Administrator Guide

deny tcp
Configure a filter that drops transmission control protocol (TCP) packets meeting the filter criteria.
Syntax
deny tcp {source mask | any | host ip-address} [bit] [operator port [port]]
{destination mask | any | host ip-address} [ttl operator] [dscp] [bit]
[operator port [port]] [count [bytes] [order] [fragments] [monitor] [no-drop]
To remove this filter, you have two choices:
• Use the no seq sequence-number command if you know the filter’s sequence number.
• Use the no deny tcp {source mask | any | host ip-address} {destination mask |
any | host ip-address} command.
Parameters
source Enter the IP address of the network or host from which the packets are sent.
mask Enter a network mask in /prefix format (/x) or A.B.C.D. The mask, when specified in
A.B.C.D format, may be either contiguous or non-contiguous.
any Enter the keyword any to specify that all routes are subject to the filter.
host ip-address Enter the keyword host then the IP address to specify a host IP address.
ttl Enter the keyword ttl to deny a packet based on the time to live value. The range is
from 1 to 255.
operator Enter one of the following logical operand:
• eq(equal to) — matches packets that contain a ttl value that is equal to the specified
ttl value.
• neq(not equal to) — matches packets that contain a ttl value that is not equal to the
specified ttl value.
• gt(greater than) — matches packets that contain a ttl value that is greater than the
specified ttl value.
• lt (less than) — matches packets that contain a ttl value that is less than the
specified ttl value.
• range(inclusive range of values) — matches packets that contain a ttl value that
falls between the specified range of ttl values.
dscp Enter this keyword dscp to deny a packet based on the DSCP value. The range is from 0
to 63.
bit Enter a flag or combination of bits:
• ack: acknowledgement field
• fin: finish (no more data from the user)
• psh: push function
• rst: reset the connection
• syn: synchronize sequence numbers
• urg: urgent field
• established: datagram of established TCP session
Use the established flag to match only ACK and RST flags of established TCP
session.
You cannot use established along with the other control flags
While using the established flag in an ACL rule, all the other TCP control flags are
masked, to avoid redundant TCP control flags configuration in a single rule. When you use
any TCP control flag in an ACL rule, established is masked and other control flags are
available.
operator (OPTIONAL) Enter one of the following logical operand:
• eq = equal to
• neq = not equal to
• gt = greater than
194 Access Control Lists (ACL)