User`s manual

User’s Manual 267
port-bitmask Decimal number representing the port bits to match. (Range: 0-65535)
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. (Range: 0-63)
Default
None
Command Mode
Extended ACL
Usage Guidelines
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. 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”
Example
This example accepts any incoming packets if the source address is within subnet 10.7.1.x. For example, if
the rule is matched; For example, the rule (10.7.1.0 & 255.255.255.0) equals the masked address (10.7.1.2
& 255.255.255.0), the packet passes through.