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• control-flags – Decimal number (representing a bit string) that
specifies flag bits in byte 14 of the TCP header. (Range: 0-63)
• flag-bitmask – Decimal number representing the code bits to match.
Default Setting
None
Command Mode
Extended ACL
Command Usage
• All new rules are appended to the end of the list.
• Address bitmasks are similar to a subnet mask, containing four
integers from 0 to 255, each separated by a period. The binary mask
uses 1 bits to indicate “match” and 0 bits to indicate “ignore.” The
bitmask is bitwise ANDed with the specified source IP address, and
then compared with the address for each IP packet entering the port(s)
to which this ACL has been assigned.
• You can specify both Precedence and ToS in the same rule. However,
if DSCP is used, then neither Precedence nor ToS can be specified.
• The control-code bitmask is a decimal number (representing an
equivalent bit mask) that is applied to the control code. Enter a
decimal number, where the equivalent binary bit “1” means to match
a bit and “0” means to ignore a bit. The following bits may be
specified:
- 1 (fin) – Finish
- 2 (syn) – Synchronize
- 4 (rst) – Reset
- 8 (psh) – Push
- 16 (ack) – Acknowledgement
- 32 (urg) – Urgent pointer
For example, use the code value and mask below to catch packets with
the following flags set:
- SYN flag valid, use “control-code 2 2”
- Both SYN and ACK valid, use “control-code 18 18”
- SYN valid and ACK invalid, use “control-code 2 18”