C
HAPTER
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| Access Control Lists
IPv4 ACLs
– 947 –
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.
time-range-name - Name of the time range.
(Range: 1-16 characters)
DEFAULT SETTING
None
COMMAND MODE
Extended IPv4 ACL
COMMAND USAGE
◆ All new rules are appended to the end of the list.
◆ Address bit masks 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 bit
mask 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”
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