Deployment Guide

deny tcp
Congure a lter that drops transmission control protocol (TCP) packets meeting the lter criteria.
Syntax
deny tcp {source mask | any | host ip-address} [bit] [operator port [port]]
{destination mask | any | host ip-address} [dscp] [bit] [operator port [port]]
[count [byte] [order] [fragments] [threshold-in-msgs [count]]
To remove this lter, you have two choices:
• Use the no seq sequence-number command if you know the lter’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 /prex format (/x) or A.B.C.D. The mask, when specied 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 lter.
host ip-address Enter the keyword host then the IP address to specify a host IP address.
dscp Enter this keyword dscp to deny a packet based on the DSCP value. The range is from 0
to 63.
bit Enter a ag or combination of bits:
• ack: acknowledgement eld
• fin: nish (no more data from the user)
• psh: push function
• rst: reset the connection
• syn: synchronize sequence numbers
• urg: urgent eld
operator (OPTIONAL) Enter one of the following logical operand:
• eq = equal to
• neq = not equal to
• gt = greater than
• lt = less than
• range = inclusive range of ports (you must specify two ports for the port
command)
port port
Enter the application layer port number. Enter two port numbers if using the range logical
operand. The range is from 0 to 65535.
The following list includes some common TCP port numbers:
• 23 = Telnet
• 20 and 21 = FTP
• 25 = SMTP
Access Control Lists (ACL) 163