 1 byte and only the low
5 bits of the byte are used as the shift count.
Pops two values from the stack and shifts the first
operand right by the number of bits specified by the
second operand. Bits shifted out of the right side of the
operand are discarded, and zeros are shifted in from
the left. The resulting value is pushed back onto the
stack. The contents of the top of the stack determines
the size of the first operand and the size of the result.
The second operand is always 1 byte and only the low
5 bits of the byte are used as the shift count.
Filter"
Filter"