Moxa UC-8410A-T-LX [51/86] Defining a policy for chain rules

UC-8410A Series Linux Software General Debian Package Usage

5-11

Observing and Erasing Chain Rules

Usage:

# iptables [-t tables] [-L] [-n]

-t tables: Table to manipulate (default: ‘filter’); example: nat or filter.

-L [chain]: List all rules in selected chains. If no chain is selected, all chains are listed.

-n: Numeric output of addresses and ports.

# iptables [-t tables] [-FXZ]

-F: Flush the selected chain (all the chains in the table if none is listed).

-X: Delete the specified user-defined chain.

-Z: Set the packet and byte counters in all chains to zero.

Examples:

# iptables -L -n

In this example, since we do not use the -t parameter, the system uses the default ‘filter’ table. Three chains

are included: INPUT, OUTPUT, and FORWARD. INPUT chains are accepted automatically, and all connections

are accepted without being filtered.

#iptables –F

#iptables –X

#iptables -Z

Defining a Policy for Chain Rules

Usage:

# iptables [-t tables] [-P] [INPUT, OUTPUT, FORWARD, PREROUTING, OUTPUT, POSTROUTING]

[ACCEPT, DROP]

-P: Set the policy for the chain to the given target.

INPUT: For packets coming into the UC-8410A-LX series.

OUTPUT: For locally-generated packets.

FORWARD: For packets routed out through the UC-8410A-LX series.

PREROUTING: To alter packets as soon as they come in.

POSTROUTING: To alter packets as they are about to be sent out.

Examples:

#iptables –P INPUT DROP

#iptables –P OUTPUT ACCEPT

#iptables –P FORWARD ACCEPT

# modprobe iptable_nat

#iptables –t nat –P PREROUTING ACCEPT

#iptables –t nat –P OUTPUT ACCEPT

#iptables -t nat –P POSTROUTING ACCEPT

In this example, the policy accepts outgoing packets and denies incoming packets.