--dport — Sets the destination port for the packet.

To configure this option, use a network service name (such as www or smtp); a port number; or a range of port numbers.

To specify a range of port numbers, separate the two numbers with a colon (:). For example: -p tcp --dport 3000:3200. The largest acceptable valid range is 0:65535.

Use an exclamation point character (!) after the --dport option to match all packets that do not use that network service or port.

To browse the names and aliases of network services and the port numbers they use, view the /etc/services file.

The --destination-port match option is synonymous with --dport.

--sport — Sets the source port of the packet using the same options as --dport. The --source-port match option is synonymous with --sport.

--syn — Applies to all TCP packets designed to initiate communication, commonly called SYN packets. Any packets that carry a data payload are not touched.

Use an exclamation point character (!) after the --syn option to match all non-SYN packets.

--tcp-flags <tested flag list> <set flag list> — Allows TCP packets that have specific bits (flags) set, to match a rule.

The --tcp-flags match option accepts two parameters. The first parameter is the mask; a comma-separated list of flags to be examined in the packet. The second parameter is a comma-separated list of flags that must be set for the rule to match.

The possible flags are:

For example, an iptables rule that contains the following specification only matches TCP packets that have the SYN flag set and the ACK and FIN flags not set:

--tcp-flags ACK,FIN,SYN SYN

Use the exclamation point character (!) after the --tcp-flags to reverse the effect of the match option.

--tcp-option — Attempts to match with TCP-specific options that can be set within a particular packet. This match option can also be reversed with the exclamation point character (!).