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10. Advanced Allow/Deny Filters
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In /etc/csf.allow and /etc/csf.deny you can add more complex port and ip
filters using the following format (you must specify a port AND an IP address):

tcp/udp|in/out|s/d=port|s/d=ip|u=uid

Broken down:

tcp/udp : EITHER tcp OR udp OR icmp protocol
in/out : EITHER incoming OR outgoing connections
s/d=port : EITHER source OR destination port number (or ICMP type)
(use a _ for a port range, e.g. 2000_3000)
s/d=ip : EITHER source OR destination IP address
u/g=UID : EITHER UID or GID of source packet, implies outgoing connections,
s/d=IP value is ignored

Note: ICMP filtering uses the "port" for s/d=port to set the ICMP type.
Whether you use s or d is not relevant as either simply uses the iptables
--icmp-type option. Use "iptables -p icmp -h" for a list of valid ICMP types.
Only one type per filter is supported

Examples:

# TCP connections inbound to port 3306 from IP 11.22.33.44
tcp|in|d=3306|s=11.22.33.44

# TCP connections outbound to port 22 on IP 11.22.33.44
tcp|out|d=22|d=11.22.33.44

Note| If omitted, the default protocol is set to "tcp", the default connection
direction is set to "in", so|

# TCP connections inbound to port 22 from IP 44.33.22.11
d=22|s=44.33.22.11

# TCP connections outbound to port 80 from UID 99
tcp|out|d=80||u=99

# ICMP connections inbound for type ping from 44.33.22.11
icmp|in|d=ping|s=44.33.22.11

# TCP connections inbound to port 22 from Dynamic DNS address
# http://www.configserver.com (for use in csf.dyndns only)
tcp|in|d=22|s=www.configserver.com